Dislocation or subluxation of the patella or “kneecap” is a common acute injury for young athletes, especially in sports and activities such as basketball, football, lacrosse, gymnastics and dance. These injuries may be routinely observed in clinic, and depending on severity, may warrant a referral to a pediatric orthopedic specialist.
The term “patellofemoral instability” can refer to both the condition in which an individual experiences a traumatic dislocation of their patella, and the general instability that a patient can feel or a physician may observe upon examination. In both cases, there are observations that may be made or treatments that can be provided that may reduce the risk of a dislocation event occurring in the future, as well as protect a young athlete from further damage.
Notes talked to Matthew Milewski, MD, a pediatric orthopedic surgeon in Boston Children’s Orthopedics and Sports Medicine Center, about how to best care for young athletes with patellofemoral instability.
How does patellofemoral instability usually present?
When someone dislocates their patella, it’s usually a traumatic event — they are hit in a sport or they take a really hard pivot, turn or awkward landing. If they twist or rotate around that lower extremity, the knee cap can slide off to the side. The patella almost always dislocates laterally towards the outside.
Sometimes a patient can suffer from patellar subluxation, which is just a small shift of the patella where it starts to dislocate but comes back into place. It’s not a full dislocation and usually doesn’t need to be pushed back into place, but it can still be quite painful for the patient and can cause them to have what we call “apprehension,” where they’re anxious about their knee cap moving out of place again.
If a pediatrician suspects a patient may have dislocated their patella, what is the best way to proceed?
The first thing I usually have other medical professionals do before they even touch the kneecap, is to try and straighten out the patient’s leg. Most of the time when you straighten out their leg, the knee cap may pop back in by itself. If you do need to give it a little bit of a push, it’s much easier to do if the knee is extended. If you try to force the patella back in – particularly if the knee is flexed – it can cause more damage to the bone or the cartilage. That can occur with the injury itself, but we don’t want to make it worse.
Sometimes, patients will require sedation or some relaxation medication, particularly in an ER setting, to allow that to happen more easily — and of course to also make the patient more comfortable. Occasionally, they will need to go to the emergency room or an urgent care center to have that patella reduced. Most patellar dislocations should get x-rays to make sure there are no obvious fractures and that the patella is reduced properly.
Are there certain factors that make an athlete more at risk for instability?
Patellar instability is incredibly common, some have reported it to be even more common than ACL injuries. We see it in a variety of different sports, certainly contact sports like football and lacrosse, but we also see it in jumping sports and sports that involve a significant amount of twisting.
From an individual and anatomic perspective, there are a number of factors that might place an athlete more at risk for this condition:
- Gender: adolescent females are generally more flexible than their male counterparts, making them more prone to patellofemoral instability.
- Family history: if a parent has experienced a dislocation, their kid is more likely to have recurrent instability.
- Genu valgum: being “knock kneed” places an adolescent at greater risk for instability.
- Patella alta: if a patient’s patella is slightly higher than normal, it may indicate that they’re more likely to experience instability or dislocation.
- Trochlear dysplasia: the groove at the end of the femur where the patella rides is shallower, meaning the patella isn’t fully captured within that groove, making it more likely to dislocate.
- Femoral anteversion: the individual’s hips are turned in a little more than normal, placing them at greater risk for knee problems.
- External tibial torsion: the individual’s feet are turned out as a result of patellofemoral malalignment.
All of these factors are small components, but contribute to the bigger problem which is that the knee cap tends to be prone to dislocation.
In what cases would you recommend a pediatric patient with patellofemoral instability be referred to an orthopedic specialist?
If their knee is significantly swollen (large effusion) and if the knee feels like it is locked or stuck, or they truly cannot bend the knee to the degree they normally should. These are sometimes signs that there could’ve been an injury to bone or cartilage within the knee, which may have been knocked off during the dislocation or during the reduction of the patella. This usually prompts us that the patient should seek further imaging — generally an MRI.
I certainly think that any patella that doesn’t slide back into place relatively easy should be sent for further evaluation immediately, preferably to a pediatric orthopedist (or sports specialist) if it is a younger patient.
What would lead you to recommend a patient for surgery?
The patients I usually recommend be referred for possible evaluation are those who have acute patellar instability with a lot of swelling, where there is concern it might be a more significant injury than just the dislocation — that a piece of bone or cartilage has been knocked off. Anyone with a big, swollen knee or any mechanical or locking symptoms definitely needs further evaluation.
In the chronic setting, I recommend further evaluation for anyone who has had multiple patellar dislocations, particularly the younger population and particularly the population that wants to get back to higher level competitive sports or activities. Sometimes conservative treatment can help, which includes bracing, physical therapy, and return to activities in a gradual process. But for patients that continue to have instability despite proper, conservative, non-operative treatment, we generally recommend surgery to help control the risk of further instability events.
Patellofemoral instability is a painful event, so reducing the risk of further instability is something that allows young athletes to get back to their sports and activities much more confidently and with less anxiety. We also want to reduce the risk to the bone and the cartilage. If it continues to be damaged, this may lead to the patient having arthritis in the future.
Learn more about the Sports Medicine Division at Boston Children’s Hospital