Evaluating the Femoral-Side Critical Corner in Posterior Cruciate Ligament Reconstruction: The Effect of Outside-In Versus Inside-Out Creation of Femoral Tunnels on Graft Contact Pressure in a Synthetic Knee Model Steven J. Narvy, M.D., George F. Hatch III, M.D., Hansel E. Ihn, B.A., Nathanael D. Heckmann, M.D., Michelle H. McGarry, M.S., James E. Tibone, M.D., and Thay Q. Lee, Ph.D. Purpose: To characterize and compare the graft contact characteristics of outside-in (OI) and inside-out (IO) femoral tunnels during single-bundle reconstruction of the anterolateral bundle of the posterior cruciate ligament in a synthetic knee model. Methods: Femoral tunnels were separately made in 16 synthetic femora (8 OI and 8 IO). Achilles tendon allografts were fixed using suspensory fixation with a pressure sensor between the allograft and femoral tunnel. Grafts were cyclically loaded; force, contact area, contact pressure, and peak pressure at the aperture were measured. This process was repeated using the same allograft to assess the other tunnel angle in a separate specimen. Results: IO specimens showed higher mean contact pressure at all loading cycles, with significance shown at 50 N (P ¼ .02). Peak pressure was also greater in IO specimens at all loading cycles and reached statistical significance at 100 N (P ¼ .04). IO specimens had a lower contact area at 150 N (P ¼ .04). No statistically significant differences in force were observed between the 2 groups. Conclusions: OI creation of the femoral tunnel for anterolateral bundle reconstruction of the posterior cruciate ligament resulted in decreased mean and peak contact pressures at the femoral aperture compared with IO tunnel creation at the specific trajectories and loading parameters tested in this synthetic femoral model. These biomechanical data suggest that OI creation of the femoral tunnel may help reduce in vivo graft contact pressure at the femoral aperture. Clinical Relevance: These data suggest that a tunnel drilled from OI may result in less graft pressure at the femoral aperture, which may prevent graft elongation and optimize graft survival. A large body of clinical and biomechanical research has been published in an attempt to optimize the clinical results of posterior cruciate ligament (PCL) reconstruction. Much research has focused on the optimal method of creating the tibial tunnel. Although the tibial inlay technique has been shown to be biomechanically superior to the transtibial technique by avoiding graft strain across the “killer turn” in the posterior tibial plateau, clinical studies comparing these 2 techniques have failed to identify a meaningful clin- ical difference. 1-3 Another possible source of graft failure is at the femoral tunnel, which may be more important to optimize clinical outcomes. Mariani et al., 4 for example, found correlation between improper femoral tunnel placement and residual laxity, suggesting that femoral tunnel placement may be more crucial in achieving an optimal clinical outcome than tibial tunnel placement. Handy et al. 5 highlighted the impact of the “critical corner” around which the PCL graft travels within the femur, which poses similar concerns regarding graft strain and elongation as can occur at the killer turn in transtibial reconstructions. They noted that traditional From the Department of Orthopaedic Surgery, Keck School of Medicine, University of Southern California (S.J.N., G.F.H., N.D.H., J.E.T.), Los Angeles; Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (H.E.I., M.H.M., T.Q.L.), Long Beach; and University of California, Irvine (H.E.I., M.H.M., T.Q.L.), Irvine, California, U.S.A. The authors report that they have no conflicts of interest in the authorship and publication of this article. Received September 11, 2016; accepted January 13, 2017. Address correspondence to George F. Hatch III, M.D., Department of Or- thopaedic Surgery, Keck School of Medicine, University of Southern Califor- nia, 1520 San Pablo St, Ste 2000, Los Angeles, CA 90089, U.S.A. E-mail: ghatch@med.usc.edu Ó 2017 by the Arthroscopy Association of North America 0749-8063/16866/$36.00 http://dx.doi.org/10.1016/j.arthro.2017.01.035 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol -, No - (Month), 2017: pp 1-5 1