- Typically occurs in patients <40 years old.
- Lateral X-rays with 30° of knee flexion used to define patella alta in complete tears.
- Outcomes are significantly improved with early surgical intervention.
- If a patent cannot extend their knee it is a marker of a surgical injury: quadriceps tendon rupture, patellar tendon rupture, or patellar fracture.
Evaluating extensor mechanism:
- Check function by asking patient to extend at the knee. Ensure there is a smooth arc motion without extension lag. Extension lag is a delay in the final 15-20° of extension which indicates accessory muscle use. The presence of extension lag indicates loss of normal extensor function.
- If struggling to overcome gravity, patient can be turned on their side to evaluate extensor mechanism function.
Loss of extension of the knee.