What is Patellofemoral Instability (Unstable kneecap)?
The patella (kneecap) is the bone that sits in front of your knee that helps to connect the thigh muscles to the shin bone (tibia). The patella sits within a groove in the femur or thigh bone. The patella is a round structure in the front part of your knee and has a V shaped undersurface. This normally tracks in the thigh bone groove, which also is V shaped, as your knee bends and straightens. The patella will move up or down in the groove during these motions.
Mechanism of Injury:
The patella can become unstable which means the patella dislocates (moves out of normal position) out of this groove. This can result from a traumatic injury like a fall or a football player being hit on the knee cap by another player or commonly a twisting type of injury. Some people are just born with anatomic factors that predispose them or make their knee cap unstable.
Diagnosis and Symptoms:
An acute dislocation of the patella usually is painful and causes a person to fall to the ground with the knee in a bent position. The patella can self-reduce, which means that it can go back in place on its own. Sometimes, a person will need to go to the emergency department to have the patella put back in proper position. Regardless, this is considered an emergency and the patella should be reduced back in place immediately to prevent permanent damage to the cartilage under the kneecap. In a chronically unstable patella, the person usually has less pain when the patella comes out of place and has experience putting the patella back in normal position by themselves. An unstable kneecap does cause apprehension when doing certain activities and often prohibits people from living normal active lifestyles.
The unstable patella should be evaluated by a physician and one that deals particularly with this complex issue. X-rays should be performed at the initial visit to rule out fractures and to evaluate the bone structures of the knee. Advanced imaging (CT scan and MRI) is often beneficial to fully delineate the problem and determine the likelihood of recurrent dislocations.
Treatment for Patellar Instability:
Initial treatment should be relocating or getting the patella back in place. Bracing, ice, elevation and anti-inflammatories are often prescribed initially. As the swelling and pain subside, Physical Therapy is often introduced to begin moving the knee and starting to activate the quadriceps (thigh) muscle. Activities can be progressed as symptoms improve. Non-operative or no surgery is often attempted with initial dislocations. If the patella continues to be unstable and this is affecting the quality of life due to fears of recurrent dislocations, then surgery can be considered. Surgery is sometimes required in the acute phases as well if there are fractures (broken bones), displacement of the cartilage of the patella, or there is substantial evidence that recurrent or continued dislocation is highly likely. The goal of surgery is to prevent further damage to the cartilage under the kneecap and make the knee cap stable by preventing it from moving out of place. Surgery can entail replacing ligaments around the knee cap, tightening the structures around the knee cap and sometimes cutting or transferring the bone, to prevent recurrence. Surgical stabilization is often effective to prevent future recurrence and further damage to the cartilage of the knee.
For more information, please consider the following link that was produced by the AAOS.
https://orthoinfo.aaos.org/en/diseases–conditions/unstable-kneecap