Symptomatic flatfoot in cerebral palsy.

PURPOSE OF REVIEW: The purpose of this review is to evaluate the current literature and best practices in the evaluation and treatment of symptomatic flatfoot in cerebral palsy. RECENT FINDINGS: While techniques to reconstruct the neuromuscular flatfoot and reestablish bony levers have remained similar over time, the concept of surgical dosing has helped guide appropriate interventions based on the magnitude of disease and functional level of the child. Moreover, the utilization of multisegment foot modeling in motion analysis has allowed quantitative description of such deformities and their impact on gait. SUMMARY: Future research should focus on refining operative indications and interventions with larger, multicenter, prospective cohorts to provide more robust evidence in surgical decision making. Long-term data are needed to confirm and compare efficacy of procedures. Radiographic data alone are not sufficient for describing functional foot position. Gait analysis with foot modeling and pedobarography along with patient-centered subjective outcomes will be needed in such investigations to make conclusive recommendations.

Impact of Internal Malrotation of the Femur Followed by Derotational Osteotomy as Demonstrated by 3D Gait Analysis: A Case Report.

CASE: An 18-year-old man with 48° of internal malrotation of the femur after nailing underwent derotational osteotomy with gait dynamics and electromyography data collected preoperatively and postoperatively. Hip abduction and internal foot progression angles were significantly deviated from normal preoperatively compared with the contralateral side. At 10 months postoperatively, the hip was abducted and externally rotated throughout the entire gait cycle. His Trendelenburg gait had resolved, and he reported no residual functional concerns. Before corrective osteotomy, walking velocity was significantly slower with shorter stride lengths. CONCLUSION: Significant internal malrotation of the femur impairs hip abduction and foot progression angles as well as gluteus medius activation during ambulation. Derotational osteotomy considerably corrected these values.

How does patellar tendon advancement alter the knee extensor mechanism in children treated for crouch gait?

BACKGROUND: The patellar tendon advancement (PTA) procedure, often coupled with a distal femoral extension osteotomy (DFEO), is increasingly used to treat persistent crouch gait. In this study, we investigated relationships between patella position, knee flexion, and the patellar tendon moment arm in children treated with the DFEO and PTA procedures. METHODS: We retrospectively analyzed pre- and post-operative radiographs and gait metrics from 63 knees that underwent DFEO and PTA procedures at Gillette Children's Specialty Healthcare. A computational musculoskeletal model of the knee was used to simulate the PTA procedure and predict the effects on the patellar tendon moment arm. RESULTS: Approximately 80% of the knees exhibited patella alta prior to surgery. Post-operatively, 86% of the knees exhibited patella baja. The surgically altered patella position produced a 13% increase in the patellar tendon moment arm in extended knee postures, which agreed well with model predictions. However, the computational model also suggests that baja may compromise patellar tendon moment arms in flexed knee postures. Crouch gait was significantly reduced postoperatively, with a 27 ±â€¯18° reduction in average knee flexion in stance. There was considerable inter-subject variability in outcomes with nine knees not exhibiting a meaningful enhancement of knee extension (<15° change). The subjects who improved were significantly younger and exhibited greater enhancement of the patellar tendon moment arm after surgery. CONCLUSIONS: This study shows that the PTA procedure enhances the lever arm of the knee extensor mechanism, and this factor may be important in resolving crouch gait.

Maternal Diets Deficient in Vitamin D Increase the Risk of Kyphosis in Offspring: A Novel Kyphotic Porcine Model.

