Muscle power and function two years after unicompartmental knee replacement

Unicompartmental knee replacement (UKR) is a commonly performed procedure, suitable for one in four patients requiring knee replacement for end-stage osteoarthritis. Recovery and return of function is quicker than with total knee replacement (TKR), but little information is known about the recovery of muscle power. We prospectively studied a cohort of forty four patients undergoing medial UKR to document their functional recovery and leg extensor power. Muscle power was measured using a Leg Extensor Power rig preoperatively and at 1 and 2 years after surgery. Function was self reported using the Oxford Knee Score (OKS) and Tegner Activity Scale (TAS). At 1 year all patients had made significant improvements on all functional measures, with a mean gain in OKS of 15.9 and TAS of 0.84. There were also significant increases in leg extensor power (LEP) of both legs. The mean change in LEP of the operated leg at 1 year was 0.50 W/kg and the non-operated leg was 0.10 W/kg. Between 1 and 2 years there were very slight improvements in strength in both legs, but these were not significant. Compared with healthy age matched normative values, the UKR LEP values at 2 years after surgery were decreased. The recovery of strength and function following UKR had stabilised by 1 year and during the following year further improvements were minimal.