Summary
This study categorizes CT tibial tunnels by: (1) the five most common morphologies, and (2) the distance between prior tibial tunnels to the ACL anatomic footprint. These relative ACLR risk factors provide valuable influence regarding potential for failure and ultimately can guide staging assessments in revision ACLRs.
Abstract
Background
Tibial bone tunnel enlargement and widening following anterior cruciate ligament reconstruction (ACLR) failure is common. Bone stock deficiency may complicate revision procedures, and a classification system for post-ACLR failure tibial tunnel morphologies with guidance for one or two-stage treatment is necessary.
Purpose
To propose a novel Computed Tomography (CT) classification system for tibial tunnel morphology in the setting of ACLR revision correlated to surgically relevant risk factors of tibial tunnel dilation and tibial tunnel footprint entry locations and sizes.
Study Design: Retrospective Cross-Sectional Study; Level of evidence, 3
Methods
An IRB-approved retrospective cross-sectional study was performed on patients presenting for ACLR graft failure between July 2019 and April 2023; two independent reviewers collected CT tibial tunnel measurements and morphology. Previous literature defined ACL footprint and anatomic ACLR tunnel center was selected as 48% max tibial plateau width from medial-lateral (ML) and 38% from anterior-posterior (AP). Inclusion criteria comprised patients who underwent revision ACLR by a single surgeon with preoperative knee CT imaging. The inter-rater agreement was calculated by intraclass correlation coefficient (ICC) using a two-way random-effects model; confidence intervals (CI) determined by alpha=0.05.
Results
Seventy-five patients underwent CT imaging for a revision ACLR and were evaluated. The overall interobserver ICC for the combined trial was 0.988 (CI: 0.986<ICC<0.989), which when separated by imaging plane were 0.993 (CI: 0.992-0.994), 0.954 (CI: 0.942-0.963), and 0.986 (CI: 0.984-0.988) for coronal, sagittal, and axial, respectively,
Five tibial tunnel 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 slices, the average tibial plateau AP width measured 54.48±4.40mm (ICC=0.85; CI=53.78-55.18). The average absolute distance between the tibial tunnel exit to the center of the ACL footprint measured 4.42± 2.66mm (ICC=0.84; CI=3.99-4.84mm), with tunnel ML and AP diameters averaging 11.49±3.20mm (ICC=0.89; CI=10.98-12.01mm) and 9.74±2.36mm (ICC=0.64; CI=9.36-10.12mm), respectively. Considering the minimum 2mm bone bridge and increased effective tibial ACLR footprint size from additional (re)revision tibial tunnel by 10mm standard reamer, 56 (74.67%) were classified as Type I (<2.5mm), 18 (24.00%) as Type II (>2.5mm and <12.5mm), and 1 (1.33%) as Type III (>12.5mm).
On coronal slices, the average tibial plateau ML width measured 75.04±6.23mm (ICC=0.93; CI=74.05-76.04) and 76.33±5.56mm (ICC=0.98; CI=75.44-77.22), respectively. On coronal views, the average tunnel diameters measured 8.25±2.93mm (ICC=0.88; CI=7.78-8.72), 9.88±2.96mm (ICC=0.81; CI=9.41-10.35), and 8.08±3.18mm (ICC=0.70; CI=7.57-8.59) at proximal, midpoint, and distal, respectively. The sagittal view average tunnel diameters measured 9.78±2.94mm (ICC=0.88; CI=9.31-10.25), 10.34±3.23mm (ICC=0.80; CI=9.82-10.85), and 8.65±3.92mm (ICC=0.73; CI=8.02-9.28) at proximal, midpoint, and distal, respectively.
Conclusion
In the setting of post-failure ACLRs, evaluation of the former tibial tunnels is required in order to assess for potential (re)revision staging. This study categorizes CT tibial tunnels by: (1) the five most common morphologies, and (2) the distance between prior tibial tunnels to the ACL anatomic footprint. These relative ACLR risk factors provide valuable influence regarding vulnerability for failure and ultimately can guide staging assessments in revision ACLRs.