BACKGROUND: The purpose of this study was to explore the role of perinatal vitamin-D intake on the development and characterization of hyperkyphosis in a porcine model. METHODS: The spines of 16 pigs were assessed at 9, 13, and 17 weeks of age with radiography and at 17 weeks with computed tomography (CT), magnetic resonance imaging (MRI), histology, and bone-density testing. An additional 169 pigs exposed to 1 of 3 maternal dietary vitamin-D levels from conception through the entire lactation period were fed 1 of 4 nursery diets supplying different levels of vitamin D, calcium, and phosphorus. When the animals were 13 weeks of age, upright lateral spinal radiography was performed with use of a custom porcine lift and sagittal Cobb angles were measured in triplicate to determine the degree of kyphosis in each pig. RESULTS: The experimental animals had significantly greater kyphotic sagittal Cobb angles at all time points when compared with the control animals. These hyperkyphotic deformities demonstrated no significant differences in Hounsfield units, contained a slightly lower ash content (46.7% ± 1.1% compared with 50.9% ± 1.6%; p < 0.001), and demonstrated more physeal irregularities. Linear mixed model analysis of the measured kyphosis demonstrated that maternal diet had a greater effect on sagittal Cobb angle than did nursery diet and that postnatal supplementation did not completely eliminate the risk of hyperkyphosis. CONCLUSIONS: Maternal diets deficient in vitamin D increased the development of hyperkyphosis in offspring in this model. CLINICAL RELEVANCE: This study demonstrates that decreased maternal dietary vitamin-D intake during pregnancy increases the risk of spinal deformity in offspring. In addition, these data show the feasibility of generating a large-animal spinal-deformity model through dietary manipulation alone.

The coupled effects of crouch gait and patella alta on tibiofemoral and patellofemoral cartilage loading in children.

BACKGROUND: Elevated tibiofemoral and patellofemoral loading in children who exhibit crouch gait may contribute to skeletal deformities, pain, and cessation of walking ability. Surgical procedures used to treat crouch frequently correct knee extensor insufficiency by advancing the patella. However, there is little quantitative understanding of how the magnitudes of crouch and patellofemoral correction affect cartilage loading in gait. METHODS: We used a computational musculoskeletal model to simulate the gait of twenty typically developing children and fifteen cerebral palsy patients who exhibited mild, moderate, and severe crouch. For each walking posture, we assessed the influence of patella alta and baja on tibiofemoral and patellofemoral cartilage contact. RESULTS: Tibiofemoral and patellofemoral contact pressures during the stance phase of normal gait averaged 2.2 and 1.0 MPa. Crouch gait increased pressure in both the tibofemoral (2.6-4.3 MPa) and patellofemoral (1.8-3.3 MPa) joints, while also shifting tibiofemoral contact to the posterior tibial plateau. For extended-knee postures, normal patellar positions (Insall-Salvatti ratio 0.8-1.2) concentrated contact on the middle third of the patellar cartilage. However, in flexed knee postures, both normal and baja patellar positions shifted pressure toward the superior edge of the patella. Moving the patella into alta restored pressure to the middle region of the patellar cartilage as crouch increased. CONCLUSIONS: This work illustrates the potential to dramatically reduce tibiofemoral and patellofemoral cartilage loading by surgically correcting crouch gait, and highlights the interaction between patella position and knee posture in modulating the location of patellar contact during functional activities.

Influence of patellar position on the knee extensor mechanism in normal and crouched walking.

Patella alta is common in cerebral palsy, especially in patients with crouch gait. Correction of patella alta has been advocated in the treatment of crouch, however the appropriate degree of correction and the implications for knee extensor function remain unclear. Therefore, the goal of this study was to assess the impact of patellar position on quadriceps and patellar tendon forces during normal and crouch gait. To this end, a lower extremity musculoskeletal model with a novel 12 degree of freedom knee joint was used to simulate normal gait in a healthy child, as well as mild (23 deg min knee flexion in stance), moderate (41 deg), and severe (67 deg) crouch gait in three children with cerebral palsy. The simulations revealed that quadriceps and patellar tendon forces increase dramatically with crouch, and are modulated by patellar position. For example with a normal patellar tendon position, peak patellar tendon forces were 0.7 times body weight in normal walking, but reached 2.2, 3.2 and 5.4 times body weight in mild, moderate and severe crouch. Moderate patella alta acted to reduce quadriceps and patellar tendon loads in crouch gait, due to an enhancement of the patellar tendon moment arms with alta in a flexed knee. In contrast, patella baja reduced the patellar tendon moment arm in a flexed knee and thus induced an increase in the patellar tendon loads needed to walk in crouch. Functionally, these results suggest that patella baja could also compromise knee extensor function for other flexed knee activities such as chair rise and stair climbing. The findings are important to consider when using surgical approaches for correcting patella alta in children who exhibit crouch gait patterns.

