Total Ankle Replacement
Thirty or so years ago when total ankle
replacement surgery was begun it was soon realized that the implant
or the prosthesis that was used at that time was not successful. Almost
all of the total ankle replacements implanted at that time ultimately
failed. The design of the prosthesis implant began to improve in the
late 1980's, and because of these changes, total ankle joint replacement
again became part of the treatment that a surgeon had available to
correct ankle arthritis. Within the past ten or more years ankle replacement
has again been taken seriously by orthopedic surgeons who perform reconstructive ankle surgery.
The results of ankle replacement today are good and the outcome of ankle replacement from a functional standpoint is better than that of arthrodesis. What does this mean? In an ankle arthrodesis, the joint is fused or glued together, limiting the up and down movement. An ankle replacement, however, allows a more normal "function". By function, we are talking about the day to day activities that a person is able to do. Movement of the ankle also prevents the stress that accumulates in joints next to the ankle following a fusion of the ankle. What happens is that if a joint is fused together the joints next to it try to adjust to some of the movement that was lost. This leads to the development of arthritis in these joints. In fact, ten years after a fusion of the ankle 100% of patients will demonstrate findings of arthritis in the joints next to the ankle. This does not mean however that all of these patients have pain with this arthritis that is seen on the XR, but it is nonetheless a very worrisome problem.
Experienced surgeons have found that it takes time for them to learn
how to put in the ankle prosthesis. It may take many years for a surgeon
to gain sufficient experience to perform the surgery predictably without
considerable complications. Recent scientific reports (from our own
institution as well as those of others) have outlined this problem
in more detail. Surgeons refer to this problem as the "learning curve." Fortunately, Dr. Myerson has extensive experience with this surgery
and has performed well over 400 ankle replacements. In the United States there is currently only one ankle that has been approved for use by the FDA. This is called the DePuy Agility ankle replacement. The design of this particular prosthesis has recently been dramatically improved (see below). This new prosthesis is now available at several selected hospitals around the country including the Institute for Foot and Ankle Reconstruction at Mercy. Here we can see what the original DePuy prosthesis looked like.
The ankle prosthesis is in two parts, separated by a plastic liner called the polyethylene. The top part of the prosthesis is called the tibial component, and fits into the leg bone, the tibia. The bottom part is called the talar component, and fits on top of the ankle bone, the talus.
Above you will see one big difference in the recently developed ankle replacement called the Agility LP prosthesis. On the left is an XR of the ankle after the original Agility was inserted, and the new LP prosthesis is shown on the right. You will note that the shape of the talar component in particular is different. This talar component covers the talus almost completely, which prevents later sinking or subsidence of the component into the talus bone.
The main advantage of total ankle replacement is the return of some
freedom of movement in the ankle. This movement is important for simple activities such as bending, walking,
exercise and climbing. Full movement of the ankle
joint is never regained even with total ankle replacement. The movement
that is present, however, is far preferable to the lack of movement
in the fused ankle. There is another very important aspect to ankle
replacement in that it avoids the stresses that occur following ankle
fusion or arthrodesis. When an ankle joint is fused, there is of course
no up and down movement in the ankle. There does however remain for
some patients a limited amount of up and down movement which occur
in the adjacent joints. The problem is exactly what was outlined above in that later on these joints
begin to take the brunt of the force in the foot, and they too begin
to develop changes of arthritis. This can be a serious dilemma, since
almost 100% of patients will after a prolonged time demonstrate changes
of arthritis in these joints next to the ankle. Not all of these patients
have symptoms of arthritis, but for many it can become debilitating,
since the only option remaining is to fuse these joints as well. What
then happens is a gradual need for further fusion of adjacent joints
in the foot, resulting in considerable incapacity.
So who is a good candidate for an ankle replacement? The ideal patient, is someone who is over the age of 50, is not too heavy, and is not extremely active. Some activity is always ideal, and it does not mean however that patients with an ankle replacement have to be sedentary. Quite on the contrary, patients can walk, hike, climb, ride a bicycle, and in some circumstances even ski after ankle replacement. The activities then which are not ideal are those which involve repetitive pounding of the ankle for example running and a job which includes heavy labor. Patients who have poor circulation in the leg, those who have diabetes, or nerve conditions of the leg are not good candidates for an ankle joint replacement. The bone quality of the ankle must be fairly healthy, and we do not normally implant a joint if the ankle bone is dead (a condition called avascular necrosis or AVN of the talus bone). When we perform an ankle replacement, one of the goals is of course to improve the movement of the joint (called the range of motion). Interestingly, the more movement of the ankle that there is before the joint replacement surgery, the more will exist later. If a patient has no motion or very poor motion of the ankle before surgery, we can improve this, but not nearly as much.
Here you see the difference in the movement or range of motion of the foot and ankle in two patients with ankle arthritis. The patient above has very poor movement in the ankle to begin with, and all that is moving up and down is a small joint in the foot. Sometimes a patient like this may be more suited to a fusion of the ankle, since she would not noticce the difference in movement after the fusion. On the other hand, the patient shown below has excellent movement of the ankle, even though the arthritis was severe. This patient would not do well with an ankle fusion, since the loss of movement would be very noticeable.
||These are XR's after total ankle
replacement. The XR on the right shows the prosthesis
with the plate and screws on the outside anklebone called
||In these two pictures, we are
looking at an XR from the side of the ankle after a total
ankle has been inserted. The XR's demonstrate the movement
that is possible after total ankle replacement. The XR
on the left shows the foot moving downward and that on
the right, with the foot moving upwards.
||This is the up and down movement
of the ankle that one would expect following a total ankle
The recovery following the total ankle replacement is very carefully monitored. Rehabilitation and exercise are essential. Our approach to rehabilitation includes an exercise bicycle and therapy in a swimming pool which begin as soon as the stitches are removed and the incision is healed. These exercises facilitate the range of motion and ultimately improve the final outcome of the joint replacement procedure.