A Descriptive Study of Lower Limb Torsional Kinematic Profiles in Children With Spastic Diplegia.

BACKGROUND: Lower limb rotational anomalies in spastic diplegic children with cerebral palsy (CP) are common and difficult to identify through physical examination alone. The identification and treatment of the overall rotational disorders must be considered to restore physiological lever-arms lengths and lever-arms orientation.The aims of the study were to assess the prevalence of lower limb rotational malalignment and to describe the distribution of the different kinematic torsional profiles in children with spastic diplegia. METHODS: Instrumented gait analysis data from 188 children with spastic diplegia were retrospectively reviewed. None of the patients had undergone surgery previously or received botulinum toxin treatment within 6 months before the review. Kinematic data, collected at the midstance phase, included: pelvic, hip, and ankle rotation and foot progression angle. RESULTS: The prevalence of kinematic rotational deviations was 98.4%. Sixty-one percent of the children walked with an internal foot progression angle and 21% exhibited external alignment. The pelvis was internally rotated in 41% of the cases and externally in another 27%. Hip rotation was internal in 29% and external in 27% of the cases. Ankle rotation was internal in 55% and external in 16% of the cases. Lower limb rotational anomalies involved more than one level in 77% of the limbs. A kinematic compensatory deviation was identified in at least one level in 48% of the limbs. CONCLUSIONS: Kinematic rotational anomalies were identified in nearly all the 188 children in the study. The multilevel involvement of lower limb malalignment was not systematically associated with compensatory mechanisms between the levels. Ankle rotational anomalies were the most frequent cause of lower limb torsional deviations followed by pelvic malalignment. LEVEL OF EVIDENCE: Level IV.

Rectus femoris distal tendon resection improves knee motion in patients with spastic diplegia.

BACKGROUND: Children with spastic diplegia frequently show excessive knee extension (stiff-knee gait) throughout swing phase, which may interfere with foot clearance. Abnormal rectus femoris activity is commonly associated with a stiff-knee gait. Rectus femoris transfer has been recommended to enhance knee flexion during swing. However, recent studies suggest the transfer does not generate a knee flexor moment but diminishes knee extension moment in swing and MRI studies show the transferred tendons can be constrained by scarring to underlying muscles. Thus, it is possible knee flexion would be improved by distal rectus release rather than transfer since it would not be adherent to the underlying muscles. QUESTIONS/PURPOSES: We therefore determined whether rectus femoris distal tendon resection improves knee ROM and kinematic characteristics of stiff-knee gait in patients with spastic diplegia. PATIENTS AND METHODS: We studied 45 patients who underwent rectus femoris distal tendon resection as a part of multilevel surgery. Rectus femoris procedures were indicated based on kinematic characteristics of stiff-knee gait. All patients were walkers and had a mean age at surgery of 13 years (range, 6-22 years). We obtained gait analyses before surgery and at mean 2-year followup. We based postoperative assessment on clinical evaluation and gait analysis data. RESULTS: At followup, rectus femoris distal tendon resection was associated with improved knee ROM and timing of peak knee flexion in swing, and the absolute values of peak knee flexion became normal for those patients who showed abnormal preoperative values. CONCLUSIONS: Kinematic parameters of stiff-knee gait improved after rectus femoris distal tendon resection. Given the preliminary nature of our report, we intend to study the same patients to assess outcomes at a longer followup. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Movement-production strategy in tennis: a case study.

