Differential Diagnosis for Patellofemoral Pain Syndrome

Single Most Likely Diagnosis

• Patellofemoral pain syndrome itself: This is the most likely diagnosis given the presentation of anterior knee pain, especially if it's related to activities that put stress on the knee, such as climbing stairs, squatting, or jumping. The pain is typically diffuse and around the patella.

Other Likely Diagnoses

• Iliotibial (IT) band syndrome: This condition causes pain on the outside of the knee and is common in runners or cyclists. It could be considered if the pain is more lateral.
• Quadriceps or patellar tendinopathy: These conditions involve inflammation of the tendons connecting the quadriceps muscle to the patella or the patella to the tibia, respectively. They can cause pain in the front of the knee.
• Chondromalacia patellae: This condition involves the softening of the cartilage on the underside of the patella, leading to knee pain and tenderness.
• Osgood-Schlatter disease (in adolescents): This condition causes knee pain, swelling, and tenderness below the knee, where the patellar tendon attaches to the shinbone.

Do Not Miss Diagnoses

• Osteonecrosis of the knee: A condition where the bone beneath the cartilage of the knee dies due to lack of blood supply. It's crucial to diagnose early to prevent further damage.
• Infection (septic arthritis): Although rare, an infection within the knee joint can cause severe pain, swelling, and redness, and requires immediate medical attention.
• Tumor: Both benign and malignant tumors can cause knee pain. Early diagnosis is critical for effective treatment.
• Fracture: A fracture around the knee, including a stress fracture, can cause significant pain and must be ruled out, especially with a history of trauma.

Rare Diagnoses

• Complex regional pain syndrome (CRPS): A condition characterized by chronic pain, inflammation, and hypersensitivity after an injury or trauma. It's rare but can cause significant disability.
• Plica syndrome: Irritation of the synovial folds within the knee joint can cause pain and snapping sensations.
• Bursitis: Inflammation of the bursae around the knee can cause pain and swelling, and while not rare, it's less common than other diagnoses on this list.
• Neurogenic causes: Such as a radiculopathy or neuropathy affecting the knee area, which would be an uncommon cause of knee pain but important to consider if other diagnoses are ruled out.