Clinical Biomechanics

Subacromial impingement syndrome is the most common disorder of the shoulder, resulting in functional loss and disability in the patients that it affects. This musculoskeletal disorder affects the structures of the subacromial space, which are the tendons of the rotator cuff and the subacromial bursa. Subacromial impingement syndrome appears to result from a variety of factors. Evidence exists to support the presence of the anatomical factors of inflammation of the tendons and bursa, degeneration of the tendons, weak or dysfunctional rotator cuff musculature, weak or dysfunctional scapular musculature, posterior glenohumeral capsule tightness, postural dysfunctions of the spinal column and scapula and bony or soft tissue abnormalities of the borders of the subacromial outlet. These entities may lead to or cause dysfunctional glenohumeral and scapulothoracic movement patterns. These various mechanisms, singularly or in combination may cause subacromial impingement syndrome.

Objective. To explain and underscore the use of principal component analysis in clinical biomechanics as an expedient, unbiased means for reducing high-dimensional data sets to a small number of modes or structures, as well as for teasing apart structural (invariant) and variable components in such data sets.

Background. In many published studies, elastic properties of bone are correlated to the bone density, in order to derive an empirical elasticity-density relationship. The most common use of these relationships is the prediction of the bone local properties from medical imaging data in subject-specific numerical simulation studies. The proposed relationships are substantially different one from the other. It is unclear whether such differences in elasticity-density relationships can be entirely explained in terms of methodological discrepancies among studies.

Parkinson disease is a progressive neurological condition characterised by hypokinesia (reduced movement), akinesia (absent movement), tremor, rigidity and postural instability. These movement disorders are associated with a slow short-stepped, shuing gait pattern. Analysis of the biomechanics of gait in response to medication, visual cues, attentional strategies and neurosurgery provides insight into the nature of the motor control de®cit in Parkinson disease and the ecacy of current therapeutic interventions. In this article we supplement a critical evaluation of the Parkinson disease gait literature with two case examples. The ®rst case describes the kinematic gait response of an individual with Parkinson disease to visual cues in the``o'' phase of the levodopa medication cycle. The second case investigates the biomechanics and motor control of turning during walking in a patient with Parkinson disease compared with elderly and young control subjects. The results are interpreted in light of the need for gait analysis to investigate complex functional walking tasks rather than con®ning assessment to straight line walking, which has been the trend to date. Ó

The etiology of rotator cuff tendinopathy is multi-factorial, and has been attributed to both extrinsic and intrinsic mechanisms. Extrinsic factors that encroach upon the subacromial space and contribute to bursal side compression of the rotator cuff tendons include anatomical variants of the acromion, alterations in scapular or humeral kinematics, postural abnormalities, rotator cuff and scapular muscle performance deficits, and decreased extensibility of pectoralis minor or posterior shoulder. A unique extrinsic mechanism, internal impingement, is attributed to compression of the posterior articular surface of the tendons between the humeral head and glenoid and is not related to subacromial space narrowing. Intrinsic factors that contribute to rotator cuff tendon degradation with tensile/shear overload include alterations in biology, mechanical properties, morphology, and vascularity. The varied nature of these mechanisms indicates that rotator cuff tendinopathy is not a homogenous entity, and thus may require different treatment interventions. Treatment aimed at addressing mechanistic factors appears to be beneficial for patients with rotator cuff tendinopathy, however, not for all patients. Classification of rotator cuff tendinopathy into subgroups based on underlying mechanism may improve treatment outcomes.

Objective. To study the reliability of gait analysis data obtained using the Calibrated Anatomical System Technique (CAST) protocol and to verify the suitability and repeatability of the extraction of a number of parameters from the waveforms obtained. Design. The experimental protocol and the parametric analysis technique were applied on a population of able-bodied subjects. Background.

Objective. To identify the influence of walking velocity and footwear condition on plantar pressure variables in healthy older adults. Design. Single session data collection during varying speed and footwear conditions. Background. Elevated plantar pressures are concerning due to the risk of tissue injury, ulceration, and pain. In young adults, increases in plantar pressure have been documented with faster walking speeds and when walking barefoot compared to wearing shoes. These relationships have not been systematically explored in older adults. Methods. Key plantar pressure factors were recorded as subjects walked barefoot and in comfortable walking shoes across a 10 m walkway at three predetermined velocities (57, 80, 97 m/min). Separate 3 • 2 analyses of variance with repeated measures identified significant differences in pressure, force, and contact area in eight anatomically defined foot regions across walking speeds and between footwear conditions. Results. Faster walking resulted in higher pressures under all foot regions except for the arch and lateral metatarsal (P 6 0:001), due primarily to greater forces under the heel, medial metatarsal and toes (P 6 0:001). Compared to wearing shoes, barefoot heel pressure was elevated (P 6 0:001) due to reduced heel contact area (P < 0:001); pressure under the central metatarsals was higher (P 6 0:001) owing to greater central metatarsals force (P < 0:001). Conclusions. Two conditions were associated with higher plantar pressures in the older adults studied: faster speeds and barefoot walking. Relevance In the presence of plantar pain and/or pathology, wearing supportive, well-fit shoes and avoiding faster walking speeds may reduce pressures. These strategies may also be useful for decreasing the risk of tissue injury and ulceration in persons with peripheral neuropathy.

