What is patellar instability?
The kneecap (patella) normally rides in a groove at the end of the thigh bone. In a dislocation, it slips fully out of that groove, almost always toward the outside of the knee. Sometimes it pops back by itself. Other times it must be put back in an emergency room.
Patellar instability means the kneecap dislocates or feels like it is about to. It can start with a twist in sport, or with a simple turn in a knee built in a way that makes the kneecap easier to move. It is most common in people aged 20 to 30 (Smith, 2023).
The main restraint that holds the kneecap inward is a band of tissue called the medial patellofemoral ligament, or MPFL. A dislocation often tears it.
What should I do after a first dislocation?
Get the knee checked soon. The exam and imaging look at two things: whether a piece of cartilage or bone broke loose, and whether the shape of your knee makes another dislocation more likely. A loose fragment can change the plan and may need earlier surgery.
Without a loose fragment, many first dislocations start with non-surgical care. This usually means a short period of protection, then physical therapy for the thigh and hip.
The evidence here is less certain than many people expect. A Cochrane review pooled 10 trials with 519 people. After a first dislocation, about 35 in 100 people treated without surgery dislocated again within two to nine years. With surgery, that risk was about 16 in 100 lower. The authors judged the certainty of this evidence to be very low, so they could not say for sure that surgery lowers the risk. They were also unsure whether surgery improves function or raises the risk of complications (Smith, 2023).
So surgery after a first dislocation is a choice to talk through, not a rule. Your age, your sport, and your knee’s shape all matter.
What if my kneecap keeps dislocating?
Repeat dislocations change the conversation. Up to 40% of people dislocate again after a first episode (Smith, 2023). Each episode is a chance to damage the cartilage, and fear of the knee giving way can limit what you do.
The risk tends to be higher when a knee has certain features:
- A shallow groove on the thigh bone
- A kneecap that sits high
- A shin bone attachment that pulls the kneecap outward
- Growth plates that are still open
When instability keeps coming back, MPFL reconstruction is a common next step. You should know that no well-sized trial has compared surgery with non-surgical care for repeat dislocation (Smith, 2023). The results below come from studies that did not compare surgery with non-surgical care.
What is MPFL reconstruction?
The surgeon rebuilds the ligament with a tendon graft, which anchors the inner side of the kneecap to the thigh bone. It acts as a check rein that limits how far the kneecap can slide outward. It is usually done with small incisions. Children who are still growing often need a modified technique that avoids the growth plate.
A review of 930 patients treated for repeat dislocation found that 92.8% of athletes returned to sport, and 71.3% returned to their earlier level or higher. Instability came back in 1.9%, and complications occurred in 8.8% (Platt, 2022). Those are group averages, not a promise for any one knee.
When is bone realignment added?
Sometimes the problem is not only the ligament but also the way the bones line up. The most common added step is a tibial tubercle osteotomy. The surgeon cuts the bony bump on the shin where the kneecap’s tendon attaches, moves it, and fixes it with screws. This changes the direction of pull on the kneecap. The groove itself or the alignment of the leg may also need attention in some knees.
When this step is truly needed is debated. The distance between the bump and the groove, called TT-TG, is often used to decide. In one review of patients with a raised TT-TG, redislocation was 3.1% after MPFL reconstruction alone and 3.2% with the osteotomy added. Return to sport was 82% and 92%, though the osteotomy group for that measure was small (Vivekanantha, 2023). A second review looked only at TT-TG above 20 mm and found no added benefit from the osteotomy, while warning that the studies varied widely (Guevel, 2023).
The decision should be made for your knee, based on your imaging and exam, and not on one number.
What are the risks of surgery?
Risks include infection, blood clots, stiffness, ongoing pain, kneecap fracture, and repeat instability. Adding an osteotomy means a bone cut that has to heal. Results vary from person to person, and no surgeon can promise a certain outcome.
Should I get a second opinion?
It can help, especially if you were told you need a bone procedure and want to know if it is necessary, or if a prior surgery did not hold. Here’s how a second opinion works.
Where can I see Dr. Pareek?
Dr. Pareek sees patients with kneecap instability at HSS in New York and at HSS in New Jersey. Bring any X-rays, MRI images, and reports you already have.
What does recovery look like?
These are typical ranges. Your surgeon’s plan comes first, and recovery varies from person to person.
- Weeks 0-2: Protect the kneeAfter MPFL reconstruction, many people use crutches and a brace, with early work on swelling and gentle bending. If bone was also moved, limits on weight are usually stricter and last longer.
- Weeks 2-6: Regain motionPhysical therapy works on knee motion and on waking up the thigh muscle. Weight on the leg builds up as your plan allows.
- Weeks 6-12: Walk normallyMost people move off crutches and out of the brace toward a normal walking pattern. Strength work starts to build.
- Months 3-6: Build strengthTherapy moves toward harder thigh and hip strength, balance, and then light running if your knee is ready.
- Months 6 and beyond: Return to sportMany people return to cutting and pivoting sports around or after six months, once strength and testing allow. These are typical ranges, and your surgeon's plan governs.
Sources
- Smith TO, et al. Surgical versus non-surgical interventions for treating patellar dislocation. Cochrane Database Syst Rev 2023;1:CD008106.
- Platt BN, et al. Return to sport after medial patellofemoral ligament reconstruction: a systematic review and meta-analysis. Am J Sports Med 2022;50:282-291.
- Vivekanantha P, et al. Isolated medial patellofemoral ligament reconstruction results in similar postoperative outcomes as medial patellofemoral ligament reconstruction and tibial-tubercle osteotomy: a systematic review and meta-analysis. Knee Surg Sports Traumatol Arthrosc 2023;31:2433-2445.
- Guevel B, et al. Does tibial tuberosity osteotomy improve outcomes when combined with medial patellofemoral ligament reconstruction in the presence of increased tibial tuberosity-trochlear groove distance? A systematic review and meta-analysis. Orthop J Sports Med 2023;11:23259671231195905.