Hindfoot flexibility assessment of cavovarus and planovalgus feet by modified Shriners Hospitals for Children - Greenville (mSHCG) foot model.

BACKGROUND: Multi-segment foot models have been used to quantify foot kinematics during walking. However, walking kinematics is not sufficient to assess hindfoot flexibility (available range of hindfoot varus-valgus motion). The modified Shriners Hospitals for Children - Greenville (mSHCG) foot model has been used to quantify hindfoot flexibility with Coleman block test (peak hindfoot valgus) and Root test (peak hindfoot varus). Sensitivity of mSHCG foot model to detect clinically relevant difference in hindfoot flexibility measures for planovalgus (PV) and cavovarus (CV) feet has not been demonstrated. RESEARCH QUESTION: Can mSHCG foot model detect statistically significant difference in hindfoot flexibility measures between PV, CV and typically developing (TD) feet? METHODS: Hindfoot flexibility assessment was completed for 32 PV (37 feet), 27 CV (37 feet) and 20 TD (40 feet) individuals. Hindfoot position relative to tibia in coronal plane was measured in three postures: standing, heel raise and Coleman block test. Radiographic measures in standing position were also completed for PV and CV individuals and their correlation with hindfoot flexibility measures were evaluated. RESULTS: Statistically significant (p<0.001) differences were observed between three groups (TD, PV, CV) in all three hindfoot flexibility measures- (i) Hindfoot varus in standing position (ii) Peak hindfoot varus in heel raise and (iii) Peak hindfoot valgus in Coleman block test. There was relatively stronger correlation (R2=0.407-0.854) between three radiographic measures and hindfoot varus in standing position. Correlation between hindfoot range of motion towards valgus from standing to Coleman block test and the three radiographic measures was weaker (R2=0.2329-0.3042). SIGNIFICANCE: Hindfoot flexibility assessment can detect statistically significant difference between PV, CV and TD feet and provides additional information about available dynamic range of motion of hindfoot in the coronal plane that cannot be predicted from radiographic measures. Therefore, hindfoot flexibility assessment may assist in treatment planning of foot deformities.

Is peak hamstrings muscle-tendon length criterion a sufficient indicator to recommend against surgical lengthening of hamstrings?

BACKGROUND: Excessive knee flexion during stance in children with cerebral palsy is often treated by surgical hamstrings lengthening. Pre-operative hamstrings muscle-tendon length can be estimated from kinematics and often used for decision making to rule out surgical lengthening if peak hamstrings muscle-tendon length is 'Not Short'. RESEARCH QUESTION: If peak hamstrings muscle-tendon length is within two standard deviations of typical, is that a sufficient indicator to rule out surgical hamstrings lengthening? METHODS: Three motion analysis centers retrospectively identified children with cerebral palsy, age 6-17 years, who had consecutive gait analyses with knee flexion at initial contact > 20° and popliteal angle > 35° at initial study. Three groups were considered: Medial Hamstrings Lengthening (MHL), Medial and Lateral Hamstrings Lengthening (MLHL), no surgical intervention (Control). Peak hamstrings muscle-tendon length at initial gait study was computed and categorized as 'Short' or 'Not Short'. Two outcomes variables were considered: change in peak knee extension (PKE) and change in pelvic tilt. Univariate comparisons of all variables were assessed along with a multivariate stepwise regression analysis to identify pre-operative characteristics that may predict post-operative improvement. RESULTS: 440 individuals met inclusion criteria. Percentage of individuals with improved PKE by grouping were- MHL-'Short': 60%, MHL-'Not Short': 65%, MLHL-'Short': 74%, MLHL-'Not Short': 74%, Control 'Short': 20%, Control 'Not Short': 19%. Percentage of individuals with worsened pelvic tilt were- MHL-'Short': 25%, MHL-'Not Short': 11%, MLHL-'Short': 42%, MLHL-'Not Short': 21% with significantly more individuals in MHL-'Short' subgroup compared to MHL-'Not Short'. Multivariate analysis suggested that pre-operative pelvic tilt and weak hip extensor strength have the largest effect on predicting post-operative increase in APT. Peak muscle-tendon length was not a significant predictor of post-operative knee kinematics or increase in APT. SIGNIFICANCE: This study suggests that hamstrings muscle-tendon length criteria by itself is not a sufficient indicator to recommend against hamstrings lengthening.

Does use of ankle foot orthoses affect the dynamic motor control index during walking in cerebral palsy and idiopathic toe walking populations?

