Reliability of a semi-automated 3D-CT measuring method for tunnel diameters after anterior cruciate ligament reconstruction: A comparison between soft-tissue single-bundle allograft vs. autograft

• Tunnel widening is a common observation after soft-tissue ACL reconstruction
• A novel 3D-CT based protocol for tunnel measurements is assessed for reliability
• This 3D-CT based method for tunnel measurement shows highly reproducible results
• We compare tunnel widening after use of soft-tissue allografts vs. autografts
• Tunnel widening was significantly higher with soft-tissue allografts vs. autografts

BackgroundPost-operative widening of tibial and/or femoral bone tunnels is a common observation after ACL reconstruction, especially with soft-tissue grafts. There are no studies comparing tunnel widening in hamstring autografts versus tibialis anterior allografts. The goal of this study was to observe the difference in tunnel widening after the use of allograft vs. autograft for ACL reconstruction, by measuring it with a novel 3-D computed tomography based method.MethodsThirty-five ACL-deficient subjects were included, underwent anatomic single-bundle ACL reconstruction and were evaluated at one year after surgery with the use of 3-D CT imaging. Three independent observers semi-automatically delineated femoral and tibial tunnel outlines, after which a best-fit cylinder was derived and the tunnel diameter was determined. Finally, intra- and inter-observer reliability of this novel measurement protocol was defined.ResultsIn femoral tunnels, the intra-observer ICC was 0.973 (95% CI: 0.922–0.991) and the inter-observer ICC was 0.992 (95% CI: 0.982–0.996). In tibial tunnels, the intra-observer ICC was 0.955 (95% CI: 0.875–0.985). The combined inter-observer ICC was 0.970 (95% CI: 0.987–0.917). Tunnel widening was significantly higher in allografts compared to autografts, in the tibial tunnels (p = 0.013) as well as in the femoral tunnels (p = 0.007).ConclusionsTo our knowledge, this novel, semi-automated 3D-computed tomography image processing method has shown to yield highly reproducible results for the measurement of bone tunnel diameter and area. This series showed a significantly higher amount of tunnel widening observed in the allograft group at one-year follow-up.Level of evidenceLevel II, Prospective comparative study.