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American Orthotic & Prosthetic Association Assembly 2005

Las Vegas is not my favorite site for a convention because I find it noisy, smoke-filled, garish, and the strip is quite expensive. But, that must not be a majority opinion since this was the best-attended AOPA national meeting in history. It is an easy and usually inexpensive destination to fly in to, but the primary reason our national meetings are in this town with increasing frequency is that we have outgrown almost all other hotel-based venues except for a handful of tourist destinations such as Vegas or Orlando. On a more positive note, virtually all of the technical and scientific sessions I attended were very well attended and many were filled to nearly capacity.

Scientific Sessions - Part One

For the first time in several years, I was able to structure my schedule to attend almost all of the scientific sessions each day. As always, there were continual concurrent programs, so only those sessions I attended are summarized here. In general, although the abstracts have steadily improved in recent years, the content frequently fell short of what the abstract promised. Many talks were thinly disguised sales pitches for this and that, although since this is the industry trade show that should not be a surprise. The session on "Microprocessor Knee-Ankles" began the first day's program.

Dave Hensley CPO reviewed the Seattle Power Knee product line, which are all microprocessor-controlled pneumatic swing phase cylinders combined with various mechanical stance stability mechanisms. The original two variants licensed from NABCO several years ago remain available: one with a friction brake knee that looks like an Otto Bock 3R15 rotated 90 degrees and the other with a fairly stable polycentric linkage. They are joined by a new model called the "Fusion" that seems to be a rotary hydraulic clone of the Bock 3R80 combined with the familiar Japanese MPC pneumatic swing phase cylinder. There was very little objective data offered but the video clips suggest that the new Fusion offers very good hydraulic stance control stability.

Kurt Lechler CPO(D) reported on a microprocessor-controlled prosthetic ankle being developed by OSSUR that adapts in the sagittal plane to uneven ground and also dorsiflexes during swing phase. Although it can be argued that dorsiflexion during swing phase is unnatural [since the normal foot is plantarflexed about 10 degrees at midswing], the Hydracadence knee-shin-foot assembly which was very popular with amputees in the 1950's and subsequent decades so we have long term clinical experience suggesting that this would be a useful "gait deviation" because it may offer some improvement in toe clearance. Furthermore, the Mauch hydraulic ankle of a few decades ago confirmed that many amputees strongly preferred its ability to adjust to changes in the slope of the terrain, so combining these two features seems promising.

OSSUR tested a prototype electronic ankle with 8 transtibial amputees by having them manually adjust the foot angle for various inclines and declines. The results tended to cluster around similar dorsi-plantarflexion angles so they repeated the trials with a second prototype where these changes controlled automatically by the computer chip. Gait data showed an increase in both symmetry and self-selected walking velocity on inclines as well as greater toe clearance during swing phase.

Ian Fothergill, MBAPO showed several video vignettes of amputees walking successfully with the RHEO MPC knee, including two bilaterals [with KD-KD and KD-TF levels]. He also presented a patient with unilateral HD and another with unilateral TP amputations, all of whom readily mastered the use of the RHEO. No hard data was offered but visually the results looked comparable to other MPC knees. One of the clinical advantages of the RHEO seems to be the ease of knee flexion because this magnetorheological fluid-based design has very little inherent resistance compared to the more common hydraulic cylinder configurations. Particularly for higher level amputations, this may result in a beneficial increase in knee flexion during early swing phase.

Kurt Collier CP highlighted a new coating that can be applied to Freedom Innovations ' silicone liners to eliminate the hassles associated with fabric coverings. Called "Parlene", this is a cross-over technology from the cardiac catheter industry where it is used to make silicone "slipperier". Kurt reported that the mild texture that results also permits writing on the outer surface of the liner to cue the patients, etcetera.

The balance of the talks in this session were mostly repeats from the prior Academy meeting so I took this opportunity to start going through the exhibit hall, which was completely filled to capacity. For the first time in recent memory, I was able to make it through the entire hall twice. Although I didn't see any earthshaking new developments, there were a number of nice incremental improvements in orthotic and prosthetic options for our patients.

Exhibit Hall

The long-rumored Otto Bock electric elbow debuted at this meeting although some of the details were still being finalized. A formal training program will be required, based on the C-Leg model, so both prosthetist and patient must initially go to Minneapolis prior to the initial order for this component. The variety of control schemes available is almost overwhelming, but the smart software seems to do a good job of guiding the decision-making process. Suffice to say, the 12K100 elbow can be operated with all the familiar OB control options as well as several newly released algorithms, using the full array of switches, transducers, and electrodes. The result is a large palate of single speed and proportional control choices that can be reprogrammed at any time to better meet the amputee's individual needs and preferences.

The electric model incorporates the Automatic Forearm Balance feature that stores energy when the elbow is extended and returns it to facilitate flexion. When combined with a stepless transmission, the result is the best live-lift capability for any electric elbow to date: up to 6 kilos [ > 13 pounds ]. The wrap clutch locking mechanism as well as forearm and turntable connections are unaltered making the 12K100 technically interchangeable with earlier body powered AFB elbows and vice versa.

The other new MPC component at the OB booth was the electronic orthotic Stance Control knee joint developed by the team at the Mayo clinic, called the Sensor Walk™ Two key distinctions between this somewhat bulky single lateral joint and similar alternatives are that it is rated for up to 300 pounds of loading and will release with up to a 30 degree knee flexion contracture.

