Type IIB Spino-Pelvic Imbalance Is an Independent Risk Factor for Flexion Contracture after Total Knee Arthroplasty.

Abstract

Sagittal imbalance leads to adjustments in the pelvis, hips, and knees to keep a level gaze with minimal energy use. People who have a stiff spine adjust their posture by extending their hips, bending their knees, and tilting their pelvis back. This study hypothesized that type IIB spino-pelvic imbalance may influence the occurrence of flexion contracture after total knee arthroplasty (TKA). We retrospectively evaluated all patients who received a robotic-assisted TKA between 2019 and 2024 at a single center. patients who had a postoperative range of motion (ROM) > 90°, a residual postoperative flexion contracture > 0°, and a final surgery report from the robotic platform confirming full extension at the end of the surgery. hip osteoarthritis or arthroplasty, preoperative stiff knees (full ROM < 70°), and limb length discrepancy > 1 cm. Patients were divided into the IA-IB-IIA-IIB categories according to the 2021 Journal of the American Academy of Orthopaedic Surgeons spino-pelvic classification. There were two different knee surgeons who meticulously measured the residual flexion contracture with a goniometer. Linear regressions were used to assess whether spino-pelvic alignment would be associated with flexion contracture. Logistic regressions assessed whether a type IIB independently predicted residual flexion contracture. Preoperative ROM, hip-knee-ankle angle, age, and body mass index were set as potential confounders. The model's fit was assessed using the Hosmer-Lemeshow (P > 0.43). A total of 112 patients were included. The postoperative median flexion contracture was two (interquartiles range, one to four) in Cohort 1 and 10 (interquartiles range 7.2 to 14) at the final follow-up. There were 31 patients who were type IA (27.7%), 20 patients (17.9%) type IB, eight patients (7.1%) IIA, and 53 patients (47.3%) IIB. A higher incidence of residual flexion contracture was found in IIB patients (24.1, P < 0.001). Logistic regression revealed IIB as an independent predictor of postoperative flexion contracture (B = 0.7, SE = 0.3, Wald = 5.6, P = 0.016, 95% confidence interval= 4.3 to 6.9). The sagittal spino-pelvic alignment is a predictor of residual postoperative flexion contracture following TKA.