The effect of ankle and knee immobilization on postural control during standing

Changes in postural strategy of the lower limb under mechanical knee constraint on an unsteady stance surface

Joint constraint could limit the available degrees of freedom in a kinematic chain for maintaining postural stability. This study investigated adaptive changes in postural synergy due to bracing of bilateral knee joints, usually thought to have a trifling impact on upright stance. Twenty-four young adults were requested to maintain balance on a stabilometer plate as steadily as possible while wearing a pair of knee orthoses, either unlocked (the non-constraint (NC) condition) or locked to restrict knee motion (the knee constraint (KC) condition). Knee constraint led to a significant increase in the regularity of the stabilometer angular velocity. More than 95% of the variance properties of the joint angular velocities in the lower limb were explained by the first and second principal components (PC1 and PC2), which represented the ankle strategy and the combined knee and hip strategy, respectively. In addition to the increase trend in PC1 regularity, knee constraint enhanced the mutual information of the stabilometer angular velocity and PC1 (MI_STBV-PC1) but reduced the mutual information of the stabilometer angular velocity and PC2 (MI_STBV-PC2). The MI_STBV-PC1 was also positively correlated to stance steadiness on the stabilometer in the KC condition. In summary, in the knee constraint condition, postural synergy on the stabilometer was reorganized to increase reliance on ankle strategies to maintain equilibrium. In particular, a stable stabilometer stance under knee constraint is associated with a high level of coherent ankle–stabilometer interaction.

The influence of wearing ski-boots with different rigidity characteristics on postural control

External supports that reduce ankle joint mobility such as ski-boots can impair postural control of healthy participants. Although this disruptive effect has been attributed to the rigidity of the external supports, the results remained controversial and no study has been conducted in order to evaluate the influence of ski-boots rigidity. Hence, the question about the influence of ankle support rigidity on postural control remains open. This study was therefore undertaken in order to investigate the effect of ski-boots rigidity on postural control. Ten healthy active participants were recruited. The wearing of soft and rigid ski-boots was compared to barefoot while standing on a seesaw generating mediolateral and anteroposterior instability. Centre of pressure displacements were sampled with a force platform. The surface electromyographic activity of the main muscles from the leg, thigh and trunk was recorded. A motion analysis system was also used to calculate the ankle, knee and hip angles. The results did not reveal any negative influence of ski-boot rigidity on postural control but rather suggest a less active postural control with the rigid ski-boots which offered a higher mechanical contribution.

Adaptation of kinematic synergy and postural control to mechanical ankle constraint on an unsteady stance surface

Joint constraint interferes with the coordinative structure in joint movements used to optimize postural stability. This study aimed to investigate changes in postural synergy when the ankle joints were bilaterally braced during a stabilometer stance. Twenty-four young adults stood on a stabilometer plate while wearing a pair of ankle-foot orthoses, which were either unlocked or locked to restrict ankle motion (the ankle constraint (AC) and non-constraint (NC) conditions). Although ankle constraint did not significantly affect the dynamics of the stabilometer movements, the size and regularity of the first principal component (PC1), which explained more than 80% of the variance of joint movements in the lower limb, were increased. In addition, PC1 exhibited higher communalities with angular movements of the knee and hip joints in the AC condition than in the NC condition. Those subjects who exhibited a constraint-induced increase in postural sway (the I group) showed greater increases in the size and regularity of PC1 than did those who exhibited reduced postural sway during ankle constraint (the D group). Constraint-induced changes in postural synergy were group-dependent. Only the I group exhibited an increase of communality of PC1 with the hip angular movement following bilateral ankle constraint. In summary, bilateral ankle constraint altered the coordination solution, with increasing reliance on compensatory knee movement to maintain a balanced posture on the stabilometer. However, accessory hip movement due to ankle constraint was not economical and was disadvantageous to stance stability.

The effects of semi-immersive virtual reality therapy on standing balance and upright mobility function in individuals with chronic incomplete spinal cord injury: A preliminary study

BACKGROUND

Individuals with chronic incomplete spinal cord injury (iSCI) commonly face persistent balance or mobility impairments. Virtual reality (VR) therapy is a useful rehabilitation approach; however, little is known about its effects in individuals with chronic iSCI.

OBJECTIVE

To investigate the effects of semi-immersive VR therapy on standing balance and upright mobility function in individuals with chronic iSCI.

METHODS

Ten subjects with chronic iSCI underwent VR therapy 30 minutes a day, 3 days a week, for 6 weeks. Limit of stability (LOS) and the Berg Balance Scale (BBS) were used to evaluate standing balance function. The Timed Up & Go (TUG) test, Activities-specific Balance Confidence (ABS) Scale, and Walking Index for Spinal Cord Injury-II (WISCI-II) were used to measure the subject's upright mobility function. Outcomes were assessed and recorded pre- and post-intervention.

RESULTS

After semi-immersive VR therapy, LOS and BBS scores were significantly increased. In addition, the TUG test results increased significantly over time, while ABC scale scores and WSCI-II levels improved significantly.

CONCLUSION

This study is the first to assess the effects of semi-immersive VR therapy for patients with chronic iSCI and limited functional abilities. These results indicated that semi-immersive VR therapy has a positive effect and is a useful intervention for standing balance and upright mobility function in patients with chronic iSCI.

Which biomechanical models are currently used in standing posture analysis?

In 1995, David Winter concluded that postural analysis of upright stance was often restricted to studying the trajectory of the center of pressure (CoP). However, postural control means regulation of the center of mass (CoM) with respect to CoP. As CoM is only accessible by using a biomechanical model of the human body, the present article proposes to determine which models are actually used in postural analysis, twenty years after Winter's observation. To do so, a selection of 252 representative articles dealing with upright posture and published during the four last years has been checked. It appears that the CoP model largely remains the most common one (accounting for nearly two thirds of the selection). Other models, CoP/CoM and segmental models (with one, two or more segments) are much less used. The choice of the model does not appear to be guided by the population studied. Conversely, while some confusion remains between postural control and the associated concepts of stability or strategy, this choice is better justified for real methodological concerns when dealing with such high-level parameters. Finally, the computation of the CoM continues to be a limitation in achieving a more complete postural analysis. This unfortunately implies that the model is chosen for technological reasons in many cases (choice being a euphemism here). Some effort still has to be made so that bioengineering developments allow us to go beyond this limit.