Kneecap Dislocation Surgery: Who Needs It and What Gets Fixed

A kneecap that pops out of place is frightening. The knee buckles, the kneecap sits visibly off to the side, and the next few minutes are a blur of pain until it slides back. For some people that is a one-time event. For others the knee never feels trustworthy again, and a second and third dislocation follow.

This guide is for people facing that second group of decisions. It covers why kneecaps dislocate, what first-line treatment looks like, which situations push surgeons toward operating, and how to prepare questions for a surgeon who has examined your knee. It is educational material, not medical advice.

How the kneecap is supposed to stay in place

The kneecap, or patella, links the big muscles at the front of the thigh to the shinbone. As the knee bends and straightens, the kneecap glides in a V-shaped groove at the end of the thighbone called the trochlea. Ligaments, muscles and the shape of the bone all work together to keep it tracking in that groove (AAOS OrthoInfo, accessed 2026).

One ligament gets particular attention: the medial patellofemoral ligament, or MPFL. It runs from the inner side of the kneecap to the thighbone and limits how far the kneecap can slide toward the outside of the knee. It is commonly damaged when the kneecap dislocates.

What makes some knees more likely to dislocate

Dislocations often happen without contact, from a pivot, a twist or an awkward landing. A direct blow can do it too. But anatomy decides a great deal about who dislocates and who does it again. AAOS lists several features that raise the risk:

• An injured or torn MPFL.
• A trochlear groove that is too shallow or flat to hold the kneecap well.
• Knock-kneed alignment of the leg.
• Abnormal rotation of the thighbone or shinbone.
• A patellar tendon that attaches too far toward the outside of the shinbone, pulling the kneecap outward.

This list explains why kneecap surgery is not one operation. A surgeon first works out which of these factors apply to you, then chooses a procedure, or a combination, that addresses them.

Recognizing recurrent instability

Recurrent patellar instability means the kneecap dislocates again and again, often with pain. Symptoms that bring people to a surgeon include:

• Apprehension: a sense that the kneecap is about to slide out, often with cutting, twisting or stairs.
• Repeat dislocations, sometimes from smaller and smaller movements.
• Pain and swelling from damage to the cartilage on the back of the kneecap or the end of the thighbone.

That last point is an important part of the decision. AAOS notes that dislocations often injure the cartilage under the kneecap and at the end of the thighbone, which can cause ongoing pain and arthritis, and that recurrent instability may increase the risk of cartilage injury. Each dislocation is therefore not just an inconvenience; it is a potential hit to the joint surface.

The workup

The exam often starts with watching you walk and bend your knee, then feeling around the kneecap, measuring the alignment of your leg and testing thigh strength. Imaging usually follows:

Test	Why it is ordered
X-rays	Usually the first image; shows bone shape and position of the kneecap
MRI	Looks for loose fragments of bone or cartilage and assesses the ligaments
CT	Ordered when limb alignment or rotation is a concern

A loose fragment of cartilage or bone floating in the joint can change the timeline. It may be a reason to operate sooner, even after a first dislocation, so make sure you understand what your MRI shows.

First-time dislocation: rehab is the usual route

When a kneecap is fully out, it has to be put back into the groove. Sometimes it slips back by itself; sometimes it needs a gentle push from a clinician, a step called reduction.

After that, AAOS recommends nonsurgical treatment for most first-time dislocations. The program centers on strengthening, often includes cycling, may use a stabilizing brace, and builds back toward full sport gradually. The stated aim is a return to normal activity in about 1 to 3 months. Nonsurgical care for a first dislocation often goes well and has a relatively low recurrence rate, although some patients are at higher risk.

Ask your surgeon directly whether your knee has features that put you in that higher-risk group. The answer shapes whether "rehab first" is a reasonable trial or a likely detour.

When surgery is recommended

AAOS describes surgery as typically reserved for three situations:

1. Very high-risk first dislocations, where anatomy or associated damage makes another dislocation likely.
2. Recurrent instability, the most common reason.
3. Maltracking, where the kneecap is severely misaligned as the knee moves.

What the operations aim to correct

Kneecap stabilization procedures fall into three broad goals, per AAOS. Your surgeon may use one or combine several, based on your exam and imaging.

Rebalancing the soft tissues

These procedures reinforce and balance the soft tissues that hold the kneecap toward the inner side of the knee. Because the MPFL is so often torn, restoring that restraint is a common part of the plan. Ask your surgeon whether they would repair or reconstruct it, and if a graft is used, where it would come from.

