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Femoral Fixation Sites for Optimum Isometry of Posterolateral Reconstruction^*

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{at}mednet.ucla.edu

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

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (R01 AR 048536). 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.

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^* Read in part at the Annual Meeting of the Orthopaedic Research Society, Chicago, Illinois, March 2006.

Methods: Relative length changes (isometry measurements) were recorded between sutures fixed at femoral grid points and appropriate fibular or tibial graft tunnel sites; sites resulting in the least change in suture length as the knee was moved from 0° to 90° of flexion were identified as optimum isometric points. Bone blocks of Achilles tendon grafts were fixed with the midpoint of the tissue's leading edge adjacent to the optimum isometric point (optimum placement). Isometry measurements were repeated with a lateral collateral ligament graft placed in a fibular tunnel and with popliteus tendon and popliteofibular ligament grafts alternately placed in appropriate tibial and fibular tunnels. The graft isometry measurements were then repeated with the bone block centered over the femoral footprint of the lateral collateral ligament or popliteus tendon.

Results: For all reconstructions, there was no difference between the relative length changes of the suture placed at the optimum isometric point and the relative length changes of the graft with an optimally placed bone block. The mean location of the optimally placed bone-block center of the lateral collateral ligament graft was within 1.85 mm of the mean center of the footprint of the lateral collateral ligament; the mean graft isometry measurements with the optimally placed bone block were not significantly different from those with the bone block centered over the lateral collateral ligament footprint. The mean optimally placed bone-block center of the popliteus tendon and popliteofibular ligament reconstructions was 11 mm anterior and 2.7 mm proximal to the center of the popliteus tendon footprint. The mean relative length changes of the popliteus tendon and popliteofibular ligament grafts with the bone block optimally placed were <0.9 mm and <1.2 mm, respectively; the means with the popliteus tendon and popliteofibular ligament bone blocks centered over the popliteus tendon footprint were 3.7 mm and 5.0 mm, respectively.

Conclusions: A popliteus tendon or popliteofibular ligament reconstruction with the bone block centered over the femoral footprint of the popliteus tendon was highly non-isometric. If the graft were fixed at 30° of flexion, it would elongate approximately 4 mm when the knee was extended to 0° and possibly stretch out.

Clinical Relevance: We found suture isometry to be a good indication of graft isometry. In situ measurements of relative suture-length changes at the time of surgery may be helpful in determining a femoral fixation site that will result in graft isometry.

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