Clinical Biomechanics

Editorial Board

2012-02-01

Investigation of abdomen surface deformation due to life excitation: Implications for implant selection and orientation in laparoscopic ventral hernia repair

Czesław Szymczak, Izabela Lubowiecka, Agnieszka Tomaszewska, Maciej Śmietański — 2011-09-19

Abstract: Background: Ventral hernia is a common medical problem. Statistically there are around 10% recurrences of the sickness. The authors' former investigation proved edges of the hernia orifice displacements to be one of the factors causing recurrence. Thus, experimental investigation of the abdomen surface deformation due to some normal activities of people is studied.Methods: Eight slim, healthy people were asked to extremely stretch their abdomens. Bending, stretching and expiration were considered. The deformations registration was made by two cameras located in front of the patient on both sides. Special calculation procedure was used in order to transform characteristic point displacements to strains of abdomen in different directions.Findings: The extreme strains, their localization and directions are identified. The study proves that the highest strains, bigger than 25% on average, appear in the upper part of the central vertical line of the abdomen and in lower sides in semi-vertical direction. The lowest strains, smaller than 7%, occur in a horizontal line situated low in the abdomen. For each patient similar zones of smaller or bigger strains are identified, however a wide discrepancy of the strain values obtained for different patients is stated. For example the strains in lower part in semi-vertical direction for one patient equals 9% and for another 134%!Interpretation: The acquired conclusions may be useful for surgeons in finding practical solutions to dilemmas concerning the choice of an implant (elastic or stiff) for a specific ventral hernia, its proper connection with fascia and orientation in the abdomen.

Which postures are most suitable in assessing spinal fusion using radiostereometric analysis?

2011-09-19

Abstract: Background: Up to now, plain radiographs are not well suited to assess spinal fusion. Radiostereometric analysis performed for two postures may deliver more reliable results. However, it is unknown, which postures are most suitable for this procedure.Methods: In a finite element study, spinal fusion at the level L4–5 was simulated assuming a posterior approach and the implantation of two cages and a spinal fixation device. The change of the distance between markers in vertebrae adjacent to the cages was calculated for moving from one of the following postures standing, flexion, extension, axial rotation, lying, and extension in a lying position to another. The changes of marker distances were calculated for the intact model, as well as for the situations: directly after surgery before fusion started, in the early-fusion-phase and in the late-fusion-phase. Differences in the marker motion between two postoperative situations were also calculated.Findings: The most anteriorly placed markers showed the greatest motion between two postures. The greatest differences in marker motions between the two situations before-fusion and early-fusion-phase (0.54mm) as well as between early-fusion-phase and late-fusion-phase (0.34mm) were found for the two postures flexion while standing and extension in a lying position.Interpretation: Pairs of X-rays taken while standing with maximum flexed upper body and while lying with maximum extended trunk are most suited for the assessment of spinal fusion when using radiostereometric analysis.

Biomechanical, psychosocial and individual risk factors predicting low back functional impairment among furniture distribution employees

2011-09-28

Abstract: Background: Biomechanical, psychosocial and individual risk factors for low back disorder have been studied extensively however few researchers have examined all three risk factors. The objective of this was to develop a low back disorder risk model in furniture distribution workers using biomechanical, psychosocial and individual risk factors.Methods: This was a prospective study with a six month follow-up time. There were 454 subjects at 9 furniture distribution facilities enrolled in the study. Biomechanical exposure was evaluated using the American Conference of Governmental Industrial Hygienists (2001) lifting threshold limit values for low back injury risk. Psychosocial and individual risk factors were evaluated via questionnaires. Low back health functional status was measured using the lumbar motion monitor. Low back disorder cases were defined as a loss of low back functional performance of −0.14 or more.Findings: There were 92 cases of meaningful loss in low back functional performance and 185 non cases. A multivariate logistic regression model included baseline functional performance probability, facility, perceived workload, intermediated reach distance number of exertions above threshold limit values, job tenure manual material handling, and age combined to provide a model sensitivity of 68.5% and specificity of 71.9%.Interpretation: The results of this study indicate which biomechanical, individual and psychosocial risk factors are important as well as how much of each risk factor is too much resulting in increased risk of low back disorder among furniture distribution workers.

