The control group matters: Pain, physical function and strength improvements relative to the comparator intervention in knee and hip osteoarthritis

Background

In knee and hip osteoarthritis (OA), the mechanism for resistance exercise improving clinical outcomes and the dose-response between strength and clinical outcomes are unknown; in part due to inconsistent trial designs across studies.

Purpose

To determine whether the effects of resistance exercise interventions on pain and function differ based on comparator group; and whether there is an association between improvements in lower extremity strength with improvements in pain and function in knee and hip OA.

Methods

We searched 6 databases (inception to January 28 2023,) for randomized controlled trials (RCTs) comparing land-based, resistance exercise-only interventions with no intervention or any other intervention. There were four subgroups for comparator intervention: NONE (none/placebo/sham/usual care), EXE (other exercise interventions alone), NONEXE (non-exercise interventions alone), COMBO (combined exercise + non-exercise interventions). The between-group effect (ES) was calculated for immediate post-intervention pain and function (activities of daily living (ADL) and sports/recreation (SPORT)). Meta-regression analyses were completed to evaluate the association between improvements in lower extremity strength (independent variable) and improvements in pain, ADL and SPORT (dependent variables), irrespective of comparator intervention.

Results

For knee OA (257 studies), there were large benefits for pain [ES (95 % CI) = -0.92 (-1.15, -0.69)], ADL [-0.79 (-1.01, -0.56)] and SPORT [-0.79 (-1.02, -0.56)] favouring resistance exercise interventions compared to NONE. For knee pain, there was also a moderate benefit favouring COMBO interventions compared to resistance exercise interventions [0.44 (0.23, 0.65)]. For hip OA (15 studies), there were moderate benefits for pain [-0.51 (-0.68, -0.33)], ADL [-0.57 (-0.78, -0.36)] and SPORT [-0.52 (-0.70, -0.35)] favouring exercise interventions compared to NONE. For hip pain, there was also a moderate benefit favouring NONEXE interventions compared to resistance exercise interventions [0.57 (0.17, 0.97)]. For knee OA, greater strength gains were associated with larger improvements in pain [β (95 % CI) = -0.24 (-0.38, -0.09)], ADL [-0.43 (-0.73, -0.12)] and SPORT [-0.37 (-0.73, -0.00)].

Conclusion

In knee and hip OA, the effects of resistance exercise on pain and function improvements depend on the comparator intervention. For knee OA, a dose-response relationship was observed between lower extremity strength gains with pain and function improvements.