Kinematic Alignment Produces Improved Flexion and Forgotten Joint Scores Compared to Mechanical Alignment in Primary...

Debates continue over which surgical approach yields better outcomes in primary total knee arthroplasty (TKA): kinematic alignment or mechanical alignment. A prospective, multicenter study was conducted comparing these strategies in patients with "ball-in-socket" medial-pivot implants. We hypothesized that kinematic alignment would yield superior outcomes. Participants undergoing primary TKA with medial-pivot implants were included. One site used unrestricted kinematic alignment, while three utilized mechanical alignment. Surgical techniques were standardized, including tourniquet use, medial parapatellar arthrotomy, patella resurfacing, posterior cruciate ligament sacrifice, manual instrumentation, and cement fixation. The Forgotten Joint Score (FJS) and range of motion were measured at 6 weeks, 6 months, 1 year, and 2 years postoperatively, with preoperative range of motion assessed as well. A total of 258 patients were enrolled, comprising 101 with kinematic alignment and 157 with mechanical alignment. The mean flexion and FJS were significantly better for the kinematic alignment group at 6 months, 1 year, and 2 years postoperatively. At 2 years, mean flexion was 132 ± 8.6 degrees for kinematic alignment and 122 ± 9.9 degrees for mechanical alignment (p < 0.0001), and the FJS was 68 ± 26.3 for kinematic and 60 ± 29 for mechanical alignment (p = 0.04). Furthermore, manipulation procedures for arthrofibrosis were required at a significantly lower rate in the kinematic group (2% vs. 7%; p = 0.05). This 2-year study demonstrated that kinematic alignment led to improved mean range of motion, FJS, and a lower manipulation rate compared with mechanical alignment in patients with medial-pivot implants. Evidence specific to medial-pivot devices implanted with different alignment philosophies remains limited, and our study addresses this gap by focusing on the medial-pivot implant in a prospective multi-center cohort. Our findings suggest that kinematic alignment offers better clinical outcomes with "ball-in-socket" medial-pivot implants. The study provides level II evidence.