Imaging the healing of cartilage grafts in dogs' knee defects

Abstract

BACKGROUND: Autologous periosteal grafting is used as treatment for cartilage defects. PURPOSE: To assess the role of MR imaging and ultrasonography in the evaluation of the post-graft repair process with imaging and histologic correlation. MATERIAL AND METHODS: Periosteal grafts obtained from the tibia of eight dogs were transplanted to the experimental cartilage defects in the femoral condyles (15 knees). The control group was comprised of three dogs (five knees). MR imaging using 4.7T and ultrasonography of the grafted specimens was performed at one, two, four, eight, and 16 weeks after transplantation. The animals were sacrificed at the time of imaging at the previously specified intervals. Histologic analysis with imaging correlation was subsequently performed. RESULTS: All specimens taken from one to 16 weeks demonstrated periosteal proliferation in the graft. At one week, experimental cartilage defects were no longer present on MR imaging. Area of high signal intensity (SI) in the defect was present which corresponded to hemorrhage, edema, and fibrosis on histology. At two, four, and eight weeks, all but two graft demonstrated heterogeneous high SI on T2-weighted image, consistent with immature cartilage. At 16 weeks, all grafts showed heterogeneous isointense to adjacent cartilage on all sequences, which corresponded to dominant mature cartilage. The repair tissue near the exposed subchondral bone revealed heterogeneous high SI on T2-weighted images. This corresponded to the fibrosis with vascular penetration and edema. In the control group, no cartilage repair was noted within cartilage defects. The serial MR features of the grafted area correlated well with the histologic findings. Serial sonographic findings were not sufficient to provide the regenerated cartilage maturity. CONCLUSION: MR imaging is capable of depicting the repair characteristics following periosteal grafting for articular cartilage defects. MR imaging may provide useful information in the assessment of the graft appearance with definite implications regarding the degree and success of incorporation.