The patella can dislocate outside of its normal position, usually round the outside of the knee. It can also partially dislocate, called a subluxation.
Symptoms of patella dislocation
Pain will be felt immediately at the time of injury. There is likely to be swelling in the knee joint and there will be an obvious displacement of the kneecap. Often the kneecap may briefly dislocated and then return to its normal position, although pain and swelling will usually be present.
Patella dislocation explained
The patella, or kneecap lies in front of the knee joint. It glides up and down a groove called the patellofemoral groove at the front of the thigh bone or femur as the knee bends. The patella is attached to the quadriceps muscle via the quadriceps tendon and acts to increase the leverage from this muscle group when straightening the knee.
The patella normally lies within the patellofemoral groove and is only designed to slide vertically within it. Dislocation of the patella occurs when the patella moves or is moved to the outside of this groove and onto the bony head of the femur (lateral femoral condyle). The patella may also sublux rather than fully dislocate, meaning it moves partially out of position. A patella dislocation is not the same as a dislocation of the knee joint itself which is a much more severe traumatic injury.
It is usually a result of an acute blow or twisting action of the knee. In most cases the patella will relocate to the patellofemoral groove on straightening of the knee, however this is usually extremely painful. The factors which make a patella dislocation more likely are insufficient quadriceps strength on the inside of the knee, over pronation of the feet and an what is known as an increased Q angle of the knee.
The vastus medialis obliqus muscle or VMO for short is the quad muscle on the inside of the thigh and is responsible for maintaining the stability of the patella towards the inside of the knee. If the VMO muscle is not strong enough, or its fibers are not adequately oriented the patella is much more susceptible to dislocation.
Over pronation of the feet is where the feet roll in or flatted too much when running. This causes the leg to turn inwards which leaves the patella susceptible to moving outwards as the quadriceps contract.
The Q-angle of the knee relates the the angle of the lower leg to the knee and people with an increased Q ankle are often termed knock kneed. When they straighten their leg patella is forced to the outside of the knee potentially resulting in patella dislocation.
Treatment of patella dislocation
What can the athlete do?
Apply RICE principles to the injured knee or rest, ice, compression and elevation. Ice can be applied for 10 to 15 minutes every hour initially reducing to 2 or 3 times a days as swelling and symptoms reduce.
Rest from any sporting activities and seek medical advice. An athlete who has had one episode of patella dislocation is often susceptible to another. A knee support can provide protection for the joint. Patella stabilizing braces have been specifically designed to provide support for the knee cap.
When the acute symptoms settle down a full knee strengthening rehabilitation program is required to help avoid future recurrance. Specifically exercises for the vastus medialis muscle on the inside of the quadriceps are important.
What can a Sports Injury Professional do?
A professional therapist can confirm the diagnosis. Patellar dislocations can sometimes have similar symptoms to an anterior cruciate ligament injury due to an audible crack or pop and the feeling of the knee giving way.
They can help with the pain by prescribing anaesthetic and repositioning the patella if it has not already relocated. NSAID's or anti inflammatory medication such as Ibuprofen may be prescribed to reduce pain, inflammation and swelling.
Patellofemoral taping techniques can provide support for the patella, especially if the patient needs to be mobile and there is a risk or further dislocations. An X-ray and / or arthroscopy will help evaluate the extent of the injury. Surgery may be necessary if there are loose fragments of bone or other major structural damage.