A twenty-six-year-old man presented with sudden onset of pain in the right knee that had occurred during a sprint eight days earlier. Physical examination showed a knee effusion with limited motion because of the pain. There was no ligamentous laxity and no patellar instability. Radiographs showed no abnormality except soft-tissue swelling. A magnetic resonance image (MRI) showed a 0.5 × 1-cm chondral defect on the medial facet of the patella and a 1.7 × 1.6-cm chondral defect on the anteromedial femoral trochlea, with a signal change of the underlying subchondral bone that was consistent with a bone bruise (Figs. 1-A and 1-B). There was a large loose body in the suprapatellar pouch and a small loose body in the medial gutter. The medial patellofemoral ligament and retinaculum were intact.
During the arthroscopy, a large chondral loose body, which was thought to be from the femoral trochlea, was observed in the suprapatellar pouch; a small fragmented chondral loose body, which was thought to be from the patella, was observed in the medial gutter. A corresponding lesion on the anteromedial femoral trochlea lacked articular cartilage and was covered with thin, whitish membrane, which appeared to be fibrous tissue. It did not have a chondral margin at the superior and medial borders of the defect. The medial facet of the patella also lacked articular cartilage and was covered with a small blood clot.
The medial parapatellar arthrotomy demonstrated a large chondral fragment with no subchondral bone underneath the articular cartilage. The lesion on the femoral trochlea was curetted to remove the thin fibrous membrane (Fig. 2-A), and microfracture was performed with an awl. The chondral fragment was found to be slightly deformed and more concave. Although the fragment did not fit exactly to the subchondral bone bed, the fragment was repaired to the base of the lesion with use of a round needle and 5-0 Prolene (Ethicon) suture (Fig. 2-B). After surgery, the knee was immobilized at full extension with a brace for eight weeks. Continuous passive motion exercises of the knee were performed beginning at two weeks after the surgery for at least one hour each day; partial weight-bearing with the knee locked in extension was also allowed at this time. The brace was worn at all times except during the continuous passive motion exercises. Full weight-bearing was allowed eight weeks after the surgery, and the continuous passive motion exercises were discontinued at this time.
Twenty-one months postoperatively, the patient had no pain with full knee motion. The activity level was the same as before the injury. A follow-up MRI at this time showed that the reattached cartilage fragment was indistinguishable from the adjacent cartilage tissue (Figs. 3-A and 3-B). A secondary arthroscopy was performed, and it revealed that the fragment had been reattached properly (Fig. 4). The fraying of the cartilage along the margin of the lesion was shaved. Consistency of the lesion was good. A core biopsy was performed at the center of the lesion with an 11-gauge biopsy needle. Histological examination showed viable chondrocytes in the articular cartilage that was integrated into the subchondral bone (Figs. 5-A and 5-B).
Note: The authors would like to thank Wonjoo Jung for providing editorial assistance.
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