Contact stress and kinematic analysis of all-epiphyseal and over-the-top pediatric reconstruction techniques for the anterior cruciate ligament

Background: Adult anterior cruciate ligament (ACL) reconstruction techniques may be inappropriate to treat skeletally immature patients because of the risk of physeal complications. "Physeal-sparing" reconstruction techniques exist, but their ability to restore knee stability and contact mechanics is not well understood.

Purpose: (1) To assess the ability of the all-epiphyseal (AE) and over-the-top (OT) reconstruction techniques to restore knee kinematics, (2) to assess whether these reconstruction techniques decrease the high posterior contact stresses seen with ACL deficiency, and (3) to determine whether the AE or OT technique produces abnormal tibiofemoral contact stresses.

Study design: Controlled laboratory study.

Methods: Ten fresh-frozen human cadaveric knees were tested using a robotic manipulator. Tibiofemoral motions were recorded with the ACL intact, after sectioning the ACL, and after both reconstructions in each of the 10 specimens. The AE technique consisted of tunnels exclusively within the epiphysis and was fixed with suspensory cortical fixation devices. The OT procedure consisted of a central and vertical tibial tunnel with an over-the-top femoral position and was fixed with staples and posts on both ends. Anterior stability was assessed with 134-N anterior force at 0°, 15°, 30°, 60°, and 90° of knee flexion. Rotational stability was assessed with combined 8 N·m and 4 N·m of abduction and internal rotation, respectively, at 5°, 15°, and 30° of knee flexion.

Results: Both reconstruction techniques off-loaded the posterior aspect of the tibial plateau compared with the ACL-deficient knee in response to both anterior loads and combined moments as demonstrated by reduced contact stresses in this region at all flexion angles. Compared with the ACL-intact condition, both the AE and OT procedures had increased posteromedial contact stresses in response to anterior load at some flexion angles, and the OT technique had increased peripheral posterolateral contact stresses at 15° in response to combined moments. Neither reconstruction technique completely restored the midjoint contact stresses. Both techniques restored anterior stability at flexion angles ≤30°; however, neither restored anterior stability at 60° and 90° of flexion. Both reconstruction techniques restored coupled anterior translation under combined moments. Additionally, the AE procedure overconstrained internal rotation in response to combined moments by 12% at 15° of flexion.

Conclusion: Both reconstruction techniques provide anterior and rotational stability and decrease posterior joint contact stresses compared with the ACL-deficient knee. However, neither restored the contact mechanics and kinematics of the ACL-intact knee.

Clinical relevance: Because the AE reconstruction technique has clinical advantages over the OT procedure, the results support this technique as a potential candidate for use in the skeletally immature athlete.