Radiographic and Respiratory Effects of Growing Rods in Children With Spinal Muscular Atrophy.

BACKGROUND: Respiratory weakness and spinal deformity are common in patients with spinal muscular atrophy (SMA). Posterior (distraction type) growing rods have recently gained favor as a treatment option in this population, due to their ability to prevent spinal deformity progression and their potential to allow lung volumes to increase over time. The objective of this study was to determine the impact of posterior growing rods on the spinal alignment and respiratory function in children with SMA with intermediate term follow-up. METHODS: A single center, retrospective review was performed on SMA patients treated with growing rods, inserted between 2004 and 2010, with a minimum of 2-year follow-up. SMA type, changes in the route of bi-level positive airway pressure respiratory support and the amount of time receiving respiratory support are reported. Pulmonary function tests (PFTs) and radiographs were reviewed and data evaluated preinsertion, postinsertion, and at latest follow-up. RESULTS: Sixteen children with SMA (5 type I, 11 type II) met inclusion criteria. The average age of insertion was 5.8 (±1.5) years, the median number of lengthenings was 4 (range, 3 to 5), and the median time between insertion and last clinical review was 4.7 (range, 2.7 to 9.5) years. Radiographic review demonstrated significant (P<0.05) improvements in the following: Spinal curve magnitude, pelvic obliquity, space available for the lung, rib vertebral angle difference, and thoracic kyphosis following growing rod implantation. Thoracic and lumbar height and chest width and depth increased significantly (P<0.05) over the lengthening process. None of the patients initially required more than noninvasive positive pressure ventilation support. Fifteen of the 16 experienced no changes in their noninvasive positive pressure ventilation support needs throughout the study duration, requiring support only at night and naps. Serial PFTs were available for 6 children with SMA type II. PFTs demonstrated significant improvements in absolute forced vital capacity (FVC), minimal changes in the maximal inspiratory and expiratory pressures, and a gradual worsening of percent predicted FVC. CONCLUSIONS: Clinical respiratory support requirements appear to stabilize following the insertion and lengthening of posterior based growing rods in the SMA population. Similar to previous studies, increased spinal height and thoracic cavity size were noted throughout the process. Despite an increasing absolute FVC, the percent predicted FVC diminished over time. LEVEL OF EVIDENCE: Level IV-therapeutic.

Tendon transfer to unossified bone in a porcine model: potential implications for early tibialis anterior tendon transfers in children with clubfeet.

