A kneecap (patella) dislocation happens when your kneecap slips out of its groove at the front of your knee, usually towards the outside. Some people are prone to it because of the shape or alignment of their knee. Others dislocate their kneecap during a sporting injury.
The first priority is to get the kneecap back into place. After that, controlling swelling, getting moving early and physiotherapy are the main steps. A specialist review is worthwhile if there is a lot of swelling, catching or locking, or if the kneecap dislocates again.
At a Glance
- A dislocated kneecap needs to be put back into place promptly, by an experienced clinician or at an emergency department.
- Ice, compression and anti-inflammatory medication can help with swelling, which may take 6–8 weeks to settle.
- Avoid using a straight knee brace for long, and start moving and putting weight on your leg early.
- Physiotherapy to strengthen your thigh and buttock muscles may reduce the chance of another dislocation.
- Significant swelling, locking or repeated dislocations warrant a specialist assessment.
What happens when your kneecap dislocates?
Your kneecap connects the muscles in your thigh to your shin bone (tibia). When it dislocates, people typically describe a sensation of the kneecap popping out to the outside of the knee, with pain.
Because of the muscle spasm that follows, the kneecap sometimes moves back into position by itself. Otherwise, a doctor may need to push it back into place after giving you pain relief.
Why did your kneecap dislocate?
Many factors can make the kneecap more likely to dislocate, including:
- A weak or torn medial patellofemoral ligament (MPFL). The MPFL acts like a check-rein that holds the kneecap in its groove.
- A shallow trochlear groove. The kneecap sits in a V-shaped groove called the trochlea. Some people are born with a shallow groove that does not hold the kneecap well.
- A high-riding kneecap. Some kneecaps sit higher than normal and take longer to engage in the groove as the knee bends, which makes dislocation more likely.
- Knee alignment. Knock knees, or valgus alignment, can make dislocation more likely.
- Rotation of the thigh and shin bones. The way your femur and tibia are rotated can allow the kneecap to dislocate with less force.
- Joint hypermobility. Some people have joints that stretch beyond normal limits, which can make dislocation more frequent.
What should you do straight after a kneecap dislocation?
Getting the kneecap back into place
The priority is to get your kneecap back where it should be. On the sports field, this can be done by an experienced sports physician or physiotherapist. If no suitable health practitioner is available, go to your nearest emergency department.
Checking for a fracture
Depending on the circumstances, your doctor may arrange an X-ray to check for a fracture within the knee.
How is the knee managed after the kneecap is back in place?
Controlling swelling
Because the injury is traumatic, the knee often becomes swollen, and the swelling can take 6–8 weeks to settle. A compression bandage (for example, Tubigrip), ice and anti-inflammatory medication (for example, diclofenac or ibuprofen) can help. Check with your doctor or pharmacist before taking anti-inflammatories.
Getting moving and putting weight on your leg
In the emergency department, you may be given a straight knee brace to keep the knee still and reduce pain. Dr Vishal Pai encourages patients to remove the brace as soon as possible and not to use it for more than five days, because bracing the knee for long periods can cause stiffness.
Early movement helps your recovery. Putting weight through the injured knee is unlikely to damage it further. You may need crutches for one to two weeks, but you can stop using them once you are comfortable.
Physiotherapy
An experienced physiotherapist can guide early range-of-motion and strengthening exercises, which may reduce the chance of another dislocation. Strengthening your quadriceps and buttock muscles helps the kneecap track in its groove. For this to work, keep up the exercises between your physiotherapy sessions. Taping the kneecap can also help it track.
When should you see a knee specialist?
Sometimes, when the kneecap dislocates, a fragment of bone and cartilage breaks off. This loose fragment can float within the knee and restrict movement.
If you have a lot of swelling, new clicking, or locking of the knee, see a knee specialist who is experienced in kneecap (patellofemoral) problems. A knee is locked when a loose fragment is stuck in the joint and stops the knee from straightening properly.
An MRI may be needed to check for cartilage damage and assess the other structures in the knee. Surgery may be needed to remove or fix a loose fragment.
What if your kneecap dislocates more than once?
If your kneecap dislocates repeatedly, it is worth seeing a knee specialist to discuss whether stabilising surgery may suit you. Repeated dislocations can damage the cartilage behind the kneecap, which may increase the risk of arthritis later in life.
There are different procedures to keep the kneecap in place, depending on the cause of the instability. As with any operation, the possible benefits need to be weighed against risks such as infection, stiffness and ongoing pain.
Summary
A dislocated kneecap should be put back into position promptly. Ice, compression and anti-inflammatory medication can help with swelling, and early movement, weight-bearing and physiotherapy support your recovery. Significant swelling, locking or restricted movement warrant an early specialist assessment, and repeated dislocations may need stabilising surgery to reduce the risk of further cartilage damage.
If you would like to discuss how this applies to your knee, you can book a consultation with Dr Vishal Pai.
Had a kneecap dislocation?
Dr Vishal Pai assesses and treats kneecap instability. He can arrange investigations to find the cause of the instability and discuss your treatment options with you.
Written by Dr Vishal Pai
Vishal is an experienced knee surgeon based in Bayside, Melbourne. He consults at Sandringham Orthopaedic Specialists and operates at The Avenue Hospital and Calvary Holmesglen Private Hospital. His practice focuses on sports knee surgery, including ACL reconstruction and meniscal repair, as well as robotic knee replacement.