BACKGROUND: The dynamic motor control (walk-DMC) index during walking is a measure of the complexity of muscle activation pattern. Ankle Foot Orthoses (AFO) are frequently used to improve the gait of children with Cerebral Palsy (CP) and Idiopathic Toe Walking (ITW). The purpose of this study was to assess the change in walk-DMC index secondary to AFO use. RESEARCH QUESTION: Does the change in walk-DMC reflect the change in walking kinematics with the use of AFO. METHODS: Individuals with diagnosis of CP or ITW with gait analysis data available for barefoot and AFO condition were retrospectively identified. For each individual, the walk-DMC index, Gait Deviation Index (GDI) and Gait Variable Scores (GVS) of knee and ankle kinematics were computed for BF and AFO conditions. Paired t-tests were used to compare key variables between BF and AFO conditions. Multi-variate stepwise regression analysis was performed to identify variables that may predict the increase in walk-DMC between BF and AFO condition. RESULTS: 253 individuals were included in the study. For CP individuals (n = 208), statistically significant but quantitatively minimal improvement was observed in walk-DMC (1 ± 9), GDI (2 ± 9) and ankle GVS (2 ± 7). For ITW individuals (n = 45), larger improvements were observed in walk-DMC (11 ± 13), GDI (9 ± 11) and ankle GVS (6 ± 7). Diagnosis of ITW, use of Solid-AFO and Posterior Leaf Spring-AFO were the significant predictor of increase in walk-DMC with AFO. Higher ankle GVS at BF condition (larger deviation from TD) led to larger increase in walk-DMC. Higher knee GVS (larger deviation from TD) led to smaller increase in walk-DMC. SIGNIFICANCE: Use of AFO can lead to improvement in walking kinematics that is reflected in increase in walk-DMC with AFO compared to BF for ITW individuals. The change in kinematics and walk-DMC with use of AFO was minimal for CP individuals.

Surgical Management of Severe Equinus Deformity in Ambulatory Children With Cerebral Palsy.

BACKGROUND: Tendo Achilles lengthening (TAL) for the management of equinus contractures in ambulatory children with cerebral palsy (CP) is generally not recommended due to concerns of over-lengthening, resulting in weakness and plantar flexor insufficiency. However, in some cases, surgical correction of severe equinus deformities can only be achieved by TAL. The goal of this study is to assess the outcomes following TAL in these cases. METHODS: A retrospective cohort study of children with CP with severe equinus contractures (ankle dorsiflexion with the knee extended of -20 degrees or worse) who underwent TAL as part of a single event multilevel surgery, with preoperative and postoperative gait analysis studies. Continuous data were analyzed by paired t test, and categorical data by McNemar Test. RESULTS: There were 60 subjects: 42 unilateral, 18 bilateral CP; 41 GMFCS II, 17 GMFCS I; mean age at surgery was 10.6 years, mean follow-up was 1.3 years. Ankle dorsiflexion with the knee extended improved from -28 to 5 degrees (P<0.001). The ankle Gait Variable Score improved from 34.4 to 8.6 (P<0.001). The ankle moment in terminal stance improved from 0.43 to 0.97 Nm/kg (P<0.001). Significant improvements (P<0.001) were seen in radiographic measures of foot alignment following surgery. There were few significant differences in the outcome parameters between subjects with unilateral versus bilateral CP (eg, only the bilateral group showed improved but persistent increased knee flexion in mid-stance). CONCLUSIONS: The outcomes following TAL for the management of severe equinus deformity in ambulatory children with CP were favorable 1 year after surgery, with significant improvements in all domains measured. SIGNIFICANCE: This study does not advocate for the widespread use of TAL to correct equinus deformity in children with CP. However, it does show that good short-term outcomes following TAL are possible in properly selected subjects with severe contractures when the dosing of the surgery is optimal (correction of contracture to between 0 and 5 degrees of dorsiflexion with the knee extended) and the procedure is performed in the setting of single event multilevel surgery with subsequent proper orthotic management and rehabilitation.

Outcomes of Patellar Tendon Imbrication With Distal Femoral Extension Osteotomy for Treatment of Crouch Gait.

