A novel classification system for measuring and interpreting tibial tunnel morphology for revision ACLR.

Abstract

Purpose: The purpose of this study was to reproducibly measure computed tomography (CT) tibial tunnel features in failed anterior cruciate ligament reconstructions (ACLRs) and to propose a CT classification system for tibial tunnel morphology in the setting of evaluation for a one- versus two-stage revision ACLR surgery.

Methods: A retrospective study was performed on 75 patients presenting for ACLR graft failure between July 2019 and April 2023. Inclusion criteria comprised patients who underwent a revision ACLR by a single surgeon with preoperative knee CT imaging. The centre of the anatomic tibial ACL footprint and the centre and size of the previously drilled ACLR tibial tunnel were used for axial classification. The size of the tibial tunnel on sagittal images was used to develop the sagittal classification system.

Results: Five tibial tunnel sagittal CT morphologies were categorized according to uniform dilation, 'tubular' (Type A; n = 39); distal dilation, 'shovel' (Type B; n = 4); midpoint dilation, 'balloon' (Type C; n = 16); dual tunnel (Type D; n = 3) and proximal dilation, 'mushroom' (Type E; n = 13). On axial CT slices, tunnels were classified as Type I (< 2.5 mm between anatomic footprint and ACLR tunnel), Type II (2.5-12.5 mm) and Type III (>12.5 mm). The average distance between the tibial tunnel and the centre of the ACL footprint measured 4.4 ± 2.7 mm (interrater correlation coefficient [ICC] = 0.84; confidence interval [CI] = 4.0-4.8 mm). Overall, 56 (74.7%) were classified as Type I, 18 (24.0%) as Type II and 1 (1.3%) as Type III.

Conclusions: This study found that there was a reproducible categorization of CT tibial tunnels by five sagittal CT morphologies and three axial CT scan categories. The study also found that relative offset of ACLR tibial tunnels to their native footprint can be reproducibly identified using CT, which may assist in the future diagnosis and identification of ACLR knees that are at greater risk of revision.

Level of evidence: Level IV, retrospective cross-sectional study.