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Early Tension Loss in an Anterior Cruciate Ligament GraftA Cadaver Study of Four Tibial Fixation Devices
Dustin M. Grover, MS1; Stephen M. Howell, MD1; Maury L. Hull, PhD1
1 Department of Mechanical Engineering (S.M.H. and M.L.H.) and Biomedical Engineering Graduate Group (D.M.G. and M.L.H.), University of California, Davis, One Shields Avenue, Davis, CA 95616. E-mail address for M.L. Hull: mlhull@ucdavis.edu
View Disclosures and Other Information
In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from The Whitaker Foundation. In addition, one or more of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity (Arthrotek, Inc.). 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 Department of Mechanical Engineering, University of California, Davis, California

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2005 Feb 01;87(2):381-390. doi: 10.2106/JBJS.C.01527
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Abstract

Background: The tensile force applied to an anterior cruciate ligament graft determines the maximal anterior translation; however, it is unknown whether the tensile force is transferred to the intra-articular portion of the graft and whether the intra-articular tension and maximal anterior translation are maintained shortly after ligament reconstruction.

Methods: Ten cadaveric knees were reconstructed with a double-looped tendon graft. The graft was looped through a femoral fixation transducer that measured the resultant force on the proximal end of the graft. A pneumatic cylinder applied a tensile force of 110 N to the graft exiting the tibial tunnel with the knee in full extension. The graft was fixed sequentially with four tibial fixation devices (a spiked metal washer, double staples, a bioabsorbable interference screw, and a WasherLoc). Three cyclic loading treatments designed to conservatively load the graft and its fixation were applied.

Results: The combined loss in intra-articular graft tension from friction, insertion of the tibial fixation device, and three cyclic loading treatments was 50% for the spiked washer (p = 0.0004), 100% for the double staples (p < 0.0001), 64% for the interference screw (p = 0.0001), and 56% for the WasherLoc (p < 0.0001). The tension loss caused an increase in the maximal anterior translation from that of the intact knee of 2.0 mm for the spiked washer (p = 0.005), 7.8 mm for the double staples (p < 0.0001), 2.7 mm for the interference screw (p = 0.001), and 2.1 mm for the WasherLoc (p < 0.0001).

Conclusions: The tensile force applied to a soft-tissue anterior cruciate ligament graft is not transferred intra-articularly and is not maintained during graft fixation. The loss in tension is caused by friction in the tibial tunnel and wrapping the graft around the shank of the screw of the spiked washer, insertion of the tibial fixation device, and cyclical loading of the knee. The amount of tension loss is sufficient to increase the maximal anterior translation.

Clinical Relevance: Surgeons should pay close attention to the technique for inserting the tibial fixation device as this study supports the assumption that this step induces the greatest change and variability in the intra-articular tension and maximal anterior translation in the knee reconstructed with a double-looped tendon graft. Cyclically loading the knee causes a further loss in intra-articular tension and an increase in the maximal anterior translation, which can be reduced by the use of fixation devices that resist lengthening at the site of fixation and by limiting cyclic loading of the knee.

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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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