Objective. Purpose was (a) to quantify changes that occur in plantar pressure following attenuation of sensory input from the plantar surface of the foot, and (b) to quantify the resultant changes in motor output as measured by the changes of muscular activation.

Objective. Develop a gender speci®c database of trunk muscle cross-sectional areas across multiple levels of the thoracic and lumbar spine and develop prediction equations for the physiological cross-sectional area as a function of gender and anthropometry. Design. This study quanti®ed trunk muscle cross-sectional areas of male and female spine loading muscles. Background. There is a lack of comprehensive data regarding the female spine loading muscle size. Although biomechanical models often assume females are the same as males, little is known regarding gender dierences in terms of trunk muscle areas and no data exist regarding the prediction of trunk muscle physiological cross-sectional areas from commonly used external anthropometric measures. Methods. Magnetic resonance imaging scans through the vertebral bodies from T 8 through S 1 were performed on 20 females and 10 males. Muscle ®ber angle corrected cross-sectional areas were recorded at each vertebral level. Linear regression techniques taking into account anthropometric measures were utilized to develop prediction equations for the physiological cross-sectional area for each muscle of interest, as well as tests for dierences in cross-sectional areas due to gender and side of the body. Results. Signi®cant gender dierences were observed for the prediction of the erector spinae, internal and external obliques, psoas major and quadratus lumborum physiological cross-sectional areas. Anthropometric measures about the xyphoid process and combinations of height and weight resulted in better predictions of cross-sectional areas than when using traditional anthropometry. Conclusions. This study demonstrates that the trunk muscle geometry of females and males are dierent, and that these dierences should be considered in the development of biomechanical models of the torso. Relevance The prediction of physiological cross-sectional areas from external anthropometric measures provide gender speci®c equations to assist in estimation of forces of muscles which load the spine for biomechanical purposes.

The time course of full lumbar flexion under a prolonged flexion moment, lasting 20 min, was documented in 27 male and 20 female subjects. Peak flexion increased by 5.5" over the 20 min. The flexion-creep data was fitted with a first-order step input response having a time constant of 9.4 mini. Maximum flexion was also documented over the recovery phase, lasting 30 min, indicating that subjects regained approximately 50% of their resting joint stiffness within 2 min of~resuming relaxed lordosis, although full recovery took longer than the flexion-creep, indicating the presence of viscoelastic hysteresis. For this reason it may be prudent to advise those who experience prolonged full flexion postures (as might a seated warehouse shipper/receiver, gardener, or construction worker) to stand and walk for a few minutes prior to performing demanding manual exertions. Indeed, temporary joint flexion laxity, following a bout of full flexion, may increase the risk of hyperflexion injury to certain tissues. Relevance The risk of injury to the lumbar spine may be influenced by activities that occur prior to the actual loading. The results of this investigation document an increase in joint laxity associated with prolonged full flexion. The range of lumbar flexion is temporarily increased such that this residual laxity may predispose certain tissues to hyperflexion injury.

Dissection studies revealed the fascicular anatomy of the trapezius. Its occipital and nuchal fibres passed downwards but mainly transversely to insert into the clavicle. Fibres from C7 and T1 passed transversely to reach the acromion and spine of the scapula. Its thoracic fibres converged to the deltoid tubercle of the scapula. Volumetric studies demonstrated that the fibres from C7, T,, and the lower half of ligamentum nuchae were the largest. The essentially transverse orientation of the upper and middle fibres of trapezius precludes any action as elevators of the scapula as commonly depicted. Rather the action of these fibres is to draw the scapula and clavicle backwards or to raise the scapula by rotating the clavicle about the sternoclavicular joint. By balancing moments the trapezius relieves the cervical spine of compression loads.

Background. Manual wheelchair users rely heavily on their upper limbs for independent mobility which likely leads to a high prevalence of shoulder pain and injury. The goal of this study was to examine the relationship between shoulder forces and moments experienced during wheelchair propulsion and shoulder pathology.

