Careful examination of the whole extensor mechanism starting with the quadriceps, quadriceps tendon, patella, patellar tendon, and insertion into the tibial tuberosity is necessary.
An injury to the extensor mechanism may have any one of these anatomic components injured and necessitates the careful exam.
Typical signs are swelling, tenderness and limited, or loss of function of the extensor mechanism.
Preservation of active knee extension does not rule out a patellar fracture if the auxiliary extensors of the knee - the medial and lateral parapatellar retinacula - are intact.
If displacement is significant, it is possible to palpate a defect between the fragments, if present. The hemarthrosis is usually obvious.
The examination must include assessment of the soft tissues, so as not to confuse with an injury to the prepatellar bursa, or to omit grading the injury if the fracture is open.
Injury to the patella may disrupt the extensor apparatus of the knee and the patient may be unable to perform an active straight leg raise. Untreated, displaced patellar fractures may lead to marked difficulty with normal gait. If there is clinical uncertainly about the correct diagnosis of disruption of the extensor apparatus of the knee, an ultrasound scan, or MRI, of the extensor apparatus, including the quadriceps tendon and patellar tendon should be obtained, in order to elucidate the correct diagnosis.