Differential Diagnosis for a 4-year-old Girl with Knee Pain
Single Most Likely Diagnosis
- Patellar fracture or stress fracture: Given the location of the pain (right below the patella) and the recent history of a knee injury, a fracture of the patella or a stress fracture in the area is highly plausible. The inability to bear weight one week after the injury suggests a significant injury that may involve a fracture.
Other Likely Diagnoses
- Medial or lateral condyle fracture of the femur: These types of fractures can occur in children and may present with pain and difficulty bearing weight, especially if the fracture is not properly aligned.
- Tibial tubercle fracture (Osgood-Schlatter disease): Although more common in early adolescence, Osgood-Schlatter disease can occur in younger children and is characterized by pain below the knee, where the patellar tendon attaches to the tibia.
- Patellar tendinitis or quadriceps tendinitis: Inflammation of the tendons around the knee can cause significant pain and stiffness, especially after an injury.
Do Not Miss Diagnoses
- Septic arthritis of the knee: Although less likely, septic arthritis is a medical emergency that requires prompt diagnosis and treatment. Symptoms can include severe pain, swelling, redness, and warmth of the knee, along with fever and inability to move the knee.
- Osteomyelitis: An infection of the bone, osteomyelitis can present with pain, swelling, and redness over the affected bone, and can be a complication of a fracture or a direct infection.
- Neoplastic processes (e.g., osteosarcoma): While rare in this age group, bone tumors can cause persistent pain and should be considered in the differential diagnosis, especially if the pain is worsening over time.
Rare Diagnoses
- Binding-Larsen-Johansson syndrome: A rare condition that affects the proximal patellar pole, causing pain and swelling, similar to Osgood-Schlatter disease but at a different location.
- Sinding-Larsen-Johansson disease: Another rare condition affecting the distal patellar pole, causing pain and swelling in the area where the patellar tendon attaches to the patella.
Each of these diagnoses should be considered based on the clinical presentation, and further evaluation with imaging studies (such as X-rays or an MRI) and possibly laboratory tests may be necessary to determine the exact cause of the symptoms.