Clinical Biomechanics

Editorial Board

2010-10-01

An analytical model for rotator cuff repairs

A. Aurora, J.E. Gatica, A.J. van den Bogert, J.A. McCarron, K.A. Derwin — 2010-06-28

Abstract: Background: Currently, natural and synthetic scaffolds are being explored as augmentation devices for rotator cuff repair. When used in this manner, these devices are believed to offer some degree of load sharing; however, no studies have quantified this effect. Furthermore, the manner in which loads on an augmented rotator cuff repair are distributed among the various components of the repair is not known, nor is the relative biomechanical importance of each component. The objectives of this study are to (1) develop quasi-static analytical models of simplified rotator cuff repairs, (2) validate the models, and (3) predict the degree of load sharing provided by an augmentation scaffold.Methods: The individual components of the repair constructs were modeled as non-linear springs, and the model equations were formulated based on the physics of springs in series and parallel. The model was validated and used to predict the degree of load sharing provided by a scaffold. Parametric sensitivity analysis was used to identify which of the component(s)/parameter(s) most influenced the mechanical behavior of the augmented repair models.Findings: The validated models predict that load will be distributed ∼70–80% to the tendon repair and ∼20–30% to the augmentation component. The sensitivity analysis suggests that the greatest improvements in the force carrying capacity of a tendon repair may be achieved by improving the properties of the bone–suture–tendon interface. Future studies will perform parametric simulation to illustrate the manner in which changes to the individual components of the repair, representing different surgical techniques and scaffold devices, may influence the biomechanics of the repair construct.

Analyzing glenohumeral torque–rotation response in vivo

2010-07-07

Abstract: Background: Because the human shoulder has many degrees of freedom that allow redundant means of producing the same net humerothoracic motion, there are many impediments to objective, repeatable assessment of shoulder function in vivo. Devices designed to date have suffered from poor reliability. In this study we introduce a new device and methods to evaluate human shoulder kinematics and evaluate its reproducibility from subject to subject and from day to day.Methods: This was a controlled laboratory study. Using electromagnetic motion sensors to record the position and orientation of the thorax, scapula, and humerus, we quantified the kinematic response of twenty four normal shoulders in response to known internal–external torque application. A four-parameter logistic function was selected to characterize the strident features of the torque–rotation relationship.Findings: Our analysis in conjunction with the measurement technique described herein, allowed the passive glenohumeral internal–external range of motion to be differentiated from other motion components and was determined to within 9.6% of full scale over three repeated trials. Range of motion was the most reliable biomechanical outcome, more so than computed indices of glenohumeral flexibility and hysteresis. The exact profile of the torque–rotation response, and therefore the repeatability of the calculated outcomes, was unique from shoulder to shoulder.Interpretation: The development of the capacity for precise, non-invasive measurement of shoulder biomechanics over time is a requisite step towards optimizing treatment of shoulder injury and disease. Our current methods are superior to previous attempts at trying to non-invasively evaluate the biomechanics of the glenohumeral joint.

Muscle activation patterns in the scapular positioning muscles during loaded scapular plane elevation: The effects of Latent Myofascial Trigger Points

Karen R. Lucas, Peter A. Rich, Barbara I. Polus — 2010-07-28

Abstract: Background: Latent Myofascial Trigger Points are pain-free neuromuscular lesions that have been found to affect muscle activation patterns in the unloaded state. The aim was to extend these observations to loaded motion by investigating muscle activation patterns in upward scapular rotator muscles (upper and lower trapezius and serratus anterior) hosting Latent Myofascial Trigger Points simultaneously with lesion-free synergists for shoulder abduction (infraspinatus and middle deltoid). This approach allowed examination of the effects of these lesions on both their hosts and their lesion-free synergists in order to understand their effects on the performance of shoulder abduction.Methods: Surface electromyography was employed to measure the timing of onset of muscle activation of the upper and lower trapezius and serratus anterior (upward scapular rotators), infraspinatus (rotator cuff) and middle deltoid (abductor of the arm) initially without load and then with light (1–4kg) dumbbells. Comparisons were made between control (no Latent Trigger Points; n=14) and Latent Trigger Point (n=28) groups.Findings: The control group displayed a relatively stable sequence of muscle activation that was significantly different in timing and variability to that of the Latent Trigger Point group in all muscles except middle deltoid (all P<0.05). The Latent Trigger Point group muscle activation pattern under load was inconsistent, with the only common feature being the early activation of the infraspinatus.Interpretation: The presence of Latent Trigger Points in upward scapular rotators alters the muscle activation pattern during scapular plane elevation, potentially predisposing to overuse conditions including impingement syndrome, rotator cuff pathology and myofascial pain.

