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Periprosthetic fracture fixation of the femur following total hip arthroplasty: A review of biomechanical testing

  • Mehran Moazen
    Correspondence
    Corresponding author.
    Affiliations
    Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
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  • Alison C. Jones
    Affiliations
    Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
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  • Zhongmin Jin
    Affiliations
    Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
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  • Ruth K. Wilcox
    Affiliations
    Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK
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  • Eleftherios Tsiridis
    Affiliations
    Academic Department of Orthopaedic and Trauma, Section of Musculoskeletal Disease, Institute of Molecular Medicine, School of Medicine, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, UK

    Department of Surgery and Cancer, Division of Surgery, Imperial College London, B-block Hammersmith Hospital, Du-Cane Road, London, W12 0HS, UK
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      Abstract

      Background

      Periprosthetic femoral fracture can occur following total hip arthroplasty. Fixation of these fractures are challenging due to the combination of fractured bone with an existing prosthesis. There are several clinical studies reporting the failure of fixation methods used for these fractures, highlighting the importance of further biomechanical studies in this area.

      Methods

      The current literature on biomechanical models of periprosthetic femoral fracture fixation is reviewed. The methodologies involved in the experimental and computational studies of this fixation are described and compared.

      Findings

      Areas which require further investigation are highlighted and the potential use of finite element analysis as a computational tool to test the current fixation methods is addressed.

      Interpretation

      Biomechanical models have huge potential to assess the effectiveness of different fixation methods. Experimental in vitro models have been used to mimic periprosthetic femoral fracture fixation however, the numbers of measurements that are possible in these studies are relatively limited due to the cost and data acquisition constraints. Computer modelling and in particular finite element analysis is a complimentary method that could be used to examine existing protocols for the treatment of periprosthetic femoral fracture and, potentially, find optimum fixation methods for specific fracture types.

      Keywords

      1. Introduction

      Periprosthetic femoral fracture (PFF) is a complication associated with total hip arthroplasty (THA). A concerning increase in the incidence of this condition has been predicted, in line with the increasing number of THA operations (
      • Learmonth I.D.
      • Young C.
      • Rorabeck C.
      The operation of the century: total hip replacement.
      ,
      • Lindahl H.
      • Malchau H.
      • Oden A.
      • Garellick G.
      Risk factors for failure after treatment of a periprosthetic fracture of the femur.
      ,
      • Tsiridis E.
      • Pavlou G.
      • Venkatesh R.
      • Bobak P.
      • Gie G.
      Periprosthetic femoral fractures around hip arthroplasty: current concepts in their management.
      ) . PFF can occur intra-operatively or post-operatively, creating a variety of fracture configurations and locations. There are various associated risk factors including the age of the patient (
      • Wu C.C.
      • Au M.K.
      • Wu S.S.
      • Lin L.C.
      Risk factors for postoperative femoral fracture in cementless hip arthroplasty.
      ), osteoporosis (
      • Lou X.F.
      • Li Y.H.
      • Lin X.J.
      Effect of proximal femoral osteoporosis on cementless hip arthroplasty: A short-term clinical analysis.
      ), the prosthesis design (
      • Garellick G.
      • Malchau H.
      • Regner H.
      • Herberts P.
      The Charnley versus the Spectron hip prosthesis: radiographic evaluation of a randomized, prospective study of 2 different hip implants.
      ,
      • Toni A.
      • Ciaroni D.
      • Sudanese A.
      • Femino F.
      • Marraro M.D.
      • Bueno Lozano A.L.
      • Giunti A.
      Incidence of intraoperative femoral fracture. Straight-stemmed versus anatomic cementless total hip arthroplasty.
      ), and whether a cemented or un-cemented prosthesis is used (
      • Berry D.J.
      Epidemology: hip and knee.
      ,
      • Schwartz J.T.
      • Mayer J.G.
      • Engh C.A.
      Femoral fracture during non-cemented total hip arthroplasty.
      ), each of which also influences the method of fixation (
      • Franklin J.
      • Malchau H.
      Risk factors for periprosthetic femoral fracture.
      ,
      • Lindahl H.
      • Malchau H.
      • Oden A.
      • Garellick G.
      Risk factors for failure after treatment of a periprosthetic fracture of the femur.
      ).
      A large number of clinical studies have investigated fracture following THA (
      • Garcia-Cimbrelo E.
      • Munuera L.
      • Gil- Garay E.
      Femoral shaft fractures after cemented total hip arthroplasty.
      ,
      • Kavanagh B.F.
      Femoral fractures associated with total hip arthroplasty.
      ,
      • Löwenhielm G.
      • Hansson L.I.
      • Kärrholm J.
      Fracture of the lower extremity after total hip replacement.
      ,
      • Tsiridis E.
      • Narvani A.A.
      • Haddad F.S.
      • Timperley J.A.
      • Gie G.A.
      Impaction femoral allografting and cemented revision for periprosthetic femoral fractures.
      ). These have led many authors to classify PFF based on fracture configuration, position along the femur and associated bone quality (
      • Duncan C.P.
      • Masri B.A.
      Fractures of the femur after hip replacement.
      ,
      • Johansson J.E.
      • McBroom R.
      • Barrington T.W.
      • Hunter G.A.
      Fracture of the ipsilateral femur in patients with total hip replacement.
      ,
      • Mont M.A.
      • Maar D.C.
      Fractures of the ipsilateral femur after hip arthroplasty. A statistical analysis of outcome based on 487 patients.
      ). One of the most commonly used systems is known as the Vancouver classification (
      • Duncan C.P.
      • Masri B.A.
      Fractures of the femur after hip replacement.
      ). Here, fractures located within the trochanter region are classified as type A. Fractures located within the stem region are classified as type B, with subsets representing those with a stable implant (B1), a loose implant (B2) and a loose implant plus insufficient bone stock (B3). Finally fractures positioned distal to the stem are classified as type C. Among these, type B fractures represent approximately 80% of all cases (
      • Corten K.
      • Vanrykel F.
      • Bellemans J.
      • Reynders Frederix P.
      • Simon J.P.
      • Broos P.L.O.
      An algorithm for the surgical treatment of periprosthetic fractures of the femur around a well-fixed femoral component.
      ,
      • Lindahl H.
      • Malchau H.
      • Oden A.
      • Garellick G.
      Risk factors for failure after treatment of a periprosthetic fracture of the femur.
      ), and these have been the focus of several clinical and laboratory studies.
      Treatment of PFF is challenging due to the combination of the fractured bone and the existing prosthesis, with the further complication, in some cases, of the cement used for prosthesis fixation. This creates a different biomechanical scenario to the fracture of an intact femur. Traditional treatment methods such as traction and bracing have been replaced by open reduction and internal fixation, along with revision of the prosthesis in some cases (
      • Lindahl H.
      • Malchau H.
      • Oden A.
      • Garellick G.
      Risk factors for failure after treatment of a periprosthetic fracture of the femur.
      ). Many authors have reported the clinical outcomes of different fixation methods (
      • Bryant G.K.
      • Morshed S.
      • Agel J.
      • Henley M.B.
      • Barei D.P.
      • Taitsman L.A.
      • Nork S.E.
      Isolated locked compression plating for Vancouver Type B1 periprosthetic femoral fractures.
      ,
      • Buttaro M.A.
      • Farfalli G.
      • Paredes Nunez M.
      • Comba F.
      • Piccaluga F.
      Locking compression plate fixation of Vancouver type-B1 periprosthetic femoral fractures.
      ,
      • Haddad F.S.
      • Garbuz D.S.
      • Masri B.A.
      • Duncan C.P.
      Structural proximal femoral allografts for failed total hip replacements: a minimum review of five years.
      ,
      • Partridge A.J.
      • Evans P.E.
      The treatment of fractures of the shaft of the femur using nylon cerclage.
      ,
      • Serocki J.H.
      • Chandler R.W.
      • Dorr L.D.
      Treatment of fractures about hip prostheses with compression plating.
      ,
      • Tsiridis E.
      • Haddad F.S.
      • Gie G.A.
      Dall-Miles plates for periprosthetic femoral fractures: A critical review of 16 cases.
      ,
      • Tsiridis E.
      • Narvani A.A.
      • Timperley J.A.
      • Gie G.A.
      Dynamic compression plates for Vancouver type B periprosthetic femoral fractures: a 3-year follow-up of 18 cases.
      ). Among these, there are several studies that report the failure of the fixation for these fractures (Fig. 1), indicating that the protocol for classifying PFF cases and subsequent selection of the fixation method are perhaps currently insufficient. Several authors have proposed treatment algorithms for different types of fracture (
      • Masri B.A.
      • Meek R.M.
      • Duncan C.P.
      Periprosthetic fracture evaluation and treatment.
      ,
      • Parvizi J.
      • Rapuri V.R.
      • Purtill J.J.
      • Sharkey P.F.
      • Rothman R.H.
      • Hozack W.J.
      Treatment protocol for proximal femoral periprosthetic fractures.
      ) in light of available fixation techniques. However, these proposals lack any significant biomechanical evidence.
      Figure thumbnail gr1
      Fig. 1Anteroposterior radiograph showing the failure of the periprosthetic femoral fracture fixation methods. Dall-Miles plate fracture from
      • Tsiridis E.
      • Haddad F.S.
      • Gie G.A.
      Dall-Miles plates for periprosthetic femoral fractures: A critical review of 16 cases.
      with permission from Elsevier.
      Biomechanical in vitro studies and computer in silico models have the potential to assess and optimise the performance of different methods of fixation. These techniques allow certain aspects of the in vivo conditions to be replicated in a controlled manner so that the biomechanical effects of various parameters can be assessed both individually and in combination. These types of study have been implemented extensively in the area of THA (
      • Crowninshield R.D.
      • Brand R.A.
      • Johnston R.C.
      • Milroy J.C.
      An analysis of femoral component stem design in total hip arthroplasty.
      ,
      • Huiskes R.
      Stress analyses of implanted orthopaedic joint prostheses for optimal design and fixation.
      ,
      • Prendergast P.J.
      • Taylor D.
      Stress analysis of the proximo-medial femur after total hip replacement.
      ) and there is a growing body of work focusing on fracture fixation (
      • Chen G.
      • Schmutz B.
      • Wullschleger M.
      • Pearcy M.J.
      • Schuetz M.A.
      Computational investigation of mechanical failures of internal plate fixation.
      ,
      • Krishna K.R.
      • Sridhar I.
      • Ghista D.N.
      Analysis of the helical plate for bone fracture fixation.
      ,
      • Perren S.M.
      The concept of biological plating using the limited contact dynamic compression plate (LC-DCP): scientific background, design and application.
      ,
      • Stoffel K.
      • Dieter U.
      • Stachowiak G.
      • Gachter A.
      • Kuster M.S.
      Biomechanical testing of the LCP- how can stability in locked internal fixators be controlled?.
      ). A number of biomechanical studies have also investigated PFF, although as yet, not all types of these fractures or fixation methods have been comprehensively evaluated.
      The aim of this review is to examine the available literature relating to the biomechanical assessment of PFF. Current experimental and computational methodologies are evaluated and the trends in the results, as well as areas of disagreement, are highlighted. Recommendations for future research and areas which require further scientific investigation are discussed.