PURPOSE: Tibialis anterior tendon transfers (TATT) are commonly performed in young children following Ponseti casting for clubfeet. The classic TATT involves advancing the tendon through a hole drilled in the ossified cuneiform. The aim of this study was to determine if tendons transferred through unossified bones have untoward effects on subsequent bone development. METHOD: Twenty-five piglets underwent one of five surgical procedures. An 18-gauge needle was then used to place a tunnel through the bony or cartilaginous portion of the calcaneus (through direct visualization) and isolated slips of the flexor digitorum superficialis (FDS) were placed through the tunnels, as determined by surgical procedure. Radiographic and/or histologic evaluations of the calcaneal apophyses were then performed. A discrete (1-4) and dichotomous "Normal" or "Abnormal" scoring system was developed and its reliability assessed to grade the appearance of the calcanei. Calcaneal appearances following the surgical procedures were then compared with controls. The average load to failure of a subset of transferred tendons was then compared using an MTS machine. RESULTS: The proposed apophyseal grading system (1-4) demonstrated an intraclass correlational coefficient (ICC) for consistency of 0.92 [95% confidence interval (CI) 0.88 < ICC < 0.95] and ICC for agreement of 0.91 (95% CI 0.86 < ICC < 0.95), indicating strong agreement and consistency. Similarly, Fleiss' kappa for the 1-4 scoring system was found to be 0.67, indicating substantial agreement between reviewers. When the 1-4 system was translated into the dichotomous scheme "Normal" and "Abnormal", the kappa value increased to 0.94, indicating strong agreement. Forty-six apophyses (13 control and 33 operative) were assessed using this scoring scheme. Apophyseal transfers were significantly more abnormal than controls (p < 0.0001), while no difference in abnormalities was found following tunnel placement alone (p = 1). Mechanical testing of the tendons transferred to bone or through the cartilaginous apophysis demonstrated no significant differences (p = 0.2). CONCLUSION: Tendon transfers through unossified bones altered subsequent bone development. SIGNIFICANCE: While the long-term consequence of these structural changes is unknown, these findings suggest that tendon transfers through unossified bones should be avoided and alternative methods of tendon fixation explored.

To Cast, to Saw, and Not to Injure: Can Safety Strips Decrease Cast Saw Injuries?

BACKGROUND: Placement and removal of fiberglass casts are among the more-common interventions performed in pediatric orthopaedic surgery offices. However, cast removal is associated with abrasive injuries and burns from the oscillating cast saw, and these injuries can occur even when the cast is removed by experienced personnel. It is unknown whether an added barrier, such as a safety strip, can mitigate injuries from blade-to-skin contact during cast removal with the oscillating saw. QUESTIONS/PURPOSES: We asked: (1) Can a safety strip provide a physical barrier during cast removal, decreasing blade-to-skin contact? (2) Does the safety strip lessen heat transfer? (3) Will the use of the safety strip prevent cast pressure from being released when the cast is split? METHODS: Standard long-arm fiberglass casts were removed by experienced and inexperienced healthcare personnel (n = 35) from life-sized pediatric models. A commercially available woven cast saw safety strip, commonly incorporated in waterproof cast constructs, was chosen as the protective strip. Each participant removed a cast with and without the safety strip present. All participants were blinded to the presence or absence of the safety strip at the time of cast removal. The number of touches was compared between cast removal with and without protective strips. A separate model was designed to assess prevention of heat transfer. Temperatures were recorded, using thermocouples, for three designated temperatures. Five to six trials were conducted at each designated temperature for each of two conditions, with and without the safety strip. Finally, to assess if the safety strip would prevent cast pressure from being released, a third model was used. Thirty standard short-arm casts were applied and removed from the arm models by one of the authors. Pressure data were collected from between the padding layers, in casts with and without the safety strip present, after application, univalving and bivalving each cast. RESULTS: Use of the safety strip reduced the number of simulated skin touches compared with casts removed without the safety strip, among experienced users (mean, 9.0 [range, 1-28] versus 0.1 [range, 0-1], mean ratio, 0.0012; 95% CI, 0.002-0.063; p < 0.001) and inexperienced users (mean, 8.5 [range, 0-31] versus 0.6 [range, 0-3], mean ratio, 0.07; 95% CI, 0.03-0.15; p < 0.001). The safety strips decreased heat transfer, preventing temperatures at the cast-skin interface from reaching 50 °C. Finally, after splitting the cast, with the numbers available, there was no increase in the pressure beneath the casts in those with the safety strip present (mean without, 0.23 [SD, 0.070] versus safety strip in the padding 0.20 [SD, 0.091] and safety strip on top padding, 0.21 [SD, 0.090]; p = 0.446 and p = 0.65 respectively). CONCLUSIONS: Our study showed the effectiveness of a safety strip in reducing simulated touches with the oscillating cast saw during cast splitting. Additional studies are warranted to investigate the clinical use and utility of the safety strip in practice. CLINICAL RELEVANCE: The findings of this study suggest that using safety strips in clinical practice could decrease blade-to-skin contact and therefore minimize cast saw injuries. However, validation of these findings in the clinical setting is necessary before drawing a definitive conclusion.