Objective. The overall response, load transmission, role of ligaments, and state of stress in various components under varus-valgus moments in the intact and collateral-deficient tibiofemoral joint are investigated. Design. A non-linear finite element model consisting of bony structures (tibia and femur), their articular cartilage layers, medial and lateral menisci and four primary ligaments (cruciates and collaterals) is utilized. Background. Valgus and varus stresses are among the primary mechanisms of injury to knee ligaments. Several in vitro studies have investigated the role of ligaments in resisting such loads and on the way deficiency in either collateral may affect the response. Methods. Cartilage layers are isotropic while menisci are non-homogeneous composite. The articulation of cartilage layers with each other and with the intervening menisci and the wrapping of the medial collateral ligament around the tibia1 edge are treated as large displacement frictionless contact problems. The non-linear elastostatic response of the joint at full extension is computed under varus-valgus moments applied to the femur with the tibia fixed. Cases simulating deficiency in collaterals and constraint on femoral axial rotation are also studied. Results. The response is non-linear with large coupled axial rotations, internal in varus and external in valgus. In intact and collateral-deficient states, the joint shows varus or valgus openings so that the articulation occurs at one plateau only, medial in varus and lateral in valgus. Large tensile forces in cruciates in collateral-cut models generate higher compression penalty on the loaded plateau. Conclusions. Collaterals are the primary load-bearing structures; their absence would substantially increase primary laxities, coupled axial. rotations, forces in cruciates, and articular contact forces. Good agreement with measurements is found. Relevance Detailed knowledge of joint biomechanics is essential in the diagnosis, prevention and treatment of observed disorders. Absence of collateral ligaments increases the loads in cruciates and contact stresses transmitted through cartilage layers and menisci, and thus places the affected components at more risk, especially when varus-valgus is accompanied by other modes of loading as well.

Objective. To develop a biomechanical model for cartilage which is capable of capturing experimentally observed nonlinear behaviours of cartilage and to investigate eects of collagen ®bril reinforcement in cartilage. Design. A sequence of 10 or 20 steps of ramp compression/relaxation applied to cartilage disks in uniaxial uncon®ned geometry is simulated for comparison with experimental data. Background. Mechanical behaviours of cartilage, such as the compression-oset dependent stiening of the transient response and the strong relaxation component, have been previously dicult to describe using the biphasic model in uncon®ned compression. Methods. Cartilage is modelled as a¯uid-saturated solid reinforced by an elastic ®brillar network. The latter, mainly representing collagen ®brils, is considered as a distinct constituent embedded in a biphasic component made up mainly of proteoglycan macromolecules and a¯uid carrying mobile ions. The YoungÕs modulus of the ®brillar network is taken to vary linearly with its tensile strain but to be zero for compression. Numerical computations are carried out using a ®nite element procedure, for which the ®brillar network is discretized into a system of spring elements. Results. The nonlinear ®bril reinforced poroelastic model is capable of describing the strong relaxation behaviour and compression-oset dependent stiening of cartilage in uncon®ned compression. Computational results are also presented to demonstrate unique features of the model, e.g. the matrix stress in the radial direction is changed from tensile to compressive due to presence of distinct ®brils in the model. Relevance Experimentally observed nonlinear behaviours of cartilage are successfully simulated, and the roles of collagen ®brils are distinguished by using the proposed model. Thus this study may lead to a better understanding of physiological responses of individual constituents of cartilage to external loads, and of the roles of mechanical loading in cartilage remodelling and pathology.

Objective. To describe a recording and processing methodology for obtaining kinematic data of the shoulder which meets three more criteria besides usual requirements regarding precision and accuracy: sufficient speed, obtaining complete 3D kinematics including joint rotations, and usage of coordinate systems based on reference points.

In recent years, obesity was considered as a global epidemic disease. There were over 300 million obese adults worldwide in 2000. This led to an increase in obesity-related morbidity and an imposition of a heavy burden on health care system. Obesity is related to several chronic diseases, such as hypertension, stroke, and various musculoskeletal disorders, in particular with lower limb my co-supervisor of the HTI, for his important suggestions on my work.

Background. Gender differences in kinematics during running have been speculated to be a contributing factor to the lower extremity injury rate disparity between men and women. Specifically, increased non-sagittal motion of the pelvis and hip has been implicated; however it is not known if this difference exists under a variety of locomotion conditions. The purpose of this study was to characterize gender differences in gait kinematics and muscle activities as a function of speed and surface incline and to determine if lower extremity anthropometrics contribute to these differences.