BACKGROUND: Crouch gait is a frequent gait abnormality observed in children with cerebral palsy. Distal femoral extension osteotomy (DFEO) with the tightening of the extensor mechanism is a common treatment strategy to address the pathologic knee flexion contracture and patella alta. The goal of this study was to review the results of a patellar tendon imbrication (PTI) strategy to address quadriceps insufficiency in the setting of children undergoing DFEO. METHODS: After institutional review board approval, all patients with crouch gait treated at a single institution with DFEO and PTI were identified. Clinical, radiographic, and instrumented gait analysis data were analyzed preoperatively and at 1 year following surgery. RESULTS: Twenty-eight patients (54 extremities) with a diagnosis of cerebral palsy and crouch gait were included. Significant improvements were appreciated in the degree of knee flexion contracture, quadriceps strength, knee extensor lag, and popliteal angle (P<0.01). Knee flexion at initial contact and during mid-stance improved significantly (P<0.0001), and knee moments in late stance were significantly reduced (P<0.01). The anterior pelvic tilt, however, significantly increased postoperatively (P<0.0001). Radiographic improvements were seen in the knee flexion angle and patellar station as assessed by the Koshino Sugimoto Index (P<0.0001). Four patients (14.2%) developed a recurrence of knee flexion contracture requiring further intervention. CONCLUSIONS: PTI is a simplified and safe technique to address quadriceps insufficiency when performing DFEO. The short-term results of patients who underwent DFEO with PTI demonstrated improvements in clinical, radiographic, and gait analysis variables of the knee. Investigating long-term outcomes, comparing techniques, and assessing quality of life measures are important next steps in research. LEVEL OF EVIDENCE: Level IV-case series.

Surgical Outcomes for Severe Idiopathic Toe Walkers.

BACKGROUND: Idiopathic toe walking (ITW) is a diagnosis of exclusion and represents a spectrum of severity. Treatment for ITW includes observation and a variety of conservative treatment methods, with surgical intervention often reserved for severe cases. Previous studies reviewing treatment outcomes are often difficult to interpret secondary to a mixture of case severity. The goal of this study was to review surgical outcomes in patients with severe ITW who had failed prior conservative treatment, as well as determine differences in outcomes based on the type of surgery performed. METHODS: After IRB approval, all patients with surgical management of severe ITW at a single institution were identified. Zone II or zone III plantar flexor lengthenings were performed in all subjects. Clinical, radiographic, and motion analysis data were collected preoperatively and at 1 year following surgery. RESULTS: Twenty-six patients (46 extremities) with a diagnosis of severe ITW from 2002 to 2017 were included. Zone II lengthenings were performed in 25 extremities (mean age=9.9 y) and zone III lengthenings were performed in 21 extremities (mean age=8.6 y). At the most recent follow-up, 100% of zone III lengthening extremities and 88% of zone II lengthening demonstrated decreased severity of ITW. Six extremities required additional treatment, all of which were initially managed with zone II lengthenings. CONCLUSIONS: Severe ITW or ITW that has not responded to conservative treatment may benefit from surgical intervention. More successful outcomes, including continued resolution of toe walking, were observed in subjects treated with zone III lengthenings. LEVEL OF EVIDENCE: Level III-case series.

A subject-specific finite element musculoskeletal framework for mechanics analysis of a total knee replacement.

Concurrent use of finite element (FE) and musculoskeletal (MS) modeling techniques is capable of considering the interactions between prosthetic mechanics and subject dynamics after a total knee replacement (TKR) surgery is performed. However, it still has not been performed in terms of favorable prediction accuracy and systematic experimental validation. In this study, we presented a methodology to develop a subject-specific FE-MS model of a human right lower extremity including the interactions among the subject-specific MS model, the knee joint model with ligament bundles, and the deformable FE prosthesis model. In order to evaluate its accuracy, the FE-MS model was compared with a traditional hinge-constraint MS model and experimentally verified over a gait cycle. Both models achieved good temporal agreement between the predicted muscle force and the electromyography results, though the magnitude on models is different. A higher predicted accuracy, quantified by the root-mean-square error (RMSE) and the squared Pearson correlation coefficient (r2), was found in the FE-MS model (RMSE = 177.2 N, r2 = 0.90) when compared with the MS model (RMSE = 224.1 N, r2 = 0.81) on the total tibiofemoral contact force. The contact mechanics, including the contact area, pressure, and stress were synchronously simulated, and the maximum contact pressure, 22.06 MPa, occurred on the medial side of the tibial insert without exceeding the yield strength of the ultra-high-molecular-weight polyethylene, 24.79 MPa. The approach outlines an accurate knee joint biomechanics analysis and provides an effective method of applying individualized prosthesis design and verification in TKR.

Kinematics and kinetics of normal and planovalgus feet during walking.

