Differential Diagnosis for Knee Pain

The following is a comprehensive differential diagnosis for knee pain, categorized for clarity and emphasis on potential severity.

• Single Most Likely Diagnosis
  • Osteoarthritis: This is often the most common cause of knee pain, especially in older adults. It is characterized by the wear and tear of the cartilage in the knee joint, leading to pain, stiffness, and limited mobility. The likelihood of osteoarthritis increases with age, obesity, and previous injuries or surgeries on the knee.
• Other Likely Diagnoses
  • Ligament sprains (e.g., ACL, MCL, LCL): These are common in individuals who participate in sports or activities that involve sudden stops, changes in direction, or direct blows to the knee.
  • Meniscal tears: These can occur from acute injuries or chronic wear and tear, especially in the context of osteoarthritis. Symptoms include pain, locking, or catching sensations in the knee.
  • Tendinitis (e.g., patellar tendinitis): Inflammation of the tendons around the knee, often due to overuse or repetitive strain, common in athletes or individuals with jobs that involve frequent kneeling or climbing.
  • Bursitis: Inflammation of the fluid-filled sacs (bursae) that cushion the knee joint, often caused by repetitive motion or direct pressure on the knee.
• Do Not Miss Diagnoses
  • Septic arthritis: A potentially life-threatening condition where the knee joint becomes infected, requiring immediate medical attention. Symptoms include severe pain, redness, swelling, and warmth around the knee, often accompanied by fever.
  • Osteonecrosis (avascular necrosis): A condition where the bone tissue dies due to lack of blood supply, which can be caused by trauma, steroid use, or excessive alcohol consumption. Early diagnosis is crucial to prevent collapse of the bone and preserve joint function.
  • Deep vein thrombosis (DVT): Although more commonly associated with calf pain, DVT can sometimes present with knee pain and swelling. It is a serious condition that requires prompt treatment to prevent pulmonary embolism.
• Rare Diagnoses
  • Rheumatoid arthritis: An autoimmune disorder that can cause inflammation and pain in the knees, among other joints. It is less common than osteoarthritis but important to diagnose due to its systemic implications and the availability of specific treatments.
  • Gout or pseudogout: Forms of arthritis characterized by sudden, severe attacks of pain, swelling, redness, and tenderness, often occurring at the base of the big toe but can also affect the knee.
  • Osgood-Schlatter disease: A condition that affects the upper tibia in adolescents, causing knee pain, especially just below the knee cap. It is related to growth spurts and overuse.
  • Knee tumors (e.g., osteosarcoma, synovial sarcoma): Although rare, these can cause knee pain and should be considered in the differential diagnosis, especially in cases where pain is persistent, worsening, or accompanied by other systemic symptoms like weight loss or fever.