Differential Diagnosis for Posterior Knee Pain with Mild Elongation of the Inferior Pole of the Patella
- Single most likely diagnosis:
- Patellar tendonitis or tendinosis (Jumper's knee): This condition is a common cause of posterior knee pain, especially in individuals with a history of jumping sports or activities that involve repetitive knee flexion and extension. The mild elongation of the inferior pole of the patella on X-ray supports this diagnosis, as it may indicate chronic strain on the patellar tendon.
- Other Likely diagnoses:
- Osgood-Schlatter disease: Although typically seen in adolescents, Osgood-Schlatter disease can persist into adulthood. The condition involves inflammation of the patellar tendon at its insertion on the tibial tubercle, which could be related to the patient's history of Sinding-Larsen-Johansson disease (a similar condition affecting the patellar tendon at its origin).
- Quadriceps tendonitis: Inflammation of the quadriceps tendon can cause anterior knee pain but may also refer pain to the posterior aspect of the knee. The history of trauma and the finding of mild elongation of the inferior pole of the patella could be consistent with this diagnosis.
- Do Not Miss diagnoses:
- Rupture of the patellar tendon: Although less likely given the description of "mild elongation," a partial or complete rupture of the patellar tendon is a serious condition that requires prompt diagnosis and treatment to avoid long-term disability.
- Deep vein thrombosis (DVT): Post-traumatic DVT can present with pain and swelling in the affected leg. While the knee pain might not be directly related to the DVT, it's crucial to consider this diagnosis due to its potential severity and the need for urgent anticoagulation therapy.
- Rare diagnoses:
- Sinding-Larsen-Johansson disease reactivation: Although the patient has a history of this condition, reactivation in adulthood is rare. This condition typically affects the inferior pole of the patella in adolescents.
- Patellar apophysitis: Similar to Sinding-Larsen-Johansson disease, this condition involves inflammation of the growth plate at the inferior pole of the patella but is less common in adults.
- Hoffa's fat pad syndrome: Inflammation of the infrapatellar fat pad can cause anterior knee pain but may also refer pain to the posterior knee. This condition is less common and might be considered if other diagnoses are ruled out.