KSSTA - 2026-09-07 - Journal Article
A novel classification system for measuring and interpreting tibial tunnel morphology for revision ACLR.
Kennedy MI, Tollefson LV, Kennedy NI, LaPrade CM, LaPrade RF
Topics
Key Takeaway
A novel CT-based tibial tunnel classification system for failed ACLRs demonstrated reproducible categorization into 5 sagittal morphologies and 3 axial offset types, with 74.7% of tunnels within 2.5 mm of the native footprint (ICC=0.84).
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Summary
This study developed and validated a CT-based classification system for tibial tunnel morphology in failed ACLRs to guide one- versus two-stage revision planning. Seventy-five revision ACLR patients underwent preoperative CT with tunnels classified by sagittal morphology (5 types: tubular, shovel, balloon, dual, mushroom) and axial footprint offset (3 types: <2.5 mm, 2.5–12.5 mm, >12.5 mm). The majority of tunnels (74.7%) were Type I (near-anatomic), with an average footprint offset of 4.4 ± 2.7 mm and strong interrater reliability (ICC=0.84).
Key Limitation
No outcome data are reported, so the classification system's ability to predict surgical staging decisions, graft incorporation, or revision success remains unvalidated.
Original 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.