High posterior tibial slope increases graft failure risk but does not impair functional outcomes after primary ACL reconstruction.

Abstract

Posterior tibial slope (PTS) has been implicated in anterior cruciate ligament (ACL) graft failure, but its relationship to objective stability and patient-reported outcomes (PROs) after primary ACL reconstruction (ACLR) remains unclear. The study evaluated whether higher PTS is associated with laximetry, graft survival, and PROs after hamstring autograft ACLR. Patients undergoing primary ACLR with semitendinosus autograft between January 2019 and January 2022 by a single surgeon were retrospectively reviewed. Radiographic PTS was measured on long-leg lateral radiographs, and anterior tibial translation (ATT) was assessed using Telos stress radiographs at baseline and follow-up. PROs included KOOS, IKDC (clinical grade), ACL-RSI, and Tegner. Patients were grouped as PTS <12° versus ≥12°. Graft failure was defined as Telos side-to-side difference (SSD) > 5 mm. Kaplan-Meier analysis estimated graft survival. We included 293 patients (mean age, 28.7 ± 4.5 years; 59.6% male). KOOS Pain, QOL and global scores improved significantly from baseline, as did ACL-RSI scores (all p < 0.05). Functional outcomes at 2 years did not differ significantly between PTS groups. However, high PTS was associated with significantly greater side-to-side ATT at 1 and 2 years (p = 0.002 and <0.001, respectively) and a higher graft failure rate (64.7% vs. 33.8%; OR, 3.2; p < 0.001). Kaplan-Meier analysis showed shorter graft survival in the high PTS group (23.1 vs. 32.8 months; p < 0.001). PTS ≥ 12° is associated with inferior objective stability and increased radiographic graft failure after primary ACLR, whereas 2-year PROs are comparable across slope groups. Tibial slope is a practical preoperative risk-stratification factor that should inform counselling and follow-up intensity. Level III.