Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Knee Extensor Injuries

(Quadriceps Tendon Tear; Patellar Tendon Tear)

By

Danielle Campagne

, MD, University of California, San Francisco

Last full review/revision Mar 2021| Content last modified Mar 2021
Click here for the Professional Version
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 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 of Knee Extensor Injuries

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 of Knee Extensor Injuries

  • 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 of Knee Extensor Injuries

  • 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
Others also read
Test your knowledge
Fractures of the Jaw and Midface
Fractures to one or more facial structures can result from a single injury. Jaw fractures may occur to the mandible, or lower jaw, or to the maxilla, bone of the upper jaw. Other structures susceptible to fracture include the eye sockets, nose, and cheek bones. Which of the following facial structures is most likely to fracture if a person falls from a great height or hits the windshield of a car face-first during a motor vehicle accident?
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest

Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
TOP