You planted your foot, turned, and your kneecap shot out to the side of your knee. Maybe it slid back in as soon as you straightened your leg. Maybe someone in the emergency department put it back for you. Either way, the knee has swollen up, it's tender along the inner edge of the kneecap, and the question on your mind is whether it's going to happen again. If this is your teenager's knee, you're in very familiar territory: most of these injuries happen to active 10- to 17-year-olds 1.
Your kneecap (the patella) sits in a shallow groove at the lower end of your thigh bone and glides up and down in it as your knee bends. On its inner side sits the medial patellofemoral ligament, or MPFL, one of the soft tissues that keep it in that groove.
The typical dislocation happens when your foot is firmly planted, your knee is pushed inwards and your thigh bone rotates inwards over the top of it. The kneecap is left behind and slips out to the side 1. In real life that looks like a netball landing, a pivot at footy training, or a slip that twists the knee. When the kneecap goes, the MPFL is injured 3. The kneecap can also scrape the joint's cartilage, or break off a small piece of bone and cartilage (an osteochondral fracture) from either the kneecap or the thigh bone 1.
Why do some knees dislocate and others don't? A few things make it more likely: an MPFL that's already been damaged, a kneecap that's unusually shaped or positioned, a shallow groove, or loose, hypermobile joints 1. Growth plates that are still open and generally flexible ligaments add to the risk. So do some things physiotherapy can work on, such as an underdeveloped inner quadriceps muscle (the VMO) or outer thigh muscles that overpower it 2.
Whether girls and women are more affected is disputed. One Australian guideline finds no clear difference between the sexes 1. Another guideline and a Cochrane review suggest it's more common in females 2,3, possibly because of limb alignment and looser joints 4.
Plenty of people arrive with a swollen, painful knee and nothing visibly out of place, because the kneecap popped back in by itself 1. A twist, a sense that something shifted, then fast swelling is also the classic story of an ACL injury. The overlap is real: a patellar dislocation is the second most common cause of bleeding into the knee joint, behind only ACL injury 1.
Some things point towards the kneecap. You may have seen it sitting out to the side, with the front of the knee looking flat and a bulge on the outer edge. The knee usually stays bent while the kneecap is still out. Afterwards, there's tenderness along the inner border of the kneecap 1.
Neither injury rules out the other, and the other ligaments need checking once the kneecap is back in place 1. That's a job for a hands-on examination, not guesswork.
Often the kneecap is already back in place by the time anyone examines the knee, so the diagnosis comes from your story, a hands-on examination and imaging together 1 2. The story that fits is a twist, a knee that looked out of shape, then one that corrected itself 1. On examination the clinician may gently glide the kneecap outwards. This is the apprehension test. A kneecap that moves a long way suggests the soft tissues on its inner side aren't holding it properly 2.
X-rays are taken from three angles once the kneecap is back in. They aren't really there to check its position. They're looking for small chips of bone, because even a small one can mean a larger piece of cartilage has come away 1.
The first days usually happen elsewhere: emergency or your GP, X-rays, a brace and an MRI. Our part begins after that. For a first dislocation with no bone or cartilage damage, the guideline pathway is physiotherapy once the brace comes off. The program focuses on getting movement back, building strength (particularly the VMO), and retraining balance and joint position sense, known as proprioception 1.
The two Australian guidelines disagree on this. One recommends about three weeks in a brace locked straight 1. The more recent physiotherapy guideline says no longer than two weeks, and that "there is no evidence to support bracing beyond this period" 2. The doctor managing your injury sets this, and we work to their plan.
Longer term, a brace that blocks the kneecap from moving outwards can replace taping 2. The guideline lists it as an option but doesn't measure how much it reduces re-dislocation. So we use it for support as you return to sport, never as a substitute for strength.
Hands-on techniques can help ease stiffness once the brace comes off. None of the evidence we've drawn on tests manual therapy specifically for patellar dislocation. That makes it an extra at most, not the main treatment.
