Report from the Academy Annual Meeting - Pt. 2

International Symposium on Osseointegration

Many prosthetists now realize that Per Branemark of Sweden first proposed that it might be possible for bone cells to permanently interlock with titanium implants back in the 1950s, and coined the term "osseointegration" or OI to describe the process. His dental implant system is now available worldwide and has proven to be extremely effective clinically for edentulous persons. Branemark also coined the term "osseoperception" to describe the ability to sense vibratory stimuli that people with osseointegrated teeth reported.

He first began to explore the possibility of using the same principles for limb prostheses in the 1990s. Since then, several dozen amputees have undergone the procedure and multi-year follow-up is now available for most of these subjects. This Academy symposium featured three members of the Branemark team who presented their long term experiences with this unique population. Stewe Jonsson CPO(S) noted that the typical protocol is to allow six months of healing time prior to loading the boney implant, although many patients do wear a socket prosthesis during that interim period. Once the bone has healed around the construct, the external abutment that protrudes through the skin is attached and progressive weight bearing exercises begin.

Mr. Jonsson and his colleagues then presented a series of brief case vignettes to illustrate upper limb applications of OI. The videos and slides demonstrated a wide range of unilateral UL applications from partial finger to humeral neck amputation. The range of motion, particularly in rotation, was very impressive and included one person who used the voluntary closing GRIP TD from TRS. Branemark's group reports having used OI in a total of 29 UL cases over the past 16 years, including body powered, externally powered, hybrid, and passive prostheses. Three of the 29 ultimately did not use a prosthesis long term. Reportedly, of the 35 OI cases performed since 1999, one developed an infection at the abutment site, and that was controlled by antiobiotics.

Roy Bloebaum PhD , who is the head for the Veteran's Administration of the Utah Amputee Research Tearm, talked about some very well coordinated research being undertaken as part of the recent Defense Advanced Research Projects Agency initiative. He was critical of the lack of peer reviewed publications by the Branemark group, noting that the lack of credible evidence was one reason that the VA decided to undertake an osseintegrated limb prosthesis development track at this time. They have assembled a very extensive and impressive team of world renowned multidisciplinary experts who will work independently and collaboratively on a well orchestrated series of research projects intended to culminate with a new generation of limb prosthesis osseointegration implants and methods.

The general consensus among the US scientists is that neither limb regeneration nor allograft procedures are likely to be feasible for long term limb replacements in the near term. Of all the new techniques presently under investigation, it appears that osseintegration holds the greatest potential for the near term. However, Dr. Bloebaum believes that socket prostheses will remain the dominant approach for many years to come, particularly for the typical new amputee who lacks sufficient circulation and bone density for OI to work well.

The first task in this multi-year DARPA-funded research will be to prevent infection since this has been a problem with some OI limb attachments. A large group of MD and PhD infection specialists are tackling this first phase. One research arm is investigating the antibacterial slime exuded by the African Claw Frog, which might be developed into a topical treatment or perhaps a protective exudate that leaches from the OI abutment itself. Bloebaum stated that the Branemark group now reports a 5% infection rate, down from 50% in the original series of patients, but decried the lack of details or peer review of these complications.

Once the infection team seems to have effective solutions to the risk of infection well under way, the second phase will use sheep experiments to test a variety of new implant configurations. Bloebaum cautioned that experience has shown that all internal implants under weight bearing fail with increasing frequency over time so it will be important that limb OI implants last for the patient's lifetime. Noting that about 15% of Branemark tooth implants ultimately fail, he argued that comprehensive design of the implant-abutment complex will be one of the key challenges of OI is to become a widely performed procedure. The basic design approach will be prevent wear and tear on the implant, abutment, and prosthetic attachment interface. He noted that it may prove useful to roughen the external surface of the implant to facilitate more aggressive in-growth of boney tissue.

The third phase of this complex of research projects will be to develop minimally invasive surgery to reduce the trauma to the residual limb structures and to hasten rehabilitation to full weight bearing through the implant itself. They will look at all levels of upper and lower limb amputation and may well develop different solutions for specific uses. In an effort to avoid catastrophic failure of the implant, both internal and external overload protections will be designed into the system.

