Predictors of flexion using the rotating concave–convex total knee arthroplasty: preoperative range of motion is not the only determinant

Purpose: The range of motion achieved after a total knee arthroplasty (TKA) affects many daily activities and overall patients’ satisfaction. This study aims to define the determinants affecting post-operative midterm active flexion according to a specific cruciate-sacrificing prosthesis, the rotating concave–convex (ROCC^®) TKA. Method: Four hundred and eighty-four consecutive patients (584 TKAs) were prospectively followed. After baseline patient demographics and anatomical characteristics, clinical and radiological post-operative assessments were periodically recorded. The rotational alignment of the femoral component was additionally reported for 120 patients. Eligibility for final inclusion was a minimum of 5-year follow-up. Univariate analyses followed by a multivariate model were fitted to determine the independent predictors of midterm active knee flexion. Results: Thirty-four TKA (5.8 %) were excluded for a secondary surgery before their 50 years, 69 patients died (11.8 %), and 21 (3.6 %) were lost to follow-up. Overall, 460 TKAs were included. The post-operative mean knee flexion angle was measured at 127.7° ± 9.3°. Significant factors affecting final flexion under univariate analyses were the patient height and body mass index, the absence of previous surgery, a depressive state, the preoperative flexion angle, a preoperative flexion contracture, a patellar residual subluxation, the reconstructed patellar height, and the rotation of the femoral component. The multivariate model confirmed the patient’s height, a depression, the preoperative flexion angle, a patellar residual subluxation, and the patellar height as statistically significant determinants. Conclusion: Aside from the preoperative flexion angle, numerous predictors of flexion, both patient- and procedure-related were identified. Surgeons should take these into account both when adequately informing their patient before surgery and when performing the arthroplasty itself. Level of evidence: Prognostic, Level II.