Differential Diagnosis for Posterior Knee Pain in a 7yo Male
- Single most likely diagnosis
- Osgood-Schlatter disease: This condition is a common cause of knee pain in adolescents, especially during periods of rapid growth. The pain is typically located below the knee and worsens with activities such as jumping, running, or climbing stairs. However, given the posterior knee pain and difficulty with the last 20 degrees of flexion, it's possible that the pain is referred or the condition is affecting the posterior aspect of the knee.
- Other Likely diagnoses
- Sinding-Larsen-Johansson syndrome: This condition is similar to Osgood-Schlatter disease but affects the patellar tendon at its origin on the inferior pole of the patella. It could potentially cause posterior knee pain if the pain is referred or if there is associated inflammation.
- Popliteal cyst (Baker's cyst): A fluid-filled cyst in the posterior knee can cause pain, especially with extension or flexion. The difficulty achieving the last 20 degrees of flexion due to pain could be related to the mechanical obstruction or inflammation caused by the cyst.
- Medial or lateral meniscus injury: Although less common in this age group, a meniscus injury could cause posterior knee pain, especially if the tear is in the posterior horn of the meniscus.
- Do Not Miss diagnoses
- Tumor (e.g., osteosarcoma, Ewing's sarcoma): Although rare, bone tumors can cause knee pain and should be considered, especially if the pain is persistent, worsening, or accompanied by other systemic symptoms like weight loss or fever.
- Infection (septic arthritis or osteomyelitis): Infections in the knee joint or bone can cause severe pain, redness, and swelling. These conditions are medical emergencies and require prompt diagnosis and treatment.
- Fracture (e.g., tibial tubercle fracture, stress fracture): A fracture could cause posterior knee pain, especially if it involves the posterior aspect of the tibia or fibula.
- Rare diagnoses
- Popliteus tendonitis or strain: Inflammation or strain of the popliteus tendon could cause posterior knee pain, especially with activities that involve twisting or bending.
- Cystic lesions (e.g., ganglion cyst, synovial cyst): These are rare causes of posterior knee pain but could be considered if other diagnoses are ruled out.
- Neurogenic causes (e.g., radiculopathy, peripheral nerve entrapment): Although rare, neurogenic causes could potentially cause posterior knee pain, especially if there is associated numbness, tingling, or weakness.