Fixation and incorporation of a tendon implanted within the bone pose theoretical as well as practical concerns for the surgeon who treats instability problems of the knee. Understanding the physiology involved in graft-bone incorporation is necessary for the appropriate rehabilitation of patients who undergo anterior cruciate ligament surgery. The purpose of the study was to examine the histologic and biomechanical changes of a semitendinosus autograft reconstruction of the anterior cruciate ligament in a rabbit model at the graft-bone tunnel interface in the femur. The results indicate that by 3 weeks, failure of the bone-graft-bone or construction is through the intraarticular portion of the graft, not as a result of pullout from the bone tunnel. Graft fixation of the bone tunnel occurs by an intertwining of graft and connective tissue and anchoring of connective tissue to bone by collagenous fibers and bone formation in the tunnels. The collagenous fibers have the appearance of the Sharpey's fibers seen in an indirect tendon insertion.

Measurements of the stress-induced changes in ultrasonic wave speeds in steels typically used in railroad rails are presented. All of the five possible relative changes in wave speeds for a uniaxial state of stress have been determined and agree, to within the limits of accuracy of the measurement, with the second-order theory of Hughes and Kelly. The third-order elastic constants are calculated from the acoustoelastic data. Subject Classification: [43]85.20, [43]85.22, [43]35.26.

The purpose of this study was to evaluate the histologic and biomechanical changes that occur between 12 and 52 weeks in an intraarticular, semitendinosus autograft placed through tibial and femoral drill holes in a rabbit model. The results of this study show that, in this rabbit model, the soft tissue graft maintained its biologic fixation in the osseous tunnel when stressed to failure at 1 year. The bony fixation occurred by the formation of an indirect tendon insertion, and this formation was complete by 26 weeks. At 52 weeks, large differences persisted in the strength and stiffness of the graft compared with the normal semitendinosus tendon and anterior cruciate ligament. Based on the results of this study, we support a cautious approach in returning patients to early full activity, including sports, after anterior cruciate ligament reconstruction with a semitendinosus autograft.

No abstract

Measurements of the stress-induced changes in ultrasonic wave speeds in several samples of steels typically used in railroad rails are presented. All of the five possible relative changes in wave speeds for an initially isotropic material subjected to a uniaxial state of stress have been determined and agree to within the limits of accuracy of the measurement with the second-order theory of Hughes and Kelly. The third-order elastic constants are calculated from the acoustoelastic data.