Unique Center of Pressure Profiles in Unilateral Compared to Bilateral End-Stage Ankle Arthritis Patients

Abstract

nkle arthritis is a debilitating condition that alters the mobility and stability of the ankle joint during both static and dynamic tasks. Symmetrical contribution to balance performance has been posited to improve balance performance. However, few studies have examined the impact of unilateral compared to bilateral joint involvement on balance in individuals with ankle arthritis. PURPOSE: To quantify balance performance in patients with unilateral (UA) compared to bilateral (BA) end-stage ankle arthritis. METHODS:Twenty-three UA and 21 BA patients performed three 10-second quiet standing trials with their feet placed together. Ground reaction forces were recorded using two force platforms, one under each foot (1200 Hz, BP600-900, AMTI). Center of pressure (CoP) measures were calculated using custom software (Matlab, Mathworks). CoP excursions in the anteroposterior (AP), mediolateral (ML) and resultant directions (RES) were calculated as described by Prieto et al. (1996). Independent samples t-tests were used to compare the involved (INV) and uninvolved limbs (UN) in the UA to the average of the left and right limbs in BA. Significance was set at p < 0.05. RESULTS:No demographic differences existed between the UA and BA patients. No differences existed between the INV and BA group for the RES (p=0.499; INV: 16.96±7.11 mm; BA: 16.08±4.48 mm), AP (p=0.190; INV: 6.05±1.41 mm; BA: 6.16±1.29 mm) or ML excursions (p= 0.431; INV: 14.39±7.26 mm; BA: 13.38±4.83 mm). When comparing the UN limb to the BA group, the UN limb had significantly greater RES (p=0.040; UN: 20.25±8.57 mm) and ML excursions (p=0.029; UN: 17.97±8.51) compared to the BA group. No differences were observed in AP excursions between the UN (p=0.255; UN: 5.83±1.67) and BA groups. CONCLUSIONS: These data indicate that the contribution of each limb to postural stability is unique in individuals with unilateral end-stage ankle arthritis. Interestingly, no differences were observed in AP CoP excursions between the two groups. Further, it should be noted that CoP excursions were significantly greater in the UN limb compared to the BA group. This is contrary to the notion of “better balance” which would generally be associated with healthy limb, but may be an effect of compensating for the INV limb.