Dual-State Hydraulic Stance-Controlled Knee Mechanism Showed Benefit

Results of a recent study published in the Journal of
Rehabilitation Research & Development
showed that
hydraulically actuated stance-controlled
knee joints offer advantages over the currently available
commercial options.

“Hybrid systems consisting of electrical stimulation and
dynamically controlled bracing can produce a total benefit that is greater than
the sum of the individual parts, and have real potential for facilitating
walking after complete paralysis due to thoracic spinal cord injury,” said
researcher Ronald J. Triolo, PhD.

Triolo is executive director of the Veterans Affairs Advanced Platform
Technology Center of Excellence, professor of orthopedics and biomedical
engineering at Case Western Reserve University, and senior research career
scientist at the Rehabilitation R&D Service in the US Department of
Veterans Affairs.

This hydraulic stance control knee mechanism (SCKM) was developed to
fully support the knee against flexion during stance. It also allows for
uninhibited motion during swing for paraplegia patients who are using
functional neuromuscular stimulation (FNS) for gait assistance.

“The device is primarily intended for use by individuals with motor
complete spinal cord injuries,” Triolo told O&P Business News.

Device evaluated

Triolo and colleagues designed and evaluated this new dual-state
hydraulic knee mechanism with the aim that it would provide a locking torque
and minimum resistance to flexion of the knee. The goal was to better support
the patient’s body weight when standing, provide single-limb support when
walking, and, alternately, unlock under load so that swing phase is unimpeded,
according to Triolo.

“Conventional commercial devices often don’t work well under
load and need to be unloaded before they can rotate freely. Our device was
conceived to work with electrical stimulation,” he said. “Walking
with electrical stimulation alone requires the quadriceps muscles to be active
for all of stance, which rapidly fatigues them and can limit walking time and

However, the development of a hybrid system such as this, consisting of
an orthosis that incorporates the dual-state knee mechanism and electrical
stimulation may be able to reduce the duty cycle of stimulation. This allows
for the muscles to rest, and the device can be unlocked for a more natural
swing phase.

Triolo and colleagues used ipsilateral and contralateral position and
force feedback to control SCKM.

Results showed that this mechanism can be readily constructed from
off-the-shelf components and controlled by a portable computer, according to
Triolo. Researchers found that the device could withstand more than 70 N-m of
flexion torque when locked, “which is more than sufficient to support
single-limb stance during walking or stationary bipedal standing and provided
minimal passive resistance when unlocked, allowing free knee extension.”

In addition, the device required no more than 13% of the torque
achievable with additional functional neuromuscular stimulation, and unlocked
under an applied flexion knee torque of up to 49 N-m.

Reduced stimulation

Triolo said that that incorporating the mechanism into a reciprocating
gait orthosis could potentially reduce stimulation by almost 70% if timed
appropriately with electrical stimulation.

“The device performed as expected and met all design
specifications, so the outcome was not surprising,” he said.

While the results of this current study confirmed the researchers’
hypothesis — they expected a significant reduction in stimulation duty
cycle — they were surprised by the actual size of the savings observed,
according to Triolo.

“These results should contribute to an increased interest in smart,
hydraulically actuated orthotic components that have received relatively little
attention,” Triolo said. “Also, the results should encourage
practitioners and researchers to investigate hybrid combinations of smart
orthotics and electrical stimulation.”

This research was funded by the US Department of Veterans Affairs and
the Department of Defense.

Triolo and colleagues are currently conducting follow-up studies to
evaluate adding a polycentric knee joint and variable damping to the mechanism
in an effort to facilitate stair descent. This should, in turn, provide a
loading response during weight acceptance in the early stance phase of gait,
according to Triolo.

“These innovations should extend the functionality of hybrid
systems and result in smoother and more efficient walking,” he said.
— by Tara Grassia

For more information:

  • To CS, Kobetic R, Bulea TC, et al. Stance control knee mechanism
    for lower-limb support in hybrid neuroprosthesis. J Rehabil Res
    . 2011;48(7):839-850.

Disclosure:Triolo has no relevant
financial disclosures.

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