The effect of outlet fixation on tunnel widening

Purpose: To compare the development of tibial tunnel widening after a standard bone-patellar tendon-bone autograft (BPTB) to a flipped BPTB that allows interference screw outlet fixation with a bone plug at both femoral and tibial tunnels, and to identify any observable clinical effect. The hypothesis of this study was that the outlet fixation achieved by the flipped BPTB technique results in diminished tunnel widening at the site of the bone plug. Type of Study: Nonrandomized control trial. Methods: The postoperative radiographs of 67 BPTB anterior cruciate ligament (ACL) reconstructions were retrospectively reviewed; 31 had conventional BPTBs and 36 had the bone plugs flipped at the tibial end to achieve interference screw fixation of the bone plug at the tibial outlet as well as the femoral outlet. Biodegradable interference screws (PLLA) were used in all cases, which facilitated tunnel measurements. One week after surgery, the maximal tibial bone tunnel widths were measured on anteroposterior and lateral radiographs 1 cm below the tibial plateau. These initial postoperative measurements were compared with measurement from radiographs taken annually thereafter. Clinical information including Lysholm, Tegner, IKDC activity, Lachman, pivot-shift, and range of motion data was also obtained and compared for the 2 groups. Results: In the conventional BPTB group, at an average follow-up of 28 months, 28 of 31 (90%) showed at least a 2-mm increase (20%) in the tibial tunnel width. The mean maximum tunnel width increase was 2.2 mm. In the flipped BPTB group, at an average follow-up of 31 months, none of these 36 showed any increase in tunnel size. In fact, 15 patients had no distinct tibial tunnel remaining and, of the other 21, the average remaining tunnel width was 3 mm. The clinical results evaluating the Tegner, Lysholm, IKDC activity levels, KT, and physical examination parameters showed no significant differences between these 2 groups. The tunnel width decreased during the first year, but remained unchanged after 12 months. No tunnel dilation was observed with bone plug outlet fixation while 90% of the conventional group had at least a 20% increase (P < .001). Conclusions: Outlet fixation with the flipped BPTB technique decreased the tibial tunnel width 1 cm below the plateau while 90% of the conventional BPTB patients demonstrated an average widening of 20%.