Clinical Biomechanics

Objective. This investigation aims to determine (1) whether shockwave treatment helps fracture healing and (2) whether the effect of shockwave treatment on fracture healing is dose dependent. Design. Shockwave was applied over tibial osteotomy in an animal model to assess its effect on the healing of the fracture. Methodology. Bilateral tibial diaphyseal transverse osteotomy was conducted on 42 rabbits, dividing into experimental and control group, immobilized using an external skeletal fixator, with one leg tested with shockwave therapy and the contralateral leg acting as the control without therapy. Serial radiography and measurement of bone mineral density via dual-energy X-ray absorptiometry were performed to assess the fracture healing. The experimental animals had two or three sessions of shockwave therapy (5000 impulses, 0.32 mJ/mm 2 , Orthopedice) over the osteotomy sites on day 7, 21 and 35; while the control group did not receive any treatment. The animals were sacrificed on day 42 or 56. Then, bilateral tibias were harvested and sent for mechanical tests as well as the histological examination. The pertinent statistic methods were applied to analyze the results. Background. Shockwave therapy has become a useful alternative approach in treating various orthopedic conditions, but the mechanism which it works remains unclear. Thus far, shockwave therapy has been found effective in treating long bone pseudoarthrosis, but whether it can benefit fresh fracture healing continues to be debated. Results. Higher union rates occurred during the early but not the late stages in the experimental group, while mechanical strength was higher in the experimental group than in the control group. No significant dose-dependent response occurred between the second and third applications of shockwave treatment. No significant difference in mechanical strength occurred between the experimental groups at 4 weeks and the control group at 6 weeks, or between the experimental groups at 6 and 8 weeks. Furthermore, no significant correlation occurred between the absolute values of maximum torque and bone mineral density. Conclusion. Based on this investigation, shockwave treatment has a positive effect on early fracture healing while its long term effects require further investigation. Relevance Shockwave therapy can be a useful alternative adjunct modality in the treatment of fresh long bone fracture.

The aim of this project was to study how the isometrical neck extensor strength varies at different joint angles in the sagittat plane in order to calculate what fractions of the maximum strength are used in sitting postures to counteract the load moment induced by the weight of the head and neck segments. Ten female subjects sat with the torso fixed in a special device. The resistive force during maximum neck extension was recorded with a strain gauge in four different positions of the lower cervical spine; extended, vertical, slightly flexed and much flexed. For each of these four positions the upper cervical spine was kept in three positions-flexed, neutral and extended. Moments of force about the bilateral motion axes of the atlanto-occipital (Occ-C,) joint and the C,-T, motion segment were calculated. Moment arms were measured from video images. The maximum muscular moment for Occ-C, did not vary systematically, either with different positions of the lower or upper cervical spine. The mean neck extensor strength for CT-T1 was lowest in the extended lower cervical spine position. In the vertical, slightly flexed or much flexed position little or nc variation in strength was seen. However, the fraction of the strength (% MUR) utilized to counteract the load moment induced by the weight of the head and neck in the different postures showed higher utilization ratios when the head-and-neck was flexed (about 10 and 17% MUR, respectively) than when it was kept in a vertical position (about 2% MUR). The results strongly indicate that the flexed cervical spine position produces higher muscular load than vertical, even when taking muscular strength into account, and should thus be avoided during prolonged sitting.

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

Objective. To assess the feasibility and reliability of ankle plantar¯exor stiness measurements in hemiplegia. Design. Repeated measurements in ®ve consecutive weeks. Background. In hemiplegia, an equinovarus positioning of the foot might be caused by an increased stiness of the m. triceps surae.

Background: Adult acquired flatfoot deformity (AAFD) is traditionally related to a tibialis posterior tendon deficiency. In the intermediate stages, treatments are commonly focused on reinforcing this tissue, but sometimes the deformation appears again over time, necessitating the use of more aggressive options. Tissue stress cannot be consistently evaluated through traditional experimental trials. Computational foot modeling extends knowledge of the disease and could help guide the clinical decisions. This study analyzes the biomechanical stress of the main tissues related to AAFD and their capacity to support the plantar arch. Methods: A FE foot model was reconstructed. All the bones, cartilages and tissues related to AAFD were included, respecting their biomechanical characteristics. The biomechanical tissue stress was quantified. The capacity of each soft tissue to support the plantar arch was measured, following clinical criteria. Findings: Biomechanical stress of the tibialis posterior tendon is considerably superior to both the plantar fascia and spring ligament stress. However, it cannot maintain the plantar arch by itself. Both the tibialis posterior tendon and spring ligament act in reducing the hindfoot pronation, while the plantar fascia is the main tissue that prevents arch elongation. The Achilles tendon action increases the plantar tissue stress. Interpretation: The tibialis posterior tendon stress increases when the spring ligament or the fascia plantar fails. These findings are consistent with the theory that regards the tibialis posterior tendon as a secondary actor because it cannot support the plantar arch and claudicates when the hindfoot has rotated around the talonavicular joint.

