Coronal Spinal Imbalance Dictated Side Preference in Symmetrically Well-Aligned Bilateral Total Knee Arthroplasty.

Abstract

Studies show better outcomes with total knee arthroplasty (TKA) when native knee alignment is restored, but few studies examined the relationship between coronal spinal and limb alignment after TKA. We retrospectively reviewed 256 patients who had bilateral TKA (BTKA) and had a minimum two-year follow-up (FU). In full-body radiographic imaging, individuals who had symmetrically well-aligned lower limbs were included. The distance between the C7 plumb line (C7PL) and the central sacral vertical line (CSVL) was measured for assessment of coronal spinal imbalance (CSI). Patients were divided into two groups: Group A, balanced spine, and Group B, imbalanced spine. Clinical outcomes and side preference were evaluated. At a mean FU of 35.0 months, 122 patients fulfilled the final evaluation (Group A, n = 51 [41.8%]; Group B, n = 71 [58.2%]) and had a mean age of 69 years (range, 53 to 88). Notably, 81.3% of the patients were women. Overall, 52.5% had neutral mechanical alignment (nMA), and 47.5% had adjusted mechanical alignment (aMA). In Group A, 71.0% showed no significant side preference. In contrast, 91.5% of Group B participants preferred the same knee toward which the spine was shifted (P < 0.0001). The mean Knee Society Score and Forgotten Joint Score of the studied group significantly improved to 154.9 and 71.7 points, respectively, with no difference between the two groups (164.6 versus 148.2, P = 0.203, and 77.6 versus 67.6, P = 0.199). Patients who had CSI preferred the knee towards the spinal shift, while both groups showed significantly improved clinical outcomes. As body weight shifts to one side, the muscles around that knee may strengthen, making that knee the dominant side. While most current studies focus on restoring knee phenotype and native alignment in TKA, assessing coronal spinal balance in weight-bearing helps surgeons predict postoperative outcomes.