Knee Extensor Mechanism Injuries (Quadriceps Tendon Tear; Patellar Tendon Tear) By Danielle Campagne, MD, University of California, San Francisco Reviewed / Revised Mar 2021 | Modified Sep 2022 View Patient Education Symptoms and Signs Diagnosis Treatment Topic Resources Musculoskeletal System of... Patellar Tendon Tear Patellar Fracture Knee extensor mechanism injuries can involve the quadriceps tendon, patellar tendon, patella, or tibial tubercle.