The present case study fell within the framework of the "absolute approach of expertise" because it assesses a "truly exceptional individual" (Chi, MTH, Cambridge Handbook of Expertise and Expert Performance, London, United Kingdom: Cambridge University Press, 2006, pp. 121-130). This technique analysis examined the movement-production strategy used by a professional tennis player performing serve-return strokes. This research enabled us to establish the relation between tennis serve-return technique and successful performance. An optoelectronic system was used to capture and analyze the expert player's stroke production in a live situation to determine the temporal trajectory of the serve-return initiation movement. Some differences between the serve-return shots were observed concerning the occurrence time of the lateral racquet displacement, the amplitude of the racquet movement, and the average latency time. No difference was observed for the gravity center (GC) movements. Backhand, forehand, and reprogramming strokes were executed with a general constancy of occurrence and average times of the GC and racquet movements. This expert player used a predictive movement-production strategy specified by a high level of reproducibility of the movement with nevertheless adaptive skills during reprogramming strokes. This adaptation supported either the development of highly consistent motor programs or the use of a more flexible strategy based on the perception-action coupling.

Addressing limitations of the Gait Variability Index to enhance its applicability: The enhanced GVI (EGVI).

Prior research has established the Gait Variability Index (GVI) as a composite measure of gait variability, based on spatiotemporal parameters, that is associated with functional outcomes. However, under certain circumstances the magnitude and directional specificity of the GVI is adversely affected by shortcomings in the calculation method. Here we present an enhanced gait variability index (EGVI) that addresses those shortcomings and improves the utility of the measure. The EGVI was further enhanced by removing some input spatiotemporal variables that captured overlapping/redundant information. The EGVI was used to reanalyze data from four previously published studies that used the original GVI. After removing data affected by the GVI's prior shortcomings, the association between EGVI and GVI values was stronger for the pooled dataset (r2 = 0.95) and for the individual studies (r2 = 0.88-0.98). The EGVI also revealed stronger associations between the index value and functional outcomes for some studies. The EGVI successfully addresses shortcomings in the GVI calculation that affected magnitude and directional specificity of the index. We have confirmed the validity of prior published work that used the original GVI, while also demonstrating even stronger results when these prior data were re-analyzed with the EGVI. We recommend that future research should use the EGVI as a composite measure of gait variability.

Changes in phase space during learning an unstable balance.

Six participants learned to maintain an unstable balance on a stabilometer, during 6 consecutive days of practice (total of 90 trials). Lateral and angular variations of body segments and body center of mass were analysed, and their evolution over the learning period was compared to the changes in dimensional variables capturing the structure of the movement itself (embedding and correlation dimension, largest Lyapunov exponent). Results indicated that (i) learning occurred, (ii) was accompanied by persistence in the dimension of the movement, and (iii) by a reduction in chaotic (or stochastic) components. Compared to other results in the learning literature, these results suggest that dimensional changes over learning are task-specific.

Changes in Gait Variability From First Steps to Adulthood: Normative Data for the Gait Variability Index.

The process of learning to walk is ongoing throughout childhood. The Gait Variability Index (GVI; A. Gouelle et al., 2013) has been proposed to quantify the variability of spatiotemporal parameters (STP) during gait. The authors' aim was to evaluate the GVI and STP of healthy children and teenagers to (a) determine changes in the GVI with age and to derive normal values in children and (b) to evaluate the influence of STP on the GVI. A total of 140 typically developing children from 1 to 17 years old were categorized into 7 groups of 20 based on age. Spatiotemporal gait parameters were recorded using an electronic walkway. GVI increased and STP changed with age. In the children-teenagers group, the GVI was positively related to step length, speed, and negatively to cadence. Following normalization by lower limb length, correlations were no longer significant. In contrast, raw base of support was not correlated with the GVI but normalized base of support was. A multiple linear regression showed that only age had a direct impact on the GVI, indicating that gait continues to change after 6-7 years. These changes were only demonstrated by the GVI, highlighting its usefulness for the evaluation of gait in young populations.

Dimensionality and the dynamics of human unstable equilibrium.

Maintaining an unstable equilibrium requires that multiple joints be coordinated so that the center of mass is kept above the base of support. The authors' aim in the present study was to discover the underlying dynamics of local (foot, hip, or head) and global (center of mass) components involved in balance control and how those dynamics are affected by changes in the available information. Participants (N = 6) had to maintain their balance on an unstable platform. Using dimensional analyses (largest Lyapunov exponent and correlation dimension), the authors examined the active degrees of freedom involved in balance control. Results indicated a similarity in dimension between local (joints) and global (center of mass) components, between a fixed point and a limit cycle. The behavior of the center of mass was found to be more predictable than the behavior of its local constituents. In addition, the available visual information affected the predictability of the postural behavior, which suggests that vision is used in the stabilization of the low-dimensional dynamics underlying balance control.