Background: Children obesity is a risk factor for several dysfunctions and diseases, with negative effects on the morphology of the locomotor system, plantar pressure and body stability. A relationship between postural control and sensorimotor information has been assumed. However, there is few data on the effects of children obesity on the availability of sensorial information from the foot during standing. Methods: Twenty obese and twenty non-obese children were evaluated for foot sensitivity and plantar pressure during unipedal and bipedal stance. Data were compared between obese and non-obese participants, between foot regions and between legs. Findings: Obese children experiences higher plantar pressure and have lower foot sensitivity than non-obese. Additionally, obese children had similar sensitivity for different foot regions, as compared to the non-obese. Interpretation: Children obesity negatively influences foot sensitivity. Bipedal stance seemed more sensitive to differentiate between obese and non-obese. Higher plantar pressure and lower foot sensitivity in obese children may affect performance of weight bearing activities, contribute to higher risk of foot injuries and have potential implication for children footwear design and clinical physical examination.

Objective. To determine the role of articular cartilage lipids in its load-bearing function. Design. Normal and delipidised, bovine articular cartilage specimens were statically loaded and both the hydrostatic excess pore pressure and creep strain were measured. From this the compression stiffness of the skeletal structures of both types of matrices was determined.

Objective. The objective was to examine the hypothesis that increased load on the medial arch in the adult flat foot can be reduced 12 through a 10 mm lateral column lengthening calcaneal osteotomy 10 mm proximal from the calcaneal cuboid joint. 13

Objective. To describe patterns of external rotation during humeral elevation, and to compare motion patterns. Design. Patterns of external rotation during forward flexion, scapular abduction and abduction in the frontal plane are described with P-spline curves with an %95% confidence interval.

Elbow joint loading was evaluated during pushup exercises at various forearm rotations. Subjects were asked to perform pushup in various forearm rotations: neutral, 90 degrees internal rotation, and 90 degrees external rotation. Training with pushup exercise is good for the muscles and joints of the upper extremities. However, excessive shear forces on the elbow might lead to injuries to either normal trainees or to handicapped people, especially for those who rely on elbow prosthesis. The kinematics and kinetics of the elbow joint were investigated under various forearm rotations. The loading biomechanics of the elbow joint differed with various forearm rotations. It was noted that greater posterior and varus forces of the elbow are encountered with internal rotation of the hand position and, consequently, full forearm pronation. Pushup with hands in internally rotated position should be prevented so as to avoid excessive shear forces or moments. Knowledge of elbow kinematics and kinetics may be helpful in preventing injuries by reducing the elbow shear force with changes of forearm rotation.

Objective. To use forward dynamic simulations of forward and backward pedaling in order to determine whether backward pedaling oers theoretical advantages over forward pedaling to rehabilitate common knee disorders. Design. A comparison of knee joint loads was performed during forward and backward pedaling. Background. Pedaling has been shown to be an eective rehabilitation exercise for a variety of knee disorders. Recently, backward gait has been shown to produce greater knee extensor moments and reduced patellofemoral joint loads compared to forward gait. But to date, no study has examined the ecacy of backward pedaling as a safe alternative to forward pedaling in rehabilitation programs. Methods. A musculoskeletal model and optimization framework was used to generate simulations of forward and backward pedaling. Tibiofemoral and patellofemoral joint reaction forces were quanti®ed. Results. Lower tibiofemoral compressive loads, but higher patellofemoral compressive loads, were observed in backward pedaling. Lower protective anterior±posterior shear force was observed in backward pedaling near peak extension. Conclusions. Backward pedaling oers reduced tibiofemoral compressive loads for those patients with knee disorders such as menisci damage and osteoarthritis, but higher patellofemoral compressive loads. Therefore, backward pedaling is not recommended for patients experiencing patellofemoral pain. Further, backward pedaling should not be recommended after anterior cruciate ligament injury or reconstruction. Relevance The results of this study indicate that the design of rehabilitation programs including pedaling exercises should be injury speci®c with particular attention paid to the mechanics of the task.

