Differential Diagnosis
- Single most likely diagnosis
- Ossification of the quadriceps tendon, also known as quadriceps tendon ossification or patellar tendinosis with ossification: This condition is characterized by the formation of bone within the quadriceps tendon, often at its attachment to the patella. The presence of joint space maintenance, small joint effusion, and ossification at the quadriceps tendon attachment on the superior pole of the patella supports this diagnosis.
- Other Likely diagnoses
- Prepatellar bursitis: Although the primary finding is ossification at the quadriceps tendon attachment, prepatellar bursitis could explain the small joint effusion and might be associated with quadriceps tendon pathology.
- Patellar tendinosis: This condition involves inflammation and degeneration of the patellar tendon, which could be related to the ossification seen at the quadriceps tendon attachment. It might not fully explain the joint effusion but could be a contributing factor.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Septic arthritis: Although the joint spaces are maintained, which argues against severe joint infection, any joint effusion warrants consideration of septic arthritis due to its potential for severe and rapid joint destruction.
- Osteosarcoma or other bone tumors: While rare, any new bone formation, such as the ossification described, could potentially be a sign of a malignant process, especially if the patient has risk factors or if the ossification is atypical in appearance or location.
- Rare diagnoses
- Chondrocalcinosis or pseudogout: This condition involves the deposition of calcium pyrophosphate dihydrate crystals within the joint, which could lead to joint effusion and, less commonly, to calcification or ossification in periarticular tissues.
- Spondyloarthritis with enthesitis: Certain types of spondyloarthritis can cause inflammation at the sites where tendons and ligaments attach to bone (entheses), potentially leading to new bone formation and ossification, as well as joint effusions.