BIOMECHANICS OF ANTERIOR CRUCIATE REPAIR

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DESCRIPTION (Adapted from the Applicant's Abstract): The long-term goal of this work is to improve the surgical treatment of the anterior cruciate ligament deficient knee, and to provide basic information in healing and remodeling of joint tissues, and the effect of force on the healing and remodeling processes. In work during the current grant period, the applicants developed methods to set graft forces intraoperatively at specific values, and then measure the in vivo forces on the graft in the functioning goat, as well as the mechanical properties of the graft as a function of time from surgery. Data to date have shown that the force in a patellar tendon graft, in parallel with a synthetic ligament augmentation device (LAD), increased from surgery to 6 weeks, whether the tendon force was initially set high or low. The differential load sharing evened out by 6 weeks so that the tendon carried close to half of the total graft force, whether it was initially set high or low at surgery. Over the range of initial set forces tested, higher set forces in the tendon tended to result in higher functional forces at 6 weeks. However, this difference in functional force was not sufficient to affect the material properties of the tendon, since the failure strength at 3 months was the same whether the tendon was initially set high or low. These conclusions apply to the case of a biologic graft in parallel with an LAD fixed rigidly at both ends, providing an effective constraint to the tendon. It is unclear how the tendon would respond it if were the only load carrying element of the graft. This is an important question, both because this type of construction is the one most often used clinically, and because the answer will provide basic information in the interaction of force and tissue response in a joint with graft reconstruction. To answer this and related questions, the Specific Aims of the proposed research are to set patellar tendon grafts at three force levels in the goat, to measure the resulting functional graft forces at 2 and 6 weeks after surgery, and in another test group, to measure the graft stiffness and strength at 3 months after surgery. During current work, the investigators have noticed cartilage degeneration in the reconstructed knees; they will assess the correlation between graft set force and cartilage degeneration in the test animals as well. After completing the above tests, they will test the graft properties in another set of animals in which the joint is reconstructed with the "standard" pretension method currently used clinically, and compare graft properties with the best results of the set force groups. This will establish whether there is any advantage to setting the graft force to some chosen value at surgery, rather than use the current method in which the graft mechanics are not well-controlled. Additional animals will be tested to add data to the current experiments to more firmly establish in vivo force levels at 6 weeks in a composite graft, and to verify 2 week calibration data.