Correlation between femoral tunnel length and tunnel position in ACL reconstruction

Background: The position of the femoral tunnel affects the osseous geometry available for drilling during anterior cruciate ligament (ACL) reconstruction. The length of the tunnel changes with changes in the tunnel position and may have implications for femoral fixation. Methods: Forty-seven patients with a single-bundle ACL reconstruction underwent computed tomography (CT) evaluation to generate three-dimensional (3D) CT bone models. With use of a previously described anatomic coordinate system, the center of the femoral tunnel was quantified in the posterior-anterior and proximal-distal dimensions on 3D CT. Tunnel length was defined as the distance between the centers of the intra-articular and extra-articular tunnel apertures. The reconstructed knees were dichotomized by anatomy and technique into anatomic (n = 20) and nonanatomic (n = 27) groups as well as according to whether they had undergone medial portal drilling (n = 20) or transtibial drilling (n = 27) for analysis. In addition, a review of the literature on the relationship between tunnel length and tendon-to-bone healing was performed. Results: Femoral tunnels drilled with nonanatomic footprints were longer (mean [and standard deviation], 43.6 ± 8.5 mm; range, 28.2 to 60.7 mm) than tunnels drilled with anatomic footprints (31.0 ± 6.3 mm; 21.2 to 42.5 mm) (p < 0.001). Tunnels drilled transtibially (44.4 ± 7.6 mm; 32.5 to 60.7 mm) were significantly longer than tunnels drilled through the medial portal (29.8 ± 5.0 mm; 21.2 to 40.3 mm) (p < 0.001). There was a strong correlation between tunnel length and posterior-anterior femoral tunnel position (r = 0.78, p < 0.05), with more anterior tunnel positioning associated with greater tunnel length. There was no correlation between posterior-distal femoral tunnel position and tunnel length (r = 20.05; p = 0.74). There was no consensus in the literature regarding adequate tunnel length for biologic fixation. Conclusions: Femoral tunnels drilled with anatomic footprints had sufficient length for adequate femoral fixation. Femoral tunnels positioned anterior to the native insertion of the ACL were longer than those in anatomic position. Clinical Relevance: The results of this study can help the surgeon to consider the relationship between tunnel position and subsequent tunnel length in ACL reconstruction.