The patella can dislocate outside of its normal position, usually round the outside of the knee. It can also partially dislocate, called a subluxation. We explain the symptoms, causes and treatment of patella dislocation.
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.
Dislocation (Subluxation) of the Patella
The patella, or kneecap, is the protective bone which lies in front of the knee joint. The patella bone glides up and down a groove (called the patellofemoral groove) at the front of the thigh bone (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 different (and less severe) to a dislocation of the knee joint.
It is usually a result of an acute blow / twisting action of the knee. In most cases the patella will relocate to the patellofemoral groove on straightening of the knee, however this is known to be extremely painful.
Causes of Patella Dislocation
- Insufficient VMO strength - The VMO (vastus medialis obliquus) functions in maintaining the patella in its desired position within the patellofemoral groove during knee movements by pulling it towards the middle of the knee joint - an action known as 'tracking'. If the muscle is not strong enough, or its fibers are not adequately oriented, the patella is much more susceptible to dislocation.
- Excessive pronation of the feet
- Q-angle - Some people have a larger than normal femoral angle (known as the Q-angle) and may have a 'knock-kneed' appearance (genu valgum). When the person straightens their leg, the patella will be forced to the outside of the knee. Thus any extra force applied to the inside of the knee may result in patellar dislocation.
Treatment of Patella Dislocation
What can the athlete do?
- Apply RICE to the injured knee.
- Immediately seek medical advice.
- Rest from training.
- Try wearing a knee support to help control the movement of the patella.
- Take a glucosamine / joint healing supplement.
- Follow a rehabilitation program.
What can a Sports Injury Professional do?
- Confirm the diagnosis - Patellar dislocations have similar symptoms to an anterior cruciate ligament injury, due to an audible 'crack or 'pop' and the feeling of the knee giving way.
- Reduce the pain by anaesthetic and reposition the patella if it has not already relocated.
- Cryotherapy (ice treatment).
- Exercises to strengthen the VMO.
- Recommend NSAID's e.g. Ibuprofen to reduce pain and inflammation.
- Patellofemoral taping techniques.
- Examine the injury by X-ray and/or arthroscopy to evaluate the extent of the injury.
- Operation may be necessary if there are loose fragments of bone or other major structural damage.