Differential Diagnosis for Sudden Pain in Right Knee of a 12-year-old Child

Single Most Likely Diagnosis

• Osgood-Schlatter Disease: This condition is a common cause of knee pain in adolescents, especially during growth spurts. It occurs due to inflammation of the patellar tendon at its insertion on the tibial tubercle, often related to overuse or repetitive stress from activities like running or jumping.

Other Likely Diagnoses

• Patellofemoral Pain Syndrome: Characterized by pain around or behind the patella, this condition is common in adolescents and can be related to activities that put stress on the knee, poor tracking of the patella, or overuse.
• Meniscal Injury: Tears in the meniscus can occur from sudden twisting motions or direct blows to the knee, leading to pain, swelling, and sometimes locking of the knee.
• Ligament Sprains: Injuries to the ligaments surrounding the knee, such as the anterior cruciate ligament (ACL) or medial collateral ligament (MCL), can cause sudden pain, especially if there was a traumatic event.

Do Not Miss Diagnoses

• Septic Arthritis: Although less common, this condition is a medical emergency. Bacterial infection within the joint space can lead to severe pain, swelling, redness, and warmth. Prompt diagnosis and treatment are crucial to prevent long-term joint damage.
• Osteosarcoma or Other Bone Tumors: While rare, bone cancers can present with sudden onset of pain, especially if the pain is persistent, worsening at night, or accompanied by swelling.
• Slipped Capital Femoral Epiphysis (SCFE): This condition involves the displacement of the femoral head from the femoral neck through the physeal plate, which can cause sudden onset of hip or knee pain, especially in obese adolescents.

Rare Diagnoses

• Kohler Disease: A rare condition causing pain and swelling in the knee due to avascular necrosis of the tibial tubercle.
• Sinding-Larsen-Johansson Syndrome: Similar to Osgood-Schlatter disease but involves the inferior pole of the patella, causing pain at the lower front part of the knee.
• Discoid Meniscus: A rare congenital anomaly of the meniscus that can cause knee pain and snapping sensation, more commonly in the lateral meniscus.

Each of these diagnoses should be considered based on the clinical presentation, history, and physical examination findings, with further diagnostic tests (like imaging studies) used to confirm the diagnosis when necessary.