Contact pressure in anterior cruciate ligament bone tunnels: Comparison of endoscopic and two-incision technique

Purpose: To investigate differences in contact pressure in the bone tunnel between the inside-out and outside-in techniques used for anterior cruciate ligament reconstruction. Type of Study: In vitro cadaveric analysis. Methods: Four fresh-frozen cadaver knees were tested. A femoral tunnel was generated through the tibial tunnel (inside-out technique). Another femoral tunnel was created using a rear-entry guide at the same intra-articular exit (outside-in technique). Aluminum cylinders containing 4-way (anterior, posterior, medial, and lateral) conductive rubber pressure sensors at the entrance of the joint were inserted into the tibial and femoral tunnels. Dynamic changes in the contact pressure of grafts in the femoral and tibial tunnels during 0° to 130° of knee flexion were measured. Results: Contact pressure of the graft migrated from the anterior to the posterior portion of the femoral tunnel upon alignment of the femoral and tibial tunnels. At 0°, 30°, and 60° of knee flexion, significantly greater contact pressure was observed at the anterior portion of the femoral tunnel made by the inside-out technique compared with that in the tunnel made by the outside-in technique. At 0°, 30°, and 60° of knee flexion, significantly greater contact pressure was observed at the lateral portion of the femoral tunnel made by the outside-in technique. Constant contact pressure was observed in the medial portion of the tunnel made by the inside-out technique. Pressure changes in the tibial tunnel were slight; moreover, changes were not influenced by the femoral tunnel direction under any conditions. Conclusions: This study shows that contact pressure in the femoral tunnel is influenced by the direction of the femoral tunnel. Clinical Relevance: The femoral tunnel direction in anterior cruciate ligament reconstruction is an important factor for femoral tunnel enlargement. A horizontal direction of the femoral tunnel might be needed for mature bone graft incorporation.