In this paper, classical consolidation theory has been used to investigate the time-dependent response of articular cartilage to static loading. An experimental technique was developed to measure simultaneously the matrix internal pressure and creep strain under conditions of one-dimensional consolidation. This is the first measurement of the internal stress state of loaded cartilage. It is demonstrated that under static compression the applied load is shared by the components of the matrix (i.e. water, the proteoglycans, and the collagen fibrillar meshwork), during which time a maximum hydrostatic excess pore pressure is developed as initial water exudation occurs. This pressure decays as water is further exuded from the matrix and effective consolidation begins with a progressive transfer of the applied stress from water to the collagen fibrils and proteoglycan gel. Consolidation is completed when the hydrostatic excess pore pressure is reduced to zero and the solid components sustain in full the applied load.

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.

Two healthy subjects were filmed on TV-video when performing 14 different steps and jumps from two different heights (0.20 m and 0.43 m) onto two Kistler force platforms that recorded the reaction forces. The ankle and knee load moments and joint forces were calculated using a sag&al plane semi-dynamic biomechanical model. Steps with the ball of the foot from the lower height induced a vertical ground reaction force (Fz) close to 1 body weight (bw) and around 2 bw from the greater height. From the greater height the knee moments for the majority of the step-downs studied were about 100 Nm, which gave knee joint compressive forces of 4-7 bw. The ankle was exposed to loads of similar magnitude but not so much influenced by step height. The reasons why patients with knee pain prefer performing backward step-downs are discussed. Relevance This study presents a method that quantifies knee and ankle joint forces that arise during steps and jumps down. Such data are useful in rehabilitation work for assessing harmful effects of muscle and joint load at various ways of performing 'step-downs' and enable comparison of the joint load with other activities.

Objective. The main objectives of this study on able-bodied gait were (a) to identify the main functions of the ankle and hip muscle moments and their contribution to support and propulsion tasks, and (b) to illustrate the interaction between the ankle and hip moment activities.

Objective. Perceptual ratings of mechanical variables were compared with biomechanical variables that are related to running injuries. Design. Eight identical running shoes with a relatively close range of midsole hardness were used. Ground reaction force (GRF), in-shoe pressure distribution and rearfoot motion were measured during running. Perceptual ratings were obtained after the running trials. Background. Previous studies reported high correlations between cushioning perception and biomechanical variables for shoes that featured large differences in midsole hardness. Mef~ods. A 15point categorical rating scale was used to judge impact severity, pressure magnitude and rearfoot motion in running. Rating scores were compared with biomechanical variables (GRF, pressure distribution and pronation values) using regression analyses. Resuk. Re$ression analyses revealed high relations between different biomechanical variables and the perception scores. The best relation to perception was analysed for the median power frequency of the vertical GRF (r2 = 0.97). A negative correlation (r2 = 0.54) between the first impect of GRF and the perception of impact severity could be revealed. Conclusion. The present study suggests that the body's sensory system seems to differentiate well between impacts of different frequency content. Based on perceptual abilities, subjects ad&p? their running style to avoid high heel impacts, Relevance Perception of injury-related variables is an important issue in the discussion of the etiology of sports injuries. The protection and prevention abilii of the human body is restricted, if runners are not able to perceive the intensity of factors that are related to running injuries.

The purpose of this study was to assess the possible role of muscles in offsetting the anterior shear forces caused by the load and upper body mass and their accelerations that act on the WLs intervertebral joint during dynamic squat lifts. Fifteen males lifted five loads from 5.8 to 32.4 kg. Anterior shear forces estimated to be acting on the lumber spine, based on model output, ranged from 492 N at 5.8 kg to 736 N at 32.4 kg. However, the peak shear force that'had to be supported by the facets and possibly the disc remained relatively constant at approximately 200 N. regardless of the load mass. The posteriorly directed fascicles of the lumbar portions of the iliocostalis lumborum and longissimus thoracis muscles increased their force output, as estimated from an EMG driven model, in proportion to the anterior load shear force demands, thereby sharing the load on the intervertebral joint. It appears that the combination of anatomical design and neural control of the musculature leads to a situation where the resultant shear force on the joint can be maintained at a relatively constant and safe level in the types of lifts studied. This 'safety' mechanism is useful only with the preservation of lordosis during lifting, when the muscles must provide the majority of the support moment.

Objective. The aim of this study was to determine the stiffness characteristics of the standard and hybrid Ilizarov fixators. Design. Five different frame models (one standard and four hybrid Ilizarov) were designed. Four full rings were used in the standard Ilizarov frame. Two rings were placed proximal and two rings were placed distal to the osteotomy line with two wires at 90°to each other on each ring. The distal tibial fixation of all the hybrid configurations and standard Ilizarov fixator were the same, and only the proximal fixations were different. In hybrid models, different numbers of 90°femoral arches (1-3) were fixed to the proximal segment by using the half-pins with different numbers (2-4) and different angles to each other (45°and 90°).