On the imitation of CP gait patterns by healthy subjects.

The comparison of gait imitated by healthy subjects with real pathological CP gaits is expected to contribute to a better distinction between primary deviations directly induced by neurological troubles and secondary compensatory deviations in relation with the biomechanics of the pathological gait. However, the ability of healthy subjects for imitating typical CP gaits such as "jump" or "crouch" gaits still remains to be determined. The present study proposes to investigate healthy subjects imitating these typical CP gait patterns. 10 healthy adult subjects performed three types of gait: one "normal" and two imitated "jump" and "crouch" gaits. Kinematics and kinetics of the hip, knee and ankle were computed in the sagittal plane. Rectified normalized EMG was also analysed. Our data were compared with reference data. For the statistical analysis, the coefficient of multicorrelation has been used. It has been demonstrated that healthy subjects were able to voluntarily modify their gait pattern with a high level of intra-session and inter-subject reproducibility as quantified by a CMC values higher than 0.76 for all parameters. The comparison with literature reference data showed that healthy subjects not could perfectly reproduce a CP gait, however could only simulate the main characteristics of "crouch" and "jump" gaits pattern. As a perspective, pathological gaits imitated by healthy subjects could be used as valuable additional material to analyse the relationship between a voluntarily modified posture and the altered muscle activation to explore a new paradigm on pathological gait pattern analysis and musculoskeletal modelling.

The gait variability index: a new way to quantify fluctuation magnitude of spatiotemporal parameters during gait.

This article describes a conglomerate measure of gait variability based on nine spatiotemporal parameters: the Gait Variability Index (GVI). Concurrent validity, inter-session reliability and minimum detectable change (MDC) were evaluated in 31 patients with Friedreich's Ataxia (FRDA), through comparisons with classically used evaluation tools such as the International Cooperative Ataxia Rating Scale (ICARS). GVI scores for the healthy population were 100.3±8.6 and were significantly reduced in FRDA patients (70.4±7.9). The GVI was correlated with the global ICARS score and was sensitive enough to differentiate between groups of FRDA patients categorized by the Posture and Gait Disturbances sub-score. The GVI was found to have a high inter-session reliability with an intraclass correlation coefficient of 0.91. A MDC of 8.6 points was found necessary to ensure that a change in GVI reflects a true change rather than measurement error. The GVI provides a quantitative measure of variability which behaves well statistically in both HP and patients with FRDA. It can be easily implemented using the supplemental data provided with this article. Complementary work is necessary to strengthen the GVI validation.

Validity of Functional Ambulation Performance Score for the evaluation of spatiotemporal parameters of children's gait.

Gait characteristics of a healthy adult population have been used to develop the Functional Ambulation Profile (FAP) score to evaluate gait in patients with neuromuscular or musculoskeletal involvement (A. J. Nelson, 1974). Further technological progress allowed a more precise recording of walk parameters and propitiated the development of the Functional Ambulation Performance Score (FAPS). The authors aimed to explore the evolution of the FAPS in healthy children to determine what the lower limit of age would be to ensure reliability of this score. Participants were 32 children with normal development. A GAITRite® walkway was used to log the spatiotemporal parameters. Compared with values obtained in adults, the average FAPS was significantly lower for children under 12 years old. The interparticipant variability was particularly high for the younger children and decreased with age. Similar trends were observed regarding the intraparticipant variability. In conclusion, the authors observed that the FAPS is not suitable to compare the gait of different children younger than 12 years old. At least, the adult standards used to calculate FAPS would need to be modified if the score has to be applied to a pediatric population.