Throughout history, some of the most significant inventions have been discovered purely by accident. Such is the case with osseointegration or bone-anchored implants. In the early 1950s, Prof. Per-Ingvar Brånemark, of Gothenburg, Sweden, implanted titanium optical chambers into rabbits to study microcirculation in bone marrow. The scientist found that the bone had completely integrated with the implant and was virtually impossible to remove without fracturing the bone. He coined the term osseointegration and postulated correctly that titanium implants could eventually be used as a type of bone anchorage in humans.
Since 1965, osseointegrated dental fixtures have been implanted in more than 1 million people worldwide. Other applications include facial prostheses, hearing aids, finger joints, thumbs and more recently, orthopedic or upper and lower extremity applications, particularly treatment of transfemoral amputees.
The first patient to be implanted with a lower extremity osseointegrated prosthesis was a bilateral transfemoral female amputee in Gothenburg, Sweden. Since that time, about 100 patients, mostly in Europe, have had successful lower extremity osseointegration procedures, mostly transfemoral. More than 30 patients have undergone osseointegration treatment for transhumeral and transradial amputations.
In the United States, the procedure is not yet approved by the Food and Drug Administration (FDA).
For carefully selected patients, osseointegrated bone-anchored prostheses have proven to have distinct advantages over traditional socket prostheses. For instance, patients do not encounter pain or pressure as they can with a conventional prosthesis. The prosthesis is quick and easy to don and doff using an Allen wrench. There is improved function and patients experience osseoperception, the increased perception of the environment through the osseointegrated prosthesis.
“The most significant advantage of the osseointegrated prosthesis is elimination of the socket,” said Rickard Brånemark, MD, MSc, PhD, an orthopedic surgeon in the department of orthopedics at Sahlgren University Hospital in Gothenburg, Sweden. “We have many patients say it was a bigger change in their lives to go from a socket to a titanium implant than it was from having a leg and losing it. In other words, they tell us it cannot be compared because it is so much better.”
According to Brånemark, his patients can do whatever they like and the bone-anchored prosthesis will always fit. There are no skin problems, it will fit in cars and while sitting on the floor, and they can walk as much as the muscles allow them to.
“And the next day, they can walk the same amount of time because they do not have any skin break down,” he said.
David J. Reisberg, DDS, medical director of the cranial facial center at the University of Illinois Medical Center, Chicago, and a specialist in maxillofacial prostheses and prosthodontics, would like to see FDA approval of osseointegrated devices for orthopedic use because often, the residual limb in the conventional prosthesis bears on the soft tissue causing discomfort.
“The osseointegrated device, on the other hand, bears on the implant rather than the soft tissue,” he said.
According to Evan Herold, marketing manager of bone anchored solutions for Cochlear Americas, a company in Denver that provides people with aesthetic facial prosthetic devices anchored by titanium implants, there has not been any documented case of someone rejecting an implant.
“There has not been one documented case in the history of medicine,” he said. “It is that much of a solid procedure.”
Facial prostheses can make a remarkable difference in the quality of patients’ lives and Reisberg assists in this process. He treats many types of patients, e.g., trauma and cancer patients or those missing part of their face due to a congenital condition. These patients may be rehabilitated in the orbital, nasal, midface or ear areas. An example of the latter would be a patient who has hemifacial microsomia, a congenital malformation where all or part of an ear is missing.
“This is when half of the face is usually smaller than the other half and it can relate to the occlusion of the teeth, the appearance of the jaw bone, and the existence of the ear and the ear canal,” Reisberg said.
Treatment of these and any facial prosthesis patients requires a team approach. The prosthetic and surgical specialists must work closely from the outset to achieve an optimal result. After determining that the patient is a candidate for an implant-retained prosthesis, Reisberg and his colleagues fabricate a template of the planned prosthesis to use as a guide during surgery. This helps to determine the number of implants to be placed, as well as their ideal locations, Reisberg said. The implants are threaded into sites in the bone that have been prepared by a series of drills and countersinks. They may be covered over by skin or immediately exposed through the skin by means of a connecting abutment. Following 3 to 6 months of healing to allow for osseointegration, fabrication of the prosthesis begins. It is first sculpted in wax and then cast in a medical grade silicone rubber that is custom colored to blend with the patient’s own skin.
“If a patient is getting a prosthetic ear, for example, the surgeon would put three little implants, about 3 mm to 4 mm in length each, in the side of the head,” added Herold. “The implants would sit there for 3 months so they could osseointegrate with the bone, becoming incredibly sturdy anchors for the ear to be attached to.”
At the end of 3 months the surgeon will take back the skin flap and attach an abutment on top of the implant and screw it in. The ear would simply snap on.
According to Reisberg, several centuries ago, patients used metal prostheses that they kept on with a wire or an early version of a rubber band or strap. Since the middle 20th century, skin adhesives have been commonly used to retain facial prostheses. Implants came to the United States by FDA approval in 1990.
“If a patient is getting a prosthetic ear, for example, the surgeon would put three little implants in the side of the head,” said Herold. “The implants would sit there for 3 months so they could osseointegrate with the bone, becoming incredibly sturdy anchors for the ear to be attached.”
To maximize success for both facial and dental applications, a good quality and quantity of bone is needed, as well as a healthy blood supply to the area to be implanted, Reisberg said. Radiation therapy can decrease the success rate, but there are certain things that can be done to increase the blood supply to an area and improve success such as hyperbaric oxygen treatments. Any surgical site, whether a leg, orbit ear or mouth, needs an adequate blood supply for healing, Reisberg said.
