Patellar tendon rupture, an overall infrequent occurance, is the third most common injury to the extensor mechanism of the knee after patellar fracture and quadriceps rupture. Rupture usually occurs unilaterally as a result of athletic injury in a patient younger than 40 years of age. Typically, an abrupt eccentric contraction of the quadriceps as the athlete lands with the knee flexed and foot planted will tear the tendon at the osseotendinous junction. In the setting of longstanding systemic inflammatory disease, diabetes mellitus, and chronic renal failure, bilateral rupture can occur . Patellar tendon rupture can also be
seen in patients who have had the central third of the tendon used as allograft for repair of the anterior cruciate ligament.
Acute rupture is associated with immediate debilitating pain accompanied by a ''pop'' or tearing sensation with inability to bear weight. Examination reveals swelling/tenderness of the anterior knee, ecchymosis, hemarthrosis, and patella alta (see later discussion for definition) with a palpable gap in the extensor mechanism .
Diagnosis can usually be made by physical exam and radiographs. Contralateral images can be helpful in assessing patellar height. Even if the diagnosis of patellar tendon rupture is clinically obvious, radiographic evaluation is recommended to evaluate for concomitant injury. The classic finding is patella alta on the lateral radiograph. If the diagnosis cannot be made on physical and plain radiographic examination, MRI is the modality of choice and easily demonstrates discontinuity of the tendon fibers, hemorrhage and edema (Fig. 4A) .
Quadriceps tendon injury is more often seen on older individuals. This injury can be difficult to diagnose clinically, and misdiagnoses are common . Complete tear is often the result of repetitive microtrauma. MR is useful in demonstrating partial or complete tears. On MR, a complete tear shows discontinuity of the tendon, hemorrhage, and edema, which is manifested as increased signal on T2-weighted sequences  (Fig. 4B).
Was this article helpful?