Of the many problems associated with low back pain, those which are most amenable to biomechanical investigation are identified. Recent advances in lumbar spinal mechanics are then reviewed in five sections dealing with mechanical function, mechanisms of failure, movements in vivo, loading in vivo, and the biological consequences of mechanical loading. The discussion suggests that mechanical fatigue damage may frequently be the underlying cause of low back pain, even when degenerative changes are evident in the tissues, and the review ends by suggesting some priority areas for future research.

To study the effects of custom-made insoles on plantar pressures and load redistribution in neuropathic diabetic patients with foot deformity. Cross-sectional. Although custom-made insoles are commonly prescribed to diabetic patients, little quantitative data on their mechanical action exists. Regional in-shoe peak pressures and force-time integrals were measured during walking in the feet of 20 neuropathic diabetic subjects with foot deformity who wore flat or custom-made insoles. Twenty-one feet with elevated risk for ulceration at the first metatarsal head were analysed. Load redistribution resulting from custom-made insoles was assessed using a new load-transfer algorithm. Custom-made insoles significantly reduced peak pressures and force-time integrals in the heel and first metatarsal head regions; pressures and integrals were significantly increased in the medial midfoot region compared with flat insoles. Custom-made insoles successfully reduced pressures in and integrals at the first metatarsal head in 7/21 feet, were moderately successful in another seven, but failed in the remaining seven. Load transfer was greatest from the lateral heel to the medial midfoot regions. Custom-made insoles were more effective than flat insoles in off-loading the first metatarsal head region, but with considerable variability between individuals. Most off-loading occurred in the heel (not a region typically at risk). The load transfer algorithm effectively analyses custom-made-insole action. Because similar insole modifications apparently exert different effects in different patients, a comprehensive evaluation of custom designs using in-shoe pressure measurement should ideally be conducted before dispensing insoles to diabetic patients with neuropathy and foot deformity.

Objective. The influence of trunk posture on musculoskeletal stability of the spine was investigated. Design. A biomechanical model was developed to evaluate the influence of posture on spinal stability. Model performance was assessed by comparing predicted muscle recruitment patterns with measured EMG activity from the trunk muscles during static lifting exertions. Method. An inverted double-pendulum model of the spine controlled by 12 muscle equivalents of the trunk was implemented to determine spinal load and stability. ...

Objective. This study investigated whether electromyographic signals recorded from the skin surface overlying the multifidus muscles could be used to quantify their activity. Design. Comparison of electromyography signals recorded from electrodes on the back surface and from wire electrodes within four different slips of multifidus muscles of three human subjects performing isometric tasks that loaded the trunk from three different directions. Background. It has been suggested that suitably placed surface electrodes can be used to record activity in the deep multifidus muscles. Methods. We tested whether there was a stronger correlation and more consistent regression relationship between signals from electrodes overlying multifidus and longissimus muscles respectively than between signals from within multifidus and from the skin surface electrodes over multifidus. Results. The findings provided consistent evidence that the surface electrodes placed over multifidus muscles were more sensitive to the adjacent longissimus muscles than to the underlying multifidus muscles. The R 2 for surface versus intra-muscular comparisons was 0.64, while the average R 2 for surface-multifidus versus surface-longissimus comparisons was 0.80. Also, the magnitude of the regression coefficients was less variable between different tasks for the longissimus versus surface multifidus comparisons. Conclusions. Accurate measurement of multifidus muscle activity requires intra-muscular electrodes. Relevance Electromyography is the accepted technique to document the level of muscular activation, but its specificity to particular muscles depends on correct electrode placement. For multifidus, intra-muscular electrodes are required.

Background. Scapulothoracic muscle activity is believed to be important for normal scapulothoracic motion. In particular, the trapezius and serratus anterior muscles are believed to play an important role in the production and control of scapulothoracic motion. The aim of this study was to determine the effects of different levels of muscle activity (active versus passive arm elevation) on three-dimensional scapulothoracic motion.

Background. Despite recent evidence supporting the use of neuromuscular training to reduce anterior cruciate ligament injury risk, female athletes continue to show an increased anterior cruciate ligament injury rate in collegiate basketball and soccer when compared to males. The purpose of the current study was to identify gender and task differences in measures that may increase the risk of anterior cruciate ligament injury in female basketball and soccer athletes.

