Steep tibial slope correlates with inferior patient‑reported knee function independent of tunnel widening

The purpose of this study was to evaluate any association between posterior tibial slope (PTS), graft failure, clinical outcome and bone tunnel widening following anterior cruciate ligament reconstruction (ACLR) using a hamstring autograft.

A retrospective, case-control study was conducted comparing 350 revision ACL reconstructions (ACL-RRs) with 350 primary ACL reconstructions (ACL-Rs). A hamstring autograft was used for reconstruction in all cases. PTS and femoral/tibial tunnel diameters were measured on plain anteroposterior (AP) and on lateral radiographs after surgery, prior to ACL revision surgery and at follow-up (FU). Clinical outcome was assessed at FU using the Lysholm score. Associations between PTS and Lysholm score were tested with linear regression (adjusted for age, sex and body mass index [BMI]). Tunnel enlargement was analyzed using Welch's test and correlated with PTS. The study demonstrated 97% power for the primary Lysholm model.

ACL graft failure was significantly associated with a higher PTS (7.9 ± 1.8° in ACL-R vs. 10.0 ± 2.1° in ACL-RR, p < 0.001). At FU (35.5 ± 9.2 months), no significant widening of bone tunnels related to tibial inclination occurred, whereas subjective outcome was significantly affected (p < 0.001) by a steep PTS. In knees exceeding a PTS threshold of 10°, each degree increase in PTS was associated with a 1.1-point decrease in Lysholm score. The difference in clinical outcome of knees with a PTS < 10° and  those ≥10° measured 5-6 points and exceeded the established minimal clinically important difference (≈5.5 pts). The proportion of patients reaching a patient acceptable symptom state (≥80 pts) lowered from ≈85% to ≈60%. Adjusted for sex and age, in subjects with a PTS ≥ 10°, the Lysholm score was approximately 4.3 points lower than in those with a PTS < 10°. Regardless of PTS, BMI had a negative effect on clinical outcome (p < 0.001).

An elevated PTS was not only associated with ACL graft failure but also contributed to poorer outcomes following ACLR. However, no association between PTS and bone tunnel expansion could be detected, suggesting other mechanisms for graft failure and reduced knee function.

Level III, retrospective comparative study.