Posterior Tibial Slope Is Associated With the Chondral Wear Pattern of the Medial Tibial Plateau

The influence of the posterior tibial slope on the knee has been extensively studied, particularly in the context of surgical outcomes in sports medicine, such as cruciate ligament reconstruction. From a biomechanical perspective, the posterior tibial slope affects not only knee kinematics but also contact pressure, potentially contributing to the development and progression of degenerative change in the joint over time. However, whether or not there is an association on the chondral wear pattern of the medial tibial plateau remains unclear.

(1) Is posterior tibial slope associated with the chondral wear pattern of the medial tibial plateau? (2) Does an increase in posterior tibial slope correlate with chondral wear in the posterior part of the medial tibial plateau?

The chondral wear pattern of the medial tibial plateau was evaluated in 2555 knees (1912 patients) that underwent primary TKA for medial osteoarthritis (OA) by a single surgeon between July 2005 and December 2022. A total of 290 knees were excluded because of (1) inflammatory arthritis, (2) extensive chondral wear across the medial tibial plateau that prevented pattern classification, or (3) prior surgeries that influenced the wear pattern. To avoid including bilateral knees from the same patient, only one knee per patient was analyzed, with the knee selected at random. Accordingly, the final study cohort consisted of 1703 patients (1703 knees). Intraoperative assessment of medial tibial plateau chondral wear patterns was recorded in a preformatted electronic database. The surgeon identified the region with the most severe wear from among three predefined areas-anterior, central, and posterior-using a categorical input. Based on this selection, chondral wear patterns were classified as anteromedial OA, centromedial OA, or posteromedial OA. To answer our primary study question, we measured the posterior tibial slope on preoperative true lateral radiographs and compared it across different chondral wear patterns. To answer our second study question, we analyzed the association between posterior tibial slope and chondral wear patterns using multinomial logistic regression, adjusting for variables such as patient demographics, mechanical hip-knee-ankle (mHKA) angle, and the presence of ACL deficiency and medial meniscus radial tear. Among the 1703 knees, 33% (562 of 1703) were classified as having anteromedial OA, 28% (477 of 1703) as centromedial OA, and 39% (664 of 1703) as posteromedial OA. The mean ± SD posterior tibial slope was 10° ± 4°, and the mean mHKA angle was 10° ± 5°.

There was a difference in posterior tibial slope between all three groups, with the slope progressively increasing as the chondral wear pattern shifted from anterior to posterior: mean ± SD 8° ± 3° in anteromedial OA, 10° ± 3° in centromedial OA, and 12° ± 3° in posteromedial OA (p < 0.001). The mHKA angle was lower in the centromedial OA group (8° ± 4°; p < 0.001) compared with the others, with no difference between the anteromedial OA (10° ± 4°) and posteromedial OA groups (10° ± 5°; p = 0.02). Medial meniscus radial tears were observed in 60% (335 of 562), 51% (242 of 477), and 67% (445 of 664) of the anteromedial OA, centromedial OA, and posteromedial OA groups, respectively. After adjustment for the investigated variables, increased posterior tibial slope remained a factor distinguishing both anteromedial OA and posteromedial OA from centromedial OA (anteromedial OR 0.84 [95% confidence interval (CI) 0.80 to 0.88]; p < 0.001 versus posteromedial OR 1.16 [95% CI 1.11 to 1.21]; p < 0.001). Higher posterior tibial slope values were associated with a progressive increase in the proportion of posteromedial OA, accompanied by a corresponding decrease in anteromedial OA.

Posterior tibial slope is associated with the chondral wear pattern of the medial tibial plateau. The anteromedial OA, centromedial OA, and posteromedial OA groups each exhibit distinct characteristics, including differences in mHKA angle and medial meniscus radial tears. Among these factors, observed chondral wear patterns shifted posteriorly as posterior tibial slope increased, suggesting an association between greater slope and the development of posterior wear patterns. These findings underscore the importance of evaluating posterior tibial slope when planning treatment for medial OA, as unintended changes may be associated with chondral wear patterns and clinical outcomes. Future studies should investigate the causal mechanisms linking posterior tibial slope and chondral wear using prospective designs and advanced imaging modalities.

Level Ⅲ, prognostic study.