The Influence of Component Alignment and Ligament Properties on Tibiofemoral Contact Forces in Total Knee Replacement.

The study objective was to investigate the influence of coronal plane alignment and ligament properties on total knee replacement (TKR) contact loads during walking. We created a subject-specific knee model of an 83-year-old male who had an instrumented TKR. The knee model was incorporated into a lower extremity musculoskeletal model and included deformable contact, ligamentous structures, and six degrees-of-freedom (DOF) tibiofemoral and patellofemoral joints. A novel numerical optimization technique was used to simultaneously predict muscle forces, secondary knee kinematics, ligament forces, and joint contact pressures from standard gait analysis data collected on the subject. The nominal knee model predictions of medial, lateral, and total contact forces during gait agreed well with TKR measures, with root-mean-square (rms) errors of 0.23, 0.22, and 0.33 body weight (BW), respectively. Coronal plane component alignment did not affect total knee contact loads, but did alter the medial-lateral load distribution, with 4 deg varus and 4 deg valgus rotations in component alignment inducing +17% and -23% changes in the first peak medial tibiofemoral contact forces, respectively. A Monte Carlo analysis showed that uncertainties in ligament stiffness and reference strains induce ±0.2 BW uncertainty in tibiofemoral force estimates over the gait cycle. Ligament properties had substantial influence on the TKR load distributions, with the medial collateral ligament and iliotibial band (ITB) properties having the largest effects on medial and lateral compartment loading, respectively. The computational framework provides a viable approach for virtually designing TKR components, considering parametric uncertainty and predicting the effects of joint alignment and soft tissue balancing procedures on TKR function during movement.

Influence of Ligament Properties on Tibiofemoral Mechanics in Walking.

Computational knee models provide a powerful platform to investigate the effects of injury and surgery on functional knee behavior. The objective of this study was to use a multibody knee model to investigate the influence of ligament properties on tibiofemoral kinematics and cartilage contact pressures in the stance phase of walking. The knee model included 14 ligament bundles and articular cartilage contact acting across the tibiofemoral and patellofemoral joints. The knee was incorporated into a lower extremity musculoskeletal model and was used to simulate knee mechanics during the stance phase of normal walking. A Monte Carlo approach was employed to assess the influence of ligament stiffness and reference strain on knee mechanics. The anterior cruciate ligament (ACL), medial collateral ligament (MCL), and posterior capsule properties exhibited significant influence on anterior tibial translation at heel strike, with the ACL acting as the primary restraint to anterior translation in mid-stance. The MCL and lateral collateral ligament (LCL) exhibited the greatest influence on tibial rotation from heel strike through mid-stance. Simulated tibial plateau contact location was dependent on the ACL, MCL, and LCL properties, while pressure magnitudes were most dependent on the ACL. A decrease in ACL stiffness or reference strain significantly increased the average contact pressure in mid-stance, with the pressure migrating posteriorly on the medial tibial plateau. These ligament-dependent shifts in tibiofemoral cartilage contact during walking are potentially relevant to consider when investigating the causes of early-onset osteoarthritis following knee ligament injury and surgical treatment.

Influence of step rate and quadriceps load distribution on patellofemoral cartilage contact pressures during running.

