Different alterations in the sit to stand movement pattern in women with early and established medial compartment knee osteoarthrits

I.A. Baert; A. Mahmoudian; I. Jonkers; F. Staes; F.P. Luyten; S. Truijen; S.M. Verschueren

Purpose: Several gait alterations including a greater loading of the medial compartment have been documented in patients with moderate to severe knee osteoarthritis (OA), but not in knee OA patients with beginning joint degeneration (early knee OA). The Sit to Stand (STS) movement is a mechanically more demanding task, requiring greater joint forces and moments, and is considered as one of the most difficult activities of daily life for patients with knee OA. Therefore, the aim of this study was to assess whether early knee OA patients did show an altered movement strategy in the more demanding STS movement compared to established knee OA patients and healthy controls. Methods: A novel classification system, incorporating Magnetic Resonance Imaging, was used to identify patients with early knee OA. Thirteen female subjects with symptomatic early medial compartment knee OA, 16 female subjects with established medial compartment knee OA (Kellgren and Lawrence grade ≥ 2+) and 16 asymptomatic female control subjects volunteered for the study. A 3D motion analysis system and force platform were used to capture the movement pattern during the STS task. Outcome measures included spatiotemporal variables (duration of movement - angular velocity), kinematic variables (joint angles) and kinetic variables (joint moments). Differences between groups were analyzed using a one-way analysis of variance. Results: The duration of the STS movement and the knee angular flexion velocity were not significantly different between the three groups. Early OA subjects showed no significant differences in kinematic variables during the STS movement. In contrast, the established OA group had a smaller knee flexion range of motion (61.0 degrees versus 67,4 degrees), related to significant more remaining knee flexion after reaching the final standing posture (15.7 degrees versus 9.9 degrees). They also showed significantly less knee abduction (11.5 degrees versus 14.4 degrees) and a significantly higher maximal knee adduction angle (6.7 degrees versus 1.9 degrees). Both OA groups showed different alterations in kinetic variables during the STS movement. Early OA patients showed a significantly higher peak hip flexion moment (0.28 Nm/kg versus 0.17 Nm/kg) and established OA patients showed a significantly larger KAM impulse (0.04 Nm/kg versus -0.02 Nm/kg) compared to controls. Conclusions: Differences in the STS movement kinematics and kinetics that were only present in patients with established knee OA and not in patients with early knee OA are most likely a consequence of structural degeneration in medial compartment knee OA and reflect mechanical overload of the medial compartment. On the other hand, the higher peak hip flexion moment during the STS movement that was present in the early stage of knee OA could reflect a compensatory mechanism in order to avoid an increase in peak knee flexion moment on their diseased knee. Higher knee flexion moments would entail higher force demand for the quadriceps, higher overall joint compression forces and, subsequently, an increase in pain. In contrast with the findings in gait analysis, early OA patients did show an adaptation in their STS movement strategy compared to healthy controls which supports the relevance of classification of early knee OA.