Differential Diagnosis for Protruding Bony Prominence on Knee
Single Most Likely Diagnosis
- Prepatellar Bursitis: This condition, also known as "housemaid's knee," is characterized by inflammation of the prepatellar bursa, which can cause a protruding bony prominence and pain with kneeling. The history of a fall and subsequent development of symptoms is consistent with this diagnosis, as trauma can cause or exacerbate prepatellar bursitis.
Other Likely Diagnoses
- Osgood-Schlatter Disease: Although more common in adolescents, this condition can occur in adults and is characterized by a painful bump on the shin bone where the patellar tendon attaches to the tibia. It could potentially cause a prominence and pain with activities like kneeling.
- Patellar Fracture: A fracture of the patella (kneecap) could cause a bony prominence and significant pain, especially with weight-bearing activities or direct pressure on the knee, such as kneeling.
- Quadriceps or Patellar Tendonitis: Inflammation of the quadriceps or patellar tendon can cause pain and swelling around the knee, potentially leading to a noticeable prominence, especially if there is significant swelling or if the condition leads to a Haglund's deformity-like condition in the patella.
Do Not Miss Diagnoses
- Infection (Septic Bursitis or Osteomyelitis): Although less likely, an infection in the bursa (septic bursitis) or bone (osteomyelitis) could present with swelling, redness, warmth, and pain. These conditions are medical emergencies requiring prompt treatment.
- Malignancy (e.g., Osteosarcoma): While rare, a new bony prominence could be a sign of a malignant bone tumor. Given the potential severity of this diagnosis, it must be considered, especially if the prominence is rapidly growing or if there are systemic symptoms like unexplained weight loss or night sweats.
Rare Diagnoses
- Ganglion Cyst: A ganglion cyst is a lump under the skin that occurs when fluid accumulates in a sac. Although more common on the wrist, they can occur near the knee and could potentially cause a bony prominence if they become large enough.
- Synovial Chondromatosis: A rare condition where cartilage grows in the synovium of the joint, potentially causing a bony prominence due to the formation of osteochondral loose bodies within the joint.