OBJECTIVE: A method has been developed to accurately measure three-dimensional (3-D) femoral-tibial contact positions of artificial knee implants in vivo from X-ray fluoroscopy images using interactive 3-D computer vision algorithms. DESIGN: A computerized graphical (CAD) model of an implant component is displayed as an overlay on the original X-ray image. An image matching algorithm matches the silhouette of the implant component against a library of images, in order to estimate the position and orientation (pose) of the component. The operator further adjusts the pose of the graphical model to improve the accuracy of the match. BACKGROUND: Previous methods for in vivo measurement of joint kinematics make only indirect measurements of joint kinematics, require invasive procedures such as markers or pins, or make simplifying assumptions about imaging geometry which can reduce the accuracy of the resulting measurements. METHODS: Fluoroscopic videos are taken of implanted knees in subjects performing weight-bearing motion. Images from the videos are digitized and stored on a computer workstation. Using computerized model matching, the relative pose of the two knee implant components can be determined in each image. The resulting information can be used to determine where the two components are contacting, the area of the contact region, liftoff angle, and other kinematic data. RESULTS: Accuracy tests done on simulated imagery and in vitro real imagery show that the pose estimation method is accurate to less than 0.5 mm of error (RMS) for translations parallel to the image plane. Orientation error is less than or equal to 0.35 degrees about any axis. Errors are larger for translations perpendicular to the image plane (up to 2.25 mm). In a clinical study, the method was used to measure in vivo contact points, and characterize the kinematic patterns of two different knee implant designs. CONCLUSIONS: The ability to accurately measure knee kinematics in vivo is critical for the understanding of the behavior of knee implant designs and the ultimate development of new, longer lasting implants. RELEVANCE: This work shows that it is possible to accurately measure the three-dimensional position and orientation (pose) of artificial knee implants in vivo from X-ray fluoroscopy images using interactive 3-D computer graphics. The method can be applied to any joint when accurate CAD models are available. The resulting data can be used to characterize the kinematics of current knee implant designs.

Background. Females have an increased incident rate of anterior cruciate ligament tears compared to males. Biomechanical strategies to decelerate the body in the vertical direction have been implicated as a contributing cause. This study determined if females would exhibit single leg landing strategies characterized by decreased amounts of hip, knee, and ankle flexion resulting in greater vertical ground reaction forces and altered energy absorption patterns when compared to males.

Background. It is hypothesized that injury or degeneration of osteoligamentous spinal structures would require compensation by trunk musculature and alterations in motor control to maintain spine stability. While, biomechanical modeling has supported this hypothesis, studies of muscle recruitment patterns in chronic low back pain patients both with and without significant osteoligamentous damage have been limited. This study utilized a non-randomized case-control design to investigate trunk muscle recruitment patterns around the neutral spine position between subgroups of patients with chronic mechanical low back pain and asymptomatic controls.

Background-The aims of this study were to determine the prevalence and incidence of patellofemoral pain (PFP) in young female athletes and prospectively evaluate measures of frontal plane knee loading during landing to determine their relationship to development of PFP. We hypothesized that increased dynamic knee abduction measured during preseason biomechanical testing would be increased in those who developed PFP relative to teammates who did not develop PFP.

Objective. To ascertain the possibility of non-uniform stress within the achilles tendon due to individual force contributions of the triceps surae. Design. Calculation of non-uniform stress through discrepancies in moments about the ankle joint. Background. Non-uniform stress over the cross-sectional area have been implied in the etiology of achilles tendon injury and may influence functional aspects. However, this has not been empirically demonstrated. Methods. In vivo achilles tendon forces were measured with an optic fibre technique during isometric plantarflexions at systematically varied knee angles and contraction intensities. A comparison to the plantar force measured underneath the metatarsal heads permitted the calculation of the achilles tendon contribution to the resultant plantarflexion moment. The achilles tendon force was further differentiated into gastrocnemius and soleus contributions. Individual muscle activation patterns were described. Results. The average achilles tendon contribution to the resultant moment was 67.4%. Variations were found at different knee angles and contraction intensities. A force discrepancy of 967 N occurred between gastrocnemius and soleus over a gastrocnemius length change of 2.67 cm. This corresponded to a stress discrepancy of 21 N/mm' over the tendon cross-sectional area. Separate muscles showed individual activation patterns. Conclusions. Non-uniform stress in the achilles tendon can occur through modifications of individual muscle contributions. Relevance Non-uniform stress in the achilles tendon has been implied in its injury etiology. This study demonstrated such loading resulting from discrepancies in individual muscle forces.

Muscle strength is frequently impaired in patients with neurological disorders. Numerous instrumented and non-instrumented options exist for measuring the strength of such patients. Such measurements are useful for clarifying patient status and documenting changes over time. Moreover the measurements are often informative of present or future function among a variety of diagnostic groups. Measurements of muscle strength are an essential component of the neurological evaluation and provide information of substantial importance to clinical1 care.