Differential Diagnosis for Lateral Knee Pain in a Middle-Aged Male After Falling Down

Single Most Likely Diagnosis

• Iliotibial (IT) Band Syndrome: This condition is a common cause of lateral knee pain, especially in individuals who have recently experienced a traumatic event like a fall. The IT band can become inflamed or irritated due to the direct impact or from the altered gait that may follow a fall, leading to pain on the lateral aspect of the knee.

Other Likely Diagnoses

• Lateral Meniscal Tear: A fall can cause a twisting injury to the knee, leading to a meniscal tear. The lateral meniscus is less commonly injured than the medial meniscus, but it can still be a source of lateral knee pain.
• Lateral Collateral Ligament (LCL) Sprain: The LCL can be injured in a fall, especially if the knee is subjected to a varus stress (a force that pushes the knee inward from the outside). This would cause pain and instability on the lateral side of the knee.
• Peroneal Nerve Injury: The peroneal nerve wraps around the lateral aspect of the fibular head and can be injured in a fall, leading to pain, numbness, or weakness in the lateral knee area and potentially affecting the foot as well.

Do Not Miss Diagnoses

• Fracture of the Lateral Tibial Plateau or Fibular Head: While less common, a fracture in this area can cause significant lateral knee pain and must be ruled out with imaging studies if suspected, as missing this diagnosis could lead to improper healing and long-term disability.
• Osteonecrosis of the Femoral Condyle: Though rare, osteonecrosis (death of bone tissue due to lack of blood supply) can occur after a traumatic event and would require prompt diagnosis and treatment to prevent further damage.
• Popliteal Artery Injury: A severe injury to the popliteal artery, which runs behind the knee, could lead to ischemia of the lower leg. This is a medical emergency and must be considered in the differential diagnosis of severe knee trauma.

Rare Diagnoses

• Ganglion Cyst: A ganglion cyst can form on the lateral aspect of the knee and cause pain, though this is less common and usually not associated with trauma.
• Bursitis of the Lateral Knee: Inflammation of one of the bursae around the lateral knee can cause pain and swelling, but this is less likely to be directly caused by a fall unless there was direct pressure on the bursa during the fall.
• Tumor: A tumor in the lateral knee area could cause pain, but this would be an extremely rare cause of knee pain following a fall and would typically be associated with other systemic symptoms or a mass.