      2. Methodology

      2.1 Experimental methods

      2.1.1 Introduction

      Experimental in vitro studies have been used to assess the biomechanical stability of various methods of PFF fixation. These studies compare the mechanical performance of different fixation methods in the laboratory by stabilising a periprosthetic fracture in a cadaveric or synthetic femur. The following section reviews the methods used and examines their robustness, with a focus on three specific aspects: the type of specimen, the loading protocol and the methods of measurement.

      2.1.2 Specimen type and repeatability

      Since the majority of studies have made comparisons between different fixation methods, it is necessary for there to be parity between the specimens used so that any differences in outcome can be attributed to the fixation method alone. Both cadaveric and synthetic samples have been used, as is summarised in Table 1.
      Table 1A summary of the specimen preparation and loading protocol in laboratory studies. Note that the isometric loading category was assigned to any study that has loaded the construct 1) under axial loading (including only the adduction angle) or 2) in pure torsion or bending. Any other loading scenario, such as those that included muscle forces or positioned the femur in flexion and adduction, was categorized as physiological loading.
      AuthorsSpecimen number and typeProsthesisFractureLoadingFemur position
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      8 CadavericCemented ATS Howmedica, NJDrill hole and reaming defect 90 mm below lesser trochanterIsometric5° of adduction
      Cemented STH Zimmer, INAxial compression to 417-500 N depending on the neck length and to keep the bending moment 35 N-m in all samples
      • Stevens S.S.
      • Irish A.J.
      • Vachtsevanos J.G.
      • Csongradi J.
      • Beaupré G.S.
      A biomechanical study of three wiring techniques for cerclage-plating.
      27 SyntheticNo prosthesisTransverse 200 mm distal to the greater trochanterPhysiological29° of adduction
      Displacement applied monotonically up to 25 mm in 50 sec then 20 displacement cycles between 25 and 15 mm at 1 Hz and finally monotonic displacement increased from 25 to 40 mm in 60 sec60° posteriorly relative to the frontal plan with the relative angle of 20°between the loading arm and femur in the anterio-posterior view
      • Schmotzer H.
      • Tchejeyan G.H.
      • Dall D.M.
      Surgical management of intra- and postoperative fractures of the femur about the tip of the stem in total hip arthroplasty.
      7 (4 left,3 right) CadavericCementless, Porous-coated Anatomic [PCA], E Series, Stryker, NJTransverse at the tip of the stemPhysiological15° flexion
      Via a rigid load arm in 10 N steps up to failure7° adduction
      • Han S.-M.
      Comparison of wiring techniques for bone fracture fixation in total hip arthroplasty.
      11 CadavericCementless, Straight tapered, collarlessInduced via a stem one size larger than the templated stemaIsometricNot clear
      Natutal, Sulzer Orthopedics, TXCompression to 890 N followed by 1780 N and 2670 N each for 15 sec
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures occurring at the tip of the stem: a biomechanical study of 5 techniques.
      30 (6 for each test) SyntheticCemented, Charnley, DePuy, INOblique 45° to shaft axis distal to the tip of the stemIsometric25° of valgus
      Axial compression to 500 N
      Lateral bending to 250 N
      Torsion to 200 N
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures: a biomechanical comparison of two techniques.
      6 matched pairs CadavericCemented, Charnley, DePuy, INOblique 45° to shaft axisIsometric25° of valgus
      Axial compression to 500 N
      Lateral bending to 250 N
      Torsion to 200 N
      • Kuptniratsaikul S.
      • Brohmwitak C.
      • Techapongvarachai T.
      • Itiravivong P.
      Plate-screw-wiring technique for the treatment of periprosthetic fracture around the hip: a biomechanical study.
      5 matched pairs CadavericCemented, Charnley, DePuy, INSpiralIsometric is not clearNot clear
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      16 CadavericNo prosthesisTransverse 100 mm distal to the base of lesser trochanterPhysiological12° of adduction
      Cyclic cranial-caudal 1.53 BW approx 0-1000 N for 100 cycles at 1 Hz simultaneously loaded under anterior-posterior 0.15 BW approx -100 to80 N at 1.5 Hz
      • Peters C.L.
      • Bachus K.N.
      • Davitt J.S.
      Fixation of periprosthetic femur fractures: a biomechanical analysis comparing cortical strut allograft plates and conventional metal plates.
      5 CadavericCemented, Premier Stem, Sulzer Orthopedics Inc, TXTransverse 15 mm below the tip of the stemIsometric Axial compression to 2250 NTwo set up tested
      1) 21° of varus
      2)30° of flexion
      • Wilson D.
      • Frei H.
      • Masri B.A.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical study comparing cortical onlay allograft struts and plates in the treatment of periprosthetic femoral fractures.
      6 CadavericCemented, Charnley-Muller, Stryker, NJTransverse at the tip of the stemPhysiological12° of adduction
      Cyclic cranial-caudal 1.53 BW approx 0-1000 N and anterior-posterior 0.15 BW approx -100 to80 N
      • Barker R.
      • Takahashi T.
      • Toms A.
      • Gregson P.
      • Kuiper J.H.
      Reconstruction of femoral defects in revision hip surgery: risk of fracture and stem migration after impaction bone grafting.
      14 SyntheticCemented Exeter, Stryker, NJCortical perforation at the tip of the standard stemPhysiological12°medially and 8°posteriorly relative to the frontal plan
      Initial loading cycled between 10 and 500 N, then every 100 cycles the peak load increased in steps of 500 N up to 2500 N
      • Fulkerson E.
      • Koval K.
      • Preston C.F.
      • Iesaka K.
      • Kummer F.J.
      • Egol K.A.
      Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.
      8 matched pairs CadavericCemented, Charnley, DePuy, INOblique 45° to shaft axis at the tip of the stemIsometric25° of valgus
      Axial compression to 500 N
      Lateral bending to 36 N-m
      Torsion to 11 N-m
      Cyclic loading in 400 N compression for 10000 cycle at 3 Hz
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      15 (5 for each test) SyntheticCemented, Exeter, Stryker, NJTransverse at the tip of the stemIsometric15° of adduction
      Axial compression
      Lateral bending
      Torsion tested with displacement control between 0.5 and 2 with a preload of 50 to 100 N
      Cyclic between 200 N-1200 N for 100000 at 3 Hz
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      20 (5 for each test) SyntheticCemented, Exeter, Stryker, NJOblique 45° to shaft axis 25 mm distal to the tip of the stemIsometric25° of adduction
      Axial compression to 500 N
      Lateral bending to 50 N
      Torsion to 100 N
      Key to content: aas a result of this crack occurred through the calcar and propagated distally from 50 mm to 165 mm.
      Cadaveric specimens more closely represent the ‘in vivo’ material but there is inherent variability between samples, including, crucially, the bone quality and geometry as well as the potential presence of pre-existing damage in the bone. This variance would likely necessitate large sample sizes to obtain statistically significant results, but this is usually impractical due to the availability of the tissue and, from Table 1, it can be seen that most sample sizes here are small. To overcome this, several authors have adopted an approach of undertaking a number of different procedures sequentially on each specimen, using a randomised ordering method to reduce the effect of any cumulative damage to the specimens. Whilst such an approach is perhaps the best that can be achieved with limited specimens, little work seems to have been undertaken to assess the effect of these repeated tests.
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      used a standard fixation method as a control for each specimen, which was retested within each variable group. Whilst this enabled results to be compared to the most recent standard, the variation in the measures of the standard during the tests was not reported.
      Radiographic assessment has been undertaken by a number of authors to detect any gross abnormalities and determine the appropriate stem size prior to testing (
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      ,
      • Han S.-M.
      Comparison of wiring techniques for bone fracture fixation in total hip arthroplasty.
      ,
      • Schmotzer H.
      • Tchejeyan G.H.
      • Dall D.M.
      Surgical management of intra- and postoperative fractures of the femur about the tip of the stem in total hip arthroplasty.
      ) as well as to verify the position of the prosthesis and cement mantle following stem insertion (
      • Kuptniratsaikul S.
      • Brohmwitak C.
      • Techapongvarachai T.
      • Itiravivong P.
      Plate-screw-wiring technique for the treatment of periprosthetic fracture around the hip: a biomechanical study.
      ,
      • Peters C.L.
      • Bachus K.N.
      • Davitt J.S.
      Fixation of periprosthetic femur fractures: a biomechanical analysis comparing cortical strut allograft plates and conventional metal plates.
      ). This technique could potentially provide a method for evaluating the bone quality or fracture type and perhaps matching specimens between groups. However, radiographic analysis does not yet appear to have been utilised for this purpose.
      To avoid the variance issues of cadaveric tissue, a number of studies have opted to use synthetic rather than natural bone for mechanical testing. Such specimens generally represent an average geometry and successive generations have been developed to more accurately match the properties of real bone (
      • Cristofolini L.
      • Viceconti M.
      • Cappello A.
      • Toni A.
      Mechanical validation of whole bone composite femur models.
      ). The results from these tests generally show lower standard deviations in the measurements taken than those using cadaveric specimens and sample sizes of 5–10 have been sufficient. However, there are some exceptions. For example, the cadaveric study of
      • Kuptniratsaikul S.
      • Brohmwitak C.
      • Techapongvarachai T.
      • Itiravivong P.
      Plate-screw-wiring technique for the treatment of periprosthetic fracture around the hip: a biomechanical study.
      reported a lower standard deviation compared to the synthetic study of
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures occurring at the tip of the stem: a biomechanical study of 5 techniques.
      . Although they both reported a similar bending stiffness (mean 394 N/mm [SD 29 N/mm] and 410 N/mm [SD 100 N/mm] respectively for plate fixation with three proximal uni-cortical screws and three distal bi-cortical screws), which shows a reasonable level of correspondence between synthetic and cadaveric samples in terms of mechanical properties.
      The periprosthetic fractures in the specimens have most commonly been generated using a saw. The position and configuration of the fracture has varied between studies, as is shown in Table 1, although in most cases, the type falls within the Vancouver B1 category. In all of the studies, the fracture configuration was kept as constant as possible between specimens, and, as yet, the effect of varying the fracture configuration on specific or different fixation methods has not been investigated.

