ARTICULAR-CARTILAGE CHANGES SEEN WITH MAGNETIC-RESONANCE IMAGING-DETECTED BONE BRUISES ASSOCIATED WITH ACUTE ANTERIOR CRUCIATE LIGAMENT RUPTURE

Occult osteochondral lesions (bone bruises) have been documented on ma gnetic resonance images in more than 80% of patients sustaining acute anterior cruciate ligament ruptures. Despite the high prevalence of th ese lesions, little is known about the histologic changes in the adjac ent articular cartilage. Ten patients with acute anterior cruciate lig ament ruptures who had a preoperatively documented (by magnetic resona nce imaging) geographic bone bruise at the sulcus terminalis on the la teral femoral condyle underwent a 3-mm diameter trephine biopsy of the articular cartilage and subchondral bone overlying the bone bruise at the time of anterior cruciate ligament reconstruction. Biopsy samples of the articular cartilage and subchondral bone were stained with hem atoxylin and eosin and toluidine blue. All patients had significant ar throscopic and histologic articular cartilage irregularity in the area overlying the bone bruise. Arthroscopic findings of the articular car tilage included softening (dimpling), fissuring, or overt chondral fra cture. Histologic examination revealed degeneration of the chondrocyte s and loss of toluidine blue staining in the articular cartilage (loss of proteoglycan). There was necrosis of osteocytes in the subchondral bone, and empty lacuna were visible. This study defines the exact his tologic changes of the articular cartilage overlying a geographic bone bruise secondary to an acute anterior cruciate ligament tear. Our fin dings suggest that a geographic bone bruise found on magnetic resonanc e imaging indicates substantial damage to normal articular cartilage h omeostasis.