The effect of lateral epicondylosis on upper limb mechanical parameters

2011-09-21

Abstract: Background: Lateral epicondylosis is a prevalent and costly musculoskeletal disorder characterized by degeneration of the common extensor tendon origin at the lateral epicondyle. Grip strength is commonly affected due to lateral epicondylosis. However, less is known about the effect of lateral epicondylosis on other functional parameters such as ability to react to rapid loading.Methods: Twenty-nine lateral epicondylosis participants and ten controls participated in a case-control study comparing mechanical parameters (mass, stiffness and damping), magnetic resonance imaging signal intensity and grip strength of injured and uninjured limbs. A mixed effects model was used to assess the effect of dominance and injury on mechanical parameters and grip strength.Findings: Significant effect of injury and dominance was observed on stiffness, damping and grip strength. An injured upper limb had, on average, 18% less stiffness (P<0.01, 95% CI [9.8%, 26%]), 21% less damping (P<0.01, 95% CI [11%, 31%]) and 50% less grip strength (P<0.01, 95% CI [37%, 61%]) than an uninjured upper limb. The dominant limb had on average 15% more stiffness (P<0.01, 95% CI [8.0%, 23%], 33% more damping (P<0.01, 95% CI [22%, 45%]), and 24% more grip strength (P<0.01, 95% CI [6.6%, 44%]) than the non-dominant limb.Interpretation: Lower mechanical parameters are indicative of a lower capacity to oppose rapidly rising forces and quantify an important aspect of upper limb function. For individuals engaged in manual or repetitive activities involving the upper limb, a reduction in ability to oppose these forces may result in increased risk for injury or recurrence.

The effects of walking sticks on gait kinematics and kinetics with chronic stroke survivors

2011-09-05

Abstract: Background: There are robust clinical paradigms against the prescription of walking sticks for people with stroke. However, there is little information on the biomechanics of gait with and without these devices to guide clinical practice. Therefore, this study investigated how the use of walking sticks (canes or crutches) affected both the kinematics and kinetics of gait in people with chronic stroke after their walking had stabilized.Methods: Nineteen people with chronic stroke walked at both comfortable and fast speeds. A 3-D motion analysis system and one force platform were used to obtain kinematic and kinetic data of the paretic lower limb during four conditions: With and without walking sticks, and at comfortable and fast speeds. Outcomes included linear kinematics (walking speeds) and angular kinematics (maximum joint angles), power, and work of the paretic hip, knee and ankle joints in the saggital plane.Findings: The use of walking sticks resulted in increases in speed during both fast (P<0.001) and comfortable (P=0.001) walking, but did not result in changes in maximum joint angles. This also led to increases in ankle plantar flexion (P<0.01), knee extension (P<0.01), and hip flexion (P<0.001) power generation, but did not result in changes in work. There were no greater changes as a result of using walking sticks during fast versus comfortable walking for any outcome.Interpretatin: The outcomes with the use of walking sticks were beneficial, which suggests that the prescription of these devices is not detrimental to walking that was stabilized in people with stroke.

Increased power generation in impaired lower extremities correlated with changes in walking speeds in sub-acute stroke patients

