Functional performance after hip resurfacing or total hip replacement: a comparative assessment with non-operated subjects.

INTRODUCTION: Several studies reported better clinical results with total hip resurfacing than with conventional total hip replacement, including in young patients, but without comparative stabilometry assessment. HYPOTHESIS: Resurfacing arthroplasty provides better functional performance than conventional total hip replacement. OBJECTIVES: To test the above hypothesis in a stabilometry study comparing balance and functional performance in patients with total hip resurfacing or conventional total hip replacement and healthy controls. MATERIALS AND METHODS: Results were analyzed on three cohorts of 20 patients: healthy control subjects, with unilateral total hip replacement or unilateral total hip resurfacing. The 40 operated patients were comparable in gender, age, weight (body-mass index), date of operation and clinical results. The 20 control subjects were younger and served as reference. Balance analysis employed a force platform commonly used in stabilometry, standardizing both leg or single leg stance balance analysis. The software interpreted individual balance by measuring plantar pressure center variation during the analysis so as to contour an individual both leg or single leg area of balance (statokinesigram, in mm(2)). RESULTS: Balance analysis on both leg found comparable results in the control and resurfacing groups. The weight-bearing statokinesigraphic both leg balance area was greater in the hip replacement than in either of the other two groups (p<0.05), and five times greater than in the resurfacing group (p<0.05). The single leg weight-bearing balance results were significantly better in the resurfacing group, with a statokinesigraphic balance area half that of the hip replacement group, whether on the operated or the non-operated side (p<0.001). DISCUSSION AND CONCLUSION: The present functional performance results confirm the advantage of resurfacing over conventional hip replacement, and help explain the excellent radioclinical results reported for total hip resurfacing. LEVEL OF EVIDENCE: III, comparative case-control study.

Postural organisation during cascade juggling: influence of expertise.

The present study investigated how posture is organised during three-ball cascade juggling according to expertise. We hypothesized that the juggling task would place constraints on the postural organisation mode and that the posture-juggling coupling would be increased with expertise. Two groups, intermediates and experts, were asked to perform a postural-cascade juggling task. A three-dimensional motion recording system recorded the position of five light-reflecting markers for 30s to analyse the ball movements, the lateral oscillations of the sacrum and the flexion/extension of the right elbow. The spatial pattern of the cascade juggling showed no significant difference between groups. Moreover, both groups presented lateral oscillations of the sacrum during the task. The latencies between the maximal flexion/extension of the right elbow and the maximal lateral oscillations of the sacrum and their standard deviations were significantly lower for the experts than for the intermediates. We conclude that postural adaptations occur to facilitate the postural-suprapostural task and that experience modifies the posture-juggling coupling.

Visual and postural control of an arbitrary posture: the handstand.

The aim of this study was to increase our understanding of postural regulation by analysing an arbitrary posture - the handstand. We assessed the relative influence of peripheral vision and central visual anchoring on the postural balance of gymnasts in the inverted-stand posture. Displacements of the centre of pressure, the angles between the body segments, and the gymnast's height in the handstand were analysed. Postural regulation in the handstand appeared to be organized according to a system similar to that in erect posture, with three articular levels suggesting the existence of a typical organization of human posture. Moreover, both intra-modal (central and peripheral vision) and inter-modal sensory systems (vision and other balance systems) contributed to the postural regulation. The results are interpreted in terms of an ecological approach to posture in which postural regulation can be considered as an emergent phenomenon.

Cholinergic system, rearing environment and trajectory learning during aging in mice.

Three, 12- and 20-month-old C57BL6/J mice, reared in standard conditions or in enriched environments, were administered subcutaneously either scopolamine hydrobromide, 0.6 or 1.2 mg kg(-1), or physiological saline (control mice) 15 min before testing their abilities to find an invisible platform in a modified version of the Morris water maze, the starting point being kept unchanged throughout the experiment to allow the aged animals to solve the task. The results demonstrated that: 1) All control mice, whatever their age, were able to learn the platform location, but the number of trials needed to reach the learning criterion (3 consecutive trials in less than 8 s) increased with age; 2) All the scopolamine-treated mice, whatever their age, were also able to learn the platform location. However, compared to age-matched controls, the number of trials needed to reach the learning criterion was greater; 3) Rearing the animals in an enriched environment antagonized the effect of scopolamine, but only in the youngest (3 month-old) mice. All control and scopolamine-treated mice, whatever their age and their rearing environment, remembered, 7 days later, the platform location.

Influence of cholinergic system on motor learning during aging in mice.

Three, 12- and 20-month-old C57Bl6 mice, reared in standard conditions or in an enriched environment, were administered subcutaneously either scopolamine hydrobromide (SIGMA), 0.6 and 1.2 mg kg(-1), or physiological saline 15 min before testing their motor skills (muscular strength, dynamic equilibrium and motor coordination) and motor learning abilities (number of trials needed to reach a learning criterion on a rotorod rotating at 27 revolutions per min). The results demonstrated a lack of correlation between motor skill scores and between motor skill and motor learning scores, suggesting that the rotorod training procedure measures motor learning and not motor skills or is insensitive to changes in motor skills. They also demonstrated that motor skills decreased with age but were insensitive to environmental rearing and to scopolamine. In contrast, the learning scores, which also decreased with age, were very sensitive to scopolamine, particularly in the oldest mice. These results are discussed according to the role of cholinergic system in motor learning during aging.