      2.1.3 Representation of the loads and surrounding conditions

      A variety of testing setups and loading regimes have been used to examine the performance of the construct. In general, these fall into two categories: physiological loading where typical in vivo conditions are represented (
      • Barker R.
      • Takahashi T.
      • Toms A.
      • Gregson P.
      • Kuiper J.H.
      Reconstruction of femoral defects in revision hip surgery: risk of fracture and stem migration after impaction bone grafting.
      ,
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      ,
      • Wilson D.
      • Frei H.
      • Masri B.A.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical study comparing cortical onlay allograft struts and plates in the treatment of periprosthetic femoral fractures.
      ), or isometric loading where a series of isolated loading modes such as pure bending, torsion and compression are applied (
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures occurring at the tip of the stem: a biomechanical study of 5 techniques.
      ,
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures: a biomechanical comparison of two techniques.
      ,
      • Fulkerson E.
      • Koval K.
      • Preston C.F.
      • Iesaka K.
      • Kummer F.J.
      • Egol K.A.
      Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.
      ,
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      ,
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      ). Examples of these regimes are given in Fig. 2. The latter approach makes it easier to identify if specific loading modes cause instability, but it may be that these cases do not occur in vivo. Conversely, physiological loading cannot capture abnormal situations such as falls which may present the highest potential for instability and failure to occur. Both of these loading types have been applied using a single loading step (
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      ,
      • Schmotzer H.
      • Tchejeyan G.H.
      • Dall D.M.
      Surgical management of intra- and postoperative fractures of the femur about the tip of the stem in total hip arthroplasty.
      ,
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      ), a cyclic loading regime (
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      ,
      • Wilson D.
      • Frei H.
      • Masri B.A.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical study comparing cortical onlay allograft struts and plates in the treatment of periprosthetic femoral fractures.
      ) or a combination of both (
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures: a biomechanical comparison of two techniques.
      ,
      • Fulkerson E.
      • Koval K.
      • Preston C.F.
      • Iesaka K.
      • Kummer F.J.
      • Egol K.A.
      Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.
      ,
      • Stevens S.S.
      • Irish A.J.
      • Vachtsevanos J.G.
      • Csongradi J.
      • Beaupré G.S.
      A biomechanical study of three wiring techniques for cerclage-plating.
      ,
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      ). However, there has been little consensus on the boundary conditions, magnitudes or directions of the loads applied, as shown in Table 1; here only the value of 500 N has been used repeatedly for non-destructive monotonic tests under axial loading (
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures occurring at the tip of the stem: a biomechanical study of 5 techniques.
      ,
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures: a biomechanical comparison of two techniques.
      ,
      • Fulkerson E.
      • Koval K.
      • Preston C.F.
      • Iesaka K.
      • Kummer F.J.
      • Egol K.A.
      Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.
      ,
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      ,
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      ).
      Figure thumbnail gr2
      Fig. 2A schematics of the loading protocol used in previous studies. A: a so-called physiological loading that includes the muscle forces in the model adopted and modified from
      • Stevens S.S.
      • Irish A.J.
      • Vachtsevanos J.G.
      • Csongradi J.
      • Beaupré G.S.
      A biomechanical study of three wiring techniques for cerclage-plating.
      ; B: a so-called isometric loading that loads the construct under pure axial, bending and torsion adopted and modified from
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      .
      Whilst some studies have implemented non-destructive loads to enable the specimen to be re-used, others have evaluated failure through a step-by-step increase in the load. However, the definition of failure is not consistent across existing studies.
      • Schmotzer H.
      • Tchejeyan G.H.
      • Dall D.M.
      Surgical management of intra- and postoperative fractures of the femur about the tip of the stem in total hip arthroplasty.
      defined failure as complete loss of the fixation, permanent displacement/rotation of the fracture fragments or displacement (or rotation) amplitude greater than 2 mm (or degrees), whereas
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      ,
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      define the “clinical failure” as either 10 mm of displacement or the first abrupt drop in load after reaching a peak load. This discrepancy is in part due to the different modes of failure anticipated with the different fixation methods used. As yet, no standard criteria have been adopted and, indeed, it would be difficult to apply a single criterion across the range of testing modes currently used.

      2.1.4 Accuracy and repeatability of measurements

      The purpose of the experimental studies has been to assess the mechanical stability of the construct, and a number of different approaches have been taken to measure this. These include methods to measure the relative movement across the fracture site as well as the larger scale performance of the whole construct in terms of the overall stiffness.
      In order to quantify the movement at the fracture site, camera systems have been used (
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      ,
      • Peters C.L.
      • Bachus K.N.
      • Davitt J.S.
      Fixation of periprosthetic femur fractures: a biomechanical analysis comparing cortical strut allograft plates and conventional metal plates.
      ). Since the fracture movement was generally found to be small, the precision of the measurement system is important. Peters et al. used an OptoTrak system (Northern Digital inc, Canada) with a quoted accuracy of 0.1 mm. The measured fracture motions ranged from 0.5 to 2 mm, indicating the potential for the measurement error to be significant. A similar system was used by
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      , however, by applying and tracking markers away from the fracture site, larger movements could be detected (>1.6 mm) from which the fracture movement was derived.
      Evaluation of the whole construct behaviour is less challenging and many studies have evaluated the specimen stiffness from the slope of load–displacement curve generated from the mechanical testing machine. Since the displacements across the whole construct are larger, then the issues of accuracy are less critical.
      Finally strain gauging has been performed in a limited number of studies (
      • Barker R.
      • Takahashi T.
      • Toms A.
      • Gregson P.
      • Kuiper J.H.
      Reconstruction of femoral defects in revision hip surgery: risk of fracture and stem migration after impaction bone grafting.
      ,
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      ) to capture the deformation of the construct under loading. This requires the attachment of strain gauges at specific locations on the construct or the bone surface. There are a number of issues with strain gauging that can affect the accuracy and repeatability of measurement. For example, thermal drift can cause changes in the measured voltage due to temperature fluctuations. This has been addressed using temperature compensating gauges and circuits (
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      ). A high reproducibility rate was also reported in the strain measurements in this study (a standard deviation of approximately 3%) suggesting that repeatable results could be obtained from strain gauges.

      2.2 Computational methods

      2.2.1 Introduction

      Finite element (FE) analysis is a computer modelling technique which allows the prediction of the mechanical behaviour of structures. Its application in the area of orthopaedic biomechanics dates back to early 1970's (see review by
      • Huiskes R.
      • Chao E.Y.S.
      A survey of finite element analysis in orthopaedic biomechanics: the first decade.
      ). A great advantage of computer modelling over laboratory experiments is the ability to test large numbers of scenarios with little extra cost per test. This is particularly useful for PFF testing where the wide variety of fracture configurations, bone quality and device types cannot realistically be compared through physical testing alone. As well as the simulation of the force–displacement behaviour and the fracture movement, as can be recorded in physical experiments, the FE method also enables the stress and strain patterns within each of the components to be predicted.
      Despite the large number of FE studies on femoral fracture fixation (
      • Beaupre G.S.
      • Carter D.R.
      • Orr T.E.
      • Csongradi J.
      Stresses in plated long-bones: the role of screw tightness and interface slipping.
      ,
      • Cegonino J.
      • Garcia Aznar J.M.
      • Doblare M.
      • Palanca D.
      • Seral B.
      • Seral F.
      A comparative analysis of different treatments for distal femur fractures using the finite element method.
      ,
      • Cheal E.J.
      • Hayes W.C.
      • White III, A.A.
      • Perren S.M.
      Three dimensional finite element analysis of a simplified compression plate fixation system.
      ,
      • Chen G.
      • Schmutz B.
      • Wullschleger M.
      • Pearcy M.J.
      • Schuetz M.A.
      Computational investigation of mechanical failures of internal plate fixation.
      ,
      • Helwig P.
      • Faust G.
      • Hindenlang U.
      • Hirschmuller A.
      • Konstantinidis L.
      • Bahrs C.
      • Sudkamp N.
      • Schneider R.
      Finite element analysis of four different implants inserted in different positions to stabilize an idealized trochanteric femoral fracture.
      ), there have been limited investigations that have implemented this technique to explore the biomechanics of PFF fixation (
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      ,
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      - see also study of
      • Pappas C.A.
      • Young P.G.
      • Lee A.J.C.
      Development of the Mennen 3 PeriPro fixation plate for the treatment of periprosthetic fractures of the femur.
      for plate development for PFF fixation). The following section reviews the computational methods used and examines their robustness. Due to the limited number of computational studies of PFF, techniques and findings from the wider pool of femoral simulation work are drawn upon. Again, three aspects are considered in depth, which reflect those discussed in the previous section: the representation of the femoral bone and the fracture within it, the loading of the construct in silico, and the accuracy of the outputs of interest.

