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AOPA Assembly 2004

As this Corner is being written, the Annual Assembly of the American Orthotic & Prosthetic Association in Hollywood, Florida has just concluded. Despite the multiple hurricanes and tropical storms that had recently battered the region, the meeting was well attended and offered a good opportunity to sample current thinking and examine recent technological developments in the field.

The exhibit hall was packed with booths, including an increasing percentage purveying prefabricated orthoses that were minor variations on a common theme. Some new components and a few significant enhancements to familiar components did debut in Hollywood, but no real breakthrough technologies created a "buzz" at this meeting. Some of the more noteworthy items are highlighted below.

Otto Bock no longer exhibits at the Academy meeting, so this was the only opportunity to view their advancements at an annual meeting until another full year elapses. They had several noteworthy items on display, including a very nice redesign of their 3R60 prosthetic knee.

The original 3R60 was the first prosthetic knee to incorporate a stance phase hydraulic cylinder in addition to the familiar swing control hydraulic mechanism, although most people didn't recognize this innovation since the stance hydraulic is buried deep inside the frame structure. This micro-hydraulic cylinder dampens stance phase knee extension, so patients using the 3R60 could walk with a significantly flexed knee during loading response without the "bouncy effect" of simpler designs having only an elastomeric spring or SF bumper.

The 3R60 was also the first knee to have a stance flexion axis that was geometrically different from the swing axis, permitting the savvy prosthetist to align the prosthesis so the knee was sufficiently "triggered" to facilitate measurable knee flexion during loading response without being unstable. Yet another innovation was the clever link geometry that moved the instantaneous center of rotation for the swing axis posteriorly during stance flexion, making the knee geometrically safer during stance flexion without requiring a lock mechanism.

The clinical result of these engineering principles was a knee that patients perceived as safe, comfortable, and predictable. Although the engineers conceived this as a good design for the moderately active individual, prosthetists soon discovered that many much more active amputees preferred this combination of features too. It was particularly well received by many with bilateral lower limb loss or high-level amputation at the hip or transpelvic level, in addition to those with unilateral transfemoral prostheses. One practical limitation of the original 3R60 was that the swing hydraulic could only dampen knee flexion at a slow to moderate pace: very active ambulators could overpower the knee and then complained that it did not keep up with their pace. Another limitation was that the accumulator chamber was the rubber shroud external to the cylinder that could be damaged by twigs and similar debris, particularly for those patients who did not wear a protective covering over the mechanism of their prosthesis. The swing adjustments were buried deep inside the frame and, even with the adjustment tool provided, it took a steady eye and hand to fine tune the hydraulic resistances.

This second generation 3R60 has a completely redesigned dual-hydraulic system that Bock says overcomes these limitations. The exterior of the cylinder is now a metal alloy, and the internal resistances are reportedly significantly higher, which should make this knee more suitable for the full range of Medicare Level 3 and Level 4 ambulators. It looked to me as if the new rubber cover on the frame also functions as a mild stance extension assist, and the whole knee seemed to flex and extend very smoothly and easily in my hands. The new 3R60 is available with several proximal connection options that integrate with the knee ball, including the ubiquitous inverted pyramid and dome assembly that Otto Bock invented decades ago, a knee disarticulation socket adapter, a canted pyramid for HD/TP applications, and a threaded portion that will accept the three-prong rotatable socket adapters and similar connectors.

In addition to these biomechanical improvements, the second-generation 3R60 is 10 percent lighter than the original and has been tested for much higher loading: up to 275 pounds or 125 kilograms. And, the swing resistances are now readily adjusted from one location with a simple hex key. If the clinical performance of this 2G 3R60 is anywhere close to expectations, it will be a very versatile choice in our armamentarium.

