Worrisome and Incidental Signs on Knee Radiographs SA–CME REVIEW pole and lateral femoral condyle (Figure 6). Corrective surgery to ad- dress predisposing ligamentous and osseous abnormalities is performed in knees deemed unstable. 28,31 Miscellaneous Worrisome Mimics Osteochondritis dissecans Osteochondritis dissecans (OD) is a chronic disease of subchondral bone that can mimic signs of fracture on knee radiographs, most commonly in the lateral region of the medial femoral condyle. Adolescents and young adults are the most likely to manifest OD, oſten presenting with knee pain, swelling, and locking. 32 Identifying advanced-stage OD before the in-situ bone fragment dis- places into the joint space improves long-term prognosis. Radiographic findings of advanced OD with an in situ fragment demon- strates an ossific fragment at the articular surface, separated from the adjacent bone by a curvilinear lucency (Figure 7). Its location at the lateral region of the medial femoral condyle and relative smooth margins of the curvilinear lucency help to dif- ferentiate OD from an acute fracture. MRI can confirm the diagnosis and provide staging information critical for treatment. Patients with unstable in-situ fragments are candidates for surgery. 32,33 Incidental Signs Degenerative Joint Disease Geode A geode is a subchondral cyst typ- ically associated with full-thickness articular cartilage loss. Geodes are A B Figure 9. Central osteophyte. (A) AP view in a patient with signs of degenerative joint space narrowing and small marginal osteophyte formation with a small osseous protuberance at the central articular surface of the lateral femoral condyle (arrow). (B) Coronal proton density MRI image shows an osseous protuberance (arrow) in continuity with the subchondral bone and without overlying articular cartilage, consistent with a central osteophyte. Figure 10. Baker cyst osteochondral body. (A) Lateral radiograph shows an osteochondral body (arrow) with peripheral mineralization in the soft tissues of the posterior knee. (B) Axial proton density fat saturated MR image shows the osteochondral body located inside of a Baker cyst. A B Applied Radiology 13 January / February 2023