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Knee Extensor Injuries

By Danielle Campagne, MD , Department of Emergency Medicine, University of San Francisco - Fresno

(Quadriceps Tendon Tear; Patellar Tendon Tear; Patellar Fracture; Tibial Tubercle Fracture)

Knee extensor injuries occur when people try to straighten (extend) their knee and an obstacle prevents them from doing so. Such injuries can tear the tendon that attaches the main muscle in the thigh (quadriceps) to the kneecap (patella), tear the tendon that attaches the kneecap to the shinbone (tibia), or break the kneecap or top of the shinbone.

In healthy people, knee extensor injuries occur only when force is significant (as occurs in a jump from a height or in high-impact car crashes). However, people may have certain conditions that make these injuries more likely. These conditions include older age, osteoarthritis, and use of certain drugs (such as corticosteroids or antibiotics called fluoroquinolones). People with one of these conditions can injure their knee when they stumble on stairs or catch their foot when walking.

Extending the Knee

Extending the knee involves several structures, which can be injured when people try to straighten their knee and are blocked from doing so. These injuries include

  • A tear (rupture) in the quadriceps tendon, which attaches the main muscle in the thigh (quadriceps) to the kneecap (patella)

  • A tear in the patellar tendon, which attaches the kneecap to the shinbone (tibia)

  • Fracture of the kneecap or top of the shinbone

Symptoms

If a tendon is completely torn, people cannot stand or extend their knee while seated. The knee is usually painful and swollen. The kneecap may be out of place (displaced), above or below its usual location.

Diagnosis

  • X-rays

  • Magnetic resonance imaging

Doctors take x-rays of the knee. Often, x-rays can show whether a kneecap is displaced or fractured, but x-rays but may appear normal. Magnetic resonance imaging (MRI) is needed to confirm the diagnosis.

Treatment

  • Surgery

Knee extensor injuries are surgically repaired as soon as possible.

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* This is the Consumer Version. *