Biomechanical analysis of the sit-to-stand movement following knee replacement: a cross-sectional observational study

The sit-to-stand [STS] movement is a functional task that generates large forces across the knee. Only a few studies have reported biomechanical variables during this movement in post knee replacement patients and none have compared these variables between unilateral and bilateral sub groups. The aim of this study was to provide a biomechanical characterisation of the STS movement post knee arthroplasty and explore differences between bilateral and unilateral patients. Sixteen post arthroplasty patients [age 67.3 +/- 4.95, height, 164cm+/- 10.1, weight 80.8Kg +/-15.0] were recruited from the same clinical site and underwent biomechanical analysis 7.9 +/- 6.92 months after surgery. Participants performed the STS movement from a set position without using their arms. Movement variables [movement time, joint rotation, peak force, loading symmetry and knee moments] were derived from a three dimensional motion analysis system. The bilateral group (n=7) performed the movement slightly faster (n/s) with better loading symmetry (mean 0.91 compared to 0.78) but smaller knee moments (mean 0.38 Nm kg-1 compared to 0.49 Nm kg-1) than the unilateral group (n=9). These results confirm patients with a knee replacement perform the STS movement differently to healthy older adults and provide comparisons between bilateral and unilateral patients.