      2.2.2 Representation of the femoral bone and fracture

      Femoral bone has an irregular geometry and is an inhomogeneous, anisotropic structure (that is, the properties vary with both location and loading direction). Computer representations of this bone have ranged from a simple cylinder with homogeneous, isotropic material properties (
      • Krishna K.R.
      • Sridhar I.
      • Ghista D.N.
      Analysis of the helical plate for bone fracture fixation.
      ), to geometrically accurate models with material properties matched to an individual cadaveric femur (
      • Schileo E.
      • Taddei F.
      • Cristofolini L.
      • Viceconti M.
      Subject-specific finite element models implementing a maximum principal strain criterion are able to estimate failure risk and fracture location on femurs tested in vitro.
      ).
      Many authors have approximated femoral bone behaviour as homogenous and isotropic (
      • Peleg E.
      • Mosheiff R.
      • Liebergall M.
      • Mattan Y.
      A short plate compression screw with diagonal bolts-A biomechanical evaluation performed experimentally and by numerical computation.
      ) while some have implemented orthotropic properties (
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      ). In cases where geometry is taken from computed tomography scans, it is possible to assign the bone material properties on an element by element basis (
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      ), which enables the inhomogenous nature of bone to be taken into account. Where the intact femur has been modelled,
      • Peng L.
      • Bai J.
      • Zeng X.
      • Zhou Y.
      Comparison of isotropic and orthotropic material property assignments on femoral finite element models under two loading conditions.
      showed that there was little difference in peak stress and nodal displacement between models using isotropic and orthotropic material properties. However,
      • Gomez-Benito M.J.
      • Garcia-Aznar J.M.
      • Doblare M.
      Finite element prediction of proximal femoral fracture patterns under different loads.
      showed that modelling bone with anisotropic rather than isotropic bone property led to a better prediction of femoral neck fracture when compared to corresponding experimental results. The key objective in a PFF fixation study is likely to be the assessment of the fracture movement, rather than the prediction of the original fracture location as studied by
      • Gomez-Benito M.J.
      • Garcia-Aznar J.M.
      • Doblare M.
      Finite element prediction of proximal femoral fracture patterns under different loads.
      ,
      • Schileo E.
      • Taddei F.
      • Cristofolini L.
      • Viceconti M.
      Subject-specific finite element models implementing a maximum principal strain criterion are able to estimate failure risk and fracture location on femurs tested in vitro.
      . However, as yet, no studies have investigated whether a simplified isotropic material property can provide reliable results or whether more sophisticated material properties should be used in this case.
      In order to represent the fracture within the bone, the fracture surfaces can be simulated with contact interactions, which allow transference of the compressive contact stress across the fracture site and, potentially, enable the friction at the interface to be simulated (
      • Krishna K.R.
      • Sridhar I.
      • Ghista D.N.
      Analysis of the helical plate for bone fracture fixation.
      ). The effect of the properties at this interface on the movement of the fracture is undoubtedly high. However, few studies have experimentally evaluated the friction coefficients of long bones (
      • Shockey J.S.
      • Von Fraunhofer J.A.
      • Seligson D.
      A measurement of the coefficient of static friction of human long bones.
      ) and the friction across the femoral fracture site has not yet been fully characterised. In addition, the use of contact algorithms significantly increases the computational time. An alternative approach involves the use of solid elements, of a much lower stiffness than the surrounding bone, at the fracture site (
      • Chen S.-H.
      • Yu T.-C.
      • Chang C.-H.
      • Lu Y.-C.
      Biomechanical analysis of retrograde intramedullary nail fixation in distal femoral fractures.
      ). This method potentially reduces the computational cost and could be used to simulate the callus formation during healing, which would limit fracture movement. However, low stiffness elements may require re-meshing if large deformations occur, which would increase the computational cost.

      2.2.3 Representation of the loads and surrounding conditions

      An advantage of the FE method is that, once a model has been developed, it is relatively straightforward to alter the loading and boundary conditions, and both isometric and physiologic loading regimes can be applied.
      Where PPF has been investigated, forces representing typical physiological loading have been assigned (
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      ,
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      ). As well as forces applied to the femoral head, physiological loading in FE models has been extended to include the muscle forces, which are difficult to apply experimentally. This commonly includes the abductor muscle (
      • Crowninshield R.D.
      • Maloney W.J.
      • Wentz D.H.
      • Levine D.L.
      The role of proximal femoral support in stress development within hip prostheses.
      ,
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      ,
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      ), but can include all the muscles attached to the femur (
      • Duda G.N.
      • Heller M.
      • Albinger J.
      • Schulz O.
      • Schneider E.
      • Claes L.
      Influence of muscle forces on femoral strain distribution.
      ). The addition of muscle forces potentially creates a more accurate representation of the in vivo scenario but it also adds extra assumptions and complexity to the modelling process. The muscle force information is generally derived from electromyography or multibody dynamic analysis (MDA), which enables the values to be estimated through a walking cycle or other activity (
      • Brand R.A.
      • Pedersen D.R.
      • Friederich J.A.
      The sensitivity of muscle force predictions to changes in physiological crosssectional area.
      ,
      • Duda G.N.
      • Schneider E.
      • Chao E.Y.S.
      Internal forces and moments in the femur during walking.
      ,
      • Shi J.F.
      • Wang C.J.
      • Laoui T.
      • Hart W.
      • Hall R.
      A dynamic model of simulating stress distribution in the distal femur after total knee replacement.
      ). Inevitably, there is considerable variation in these forces from person to person, for example due to size, weight and level of activity. Therefore assumptions have to be made as to whether the derived forces are representative of those that would be applied to the femur being modelled.
      In addition to physiological loading, some studies have used finite element methods to investigate the femur under isometric loading. In a similar manner to that used experimentally, the femur model has been constrained at the distal end and loaded under compression, torsion and bending via the proximal section (
      • Krishna K.R.
      • Sridhar I.
      • Ghista D.N.
      Analysis of the helical plate for bone fracture fixation.
      ,
      • Stoffel K.
      • Dieter U.
      • Stachowiak G.
      • Gachter A.
      • Kuster M.S.
      Biomechanical testing of the LCP- how can stability in locked internal fixators be controlled?.
      ,
      • Yoon Y.S.
      • Jang G.H.
      • Kim Y.Y.
      Shape optimal design of the stem of a cemented hip prosthesis to minimise stress concentration in the cement layer.
      ). The FE method allows the effects of individual isometric loading modes to be evaluated with more certainty than experimentally, because the forces can be controlled to prevent unintentional loading in other modes. To our knowledge, these methods have not, as yet, been applied to models specifically to examine PFF.