Correcting bony alignment

When the patellar tendon attaches too far to the outside, or the leg alignment is pulling the kneecap off course, the surgeon may correct the alignment of bone. Bone procedures generally involve a different recovery from soft-tissue work, because bone needs time to heal.

Reshaping the groove

For a trochlea that is too shallow to hold the kneecap, surgeons can reshape the groove itself. This is more specialized surgery, and it is reasonable to ask how often your surgeon performs it.

Cartilage damage found at the time of surgery may also be treated in the same operation. If your MRI already shows a cartilage defect, ask whether it will be addressed and how that changes your rehab.

Outcomes and honest expectations

AAOS describes surgical results for recurrent instability as very good, with a re-dislocation rate of less than 10% after surgery. That figure is a general one. Your own odds depend on which risk factors you have and how well they were corrected.

Stabilizing the kneecap prevents further dislocations; it cannot undo cartilage damage that has already happened. If you have had many dislocations, discuss whether you may still have some kneecap pain even with a stable knee.

Recovery planning

Recovery depends heavily on which procedures were done. A soft-tissue reconstruction alone and a reconstruction combined with a bone realignment are different journeys in terms of bracing, crutches and how quickly you can bend the knee. Get your surgeon's protocol in writing, and use it to plan:

• Time off school, work or sport, and whether you can manage stairs at home.
• Crutches and any brace that needs to be fitted before surgery.
• Physical therapy appointments starting soon after surgery.
• Driving restrictions, especially if the operated leg is your right leg.
• Criteria, not just dates, for returning to cutting and pivoting sports.

Younger patients

If the patient is a teenager who is still growing, ask how open growth plates affect which procedures are possible and whether any part of the surgery should wait until growth is complete.

Living with an unstable kneecap while you decide

The time between a dislocation and a decision about surgery can be anxious, especially for athletes and parents of teenage athletes. A few practical steps help:

• Do the rehab properly even if surgery is likely. Strong thigh and hip muscles help control the kneecap now and make recovery after surgery easier.
• Use the brace as prescribed for activities your therapist or surgeon has approved, rather than as a ticket to return to cutting sports early.
• Note every episode. Write down each time the kneecap slips or fully dislocates, what you were doing and how long the swelling lasted. That record helps your surgeon judge your risk.
• Get any new swelling checked. A large swelling after a new episode can mean fresh cartilage damage, which may change the timing of surgery.

For parents

If your child has had more than one dislocation, ask the surgeon to explain in plain terms which anatomic factors they see on the imaging and how growth affects the options. It is reasonable to ask for a second opinion before major bone surgery on a young knee.

Questions to ask your surgeon

• Which of the anatomic risk factors do I have?
• Is there a loose fragment or cartilage injury that changes the urgency?
• Which procedure or combination of procedures do you recommend, and why?
• Will bone be cut or moved, and how does that change my recovery?
• What brace, crutch and therapy plan should I expect?
• How will we know when I am ready for sport?

Frequently asked questions

My kneecap went back in on its own. Do I still need to see a doctor?

Yes. Even when the kneecap slides back by itself, the dislocation can damage the MPFL and the cartilage behind the kneecap or at the end of the thighbone. An exam, and often X-rays or an MRI, can show whether there is a loose fragment or other injury that changes treatment.

Why is rehab recommended first after a first dislocation?

AAOS recommends nonsurgical treatment for most first-time dislocations because it often has good results and a relatively low recurrence rate. Strengthening, cycling, bracing and a graded return to sport aim to get people back to normal activity in about 1 to 3 months.

What is the MPFL and why does it matter?

The medial patellofemoral ligament runs from the inner edge of the kneecap to the thighbone and limits how far the kneecap can move toward the outside of the knee. It is commonly injured in dislocations, and restoring it is a frequent part of stabilization surgery.

How likely is the kneecap to dislocate again after surgery?

AAOS describes surgical outcomes for recurrent instability as very good, with a re-dislocation rate of less than 10%. Your personal risk depends on your anatomy and which factors your surgery corrected.

Can stabilization surgery stop kneecap arthritis?

It can reduce further dislocations, which matters because repeated dislocations can injure cartilage. It cannot reverse cartilage damage that has already occurred, so some people still have kneecap pain after a successful stabilization.