Does measuring the range of motion of the hip and knee add to the assessment of disability in people undergoing joint replacement?

Background and hypothesis: Range of motion (ROM) is a core component of some commonly used measures of disability, such as the American Knee Society Score and Harris Hip Score. However, the relationship between ROM and function is contested. The aim of this cross-sectional analysis was to investigate the relationship between pre-operative range of motion (ROM) and disability in patients undergoing hip and knee joint replacement.

Patients and methods: Two hundred and forty-nine patients recorded on NHS records as listed for joint replacement completed a range of measures prior to surgery. Pre-operative hip or knee ROM was measured by a trained research nurse using a hand-held goniometer. Joint pain severity was assessed using the WOMAC Pain Scale. Self-report activity limitations and participation restrictions were measured with the WOMAC Function Scale and the Aberdeen Impairment, Activity Limitation and Participation Restriction Measure. Observed activity limitations were assessed through three performance tests: 20-metre timed walk, sit-to-stand-to-sit, and 20-cm step tests.

Results: Pre-operative hip and knee ROM correlated weakly with self-report activity limitations (0.11 to 0.43), observed activity limitations (0.09 to 0.39) and self-report participation restrictions (-0.32 to 0.06). In comparison to ROM, correlations between joint pain and self-report activity limitations and participation restrictions were consistently moderate-high (-0.53 to 0.80). However, patients with restricted knee joint flexion (<110°) had significantly worse pain, activity limitations and participation restrictions than patients with non-restricted flexion (≥110°). Patients with restricted hip joint flexion (<95°) had greater activity limitations on some measures than patients with non-restricted flexion (>95°).

Discussion: This study suggests that modest restrictions of ROM are of little relevance to functional ability but that a certain amount of flexion is required for adequate function. We recommend that ROM is not the best means of assessing patients' disability prior to surgery.

Level of evidence: III - cohort study.