Differential Diagnosis of Knee Pain Along the Medial Joint Line with No History of Trauma

Single Most Likely Diagnosis

• Medial Meniscal Tear: This is a common cause of knee pain along the medial joint line, even without a history of trauma. Meniscal tears can occur due to degenerative changes, especially in older adults, and can cause pain and stiffness in the knee.

Other Likely Diagnoses

• Medial Compartment Osteoarthritis: Osteoarthritis (OA) is a degenerative joint disease that can cause pain and stiffness in the knee, particularly along the medial joint line. It is more common in older adults and can be associated with activities that increase stress on the knee joint.
• Pes Anserine Bursitis: This condition involves inflammation of the bursa located on the medial aspect of the knee, which can cause pain and swelling in the area. It is more common in older adults and individuals with OA or knee deformities.
• Medial Collateral Ligament (MCL) Strain: Although less likely without trauma, a mild strain of the MCL can cause medial knee pain. This could be due to overuse or minor, unreported trauma.

Do Not Miss Diagnoses

• Septic Arthritis: Although less common, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. It can cause severe knee pain, swelling, and systemic symptoms such as fever.
• Osteonecrosis of the Knee: This condition involves the death of bone tissue due to lack of blood supply and can cause severe knee pain. It is more common in older adults and can be associated with corticosteroid use or other medical conditions.
• Tumor or Cyst: Rarely, a tumor or cyst (such as a meniscal cyst) can cause knee pain and should not be missed due to the potential for serious underlying conditions.

Rare Diagnoses

• Chronic Regional Pain Syndrome (CRPS): A rare condition characterized by chronic pain, inflammation, and hypersensitivity, which can affect one limb, including the knee.
• Inflammatory Arthritis (e.g., Rheumatoid Arthritis, Lupus): These conditions can cause knee pain and swelling, but are less common causes of isolated medial knee pain without systemic symptoms.
• Neurogenic Causes (e.g., Nerve Entrapment): Rarely, nerve entrapment or other neurogenic causes can refer pain to the medial knee area, which would require a thorough neurological examination to diagnose.