Effects of Soft Tissue Artifacts on the Calculated Biomechanical Variables in Patients with Total Knee Replacements During Stair-Ascent

Total knee replacement (TKR) has been the main choice of treatment for advanced knee osteoarthritis (OA). Biomechanics of the knee during stair-ascent has mostly been studied using skin marker-based motion analysis techniques, but no study has reported a complete assessment of the soft tissue artifacts (STA) and their effects on the calculated joint center translation, angles and moments at the knee in TKR patients during this activity. Quantification of the effects of the STA on calculated knee kinematics and kinetics will help for the understanding of the measurement errors on target activities. The purposes of this study were to integrate a model-based 3D fluoroscopy method, skin marker-based stereophotogrammetry, and a forceplate to quantify the movement of the markers relative to the underlying bones, and to assess its effects on the calculated kinematic and kinetic variables at the knee in six patients with total knee replacements (TKR) during stair-ascent. Considerable STA during stair-ascent were found, leading to significantly underestimated flexion and extensor moments, but overestimated joint center translations.