The effect of age-related declines in proprioception and total knee replacement on postural control

Background. An experiment was designed to examine the effects of a decrease in threshold joint position sense (TJPS) at the knee and ankle and of tota l knee replacement (TKR) on postural control in older adults. It was hypoth esized that older adults with a decrease in TJPS and those who had undergon e TKR would display increased center of pressure (COP) variance during quie t stance and late onsets for muscle responses to balance threats. Methods. Older adult subjects (greater than or equal to 70 years) were eval uated and grouped according to the status of their ankle and knee threshold joint position sensation as well as their surgical history. COP data were collected while subjects stood on a force plate with feet together under ey es-open and -closed conditions. Threats to balance were given using a platf orm that moved forward and backward. Results. Older subjects with poor knee extension TJPS had significantly inc reased COP variance, although those with very poor knee flexion and extensi on TJPS demonstrated even greater increases. Similarly, subjects with decre ased ankle TJPS demonstrated increased COP variance. However, reduced TJPS did not affect the ability of subjects to re spend to threats to balance. P ost-TKR subjects showed no reductions in any aspect of postural control. Conclusions. This study showed that the task of standing quietly has a dire ct relationship to threshold JPS, although the task of recovering from an a brupt perturbation does not. Older adult TKR results suggest that there is no negative effect on balance from elective joint replacement.