Differential Diagnosis for Knee Pain and Inability to Extend Knee
- Single Most Likely Diagnosis
- Patellar fracture or patellar tendinosis: The inability to extend the knee is a common presentation of patellar fractures or severe patellar tendinosis, as the patella and its tendon play a crucial role in knee extension.
- Other Likely Diagnoses
- Quadriceps tendon rupture: A rupture of the quadriceps tendon can lead to an inability to extend the knee, as it disrupts the continuity of the extensor mechanism.
- Meniscal tear: A large meniscal tear, especially a bucket-handle tear, can mechanically block knee extension.
- Ligamentous sprain (e.g., ACL, PCL): Severe ligamentous sprains can cause pain and instability, potentially limiting knee extension.
- Osteoarthritis: Advanced osteoarthritis can cause pain and mechanical obstruction, leading to limited knee mobility, including extension.
- Do Not Miss Diagnoses
- Septic arthritis: Although less common, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. Knee pain and limited mobility can be presenting symptoms.
- Osteonecrosis: Avascular necrosis of the femoral condyle can cause severe knee pain and limited mobility, including an inability to extend the knee.
- Tumor (e.g., osteosarcoma): Bone tumors can cause pain, swelling, and limited mobility. Although rare, they are critical to diagnose early.
- Rare Diagnoses
- Rheumatoid arthritis: Although not typically presenting with a sudden inability to extend the knee, rheumatoid arthritis can cause severe knee inflammation and limited mobility in advanced cases.
- Hemophilia: In patients with hemophilia, a hemorrhage into the knee joint (hemarthrosis) can cause severe pain, swelling, and limited mobility.
- Complex regional pain syndrome (CRPS): A rare condition characterized by chronic pain, inflammation, and hypersensitivity, which can affect the knee and limit its mobility.