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Knee Extensor Injuries

(Quadriceps Tendon Tear; Patellar Tendon Tear)

By

Danielle Campagne

, MD, University of San Francisco - Fresno

Last full review/revision Oct 2019| Content last modified Oct 2019
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NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
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Topic Resources

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

People with one of these conditions can injure their knee when they stumble on stairs or catch their foot when walking.

Extending the knee involves several structures. The quadriceps tendon attaches the main muscle in the thigh (quadriceps) to the kneecap (patella). The patellar tendon attaches the kneecap to the shinbone (tibia).

In healthy people, the tendons are so strong that the kneecap often fractures before a tendon tears. The quadriceps tendon is injured more often than the patellar tendon, particularly in the older people.

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

Extending the Knee

Symptoms

If a tendon is completely torn, people cannot stand, do a straight leg lift while lying on their back, 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

  • A doctor's evaluation

  • X-rays

  • Magnetic resonance imaging

By examining the knee, doctors may be able to tell which structure is injured. If a person has knee swelling and pain after an injury, doctors ask the person to sit and try to extend the injured leg or to lie on their back and lift their injured leg. If the person cannot extend or lift the leg, a knee extensor mechanism injury is likely.

Doctors also take x-rays of the knee. Often, x-rays can show whether a kneecap is displaced or fractured. For example, x-rays may show a knee cap that is positioned higher than its usual place over the knee joint (called a high-riding or raised patella). This finding suggests that the patellar tendon is torn. However, x-rays may appear normal.

Magnetic resonance imaging (MRI) can confirm the diagnosis.

Treatment

  • Surgery

Knee extensor injuries are surgically repaired as soon as possible.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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