A patellar dislocation is the kneecap coming out of the groove it normally runs in, almost always slipping toward the outside of the knee. Instability is what it becomes when that keeps happening — or when the kneecap never fully dislocates but no longer feels trustworthy. They are the same problem at different points on one line, which is why they belong on one page.
The distinction worth understanding at the outset: a first dislocation is an injury. Recurrent instability is usually anatomy. Treating the second like the first is the commonest way this goes wrong.
What actually happens
Most dislocations are not a direct blow. They happen on a twist — planting the foot and turning, landing awkwardly, a sudden change of direction — with the kneecap driven sideways out of its groove. Many go back in on their own the moment the knee straightens, which is why some people arrive describing only that the knee "gave way and swelled up."
The structure that tears is the medial patellofemoral ligament, a band on the inner side of the knee that acts as the check-rein stopping the kneecap travelling outward. It is torn in the large majority of first-time dislocations.
Two other things commonly happen at the same time, and both matter:
- Cartilage injury. As the kneecap goes out and comes back, the surface on its underside and the outer edge of the groove strike each other. Bruising is usual; a sheared-off fragment of cartilage or bone is not rare.
- A tense, immediate swelling — blood in the joint within hours rather than a gradual puffiness over a day. That timing is a useful clue that something structural happened.
A loose fragment is the finding that changes everything about the plan, because it is one of the clearest reasons to operate early rather than rehabilitate and see.
Why some knees keep doing it
This is the part that generic patient information tends to skip, and it is the part that predicts what happens next.
Some knees are simply built in a way that makes the kneecap harder to hold in place:
- A shallow groove for the kneecap to sit in. A deep groove is a wall; a flat one is a ramp.
- A high-riding kneecap that sits above the deepest, most secure part of the groove for the first part of bending.
- A tendon attachment sitting too far to the outside on the shin bone, so the pull on the kneecap has a constant outward component.
- Knock-kneed alignment, or rotation in the thigh or shin bone.
- Generalised ligament laxity — people who are simply more flexible everywhere.
Recurrence is substantially more likely in younger patients, particularly adolescents, and in anyone carrying several of those features. Someone who has dislocated more than once has already demonstrated the tendency.
Rehabilitation can compensate for a great deal of this. It cannot deepen a groove or move a bony attachment. Being clear about that distinction early saves people from a second and third episode spent proving it.
How the knee is assessed here
The examination looks at how the kneecap tracks as the knee bends and straightens, whether pushing it outward produces genuine apprehension, how much sideways travel it has compared with the other side, the alignment of the whole limb standing, and whether the patient is generally hypermobile.
Imaging is used to answer specific questions, not as a formality. X-rays include a dedicated view down the groove — the standard two views of a knee show this compartment poorly, which is a recurring theme in kneecap problems. An MRI shows the torn ligament, reveals cartilage damage or a loose fragment, and allows the underlying anatomy to be measured rather than estimated.
Ultrasound is used in the room for the soft tissues and for any guided injection, with the needle visible throughout rather than placed by feel.
Treating a first dislocation
For a first episode in a knee without a loose fragment, the answer is usually not surgery.
A short period of protection to let the acute injury settle, then structured rehabilitation — quadriceps, and just as importantly the hip muscles that control the position of the thigh under the pelvis. A knee that collapses inward on landing puts the kneecap under an outward force with every step, and that is trainable.
Return to sport is staged rather than dated. The knee has to demonstrate control under load and fatigue, not merely feel comfortable walking.
When the anatomy has to be addressed
Surgery becomes the honest recommendation in a few reasonably clear situations: a loose cartilage or bone fragment; recurrent dislocation despite genuine rehabilitation; and a knee whose measured anatomy makes further episodes likely enough that waiting has a real cost — each dislocation risks more cartilage.
The operation is matched to the problem rather than chosen off a shelf. Reconstructing the torn medial ligament restores the check-rein and is the workhorse. Moving the tendon attachment on the shin bone is added when the pull itself is misdirected or the kneecap rides too high — addressing a ligament while leaving a bony malalignment in place asks the reconstruction to do a job it will eventually lose.
Where cartilage has been genuinely damaged rather than bruised, that is a separate problem with its own answers, covered on the cartilage restoration page.
Where orthobiologics fit, and where they do not
Worth being blunt, because this is a page where an injection-led clinic would be tempted to overreach.
PRP and bone marrow concentrate do not treat instability. They cannot restore a torn check-rein, and they certainly cannot deepen a shallow groove. Anyone offering an injection as a solution to a kneecap that keeps coming out is selling something that does not address the problem.
What they can reasonably be considered for is the collateral damage:
- Cartilage injury and the pain that follows a dislocation — a knee left sore and irritable after the instability itself has settled.
- Patellofemoral pain and early arthritis in a knee with a long history of maltracking, where the joint surface has taken years of uneven load. That overlaps with the knee arthritis page.
Those are real indications. Stopping the kneecap dislocating is not one of them, and you should expect to be told so.
How the choice actually gets made
Age, how many episodes, what the imaging shows about the underlying build of the knee, whether cartilage has been damaged, and what the person needs the knee to do — a sixteen-year-old who plays a cutting sport and a fifty-year-old who wants to walk comfortably are not the same decision.
Dr. Buford performs the injections and the surgery. On this condition that matters in an unusual direction: it is what makes it straightforward to say that an injection is the wrong tool here, because there is no incentive to reach for it.
Request an appointment or call (877) 777-8883.
Common questions
Does a first kneecap dislocation need surgery?
Usually not. A first dislocation in a knee with reasonably normal anatomy is generally treated without surgery: a short period of protection, then structured rehabilitation. The important exception is a loose fragment of cartilage or bone knocked off during the dislocation, which is a reason to operate early rather than wait.
Why does my kneecap keep dislocating?
Because in most recurrent cases the knee was built in a way that makes it likely. A shallow groove for the kneecap to sit in, a kneecap that rides high, the attachment point of the tendon sitting too far to the outside, knock-kneed alignment, rotation in the thigh or shin bone, or generalised ligament laxity. Rehabilitation can compensate for some of that. It cannot deepen a groove.
What actually tears when the kneecap dislocates?
The medial patellofemoral ligament, a band on the inner side that acts as the main check-rein stopping the kneecap sliding outward. It is torn in the large majority of first-time dislocations. Cartilage on the back of the kneecap or the outer edge of the groove is frequently bruised at the same time, and sometimes a fragment is sheared off.
Can PRP fix patellar instability?
No, and it would be dishonest to suggest otherwise. Instability is a structural problem: a torn or stretched restraint, and often a groove that is too shallow. An injection cannot restore a ligament restraint or reshape bone. Where biologics do have a genuine role is the cartilage damage that dislocation causes, and in the pain and swelling that follow, which is a different question from stopping the kneecap coming out.
How long is recovery from a kneecap dislocation?
For a first dislocation treated without surgery, expect a short period of protection followed by several weeks to a few months of progressive rehabilitation before returning to sport. After a stabilising operation the timeline is longer, and it is set by the procedure performed and the tissue involved rather than estimated in advance.
Who is most likely to dislocate a kneecap again?
Younger patients, particularly adolescents, and anyone whose imaging shows the anatomical risk factors: a shallow trochlear groove, a high-riding kneecap, or a tendon attachment sitting well to the outside. Having already dislocated more than once is itself a strong predictor. Those knees are the ones where addressing the anatomy earlier is worth discussing rather than waiting for the next episode.
