High posterior tibial slope is associated with higher failure rates in nonoperative management of primary anterior cruciate ligament injury.

Purpose: To evaluate the impact of posterior tibial slope (PTS) on patient-reported outcome measures (PROMs) and treatment failure in patients with primary anterior cruciate ligament (ACL) injury who elected to undergo nonoperative treatment. Methods: Patients with primary ACL injury who underwent nonoperative treatment were included in this retrospective study. A chart review was conducted to collect demographic data. Medial PTS was measured on strict lateral radiographs using a standardised method. Validated PROMs were collected at final follow-up. A correlation analysis was conducted to assess the relationship between PTS and PROMs. A logistic regression analysis was performed to assess whether PTS could predict failure of nonoperative treatment. Failure was defined as conversion to ACL reconstruction after a minimum of 3 months of nonoperative treatment. Results: A total of 113 patients with a mean age of 31.7 ± 10.5 years at the time of ACL injury and a mean follow-up period of 6.6 ± 1.5 years were included in this study. Nonoperative treatment failure occurred in 82 patients (73%) after a median time of 10.0 months (interquartile range, 7 months) from injury. Patients experiencing nonoperative treatment failure showed a significantly higher PTS compared to patients without treatment failure (10.5° ± 2.8° vs. 8.1° ± 2.1°; p < 0.05). Thirty-two per cent of patients with nonoperative treatment failure had a PTS ≥ 12°, while 100% of patients without nonoperative treatment failure had a PTS < 12° (p < 0.001). Each one-degree increase in PTS was associated with a 1.5-fold increase in the odds of nonoperative treatment failure (p < 0.05) after primary ACL injury. No significant correlations were observed between PTS and PROMs. Conclusions: A high PTS was associated with an increased risk of nonoperative treatment failure in primary ACL injury and often required delayed ACL reconstruction. However, PTS was not an independent predictor. Treatment decisions should also consider established factors such as patient age and activity level. Level of Evidence: Level III, retrospective case series.