Planovalgus deformity is prevalent in cerebral palsy patients, but very few studies have quantitatively reported differences between planovalgus and normal foot function. Intersegmental foot kinetics have not been reported in this population. In this study, a three segment (hindfoot, forefoot, hallux) kinematic and kinetic model was applied to typically developing (n=10 subjects, 20 feet) and planovalgus (n=10 subjects, 18 feet) pediatric subjects by two clinicians for each subject. Intra-clinician and inter-clinician repeatability of kinematic variables have been previously reported. Variability of kinetic outcomes (joint moments and power) is reported and found to be equally repeatable in typically developing and planovalgus groups. Kinematic differences in the planovalgus foot including excessive ankle eversion (valgus) and plantarflexion, reduced ankle flexion range of motion, and increased midfoot joint dorsiflexion and pronation reflected the reported pathology. Contrary to clinical expectations no significant difference was observed in midfoot flexion or ankle eversion ranges of motion. Kinetic differences in planovalgus feet compared to typically developing feet included reduced ankle plantarflexion moment, ankle power and midfoot joint power.

A multi-segment foot model based on anatomically registered technical coordinate systems: method repeatability and sensitivity in pediatric planovalgus feet.

Several multisegment foot models have been proposed and some have been used to study foot pathologies. These models have been tested and validated on typically developed populations; however application of such models to feet with significant deformities presents an additional set of challenges. For the first time, in this study, a multisegment foot model is tested for repeatability in a population of children with symptomatic abnormal feet. The results from this population are compared to the same metrics collected from an age matched (8-14 years) typically developing population. The modified Shriners Hospitals for Children, Greenville (mSHCG) foot model was applied to ten typically developing children and eleven children with planovalgus feet by two clinicians. Five subjects in each group were retested by both clinicians after 4-6 weeks. Both intra-clinician and inter-clinician repeatability were evaluated using static and dynamic measures. A plaster mold method was used to quantify variability arising from marker placement error. Dynamic variability was measured by examining trial differences from the same subjects when multiple clinicians carried out the data collection multiple times. For hindfoot and forefoot angles, static and dynamic variability in both groups was found to be less than 4° and 6° respectively. The mSHCG model strategy of minimal reliance on anatomical markers for dynamic measures and inherent flexibility enabled by separate anatomical and technical coordinate systems resulted in a model equally repeatable in typically developing and planovalgus populations.

A multi-segment foot model based on anatomically registered technical coordinate systems: method repeatability in pediatric feet.

Several multi-segment foot models to measure the motion of intrinsic joints of the foot have been reported. Use of these models in clinical decision making is limited due to lack of rigorous validation including inter-clinician, and inter-lab variability measures. A model with thoroughly quantified variability may significantly improve the confidence in the results of such foot models. This study proposes a new clinical foot model with the underlying strategy of using separate anatomic and technical marker configurations and coordinate systems. Anatomical landmark and coordinate system identification is determined during a static subject calibration. Technical markers are located at optimal sites for dynamic motion tracking. The model is comprised of the tibia and three foot segments (hindfoot, forefoot and hallux) and inter-segmental joint angles are computed in three planes. Data collection was carried out on pediatric subjects at two sites (Site 1: n=10 subjects by two clinicians and Site 2: five subjects by one clinician). A plaster mold method was used to quantify static intra-clinician and inter-clinician marker placement variability by allowing direct comparisons of marker data between sessions for each subject. Intra-clinician and inter-clinician joint angle variability were less than 4°. For dynamic walking kinematics, intra-clinician, inter-clinician and inter-laboratory variability were less than 6° for the ankle and forefoot, but slightly higher for the hallux. Inter-trial variability accounted for 2-4° of the total dynamic variability. Results indicate the proposed foot model reduces the effects of marker placement variability on computed foot kinematics during walking compared to similar measures in previous models.

A musculoskeletal foot model for clinical gait analysis.

Several full body musculoskeletal models have been developed for research applications and these models may potentially be developed into useful clinical tools to assess gait pathologies. Existing full-body musculoskeletal models treat the foot as a single segment and ignore the motions of the intrinsic joints of the foot. This assumption limits the use of such models in clinical cases with significant foot deformities. Therefore, a three-segment musculoskeletal model of the foot was developed to match the segmentation of a recently developed multi-segment kinematic foot model. All the muscles and ligaments of the foot spanning the modeled joints were included. Muscle pathways were adjusted with an optimization routine to minimize the difference between the muscle flexion-extension moment arms from the model and moment arms reported in literature. The model was driven by walking data from five normal pediatric subjects (aged 10.6+/-1.57 years) and muscle forces and activation levels required to produce joint motions were calculated using an inverse dynamic analysis approach. Due to the close proximity of markers on the foot, small marker placement error during motion data collection may lead to significant differences in musculoskeletal model outcomes. Therefore, an optimization routine was developed to enforce joint constraints, optimally scale each segment length and adjust marker positions. To evaluate the model outcomes, the muscle activation patterns during walking were compared with electromyography (EMG) activation patterns reported in the literature. Model-generated muscle activation patterns were observed to be similar to the EMG activation patterns.