Intramedullary nailing vs. palmar locked plating for unstable dorsally comminuted distal radius fractures: A biomechanical study

2010-07-08

Abstract: Background: The purpose of this study was to compare the stability of a 2.4mm palmar locking compression plate and a new intramedullary nail-plate-hybrid Targon DR for dorsally comminuted distal radius fractures.Methods: An extraarticular 10mm dorsally open wedge osteotomy was created in 8 pairs of fresh frozen human radii to simulate an AO–A3-fracture. The fractures were stabilized using one of the fixation methods. The specimens were loaded axially with 200N and dorsal-excentrically with 80N. 2000cycles of dynamic loading and axial loading-to-failure were performed.Findings: Axial loading revealed that intramedullary osteosynthesis (Targon DR: 369N/mm) was significantly (p=0.017) stiffer than plate osteosynthesis (Locking compression plate: 131N/mm). With 214N/mm the intramedullary nail also showed higher stability during dorsal excentric loading than the Locking compression plate with 51N/mm (p=0.012). After 2000cycles of axial loading with 80N the Targon DR-group was significantly stiffer than the Locking compression plate-group under both loading patterns. Neither group showed significant changes in stiffness after 2000cycles. Under dorsal excentric loading the Targon DR-group was still significantly stiffer with 212N/mm than the Locking compression plate-group with 45N/mm (p=0.012). The load to failure tests demonstrated higher stability of intramedullary nailing (625N) when compared to plate osteosynthesis (403N) (p<0.025).Interpretation: The study shows that intramedullary fixation of a distal AO–A3 radial fracture is biomechanically more stable than volar fixed-angle plating under axial and dorsal-excentric loading in an experimental setup.

Biomechanics of the transverse carpal arch under carpal bone loading

Kai-Hua Xiu, Joo-Han Kim, Zong-Ming Li — 2010-06-28

Abstract: Background: Carpal tunnel release and conservative interventions are widely used in clinical therapies of carpal tunnel syndrome. The efficacy of these treatment and interventions mainly lies in the exploitation of the mechanical properties of carpal tunnel. This study investigated the structural mechanics of the transverse carpal arch using cadaveric hands.Methods: Paired force was applied to the insertion sites of the transverse carpal ligament at both the distal (hamate–trapezium) and proximal (pisiform–scaphoid) levels of the carpal tunnel. The two pairs of forces were simultaneously applied in an inward or outward direction when the transverse carpal ligament was intact and transected. Transverse carpal arch and carpal tunnel compliance in response to the forces were analyzed. Three-way repeated measures ANOVA were used to examine the effect of the transverse carpal ligament status (intact/transected), the level of the carpal tunnel (distal/proximal) and the force application direction (inward/outward) on the biomechanics of the transverse carpal arch.Findings: Transverse carpal ligament plays a stabilizing role in resisting outward deformation of the carpal tunnel. The carpal tunnel at the proximal level is more flexible than the carpal tunnel at the distal level. The carpal tunnel is more compliant under the inward force application than under the outward force application.Interpretation: The understanding of carpal tunnel mechanics potentially helps to improve the existing strategies and to develop alternatives for the treatment of carpal tunnel syndrome.

