Mechanism of Injury for Patellar Tendon Rupture
Patellar tendon rupture typically occurs from forceful eccentric contraction of the quadriceps muscle on a partially flexed knee during activities involving sudden deceleration or landing. 1, 2
Classic Injury Pattern
The injury mechanism involves:
- Eccentric quadriceps contraction - The quadriceps muscle contracts forcefully while simultaneously being stretched, typically when the knee is in a flexed position 2
- Sudden deceleration or landing movements - Most commonly occurs during sports-related activities involving jumping, cutting, or rapid changes in direction 1
- Minor trauma in predisposed individuals - The rupture often results from what appears to be relatively minor trauma, as the injury usually represents the end stage of chronic tendon degeneration rather than acute injury to healthy tissue 2
Important Clinical Context
Rupture of a healthy patellar tendon is extremely rare - these injuries almost always occur in tendons that have undergone chronic degenerative changes from repetitive microtrauma and overuse 2. This explains why seemingly minor mechanisms can result in complete rupture.
Age and Activity Distribution
- Most common in men under 40 years of age during sports activities 3, 4
- Indirect, low-velocity injuries peak in the 30-40 year age group 5
- Sports-related activities represent the most frequent cause overall 1
Risk Factors That Lower the Threshold for Injury
The following predispose to rupture from lower-energy mechanisms 2:
- Increasing age
- Repetitive microtrauma and overuse
- Systemic diseases (diabetes, chronic kidney disease, rheumatologic conditions)
- Certain medications (corticosteroids, fluoroquinolones)
- Prior injury to the extensor mechanism
Bilateral Ruptures
Bilateral concurrent patellar tendon ruptures are exceptionally rare (only 19 cases reported as of 2003), but when they occur, the mechanism remains the same: forceful quadriceps contraction on partially flexed knees 1. These cases underscore the importance of underlying tendon pathology, as simultaneous rupture of both tendons from physiologic forces would be impossible in healthy tissue.