chapter 11: Articular Cartilage Lesions in Patellofemoral Pain Patients
OSTEOCHONDRITIS DISSECANS AND OSTEONECROSIS
Patellar osteochondritis is a rare cause of anterior knee pain (84). Occasionally, the clinician may notice an osteochondritis dissecans of the patella or trochlea. Although uncommon, such lesions can cause persistent pain, particularly in the athlete. As in osteochondritis dissecans of the medial femoral condyle, there is some possibility that the lesion may heal in a skeletally immature patient, so a period of immobilization (approximately 6 weeks) is appropriate in these patients. In adults, healing of the osteochondritis dissecans fragment is unlikely, and removal of the fragment may become necessary if it will not compromise articular surface congruity. If the osteochondritis dissecans fragment is so large that patellofemoral congruence or stability might be compromised, fixation with screws or wires will result in healing in most cases. Following fixation, a period of immobilization is wise, particularly if the fragment will undergo significant pressure during knee motion. Immobilization of the knee in full extension will minimize contact pressure on the healing fragment.
Removal of a small fragment can give satisfactory results when immobilization, modification of activity, and symptomatic treatment fail. In the author's experience, however, it is not uncommon to have some residual symptoms, even after removal of the fragment. Although patients are improved, a perfect result seems difficult to achieve following removal of small osteochondritis dissecans fragments from the patella. In the author's opinion, this procedure is best done open to permit thorough debridement of the defect.
Osteonecrosis may occur in patients following laser debridement of articular cartilage fragments. The author is aware of several cases in which patients underwent laser debridement of loose articular cartilage fragments and later experienced subchondral bone fragmentation with resulting loose body. Surgeons should be alert to subchondral fragmentation, presumably related to thermal necrosis of bone, following laser debridement of articular cartilage. It is possible that this phenomenon is less common with newer lasers. Osteonecrosis of the patella is also possible following steroid therapy. Mizuta et al (85) report a case of bilateral patellar osteonecrosis during steroid therapy. Hodge et al (86) have pointed out that CT arthrography is a very accurate and helpful technique for identifying significant synovial plicae, and therefore recommend this technique as a way of differentiating thick from thin plicae. Galloway and Noyes reported cystic degeneration of the patella following arthroscopic debridement and subchondral bone perforation (87).
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