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.
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. Other times, a sudden twisting force or trauma can cause the patella to dislocate.
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 following a dislocation include a feeling of a “pop”, swelling, a feeling of instability or knee “buckling” or a change in appearance of the knee.
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 and they are unable to flex or extend the knee, go to the emergency room. To put the kneecap back in place, your doctor may give your child pain medication to relax his or her knee muscles, and then gently apply pressure to move the kneecap back into place. This process is called a "reduction." Your child may be given crutches and put into a knee immobilizer following their dislocation before seeing an orthopedist.
Once they see an orthopedist, our immediate concerns are determining if the patella is in the correct position (not still dislocated), whether or not any other damage has been done in the knee, and restoring motion and strength.
When the patella dislocates, the knee undergoes a significant trauma. The patella almost always dislocates laterally (to the outside of the knee). The restraining ligament on the inside of the knee called the medial patellofemoral ligament (MPFL) almost always tears or is significantly stretched out. When the patella skips out of the groove that is supposed to stabilize it, there is a potential to shear cartilage off the undersurface or even fracture the patella creating a loose piece of bone within the joint. It is also possible to damage other structures in the knee as well. Therefore, at your first office visit with your orthopedic surgeon, they will probably obtain xrays to look at the position of the patella and to see if any fractures exist. Beyond that, an MRI may then be obtained to look at the MPFL and to assess any cartilage or structural damage not able to be seen on the xrays.
Primary treatment for a patella dislocation is conservative care unless other injuries exist (such as a loose body from a fracture within the joint) that require early surgical treatment. Your child will be treated initially with immobilization. Ice, elevation and anti-inflammatories will help to decrease swelling following the dislocation. The less swelling in the knee, the easier range of motion will be. We will try to wean patients off of the crutches, and allow full weightbearing and range of motion exercises as early as possible. Assuming no other damage has been done, we try to get patients into physical therapy early to help regain motion and strengthen the muscles around the knee. Return to sports and activities typically occurs 3 to 6 weeks after injury, sometimes with the aid of a patella stabilizing brace.
Most often, a single time dislocation will not recur. However, because a dislocation often damages knee tissue, the patella often remains looser, or more unstable, than it was before the injury. As a result, the patella may dislocate again. Recurrences also are common if the dislocation was caused by an irregularity in the knee structure. If your child's patella dislocates multiple times, or continues to be unstable despite therapy and bracing, surgery may be recommended to correct the problem. The type of surgery will depend on the cause of the unstable kneecap.
Surgical treatments often involve reconstructing the ligaments that hold the patella in place sometimes with the assistance of an arthroscopy (looking inside the knee with a camera).
Almost all patient’s who experience a patella dislocation will be able to go back to all activities they like to do.