John Brincks, Jørgen Feldbæk Nielsen — 2011-09-07

Abstract: Background: Establishing changes in net joint power in the lower extremity of patients during recovery of walking might direct gait training in early stroke rehabilitation. It is hypothesized that (1) net joint power in the lower extremity joints would increase in sub-acute stroke patients following gait rehabilitation, and (2) the improvements in net joint power would be significantly correlated with changes in walking speed.Methods: Thirteen sub-acute patients (<3months from stroke onset) participated in the study. All patients completed 6weeks of gait training (3weeks of robotic gait training and 3weeks of physiotherapy). The gait patterns were analyzed using 3D motion analysis before and after training. The assessed variables were; gait speed and the net peak joint power of the ankle plantar flexors, hip extensors, hip flexors, hip abductors, and knee extensors.Findings: Ankle plantar flexor power in the impaired limb and hip extensor power in the unimpaired limb increased significantly following training (133% and 77%, respectively; P<0.002). Improvements (from 20% to 133%) in net joint power of the ankle plantar flexors, hip extensors, hip flexors, and hip abductors of the impaired limb and ankle plantar flexors and hip abductors of the unimpaired limb significantly correlated with the recovery of walking speed following training (0.24m/s to 0.51m/s) (r=0.71–0.86).Interpretation: The findings suggested investigations for strengthening the plantar flexors, hip flexors, hip extensors, and hip abductors concentrically, and knee extensors eccentrically in the impaired limb to determine the effectiveness in improving gait performance.

Foot placement variability as a walking balance mechanism post-spinal cord injury

Kristin V. Day, Steven A. Kautz, Samuel S. Wu, Sarah P. Suter, Andrea L. Behrman — 2011-10-17

Abstract: Background: Spinal cord injury affects walking balance control, which necessitates methods to quantify balance ability. The purposes of this study were to 1) examine walking balance through foot placement variability post-injury; 2) assess the relationship between measures of variability and clinical balance assessments; and 3) determine if spatial parameter variability might be used as a clinical correlate for more complex balance measurements.Methods: Ten persons with spinal cord injury walked without devices on a split-belt treadmill at self-selected speeds. Ten healthy controls walked at 0.3 and 0.6m/s for comparison. Variability of step width and length, anteroposterior and mediolateral foot placements relative to center-of-mass, and margin-of-stability were calculated. Clinical assessments included Berg Balance Scale and Dynamic Gait Index.Findings: Participants with spinal cord injury demonstrated significantly different variability in all biomechanical measures compared to controls (P≤0.007). Berg Balance Scale scores were significantly inversely associated with step length as well as anteroposterior and mediolateral foot placement variability (P≤0.05). Dynamic Gait Index scores were significantly inversely associated with mediolateral foot placement variability (P≤0.05). Participants with spinal cord injury showed significant correlations between spatial parameter variability and all other measures (P≤0.005), except between step length and margin-of-stability (P=0.068); controls revealed fewer correlations.Interpretation: Persons post-spinal cord injury exhibit an abnormal amount of stepping variability when challenged to walk without devices, yet preserve the ability to avoid falling. When complex laboratory measures of variability are unavailable clinically, spatial parameter variability or standardized balance assessments may be plausible indicators of walking balance control.

Short-term changes in protective stepping for lateral balance recovery in older adults

2011-10-17

Abstract: Background: Fall prevention for older adults is dependent on the ability to maintain protective balance. This study measured the short-term changes of protective stepping following waist-pull perturbations in the medio-lateral direction, to identify what, if any, properties of protective stepping are improved with repeated perturbation exposures.Methods: Sixty waist-pulls (2 directions×5 intensities×6 repetitions) from a single session were analyzed separately as early, middle, and late testing periods, for a comparison over time of typical responses. Outcome measures included the number of evoked steps, type of step, incidence of interlimb collisions, and kinematic and kinetic properties of the first step in frequently used crossover-type responses.Findings: Improvements were evident as significantly reduced number of steps and collisions. However, these improvements could not be completely accounted for by significant changes in first step kinematic or kinetic properties.Interpretation: We infer that older individuals experiencing repeated lateral waist-pull perturbations optimize the predictive or feed-forward motor control for balance recovery through stepping.

