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Biomechanical Studies of Double-Bundle Posterior Cruciate Ligament Reconstructions
Keith L. Markolf, PhD1; Brian T. Feeley, MD1; Steven R. Jackson1; David R. McAllister, MD1
1 Biomechanics Research Section, Department of Orthopaedic Surgery, University of California at Los Angeles Rehabilitation Center, 1000 Veteran Avenue, Room 21-67, Los Angeles, CA 90095-1759. E-mail address for K.L. Markolf: kmarkolf@mednet.ucla.edu
View Disclosures and Other Information
Note: The authors acknowledge the contributions of Daniel Martin, MS, and Samir Tejwani, MD, during the initial phases of testing.
In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from NFL Charities. Graft tissues and knee specimens were provided by the Musculoskeletal Transplant Foundation. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Biomechanics Research Section, Department of Orthopaedic Surgery, David Geffen School of Medicine at the University of California at Los Angeles, Los Angeles, California

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2006 Aug 01;88(8):1788-1794. doi: 10.2106/JBJS.E.00427
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Abstract

Background: Double-bundle reconstruction of the posterior cruciate ligament has been advocated to better replicate the anatomy of the native ligament and restore normal knee biomechanics. The goal of this study was to measure knee laxities and graft forces following single and double-bundle reconstructions and to compare these values with those for the intact knee in a cadaver model.

Methods: Forces in the posterior cruciate ligament were measured as the knee was passively extended from 120° to 0° with applied tibial loading. Anterior-posterior laxities were measured as well. An anterolateral tunnel was located at the anterolateral margin of the native ligament footprint, and a posteromedial tunnel was placed at one of two locations within the footprint; one location resulted in a wide bridge separating the tunnels and the other, a narrow bridge. Testing was repeated with a single anterolateral graft tensioned to match, within ±1 mm, the laxity in the intact knee at 90° of flexion. Double-bundle reconstructions were tested with the addition of a posteromedial graft tensioned at 30° of flexion. Two levels of posteromedial graft tension (10 and 30 N) were studied in both the narrow and the wide-bridge posteromedial tunnels.

Results: Mean laxities with a single anterolateral graft were 1.1 to 2.0 mm greater than normal between 0° and 30° of flexion. With the posteromedial graft tensioned to 10 N in the wide-bridge tunnel, the mean laxity of the double grafts was not significantly different from that in the intact knee at any flexion angle. With the posteromedial graft tensioned to 10 N in the narrow-bridge tunnel, the mean laxity at 0° was 0.9 mm greater than that in the intact knee. With the posteromedial graft tensioned to 30 N, the mean laxity at 10° was 1.7 mm less than the intact-knee value in the wide-bridge tunnel and 1.3 mm less than the intact-knee value in the narrow bridge-tunnel. Increasing posteromedial graft tension from 10 to 30 N decreased the mean laxities by 0.5 to 1.1 mm between 0° and 30°. Mean graft forces following a single anterolateral reconstruction were not significantly different from the native posterior cruciate ligament forces under any mode of loading except valgus moment. With the wide-bridge tunnel, the mean forces with the posteromedial graft tensioned to 10 N were somewhat higher than the native posterior cruciate ligament forces at full extension; when the graft was tensioned to 30 N, the mean forces were substantially higher.

Conclusions: A single anterolateral graft best reproduced the normal posterior cruciate ligament force profiles, but laxities were greater than normal between 0° and 30° of knee flexion. The addition of a second, posteromedial graft reduced laxity in this flexion range but did so at the expense of higher-than-normal forces in the posteromedial graft.

Clinical Relevance: The results of this study suggest that it is reasonable to question the rationale for adding a second, posteromedial graft.

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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