      2.2.4 Simulation predictions and accuracy

      In both experimental and computational PFF studies, the main measurements of interest are the construct stiffness, measured through bulk force–displacement data, and the potential for healing, judged by movement at the fracture site. In addition, some studies have examined the likelihood of construct failure, as well as the stress and strain within the bone and implanted devices. In an FE model, the accuracy of these predictions depends on the choice and sophistication of the input parameters, as well as the number of computations used to derive the solution, which is related to the number and type of elements in the model (
      • Anderson A.E.
      • Ellis B.J.
      • Weiss J.A.
      Verification, validation, and sensitivity studies in computational biomechanics.
      ).
      The choice of input parameters for a PFF model will depend on how much each input affects the output of interest. For example, Papini et al. found that the effect of the presence of cancellous bone on the axial and torsional stiffness of a simulated synthetic femur was less than 1% (
      • Papini M.
      • Zdero R.
      • Schemitsch E.H.
      • Zalzal P.
      The biomechanics of human femurs in axial and torsional loading: comparison of finite element analysis, human cadaveric femurs, and synthetic femurs.
      ), and therefore reduced the complexity of their model by neglecting this section of the bone. Whilst the geometry and properties of the implanted devices are usually well documented, those of the bone region are more challenging, and are expected to affect the bulk stiffness of the simulated construct. Equally, the representation of the bone fracture is expected to heavily influence the movement at the fracture site.
      The resolution of the finite element mesh directly affects the accuracy of the solution, and should therefore be calibrated at the beginning of each study (
      • Viceconti M.
      • Olsen S.
      • Nolte L.P.
      • Burton K.
      Extracting clinically relevant data from finite element simulations.
      ). The two finite element studies simulating PFF fixation, in two-dimensions (
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      ) and in three-dimensions (
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      ), both generated low resolution meshes in comparison to current computational capabilities (
      • Helwig P.
      • Faust G.
      • Hindenlang U.
      • Hirschmuller A.
      • Konstantinidis L.
      • Bahrs C.
      • Sudkamp N.
      • Schneider R.
      Finite element analysis of four different implants inserted in different positions to stabilize an idealized trochanteric femoral fracture.
      ,
      • Schileo E.
      • Taddei F.
      • Cristofolini L.
      • Viceconti M.
      Subject-specific finite element models implementing a maximum principal strain criterion are able to estimate failure risk and fracture location on femurs tested in vitro.
      ), and do not report how the mesh resolution affects the accuracy of their results. More recently, a whole-femur mesh of 44,000 elements was used by Papini et al. to predict bulk stiffness. Although, in that case, increasing the mesh resolution was found to change the displacement by less than 1%, studies which analyse local bone stress would likely need further mesh refinement.

