Background: We aimed to compare tibial soft tissue and bony slopes in patients with failed and non-failed ACL reconstructions (ACLR). We hypothesized that patients with failed ACLR have increased slopes compared to non-failed ACLR, and unexplained failures have higher slopes than failures with clear technical errors and failed synthetic ligaments.
Methods: Between 2015 and 2022, 130 patients with failed ACLR were retrospectively identified; 79 knees with adequate MRI scans were analyzed. These were compared to 57 non-failed ACLRs. MRI measurements included lateral and medial tibial bony slope (LBS, MBS) and lateral and medial meniscal slope (LMS, MMS). Subgroup analysis assessed for failures with technical errors and failed synthetic ligaments.
Results: In all patients, the LMS and MMS reduced the bony slope towards the horizontal without reaching statistical significance. Failed ACLR had significantly higher MBS (7.1° ± 2.9 vs. 4.6° ± 2.5, p < 0.001) and MMS (5.6° ± 3.5 vs. 3.4° ± 2.8, p < 0.001). The area under the curve for MBS was 0.721 (CI: 0.628-0.813). The Youden optimal threshold value of MBS ≥ 5.1° (sensitivity 80 %, specificity 56.1 %) yielded an odd's ratio for failure of 5.1 (CI:2.3-11.6; p < 0.001). Revisions with technical errors had slopes that were not significantly different to non-failed ACLR. Revisions with synthetic grafts had MBS (7.3° ± 3.2 vs. 4.6° ± 2.5; p = 0.007) and MMS (6° ± 3.8 vs. 3.4° ± 2.8; p = 0.021) that were significantly higher to non-failed ACLR.
Conclusion: Medial bony and meniscal slopes are higher in patients with unexplained failed ACLRs and revisions with synthetic grafts, but ACLR with technical errors failed with slopes similar to non-failed ACLRs. Increased medial slope values are a risk factor for surgical failure.
Level of evidence: III.
Keywords: ACL; ACL reconstruction; ACL tear; Medial slope; Slope.
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