Knee joint anatomy predicts high-risk in vivo dynamic landing knee biomechanics

Scott G. McLean, Sarah M. Lucey, Suzan Rohrer, Catherine Brandon — 2010-07-05

Abstract: Background: With knee morphology being a non-modifiable anterior cruciate ligament injury risk factor, its consideration within injury prevention models is limited. Knee anatomy, however, directly influences joint mechanics and the potential for injurious loads. With this in mind, we explored associations between key knee anatomical and three-dimensional biomechanical parameters exhibited during landings. We hypothesized that lateral and medial posterior tibial slopes and their ratio, and tibial plateau width, intercondylar distance and their ratio, were proportional to peak stance anterior knee joint reaction force, knee abduction and internal rotation angles.Methods: Twenty recreationally active females (21.2 (1.7) years) had stance phase three-dimensional dominant limb knee biomechanics recorded during ten single leg land-and-cut tasks. Six anatomical indices were quantified for the same limb via a series of two dimensional (sagittal, transverse and coronal) magnetic resonance images. Linear stepwise regression analyses examined which of these anatomical factors were independently associated with each of the three mean subject-based peak knee biomechanical measures.Findings: Lateral tibial slope was significantly (P<0.0001) correlated with peak anterior knee joint reaction force, explaining 60.9% of the variance. Both tibial plateau width:intercondylar distance (P<0.0001) and medial tibial slope:lateral tibial slope (P<0.001) ratios were significantly correlated with peak knee abduction angle, explaining 75.4% of the variance. The medial tibial slope:lateral tibial slope ratio was also significantly (P<0.001) correlated with peak knee internal rotation angle, explaining 49.2% of the variance.Interpretation: Knee anatomy is directly associated with high-risk knee biomechanics exhibited during dynamic landings. Continued understanding of multifactorial contributions to the anterior cruciate ligament injury mechanism should dictate future injury screening and prevention efforts in order to successfully cater to individual joint vulnerabilities.

Factors influencing the tensile strength of repaired Achilles tendon: A biomechanical experiment study

2010-06-21

Abstract: Background: Operative treatment has been advocated as the method of choice to repair Achilles tendon rupture as surgery results in reduced re-rupture rate and faster rehabilitation. Many surgical techniques have been introduced allowing for postoperative early motion of the ankle joint. However, it is currently very difficult for surgeons to determine the optimal treatment conditions for ruptured Achilles tendon with an increasing number of end-to-end suture methods, suture materials, and epitenon suture techniques.Methods: In the present biomechanical experiment study based on an orthogonal design, thirty-two New Zealand white rabbits received Achilles tendon tenotomy and subsequent operative treatment to repair the tendon employing four end-to-end suture methods, four suture materials, and four epitenon suture techniques. The tensile strength of the repaired Achilles tendon was investigated at four rehabilitation periods, and in comparison with the results of another sixteen rabbits with normal Achilles tendons.Findings: The end-to-end suture method contributed most to the final Achilles tendon tensile strength in addition to rehabilitation period, with the highest values occurring with the use of the parachute-like (“Pa” bone) suture method. The other two factors, namely, suture material and epitenon suture technique, had relatively little influence on the results.Interpretation: The parachute-like (“Pa” bone) surgical technique is superior to the other three end-to-end suture methods, with enhanced tensile strength of the repaired tendon. This method allows for postoperative early kinesitherapy of the ankle and knee joints. Therefore, this technique is highly recommended in clinical situations for treatment of ruptured Achilles tendon.

The effects of walking speed on forefoot, hindfoot and ankle joint motion

2010-07-12

Abstract: Background: Foot and ankle joint kinematic differences have been identified between healthy subjects and subjects with various pathologies suffering from foot and ankle impairments. Changes in temporal factors such as walking speed and double stance time are also found in these pathological conditions. As such, in theory, these factors would also influence the kinematics and hence make it difficult to ascertain the effects of the disease on the kinematics. The aim of this study was to analyse foot and ankle kinematics from gait recordings of healthy subjects walking at comfortable and slower speeds.Methods: Gait patterns of 14 healthy subjects were recorded. The subjects were first asked to walk at a comfortable speed and then at predefined speeds of 75% and 50% of their comfortable walking speed respectively. Temporal variables were calculated. Foot and ankle joint kinematics were determined from marker-recordings.Findings: The subjects walked at mean velocities of 1.28m/s, 0.97m/s and 0.65m/s. With decreasing walking speed the minimum tibio-talar plantar-flexion and maximum hallux dorsi-flexion at toe-off decreased significantly between 3° and 9°. The minimum medial arch at toe-off and minimum midfoot supination at mid-stance were significantly affected by the walking speed. The corresponding individual session differences were small (1°–2°), but the reliability was high and hence the differences were considered clinically relevant.Interpretation: Walking speed significantly affected foot and ankle kinematics. Studies aiming to improve the understanding of the effects of foot and ankle pathologies on foot and ankle kinematics should take the walking speed into account.

