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Patellar Instability

The patella (kneecap) sits on the anterior (front) aspect of the knee and articulates with the trochlea groove on the femur (thigh bone).  The patella tracks up and down the groove when the knee bends.

The patella is joined to the quadriceps tendon above and the patella tendon below, which then inserts in to the tibia, the larger of the lower leg bones.  Its function is to extend the lever arm of the quadriceps muscle, increasing its effective strength.

Patellar instability

Patellar instability occurs when the patella does not remain in its groove, resulting in a partial or complete dislocation.

Pain from the patella and patellofemoral joint are often categorised as Anterior Knee Pain


Instability can occur after an accident or trauma to the knee and is a relatively common injury in contact sports. Injuries to the knee are often complex, involving several structures.  It is important to have the knee fully assessed to ensure that any damage is identified. Imaging can include Xrays to assess the bones and ultrasound or MRI to view the soft tissues including tendons, ligaments, the joint capsule and the meniscii.

Following a dislocation of the patella which hasn’t involved any other structures, rest and physiotherapy can be sufficient to prevent further problems.

If other structures have been involved, dislocations keep occurring or if the knee remains painful, then surgery may be required.  Detailed imaging of the knee can show injury to the tendons and/or other structures which may require surgical repair.

Congenital / development instability

The exact shape and size of the patella and the trochlea groove on the femur can effect patella stability.  If the groove which the patella articulates with is shallow or does not match the shape of the patella, the patella can be prone to partial or full dislocations.

The patella can be pulled to the side, away from the correct location, either through tightness in the surrounding tissues or through the quadriceps tendon inserting too close to the side of the patella.  These problems can also lead to instability.

Treatment for patellar instability

If the patella is being pulled to the side, physiotherapy can sometimes be enough to relieve the pressure on the tendon.

If a course of physiotherapy is not suitable, does not relieve pain or prevent further instability, surgery may be required.  This can involve the release of tissues to relieve tension and allow the patella to move back to the correct position.

In severe cases involving the shape of the bones and recurrent dislocations, surgery to the patella or femur may be required.  This can involve changing the shape and resurfacing the joint surfaces.

Your Consultant will discuss the most suitable treatment plan for your individual condition.

Knee Clinic

The Knee Unit at St John & St Elizabeth Hospital comprises a dedicated team specialising in the diagnosis and treatment of knee pain and stiffness caused by knee conditions or injuries.

A patient speaking to a receptionist

Patient information

Our Hospital is renowned for providing exemplary levels of care across more than 90 services. From orthopaedics, to urology, our private GP practice and Urgent Care Clinic, our services are led by some of London’s leading Consultants. For more information, and to find a service suitable for your care, find out more about the services that we offer.

Make an enquiry

If you have any questions relating to treatment options or pricing information, get in touch with us by filling out one of our contact boxes or giving us a call on 020 7432 8328.

Our Appointments Team have a dedicated and caring approach to finding you the earliest appointment possible with the best specialist.

If you are self-paying you don’t need a referral from your GP for a consultation. You can simply refer yourself* and book an appointment.

If you have health insurance (e.g. Bupa, Axa Health, Aviva), you will need to contact your insurer to get authorisation before any treatment, and in most cases you will also require a referral letter from your GP.

If you are not registered with a GP, we have an in-house private GP practice you can use. Alternatively, we can suggest the most appropriate course of action for you to take, given your location and individual circumstances.

*Please note – for investigations such as X-rays and MRIs, a referral will be required. However, we may be able to arrange this for you through our on-site private GP.

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