Interventions used to treat patellofemoral pain in runners are often designed to alter patellofemoral mechanics. This study used a computational model to investigate the influence of two interventions, step rate manipulation and quadriceps strengthening, on patellofemoral contact pressures during running. Running mechanics were analyzed using a lower extremity musculoskeletal model that included a knee with six degree-of-freedom tibiofemoral and patellofemoral joints. An elastic foundation model was used to compute articular contact pressures. The lower extremity model was scaled to anthropometric dimensions of 22 healthy adults, who ran on an instrumented treadmill at 90%, 100% and 110% of their preferred step rate. Numerical optimization was then used to predict the muscle forces, secondary tibiofemoral kinematics and all patellofemoral kinematics that would generate the measured primary hip, knee and ankle joint accelerations. Mean and peak patella contact pressures reached 5.0 and 9.7MPa during the midstance phase of running. Increasing step rate by 10% significantly reduced mean contact pressures by 10.4% and contact area by 7.4%, but had small effects on lateral patellar translation and tilt. Enhancing vastus medialis strength did not substantially affect pressure magnitudes or lateral patellar translation, but did shift contact pressure medially toward the patellar median ridge. Thus, the model suggests that step rate tends to primarily modulate the magnitude of contact pressure and contact area, while vastus medialis strengthening has the potential to alter mediolateral pressure locations. These results are relevant to consider in the design of interventions used to prevent or treat patellofemoral pain in runners.

Prediction and Validation of Load-Dependent Behavior of the Tibiofemoral and Patellofemoral Joints During Movement.

The study objective was to construct and validate a subject-specific knee model that can simulate full six degree of freedom tibiofemoral and patellofemoral joint behavior in the context of full body movement. Segmented MR images were used to reconstruct the geometry of 14 ligament bundles and articular cartilage surfaces. The knee was incorporated into a lower extremity musculoskeletal model, which was then used to simulate laxity tests, passive knee flexion, active knee flexion, and human walking. Simulated passive and active knee kinematics were shown to be consistent with subject-specific measures obtained via dynamic MRI. Anterior tibial translation and internal tibial rotation exhibited the greatest variability when uncertainties in ligament properties were considered. When used to simulate walking, the model predicted knee kinematic patterns that differed substantially from passive joint behavior. Predictions of ean knee cartilage contact pressures during normal gait reached 6.2 and 2.8 Pa on the medial tibial plateau and patellar facets, respectively. Thus, the dynamic modeling framework can be used to simulate the interaction of soft tissue loads and cartilage contact during locomotion activities, and therefore provides a basis to simulate the effects of soft tissue injury and surgical treatment on functional knee mechanics.

Hip muscle loads during running at various step rates.

STUDY DESIGN: Controlled laboratory study, cross-sectional. Objectives To characterize hip muscle forces and powers during running, and to determine how these quantities change when altering step rate for a given running speed. BACKGROUND: Hip musculature has been implicated in a variety of running-related injuries and, as such, is often the target of rehabilitation interventions, including resistance exercises and gait retraining. The differential contributions of the hip muscles to the task of running are not well understood, and may be important for recognizing the biomechanical mechanisms of running-related injuries and refining current treatment and prevention strategies. METHODS: Thirty healthy participants ran at their preferred speed at 3 different step rates: 90%, 100%, and 110% of their preferred step rate. Whole-body kinematics and ground reaction forces were recorded. A 3-D musculoskeletal model was used to estimate muscle forces needed to produce the measured joint accelerations. Forces and powers of each muscle were compared across step-rate conditions. RESULTS: Peak force produced by the gluteus medius during running was substantially greater than that of any other hip muscle, with the majority of muscles displaying a period of negative work immediately preceding positive work. The higher running step rate led to an increase in hip flexor, hamstring, and hip extensor loading during swing, but, conversely, substantially diminished peak force and work during loading response for several hip muscles, including the gluteal muscles and piriformis. CONCLUSION: Increasing running step rate for a given running speed heightened hamstring and gluteal muscle loading in late swing, while decreasing stance-phase loading in the gluteal muscles and piriformis. These results may enable clinicians to support and refine current treatment strategies, including exercise prescription and gait retraining for running-related injuries.

