The patella (kneecap) can dislocate outside of its normal position. A dislocated kneecap is not the same as a dislocation of the knee joint.
The kneecap connects the muscles in the front of the thigh to the shinbone (tibia). As you bend or straighten your leg, the kneecap is pulled up or down. The thighbone (femur) has a V-shaped notch (femoral groove) at one end to allow the kneecap to move. Normally, the patella fits perfectly in the groove. But if the groove is uneven or too shallow, the patella could slide off, resulting in a partial or complete dislocation.
A patellar dislocation is usually a result of a sudden blow or twisting action of the knee. In most cases the patella will relocate to the patellofemoral groove when you straighten your knee, however this is usually quite painful. Factors which make a patella dislocation more likely are insufficient quadriceps strength on the inside of the knee, over pronation of the feet and what is known as an increased Q angle of the knee.
Dislocated kneecap symptoms
- Immediate pain
- Swelling in the knee joint
- Knee buckles under weight
- Cracking sounds during movement
- Obvious displacement of the kneecap
To determine whether you have a dislocated patella, your physician will ask you to walk around or straighten and bend your knee. Typically your physician will also feel around your patella and take measurements to determine if the bones are out of alignment or if the thigh muscles are weak. An X-ray may be necessary to see how the kneecap fits in the groove or to eliminate other possible reasons for pain.
Patellar dislocation treatment
If you have a completed dislocated patella, the first step is to return it to the correct place. This is called “reduction” and often times it spontaneously happens before the person is able to seek medical treatment. Sometimes, your physician will apply gentle force to place the patella back in place.
If the patella is only partially dislocated (subluxated), your physician may recommend nonsurgical treatment such as physical therapy and bracing. If your patella repeatedly dislocates, surgery may be necessary to realign the bones or reconstruct the ligaments.
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