Summary

Patients with one or multiple ACL graft insufficiencies showed an overall high prevalence (35% (95% CI [29%; 42%])) of a PTS greater than or equal to 12° and the group of patients with a PTS greater than or equal to 12° showed a significant shorter survival of their first ACL graft.

Abstract

Purpose

A posterior tibial slope (PTS) greater than or equal to 12° is a well described important risk factor for recurrent anterior cruciate ligament (ACL) graft insufficiency. The primary aim was to determine the prevalence of an “increased PTS” (PTS greater than or equal to 12°) in an ACL graft insufficient population. The secondary aims were to investigate if the prevalence of increased PTS and the absolute PTS increases with the increasing number of ACL graft insufficiencies, as well as to investigate the survival time of the first ACL graft. The main hypothesis was that there is a high prevalence of increased PTS in ACL graft insufficient patients. Further hypothesises were that the prevalence as well as the absolute PTS increases with the increasing number of ACL graft insufficiencies and that the survival of the ACL graft was shorter in patients with increased PTS.

Methods

Between January 2021 and March 2022, all patients with an ACL graft insufficiency were included. Exclusion criteria were previous multi-ligament surgery or new multi-ligament injury requiring multi-ligament surgery; previous ipsilateral septic knee arthritis; previous ipsilateral osteotomy; incomplete medical records; previous used ACL graft other than quadriceps, hamstring or patellar tendon autograft, or allograft tendon; previous ACL repair and no true lateral knee radiograph. The PTS was measured as the angle between tangent to the medial tibial plateau and a line perpendicular to the proximal anatomical tibial axis. Patients were divided into groups depending on number of ACL graft insufficiencies: group A, 1 graft insufficiency; group B, 2 graft insufficiencies; group C 3 or more graft insufficiencies. Chi-square, fisher’s exact or independent student T tests were used to compare the prevalence of increased PTS and absolute PTS between groups. The Kaplan-Meier curve and Log-rank test was used to compare the survival of the first ACL graft between patients with or without increased PTS. Significance was set at p<0.05.

Results

In total 206 patients (147 men / 59 women) were included. 73 patients showed an increased PTS with an overall prevalence of 35% (95% confidence interval (CI) [29%; 42%]). 155 patients were included in group A, 42 patients were included in group B and 9 patients were included in group C. The prevalence of increased PTS for group A, B and C was, 32% (95% CI [25%; 40%]), 38% (95% CI [23%; 53%]) and 78% (95% CI [51%; 100%]), respectively. The prevalence of increased PTS and mean PTS did not increase significantly between group A and B (p>0,05). However, both increased significantly between group A and C, and group B and C (p<0,05). The survival time of the first ACL graft in patients with an increased PTS was significantly shorter (p<0,001).

Conclusion

There is a 35% overall prevalence of increased PTS in the studied ACL graft insufficient patient population. The survival of the first ACL graft is shorter in patients with an increased PTS. Surgeons should be aware of the high prevalence of increased PTS when consulting patients for revision ACL reconstruction as it is an important risk factor for recurrent instability that may need to be addressed.