An operation is needed when the MRI shows a significant loose piece of cartilage or bone 1. Reconstructing the torn soft tissues straight after a first dislocation usually isn't needed, as it doesn't appear to change the long-term outcome 1. For surgery versus non-surgical care more broadly, the evidence is unsettled. A 2023 review of 10 trials found that surgery might mean fewer repeat dislocations. But all of the evidence was very low certainty, it was unclear whether surgery improved knee function, and satisfaction was similar either way 3. That decision belongs to you and an orthopaedic surgeon.
After a kneecap dislocation, rehabilitation follows The Well Motion Recovery Path™. Your knee earns each step up by passing tests, whatever the date.
How long it usually takes. A panel of specialists who treat adolescents put return to sport at 2 to 4 months after a first dislocation. Only 68% of them agreed, and it is expert opinion, not measured outcomes 7. At six months the injured leg is commonly still about 80% as strong as the other 2. If you need surgery, your surgeon's protocol sets the timeline.
The best exercise program after a dislocation is still unknown 6. What has been measured is who dislocates again:
None of this means the worst has happened. Most of the time it means getting the right information early, so your rehabilitation is built on it.
We start by listening: how it began, what makes it worse, and what it's stopping you from doing. Then we examine the area, explain what we find in plain English, and agree a plan with you. Your first visit is 40 minutes at Engadine and 30 minutes at our other clinics.
We see patients at Engadine, Mount Annan, Narellan and Appin, and at home through our mobile physiotherapy service. If you have private health cover, here's how health fund rebates work for physiotherapy.
First the kneecap is put back, usually by gently straightening the knee with pressure on the side of the kneecap 1. Then comes a short period in a brace, an MRI to check for bone or cartilage damage, and a physiotherapy program for movement, strength and balance 1,2. Surgery is kept for loose fragments or repeated dislocations 1,2.
More serious than it often feels once the kneecap is back in. Bone or cartilage fractures occur in 25 to 75% of cases 1. After the first dislocation, a knee is seven times more likely to dislocate again 2.
Many people do, but an honest answer includes the risks. Over a third of people end up with recurrent instability. The children's hospital guideline also reports that nearly half never return to sport because the knee keeps feeling unstable 1. Ongoing pain and early wear behind the kneecap are reported too 2. That's the case for criteria-based rehabilitation: progressing on measured strength, balance and hop tests rather than the calendar 2.
Don't force it back yourself. Call us if it's still out. If it has gone back in, book an assessment with us within three days; an MRI within about seven days is recommended 1.
They're different injuries rather than better or worse versions of one another. A dislocated kneecap injures the MPFL 3 and can damage the cartilage 1. An ACL injury involves a different ligament. Both commonly cause bleeding into the knee 1, and a proper examination is how you find out which one you're dealing with.
A twist or sudden change of direction, often with a pop at the time, and a knee that hasn't felt trustworthy since.
Read morePain on the outside of the knee that builds through a run, settles with rest, then comes straight back on the next one.
Read moreAn ache at the front, around or behind the kneecap. Worse on stairs, on hills, and after long sitting.
Read moreCatching, locking or swelling after a twist, sometimes with a knee that won't fully straighten.
Read moreA tender, bony lump just below the kneecap in a growing, sporty teenager.
Read moreMorning stiffness and an ache after activity, building over years rather than days.
Read moreThe MCL runs down the inside of your knee. Most injuries happen when something hits the outside of the knee and forces it inwards; it's the ligament most commonly injured in knee trauma.
Read moreA bursa is a small fluid-filled sac that cushions bone from the soft tissue around it. The prepatellar bursa sits at the front of your knee, over the kneecap. When it's irritated it swells, and a tender, warm swelling right over the bursa is the classic sign.
Read morePatellar tendinopathy, often called jumper's knee or patellar tendonitis, is pain in the tendon just below your kneecap that builds when the tendon is overloaded.
Read moreA Baker's cyst is a build-up of fluid behind the knee, usually excess fluid from the knee joint itself.
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