Patella Dislocation

Your child’s kneecap (patella) is usually right where it should be—resting in a groove at the end of the thighbone (femur). When the knee bends and straightens, the patella moves straight up and down within the groove. Sometimes, the patella slides too far to one side or the other. When this occurs — such as after a hard blow or fall — the patella can completely or partially dislocate.
When the patella slips out of place — whether a partial or complete dislocation — it typically causes pain and loss of function. Even if the patella slips back into place by itself, it will still require treatment to relieve painful symptoms. Be sure to take your child to the doctor for a full examination to identify any damage to the knee joint and surrounding soft tissues.
Cause
There are a several ways in which the kneecap can become unstable or dislocate. In many cases, the patella dislocates with very little force because of an abnormality in the structure of a child’s knee.
A shallow or uneven groove in the femur can make dislocation more likely.
Some children’s ligaments are looser, making their joints extremely flexible and more prone to patellar dislocation. This occurs more often in girls, and the problem may affect both knees.
Children with cerebral palsy and Down syndrome may have kneecaps that dislocate frequently due to imbalance and muscle weakness.
Rarely, children are born with unstable kneecaps causing dislocations at a very early age, often without pain.
In children with normal knee structure, patellar dislocations are often the result of a direct blow or a fall onto the knee. This incidence is more common in high-impact sports, such as football.
Dislocations can occur without contact, as well. A common example is that of a right-handed baseball player who dislocates the right patella while swinging the bat. When the right foot is planted on the ground and the torso rotates during the swing, the patella lags behind, resulting in dislocation.
Symptoms
The symptoms associated with a patellar dislocation depend on how far out of place the patella has moved and how much damage occurred when it happened.
Some general symptoms your child may experience include:
Pain
Feeling the kneecap shift or slide out of the groove
Feeling the knee buckle or give way
Hearing a popping sound when the patella dislocates
Swelling
A change in the knee’s appearance — the knee may appear misshapen or deformed
Apprehension or fear when running or changing direction.