The patella is the small bone in front of the knee that we commonly refer to as the kneecap. It is almost triangular in shape and is the largest of the seasamoid bones in the human body. Seasamoid bones are the ones embedded in tendons (muscle to bone fibrous attachments) at the spot where these tendons cross over a joint. The patella is embedded in the tendon of the quadriceps muscle at the point where it crosses the front of the knee joint.
The patella serves to protect the front aspect of the knee; it also increases the leverage of the quadriceps tendon, playing an important role in knee extension. During movement at the knee joint, the patella slides up and down in a small groove formed between the two condyles of the femur. Patellar dislocation refers to its partial or complete displacement from its normal path of movement in the groove. It may occur more than once, loose ligaments being a common cause.
Patellar dislocation is not an uncommon condition. It is particularly common among young athletes, especially females. The patella usually displaces to the lateral side and is associated with quite severe pain and often swelling. The patella may be relocated to its normal position in the groove by extending the leg.
In dislocation, the patella shifts laterally and is stuck out of place while in subluxation, the patella slides laterally leaving its normal track.
Patellar dislocation may result from:
- An abnormal twisting movement of the leg: forceful contraction of the quadriceps tendon drags the patella out of the groove.
- Direct impact on the knee, forcing the patella out of its place
- A weak muscle (part of the quadriceps femoris) that is unable to keep the patella stable in its normal position
- An abnormally high location of the patella on the knee
- An increased Q angle (quadriceps angle), which can put extra stress on the knee joint, predisposing it to pain and patellar dislocation (it should be noted that in females the hips are wider and the Q angle is greater compared to males, this accounts for the greater incidence of patellar dislocation in females).
- There is acute pain immediately after the dislocation
- The deformity may be quite obvious
- The pain is usually felt on the inside of the knee and exists until the patella is relocated. The dislocated patella mostly relocates on its own, when the knee is extended.
- Swelling develops rapidly
- Impaired movement at the joint
- There may also be bruising at the site
Clinical examination and plain radiography are helpful tools to reach a definitive diagnosis. X-rays help to locate any bone fractures when there is a history of trauma. CT scan and MRI are great aids to calculate the extent of injury to the associated ligaments and other soft tissues.
Studies have shown no significant difference in the outcomes of both conservative and surgical treatments. Moreover, both treatments require weeks or months of rehabilitation.
Recurrent patellar dislocations require longer to treat properly.
The first line of therapy includes:
- Cessation of any painful activity
- Application of ice packs and compression as well as elevating the affected leg (this helps to control swelling and pain).
- NSAIDs or glucosamine are recommended for pain control.
This is the preferred method of treatment where applicable. Usually, the knee is immobilised for a short time period (7-10 days) using plaster casts or splints. Once the initial pain and swelling subside, rehabilitation can begin.
The joint is gradually mobilised. Physiotherapy includes exercises to strengthen the quadriceps muscle.
In certain scenarios, that is when there is:
- Concurrent injury to the bone or other joint structures
- Repeated patellar dislocations
- The person’s life style and work demands (increased risk of re-injury) surgery is highly recommended.
Surgical treatment involves alteration in the surrounding soft tissue tension to hold the patella in place inside the groove. It is a relatively simple procedure and requires less time to heal. Rehabilitation may start after a week.
There are cases in which it is required to alter the shape of the bone (osteotomy); in which case the healing phase is prolonged to about two to three months.
In recurrent cases, surgical treatment has shown to reduce the risk of patellar dislocation significantly.
Rehabilitation involves exercises to:
- Strengthen the knee muscles, particularly the quadriceps and hamstring.
- Condition the hip muscles.
- Improve the flexibility and range of motion of the leg muscles
- Improve one’s balance by proprioceptive exercises, this helps to coordinate the muscle and joint movements and reduces the risk of injury.