Bock has also incrementally improved their dynamic response foot with an S-shaped keel, now called the 1D35. The original design had a very stiff plantar flexion resistance, which some patients did not like. This redesign is said to have an ankle torque curve that more closely approximates that of the normal ankle, so this characteristic should be better. Bock was also showing yet another "Oreo" foot with the Springlite-style carbon fiber plate-polyurethane rubber block-carbon fiber plate construction, called the 1E56. Externally, it looked very much like the low profile configuration that Freedom Innovations introduced a year or two ago with their FS-2000 LP.

In their upper limb stable of components, some of the body-powered hooks from Germany are now available with a 1/2 - 20 thread compatible with US wrist units. There are two different configurations of "2-load" hooks that feature a simple lever the patient can engage to change to a much stronger grip force when desired. Unlike the US hooks, it uses springs to provide the pinch force, which should be more durable than rubber bands. They also swore that the 21A35=1 triple control harness kit is now in stock.

Most of the changes in externally powered components were software based, such as the new ability to govern the maximum velocity of the fingers of the SensorSpeed hand. Now that we finally have grasping components whose finger closing speed approximates that of a normal hand, some patients have trouble controlling them, particularly when initially fitted - as Dudley Childress predicted many decades ago, based on his research at Northwestern University. A simple interface connector inserts into the connection plug of the hand, allowing the practitioner to limit the maximum speed to the patient's preference.

The familiar rectangular Bock electrodes have also been redesigned to be more responsive, less subject to interference, and to better-maintain contact with the residual limb. The integrated electrode contacts are noticeably larger than the original version, although the overall dimension of the electrode-amplifier package is unchanged. It is great to see the rapid advancement in terminal device technology driving improvements in EMG controllers that in turn permits development of electronic TDs that are even closer the human hand performance. If arbitrary reimbursement reductions don't kill this momentum, we will likely see a spate of new upper limb technology for our patients in coming years.

TiMed was showing a new BK kit with a 34mm carbon fiber pylon and connectors that are rated for 500 pounds of loading when used with a Kingsley heavy duty foot. This is the highest rated endoskeletal system I am aware of, and is the only available option for transtibial amputees whose body weight exceeds the 300+ pound weight limits of other systems.

OSSUR debuted an interesting inframalleolar dynamic response foot called the Axia. The two carbon fiber plates are separated by a wedge of urethane, yet another example of "oreo" construction. But, two things are unique about the Axia. First, the urethane block has a series of vertical slits that can be stiffened by inserting urethane plugs. More intriguing, the upper plate is designed to be assymetrical so that the movement of the center of pressure deflects medially in late stance, similar to that of the biological foot. Orthotists have used "gait plates" for decades to influence the way pediatric patients walk, but this is the first prosthetic application I have seen. OSSUR had a poster display with gait analysis data demonstrating that the COP under the foot moved as they claimed.

There were a number of people walking around on the Rheo Knee at the OSSUR booth, so it is now apparently ready for clinical application. It is my understanding that they will offer one-on-one instruction in the proper use of this microprocessor-controlled knee, as Endolite has done in the US with their Adaptive knee. The use of MR fluid is innovative and eliminates the need for a piston-cylinder arrangement with high-pressure seals. The load limit for the Rheo is modest at 198 pounds and it is limited to moderate impact loads, but it can be used with any ankle-foot mechanism, so this will be an interesting addition to our stable of electronic prosthetic knees.

Sievert Industries was a new exhibitor at the AOPA meeting. They were showing an extensive line of small, refillable, self-igniting butane-powered torches that seemed well made and reasonably priced. Some were apparently based on catalytic heater technology because they produced very hot air without any flame. They had a very small soldering iron and a slick looking "pocket heat gun" as well. These tools would be very handy for test socket and thermoplastic orthosis adjustments, particularly during hospital calls or other off-site visits.

Liberating Technologies showed a new locking shoulder joint that seems to be smoother and easier for the patient to operate than the earlier LTI-Collier design. Although this is a niche component, it is great to see the steady improvement in prosthetic shoulder joints in recent years, since they are very useful to those patients who need them.