Abstract
BACKGROUND: An increased posterior tibial slope (PTS) has been shown to be a risk factor for anterior cruciate ligament (ACL) ruptures, but the difference in the mean PTS between patients with ACL ruptures and patients with intact ACLs is only approximately 1°, and the PTS has a wide range between 1° and 22°. Therefore, an ACL rupture may be associated with other morphological differences along with the PTS. PURPOSE: To evaluate whether the predictive value of the PTS can be increased with new parameters associated with the proximal tibia, distal femur, and extensor mechanism. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: This study included 81 patients who underwent surgical treatment for isolated ACL ruptures and 81 patients with intact ACLs as the control group.Lateral PTS (LPTS), medial PTS (MPTS), lateral femoral condylar offset, anterior patellar offset (APO), lateral tibial plateau offset, and tibial tubercle offset were measured on magnetic resonance imaging. The patella-lateral tibial plateau ratio (P-LTPR) was obtained by dividing the APO by the lateral tibial plateau offset, and the patella-tibial tubercle ratio (P-TTR) was obtained by dividing the APO by the tibial tubercle offset. Patients with ACL ruptures and intact ACLs were subdivided according to an LPTS ≥8° and an LPTS <8° and compared. RESULTS: The parameters independently associated with ACL ruptures were P-LTPR (P = .001), P-TTR (P = .006), LPTS (P = .016), and MPTS (P = .047). In patients with intact ACLs and an LPTS ≥8°, P-LTPR was negatively correlated with LPTS and MPTS (P = .015 and P < .001, respectively; r = -0.736 and r = -0.758, respectively). In patients with an LPTS ≥8°, P-LTPR was associated with ACL ruptures, with 77.8% sensitivity and 73.7% specificity, at values >1.38, while P-TTR was associated with ACL ruptures, with 68.3% sensitivity and 67.7% specificity, at values >1.77. In patients with an LPTS <8°, P-TTR was associated with ACL ruptures, with 68.7% sensitivity and 77.2% specificity, at values >1.86. CONCLUSION: An evaluation of the P-LTPR and P-TTR parameters when assessing anatomic risk factors for an ACL rupture may increase the predictive information provided by the PTS. P-LTPR may be especially useful in re-evaluating the risk of ACL ruptures in patients who are considered to have a high risk because of a high PTS but an intact ACL, and P-TTR may be useful in re-evaluating the risk of ACL ruptures in patients who are considered to have a low risk because of a low PTS.