Differential Diagnosis for a Lump on the Medial Aspect of the Knee
- Single most likely diagnosis
- Bipartite patella: The patient's X-ray already shows a bipartite patella, which is a congenital condition where the patella is made up of two separate bones instead of one. This condition can sometimes cause a lump or bump on the knee, especially if one of the fragments is larger or more prominent than the other.
- Other Likely diagnoses
- Bursitis: Prepatellar or pes anserine bursitis could cause a lump on the medial aspect of the knee. These conditions involve inflammation of the bursae, which are fluid-filled sacs that cushion the joints and reduce friction between bone and soft tissue.
- Ganglion cyst: A ganglion cyst is a lump under the skin that occurs when fluid leaks from a joint or tendon. These cysts can appear on the medial aspect of the knee and may be mistaken for other conditions.
- Lipoma: A lipoma is a benign tumor made up of fat tissue. It can appear as a lump under the skin and could be located on the medial aspect of the knee.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Soft tissue sarcoma (e.g., anacoarcoma, as the patient is concerned): Although rare, soft tissue sarcomas can present as a lump on the knee. It's crucial to consider this diagnosis, especially given the patient's concern, to ensure timely diagnosis and treatment if present.
- Osteosarcoma: A type of bone cancer that can cause a lump or swelling, typically around the knee. Early detection is critical for effective treatment.
- Rare diagnoses
- Synovial chondromatosis: A rare condition where cartilage grows in the synovium (the lining of the joints), leading to the formation of loose bodies within the joint. It could potentially cause a lump if the synovium or loose bodies protrude outside the joint capsule.
- Pigmented villonodular synovitis (PVNS): A rare disease that causes the synovium to thicken and overgrow, leading to swelling and potentially a palpable mass around the joint.