The modern lower extremity prosthesis continues to evolve with the
addition of a technologically advanced and military-tailored X3 microprocessor
knee. Designed for transfemoral amputees, the first generation X2 by Otto Bock
HealthCare was released 2 years ago as a precursor to the X3.
To meet certain military criteria, the X2 microprocessor knee was built
with five sensors that recognize the actions of the user, allowing for a more
natural gait and less cognitive demand. The combination of microprocessor
sensors, gyroscopes, accelerators and hydraulics create a more stable knee that
can intuitively switch from walking mode to running mode for the user. The X3
is essentially the same knee as the X2, only further ruggedized to meet
military mission needs.
“The C-Leg was a great breakthrough in development, addressing
safety, stance stability and swing control compared to previous knees,”
Zach T. Harvey, CPO, chief prosthetist, Walter Reed National Military
Medical Center (WRNMMC) said. “The Genium, X2, and X3 are examples of
knees furthering improvement in terms of adaptation to various terrains,
efficiency of gait, and modeling more closely normal biomechanics.”
A government grant partially funded Otto Bock to develop a knee that was
versatile and durable enough to return some combat injured amputees to active
duty, according to Harvey. Compared with the C-Leg, the X3 increases dynamic
response, facilitates walking backwards and has increased durability. Tailored
to the military user’s needs, the X3 is waterproof up to 1 meter for
approximately 10 minutes.
“The initial benefits of the X2 and X3 appear to be the utilization
of stance flexion with the optimized physiological gait programming
feature,” Harvey told O&P Business News. “In theory, this
restores shock absorption and lessens work of the lower back and hip extensor
musculature. Standing mode has been reported to reduce the necessity to push
back in the socket and support weight acceptance, thus alleviating stress on
the lower back and contralateral limb.”
Who gets the X3?
The first 36 X2 units were supplied under the condition that they would
be exchanged for the X3, once it was available. The data and wear patterns from
the used X2s were assessed by the manufacturer in order to make future
improvements. WRNMMC completed a research study in conjunction with Brooke Army
Medical Center on the X2 and manuscripts will soon be submitted for
publication, according to Harvey.
“Some X3 knees have been exchanged for some of the original X2
knees,” Harvey said. “The advances with the X3 over the X2, such as
being waterproof, do not affect the functional performance of the individual.
There is no formal study under way regarding X3 knees, although clinical gait
evaluations are often being performed in order to optimize gait and
The X2, both in terms of functionality and technological advancement,
was considered an overwhelming success. Because of the positive feedback, will
users want to switch to the X3?
“The necessity of the additional ruggedized features of the X3
versus the X2 would be dependent upon the type of work and conditions under
which the work would be performed,” Harvey said. “Individuals who
have requirements for the X3 will switch over. When full production of the X3
begins, production of the X2 will cease. The X3 will then become one of the
options for our patients. Specific needs will determine if they need an X3, a
mechanical knee, a power knee, or some other microprocessor knee unit.”
According to the Army Times, as of early March, the Army is
collecting user feedback on the X3. It is currently only available to military
personnel. — by Anthony Calabro
For more information:
Tan, Michelle. Army Times. DoD says amputations reached wartime
high. Available at:
Accessed: April 9, 2012.
Disclosure: Harvey had no financial disclosures. The views
expressed in this article are those of the authors and do not necessarily
reflect the offcial policy or position of the Department of the Navy,
Department of the Army, Department of Defense, nor the US government.