Primary stability and strain distribution of cementless hip stems as a function of implant design

2011-09-02

Abstract: Background: Short stem prostheses have been developed to preserve the femoral bone stock. The purpose of this study was to evaluate the stress-shielding effect in the proximal femur as well as the micromotion between bone and implant as a measure of primary stability for a new short stem in comparison to a clinically successful short stem and a straight stem.Methods: Using paired fresh human femurs, stress shielding was examined by using tri-axial strain gage rosettes. The strain distribution of the proximal femur was measured before and after implantation of three cementless prostheses of different design concepts and stem lengths. Furthermore, interface motion and rotational stability were investigated under dynamic loading (100–1600N) after 100,000 load cycles using inductive miniature displacement transducers.Findings: A reduction of longitudinal cortical strains in the proximal femur was displayed for all three implants. The reduction was less pronounced for the shorter stem implants, however.Interface motion was below the critical threshold of 150μm at almost all measuring points for all three stems, with a tendency for greater rotational stability in the shorter stem implants.Interpretation: The new short stem prosthesis displayed reduced stress shielding and comparable primary stability to an established short stem and a conventional shaft design. Shortening the stem did not negatively influence primary stability. The clinical implications of these findings remain to be proven.

Femoral head to neck offset after hip resurfacing is critical for range of motion

J. Girard, N. Krantz, D. Bocquet, G. Wavreille, H. Migaud — 2011-09-19

Abstract: Background: Range of motion after hip arthroplasty may be limited by soft tissues around the hip, extra-articular contact and femoral stem-neck contact with the acetabular articular surface. Femoral head–neck diameter ratio is recognized as a major factor influencing hip range of motion. In hip resurfacing, range of motion is constrained by “cup component to femoral neck” contact. To avoid cup-to-bone contact or to increase the degree of flexion at which it occurs, anterior translation of the femoral component relative to the central femoral neck axis may improve anterior head–neck offset and hip flexion. We questioned whether low or high anterior femoral head to neck offset, cup inclination, stem anteversion, and component size influenced postoperative range of motion and hip flexion in patients who had undergone hip resurfacing.Methods: We prospectively followed 66 patients (68 hips) who underwent hip resurfacing at a mean age at operation of 46.4years (range, 19–60years). Mean follow-up was 37.5months (range, 33–41months). No patient was lost to follow-up. All patients were evaluated clinically and range of motion was precised. Radiological measurement evaluated the anterior femoral head–neck offset.Findings: Mean anterior neck–head offset was 7.5mm (range, 5–12mm). We found significant linear regression correlation between anterior offset and flexion (R=0.66) and between anterior offset and global range of motion (R=0.51). One millimeter of anterior offset increased hip range of motion by 5° in flexion. No significant correlations were found between global range of motion or flexion arc of motion and component size, stem anteversion, cup inclination, gender ratio, preoperative arc of flexion or global range of motion.Interpretation: Restoring or improving deficient anterior femoral head–neck offset appears important for restoring postoperative range of motion and specifically hip flexion.

Effect of lower limb dominance on knee joint kinematics after anterior cruciate ligament reconstruction

Hongsheng Wang, James E. Fleischli, Naiquan Nigel Zheng — 2011-09-07

Abstract: Background: Normal ambulatory kinematics of the knee joint is often not fully restored after anterior cruciate ligament reconstruction, which may increase the risk for cartilage degeneration and premature osteoarthritis in the involved knees. Lower limb dominance may have impacts on knee joint kinematics after anterior cruciate ligament reconstruction, which may lead to a different prevalence of cartilage degeneration. This study aimed to evaluate the knee joint kinematics among patients with reconstruction on the dominant and non-dominant side.Methods: Forty-one subjects with unilateral anterior cruciate ligament reconstruction (19 dominant, 22 non-dominant) were recruited after being discharged from rehabilitation programs. Twenty healthy subjects were recruited as the control group. Six degrees-of-freedom tibiofemoral motion during level walking was determined using a redundant point cluster-based marker set. Tibiofemoral joint motion and its bilateral differences were compared within each group and between groups.Findings: The non-dominant reconstructed knees had less extension compared to their contralateral knees at heel strike and during middle stance phase (P=0.02); whereas, the dominant reconstructed knees exhibited significantly reduced varus rotation (−2.1° on mean, P=0.027) and internal tibial rotation (P=0.034) compared to their contralateral knees during both stance and swing phases.Interpretation: The results show that different kinematics has been developed between the involved dominant and non-dominant knees after anterior cruciate ligament reconstruction, especially the secondary rotations. The differences are consistent with the unequal prevalence of cartilage degeneration in the knee joint. The findings demonstrated that the lower limb dominance had a significant effect on post-surgery knee kinematics.