      3. Overview of results

      The cases studied and the key results of the experimental and two FE studies are summarised in Table 2. Whilst the results of individual studies allow comparison between the different fixation configurations tested, the lack of standardisation in the tests undertaken prevents direct comparison between tests. There are, however, a number of general trends that can be observed. Most of the results indicate, as would be expected, that increasing the overall rigidity of the construct increases the stability of the fracture, as measured by the overall stiffness of the instrumented femur or by the motion across the fracture (see review by
      • Howell J.R.
      • Masri B.A.
      • Garbuz D.S.
      • Greidanus N.V.
      • Duncan C.P.
      Cable plates and onlay allografts in periprosthetic femoral fractures after hip replacement: laboratory and clinical observations.
      ). This increase in rigidity has been achieved by:
      Table 2A summary of fixation method and results of the current laboratory and computational studies investigating biomechanics of the periprosthetic femoral fracture fixation.
      AuthorsTest caseResults
      Experimental studies
      Plate and strut fixation
      Lateral plate fixationStrut fixation
      ProximalDistalPositionStrut length (mm)ProximalDistal
      Unicortical ScrewCable/wireBicortical ScrewCable/wireCable/wire
      • Schmotzer H.
      • Tchejeyan G.H.
      • Dall D.M.
      Surgical management of intra- and postoperative fractures of the femur about the tip of the stem in total hip arthroplasty.
      Med & lat1603 C3 CLong stem with allograft and cable provided the highest force to failure.
      Med & lat1603 C3 C(LS)
      This test was performed with a long stem compared to the standard stem in other cases.
      4 C4
      4 or 5
      Based on the description and available data in the paper we are not confident if 4 or 5 unicortical screws have been used for the proximal fixation of the plate.
      4
      1603 W
      Med & lat3 W
      -(LS)
      This test was performed with a long stem compared to the standard stem in other cases.
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures occurring at the tip of the stem: a biomechanical study of 5 techniques.
      3 C
      Plate fixation was performed with three proximal and three distal cables.
      Constructs with screws or screws and cables were more stable than cables alone.
      3 C3
      33
      33C3
      Ant & lat1203 C3C
      • Dennis M.G.
      • Simon J.A.
      • Kummer F.J.
      • Koval K.J.
      • Di Cesare P.E.
      Fixation of periprosthetic femoral shaft fractures: a biomechanical comparison of two techniques.
      3 C3 COgden concept provided a more rigid fixation than the allograft. Screws provided higher fixation rigidity than cables.
      Ant & lat1603 C3 C
      • Kuptniratsaikul S.
      • Brohmwitak C.
      • Techapongvarachai T.
      • Itiravivong P.
      Plate-screw-wiring technique for the treatment of periprosthetic fracture around the hip: a biomechanical study.
      A seven hole broad plate has been used. However the authors do not specify exactly how many screws and wires they used. We think that they have used three screws proximally and three screws distally.
      33Double plating using an anterior and lateral plate provided significantly higher stability compared to single plate fixation methods.
      33 W3
      3
      Two seven hole broad plates fixed laterally and anteriorly each with unicortical screws proximally and bicortical screws distally.
      3
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      Ant &lat2003 C H T3 C HTCables generated higher stability than wires and increasing the cable tension decrease fracture motion. Increasing the number of cables enhanced the fracture stability and decreasing strut length decreased axial rotation. No clear trend was found between strut length and fracture movement in anteroposterior and mediolateral planes.
      Ant & lat2003 C L T3 C LT
      Ant & lat2003 W HT3 W HT
      Ant & lat2002 C HT2 C HT
      Ant & lat2004 C HT4 C HT
      Med & lat2003 C H T3 C H T
      Ant2003 C H T3 C H T
      Lat2003 C H T3 C H T
      Ant & lat1603 C H T3 C H T
      Ant & lat1203 C H T3 C H T
      • Peters C.L.
      • Bachus K.N.
      • Davitt J.S.
      Fixation of periprosthetic femur fractures: a biomechanical analysis comparing cortical strut allograft plates and conventional metal plates.
      Lat1603 W3 WIncreasing the length and number of struts increase the stability. Allograft struts are biomechanically equivalent to plate fixation using screws and cables.
      Lat2003 W3 W
      Ant & lat2003 W3 W
      Med & lat2003 W3 W
      Lat2003 C3 C
      3 C4
      • Wilson D.
      • Frei H.
      • Masri B.A.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical study comparing cortical onlay allograft struts and plates in the treatment of periprosthetic femoral fractures.
      4 C4Ant2004 CCombining plate and strut graft with two unicortical screws above the fracture side provided the most stable fixation construct.
      24 C4Ant2004 C
      4 C4
      24 C4
      Ant & lat2004 C4 C
      Ant & lat1204 C4 C
      • Fulkerson E.
      • Koval K.
      • Preston C.F.
      • Iesaka K.
      • Kummer F.J.
      • Egol K.A.
      Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.
      3
      A locking plate has been used in this case.
      3The locking plate was stiffer in axial and torsional loading compared the Ogden construct.
      3 C3
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      23Ant2202 C2 CThe allograft strut-plate construct showed higher stiffness in bending and had a higher load to failure than the plate alone.
      4
      A locking plate has been used in this case.
      4
      2
      A locking plate has been used in this case.
      3Ant2202 C2 C
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      4
      A locking plate has been used in this case.
      4Allograft struts with non-locking plates showed higher stiffness compared to other methods.
      2
      A locking plate has been used in this case.
      2 C4
      22 C4
      24Ant2202 C2 C
      Long stem
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      The effect of stem length (250, 200, 180,170-100 with 10 mm increment) using two different cemented prosthesis design without any additional fixation tested.By passing the femoral defect by 1.5 FD minimize the stress raiser effect.
      • Barker R.
      • Takahashi T.
      • Toms A.
      • Gregson P.
      • Kuiper J.H.
      Reconstruction of femoral defects in revision hip surgery: risk of fracture and stem migration after impaction bone grafting.
      Femoral defect following impaction bone grafting fixed using X-change femoral mesh, mesh and Dall-Miles plate, mesh and strut graft using standard and long stem prosthesis.Following impaction bone grafting for revision of THR in the presence of a femoral defect using either a longer stem or extramedullary augmentation reduces the defect strain to a greater degree compared to a standard stem without augmentation.
      Wiring
      • Stevens S.S.
      • Irish A.J.
      • Vachtsevanos J.G.
      • Csongradi J.
      • Beaupré G.S.
      A biomechanical study of three wiring techniques for cerclage-plating.
      Extramedullary plate fixed using six wires in all cases three wires used proximally and three wires used distally and three different wiring methods compared 1) single wrap 2) double wrap 3) double wrap using six plate inserts each time wires passing through eyelet of the insert plate.Double wrap with insert plate was more rigid and stable that the other two methods.
