Comparison of transportal inside-out and outside-in femoral drilling techniques in anatomic ACL reconstruction

The purpose of this study was to examine tunnel length and incidence of posterior wall breakage during drilling of the femoral anteromedial (AM) tunnel in anatomic anterior cruciate ligament (ACL) reconstruction and compare those results between inside-out (transportal) and outside-in techniques. The study population comprised 68 patients (30 females and 38 males) with a mean age at surgery of 24.1 years (range, 14–45 years). In the reconstructive procedure, the femoral AM bone tunnel was drilled inside-out through the anteromedial portal in 32 knees, while the outside-in technique was employed in the remaining 36 knees. The intra-articular aperture of the femoral AM tunnel was located behind the resident's ridge in all knees as assessed by the postoperative computed tomography (CT) image. Length of the bony tunnel was measured with the depth gauge intraoperatively, while incidence of the posterior bony wall breakage (blowout) was assessed on the postoperative CT image. Thereafter, the obtained results were compared between the groups (transportal inside-out drilling vs. outside-in drilling). Knee stability was assessed at 12 months using a KT arthrometer. The mean length of the femoral AM tunnel in the inside-out group (32.2 ± 4.7 mm) was significantly shorter than that in the outside-in group (36.3 ± 4.6 mm). In the inside-out groups, posterior wall breakage was encountered in one patient (3.6%), and a lack of the tunnel length precluded the use of the EndoButton CL in three patients (10.7%). By contrast, no such complication was encountered in the outside-in group. No significant difference in knee stability was detected between the groups. During the femoral AM tunnel drilling in the current anatomic ACL reconstruction, the potential risks for the problems such as short tunnel length and posterior wall breakage were higher in the transportal inside-out drilling than the outside-in procedure. Adoption of the outside-in technique can reduce the risk of complications associated with femoral drilling.Level of evidenceLevel IV, case series.