Mimicking anatomical condylar configuration into knee prosthesis could improve knee kinematics after TKA — A computational simulation

2011-09-13

Abstract: Background: Restoration of femoral rollback and tibial internal rotation are two of the major objectives following total knee arthroplasty. Previously, we improved prosthetic knee kinematics by replicating the convexly lateral tibial plateau of intact knee. This study attempted to regain more normal knee kinematics through a posterior cruciate ligament retaining knee, which simultaneously incorporated convexly lateral tibial plateau and anatomical condylar configuration into the prosthesis design.Methods: Computational simulation was utilized to analyze motion of three-dimensional knee models. Three total knee systems with consistent convex insert design but with different condylar heights of 0, 2.7 and 4.7mm were investigated in present study. Magnetic resonance images of the subject were utilized to construct the bone models and to distinguish the attachment sites of ligaments and tendons. The distal femurs were modeled to rotate about designated flexion axes of femoral components, and the motion of the proximal tibia was unconstrained except further activity of flexion/extension. Movements of the medial/lateral condyles and tibial rotation were recorded and analyzed.Findings: Significant improvements in posterior movement of the lateral condyle and in tibial internal rotation were observed for knee models with different condylar heights, as compared to the knee model with consistent condylar height, when flexion exceeded 100°. Results also revealed that excessive difference in condylar height over anatomical condylar configuration provided no contribution to the restoration of normal knee kinematics.Interpretation: Replicating the morphology of anatomical condylar configuration of the intact knee into knee prostheses could improve knee kinematics during higher knee flexion.

A novel intramedullary nail for micromotion stimulation of tibial fractures

2011-09-22

Abstract: Background: Animal studies and clinical trials have suggested that early application of controlled axial micromotion can accelerate healing of long bone fractures compared to rigid fixation. However, experimental investigations of micromotion constructs have been limited to external fixators, which have a higher incidence of complications than intramedullary nails. The purpose of this study was to assess whether a novel intramedullary nail design can generate stimulatory micromotion under minimal weight-bearing loads typical of the early healing period.Methods: Eight cadaver tibiae were reamed, osteotomised, and implanted with commercially-available IM nails fitted with a custom insert that allowed 1mm of axial micromotion after proximal/distal interlocking. Specimens were mounted in a materials testing machine and subjected to cyclic axial loading while interfragmentary motion was measured using an extensometer. Implants were also tested in standard statically-locked mode.Findings: The average force required to cause distraction of the fracture gap in micromotion mode was 37.0 (SD 21.7) N. The mean construct stiffness was 1046.8 (SD 193.6) N/mm in static locking mode and 512.4 (SD 99.6) N/mm in micromotion mode (significantly different, P<0.001).Interpretation: These results support the development of a micromotion-enabled IM nail because the forces required to cause interfragmentary movements are very low, less than the weight of the hanging shank and foot. In contrast to rigid-fixation nails, which require significant weight-bearing to induce interfragmentary motion, the micromotion-enabled nail may allow movement in non-weight-bearing patients during the early healing period when the benefits of mechanical stimulation are most critical.

The role of ankle ligaments and articular geometry in stabilizing the ankle

2011-10-17

Abstract: Background: Ankle joint stability is a function of multiple factors, but it is unclear to what extent extrinsic factors such as ligaments and intrinsic elements such as geometry of the articular surfaces play a role. The purposes of this study were to determine the contribution of the ligaments and the articular geometry to ankle stability and to determine the effects of ankle position and simulated physiological loading upon ankle stability.Methods: Sixteen cadaveric lower extremities were studied in unloaded and with axial load equivalent to body weight. Anterior–posterior, medial–lateral translation and internal–external rotation tests were performed in neutral, dorsiflexion and plantarflexion ankle positions. Intact ankle stability was measured; ankle ligaments were serially sectioned and retested.Findings: For unloaded condition, the lateral ligament accounted for 70% to 80% of anterior stability and the deltoid ligaments for 50% to 80% of posterior stability. Both ligaments contributed 50% to 80% to rotational stability; however, the ligaments did not provide the primary restraints to medial–lateral stability. For loaded ankle condition, articular geometry contributed 100% to translational and 60% to rotational stability. The ankle was less stable in plantarflexion and more stable in dorsiflexion.Interpretation: The contribution of extrinsic and intrinsic elements to ankle stability is dependent upon the load and direction of force applied. This study underscores the importance of restoring soft tissues about the ankle to the anatomic condition during reconstruction operations for instability, trauma and arthritis.