Ability of sagittal kinematic variables to estimate ground reaction forces and joint kinetics in running.

STUDY DESIGN: Controlled laboratory study, cross-sectional design. OBJECTIVE: To determine if sagittal kinematic variables can be used to estimate select running kinetics. BACKGROUND: Excessive loading during running has been implicated in a variety of injuries, yet this information is typically not assessed during a standard clinical examination. Developing a clinically feasible strategy to estimate ground reaction forces and joint kinetics may improve the ability to identify those at an increased risk of injury. METHODS: Three-dimensional kinematics and ground reaction forces of 45 participants were recorded during treadmill running at self-selected speed. Kinematic variables used to estimate specific kinetic metrics included vertical excursion of the center of mass, foot inclination angle at initial contact, horizontal distance between the center of mass and heel at initial contact, knee flexion angle at initial contact, and peak knee flexion angle during stance. Linear mixed-effects models were fitted to explore the association between the kinetic and kinematic measures, including step rate and sex, with final models created using backward variable selection. RESULTS: Models were developed to estimate peak knee extensor moment (R(2) = 0.43), energy absorbed at the knee during loading response (R(2) = 0.58), peak patellofemoral joint reaction force (R(2) = 0.55), peak vertical ground reaction force (R(2) = 0.48), braking impulse (R(2) = 0.50), and average vertical loading rate (R(2) = 0.04). CONCLUSION: Our findings suggest that insights into important running kinetics can be obtained from a subset of sagittal plane kinematics common to a clinical running analysis. Of note, the limb posture at initial contact influenced subsequent loading patterns in stance.

Empirical evaluation of gastrocnemius and soleus function during walking.

Distinguishing gastrocnemius and soleus muscle function is relevant for treating gait disorders in which abnormal plantarflexor activity may contribute to pathological movement patterns. Our objective was to use experimental and computational analysis to determine the influence of gastrocnemius and soleus activity on lower limb movement, and determine if anatomical variability of the gastrocnemius affected its function. Our hypothesis was that these muscles exhibit distinct functions, with the gastrocnemius inducing limb flexion and the soleus inducing limb extension. To test this hypothesis, the gastrocnemius or soleus of 20 healthy participants was electrically stimulated for brief periods (90 ms) during mid- or terminal stance of a random gait cycle. Muscle function was characterized by the induced change in sagittal pelvis, hip, knee, and ankle angles occurring during the 200 ms after stimulation onset. Results were corroborated with computational forward dynamic gait models, by perturbing gastrocnemius or soleus activity during similar portions of the gait cycle. Mid- and terminal stance gastrocnemius stimulation induced posterior pelvic tilt, hip flexion and knee flexion. Mid-stance gastrocnemius stimulation also induced ankle dorsiflexion. In contrast mid-stance soleus stimulation induced anterior pelvic tilt, knee extension and plantarflexion, while late-stance soleus stimulation induced relatively little change in motion. Model predictions of induced hip, knee, and ankle motion were generally in the same direction as those of the experiments, though the gastrocnemius's results were shown to be quite sensitive to its knee-to-ankle moment arm ratio.

Sensor-based assessment of cast placement and removal.

Appropriate pressure during the application of a cast is critical to provide adequate stabilization of fractures. Force-sensing resistors (FSR) were used to measure pressure during cast placement and removal. The data demonstrated a signature pattern of skin pressure during the different steps of cast placement and removal. This reproducible signal provides validity evidence for our model.

Increasing running step rate reduces patellofemoral joint forces.

