Monday, May 9, 2011

Treating a patella dislocation

Patellar dislocation is a relatively uncommon injury that is normally seen in athletes and adolescent girls, likely due to different mechanisms of injury. It usually occurs in high impact collisions that involve twisting, but it can happen in any scenario involving contraction of the quadriceps muscle.

Once a dislocation has occurred, the patient's patella is usually displaced towards the outside of the leg and the patient's leg is usually moderately flexed at the knee. The patients are usually in a reasonable amount of pain at this point. The dislocation is reduced, or made normal again, by getting the patient to relax their leg muscles (easier said than done), straightening their leg, and gently slipping the patella back into the right place.

Patellar dislocation can be associated with popliteal artery damage, MCL and ACL tears, and fracture of the patella. A physician must perform a neurovascular exam and x-ray the knee to assess for popliteal artery damage and patellar fracture. With the exception of a very obvious MCL injury, it is unlikely that a physician will be able to assess MCL/ACL damage because the swelling from the dislocation makes it difficult to examine the ligaments. The MCL and ACL can be reassessed when the swelling has reduced, which can take 3-4 weeks.

Patellar dislocation is rarely treated surgically. However, there are multiple conservative options available. This article mentions three different conservative treatments. A plaster cast, a posterior splint, and patellar bandage/brace.

Plaster cast
A plaster cast ensures that the patient's leg does not bend. It will definitely keep the leg straight.

Posterior splint
A posterior splint is a foam or cloth object that patients can wrap around their leg. It has a metal bar running through the material that should be oriented so it runs up and down along the back of the patient's knee. This keeps the leg straight, like the plaster cast. However, it has more give allowing the patient to flex his knee slightly. Also, the patient can take the posterior splint off if he wants to try bending their knee.

Patellar bandage/brace
A patellar bandage is a cloth that wraps around the knee. A patellar brace is similar to a bandage, but may have additional support.

The study found that patients had the best results if they used a posterior splint for 2-3 weeks after their dislocation was reduced. If they used the patellar bandage/brace, they were more likely to have a subsequent knee dislocation later. If they used the plaster cast, they were more likely to have limitations to the range of motion of their knee.

However, there were some serious limitations to this study. First and foremost, this was not a randomized control trial. Physicians would decide which patient received which treatment. This selection process is incredibly prone to bias. For instance, one physician may think that all of the older patients need additional support and decide that they all receive plaster casts. A good study compares oranges to oranges and if you have a significant selection bias, this can't be done. Also, the sample size is too small. A study with only 100 patients is not large enough to draw any large scale conclusions. Especially when there is a disporportionate number of patients in each therapeutic group. For instance, plaster casting alone had 60 patients, while 17 were put in posterior splints and 23 in patellar braces/bandages. Making conclusions about posterior splints based on the results of 17 patients would be a mistake. The reality is that a larger, better designed study needs to be made, conducted, and analyzed before we can conclude how to best treat patellar dislocation.

An orthopedic surgeon told me that, in the end, they try to balance protection of the knee with loss in range of motion (I will explain why the loss in range of motion happens in an other post). So he makes treatment decisions based on the personality and activity level of his patients.