gms | German Medical Science

Objectives: The posterior tibial slope is defined as the angle between a line tangent to the lateral tibial plateau and a line orthogonal to the longitudinal axis of the tibia and as such it is seen as a modifiable risk factor in the sense that it can be corrected using slope correcting proximal tibial osteotomies. Seeing that the cut-off value for the indication of slope correcting proximal tibial osteotomies is still unclear, we introduced a novel approach to determine the cut-off value in primary and secondary ACL ruptures, thus our null hypothesis was that there is another cut-off value, than those traditionally used, in the group of secondary ACL ruptures compared to healthy subjects and it that it represents a risk factor for ACL re-ruptures.

Methods: This study was conducted as a case-control study, with an initial pool of 5,000 patients who underwent primary and secondary ACL reconstructions in our clinic in the period between 2004 and 2020. We performed a power analysis for the sample needed to confirm our null hypothesis and came to the conclusion that groups of 290 patients are needed to perform this study. After applying our extensive inclusion and exclusion criteria three groups of 350 patients were formed, those were patients with primary, and secondary ACL ruptures with a control group of healthy subjects. Data was then obtained from conventional radiographs through three observers using the double-circle method with determined intra- and interrater reliability. The collected data was subsequently analysed using ROC curves and contingency table analysis.

Results and conclusion: From our 1,050 analysed patients 443 were female and 607 male. The measured PTS had an average of 6.6 (SD 1.9 with the maximum measured 12 and minimum 3.6) in the control group and 7.8 average (SD 1.8 with maximum 13 an minimum 4.2) in the primary ACL ruptures group with an average of 10.0 (SD 2.2 with maximum 15 and minimum 5) in the group of secondary ACL ruptures. The intra- and interrater reliability was very good in all groups, no significant difference between male and female PTS values was found excepts in the group of secondary ACL ruptures. Using ROC analysis a cut- off value of 7.8 (Sensitivity 50%, Specificity 75%) was determined in the group of primary ACL ruptures, and 10.1 (Sensitivity 43%, Specificity 98%) in the group of secondary ACL ruptures, subsequently a contingency table analysis and determination of the OR found that there is an increased risk of 11.29 times having a PTS of more than 10.1 in the secondary ACL group than compared to healthy controls, as such there is an increased risk of developing a secondary ACL rupture when compared to health individuals of 11.29 times when the PTS is more than 10.1. A PTS more than 7.8 is not a risk factor for developing primary ACL ruptures when compared to healthy subjects.

This study provides a novel cut-off value of the PTS (10.1 when compared to a previous cut-off value of 12) based on ROC Analysis and contingency table analysis.