Normalized knee-extension strength or leg-press power after fast-track total knee arthroplasty: which measure is most closely associated with performance-based and self-reported function?

OBJECTIVE: To investigate which of the 2 muscle-impairment measures for the operated leg, normalized knee extension strength or leg press power, was most closely associated with performance-based and self-reported measures of function shortly after total knee arthroplasty (TKA).
DESIGN: Cross-sectional, exploratory study.
SETTING: Laboratory at a regional hospital. PARTICIPANTS: Individuals (N=39) with an average age ± SD of 65.5±10.3 years, who all had unilateral TKA 28 days prior.
INTERVENTIONS: None. MAIN OUTCOME MEASURES: The patients performed maximal isometric knee extensions and dynamic leg presses to determine their body-mass normalized knee extension strength and leg press power, respectively. The 10-meter fast speed walking- and 30-second chair stand tests were used to determine performance-based function, while the Western Ontario and McMaster Universities Osteoarthritis Index and Oxford Knee Scores were used to determine self-reported function.
RESULTS: Normalized leg press power was more closely associated with both performance-based (r=.82, P<.001) and self-reported (r=.48, P=.002) measures of function compared with normalized knee extension strength (r=.51, P=.001 and r=.39, P=.015, respectively).
CONCLUSIONS: Normalized leg press power was more closely associated with both performance-based and self-reported function early after TKA than normalized knee extension strength. It may be explained by the fact that performance-based measures of function are typically closed kinetic chain tasks, such as walking or rising from a chair, and self-reported measures of function typically include questions that address perceived difficulty with performing these same tasks.