The impact of Mechanical and Restricted Kinematic Alignment on Knee Anatomy in Total Knee Arthroplasty

Abstract Background Total knee arthroplasty (TKA) aiming at neutral mechanical alignment (MA) inevitably modifies the patient’s native knee anatomy. Another option is kinematic alignment (KA), which aims to restore the original anatomy of the knee. The aim of this study was to evaluate the variations in lower limb anatomy of a patient population scheduled for TKA, to assess the use of a restricted KA TKA protocol and compare the resulting anatomy modifications with the standard MA technique. Methods 4884 knee CT scans were analysed from a database of patients undergoing TKA with patient specific instrumentation. The Lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA) and hip knee ankle angle (HKA) were measured. Bone resections were compared using standard MA and a restricted KA aiming for independent tibial and femoral cuts of maximum ±5° deviation from the coronal mechanical axis and a resulting overall coronal HKA within ±3° of neutral. Results The mean MPTA was 2.9° varus, LDFA was 2.7° valgus and overall HKA was 0.1° varus. Using our protocol, 2475 knees (51%) could have undergone KA without adjustment. To include 4062 cases (83%), mean corrections of 0.5° for MPTA and 0.3° for LDFA were needed, significantly less than with MA (3.3° for MPTA and 3.2° for LDFA) (p