By Dick Mooney

At the 1999 Amputee Coalition annual meeting in Reno I had the pleasure of hearing Dudley Childress talk about the latest innovations in prosthetics. Dr. Childress is the Director of the Northwestern University Prosthetics Research Laboratory and Rehabilitation Engineering Research Program, and is a man I always considered to be the Dean of prosthetics education and research in the United States. At the end of his presentation he talked about innovations he labeled as "on the horizon." These included osseointegration, which I had never heard of but which fascinated me with its possibilities.

Then that Fall, when I was in Edinburgh to speak to a United Kingdom-wide meeting of college and university purchasing people, I made a side trip to the Princess Margaret Hospital, where I had heard researchers were making articulated fingers for prosthetic hands. I learned about that work, of course, but when they showed me a video about osseointegration I was completely hooked. I had to learn more!

"Osseo" refers to bone and "integration" refers to how a prosthesis can be integrated with the bone in residual limbs--both arms and legs. The implications of this are really fascinating. To understand them one has to understand how artificial limbs are currently attached to the body and the shortcomings of that method. For the purposes of this article, let's only talk about legs.

Presently, as all of you know, a prosthetist fashions a "socket," usually Fiberglas or plastic, into which the residual limb (RL) fits like a thumb in a thimble. The role of the socket is to fully contain the soft tissues of the RL so the prosthesis' motion can be controlled as precisely as possible by the motion of the user's RL. But, because the connection between the prosthesis and the body can never be absolute given the soft tissue "padding" between the RL and the bone in the leg, the prosthesis can never be controlled as accurately as a real leg. You're never quite certain where your foot is and you're constantly aware that your leg isn't quite connected to you.

Because of this "soft" interface, the prosthesis always feels heavier than a real limb would, although in actuality, it might weigh less. Also, because of the inaccurate connection, more energy is required to manipulate the prosthesis than a real leg--up to 80% more for an AK wearer.

Conventional Prosthesis

Another problem: Since leg RLs can't be end-bearing except for knee and ankle disarticulations, the weight of the body must be borne by other areas, such as the Ischial Tuberosity in the AK wearer's tush. Thus when one walks with an AK prosthesis, one essentially walks on one's tush, not on the end of one's RL. 

Finally, since the socket must contain the RL's soft tissues tightly and the socket material can't "breathe," the wearer must always fight skin problems such as dermatitis, which have the potential of causing pain at best and temporarily putting them back on crutches at worst. There is rubbing that can produce skin rashes, blistering, and breakdown of tissue. The RL shrinks and swells with the weather and with the wearer's weight, which can change the fit--sometimes disastrously.

Osseointegration shows great potential for solving all these problems!

The osseointegration phenomenon was discovered by accident. In the late 50s and 60s. Professor Per-Ingvar Brånemark in Gothenburg, Sweden, was studying how blood flows back into bone after the circulation has been cut off. As a part of his study he had some medical students who agreed to have a titanium cylinder placed into the bone in their arm. He found that when the study was over and he went to remove these cylinders, he couldn't get them out. Rather than this being an irritation to him, he switched his whole research over to it.

The first practical application developed by Professor Brånemark was a way to connect false teeth to the bone of the jaw using titanium implants. A titanium pin is placed in the jawbone and a tooth is attached to the top of the pin that projects through the gum. This technique has been employed since 1965 and more than 800,000 patients have received these implants. The technique was later employed to anchor an artificial jaw after a facial trauma. Then it became a means of attaching artificial ears. Then there were three cases of direct skeletal attachment of a prosthetic thumb and partial hand.

More recently, essentially the same technique has been employed to attach artificial limbs to the bone that remains in the RL. A company called, Integrum AB, which is situated at the Sahlgrenska Biomedical Innovation Centre in Gothenburg, Sweden, has successfully implanted over 40 patients with the osseointegrated system since 1990. The treatment is performed by a team consisting of orthopaedic surgeons, physiotherapists, and prosthetists. I've also found reference to the technique also being employed in Melbourne, Australia, by Steven Gray at The Alfred Hospital, and Andrew Nunn at Caulfield General Medical Centre.

Here's how it works: During the original amputation or during a revision to prepare the patient for osseointegration, a surgeon exposes the femur, the bone in the AK stump, and installs a titanium implant, which is like a bolt that's inserted into the cavity of the bone. That's the first stage.

After six months, during which time the living bone cells attach themselves firmly to the surface of the titanium, the second stage of the surgery exposes the end of the femur and the head of the implant and connects to that another titanium component, called an abutment, which then comes through the skin and through the end of the patient's stump. This is shown in the following photo. The limb can then be attached to the abutment with an allen wrench! 

Attachment to Bone

Titanium is the key to the technique. Titanium is biocompatible. It's an inert material which the body doesn't react to. If you put a stainless steel pin in a bone, that pin will eventually come out. It's like a nail in a piece of wood. But if the wood grew onto the metal, you'd have a hard time getting that nail out. That's what happens if you put titanium in bone.

What's the bottom line? As can be seen from comparing the photos of a conventional AK prosthesis and an osseointegrated one, the osseointegrated prosthesis has no socket, since it attaches firmly to the bone-anchored titanium implant. This means, to highlight how the osseointegrated prosthesis fixes the problems of the conventional socket prosthesis mentioned earlier:

• There is no feeling of increased weight,
• no lack of positive prosthesis control,
• no increase in energy consumption to operate the prosthesis,
• no need to bear weight on other parts of the body,
• no fitting problems due to weight gain or loss,
• no socket induced skin irritation, and
• no problems donning and doffing the prosthesis

In fairness, it should be observed that whenever a "foreign object," such as the titanium abutment, permanently pierces the skin, the danger of infection is always present. In fact, infection seems to be the chief complication, although the literature reports that most can be effectively treated with antibiotics. I imagine that the osseointegrated patient must have to make a special effort to keep that area clean at all time

Currently, the process is quite expensive--around $38,000 for the surgery and surgical components. The good news is that insurance is paying in the countries where the technique is being employed. The other side of the cost coin is that socketless prostheses are less expensive to make. Also, patients wearing traditional socket limbs may have to have new sockets made relatively frequently and they may have to have three or four made each time to find one that fits well. This adds up to many thousands of dollars that aren't necessary with osseointegrated prostheses, which may mean that there's a cost saving in the long term that may more than adequately compensate for the high initial cost.

Who will benefit from this technique in the United States? Probably no one who reads this article, unfortunately. Currently, osseointegration is not performed in this country. Where it is performed, generally only younger unilateral amputees who can't be successfully fitted by conventional means are considered. Moreover they must have a sound bone in the RL, not have systemic diseases, such as diabetes or peripheral vascular disease, and not be smokers. Keep in mind that the technique is still considered experimental and the amputees who are accepted for osseointegration are considered experimental subjects. But if this development continues to progress as effectively as it has begun it seems certain that future generations of amputees will reap the benefits of this exciting technology!