Reproducibility of hand-held ankle dynamometry to measure altered ankle moment-angle characteristics in children with spastic cerebral palsy

2010-06-14

Abstract: Background: In children with spastic cerebral palsy, the range of motion of the ankle joint is often limited. Measurement of range of motion may be hampered by a non-rigid foot deformity. We constructed a hand-held instrument which allows measurements of static ankle angle and moment in children with cerebral palsy while correcting for foot deformity. This study aimed to test the reproducibility of the instrument and to use it for measuring ankle moment-angle characteristics in individual children who are typically developing and children with cerebral palsy.Methods: Ankle angles and moments were measured at five standardized positions in ten children who are typically developing and ten children with cerebral palsy. The intraclass correlation coefficient was calculated for test–retest reliability. For precision, the standard error of measurement and smallest detectable difference were determined. The ankle range of motion and the slope of the moment-angle curve were determined, both towards plantar flexion and dorsiflexion.Findings: The reproducibility study revealed a high reliability of the dynamometer at 5 repetitions (>0.97). Precision lies within 5° for angle measurements and within 0.2 Nm for moment measurements. In the children with cerebral palsy, the range of motion towards dorsiflexion was 18° lower and the slope of the moment-angle curve towards dorsiflexion was substantially higher.Interpretation: We developed a hand-held dynamometer which allows reliable and precise measurements of static ankle angle and moment in children with cerebral palsy. The hand-held dynamometer allows corrections of foot deformities and is qualified to reproducibly evaluate moment-angle characteristics in a clinical context.

Metabolic cost and mechanical work during walking after tibiotalar arthrodesis and the influence of footwear

2010-06-23

Abstract: Background: This study examined metabolic energy cost and external mechanical work for step-to-step transitions after tibiotalar arthrodesis, and the effect of MBT rocker bottom shoes.Methods: Oxygen uptake, forceplate and kinematic data were recorded in 18 controls and 15 patients while walking at a fixed speed of 1.25m/s in three walking conditions: barefoot, normal walking shoes and MBT rocker bottom shoes. Metabolic energy cost, external mechanical work, and the roll-over shape of the ankle–foot complex were analyzed.Findings: Tibiotalar arthrodesis leads to higher metabolic energy cost during walking. During step-to-step transitions positive work during push-off with the impaired ankle was decreased but negative work during collision was not affected. The roll-over shape of the ankle–foot complex did not differ between groups and shoe conditions. However, both in patients and controls rocker bottom shoes did lead to decreased positive work at push-off and increased negative work at collision and consequently higher metabolic energy cost of walking.Interpretation: External mechanical work for step-to-step transitions is not different between patients and controls and could not account for the higher metabolic energy cost in patients. Apparently, patients adopt a different walking strategy that limits step-to-step transition cost but nevertheless induces a higher metabolic energy cost. Despite restricted ankle movement, patients retain a normal roll-over shape of the ankle–foot complex. MBT shoes do not affect roll-over shape and appear to have a counterproductive effect on step-to-step transition cost and walking economy.

Short and long term adaptation of variability during walking using unstable (Mbt) shoes

Thomas Stöggl, Anita Haudum, Jürgen Birklbauer, Markus Murrer, Erich Müller — 2010-06-28

Abstract: Background: The purpose of the study was to compare the variability of biomechanical variables during treadmill walking using unstable shoes (Masai Barefoot Technology, MBT, Roggwil, Switzerland) and conventional shoes, before and after a 10week (wk) training period.Methods: Cycle characteristics, plantar pressure distribution, whole body 3D kinematics, and electromyographic signals of selected leg muscles during ground contact were recorded on 12 Sport Science students while walking on a treadmill with both conventional and unstable shoes before and after a 10wk training intervention. The intervention consisted of more than 4h use of unstable shoes during daily activity. The standard deviation of 15 consecutive cycles in each analyzed variable was taken as the measure for variability.Findings: The main pattern was marked by a 35% (SD 10%) higher variability with the unstable shoes at pretest when compared with the conventional shoes, but decreased 30% (SD 12%) (both P<0.05) during the training intervention to almost equal variability in between the two shoe situations. This was especially true with regard to variables representing within gait characteristics (peak foot force, joint angles, etc.), whereas in variables describing the overall gait cycle (e.g. cycle rate, impulse of total force, etc.) no difference between MBT and conventional shoes at pre and post tests were found.Interpretation: The current study supports the idea that the unstable shoe serves as a motor constraint applicable during everyday activity, provoking increased variability during walking. In addition, a decrease in movement variability on the MBT shoes during the training intervention to the level of conventional shoes was observed.

