Extensor Tendon Injuries of the Knee
A 30 year old male presents to the clinic several days after developing acute right knee pain while playing basketball. He states he came down from a rebound and as he was landing he felt a pop in his knee. He was unable to continue playing. On exam, he has a moderate sized joint effusion and tenderness at the insertion of the tibial tubercle. He is unable to actively extend his knee. You obtain radiographs of the affected knee. Which of the following is most likely to be seen on radiographs?
A) Tibial Plateau fracture
B) Patella fracture
C) Patella Alta
D) Patella Baja
The overall prevalence in a british study was 1.37 (QT) and 0.6 (PT) per 100,000 person years (Clayton 2008). QT ruptures are more common in patients older than 40 and typically associated with degenerative tears. They also occur at a rate approximately 6 times more frequently than PT ruptures (Saragaglia 2013). PT ruptures are more commonly seen in patients under 40 years of age and are associated with either direct trauma or some consider it to be the end stage of patellar tendinopathy (Kannus 1991).
Image 1. Illustration of normal, patella baja, patella alta (adopted from braceability.com)
Image 2. Complete tear of quadriceps tendon above the patella shown in long axis. Note the tendon defect and associated hematoma (adopted from radiopaedia.org)
Answer is C, patella alta. This patient has a history and exam highly suspicious for a patellar tendon rupture. When this occurs, the quadriceps tendon has unopposed tension pulling the patella proximal resulting in patella alta on radiographs. Quadriceps tendon has the opposite effect, the unopposed tension of the patella tendon pulls the patella inferiorly resulting in patella baja. The patient may have a patella fracture, however the mechanism is not consistent with this injury and he is not tender along the patella. Tibial plateau fracture is also possible however far less likely given the mechanism and the patients pain would typically be along the medial or lateral plateau with an intact extensor mechanism.
1. Clayton RAE, Court-Brown CM. The epidemiology of musculoskeletal tendinous and ligamentous injuries. Injury. 2008;39:1338–44.
2. Saragaglia, D., A. Pison, and B. Rubens-Duval. “Acute and old ruptures of the extensor apparatus of the knee in adults (excluding knee replacement).” Orthopaedics & Traumatology: Surgery & Research 99.1 (2013): S67-S76.