PURPOSE: Increasing step rate has been shown to elicit changes in joint kinematics and kinetics during running, and it has been suggested as a possible rehabilitation strategy for runners with patellofemoral pain. The purpose of this study was to determine how altering step rate affects internal muscle forces and patellofemoral joint loads, and then to determine what kinematic and kinetic factors best predict changes in joint loading. METHODS: We recorded whole body kinematics of 30 healthy adults running on an instrumented treadmill at three step rate conditions (90%, 100%, and 110% of preferred step rate). We then used a 3-D lower extremity musculoskeletal model to estimate muscle, patellar tendon, and patellofemoral joint forces throughout the running gait cycles. In addition, linear regression analysis allowed us to ascertain the relative influence of limb posture and external loads on patellofemoral joint force. RESULTS: Increasing step rate to 110% of the preferred reduced peak patellofemoral joint force by 14%. Peak muscle forces were also altered as a result of the increased step rate with hip, knee, and ankle extensor forces, and hip abductor forces all reduced in midstance. Compared with the 90% step rate condition, there was a concomitant increase in peak rectus femoris and hamstring loads during early and late swing, respectively, at higher step rates. Peak stance phase knee flexion decreased with increasing step rate and was found to be the most important predictor of the reduction in patellofemoral joint loading. CONCLUSION: Increasing step rate is an effective strategy to reduce patellofemoral joint forces and could be effective in modulating biomechanical factors that can contribute to patellofemoral pain.

The modulation of forward propulsion, vertical support, and center of pressure by the plantarflexors during human walking.

The gastrocnemius and soleus both contribute to the ankle plantarflexor moment during the mid- and terminal stance phases of gait. The gastrocnemius also generates a knee flexion moment that may lead to dynamic function that is unique from the soleus. This study used a muscle stimulation protocol to experimentally compare the contributions of individual plantarflexors to vertical support, forward propulsion and center of pressure (CoP) movement during normal gait. Twenty subjects walked on an instrumented treadmill at self-selected speeds with stimulating surface electrodes affixed over the medial gastrocnemius and soleus muscles. Short duration pulse trains (90 ms) were used to stimulate either the gastrocnemius or soleus at 20% or 30% of the gait cycle (GC) of random strides. Changes in ground reactions between stimulated and non-stimulated strides were evaluated to characterize the influence of each muscle on whole body movement during mid- (stimulation onset at 20% GC) and late (30% GC) stance. The gastrocnemius and soleus each induced an increase in vertical support and anterior progression of the CoP in mid-stance. However, late stance gastrocnemius activity induced forward acceleration, while both mid- and terminal stance soleus activity induced braking of forward velocity. The results suggested that the individual plantarflexors exhibit unique functions during normal gait, with the two muscles having opposite effects on forward propulsion. These empirical results are important both for enhancing the veracity of models used to predict muscle function in gait and also clinically as physicians seek to normalize gait in patients with plantarflexor dysfunction.

Empirical assessment of dynamic hamstring function during human walking.

The hamstrings are often associated with the development of crouch gait, a fatiguing form of walking characterized by excessive hip flexion, knee flexion and ankle dorsiflexion during stance. However, recent studies have called into question whether abnormally active hamstrings induce the limb to move into a crouch posture. The purpose of this study was to directly measure the influence of the hamstrings on limb posture during stance. Nineteen healthy young adults walked on an instrumented treadmill at their preferred speed. A 90 ms pulse train was used to stimulate the medial hamstrings during either terminal swing or loading response of random gait cycles. Induced motion was defined as the difference in joint angle trajectories between stimulated and non-stimulated strides. A dynamic musculoskeletal simulation of normal gait was generated and similarly perturbed by increasing hamstring excitation. The experiments show that hamstring stimulation induced a significant increase in posterior pelvic tilt, knee flexion and ankle dorsiflexion during stance, while having relatively less influence on the hip angular trajectory. The induced motion patterns were similar whether the hamstrings were stimulated during late swing or early stance, and were generally consistent with the direction of induced motion predicted by gait simulation models. Hence, we conclude that overactive hamstrings have the potential to induce the limb to move toward a crouch gait posture.