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Biomechanical Consequences of a Tear of the Posterior Root of the Medial MeniscusSimilar to Total Meniscectomy
Robert Allaire, MD1; Muturi Muriuki, PhD1; Lars Gilbertson, MD2; Christopher D. Harner, MD3
1 Department of Orthopaedic Surgery, University of Pittsburgh, 3471 Fifth Avenue, Suite 1011, Pittsburgh, PA 15213. E-mail address for R. Allaire: allairerb@upmc.edu
2 Spine Institute Research Laboratory, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195
3 Center for Sports Medicine, University of Pittsburgh Medical Center, 3200 South Water Street, Pittsburgh, PA 15203
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the University of Pittsburgh, Pittsburgh, Pennsylvania

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Sep 01;90(9):1922-1931. doi: 10.2106/JBJS.G.00748
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Background: Tears of the posterior root of the medial meniscus are becoming increasingly recognized. They can cause rapidly progressive arthritis, yet their biomechanical effects are not understood. The goal of this study was to determine the effects of posterior root tears of the medial meniscus and their repairs on tibiofemoral joint contact pressure and kinematics.

Methods: Nine fresh-frozen cadaver knees were used. An axial load of 1000 N was applied with a custom testing jig at each of four knee-flexion angles: 0°, 30°, 60°, and 90°. The knees were otherwise unconstrained. Four conditions were tested: (1) intact, (2) a posterior root tear of the medial meniscus, (3) a repaired posterior root tear, and (4) a total medial meniscectomy. Fuji pressure-sensitive film was used to record the contact pressure and area for each testing condition. Kinematic data were obtained by using a robotic arm to record the position of the knees for each loading condition. Three-dimensional knee kinematics were analyzed with custom programs with use of previously described transformations. The measured variables were axial rotation, varus angulation, lateral translation, and anterior translation.

Results: In the medial compartment, a posterior root tear of the medial meniscus caused a 25% increase in peak contact pressure compared with that found in the intact condition (p < 0.001). Repair restored the peak contact pressure to normal. No difference was detected between the peak contact pressure after the total medial meniscectomy and that associated with the root tear. The peak contact pressure in the lateral compartment after the total medial meniscectomy was up to 13% greater than that for all other conditions (p = 0.026). Significant increases in external rotation and lateral tibial translation, compared with the values in the intact knee, were observed in association with the posterior root tear (2.98° and 0.84 mm, respectively) and the meniscectomy (4.45° and 0.80 mm, respectively), and these increases were corrected by the repair.

Conclusions: This study demonstrated significant changes in contact pressure and knee joint kinematics due to a posterior root tear of the medial meniscus. Root repair was successful in restoring joint biomechanics to within normal conditions.

Clinical Relevance: This study provides a biomechanical rationale for surgical repair of posterior root tears of the medial meniscus. Clinical studies are required to define the appropriate patient population for, and to determine the clinical efficacy of, surgical treatment of this injury.

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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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