The influence of posterior-inferior tibial slope in ACL injury.

PURPOSE: To explore the effect of different posterior-inferior tibial slope (PITS) angles on ACL injury at non-contact sports, knee laxity and the need for ACL reconstruction. METHODS: One hundred patients with an acute, arthroscopically verified total ACL rupture were followed prospectively with the intention of treating the injury without reconstruction. Knee laxity was assessed with the Lachman and pivot shift tests with the patients under general anesthesia within 10 days of injury. After 15 years, 22 patients of 94 available for follow-up had undergone reconstruction a mean of 4 years after injury. Reconstruction was performed in case of repeated giving-way episodes (n = 16) or meniscus lesions suitable for fixation (n = 6). Knee radiographs were available from 82 patients. Two independent readers determined the PITS angle. RESULTS: Patients injured in contact sports had a greater mean PITS angle than those injured in non-contact sports (10.5° and 9.3°, respectively, P = 0.03). The mean PITS angle was 10.1 (SD = 2.3) for non-reconstructed knees and 9.1 (SD = 3.0) for reconstructed knees (P = NS). Eight of 17 reconstructed knees showed a PITS angle of less than 7.6° (P = 0.006), and the odds ratio of need for reconstruction was 3.9 (CI 1.26-12.3, P = 0.02). No significant difference in PITS angle was found between patients with low- and high-grade instability. CONCLUSION: The main finding of the study was that reconstructed knees were overrepresented in knees with extremely low PITS angles. Additionally, patients injured in contact sports had higher PITS angles than those injured in non-contact sports, and PITS angle did not influence knee laxity