Patellar Realignment for Instability
Anteromedialization of Tibial Tubercle (AMZ) or Fulkerson Osteotomy
Patellar instability is a very debilitating condition. The instability can be acute, such as after a traumatic dislocation, or it can be more chronic and related to how your bones formed. Some people have an anatomic propensity to dislocate their patella, either from being knock kneed, having a shallow trochlea (groove where the patella sits), having a tibial tubercle (the place where the kneecap tendon attaches on the shin bone) that is too far to one side, or a combination of everything.
A one-time patellar dislocation without cartilage damage or a fracture can typically be treated without surgery. Surgery is needed for instability that has been recurrent and/or that has failed a course of physical therapy with bracing, taping, and muscle strengthening. Often times, we also focus on getting your gluteal (butt muscles) stronger, which helps with your gait pattern. You may also have flat feet, which can predispose you patellar issues. In this case we may also recommend a set of orthotics.
X-rays are typically taken in the office to look at your bony anatomy. The x-rays are very specialized views taken at certain knee angles. In addition, we also obtain an MRI or CT scan to look at your cartilage and to take special measurements of your bones. One of these measurements is called the Tibial Tubercle Trochlear Groove (TTTG) measurement. This helps us to decide whether we need to do surgery near the patellar tendon attachment on the tibial tubercle (the attachment on the shin bone) or closer to the side of the patella. This article talks about the surgery done to the tibial tubercle, called an AMZ or Fulkerson osteotomy. There is another article on surgery closer to the kneecap called a Medial Patellofemoral Ligament (MPFL) reconstruction. Occasionally we do both of the procedures together.
The surgery for a Fulkerson osteotomy is typically a 23 hour stay (i.e. overnight) procedure. You will receive a general anesthetic, in addition to a nerve block to your operative side. The nerve block is placed by the anesthesia service and allows you to wake up relatively pain-free. The block lasts for approximately 12-18 hours, after which you can start easing into your pain medication.
You are positioned flat on the operating room table, with all of your extremities carefully padded. We use a tourniquet during the procedure to help with the bleeding and with visualization. After performing a “time out”, where we verify the operative site, your leg is cleaned and sterilely draped. We typically perform an arthroscopy of the knee to visualize the kneecap and get an idea of how it is tracking and where it is dislocating/subluxating. There can also be other cartilage issues in the knee that are addressed during the arthroscopic portion of the procedure. Once this portion is completed, the rest of the operation is done open, but at the end we use the arthroscopic camera to make sure your kneecap is tracking well.
For the open part of the procedure, we make an incision from the outside border of the kneecap down past the tibial tubercle. We take this incision down until we see your kneecap tendon. Up by the outer side of the kneecap, we open up the tissues so we can visualize the knee itself. This is called a lateral release. We free up scar tissue that can tether the kneecap in a subluxated or dislocated position. Further down the leg, we identify where the patellar tendon (kneecap tendon) attaches and then also take down some of the muscle on the outer part of the leg. This muscle is later repaired at the end of the case.
We use special instruments to help us make the bone cut under the kneecap tendon. We base this cut off the measurements from the MRI and also what we find during the arthroscopic portion of the procedure. The Fulkerson osteotomy is a biplanar osteotomy, meaning that the cut is just not flat. We are able to angle the cut so that we are able to not only make the kneecap stop dislocating but also relieve the pressure under the kneecap. Once we perform all of the cuts for the osteotomy, we carefully hinge the osteotomy and move it approximately 1 centimeter towards the inside of the knee. We hold it in that position with some pins, and then use the camera to look inside the knee to verify your kneecap is tracking in the correct pattern. We can make small adjustments at this time.
The osteotomy (bone cut) is then fixed using screws going from the front to the back of the tibia (i.e. shin bone). The screws are placed in a “lag” type fashion, which is the same way you join two pieces of wood. Once the screws are placed, we again verify the tracking of the kneecap and then test the motion of your knee.
Occasionally at this point, if we have a very severe dislocation or maltracking of your kneecap, we have to supplement the procedure with a tendon reconstruction on the inside of the knee, called a Medial Patellofemoral Ligament Reconstruction (MPFL). There is a separate article on this.
With the kneecap in a reduced position, we close up the incisions. We reattach the muscle on the outside part of the knee. We typically place a drain in the knee overnight to help with the swelling, and the drain is removed the next day. The leg is also placed in a knee immobilizer, which you will use for support for the first 6 weeks after the surgery. It is very important that you stay in the immobilizer except for the specific knee motions you are taught.
Sometimes we move the knee very quickly after the procedure, but other times we keep you in the immobilizer for a couple of weeks prior to even moving the knee. This will be explained to you after the procedure and very specific instructions will be given to you and your therapist.
Once your pain is under control, you are eating and keeping food down, and you are medically stable, you can be discharged home. You will get a full set of instructions of Do’s and Don’ts. Basically make sure to keep your incision clean and dry. No showering until your postoperative visit. If you have any questions on what you should be doing or not doing to your shoulder, make sure to ask your surgeon or the nurses/residents. You will be seen in the office for a check up and to remove any staples or sutures in 7 – 10 days after surgery. You will also be given a pain medication prescription. Please take the pain medication as directed. Eat a healthy diet and get plenty of rest. Also remember that ICE is a form of pain relief and you should ice the knee regularly.
Typically you are in the immobilizer for 6 weeks after surgery but are coming out of the sling for very prescribed movements that you will be taught. Most of the movements can be done without a therapist, and formal physical therapy starts at approximately the six week mark.
The most important part of the initial healing phase is to get the osteotomy (bone cut) to heal. You need to be completely non-weight bearing, with either crutches or a walker. Placing too much weight too soon on the leg can lead to a fracture. Because the bone cut is hooked up to the kneecap tendon, which is also hooked up to your quadriceps muscle, we do not want you actively extending your leg (i.e. using your muscles to make your leg straight). This all has to be done in a passive manner. We do want your leg to be straight when not doing any exercise, which includes at night. In order to help with getting the leg out straight, we do not want any pillows under the knee, only under the calf and ankle. In this way, when you elevate the leg, gravity helps to pull the leg out straight.
Once or twice a day, we want you coming out of your brace to bend the knee. The knee bending will only be to 90 degrees of motion. Sometimes we only bend the knee to 60 degrees, but you will be specifically told what to do. The first couple of times you attempt to bend the knee, it will be stiff. Take your time and take things in “baby steps”. If you can only get a couple of degrees of knee motion, do what you can and come back at a later time to get a little bit more. If you do it in a step-wise fashion, you will see that your knee motion will come back nicely.
You will be seen in the office for regular visits to monitor the progress of the bony healing with x-rays. Once we see healing of the fragment, we can start putting weight on the leg and get into a more formal physical therapy program. Full healing from this type of surgery is approximately 5 – 6 months. Because the screws are in the front of the knee, they can be irritating in the future with activities such as squatting and kneeling. If this is the case, they can be removed with a very quick outpatient procedure, but not before 9 months after the initial operation, assuming everything healed properly.
We hope this provides a bit more insight into your surgical procedure for an Anteromedialization (AMZ) or Fulkerson osteotomy. As always, if you have any questions, please contact our office at 248-988-8085.