[Posterior Tibial Slope as a Morphological Risk Factor for Anterior Cruciate Ligament Reconstruction: a Retrospective Cohort Study].

PURPOSE OF THE STUDY Increased tibial slope facilitates anterior translation of tibia relative to the femur, thereby increasing the load on both the native and replaced anterior cruciate ligament. This study aims to retrospectively review the posterior tibial slope in a cohort of our patients after the ACL reconstruction and revision ACL reconstruction. Based on the results obtained by measurements, we aimed to confirm or disprove the claim that the increased posterior tibial slope is one of the risk factors of the ACL reconstruction failure. Another aim of the study was to assess whether there are any correlations between the posterior tibial slope and basic somatic parameters (height, weight, BMI) or the patient s age. MATERIAL AND METHODS The posterior tibial slope was measured retrospectively on lateral X-rays of 375 patients. There were 83 revision reconstructions and 292 primary reconstructions performed. The patient s age at the time of injury, height and weight were recorded and the BMI was calculated. The findings were then statistically analysed. RESULTS The mean posterior tibial slope in 292 primary reconstructions was 8.6 degrees, whereas the mean posterior tibial slope in 83 revision reconstructions was 12.3 degrees. The difference between the studied groups was statistically (p<0.0001) and substantively significant (d=1.35). In the breakdown into men and women, the mean tibial slope was 8.6 degrees in the group of men with primary reconstruction and 12.4 degrees in the group of men with revision reconstruction (p < 0.0001, d = 1.38). A similar result was achieved in women where in the group with primary reconstruction the mean tibial slope was 8.4 degrees, while in the group with revision reconstruction it was 12.3 degrees (p < 0.0001, d = 1.41). Furthermore, a higher age in men at the time of revision surgery (p = 0.009; d = 0.46) and a lower BMI in women at the time of revision surgery (p = 0.0342; d = 0.12) were observed. Conversely, neither height nor weight were different, both when comparing the whole groups and the groups in a breakdown by sex. DISCUSSION As regards the main aim, our results are in line with the results reported by majority of other authors, and they are substantively significant. The posterior tibial slope is a significant risk factor in anterior cruciate ligament replacements, with tibial slope above 12 degrees increasing the risk of ligament failure, namely both in men and women. On the other hand, this is obviously not the sole cause of the ACL reconstruction failure since there are also other risk parameters. It is not yet clear whether it makes sense to indicate correction osteotomy before the ACL replacement in all patients with an increased posterior tibial slope. CONCLUSIONS Our study confirmed a greater posterior tibial slope in the revision reconstruction group compared to the primary reconstruction group. Thus, we confirmed that greater posterior tibial slope may be a factor leading to the ACL reconstruction failure. Since the posterior tibial slope is easily measured on the baseline X-rays, we recommend to perform this measurement routinely before each ACL reconstruction. In the case of a high posterior tibial slope, slope correction should be considered to prevent potential ACL reconstruction failure. Key words: anterior cruciate ligament reconstruction, ACL graft failure, morphological risk factors, posterior tibial slope.