Variability in knee pivoting behavior and condylar translation: Insights from a dynamic CT study

BACKGROUND: Replicating physiological knee kinematics is a main goal in total knee arthroplasty (TKA), yet natural variability in pivoting behavior remains underexplored. This study characterized pivot patterns and femoral condyle translation in healthy and osteoarthritic (OA) knees using dynamic computed tomography (CT). METHODS: We analyzed dynamic CT scans from 98 healthy right knees (28 men, 70 women; 24.4 ± 3.6 years) and 11 OA knees scheduled for TKA (6 men, 5 women; 65.8 ± 8.0 years) during non-weight-bearing flexion-extension (median range: healthy knees 82.5°, OA knees 67.0°). Femoral condyle motion and center of rotation (CoR) were assessed by fitting cylinders through the femoral condyles and projecting their centers onto a transverse tibial plane. The CoR was classified as medial, central, lateral, or no pivot. RESULTS: Healthy knees mainly exhibited medial pivot (58.2%), followed by no (31.6%), central (6.1%), and lateral pivots (4.1%). In the small OA cohort knees most often showed no pivot (45.5%), followed by lateral (27.3%), medial (18.2%), and central (9.1%) pivots. Medial condylar translation was greater in OA knees than in healthy knees (6.2 vs. 3.7 mm; P = 0.002), while lateral translation did not differ (P = 0.109). CONCLUSION: Healthy knees most frequently exhibit medial pivot during non-weight-bearing extension, whereas OA knees show a shift toward alternative pivot patterns, with more medial femoral condyle translation. Although only a small number of patients were analyzed, preoperative pivot patterns in OA knees may differ from physiological motion and should be interpreted cautiously when informing personalized TKA alignment.