Plantar load transfer in children: a descriptive study with two pathological case studies.

BACKGROUND: Typical gait is often considered to be highly symmetrical, with gait asymmetries typically associated with pathological gait. Whilst gait symmetry is often expressed in symmetry ratios, measures of symmetry do not provide insight into how these asymmetries affect gait variables. To fully understand changes caused by gait asymmetry, we must first develop a normative database for comparison. Therefore, the aim of this study was to describe normative reference values of regional plantar load and present comparisons with two pathological case studies. METHODS: A descriptive study of the load transfer of plantar pressures in typically developed children was conducted to develop a baseline for comparison of the effects of gait asymmetry in paediatric clinical populations. Plantar load and 3D kinematic data was collected for 17 typically developed participants with a mean age of 9.4 ± 4.0 years. Two case studies were also included; a 10-year-old male with clubfoot and an 8-year-old female with a flatfoot deformity. Data was analysed using a kinematics-pressure integration technique for anatomical masking into 5 regions of interest; medial and lateral forefoot, midfoot, and medial and lateral hindfoot. RESULTS: Clear differences between the two case studies and the typical dataset were seen for the load transfer phase of gait. For case study one, lateral bias was seen in the forefoot of the trailing foot across all variables, as well as increases in contact area, force and mean pressure in the lateral hindfoot of the leading foot. For case study two, the forefoot of the trailing foot produced results very similar to the typical dataset across all variables. In the hindfoot of the leading foot, medial bias presents most notably in the force and mean pressure graphs. CONCLUSIONS: This study highlights the clinical significance of the load transfer phase of gait, providing meaningful information for intervention planning.

Flip-flops do not alter the neuromuscular function of the gastrocnemius muscle and tendon during walking in children.

INTRODUCTION/AIM: Flip-flops are a popular choice of footwear for children. However, their inherent design provides minimal support to the foot and ankle and has been suggested to increase the work performed by muscle and tendon structures, potentially predisposing them to injury. Therefore, the aim of this study was to compare the length change behaviour of the medial gastrocnemius (MG) muscle fascicles and muscle tendon unit (MTU) and their mechanical function at the ankle and subtalar joints in children during walking with and without flip-flop. METHODS: Eight healthy children walked barefoot and with flip-flops whilst 3D gait analysis and simultaneous B-mode ultrasound images of the MG fascicles during level walking were collected. Joint kinematics, kinetics and MTU lengths were analysed using musculoskeletal modelling and fascicle lengths using a semi-automated tracking algorithm. RESULTS: The muscles and tendons across the ankle absorbed greater amounts of power during barefoot walking compared to flip-flop walking. The muscle activations of the lateral gastrocnemius, soleus and tibialis anterior remained invariant across the conditions as did the activation, and fascicle length change behaviour of the medial gastrocnemius. In the barefoot condition, there was a trend of greater MTU lengthening, to potentially absorb greater amounts of power, although no differences in shortening was observed during late stance. CONCLUSION: Walking with flip-flops does not increase the mechanical work performed by the MG muscle at the ankle and subtalar joints, suggesting that flip-flops do not increase the stresses and strains of the Achilles tendon and hence its predisposition to strain induced injury. Instead, our results suggest that flip-flops, act as a compliant surface and absorb energy during contact and hence the strain experienced by the Achilles tendon.

Increasing level of neuromusculoskeletal model personalisation to investigate joint contact forces in cerebral palsy: A twin case study.

