Healing phases in autogenous posterior cruciate ligament replacement. A decision aid for after-care. A biomechanical and histologic study

In a sheep model for reconstruction of the posterior cruciate ligament using the central one-third of the autogenous patellar tendon and immediate mobilization, the incorporation course was studied biomechanically, histomorphometrically and radiographically at eight different points in time up to 1 year after surgery. Four different phases of autograft healing were demonstrated on the basis of the histological events. The biomechanical data were correlated with the morphological findings. Phase 1--necrosis--was characterized by a maximum of necrotic autograft tissue 2 weeks postoperatively. Initially, graft strength was determined by the surgical fixation strength. During phase 2--revitalization--the autograft showed cellular proliferation and revascularization, starting from the periphery. The autograft was determined to be weakest during this phase. Phase 3--collagen formation--revealed a marked increase in newly formed collagen tissue between weeks 12 and 16. A significant increase in maximum load and stress was measured. In phase 4--remodeling--the longest phase, the collagen tissue appeared more compact and less cellular. The fiber bundles were arranged more longitudinally. However, the biomechanical properties remained clearly below that of a normal posterior cruciate ligament.