Differential Diagnosis for Left Knee Pain

The patient's complaint of left knee pain, with a history of trauma and previous surgeries, requires a thorough evaluation of potential causes. The following differential diagnosis is organized into categories to guide further investigation and management.

• Single Most Likely Diagnosis
  • Osteoarthritis (OA): The patient's history of knee trauma in high school, previous surgery on the right knee, and recent steroid injection with temporary relief suggest degenerative changes. OA is a common condition in older adults, especially with a history of joint trauma or surgery.
• Other Likely Diagnoses
  • Meniscal tear: Given the patient's history of knee trauma, a meniscal tear is possible, especially if the initial injury was not fully addressed or if there have been subsequent injuries.
  • Ligament sprain or tear: Similar to a meniscal tear, ligament injuries could be a cause of chronic knee pain, especially if the patient has continued to be active.
  • Patellofemoral pain syndrome: This condition, characterized by pain around or behind the patella, could be a contributing factor, especially if the patient's knee alignment or movement patterns have been altered by previous injuries or surgeries.
• Do Not Miss Diagnoses
  • Septic arthritis: Although less likely, given the patient's recent steroid injection and lack of reported fever or significant swelling, septic arthritis is a potentially deadly condition that must be considered, especially if the patient's condition worsens or does not improve with treatment.
  • Osteonecrosis: This condition, which can be caused by steroid use, trauma, or other factors, leads to bone death and can cause severe, persistent pain. It is crucial to consider, given the patient's recent steroid injection.
  • Tumor: Although rare, bone or soft tissue tumors could cause knee pain and must be considered, especially if the pain is persistent, worsening, or accompanied by other systemic symptoms like weight loss or fever.
• Rare Diagnoses
  • Pigmented villonodular synovitis (PVNS): A rare condition characterized by synovial proliferation and pigmentation, PVNS can cause chronic knee pain and swelling.
  • Synovial chondromatosis: This rare condition involves the growth of cartilage in the synovium, leading to joint pain and swelling.
  • Hemophilic arthropathy: If the patient has a history of hemophilia, this condition could be a cause of chronic knee pain due to recurrent hemarthroses.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and potentially, further diagnostic testing such as imaging studies or arthrocentesis.