MR imaging of cartilage repair in the knee and ankle.

Because of the relative avascularity of articular cartilage, lesions that are caused by trauma or degeneration of the cartilage do not heal spontaneously and must be repaired surgically. The interventional procedures that have been developed for the repair of such lesions include abrasion, microfracture, autologous osteochondral transplantation, allograft transplantation, and autologous chondrocyte implantation. An accurate imaging assessment of the repair tissue is necessary in order to objectively evaluate the postoperative outcome. Magnetic resonance (MR) imaging and arthroscopy provide complementary information and are especially useful for follow-up evaluation of cartilage repair in the knee and ankle. Standard MR imaging techniques may be used postoperatively to evaluate the success of implantation and the state of cartilage healing. Newer matrix assessment techniques, which include delayed gadolinium-enhanced MR imaging and mapping of T1rho and T2 values, may provide useful supplemental information about the histologic and biochemical contents of reparative tissue. The normal postoperative appearance of the joints after cartilage repair varies according to the surgical technique used and the stage of healing. To identify potential complications, it is important to be familiar with the various repair procedures and the characteristic MR imaging features of the repair tissue at various postoperative intervals.