What is patellar instability?
The patella (kneecap) attaches to the femur (thigh bone) and tibia (shin bone) by tendons. The patella fits into a groove at the end of the femur (trochlear groove) and slides up and down as the knee bends and straightens. Patellar instability occurs when the kneecap moves outside of this groove.
There are two types of patellar instability. The first is known as a traumatic patellar dislocation. This is most often the result of an injury to the knee. In a patellar dislocation, the patella gets pushed completely out of the groove. The other type of instability is known as chronic patellar instability. In this type, the kneecap usually only slides partly out of the groove. This is known as a subluxation.
What are the signs and symptoms of patellar instability?
Your child may experience pain, swelling, stiffness, difficulty walking on the affected limb, and/or buckling, catching, or locking sensation in the knee. Lastly, there may also be a noticeable deformity in the affected knee.
Most patients experience a sensation that the kneecap has shifted or moved out of place. Usually, the kneecap will move back in on its own but sometimes it will need to be put back in place in the Emergency Room.
With chronic patellar subluxations, the pain may be less severe than in a traumatic injury.
Patients may complain of pain underneath the kneecap, especially with activities that involve deep knee bending.
Patellar Instability Diagnosis
Your provider will most likely make the diagnosis by taking a medical history and performing a physical exam. X-rays will most likely be obtained, but may be normal if the kneecap has already returned to its normal position. An MRI may also be ordered to evaluate possible cartilage damage caused by a traumatic patellar dislocation. However, an MRI is usually not recommended until you have given your knee a chance to heal.
Patellar Instability Treatment
If the kneecap does not go back in place (reduce) on its own, prompt medical attention is necessary to reduce the patella. Initial dislocations are generally managed non-operatively with rest and often a knee brace and crutches. After a period of rest, Physical Therapy is usually begun to strengthen the muscles in the knee that help keep the kneecap from sliding out of the groove.
There are some circumstances in which operative treatment may be warranted. In episodes of acute patellar dislocations, there may be cartilage that is knocked loose and sits in the knee. This is called a loose body and will need to be removed.
If there are ruptured ligaments in the knee, such as the medial patellofemoral ligament, reconstruction of the ligament may be recommended.
If your child has recurrent patellar dislocations (the kneecap continues to come out of the groove) despite non-operative management, he/she may be a candidate for a surgical procedure to re-align the kneecap and put the patella in a better position. One of these procedures can be done arthroscopically. Another “open” procedure involves an osteotomy, which means cutting the bone and moving it to improve patellar tracking (the way the patella moves when you bend and straighten your knee).