Patella (kneecap) instability

Patella instability occurs when the kneecap doesn't rest in the groove at the lower end of the thigh bone (femur) where it should, causing pain and increasing the risk of other knee conditions developing. 

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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.
The London Hip Unit, July 2021

What are the symptoms of patella instability?

Patella instability may arise suddenly and with no warning, or after a sharp blow to the kneecap pops it out of place. Symptoms can include:
  • Pain, stiffness and swelling across the front and side of your knee
  • A sensation of something ‘giving way’ or ‘popping out’, as well as buckling, catching or locking in the knee
  • A visible deformity of the knee due to the kneecap moving out of position
  • Difficulty standing upright, or straightening or walking on the affected leg
  • Cracking or popping sounds in the knee when you bend it
  • There may be a rapid onset of swelling in the first couple of hours after injury
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How is patella instability diagnosed?

Your consultant will view your medical history and perform a physical assessment of your knee. The physical assessment will involve testing your knee's range of motion, which could cause some pain or discomfort. Rest assured that your consultant will only do this gently, to help them gain a more complete understanding of your condition.

You'll likely also need to undergo a MRI or CT scan so your consultant can better evaluate your kneecap and the surrounding ligaments, as well as assess how much damage the cartilage has sustained. With our orthopaedic services at HCA UK, you can get any required imaging on the same day as your consultant appointment, helping reduce the impact on your schedule.

Patella instability puts you at risk of developing other knee conditions, so you should see a consultant even if your kneecap moves back into place on its own. 

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.

Why choose HCA UK

Why choose HCA UK for patella instability treatment?

Specialist care: Our consultants have vast experience of patella instability and kneecap dislocations, so you can count on us to offer you the most effective treatment.

Convenient access: We'll confirm your appointment within 24 hours. You can also get any imaging you need on the same day, minimising the impact on your schedule.

Advanced imaging: Our diagnostic centres use state-of-the-art equipment. Imaging is reported on by expert musculoskeletal radiologists who ensure we get a complete and detailed picture of your knee joint and the surrounding soft tissues.

Outstanding ratings: We have the highest proportion of leading ratings from the Care Quality Commission (CQC) out of all private hospital groups in the UK.

Strict standards: Our knee experts follow the British Orthopaedic Association's (BOA) code of practice and you can check their performance on the National Joint Registry.

Trusted by patients: 96% of our orthopaedic patients said they'd recommend us to their family and friends in our 2022 patient satisfaction survey.

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Book an appointment with a knee specialist

Get in touch with us and have an appointment with a specialist consultant confirmed within 24 hours. We can answer your questions and arrange any imaging or physiotherapy appointments you may require. 

Our Patella (kneecap) instability locations

Institute of Sport Exercise and Health (ISEH)

Institute of Sport Exercise and Health (ISEH)

170 Tottenham Court Road W1T 7HA London
The Harley Street Clinic

The Harley Street Clinic

35 Weymouth Street W1G 8BJ London
The Portland Hospital

The Portland Hospital

205-209 Great Portland Street W1W 5AH London
The Princess Grace Hospital

The Princess Grace Hospital

42-52 Nottingham Place W1U 5NY London
The Lister Hospital

The Lister Hospital

Chelsea Bridge Road, SW1W 8RH London
The Shard Outpatients

The Shard Outpatients

The Shard, 32 St Thomas Street SE1 9BS London

This content is intended for general information only and does not replace the need for personal advice from a qualified health professional.