The patella (kneecap) is normally resting in a groove at the end of the thighbone (femur). As the knee moves, the patella moves up and down within the groove. Sometimes the patella can shift out of the groove during an injury or sudden movements - this is called subluxation if it partially moves or dislocation if it jumps all the way out.
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. Often the ligament and tissue around the knee cap can stretch or tear and lead to long lasting problems of giving way.
There can be several causes and predisposing factors leading to instability/dislocation:
- A shallow groove/trough in the femur can allow the kneecap to slip sideways
- Abnormal Alignment knee (knock knee)
- Twisting of Thigh Bone of Lower Leg - usually congenital deformity
- Severe Flatfoot deformity
- Poor Muscle Tone to Thigh
- Loose Ligaments -as commonly seen in young girls
- Neurological Muscle Control problems such as cerebral palsy
- Rarely Some children are born with dislocated kneecaps
In children with normal knee structure, patellar dislocations are often the result of an injury or direct blow to the knee. This is more common in sport such as football.
Dislocations can occur with little injury such as the example is that of a soccer player who plants his right foot and suddenly pivots his upper body to the left. causing a twisting injury that forces the kneecap out of position as the patella lags behind.
- Kneecap shift or slide out of the groove
- Buckling or give way
- Hearing a popping sound as kneecap shifts
- Knee may appear misshapen or deformed after inury
- Fear or Apprehension when running or changing direction.
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.
Your physician will obtain a good history about the detail of how, when, why, where the knee injury occurred.
- X-rays - Can show knee structure such as a shallow groove in the femur or a chipped piece of bone in the joint.
- Magnetic resonance imaging (MRI) scans - Can clearly show soft tissue, ligament, tendon, bone and cartilage injury; however, this test is not always required unless there are other concerns of joint injury.
If your child's patella remains dislocated it will need to be placed back into proper position. This is usually done in the Emergency Room.
- Immobilization - A brace can stabilize the patella while the soft tissues heal. A knee immobilizer or Functional Patella Brace may be used.
- Weight bearing - Crutches and Limited Weight Bearing may be necessary to limit pain and allow healing for 1-2 weeks.
- Physical therapy - Once the knee has started to heal, physical therapy can help your child regain normal motion. Specific exercises will strengthen the thigh muscles holding the knee joint in place. Your child's commitment to the exercise program is very important for a successful recovery. Typically, children return to activities 3 to 6 weeks after the injury.
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 ligament that holds the patella in place. Repeated dislocation caused by a congenital or other bone deformity may require a more complex surgical treatment.