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When it slips out of its groove, this is called patella instability or subluxation. When the kneecap comes all the way out of its groove, it is called a dislocation.

It is usually painful and your knee will be stiff and swollen. If it remains out, it requires early relocation either in the field or in the ED.

An orthopaedic knee specialist will assess for fractures, damaged cartilage, or other injuries with an x-ray and MRI scan. All patients require early physiotherapy and most do not need surgery immediately.

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The kneecap (patella) moves through a groove in the middle of the femur when your knee bends.

When it slips out of its groove, this is called patella instability or subluxation. When the kneecap comes all the way out of its groove, it is called a dislocation.

A dislocated patella is often called a dislocated knee, although a true dislocated knee joint involves the femur bone and tibia bone coming apart. Patella subluxation and dislocation usually affects adolescents and sportspeople with a contact injury.

Kneecap dislocation is common in young people who play sports and is caused by a direct blow to the kneecap. The ligament on the inside of the knee which connects the kneecap (patella) to the thigh bone (femur) is nearly always torn at the time of injury.

Some people have certain features that put them at higher risk for patella instability. This can include over rotation of the hips, knock-kneed posture, in-toeing, a patella sitting higher in the knee than usual, and a shallow groove in the femur. These patients tend to have multiple small instability events rather than one big injury.

You may have heard a pop at the time of injury and/or seen the kneecap sitting over to the outside of the knee. It may have popped back on its own or needed help from a medical professional. The inside of the knee is usually painful and the whole knee can swell. The inside of the knee is likely to stay tender to touch.

The knee will usually feel weak and unstable, and may collapse if you try to walk.

If your kneecap partially or fully comes out many times, the subluxation may not be painful although the progressive cartilage damage can lead to pain. You usually either dislike the sensation or just can’t trust the knee for sports or daily activities.

If you dislocate your kneecap during sport, it is usually diagnosed by the team’s medical staff or physiotherapists. You will usually visit the emergency department for scans and to relocate the kneecap if necessary. They will take x-rays to check for fractures or chunks of cartilage that have bone attached. You will then be put in a non-bending knee brace and given crutches and painkillers.

Seeing an orthopaedic knee specialist or a sports physiotherapist as soon as possible is vital They can ensure there are no other injuries and start the recovery process.

You also need an MRI to check for loose cartilage chunks as they don’t show up in x-rays.

You need a physiotherapist to test your thigh muscle function and make sure it can support your weight before your brace comes off.

We help you to settle your knee down so that it can be used for day to day activities without pain. This involves anti-inflammatories such as ibuprofen, diclofenac or meloxicam for 1 to 2 weeks, which reduces swelling and pain – please check with your doctor or specialist that these medicines are safe for you first. Some compression bandaging can be useful, as can ice packs. 

The next stage is a thorough assessment by a physiotherapist to test the strength and function of your legs – not just in the knees, but your hips and core. Your physiotherapist can then direct your exercise program to target weaknesses, especially in your thigh and hip muscles (quadriceps and gluteal). The exercise program can take 2-3 months to make a difference but it works in most simple patella dislocations.

As your orthopaedic knee specialists, we check the alignment of your legs to see what risk factors you may have. We can then advise you on the risks of this happening again with or without surgery. 

There are a number of different options for surgical treatment of patella instability ranging from arthroscopic cartilage repair, ligament reconstruction and altering the alignment of the leg bones(osteotomy). 

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