Patients undergoing staged bilateral knee arthroplasty are less aware of their kinematic aligned knee compared to their mechanical knee.

Abstract

To compare knee joint awareness following kinematic alignment (KA) TKA in patients who had previously undergone mechanical alignment (MA) on their contralateral knee. We performed a retrospective study of all consecutive patients who underwent staged bilateral TKA, the first using MA technique and the second utilizing the KA technique, without patient specific instrumentations. Primary outcome was assessed by the Forgotten Joint Score (FJS) with a minimum 1-year follow-up. Differences between knees were also assessed by three predefined key questions. Secondary outcome were differences in knee alignment assessed by long standing x-rays. Overall, 38 patients (76 knees) met inclusion criteria and were included in the analysis. The mean time for follow up was significantly shorter (P < 0.01) in the KA knees (1.8 years, SD 0.3) compared to the MA knees (3.1 years, SD 0.8). Nonetheless, patients were significantly less aware of their KA knees compared to their MA knees; median FJS scores were 74.0 for the KA group (IQR¼ 54.5-92.0) and 67.0 for the MA group (IQR¼ 43.7-88.0) (p = 0.01). Overall, 31 patients (81.6%) preferred their KA knee over their MA knee 6 (15.8%) (p < 0.001). KA bone cuts resulted in net varus of the medial proximal tibia (86.9, SD 2.0) and valgus of the distal femur (86.6, SD 2.8). However, the overall alignment was similar (femorotibial angle 5.4 ± 2.3 vs. 4.7 ± 2.4, p = 0.45). Patients who underwent staged bilateral knee arthroplasty were less aware of the knee that was kinematically aligned compared to the knee that was mechanically aligned. Future studies should focus on the long-term survivorship of KA TKA.