CRUCIATE LIGAMENT REPLACEMENT - THE HEALING-PROCESS IN A SHEEP MODEL

The patellar tendon autograft is widely used in cruciate ligament replacement. Knowledge of the basic processes involved in graft healing and of factors regulating the healing process is still limited. The patellar tendon and cruciate ligament are morphologically and biochemically distinct, which reflects the different mechanical forces acting on them. Based on morphological studies in posterior cruciate ligament replacement in a sheep model, the patellar tendon autograft undergoes a remarkable transformation process during healing. Distinct healing phases similar to those in wound healing can be differentiated. During the phase of necrosis and degeneration the graft tissue becomes disorganized and mechanically weak. During the following phase of revitalization, which is characterized by revascularization, cellular proliferation and formation of collagen and other components of the extracellular matrix, the mechanical properties gradually improve. Even after the phase of remodeling the autograft tissue differs structurally and mechanically from a ligament, suggesting that the autograft only heals to a scar-like replacement tissue. The lack of a fascicular structure, the widespread presence of type III collagen and fibronectin, and the predominance of thin collagen fibrils correlate with a maximum stress of 60 % and an elastic modulus of 70 % compared with control values. In the sheep model cartilage alterations in the treated knees are similar to those in controls even though reconstruction of the posterior cruciate ligament cannot restore joint stability of controls. Conclusions relating to clinical practice are still tentative, but experimental studies provide a deep insight into the biological healing process of autografts after cruciate ligament replacement and may provide a rationale on which to base a realistic evaluation of a biological cruciate ligament reconstruction.