A teenager lands awkwardly during a game, the knee buckles, and the kneecap visibly jumps to the outer side of the knee before slipping back. It is dramatic and painful, and the first question afterwards is always the same: will it happen again? For some people it never does. For others it becomes a recurring problem that steals their confidence in the knee. The difference is mostly about anatomy, and understanding it is the key to stopping the cycle.
What actually happens in a kneecap dislocation
The kneecap (patella) normally glides up and down in a groove at the end of the thigh bone, called the trochlear groove. When it dislocates, it almost always slips towards the outer side of the knee. As it does, it tears the main soft-tissue restraint on the inner side, the medial patellofemoral ligament (MPFL), which is the structure that normally stops the kneecap drifting outwards. Sometimes a flake of bone or cartilage is knocked off as the kneecap relocates, which matters because a loose fragment can need surgery in its own right.
So how likely is it to recur?
This is where honest numbers help. According to a systematic review of children and adolescents indexed on PubMed, the kneecap dislocated again in about 31 percent of knees managed without surgery, compared with about 22 percent of those managed surgically. In other words, after a first dislocation treated with rehabilitation alone, roughly one in three younger patients will have it happen again. The same review found that two anatomical features in particular raise the risk: a shallow or poorly formed trochlear groove (trochlear dysplasia) and skeletal immaturity, meaning the bones are still growing.
Recurrent dislocation in children and adolescents
Systematic review · via PubMed
≈31%
dislocated again after non-surgical (rehabilitation) management
Roughly one in three≈22%
dislocated again after surgical management in the same review
Lower, but not zeroTrochlear dysplasia and skeletal immaturity were linked to higher recurrence risk.
Why some kneecaps keep slipping out
Recurrence is rarely bad luck. It usually reflects how the knee is built. The common reasons a kneecap is unstable include:
Anatomy that predisposes to recurrence
- A shallow trochlear groove (trochlear dysplasia), so the kneecap has no deep track to sit in.
- A high-riding kneecap (patella alta) that sits above the groove for longer.
- A kneecap that tracks too far outward, often measured on a scan.
- Loose ligaments or generalised flexibility, and rotational alignment of the limb.
- A previously torn MPFL that has healed loose, leaving less restraint than before.
When several of these are present, especially in a young, active person, the kneecap has little holding it in place, and each dislocation makes the next one easier. That is the cycle we want to break.
Every time a kneecap dislocates, it can damage the cartilage. Stopping recurrent instability is not just about comfort and confidence; it is about protecting the joint for the decades ahead.
How we stop it
For a first dislocation, the answer is usually not surgery. We protect the knee briefly, control swelling, and then focus on physiotherapy to rebuild the quadriceps and hip muscles, restore control, and retrain the knee. Many people never dislocate again. Where a loose fragment of bone or cartilage has broken off, that may need arthroscopic treatment regardless.
When the kneecap keeps dislocating despite good rehabilitation, surgery shifts the odds firmly in your favour. The most common procedure reconstructs the torn MPFL with a graft to re-establish the inner restraint. If the bony alignment is a major driver, that may be corrected at the same time, for example by adjusting where the kneecap tendon attaches. The right combination depends entirely on your anatomy, which is why imaging and a careful assessment come first. You can read more about keyhole knee procedures on the knee arthroscopy page.
What I would tell a worried parent or athlete
A single kneecap dislocation is common and often a one-off, so do not assume the worst after the first event. Commit to the rehabilitation, because it genuinely reduces the chance of recurrence. But if the kneecap starts going out repeatedly, do not keep pushing through it. Each dislocation risks the cartilage, and at that point a proper assessment of why your knee is unstable, and a targeted operation to fix it, is the way to protect the joint and get your confidence back.