BACKGROUND: Cerebral palsy is a complex neuromuscular disorder that affects the sufferers in multiple different ways. Neuromusculoskeletal models are promising tools that can be used to plan patient-specific treatments for cerebral palsy. However, current neuromusculoskeletal models are typically scaled from generic adult templates that poorly represent paediatric populations. Furthermore, muscle activations are commonly computed via optimisation methods, which may not reproduce co-contraction observed in cerebral palsy. Alternatively, calibrated EMG-informed approaches within OpenSim can capture pathology-related muscle activation abnormalities, possibly enabling more feasible estimations of muscle and joint contact forces. METHODS: Two identical twin brothers, aged 13, one with unilateral cerebral palsy and the other typically developing, were enrolled in the study. Four neuromusculoskeletal models with increasing subject-specificity were built in OpenSim and CEINMS combining literature findings, experimental motion capture, EMG and MR data for both participants. The physiological and biomechanical validity of each model was assessed by quantifying its ability to track experimental joint moments and muscle excitations. FINDINGS: All developed models accurately tracked external joint moments; however EMG-informed models better tracked muscle excitations compared to neural solutions generated by static optimisation. Calibrating muscle-tendon unit parameters with EMG data allowed for more physiologically plausible joint contact forces estimates. Further scaling the maximal isometric force of muscles with MR-derived muscle volumes did not affect model predictions. INTERPRETATION: Given their ability to identify atypical joint contact forces profiles and accurately reproduce experimental data, calibrated EMG-informed models should be preferred over generic models using optimisation methods in informing the management of cerebral palsy.

Effects of hip joint centre mislocation on gait kinematics of children with cerebral palsy calculated using patient-specific direct and inverse kinematic models.

Joint kinematics can be calculated by Direct Kinematics (DK), which is used in most clinical gait laboratories, or Inverse Kinematics (IK), which is mainly used for musculoskeletal research. In both approaches, joint centre locations are required to compute joint angles. The hip joint centre (HJC) in DK models can be estimated using predictive or functional methods, while in IK models can be obtained by scaling generic models. The aim of the current study was to systematically investigate the impact of HJC location errors on lower limb joint kinematics of a clinical population using DK and IK approaches. Subject-specific kinematic models of eight children with cerebral palsy were built from magnetic resonance images and used as reference models. HJC was then perturbed in 6mm steps within a 60mm cubic grid, and kinematic waveforms were calculated for the reference and perturbed models. HJC perturbations affected only hip and knee joint kinematics in a DK framework, but all joint angles were affected when using IK. In the DK model, joint constraints increased the sensitivity of joint range-of-motion to HJC location errors. Mean joint angle offsets larger than 5° were observed for both approaches (DK and IK), which were larger than previously reported for healthy adults. In the absence of medical images to identify the HJC, predictive or functional methods with small errors in anterior-posterior and medial-lateral directions and scaling procedures minimizing HJC location errors in the anterior-posterior direction should be chosen to minimize the impact on joint kinematics.

Reliability of four models for clinical gait analysis.

Three-dimensional gait analysis (3DGA) has become a common clinical tool for treatment planning in children with cerebral palsy (CP). Many clinical gait laboratories use the conventional gait analysis model (e.g. Plug-in-Gait model), which uses Direct Kinematics (DK) for joint kinematic calculations, whereas, musculoskeletal models, mainly used for research, use Inverse Kinematics (IK). Musculoskeletal IK models have the advantage of enabling additional analyses which might improve the clinical decision-making in children with CP. Before any new model can be used in a clinical setting, its reliability has to be evaluated and compared to a commonly used clinical gait model (e.g. Plug-in-Gait model) which was the purpose of this study. Two testers performed 3DGA in eleven CP and seven typically developing participants on two occasions. Intra- and inter-tester standard deviations (SD) and standard error of measurement (SEM) were used to compare the reliability of two DK models (Plug-in-Gait and a six degrees-of-freedom model solved using Vicon software) and two IK models (two modifications of 'gait2392' solved using OpenSim). All models showed good reliability (mean SEM of 3.0° over all analysed models and joint angles). Variations in joint kinetics were less in typically developed than in CP participants. The modified 'gait2392' model which included all the joint rotations commonly reported in clinical 3DGA, showed reasonable reliable joint kinematic and kinetic estimates, and allows additional musculoskeletal analysis on surgically adjustable parameters, e.g. muscle-tendon lengths, and, therefore, is a suitable model for clinical gait analysis.

Instantaneous progression reference frame for calculating pelvis rotations: Reliable and anatomically-meaningful results independent of the direction of movement.