Although it's always easy to criticize someone else's work, I was impressed by the comprehensive plan for systematic investigations put together by this research team. Their results will be peer reviewed and readily available for scrutiny, so even if the final outcome falls short of the ambitious goals, their efforts are virtually certain to add significantly to our collective understanding of OI for limb prostheses.

Orthotic Management of Stroke

This year's Academy Annual Meeting was also the debut of a new certificate program on Orthotic Management of Stroke, based in large part on the recent consensus conference convened by the International Society for Prosthetics & Orthotics. The first presentation was an overview presented by Jim Campbell PhD, CO . To illustrate the importance of this topic, Jim noted that stroke is the number two cause of death worldwide, and the third leading cause of death in the developed world. Europe devotes five per cent of their total hospital budget to the treatment of stroke. Despite the long history of using custom orthoses to restore functional gait for survivors of stroke, there are no scientific papers about AFO control in the transverse plane or the influence at the hip for this population. Clearly, there is a great need for both basic and advanced scientific study of the clinical use of custom orthoses for this group of patients.

There are a number of studies demonstrating a spontaneous increase in the patient's self-selected walking speed with an AFO although this is not always the case. Jim commented that when the treatment increases the velocity of gait that is generally a significant marker for an improved gait pattern. He concluded by suggesting that it may be more productive for future work to compare ambulation with and AFO to typical post-stroke gait rather than to normal locomotion.

Stefania Fatone PhD discussed practical implications of the biomechanics of gait for persons with stroke and emphasized that normal gait is quite energy efficient over a large range of speeds but post-stroke gait is usually confined to one slow pace. It has been calculated that normal gait is 50-70% efficient while ambulation after stroke is only 20% efficient.

Reducing gait compensations is often the best approach to reducing the energy cost of pathologic gait, and this is the primary rationale for many custom AFOs. Metabolic energy expenditure increases with each more proximal level of involvement and spasticity itself consumes additional energy. Since stroke affects one half of the entire body, the labored gait that results is very difficult to maintain.

In normals, steady state gait occurs within about three steps. After a stroke, the gait becomes semi-static, which prevents the patient from taking advantage of the momentum that makes normal gait efficient and almost effortless. Inability to flex the knee severely disrupts gait but knee flexion during swing phase makes the leg a double pendulum, reducing the moment of inertia and enabling the leg to swing more rapidly with less effort. There is some evidence that having the stroke survivor lead with the affect limb results in a more normal progression of the Center of Pressure beneath the foot.

Tom DiBello CO gave a very well organized overview of clinical principles that are useful when managing post-stroke gait. He emphasized the value of remembering that the orthosis treats tertiary problems but not the underlying problem. That is, the stroke is the primary problem and it gives rise to spasticity, weakness, and related neuromuscular deficits. The pathologic gait is the result of those sequelae. The fundamental goals of a lower limb orthosis for this population are typically to minimize tone-induced patterning, improve swing phase positioning, and control stance phase deviations. An anterior stop is often very useful clinically to improve the patient's ability to balance over the affected limb.

Tom highlighted a number of clinical "pearls" based on his extensive experience with this disorder. For example, he advised against for an AFO with the foot in maximum dorsiflexion, particularly when the patient is seated, because gastrocnemius tightness might then prevent full knee extension. Casting in a few degrees less than the patient's maximum DF facilitates full range of motion at the knee during ambulation. Tom believes that enhancing as much of stance phase function as possible will enhance swing on both the ipsi- and contralateral sides.

Tom concluded by discussing Owens' concept of a shank-vertical-angle [SVA] as a method to define the shin position within the AFO-shoe complex rather than trying to describe the "dorsiflexion angle" and the importance of the SVA when optimizing stroke gait. If the SVA angle is less than perpendicular to the floor, it is termed "reclined" while angles greater than perpendicular are termed "inclined". This is a very clinically useful construct because a solid ankle AFO holding the foot in 5 degrees of dorsiflexion with a 10 millimeter heel height may have an identical SVA to an AFO holding a foot in 5 degrees of plantarflexion with a 25 millimeter heel height.