Objective. To measure and compare the mechanical properties in bending of the four-ring, and three-ring/one-tube hybrid external fixation frames. Design. In vitro measurements of the mechanical behaviour of ring and ring-tubular external fixation frames. In the latter, one ring of the full circular frame was replaced by one tube and Schanz screws. Background.

This review constitutes the ®rst of four reviews that systematically address contemporary knowledge about the mechanical behavior of the cervical vertebrae and the soft-tissues of the cervical spine, under normal conditions and under conditions that result in minor or major injuries. This ®rst review considers the normal kinematics of the cervical spine, which predicates the appreciation of the biomechanics of cervical spine injury. It summarizes the cardinal anatomical features of the cervical spine that determine how the cervical vertebrae and their joints behave. The results are collated of multiple studies that have measured the range of motion of individual joints of the cervical spine. However, modern studies are highlighted that reveal that, even under normal conditions, range of motion is not consistent either in time or according to the direction of motion. As well, detailed studies are summarized that reveal the order of movement of individual vertebrae as the cervical spine¯exes or extends. The review concludes with an account of the location of instantaneous centres of rotation and their biological basis.

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

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.

Objective. An experimental study of the sit-to-stand transfer in healthy adults with/without arm-support and in paraplegic patients with/without electrical stimulation of the quadriceps muscles was performed. The study was aimed to compare the joint torques, momentum transfer hypothesis, and stability of the sit-to-stand transfer in the healthy and paraplegic subjects.

Objective. The main purpose of this study was to estimate lower extremity joint impact loading in running and the influences of muscles on this loading. Design. A 2D simulation model that included skeletal motion, muscles, and soft-tissue movement was developed in this study. Background.

Objective. To measure load and moment changes acting on the lumbar spine during rotatory sitting. Background. A new chair concept generating dynamic stimuli by alternating rotations in the horizontal plane of the chairÕs seat was recently developed.

The purpose of this study was to measure the forces exerted during spinal manipulative therapy of the thoracic spine simultaneously with corresponding cavitation signals. Forces were measured using a thin, flexible pressure mat which was placed on patients over the contact area between doctor and patient. Cavitation signals were measured using a skin mounted accelerometer on the spinous process of a vertebral body adjacent to the manipulated vertebral body. Mean forces of spinal manipulative therapy at the instant of cavitation were 364 N with a standard deviation of 106 N. These values are considerably larger than corresponding values reported for cavitation at metacarpophalangeal joints. The precise factors causing cavitation of the spinal joints could not be determined. Study designs which may allow identification of these factors are suggested. Relevance Many clinicians judge the success of a spinal manipulative treatment by the sound of cavitation. However, quantitative data relating external treatment forces to cavitation sounds are not available for spinal joints. Therefore, we have tried to relate the force-time history of manipulative thrusts to the perceived cavitation signal in order to gain insight into the mechanisms of cavitation during spinal manipulative therapy. The information presented here may be used for teaching the technique to students of chiropractic, osteopathy, physiotherapy, and medicine.

Background. Anterior cruciate ligament (ACL) deficiency can be a major problem for athletes and subsequent reconstruction of the ACL may be indicated if a conservative regimen has failed. After ACL reconstruction signs of abnormality in the use of the leg remain for a long time. It is expected that the landing after a single-leg hop for distance (horizontal hop) might give insight in the differences in kinematics and kinetics between uninjured legs and ACL-reconstructed legs. Before the ACL-reconstructed leg can be compared with the contralateral leg, knowledge of differences between legs of uninjured subjects is needed.

Background Today a number of prosthetic suspension systems are available for transtibial amputees. Consideration of an appropriate suspension system can ensure that amputee’s functional needs are satisfied. The higher the insight to suspension systems, the easier would be the selection for prosthetists. This review attempted to find scientific evidence pertaining to various transtibial suspension systems to provide selection criteria for clinicians. Methods Databases of Pub Med, Web of science, and science Direct were explored to find related articles. Search terms were as follows: “Transtibial Prosthesis (32), prosthetic suspension (48), lower limb prosthesis (54), below-knee prosthesis (58), prosthetic liner (20), transtibial (193), and prosthetic socket (111). Two reviewers separately examined the papers. Study design (case series of five or more subjects, retrospective or prospective), research instrument, sampling method, outcome measures and protocols were reviewed. Findings B...

Objective. The aim of this study was to provide new information on the myoelectrical activation of the quadratus lumborum, the deep lateral and the superficial medial lumbar erector spinae, the psoas, and the iliacus muscles in various motor tasks.