The patella is the small bone located at the front of the knee joint also known as the kneecap. The role of the patella is to protect the knee joint and to enable the quadriceps muscle to work with more strength. At the front of the knee there is a groove (patellofemoral groove) that provides a space for the patella to sit. This groove allows the patella to glide up and down over the knee joint as the knee bends and straightens. The patella is held in position by tendons at its top and bottom surfaces. Ligaments on either side play important role in maintaining the alignment of the patella
Dislocation of the patella occurs where the patella comes out of its normal position in the patellofemoral groove. It usually dislocates towards the outer side of the knee joint.
The main causes of patella dislocation are:
- A sharp blow to the patella
- Sudden change in direction when the foot is planted on the ground such as could occur in high impact sports or dancing
Dislocation of the patella is more likely to occur when there are:
- Weak muscles surrounding the joint
- Abnormalities of the shape of the patella or the patellofemoral groove
The symptoms of patella dislocation are:
- Deformity of the knee – the patella may relocate itself back within the patellofemoral groove or it may remain to the side of the knee joint resulting in visible deformity.
- Pain – particularly on weight-bearing
- Swelling of the knee
- Feeling of instability – feeling that your knee may give way
- Creaking or cracking during movement
Your doctor will ask you about the nature of the injury and examine your knee.
Where the knee is visibly deformed, your doctor will apply gentle pressure to put the patella back in its place. Where the patella is not visibly displaced, an x-ray can provide a clear picture of the patella and the patellofemoral groove.
When a patella dislocation occurs as a result of a sharp blow such as a sporting injury, your doctor may also require an MRI (magnetic resonance imaging) scan to assess any damage to other structures in the knee joint such as cartilage, ligaments or tendons.
Initial treatment involves relocating the patella back within the patellofemoral groove if this did not occur spontaneously at the time of injury. This should only be performed by an experienced health professional.
Initial treatment for patella dislocation once it has been relocated include:
- Rest – avoid placing weight on your knee. Crutches may assist with this
- Ice the affected knee for 20 minutes at a time for the first few days, taking care not to apply ice directly to skin
- Medication to manage pain and inflammation
- Sometimes a brace or splint may be recommended
- Physiotherapy – to strengthen and condition the muscles surrounding the joint
Surgery may be required following a patella dislocation. The injury may have caused damage to other structures such as cartilage, tendons or ligaments within the knee joint that may require surgery to repair. Surgery may also be indicated if there is ongoing instability of the patella resulting in multiple episodes of dislocation. This may be performed arthroscopically or with small incisions.
Dislocation of your patella may be a one off event, however, past dislocations do put you at risk of it occurring again. To prevent further dislocations, physiotherapy is recommended to strengthen the muscles surrounding the knee to help hold the patella firmly in place during movement.