Extensor mechanism injuries (Smarty PANCE)

What structures make up the knee’s extensor mechanism?

Quadriceps tendon, patella, patellar tendon

What is the hallmark clinical sign of extensor mechanism injury?

Inability to perform a straight leg raise or extend the knee

What radiographic sign suggests patellar tendon rupture?

Patella alta (high-riding patella)

- When the patellar tendon ruptures, the kneecap is no longer anchored to the tibia below. This allows the quadriceps muscle to pull the patella upward, resulting in a high-riding patella seen on lateral X-ray.

What radiographic sign suggests quadriceps tendon rupture?

Patella baja (low-riding patella)

A quadriceps tendon rupture disconnects the quadriceps muscle from the top of the patella. Without the upward pull of the quadriceps, the patella is pulled downward by the intact patellar tendon, resulting in a low-riding patella on lateral X-ray.

What age group is most often affected by quadriceps tendon rupture?

Patients over 40 years old

What age group is most often affected by patellar tendon rupture?

Patients under 40 years old

What conditions increase the risk of extensor mechanism injuries?

Chronic renal failure, diabetes, systemic steroid use

What imaging modalities can confirm extensor mechanism injuries?

Plain radiographs, ultrasound, MRI

How are complete extensor mechanism ruptures treated?

Prompt surgical repair

What complication can arise from untreated extensor mechanism injuries?

Extensor lag, permanent weakness, knee stiffness