The ultimate goal of prosthetic device designers is to precisely
replicate the construction, function and feel of a natural limb. The interface
design — uniting together device with residual limb — plays an
integral role in that ability. Experts and prosthetic users alike agree that
the functionality of the prosthesis means little if it does not seamlessly
attach to the body.
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| Randall Alley |
The patent-pending High-Fidelity Interface was created by Randall Alley,
BSc, CP, LP, FAAOP, chief executive officer of biodesigns inc., and
O&P Business News Practitioner Advisory Council member, to
accomplish just that.
Traditional interface designs have been based on outdated schools of
thought, Alley told O&P Business News. This philosophical
approach positions the interface as merely a vehicle for attaching components,
providing comfort and suspending the device.
“This limited view of the role interfaces play has caused us far
too often to view the interface in terms of prosthetic acceptance, rather than
prosthetic performance,” he said. “The two are inseparable, and our
limited view of its role has in turn limited development of interface design
for far too long.”
Alley has applied his years of research and knowledge of new technology
to creating the High-Fidelity Interface. According to a press release, the
device achieves skeletal stabilization with a series of alternating soft tissue
compression and release areas oriented carefully along the long axis of the
intrinsic bone. A specialized sensor can ensure adequate blood flow at the
interfacial boundary where compression occurs and pressure mapping can give an
indication of the intrinsic environment of the High-Fidelity Interface.
The High-Fidelity Interface works with both upper and lower limb
prostheses, with all myoelectric, body-powered or hybrid control systems, and
with any type of suspension system, including self-suspending, auxiliary
suspension, negative pressure and elevated vacuum. The technique also is
effective when applied in orthotic devices.
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| The High-Fidelity Interface engages the bone structure using alternating soft tissue compression and release making the biomechanical attributes similar to osseointegration without surgery. |
| Image: biodesigns inc. |
“At its core, the High-Fidelity Interface is a biomechanically
optimized system of alternating compressive struts and soft tissue release
areas that coalesce to form a method of better capturing and controlling
intrinsic skeletal motion,” he said. “The surprising thing to me was
the magnitude of the observed improvement in so many areas.”
Both the open and closed designs of the interface allow a considerable
amount of soft tissue to be released out of the field of compression, which
provides a high soft tissue preload within that field of compression, Alley
explained. The preloaded tissue overlies the bone so that the initiation of
skeletal motion causes a near-instantaneous response by the interface. The
prosthesis follows suit.
“It is remarkable how this is manifested both functionally —
with regard to lower heart rates during ambulation, improved energy retention,
range of motion, improved ability to handle higher loads and improved stability
— as well as cognitively — with respect to reported weight perception
[because the prosthesis feels like it weighs less], greater proprioceptive and
kinesthetic awareness and comfort,” he said. “My most recent lower
limb patient stated she could ‘walk with less effort. The prosthesis feels
much lighter and feels more like a part of me.’ At one point she said she
wanted to skip. Now that made me smile.”
Alley compared the interface to
osseointegration, without the surgery. Both options focus on
the skeleton to support the prosthesis, instead of the surrounding tissue of
the residual limb. He acknowledged that an external surface-mounted system
cannot achieve as direct a connection as one that is achieved by drilling into
bone — which is precisely what he intended.
“I don’t want that direct connection because, in my mind, the
price is too high,” he said. “Nevertheless we are both chasing the
same thing, skeletal control, and fortunately, both techniques offer a person
additional options.”
The downfalls of osseointegration, he said, are the possibility of
complications from invasive surgery, exposed wound areas at the point of
insertion and the added risks of leaving part of the skeletal system exposed to
the outside world.
“I am rooting for the day when osseointegration becomes safer, less
costly and an easier decision for an individual to make when considering the
array of rehabilitation choices available in the United States, where it
currently is not approved by the FDA,” he said.
Until then, however, he will advocate for this interface, incorporating
nearly the same level of biomechanical capability of osseointegration into a
safe, non-invasive design.
The High-Fidelity Interface currently is available for biodesigns’
patients only, however there are plans for field trials to document the range
of benefits this interface system offers. Alley is involving surgeons in his
trial, as the High-Fidelity Interface could change the way certain amputations
are performed; details were unavailable at the time of publication.
A few select institutions and individuals currently are working with the
interface under Alley’s guidance, including Matt Albuquerque, CPO, at Next
Step Orthotics & Prosthetics in Manchester, N.H., and John Brandt, CPO, and
Scott Schall, MSE, BSME, of Optimus Prosthetics in Dayton, Ohio. Both
biodesigns and Next Step are consultants for DEKA Research, which is creating
the “Luke Arm” under the Defense Advanced Research Projects Agency
Revolutionizing Prosthetics Project.
Alley is in the process of developing procedures and protocols so he can
eventually license the technology to a select group of prosthetists and
institutions. He already has had almost 30 prosthetists contact him with
interest in learning his system. — by Stephanie Z. Pavlou
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