Differential Diagnosis for Knee Pain

The patient presents with a history of trauma to the knee during soccer, followed by a dull pain that worsens with strain, particularly at deep angles, and is accompanied by swelling under the knee cap. The pain is located above, below, and medial to the knee cap on the right leg. Based on these symptoms, the following differential diagnoses are considered:

• Single Most Likely Diagnosis

  • Patellofemoral Pain Syndrome (PFPS): This condition is characterized by pain around or behind the patella (knee cap), often associated with activities that put stress on the knee, like climbing stairs, squatting, or jumping. The patient's symptoms of dull pain with strain, especially at deep angles, and the location of the pain relative to the knee cap, are consistent with PFPS. The swelling under the knee cap also supports this diagnosis.

• Other Likely Diagnoses

  • Medial Meniscus Tear: A meniscus tear can cause pain, especially with twisting or bending movements. The location of the pain (medial to the knee cap) and the mechanism of injury (trauma during soccer) make this a plausible diagnosis. However, meniscus tears often present with more acute, sharp pain and mechanical symptoms like locking or catching, which are not prominently featured in the patient's description.
  • Ligament Sprain: Ligament sprains around the knee can occur from trauma and cause pain and swelling. The patient's history of playing soccer and the presence of swelling under the knee cap could suggest a ligament sprain, although the specific location and nature of the pain might not perfectly align with typical presentations of ligament sprains.

• Do Not Miss Diagnoses

  • Septic Arthritis: Although less likely given the subacute presentation and lack of systemic symptoms like fever, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. It can present with pain, swelling, and decreased range of motion of the affected joint.
  • Osteonecrosis of the Knee: This condition involves the death of bone tissue due to a lack of blood supply and can cause severe pain. It might not be the first consideration given the patient's age and presentation, but it's crucial not to miss it due to its significant implications for joint health.

• Rare Diagnoses

  • Osgood-Schlatter Disease: Typically seen in adolescents, this condition involves inflammation of the patellar tendon at its insertion on the tibia, causing knee pain and swelling. Given the patient's description and the fact that Osgood-Schlatter disease is more common in younger individuals, this might be less likely but should be considered if the patient is within the appropriate age range.
  • Tumor or Cyst: Although extremely rare, tumors or cysts around the knee can cause pain and swelling. These would be unusual diagnoses to consider first without additional symptoms like night pain or significant swelling, but they should remain on the differential until ruled out by imaging studies if necessary.