Effect of Transosseous Tunnels on Patella Fracture Risk After Medial Patellofemoral Ligament Reconstruction: A Cadaveric Study

Purpose To determine whether (1) tunnels that breach the anterior cortex of the patella result in increased fracture risk and (2) transosseous tunnels drilled across the patella significantly reduce the tensile force needed to fracture the patella. Methods Twenty-six fresh-frozen cadaveric human patellas were randomized to 1 of 3 groups: a control group with unmodified patellas, a group with 2 transverse tunnels (TT) that did not breach the anterior cortex, and a group with 2 TT that breached the anterior cortex of the patella (PA). Patellas were connected in series to a load cell via freeze clamp attachments to the quadriceps and patellar tendons. Pull was fixed at 45° with the patella set in the trochlear groove of a synthetic femur. Patellas were loaded cyclically, then to failure. Results Twenty-six patellas were tested (mean age = 71.4 years; range = 37-95, standard deviation [STD] = 11.5 years). PA patellas were more likely to fracture through the tunnel than TT patellas (100% vs 25%, P =.033). Control, TT, and PA groups failed at 1,915 N (STD = 508 N), 1,901 N (STD = 884 N), and 1,640 N (STD = 625 N), respectively. There was no statistically significant difference in overall load to failure between control and TT (P =.969), control and PA (P =.321), and TT and PA (P =.488) groups. Conclusions Transosseous patellar tunnels for medial patellofemoral ligament reconstruction that breached the anterior cortex were more likely to fracture during longitudinal load than those that did not breach the anterior cortex. However, we found no statistically significant difference in the tensile load to failure between native patellas and patellas with either type of transosseous tunnel. Clinical Relevance The results of this study show that breaching the anterior cortex during transosseous drilling increases the risk of a patellar fracture occurring through the transosseous tunnel.