Prevalence and MRI-anatomic correlation of bone cysts in osteoarthritic knees.

Objective: The objectives of this study were to determine the prevalence of cysts in the weight-bearing areas and interspinous bone cysts in tibial plateau specimens derived from knees with advanced osteoarthritis, to perform MRI-anatomic correlation of these cysts, and to define their histologic characteristics.

Materials And Methods: Forty-two tibial plateau specimens were recovered from patients undergoing total knee replacement surgery for severe osteoarthritis (14 men and 28 women; mean age, 74 years; age range, 58-87 years). The tibial specimens underwent MRI with T1- and T2-weighted MR sequences. No radiographic data were available before MRI. Tibial specimens were sectioned using a high-speed rotating diamond disk into 3-mm-thick slices. MR images and anatomic specimens were analyzed for the presence of cysts in the interspinous and weight-bearing areas. Histologic staining methods included routine Harris hematoxylin stain, trichrome stain, and Alcian blue-PAS stain.

Results: Twenty-three (54%) of 42 specimens contained one or more cystic areas, with a total of 30 cystic areas. The cysts were distributed in the weight-bearing area (14/30) and interspinous area (16/30). All cysts seen on the anatomic slices could also be depicted on both MRI sequences. Histologic findings were identical for all noncommunicating cysts and revealed necrotic bone fragments with dead denuclearized cells. The cavities were surrounded by a layer of fibrous connective tissue containing adipocytes and osteoblasts. No evidence of epithelial components was found in the lining of the cavities.

Conclusion: Interspinous and weight-bearing tibial cysts are common in severe knee osteoarthritis. The cysts contain necrotic bone fragments and are lined by a nonepithelial fibrous wall. Our findings support the hypothesis that interspinous cysts could result from repetitive bone stresses through the cruciate ligaments. Our findings do not support the use of the term "herniation cyst."