Tibial tunnel aperture irregularity after drilling with 5 reamer designs: A qualitative micro-computed tomography analysis

Background: There is limited information in the literature on comparisons of antegrade versus retrograde reaming techniques and the effect on the creation of anterior cruciate ligament (ACL) tibial tunnel entry and exit apertures. Hypothesis: Proximal and distal apertures of ACL tibial tunnels, as created with different reamers, will be affected by type of reamer design. Study Design: Controlled laboratory study. Methods: Forty skeletally mature porcine tibias with bone mineral density values comparable with a young athletic population were included in this study. Five 9-mm reamer models were used (3 antegrade: A1, smooth-bore reamer; A2, acorn-head reamer; A3, flat-head reamer; 2 retrograde: R1, retrograde acorn reamer; R2, single-blade retrograde reamer), and a new reamer was used for each tibia (8 reamer-tibia pairs per reamer model). All specimens underwent micro-computed tomography scanning, and images were reconstructed and analyzed using 3-dimensional image analysis software. Aperture rim fractures were graded on a 0-IV scale that described the proportion of the fractured aperture circumference. Specimens with incomplete apertures were also recorded. Because of the unique characteristics of various tunnels, intratunnel characteristics were observed and recorded. Results: In sum, 1 proximal and 7 distal aperture rim fractures were found; 3, 0, and 4 distal aperture rim fractures were found with groups A1, A2, and A3, respectively. Incomplete apertures were more commonly found at the distal aperture (n = 15) than the proximal aperture (n = 8); there were no tibias with this finding at both apertures. All incomplete distal apertures occurred with the retrograde technique, and all incomplete proximal apertures occurred with the antegrade technique, most commonly with reamer design A3. An added finding of tunnel curvature at the distal aspect of the tunnel was observed in all 8 tibias with R1 reamers and 5 tibias with R2 reamers. This phenomenon was not observed in any of the tibias reamed with the antegrade technique. Conclusion: Anterior cruciate ligament tibial tunnel aperture characteristics were highly dependent on reamer design. Optimal proximal aperture characteristics were produced by the retrograde reamers, whereas optimal distal aperture characteristics were obtained with the antegrade reamers. In addition, a phenomenon of tunnel curvature in retrograde-type reamers was found, which may have effects on ACL graft or screw fixation. Clinical Relevance: Differences in tunnel aperture shapes and fractures depend on reamer design. This information is important for the creation of ACL reconstruction tunnels with different reamer designs.