Differential Diagnosis for Left Knee Pain

The patient presents with left knee pain, swelling, dizziness, and weakness, which began 3 days ago. The following differential diagnosis is organized into categories:

• Single Most Likely Diagnosis
  • Osteoarthritis: This is a common cause of knee pain, especially in older adults. The patient's symptoms of knee pain and swelling could be indicative of an osteoarthritis flare-up. However, the acute onset and associated symptoms of dizziness and weakness are not typical, making this less likely.
• Other Likely Diagnoses
  • Meniscal tear: Although the patient denies twisting or falling, a meniscal tear could still occur from a minor injury or degenerative changes. The pain and swelling are consistent with this diagnosis.
  • Ligament sprain: A ligament sprain could occur without a significant injury, especially if the patient has underlying ligamentous laxity. The symptoms of pain and swelling are consistent with this diagnosis.
  • Bursitis: Prepatellar or pes anserine bursitis could cause knee pain and swelling, especially if the patient has been engaging in activities that involve repetitive knee flexion.
• Do Not Miss Diagnoses
  • Septic arthritis: This is a medical emergency that requires prompt diagnosis and treatment. The patient's symptoms of acute onset knee pain, swelling, and systemic symptoms such as dizziness and weakness could be indicative of septic arthritis.
  • Deep vein thrombosis (DVT): DVT could cause knee pain and swelling, especially if the patient has been immobile or has a history of clotting disorders. The associated symptoms of dizziness and weakness could be indicative of a pulmonary embolism.
  • Osteonecrosis: This is a serious condition that could cause knee pain and swelling, especially if the patient has a history of steroid use or other risk factors.
• Rare Diagnoses
  • Rheumatoid arthritis: Although this is a less common cause of knee pain, it could still be a consideration, especially if the patient has a family history or other systemic symptoms.
  • Hemarthrosis: This is a rare condition that could cause knee pain and swelling, especially if the patient has a bleeding disorder or has been taking anticoagulant medications.
  • Neuropathic pain: This is a rare cause of knee pain, but could be considered if the patient has a history of nerve damage or other neuropathic conditions.