Knee joint stabilization therapy in patients with osteoarthritis of the knee and knee instability: subgroup analyses in a randomized, controlled trial.

Objective: To test whether knee stabilization therapy, prior to strength/functional training, may have added value in reducing activity limitations only in patients with knee osteoarthritis who have knee instability and (i) low upper leg muscle strength, (ii) impaired knee proprioception, (iii) high knee laxity, or (iv) frequent episodes of knee instability.
Design: Subgroup analyses in a randomized controlled trial comparing 2 exercise programmes (with/without knee stabilization therapy) (STABILITY; NTR1475).
Patients: Participants from the STABILITY-trial with clinical knee osteoarthritis and knee instability (n = 159).
Methods: Effect modification by upper leg muscle strength, knee proprioception, knee laxity, and patient-reported knee instability were determined using the interaction terms "treatment group subgroup factor", with the outcome measures WOMAC physical function (primary), numeric rating scale pain and the Get up and Go test (secondary).
Results: Effect modification by muscle strength was found for the primary outcome (p = 0.01), indicating that patients with greater muscle strength tend to benefit more from the experimental programme with additional knee stabilization training, while patients with lower muscle strength benefit more from the control programme.
Conclusion: Knee stabilization therapy may have added value in patients with instability and strong muscles. Thus it may be beneficial if exercises target muscle strength prior to knee stabilization.