Kneecap (patellar) instability

The kneecap (patella) glides in a groove at the end of the thigh bone. In some people it slips partly or completely out of the groove, known as subluxation or dislocation. It’s most common in teenagers and young adults.

Why it happens

A first dislocation can follow a twisting injury. Some people have features that make instability more likely, such as a shallow groove, a high-riding kneecap, or looser ligaments. The main ligament holding the kneecap in place, the medial patellofemoral ligament (MPFL), is usually torn when the kneecap dislocates.

Symptoms

• The kneecap visibly moving out of place
• Pain and swelling after an episode
• Feeling that the kneecap is about to slip, especially when twisting
• Avoiding sport or activities through lack of confidence

Treatment

After a first dislocation, most people are treated with physiotherapy to strengthen the muscles that control the kneecap. An MRI scan checks for damage to the cartilage; a loose fragment may need early surgery.

If the kneecap keeps dislocating, surgery can stabilise it. Options include:

• MPFL reconstruction: a new ligament is created using a tendon graft to hold the kneecap in place
• Tibial tubercle osteotomy: the bony attachment of the kneecap tendon is moved to improve its alignment
• Other procedures for specific anatomy, which I’ll explain if they apply to you

The operation is planned around your own anatomy, using your scans.

Recovery

0 to 2 weeks	Crutches and early movement
2 to 6 weeks	Walking normally, physiotherapy to regain movement and strength
3 months	Running
6 to 9 months	Return to sport

Recovery is longer if a bone realignment is also needed.

Risks

Include infection, blood clots, stiffness, recurrent instability and, with osteotomy, delayed bone healing.

Frequently asked questions

I’m a parent. Should my teenager have surgery?

Most young people are treated first with physiotherapy. Surgery is considered for recurrent dislocations or specific injuries. Growth plates are taken into account when planning.