61-year-old female with left knee swelling and history of diabetes. Evaluate for osteomyelitis. There is a large knee joint effusion with enhancement of the synovium. Small foci of gas density within the effusion could either reflect attempted aspiration or infection. Little if any fluid concentrates posteriorly within the joint. The joint effusion herniates anteriorly through a full-thickness defect in the quadriceps tendon that we suspect represents a chronic tear, with retraction of the proximal fibers by at least 6 cm relative to the distal fibers. The signal intensity of the marrow of the patella, distal femoral epiphysis, and proximal tibia is normal.The distal intramuscular tendinous structures of the quadriceps appear thickened, possibly due to chronic scarring. Increased signal intensity within the mid to distal vastus medialis, intermedius, and lateralis muscles on fat suppressed T2-weighted images is suggestive of edema, but minimal enhancement is seen within these structures on postcontrast images. There is mild edema in the subcutaneous fat of the distal thigh and in the deep fat posterior to the distal femur. Other than the aforementioned joint effusion, there is no discrete drainable abscess or soft tissue fluid collection.Patchy areas of signal abnormality within the mid to distal femoral diaphysis are iso to hyperintense compared to skeletal muscle on T1 and T2-weighted images and show minimal enhancement following contrast administration. These findings are nonspecific and while osteomyelitis cannot be entirely excluded, the likelihood is low based on signal characteristics, distribution, and relative lack of surrounding edema/enhancement. Other differential considerations include peculiar foci of reconverted red marrow or small areas of ischemic or infarcted bone.Small amount of fluid within both hip joints on large FOV images. Moderate osteoarthritis affects the right knee.
1.Large knee joint effusion with foci of gas density that may reflect infection or attempted aspiration.2.Full-thickness quadriceps tendon tear, presumably chronic in etiology, with edema and scarring of the quadriceps musculature.3.Small foci of signal abnormality within the mid to distal femoral diaphysis. These foci are nonspecific but would be an unusual appearance of osteomyelitis, and may instead reflect residual red marrow or areas of bone marrow ischemia/infarction.