      • Han S.-M.
      Comparison of wiring techniques for bone fracture fixation in total hip arthroplasty.
      Four different wiring methods compared 1) a wire applied parallel to the fracture line 2) a wire applied normal to the fracture line 3)a second wire added parallel to the wire in case 2 4)a third wire added parallel to the wires in case 3.Placement of wires normal to the fracture line reduce the stem subsidence and crack opening in comparison to wiring in parallel to the fracture line.
      Computational studies
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      Three techniques were compared: 1)revision to a long stem prosthesis where effect of 3 stem lengths (passing the fracture site with 1, 2, and 3 FD) studied without any other additional fixation 2)lateral plating with a cortical bone allograft strut and cerclage wires (11 pass proximally and 8 pass distally) 3)plate with 5 proximal Parham bands and distal cortical screws –Ogden concept(rigid fixation considered between the plate and distal bony fragments).In long stem revision bypassing the fracture by 3 FD can lead to a further stress shielding at the fracture site. In plate fixation allograft strut transfer the stress more evenly than Ogden plate.
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      The effect of stem length (273, 240, 207,173 and 140 mm) using a cemented prosthesis design without any additional fixation tested.A stem prosthesis bypassing the femoral defect by 2 FD (207 mm) will reduce the risk of loosening of cemented revision cases to higher degree than a short stems.
      Key to content: C, cable; W, wire; HT, high tension; LT, low tension; Ant, anterior; Lat, lateral; Med, medial; LS, long stem; FD, femoral diameter.
      a Based on the description and available data in the paper we are not confident if 4 or 5 unicortical screws have been used for the proximal fixation of the plate.
      b This test was performed with a long stem compared to the standard stem in other cases.
      c Plate fixation was performed with three proximal and three distal cables.
      d A seven hole broad plate has been used. However the authors do not specify exactly how many screws and wires they used. We think that they have used three screws proximally and three screws distally.
      e Two seven hole broad plates fixed laterally and anteriorly each with unicortical screws proximally and bicortical screws distally.
      f A locking plate has been used in this case.
      There are also some contradictions between studies. For example,
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      ,
      • Wilson D.
      • Frei H.
      • Masri B.A.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical study comparing cortical onlay allograft struts and plates in the treatment of periprosthetic femoral fractures.
      did not find a clear trend between increasing the strut length and reduction in fracture movement (in anteroposterior and mediolateral plane).
      • Haddad F.S.
      • Dehaan M.N.
      • Brady O.
      • Masri B.A.
      • Garbuz D.S.
      • Goertzen D.J.
      • Oxland T.R.
      • Duncan C.P.
      A biomechanical evaluation of cortical onlay allograft struts in the treatment of periprosthetic femoral fracture.
      reported that decreasing strut length decreased axial rotation. They suggested that the fit of the strut to the femur could have a major role on fracture stability, with a smaller strut providing better fit to the bone. The closer cable spacing for shorter strut was also thought to be a contributing factor. In contrast,
      • Peters C.L.
      • Bachus K.N.
      • Davitt J.S.
      Fixation of periprosthetic femur fractures: a biomechanical analysis comparing cortical strut allograft plates and conventional metal plates.
      found that the strength of fixation in mediolateral plane, under single-leg stance loading, was significantly improved with the longer struts. They also did not find any significant difference under stair-climb loading between 160 and 200 mm strut lengths. This could suggest that femoral fixture design could be a potential factor that has led to difference in results of these studies with loading protocol being another important factor (cyclic loading in studies of Haddad et al. and Wilson et al. versus monotonic protocol in study of Peters et al.).
      There is also disagreement about the relative benefits of locking and non-locking plates. 
      • Fulkerson E.
      • Koval K.
      • Preston C.F.
      • Iesaka K.
      • Kummer F.J.
      • Egol K.A.
      Fixation of periprosthetic femoral shaft fractures associated with cemented femoral stems: a biomechanical comparison of locked plating and conventional cable plates.
      found that the locking construct was stiffer than the non-locking, Ogden, construct in axial and torsional loading but not under bending. In addition, although there was no statistical difference between the torsional failure loads, the locking construct failed at the screw holes in the proximal bone, whereas the Ogden construct allowed large rotations of the proximal bone fragment due to cable loosening. However, in similar comparisons between locking and non-locking plates, both
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      ,
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      did not find a marked difference between the two different designs.
      • Zdero R.
      • Walker R.
      • Waddell J.P.
      • Schemitsch E.H.
      Biomechanical evaluation of periprosthetic femoral fracture fixation.
      suggested that the discrepancy may lie in the specimens used, since both their study and that of
      • Talbot M.
      • Zdero R.
      • Schemitsch E.H.
      Cyclic loading of periprosthetic fracture fixation constructs.
      tested synthetic specimens whereas Fulkerson et al. used cadaveric tissue. Locking plates may be more effective where the bone quality is poor, a factor that is not captured in the synthetic specimens.
      In the case of long stem revision, the results of some studies (
      • Mihalko W.M.
      • Beaudoin A.J.
      • Cardea J.A.
      • Krause W.R.
      Finite-element modelling of femoral shaft fracture fixation techniques post total hip arthroplasty.
      ,
      • Panjabi M.M.
      • Trumble T.
      • Hult J.E.
      • Southwick W.O.
      Effect of femoral stem length on stress raisers associated with revision hip arthroplasty.
      ) show that bypassing the femoral defect by 1.5–2 femoral diameters could reduce the stress riser effect of the implant and
      • Mann K.A.
      • Ayers D.C.
      • Damron T.A.
      Effects of stem length on mechanics of the femoral hip component after cemented revision.
      showed that by passing the femoral defect by two femoral diameters would be most effective in minimising the risk of loosening. In contrast,
      • Barker R.
      • Takahashi T.
      • Toms A.
      • Gregson P.
      • Kuiper J.H.
      Reconstruction of femoral defects in revision hip surgery: risk of fracture and stem migration after impaction bone grafting.
      did not find that longer stems reduced the subsidence. They suggested that this difference in results compared to Mann et al. could be due to the impacted bone layer around the stem that was included in their experiments but not in the computational model of Mann et al.

