Does laxity alter the relationship between strength and physical function in knee osteoarthritis?

Objective. Since strengthening interventions have had a lower-than-expected impact on patient function in studies of knee osteoarthritis (OA) and it i s known that laxity influences muscle activity, this study examined whether the relationship between strength and function is weaker in the presence o f laxity. Methods, One hundred sixty-four patients with knee OA were studied. Knee OA was defined by the presence of definite osteophytes, and patients had to h ave at least a Little difficulty with knee-requiring activities. Tests were performed to determine quadriceps and hamstring strength, varus-valgus lax ity, functional status (Western Ontario and McMaster Universities Osteoarth ritis Index Physical Functioning subscale [WOMAC-PF] and chair-stand perfor mance), body mass index, and pain. High and low laxity groups,were defined as above and below the sample median, respectively. Results. Strength and chair-stand rates correlated (r = 0.44 to 0.52), as d id strength and the WOMAC-PF score (r = -0.21 to -0.36), In multivariate an alyses, greater laxity was consistently associated with a weaker relationsh ip between strength (quadriceps or hamstring) and physical functioning (cha ir-stand rate or WOMAC-PF score). Conclusion. Varus-valgus laxity is associated with a decrease in the magnit ude of the relationship between strength and physical function in knee OA, In studies examining the functional and structural consequences of resistan ce exercise in knee OA, stratification of analyses by varus-valgus laxity s hould be considered. The effect of strengthening interventions in knee OA m ay be enhanced by consideration of the status of the passive restraint syst em.