At HCA UK, we can diagnose your patellar instability and recommend the most effective treatment. 

• Leading orthopaedic consultants with experience of treating patellar instability
• Knee specialist appointments are confirmed within 24 hours
• We're rated 'excellent' or 'very good' by 97% of our orthopaedic patients

What is patella instability?

The patella is the medical name for the kneecap – the bone that protects the knee joint and helps the underlying muscles, tendons and ligaments work correctly. Its correct position is in a V-shaped notch at the end of the femur called the trochlear groove. It slides up or down when you bend or straighten your knee. Patella instability occurs when your kneecap slides laterally outside of the trochlear groove. 

There are three types of patella instability: 

1. Traumatic patella dislocation: The kneecap gets pushed completely out of the trochlear groove, usually because of acute trauma to the knee. 
2. Chronic patella instability: The kneecap undergoes recurring instances of subluxation – a partial movement out of position or dislocation from the trochlear groove. 
3. Complex patella instability: Malformation of the femur and tibia bones places greater stress on the medial patellofemoral ligament (MPFL) and other ligaments, making the kneecap unstable.

Not only does patella instability cause pain and swelling and make it difficult for you to use your knee, but it also increases the risk of knee dislocations, anterior cruciate ligament (ACL) injuries and knee arthritis. 

What causes patella instability?

Anyone can develop patella instability, but women are more prone to the condition as they tend to have more laxity in their ligaments. This means the patella is not held in place as securely and is more likely to move out of the trochlear groove. 

Additionally, people with certain underlying conditions are more at risk of developing patella instability. There are several risk factors for patella instability, including:

• A shallow, uneven or deformed trochlear groove, which doesn't contain and control the patella as effectively. 
• Tight lateral knee ligaments, which can create instability by subjecting the patella to excessive lateral forces.
• Malalignment conditions, such as valgus (knock) knee, which subject the patella to excessive lateral forces that pull it out of the trochlear groove.
• Lax ligaments or extremely flexible joints, which are less effective at restraining the patella and keeping it securely in the trochlear groove. 
• Health conditions that cause loose connective tissue, such as cerebral palsy or Ehlers-Danlos syndrome.
• Weakness of the vastus medialis muscle (part of the quadriceps), which is less able to help restrain the patella from moving laterally.

Traumatic causes of patella instability

You may be at higher risk of suffering a traumatic injury that causes patella instability if you play high-impact sports or other activities that require frequent pivoting, such as football, tennis or dancing. Two main types of traumatic injury can cause patella instability:

• Trauma to the kneecap during a sports injury, fall or another type of incident, which forcibly moves the patella out of the patella groove.
• Non-contact twisting injuries, which occur when the knee is extended and the foot is rotated externally.

Patella instability treatment options

The right treatment will depend on the circumstances and severity of your patella instability, as well as the impact it has on your day-to-day life. You should seek prompt medical attention to put the kneecap back in place if it doesn't return on its own. 

Non-surgical treatments for patella instability

• In the first instance, your consultant will recommend non-surgical treatments for your patella instability. These include rest, painkillers and the use of knee supports, braces or crutches. 
• After giving the knee enough time to heal, you can begin physiotherapy to strengthen the muscles and ligaments that help stop the kneecap from slipping out of its groove. 

Surgery for patella instability

Many people recover from patella instability without the need for surgery. Yet if you have chronic patella instability and non-surgical treatments don't help prevent your kneecap from coming out of its groove, patella stabilisation surgery may be the most effective treatment. 

The exact nature of this surgery will depend on the factors contributing to your patella instability, as well as the extent of the damage your knee joint has sustained. Possible surgeries include: 

• Trochleoplasty: This procedure involves reshaping the trochlear groove so that it controls the patella more effectively. Trochlear dysplasia is the name of the condition in which the trochlear groove is abnormally shaped, having either a flat or dome shape. In either case, it’s too shallow to provide adequate support for the patella, causing it to slip out. Trochleoplasty creates a new groove that is the right shape to properly contain the patella, preventing recurrent subluxations or dislocations.
• Medial patellofemoral ligament (MPFL) reconstruction: The MPFL is a ligament on the inside of the knee that helps stabilise patella in the trochlear groove. MPFL reconstruction involves reconstructing the ligament, either with your own tissue or with that of a donor. It’s usually recommended for people who’ve experienced repeated patella dislocation. Subluxations and dislocations typically stretch or tear the MPFL, making future subluxations and dislocations more likely. Reconstructing the MPFL helps stabilise the kneecap and prevent future subluxations and dislocations from occurring. 
• Knee osteotomy: This is a category of knee realignment surgeries to treat malalignment issues that can cause patella instability. This includes a tibial tuberosity transfer (TTT). The tibial tuberosity is a small bump in the front of the shin bone, the malalignment of which can cause patella instability. A TTT involves removing the tibial tuberosity and reattaching it towards the inside of the knee using screws. This corrects malalignment, allowing the patella to track in a better position and helping prevent subluxations and dislocations. For patients with malalignment conditions of the leg bones such as knock (valgus) knees, a more invasive procedure may be required to reposition the leg bones with the correct angle. Usually performed as a tibial osteotomy, this procedure involves cutting a wedge from the tibia and fixing it in place at the correct angle using metal plates and screws. This helps alleviate the lateral forces on the kneecap that can pull the patella out of the trochlear groove. 

Your consultant might recommend an operation for several reasons besides preventing further instances of subluxation or dislocation, including:

• To remove cartilage that was displaced after a traumatic injury caused your patella instability
• To repair ligaments that were ruptured when your kneecap dislocated
• If a knee arthroscopy could help evaluate the amount of cartilage damage and the degree of instability present
• If you completely dislocate your kneecap

Rest assured that if your consultant recommends surgery for your patella instability, it's because they think it's the most effective treatment possible. They'll explain what it involves and make sure you understand all the risks and benefits, so you can make a fully informed decision.