Blood perfusion and transcutaneous oxygen level characterizations in human skin with changes in normal and shear loads — Implications for pressure ulcer formation

2010-07-21

Abstract: Background: Decubitus ulcers (pressure ulcers) are localized areas of tissue breakdown in the skin and the underlying regions. Decubitus ulcers affect approximately 3million people in the USA every year, including seniors, individuals with diabetes, and those who spend long periods in wheelchairs. Experimental studies demonstrate that static or dynamic normal loads cause blood occlusion in the skin, while prolonged loading conditions can result in skin damage. However, few studies report the effects of ‘normal and shear’ combined loading on blood perfusion. The goal of this research was to study alterations of transcutaneous oxygen levels and blood perfusion in human skin when both normal and shear loads were applied.Methods: Fifteen human subjects were evaluated under seven different conditions for changes in transcutaneous oxygen and blood perfusion levels during applications of normal and shear loading on the forearm. Transcutaneous oxygen levels and blood perfusion were continuously measured using a Laser Doppler system, while applied forces were quantified with a multi-axis load cell.Findings: Transcutaneous oxygen and blood perfusion levels decreased when shear loads were applied in addition to normal loads. Further, blood perfusion during recovery periods increased gradually from the first to the last test condition.Interpretation: Results indicate that adding shear loads decreased transcutaneous oxygen and blood perfusion levels in the skin. Based on these findings, shear force may play a role in skin damage, and both shear and normal loads should be considered when trying to prevent ulcer development.

A feasibility study for in vitro evaluation of fixation between prosthesis and bone with bone marrow-derived mesenchymal stem cells

Yusuke Morita, Kenichi Yamasaki, Koji Hattori — 2010-06-21

Abstract: Background: It is difficult to quantitatively evaluate adhesive strength between an implant and the neighboring bone using animal experiments, because the degree of fixation of an implant depends on differences between individuals and the clearance between the material and the bone resulting from surgical technique.Methods: A system was designed in which rat bone marrow cells were used to quantitatively evaluate the adhesion between titanium alloy plates and bone plates in vitro. Three kinds of surface treatment were used: a sand-blasted surface, a titanium-sprayed surface and a titanium-sprayed surface coated with hydroxyapatite. Bone marrow cells obtained from rat femora were seeded on the titanium alloy plates, and the cells were cultured between the titanium alloy plates and the bone plates sliced from porcine ilium for 2weeks. After cultivation, adhesive strength was measured using a tensile test, after which DNA amount and Alkaline phosphatase activity were measured.Findings: The seeded cells accelerated adhesion of the titanium alloy plate to the bone plate. Adhesive strength of the titanium-sprayed surface was lower than that of the sand-blasted surface because of lower initial contact area, although there was no difference in Alkaline phosphatase activity between two surface treatments. A hydroxyapatite coating enhanced adhesive strength between the titanium alloy palate and the bone plate, as well as enhancing osteogenic differentiation of bone marrow cells.Interpretation: It is believed that this novel experimental method can be used to simultaneously evaluate the osteogenic differentiation and the adhesive strength of an implant during in vitro cultivation.

Optimally strong tendon repair using braided polyethylene strand: 2-Strand heavy-gauge locking technique vs. multiple-strand technique