Speaking of stance control orthoses, Horton's Technology showed their SCOKJ® Jr. orthotic knee joints, which reportedly will be available after the first of the year. This is a much smaller package than the original design, suitable for pediatric applications and smaller adults. The weight limit has not yet been finalized since testing is still underway but is said to be "greater than 100 pounds". It offers the same three biomechanical modes as the original SCOKJ®: stance control, manual lock, and free swing. However, in the smaller version the locking mode can be "preselected" with the knee flexed allowing the patient to stand up without resistance but assuring that no further knee flexion is permitted. Once the patient is standing, the joints are then locked in full extension, directly analogous to the manual locking feature on the Mauch SNS prosthetic knee.

Almost every supplier in the industry has added minute amounts of silver to their existing product line to increase the "antimicrobial" effect. This trend continues to escalate at each meeting despite the lack of any significant evidence that this is highly beneficial to the overwhelming majority of amputees with intact skin. Scientific studies have clearly shown that small bits of silver discourage the growth of microbes and there is some evidence that this is useful in the presence of open wounds. Whether this characteristic will be of general benefit to amputees is unknown at this time: there is no guarantee "silverizing" prosthetic items will be as beneficial as disinfectant hand cleansers.

One of the more novel applications was North Sea Plastics ' introduction of antimicrobial flexible thermoplastics for prosthetic sockets. Since these materials are usually worn directly against the skin in an environment that pools perspiration, this application may reduce the development of "locker room odors" that often emanate from well-worn prostheses of this type. Only clinical experience will tell if this proves to be a long term advantage to the patient or not.

KISS Technologies has developed a slick little wrinkle on their Keep It Simple Suspension system, a hook-and-loop lanyard providing easy donning and enhanced rotational control. Their new KISS™XD provides a direct connection for perspiration collection and expulsion when combined with the Bock Harmony™ System. More details are online at www.kiss-suspension.com .

Three novel new carbon fiber dynamic response prosthetic feet caught my eye at this meeting. Freedom Innovations has released an interesting design that offers greater flexibility in all three planes than their prior products. Rather than having a solid carbon fiber plantar plate inside the foot shell, the Silhouette has a plantar element with compressible polyurethane rubber along the medial and lateral borders. Reducing the amount of carbon fiber diminishes the dynamic response somewhat but increases the available inversion and eversion motion.

The slightly thinner anterior blade is also a bit less dynamic than the Renegade and related feet but can rotate a few degrees within the foot shell, providing very low resistance to initial transverse rotation. Once the blade contacts the sides of the foot shell, the transverse rotation is dampened, but if a large enough rotary force is applied the shin blade then begins to twist. The patient models I spoke with reported a similar overall range of motion to other high profile feet with large polyurethane blocks that are bonded to the anterior and plantar blades but less rotation than those designs that incorporate a adjustable torque absorbing element.

American Prosthetic Components was showing a reincarnation of the old "Cirrus" foot concept called the SpringFlex™ that is rated, in the larger sizes, for up to 400 pound individuals. Initial clinical feedback about the old "Cirrus" was generally favorable, particularly its flexibility and smooth rollover; American makes similar claims for their design. The fatal flaw with the "Cirrus" was the chronic wear and noise problems that inevitably arose and could not be remedied. This approach appears to be simpler mechanically [three C-shaped elements rather than five] and should therefore be less prone to such troubles. American also promotes this as offering "true vertical shock" and offers a three-year warranty on the foot itself [but presumably not the foot shell].

Perhaps the most unusual configuration was the PerfectStride™ foot shown at Townsend 's exhibit. This high profile component is a hybrid design that integrates a titanium shank spring with an aluminum ankle housing and a carbon fiber foot plate. It also offers a patient-adjustable heel height adjustment. The claimed improvements in power generation were intriguing but not specific supportive data was offered either during Barry's talk or at the booth. The concept of tweaking dynamic response foot designs to release the stored energy later in stance phase, when it may to the amputee more good, is an increasing trend in the industry. This product is not yet commercially available but it sufficiently intriguing to be worth watching.

I spotted two body powered upper limb advances. The first is a very elegant-looking and light weight wrist flexion unit from Texas Assistive Devices . This clever design provides a quick disconnect option for body powered terminal devices and fits into the standard Otto Bock ball-bearing myoelectric wrist unit. This is the first new flexion unit since the APRL era and a unique addition to our upper limb armamentarium.

Perhaps the most original concept I saw this year was the body powered articulated finger prosthesis from Didrick Medical . Actually, this item debuted at the prior Academy meeting but I missed it among all the more familiar booths.

The mechanism is basically a proximal metacarpal-phalangeal-driven four bar linkage covered with a silicone finger shell. Unlike the widely available passive silicone finger restorations, the X-Finger™ actively flexes and extends the PIP and DIP joints when the patient moves their metacarpal-phalangeal joint. This is not a complete product; they recommend that you contract with a local stereolithography firm to make the necessary silicone covering. Durability is unknown at this time but the samples they showed seem pretty resilient. They report that the anchoring framework will distort if overloaded but that the articulation itself will not fail. They recommend that the patient simple straighten out the anchoring framework if it is bent from application of too much stress.