Does Posterior Tibial Slope Influence Knee Functionality in the Anterior Cruciate Ligament-Deficient and Anterior Cruciate Ligament-Reconstructed Knee?

Purpose: The purpose of this study was to investigate the relation between knee functionality and posterior tibial slope in anterior cruciate ligament (ACL)-deficient and ACL-reconstructed patients. Methods: Patients with isolated ACL injuries on the surgical waiting list and patients who underwent ACL reconstruction with bone-patellar tendon-bone grafts between 18 and 24 months after surgery were recruited from the orthopaedic sports injury clinic. The study included 44 ACL-deficient patients (range 16-49) with a mean age of 26.4 years and 24 ACL-reconstructed patients with a mean age of 27.2 years (range, 25 to 49 years). Posterior tibial slope was measured on a digitalized lateral radiograph by use of the posterior tibial cortex as a reference. The Cincinnati scoring system was used to assess knee functionality. Results: The posterior tibial slope averaged 6.10 degrees +/- 3.57 degrees (range, 0 degrees to 17 degrees) in the ACL-deficient group and 7.20 degrees +/- 4.49 degrees (range, 0 degrees to 17 degrees) in the ACL-reconstructed group. An anterior tibial slope was not measured in any of the participants. The mean Cincinnati score was 62.0 +/- 14.5 (range, 36 to 84) in the ACL-deficient patients and 89.3 +/- 9.5 (range, 61 to 100) in the ACL-reconstructed patients. There was a moderate but nonsignificant correlation (r = 0.47) between knee functionality and slope in the ACL-deficient patients. When we divided posterior tibial slope into intervals of 0 degrees to 4 degrees (mean score, 58.4), 5 degrees to 9 degrees (mean score, 59.6), and greater than 10 degrees (mean score, 75.4), a strong significant correlation (r = 0.91, P = .01) was observed between knee functionality and slope. There was a weak but nonsignificant correlation (r = 0.24) between knee functionality and slope in the ACL-reconstructed patients. When we divided posterior tibial slope into intervals of 0 degrees to 4 degrees (mean score, 78.2), 5 degrees to 9 degrees (mean score, 86.1), and greater than 10 degrees (mean score, 89.4), a strong and significant correlation (r = 0.96, P = .0001) was observed between knee functionality and slope. Conclusions: The results of this study suggest that ACL-deficient and ACL-reconstructed patients with higher posterior tibial slope have more functional knees. Level of Evidence: Level IV, therapeutic case series.