Differential Diagnosis for 58 YOM with Left Anterior Thigh Injury

Single Most Likely Diagnosis

• Quadriceps Tendon Rupture: The patient's description of a "pop" in the left anterior thigh, significant swelling just above the patella, and gapping without patella baja (inferior displacement of the patella) are classic signs of a quadriceps tendon rupture. This injury is common in middle-aged individuals who experience a sudden contraction of the quadriceps muscle, such as during a fall.

Other Likely Diagnoses

• Patellar Fracture: Although the patient does not have patella baja, a fracture of the patella could still occur, especially if the fall was directly onto the knee. Swelling and pain along the IT band could be referred pain or due to associated soft tissue injury.
• Quadriceps Strain or Tear: A less severe injury to the quadriceps muscle or tendon could also present with pain, swelling, and a feeling of a "pop," though the severity of symptoms might be less than with a complete rupture.
• Hemarthrosis: Bleeding into the knee joint from any injury could cause significant swelling and pain, and while not a diagnosis of the tendon or muscle itself, it's a condition that could be associated with the initial trauma.

Do Not Miss Diagnoses

• Popliteal Artery Injury: Although less likely given the description, any significant trauma to the knee warrants consideration of vascular injury, including the popliteal artery. Missed vascular injuries can lead to severe complications, including limb loss.
• Compartment Syndrome: This is a condition that can arise from increased pressure within the muscle compartments of the leg, potentially leading to muscle and nerve damage. It's a medical emergency that requires prompt recognition and treatment.

Rare Diagnoses

• Patellar Tendon Rupture with Patella Alta: While less common than quadriceps tendon ruptures, patellar tendon ruptures can occur, especially in older adults. The presentation might include a high-riding patella (patella alta) and significant weakness in knee extension.
• Osteonecrosis of the Patella or Femur: Though rare and more of a long-term complication, significant trauma to the knee could potentially lead to osteonecrosis (death of bone tissue due to lack of blood supply) in the patella or the femur. This would likely present later with persistent or worsening pain.