Dynamic impression insole in rheumatoid foot with metatarsal pain

Bao-Chi Chang, Jia-Yi Wang, Biing-Shiun Huang, Hsiao-Yi Lin, Winson C.C. Lee — 2011-09-05

Abstract: Background: Custom molded insoles with metatarsal supports are used to redistribute excessive loading under the metatarsal heads in patients with metatarsalgia. However, these pressure reductions are usually insufficient for the rheumatoid foot with painful deformed metatarsal heads. We developed an effective insole made by sequential foam padding under successive walking impression.Methods: Seventeen consecutive rheumatoid arthritic outpatients with metatarsal pain participated in this repeated measures study of 7-mm flat Ethylene Vinyl Acetate, custom molded and dynamic impression insoles. Peak plantar pressure, pressure-time integral, contact area and mean force were measured by a Pedar-X mobile system. Pain levels were assessed using a Visual Analog Scale (0–10).Findings: Compared to the Ethylene Vinyl Acetate control, the metatarsal head peak pressure and pressure–time integral were significantly reduced in dynamic impression insoles by 46.3% (P<0.001) and 48.9% (P<0.001), respectively. Compared to the custom molded insole, the dynamic impression insole significantly reduced 18.3% of peak pressure (P<0.001) and 20.1% of pressure–time integral (P<0.001) by increasing 8.1% of contact area (P=0.005) at the metatarsal heads, but there were no significant differences in all variables at the heel. After using the dynamic impression insole, the mean pain score was significantly reduced from 7.6 to 1.1 (P<0.001), and six participants experienced total pain-relief in walking.Interpretation: Dynamic impression insoles effectively relieve metatarsal pain because of a larger weight-bearing area. Forefoot shape during walking should be taken into consideration in orthotic designs for maximum pressure reduction. Consequently, we recommend using materials with memory properties to dynamically accommodate painful metatarsal heads.

Comfort and midfoot mobility rather than orthosis hardness or contouring influence their immediate effects on lower limb function in patients with anterior knee pain

Kathryn Mills, Peter Blanch, Bill Vicenzino — 2011-09-19

Abstract: Background: Despite evidence for use of foot orthoses in the treatment of anterior knee pain, there is a paucity of research into their mechanisms of action. This study (i) determined the immediate lower limb kinematics and muscle activity adaptations, and (ii) evaluated the effect of individual's comfort and foot mobility.Methods: Forty individuals diagnosed with anterior knee pain were measured for lower limb kinematics and electromyographic activity (via surface electrodes) while they jogged in three prefabricated contoured orthoses (hard, medium and soft) and a soft-flat orthosis. Subjects ranked orthoses in order of comfort.Findings: Soft orthoses were more comfortable. No immediate adaptations in kinematics and electromyographic activity were observed when orthoses were added to shoes. There were few effects of perceived comfort and foot mobility, one being a significant interaction in frontal plane hip motion (Pillai's V=0.089, P=0.031) with the least comfortable orthosis producing the greatest relative adduction in those with mobile feet (0.54° (standard deviation 0.87)). Other main effects were a significant increase in vastus lateralis activity when wearing the least comfortable orthosis (6.94%, P=0.007) and a delay in offset of medial gastrocnemius in individuals with less mobile feet (1.51%, P=0.045).Interpretation: It is becoming apparent that it is important to use more comfortable foot orthoses in a condition like anterior knee pain, where there is an associated increased hip adduction and vastus lateralis activity with least comfortable orthoses. Future research is needed to determine adaptations after ongoing wearing of orthoses.