The Effect of Posterior Tibial Slope Change on Functional Outcomes After Posterior-Stabilized Total Knee Arthroplasty: An Analysis of 370 Patients Who Had A Minimum 4-Year Follow-Up.

Abstract

Posterior tibial slope (PTS) is an important sagittal alignment parameter in posterior-stabilized total knee arthroplasty (PS-TKA). Although excessive PTS may influence knee biomechanics, the clinical relevance of postoperative PTS changes remains controversial. This single-center retrospective cohort study included 370 patients who underwent primary cemented PS-TKA using a single implant design, with a minimum follow-up of 48 months. The cohort consisted of 370 patients who had a mean age of 71 years (range, 55 to 90) and a mean follow-up duration of 64.6 months (range, 48 to 74). Sex distribution and operated side were comparable across PTS change groups. Preoperative and postoperative PTS were measured on standardized lateral radiographs. Posterior tibial slope measurements were performed independently by two blinded observers, and interobserver reliability was assessed using intraclass correlation coefficients. The PTS change was analyzed according to direction (decrease, neutral, or increase), magnitude (≤3, 4 to 9, and ≥10°), and a cut-off based on the mean absolute change (5.47°). Clinical outcomes included Visual Analog Scale, Western Ontario and McMaster Universities Osteoarthritis Index, Knee Society Score, Oxford Knee Score, Forgotten Joint Score-12, and knee range of motion. Multivariable statistical analyses were performed. All patient-reported outcome measures demonstrated significant improvement following surgery. Neither the direction nor the magnitude of PTS change was associated with postoperative pain, functional outcomes, or overall clinical improvement (all P > 0.05). An increase in PTS was associated with a modest increase in postoperative knee flexion (0.53° per one-degree increase; P < 0.001); however, this gain in range of motion did not translate into improved patient-reported functional outcomes. Across all analyses, preoperative functional status was the strongest predictor of postoperative results. Within accepted surgical ranges, changes in PTS do not have a clinically meaningful impact on functional outcomes after PS-TKA. Postoperative success appears to be driven primarily by preoperative functional status rather than by small deviations in tibial slope.