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.
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.
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.
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:
If your child’s patella has slid back into place, you should see your doctor as soon as possible. If your child’s patella is still out of place, go to the emergency room.
During the examination, your doctor will ask you and your child about how the injury occurred and specific symptoms. Your doctor also will evaluate the range of motion, tenderness, and appearance of the knee.
Imaging tests can help your doctor diagnose patellar instability, as well as determine a treatment plan.
Sometimes a piece of bone or cartilage can dislodge or loosen when the patella dislocates. This can be seen on an x-ray or MRI scan.