      4. Discussion

      The current biomechanical literature relating to periprosthetic fractures was reviewed in this paper. Whilst there is some agreement in the results presented, there were also a number of differences, and it is clear that several issues need to be resolved if biomechanical studies are to provide clinically relevant information.
      Firstly, there is currently a lack of standardisation in the methods used. In the experimental studies, there is a lack of consistency in both the testing procedures and the measurements. This means it is difficult to make conclusive comparisons between the findings, which would be particularly useful since each experimental study can only examine a small subset of the patient variables and fixation methods available. A similar issue is also apparent in the computational studies. In this field, there is currently a drive towards the development of minimum standards of model validation, verification and sensitivity analysis to prove the robustness of the model and the conclusions drawn from it (
      • Anderson A.E.
      • Ellis B.J.
      • Weiss J.A.
      Verification, validation, and sensitivity studies in computational biomechanics.
      ,
      • Viceconti M.
      • Olsen S.
      • Nolte L.P.
      • Burton K.
      Extracting clinically relevant data from finite element simulations.
      ). As yet, the computational studies undertaken in the area of PFF have not fully demonstrated their compliance with these standards. Without such published information, it is difficult to gauge the validity of the results or the range of cases over which they apply.
      Secondly, the level of sophistication in both experimental and computational models is variable. In the experimental tests, there is generally a trade-off to be made between accuracy and consistency. This can be seen in the choice of specimen (cadaveric versus synthetic), and type of loading (physiological versus isometric). In the computational studies, this balance is between realism and time for development and processing, for example in the complexity of the geometry, material properties, fracture representation and loading. In both cases, there has yet to be consensus on the level of complexity required to generate clinically relevant results.
      Thirdly, from the methods shown in Table 1, it is clear that at present, biomechanical studies have concentrated on a relatively small subset of the types of periprosthetic fracture seen clinically. In fact, most of the experimental studies have focused on Vancouver type B1 fractures with types B2 and B3 being more challenging to test. Less attention has paid to types A and C fractures perhaps due to lower clinical incidence rates (
      • Corten K.
      • Vanrykel F.
      • Bellemans J.
      • Reynders Frederix P.
      • Simon J.P.
      • Broos P.L.O.
      An algorithm for the surgical treatment of periprosthetic fractures of the femur around a well-fixed femoral component.
      ,
      • Lindahl H.
      • Malchau H.
      • Oden A.
      • Garellick G.
      Risk factors for failure after treatment of a periprosthetic fracture of the femur.
      ). Here, there is real potential for a computational approach to test and evaluate the effective fixation methods for much greater range of fracture scenarios.
      Finally, and perhaps most importantly, the relationship between the results presented and the clinical situation needs to be better defined. At present, it is not clear how an ‘optimum’ construct would perform. There is currently a tendency to focus on the construct stiffness, but this may be misleading, especially because a high stiffness plate may cause stress shielding in the underlying bone. From a clinical point of view, there are two main issues: firstly that the fracture heals and secondly that the construct itself does not fail (
      • Buttaro M.A.
      • Farfalli G.
      • Paredes Nunez M.
      • Comba F.
      • Piccaluga F.
      Locking compression plate fixation of Vancouver type-B1 periprosthetic femoral fractures.
      ,
      • Tsiridis E.
      • Haddad F.S.
      • Gie G.A.
      Dall-Miles plates for periprosthetic femoral fractures: A critical review of 16 cases.
      ). At present, neither of these are fully quantified in the biomechanical literature relating to PPF.
      If biomechanical studies of PFF are to be used to optimise clinical performance, then all of these issues need to be tackled. One approach would be to use a parallel experimental and computational testing programme to utilise the advantages of each. The computational approach would enable parameters including bone quality, fracture configuration and location to be easily varied so that a much wider range of scenarios could be examined than has been undertaken so far. These models would, however, require validation (
      • Viceconti M.
      • Olsen S.
      • Nolte L.P.
      • Burton K.
      Extracting clinically relevant data from finite element simulations.
      ). This could be achieved through parallel experimental testing which, with careful selection, could be undertaken on a much smaller subset of cases. The computational models could also be used to run more thorough sensitivity analyses to gain a greater understanding of the importance of the different input parameters and the level of sophistication required. The outcomes of the sensitivity analysis could, in turn, be used to determine the most robust experimental procedure and aid in the development of experimental standards.
      In order to tackle this final issue, there is a need to draw more information from animal and in vivo studies (
      • Claes L.E.
      • Heigele C.A.
      • Neidlinger-Wilke C.
      • Kaspar D.
      • Seidl W.
      • Margevicius K.J.
      • Augat P.
      Effects of mechanical factors on the fracture healing process.
      ,
      • Goodship A.E.
      • Kenwright J.
      The influence of induced micromovement upon the healing of experimental tibial fractures.
      ) and available measuring techniques for fracture healing (
      • Cunningham J.L.
      • Kenwright J.
      • Kershaw C.J.
      Biomechanical measurement of fracture healing.
      ) to determine the window of conditions across the fracture site that will enable healing to take place. There is also a need to gain a greater understanding of the failure mechanisms occurring clinically, which are not well documented at present. If more information could be gleaned on the likely loading at the time of failure, and whether this were due to repeated cycles of fatigue or single adverse occurrences such as falls, then these situations could be better replicated in the biomechanical models. There is therefore a need for the biomechanics community to work more closely with both biologists and clinicians to ensure that the knowledge in these areas is fully taken into account in the evaluation of PFF.
      As the incidences of periprosthetic fracture continue to grow, the need for biomechanically optimised fixation methods becomes more pressing. The literature reviewed in this paper provides a foundation of experimental and computational procedures that evaluate a small subset of the situations seen clinically. This work could now be built on by combining the two approaches, along with better clinical information on fracture healing and modes of failure. This would enable more robust, clinically-relevant models to be developed and biomechanically optimised treatments for these types of fractures to be found.

      Conflict of interest

      The authors confirm that there is no conflict of interest in this manuscript.

      Acknowledgements

      This work is supported by British Orthopaedic Association (BOA) through the Latta Fellowship. In addition, it was partially funded through WELMEC, a Centre of Excellence in Medical Engineering funded by the Wellcome Trust and EPSRC, under grant number WT 088908/Z/09/Z and additionally supported by the NIHR (National Institute for Health Research) as part of a collaboration with the LMBRU (Leeds Musculoskeletal Biomedical Research Unit).

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