Effect of tibial plateau leveling on cranial and caudal tibial thrusts in canine cranial cruciate[ndash ]deficient stifles: An in vitro experimental study

We investigated the revascularization pattern of patellar tendon grafts used to replace the anterior cruciate ligament in thirty-six dogs by histological and tissue-clearing (Spalteholz) techniques. Initially the grafts were avascular, but by six weeks they were completely ensheathed in a vascular synovial envelope. The soft tissues of the infrapatellar fat pad, the tibial remnant of the anterior cruciate ligament, and the posterior synovial tissues contributed to this synovial vasculature. Intrinsic revascularization of the patellar tendon graft progressed from the proximal and distal portions of the graft centrally and was complete by twenty weeks. The tibial attachment of the patellar tendon graft did not contribute any vessels to the revascularization process. At one year, the vascular and histological appearance of the patellar tendon graft resembled that of a normal anterior cruciate ligament. The absence of perfused vessels within the patellar tendon graft immediately after transplantation within the knee joint and the failure of the osseous insertion of the graft to contribute vessels to the revascularization process suggest that although it is left attached at the tibia, the patellar tendon graft is essentially an avascular free graft at transplantation. The contribution of the soft tissues of the knee to the revascularization process of the graft suggests preservation and utilization of the infrapatellar fat pad and synovial tissue to optimize the graft's revascularization and ultimate viability.

This study investigated the impact of a combination of axial compressive and anterior-posterior tibial loads on the in situ forces in the anterior cruciate ligament. An axial compressive load is believed to contribute to increased stability of the knee joint; however, its effect on in situ forces in the anterior cruciate ligament has not been clearly defined, to our knowledge. It was hypothesized that the application of an axial compressive load, when combined with an anterior tibial load, would result in larger in situ forces in the anterior cruciate ligament than those caused by an isolated anterior tibial load. With use of a porcine knee model, the results confirmed this hypothesis; the addition of a 200 N axial compressive load to a 100 N anterior tibial load increased knee stability by reducing anterior-posterior tibial translation and internal-external tibial rotation and also caused a significant increase in in situ forces in the anterior cruciate ligament (p < 0.05). Specifically, there was a 34% increase in the in situ force at 30 degrees of flexion, a 68% increase at 60 degrees of flexion, and an 84% increase at 90 degrees of flexion compared with those for an isolated anterior tibial load of 100 N. Additionally, there was a statistically significant increase of the in situ forces in the anterior cruciate ligament at 60 and 90 degrees as compared with those at 30 degrees. These results suggest that axial compressive loads on the knee may play a role in injury of the anterior cruciate ligament when the knee is flexed.