Differential Diagnosis for Lateral Knee Pain with Difficulty Extending Knee and Negative X-ray
- Single Most Likely Diagnosis
- Iliotibial (IT) Band Syndrome: This condition is characterized by inflammation of the iliotibial band, a ligament that runs down the outside of the thigh from the hip to the knee. It's a common cause of lateral knee pain, especially in runners or cyclists, and can cause difficulty extending the knee due to pain and swelling.
- Other Likely Diagnoses
- Lateral Meniscus Tear: A tear in the lateral meniscus, which is the cartilage structure in the knee joint, can cause lateral knee pain and difficulty extending the knee. Although an X-ray might not show this, an MRI would be more diagnostic.
- Lateral Collateral Ligament (LCL) Sprain: An injury to the LCL, which connects the femur to the fibula, can lead to lateral knee pain and instability, potentially causing difficulty with knee extension.
- Popliteus Tendinitis: Inflammation of the popliteus tendon, which helps to rotate the knee, can cause lateral knee pain, especially with activities that involve twisting or bending.
- Do Not Miss Diagnoses
- Osteonecrosis of the Femur or Tibia: Although less common, osteonecrosis (death of bone tissue due to lack of blood supply) in the femur or tibia can cause knee pain and should not be missed due to its potential for serious complications if left untreated.
- Infection (Septic Arthritis): An infection within the knee joint can cause severe pain, swelling, and difficulty moving the knee. It's a medical emergency that requires prompt diagnosis and treatment.
- Tumor: Although rare, a tumor in the bone or soft tissue around the knee can cause pain and difficulty with movement. It's crucial to consider this possibility to ensure timely diagnosis and treatment.
- Rare Diagnoses
- Pellegrini-Stieda Syndrome: This is a rare condition characterized by ossification of the medial collateral ligament, but it can also affect the lateral aspect of the knee, leading to pain and stiffness.
- Synovial Chondromatosis: A rare condition where cartilage grows in the synovium of the knee joint, leading to pain, swelling, and decreased mobility. It might not be visible on an X-ray but could be detected with an MRI.