Differential Diagnosis for Knee Injury

The patient's symptoms and history suggest several possible diagnoses. Here's a categorized list of potential causes:

• Single most likely diagnosis

  • Medial Meniscus Tear: The patient's complaint of dull pain when sitting and sharp pain when walking or fully extending the leg is consistent with a meniscus tear. The mechanism of injury, although not directly hitting the knee, could have caused a twisting or bending force leading to a meniscus tear. The spasm-like feeling after sitting for a long period could be due to irritation of the meniscus or surrounding structures.

• Other Likely diagnoses

  • Ligament Sprain: The injury could have caused a sprain to one of the knee ligaments, such as the medial collateral ligament (MCL) or anterior cruciate ligament (ACL). The sharp pain with movement and spasm-like feeling could be indicative of ligamentous instability.
  • Contusion or Bruising: Although the patient does not recall hitting the knee directly, the collapse of the bench could have caused a contusion or bruising to the soft tissues around the knee, leading to pain and stiffness.
  • Patellofemoral Pain Syndrome: The patient's complaint of pain when sitting and sharp pain with movement could be related to patellofemoral pain syndrome, especially if the patient has a history of knee problems or biomechanical issues.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Popliteal Artery Injury: Although unlikely, a popliteal artery injury could occur due to the trauma, leading to ischemia or even limb loss if not promptly addressed.
  • Fracture: A fracture, such as a tibial plateau fracture, could have occurred due to the fall, and it's essential to rule out this possibility with imaging studies if necessary.
  • Neurovascular Compromise: The patient's symptoms could be indicative of neurovascular compromise, such as peroneal nerve injury or compartment syndrome, which require prompt medical attention.

• Rare diagnoses

  • Osteochondritis Dissecans: A rare condition where a piece of cartilage and bone becomes detached, causing pain and stiffness in the knee.
  • Spontaneous Hemarthrosis: A rare condition where bleeding occurs in the knee joint without any apparent trauma, which could be caused by various underlying conditions.