In general, individuals with uncontrolled diabetes, autoimmune diseases, smokers or anyone with any medical condition that would prevent healing, are generally not good candidates for any osseointegration procedure, including lower extremity amputees. However, there are no hard and fast rules, Reisberg said.
For lower extremity patients, the best candidates are young, traumatic, unilateral transfemoral amputees who are psychologically stable, Brånemark added.
“Dysvascular amputees or elderly patients with poor circulation are not good candidates,” he said.
The surgical procedure for titanium implants is generally the same whether it be dental, facial or orthopedic. Low-speed drilling is used to maintain the integrity of the bone tissue. It is a two-stage process. The first stage involves a fixture that is threaded into the bone and the wound is closed for 6 months to allow bone healing to occur around the implant. In the case of a transfemoral amputee, the fixture is threaded into the medullary cavity. It is important that during this stage the implant is not loaded so the bone can grow into the threads. Movement of the implant during this time may cause loosening.
At 6 months or stage 2, the implanted fixture is exposed again and an abutment or titanium elongation of the skeleton is attached to the fixture. This abutment is a sort of safety component so if the implant is overloaded, it will break instead of the implant. The wound is closed with the abutment penetrating the skin. The prosthesis is attached to the abutment in various ways, depending on the application. During the second stage for a lower extremity amputee, the implant is gradually loaded which may take up to 6 months to achieve full weight bearing. The whole osseointegration process takes 12 months and with some patients who have poor quality bone, 18 months.
Risks and complications
Almost all surgical procedures have risks or drawbacks. Osseointegration takes more time in terms of rehabilitation. The implant needs to be loaded carefully. In the transfemoral patient, there is the potential risk of loosening or the patient falling and possibly fracturing the bone while it is healing. There could also be some mechanical problems of the implant such as bending or fracture of the abutment or fixture. The fitting of the abutment in the fixture might wear out by excessive use or the abutment might need a change to a somewhat bigger abutment. This can be accomplished as an outpatient procedure since the implant system is modular to allow easy change of the abutment.
According to Brånemark, during the beginning years of the procedure, there were some great success and also some problems with mainly loosening of the implant.
“During the onset of loosening, you have micromotion and micromotion makes it easier for bacteria to enter into the body and that created infection,” Brånemark told O&P Business News. “We now have few loosenings, less than 5%, and we have almost no severe infections.”
Some patients have irritation now and then, but that is not considered a severe complication by either the patient or the physician. Reisberg said that the only problem with infection is the one risk that would be present in any normal surgical procedure.
Brånemark currently has 18 patients who have been followed for more than 2 years in a prospective study. Of the 18 patients, there is one failure and all the others experienced great improvements in function and quality of life. Brånemark said that he has had only had one reamputation, which occurred in 1995,
“When my father was a young researcher, he asked other researchers what kind of material he should use for this optical experimental implant,” Brånemark said. “Someone told him, ‘There is new material called titanium and it is supposed to be good with bone. So he sort of by accident found that it was good in bone tissue. So far, I do not think there is another material that has proven to be better.”
Titanium has an inert oxide on its surface. This oxide is like a ceramic material on the outside. No one understands in detail why it works so well in the body.
“Some laboratory results indicate that the oxide has slight anti-inflammatory properties,” Brånemark said.
Reisberg added that titanium is probably one of the most inert if not the most inert material for the body.
“The body does not reject it as a foreign material,” he said.
What the future holds
Will sockets be obsolete in the future? Brånemark believes that they will be an alternative for the elderly, but for others, titanium implants will be a much better option.
“With time, this will become a primary procedure in selective patients, Brånemark said. “I also hope that the improved anchorage to the body will force the development of better prosthetic components.”
Herold added that from the perspective of the facial implant business, it has been a bit slow for people to move away from the old fashioned adhesive retained prosthesis.
“The bone anchored implants show so much more viability,” he said. “People can go out and live without fear of their ear, eye or nose being dislodged.”
Brånemark thinks the procedure for orthopedic use will be approved by the FDA for use in the United States within 5 years.
“I think it will be faster if the Veterans Administration or military would be interested in bringing in this technology,” he said.
Neuroprosthetics is the development of artificial devices to replace or improve the function of an impaired nervous system. Essentially, a neuroprosthetic is a surrogate for any component of the central nervous system or a device which enhances the function of any component of the central nervous system. Neuroprosthetics is a type of brain-machine interface.
Presently, the neuroprosthesis used most extensively is the cochlear implant which is used by about 100,000 people worldwide. Research is ongoing in several areas including retinal implants and seizure-preventing implanted electrode arrays. Scientists are also studying microchips that can be implanted in the brain that interface with osseointegrated prostheses. It may be possible in the near future to control artificial prosthetics by thought patterns.
“Brain waves or electroencephalograms can be used by some patients with paraplegia to control computers,” said Brånemark. “The patients cannot do complex things yet, but they can learn to do simple things like controlling an on/off switch, for instance. This means that today there are ways of directing simple prosthetic devices. For the prosthetic devices to be effective, more complex controlling mechanisms are needed, but this is an important first step.”
For more information:
- Neuroprosthetics, Brain Emulation and Mind Uploading: The Ultimate VR Concepts. Available at: http://www.virtualworldlets.net/Resources/Hosted/Resource.php?Name=NeuroprostheticsBrainEmulation. Accessed Dec. 4, 2006.
- Orthopaedic Osseointegration. PowerPoint Presentation. Available at: http://sdnp3.ucsd.edu/osseointegration.htm. Accessed Nov. 9, 2006.
Rachel Kelley is a staff writer for O&P Business News.