Knee > Kneecap Dislocation

What is the Patella?

The kneecap (patella) is a small, triangular bone in the front of your knee that moves and glides up and down along a track (trochlea) at the end of the thighbone (femur). The kneecap gives the front thigh muscles (quadriceps) extra leverage for straightening the leg, and protects the other bones in the knee against collisions and falls. There are several tendons and ligaments, including those attached to the upper leg and lower leg, connected to the kneecap.

The kneecap (patella) is a small, triangular bone in the front of your knee that moves and glides up and down along a track (trochlea) at the end of the thighbone (femur). The kneecap gives the front thigh muscles (quadriceps) extra leverage for straightening the leg, and protects the other bones in the knee against collisions and falls. There are several tendons and ligaments, including those attached to the upper leg and lower leg, connected to the kneecap. A dislocation is when your kneecap is completely off its normal track, and is visibly sitting off to one side. When your kneecap is partially off its normal track, it is called a subluxation.

Kneecap (patellar) dislocations are usually the result of a dramatic event in which sudden contraction of the front thigh muscles (quadriceps) with a partially- flexed and twisted knee causes the kneecap to displace out of its normal track and dislocate to one side. These twisting motions and quick directional changes while running at high speeds often occur in soccer, gymnastics, and basketball. Your kneecap can also be pulled out of its track if your overall knee alignment is off-balance. Physicians call this a biomechanical problem. If your lower extremity biomechanics are abnormal, your knee joint may be malaligned, the muscles attached to your kneecap may pull unevenly on your kneecap and predispose it to subluxating or dislocating to the side. In general, women are at greater risk for dislocating their kneecaps as their kneecaps tend to sit off more to the side than their male counterparts.

There usually are three parts to an orthopedic evaluation: medical history, a physical examination, and tests that your doctor may order.

Your doctor will ask you how and when you injured your knee, how it has been feeling since the injury, and if your knee has been previously injured. Physicians also typically ask if you have any other conditions, have had prior surgery, are taking any medications, or have any allergies to medications. The doctor may also ask about your physical and athletic goals - information that will help him decide what treatment might be best for you in achieving those goals.

A physician can often diagnose a dislocated kneecap by asking you about the details of your accident and examining you. Your physician will examine your knee and focus on the area of tenderness, swelling, and deformity. Since the kneecap is easily palpable and readily visualized, it can quickly be examined. If your kneecap is dislocated, it will displace to the side. Your physician will also ask you to raise your leg and/or extend your knee, possibly after giving you a local anesthetic to eliminate pain, to help determine whether there may be additional injuries in and around your knee. After your kneecap has been moved back to its correct location, your physician may flex and extend you knee.

TESTS

Your physician will obtain X-rays of your knee and may obtain CT or MRI (magnetic resonance imaging) scans if other injuries are suspected.

   X-rays, taken from different angles, are the best way to determine if a kneecap is dislocated and successfully moved back into place (reduced). X-rays are also the best test to screen for additional injuries, including associated fractures.

   MRI may be obtained to see if the kneecap dislocation has caused any damage to soft tissue (i.e. muscle, ligament, tendon, and meniscus) structures. MRI results are usually available in one to two days after the study is performed.

RELATED TOPICS

   Imaging techniques

Kneecap dislocations can damage the joint cartilage under your kneecap, which can eventually cause pain from chondromalacia and arthritis. Recurrent dislocations cause progressive damage to the joint cartilage with increased associated pain and greater instability, which make repeated dislocations more likely. It is important to seek treatment from an orthopedist soon after your first kneecap dislocation. Most people respond well to non-operative treatments and are able to return to their previous activities after a kneecap dislocation. In rare cases, surgery is performed soon after the injury to repair the medical retinaculum, which is torn when the kneecap displaces laterally, or if a fracture or loose body occurs with the dislocation. Surgery is reserved for those cases with recurrent dislocations or severe pain due to chondromalacia or arthritis that have failed non-operative treatment, such as temporary immobilization followed by physical therapy and, if necessary, bracing or taping.