Tadahiko Yotsumoto, Ryuji Mori, Hitoshi Hatanaka, Yuji Uchio — 2010-07-20

Abstract: Background: We conducted an in vitro study to investigate the strongest tensile force for tendon repair using a braided polyblend suture strand material, employing a 2-strand heavy-gauge side-locking loop technique, comparing it with other multiple-strand repair techniques.Methods: Using the United States Pharmacopeial Convention (USP) 2 and 5-sized braided polyblend strands, 3 repair techniques were evaluated after suturing transacted bovine gastrocnemius tendons: 2-strand side-locking loop, 4-strand Savage, and 6-strand Yoshizu-1 techniques. Ultimate tensile force and mode of failure at strand rupture were examined (n=5 for each combination).Findings: The ultimate tensile forces was observed with USP2-side-locking loop (mean 402N), USP5-side-locking loop (mean 748N), USP2-Savage (mean 552N), and USP2-Yoshizu-1 Groups (mean 598N). The USP5-side-locking loop Group had proportionally greater ultimate tensile force than the USP2-side-locking loop Group. However, with the number of strands doubled or tripled, resulting strengths were only 1.4 times or 1.5 times greater. The mode of failure was rupture at the locking loop portion in all side-locking loop Group samples, pull-through of the strand from the tendon in all Savage Group samples, and either pull-through of the strand from the tendon (40%) or rupture at the knot (60%) in the Yoshizu-1 Group samples.Interpretation: Greater numbers of strands do not achieve proportionally greater strong tensile force in the repaired tendon. When employing the side-locking loop technique for secured locking formation, the heavier strand yields markedly greater tensile force even with only 2 strands, and thus greater holding ability.

Muscle activity and acceleration during whole body vibration: Effect of frequency and amplitude

2010-06-11

Abstract: Background: Whole body vibration may improve muscle and bone strength, power and balance although contradictory findings have been reported. Prolonged exposure may result in adverse effects. We investigated the effects of high (5.5mm) and low (2.5mm) amplitude whole body vibration at various frequencies (5–30Hz) on muscle activity and acceleration throughout the body.Methods: Surface electromyographic activity was recorded from 6 leg muscles in 12 healthy adults (aged 31.3 (SD 12.4) years). The average rectified acceleration of the toe, ankle, knee, hip and head was recorded from 15 healthy adults (36 (SD 12.1) years) using 3D motion analysis.Findings: Whole body vibration increased muscle activity 5–50% of maximal voluntary contraction with the greatest increase in the lower leg. Activity was greater with high amplitude at all frequencies, however this was not always significant (P<0.05–0.001). Activation tended to increase linearly with frequency in all muscles except gluteus maximus and biceps femoris. Accelerations throughout the body ranged from ∼0.2 to 9g and decreased with distance from the platform. Acceleration at the head was always <0.33g. The greatest acceleration of the knee and hip occurred at ∼15Hz and thereafter decreased with increasing frequency.Interpretation: Above the knee at frequencies >15Hz acceleration decreased with distance from the platform. This was associated with increased muscle activity, presumably due to postural control and muscle tuning mechanisms. The minimal acceleration at the head reduces the likelihood of adverse reactions. The levels of activation are unlikely to cause hypertrophy in young healthy individuals but may be sufficient in weak and frail people.

Quadriceps activation following aerobic exercise in persons with low back pain and healthy controls

Joseph M. Hart, Arthur Weltman, Christopher D. Ingersoll — 2010-06-21

Abstract: Background: A relationship between the muscles that stabilize the lumbar spine and the lower extremity exists that may result in neuromuscular and biomechanical changes during prolonged aerobic exercise in those with low back pain.Methods: Twenty recreationally active adults with healthy lower extremity joints, 7 with recurring episodes of low back pain performed a standard 15-minute aerobic exercise protocol on a treadmill. Quadriceps torque during a maximal isometric voluntary contraction, quadriceps central activation ratio and superimposed burst torque as measured with the superimposed burst technique, and vastus lateralis median frequency were recorded before and after treadmill exercise. A burst of electrical stimuli was superimposed during maximal knee extension causing a transient increase in torque. Quadriceps central activation was calculated as the ratio between maximal volitional and superimposed burst torques. We recorded vastus lateralis surface Electromyography (EMG) during knee extension contractions and calculated the median frequency.Findings: We observed a 12.4% reduction in the quadriceps central activation ratio after aerobic exercise in participants with recurrent low back pain; healthy controls only experienced a 1.7% reduction. There was no change in quadriceps median frequency following aerobic exercise.Interpretation: Deteriorated quadriceps function following aerobic exercise was observed in patients with recurrent episodes of low back pain who had healthy knee joints. This reduction is mediated by a central process that may arise from poor strength and endurance in the muscles surrounding the spine, which is common in persons with recurrent low back pain.

Announcement: First International Congress, Scientific Testing of Orthotic Devices

2010-10-01