In motion analysis, pelvis angles are conventionally calculated as the rotations between the pelvis and laboratory reference frame. This approach assumes that the participant's motion is along the anterior-posterior laboratory reference frame axis. When this assumption is violated interpretation of pelvis angels become problematic. In this paper a new approach for calculating pelvis angles based on the rotations between the pelvis and an instantaneous progression reference frame was introduced. At every time-point, the tangent to the trajectory of the midpoint of the pelvis projected into the horizontal plane of the laboratory reference frame was used to define the anterior-posterior axis of the instantaneous progression reference frame. This new approach combined with the rotation-obliquity-tilt rotation sequence was compared to the conventional approach using the rotation-obliquity-tilt and tilt-obliquity-rotation sequences. Four different movement tasks performed by eight healthy adults were analysed. The instantaneous progression reference frame approach was the only approach that showed reliable and anatomically meaningful results for all analysed movement tasks (mean root-mean-square-differences below 5°, differences in pelvis angles at pre-defined gait events below 10°). Both rotation sequences combined with the conventional approach led to unreliable results as soon as the participant's motion was not along the anterior-posterior laboratory axis (mean root-mean-square-differences up to 30°, differences in pelvis angles at pre-defined gait events up to 45°). The instantaneous progression reference frame approach enables the gait analysis community to analysis pelvis angles for movements that do not follow the anterior-posterior axis of the laboratory reference frame.

Sensitivity of the Oxford Foot Model to marker misplacement: A systematic single-case investigation.

The purpose of this paper was to systematically assess the effect of Oxford Foot Model (OFM) marker misplacement on hindfoot relative to tibia, and forefoot relative to hindfoot kinematic calculations during the stance phase of gait. Marker trajectories were recorded with an 8-camera motion analysis system (Vicon Motion Systems Ltd., UK) and ground reaction forces were recorded from three force platforms (AMTI, USA). A custom built marker cluster consisting of 4 markers in a square arrangement (diagonal distance 2 cm) was used to assess the effect of marker misplacement in the superior, inferior, anterior and posterior direction for the sustentaculum tali (STL), the proximal 1st metatarsal (P1M), distal 5th metatarsal (D5M), proximal 5th metatarsal (P5M) and lateral calcaneus (LCA) markers. In addition manual movement of the heel complex 1 cm superiorly, inferiorly, medially and laterally, and also an alignment error of 10° inversion and 10° eversion was assessed. Clinically meaningful effects of marker misplacement were determined using a threshold indicating the minimal clinically important difference. Misplacement of the heel-wand complex had the most pronounced effect on mean kinematic profiles during the stance phase across all degrees-of-freedom with respect to hindfoot-tibia and forefoot-hindfoot angles. Vertical marker misplacement of the D5M and P5M markers affected the sagittal plane, and to a lesser extent frontal plane, forefoot-hindfoot kinematics. In conclusion, the OFM is highly sensitive to misplacement of the heel-wand complex in all directions and the P5M marker in the vertical direction.

The effect of femoral derotation osteotomy on transverse plane hip and pelvic kinematics in children with cerebral palsy: a systematic review and meta-analysis.

The purpose of this study was to systematically review the current literature to determine the effect of a femoral derotation osteotomy (FDRO) on hip and pelvic rotation kinematics during gait compared to no intervention in children with spastic cerebral palsy (CP). We performed a systematic search for prospective and retrospective cohort studies of children with CP, who were treated with a FDRO, and were assessed with pre and post surgery three-dimensional gait analysis. Medline, CINAHL, EMBASE, the Cochrane Library and Web of Science were searched up to December 2013. Data sources were prospective and retrospective studies. Mean differences were calculated on pooled data for both pelvic and hip rotation kinematics. Thirteen of 196 articles met the inclusion criteria (5 prospective, 8 retrospective). All included studies were of sufficient quality for meta-analysis as assessed using a customised version of the STROBE checklist. Meta-analysis showed that FDRO significantly reduced pelvic retraction by 9.0 degrees and hip internal rotation by 17.6 degrees in participants with unilateral CP involvement and hip internal rotation by 14.3 degrees in participants with bilateral CP involvement. Pelvic symmetry in children with unilateral spastic CP is significantly improved by FDRO. Patients with bilateral involvement do not improve their transverse plane pelvic rotation profiles during gait as a result to FDRO, although this result should be interpreted with caution due to the heterogeneous nature of these participants and of the methods used in the studies assessed.