Artificial Limbs 2

What are prosthetics used to help with

• problems with blood circulation

• injuries

• cancer

• birth defects

what is the economic strain of undergoing an amputation of patients with diabetes mellitus

Patients with diabetes mellitus have an astounding 30 times greater lifetime risk of undergoing an amputation when compared to patients without diabetes mellitus, which translates to an economic strain in healthcare systems of over $4.3billion in annual costs in the USA alone

Transfemoral

amputation above knee

knee disarticulation

amputation at knee

transtibial

amputation below knee

What are the parts of the lower limb prosthetics

socket, knee, adaptors/pylon, foot

lower limb prosthetic sockets

Sockets house the user's residual limb and facilitate the load transfer of walking from prosthesis to limb, also house the suspension system that hold the prosthesis onto the user, most common component leading to pain and discomfort

How are lower limb prosthetics sockets fabricated

casting, rectified mould, lamination, trim/fitting

How are prosthetic socket loaded

for lower limb prosthetic the socket is the load transfer interface and there are limited pressure tolerant areas on the residuum. Pressure distribution is normally achieved through material addition and reduction in the mould rectification stages

suspension

method of affixing the prosthesis onto the limb

what are the different types of prosthetic suspension

cuff, sleeve, vacuum, pin lock and magnetic

what is involved when tissue response to external forces

tissue deformation, interstitial fluid flow, ischemia, reactive hyperemia, sweat, pain and skin discoloration

what can happen when moderate static forces are applied to the skin

When moderate static forces are applied to the skin, the underlying blood vessels and lymphatic drainage can be occluded (fully or partially) and metabolism impaired

what can happen when there is impaired tissue function

Impaired tissue function can lead to tissue breakdown (superficial and deep)

osseointegration

• Osseointegration involves affixing an implant to the bone that allows direct fitment of limbs.

• The implant permanently protrudes from the skin

• This replaces the socket

• If there is a fault with this implant then further amputations may be required

• Implant technologies may become outdated

• Risk of infections is increased during both surgery and post operation

alignment of the prostheses

The alignment of the prostheses is the spatial relationship between the socket and foot. It is tuned by a prosthetist through bench, static and dynamic alignment procedures in the clinic

why does the prosthetic foot require alignment with the other limb

ensures a comfortable walking gait

what are the factors affecting alignment

biological limb dimensions, shoe type and heel height and pyramid positions for components

what are the different types of alignment/adaptor

pyramid/angle adaptors, rotation adaptor, shift adaptor, tube/length adaptor

SACH (Solid Ankle Cushion Heel)

• basic,

• durable

• inexpensive

• suitable for individuals who have limited walking requirements

• does not adapt to terrain

ESR (Energy Storage and Return)

• designed to store energy during early stance and then release a portion of that energy during late stance.

• during gait, work is provided by the weight of the body to load the spring into compression.

• The material of the prosthesis stores this work as potential energy

• the energy is then released as work to act upon another object when the compressive force is released

hydraulic foot

combines traditional prosthetic feet with the hydraulically-regulated movement of a mechanical ankle

e.g. a dynamic carbon fiber foot comprising independent toe and heel springs with a double cylinder hydraulic self-aligning ankle, allows a more natural rocking motion

what is hydraulic damping used to influence

Hydraulic damping is used to influence the movement of this joint, producing a viscoelastic property closer to the behaviour of human muscle (allows the ankle to self align and adapt)

MPF (microprocessor-controlled prosthetic foot)

hydraulic ankle/feet that use various sensors to continuously monitor the user’s movement and adjust both the angle and stiffness of the hydraulic ankle in real time

What are the critical design points of prosthetic feet

• create as natural of a walking gait as possible

• user comfort

• weight

• cost

• reduced energy/expenditure activity level

• life span

• technology/materials/improvements

K1 prosthesis

Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence. Typical of the limited and unlimited household ambulator

K2 prosthesis

Has the ability or potential for ambulation with the ability to traverse low-level environmental barriers such as curbs, stairs, or uneven surfaces. Typical of the limited community ambulator

K3 prosthesis

Has the ability or potential for ambulation variable cadence. Typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilisation beyond simple locomotion

K4 prosthesis

Has the ability or potential for prosthetic ambulation that exceeds the basic ambulation skills, exhibiting high impact, stress, or energy levels, typical of the prosthetic demands of the child, active adult, or athlete

what can the knee be considered as

The knee joint can be considered similar to an eccentric rolling joint rather than a single axis revolute joint

flexion mechanics simulated by

• This motion can be simulated with a 4 bar link mechanism.

• Prosthetics must simulate this motion without necessarily being placed in the same location as the removed biological knee joint.

• Other solutions (bioinspired) have been proposed

Materials for prosthetics

thermoplastics, carbon composites, fiberglass, titanium alloys, stainless steel, silicones

microprocessor lower limb prosthetics

Microprocessor lower limb prosthetics nominally work by estimating the stage in walking gait using accelerometers, and position sensors.

microprocessor controlled knees

Microprocessor-controlled knees provide the amputee with more stability on all kinds of terrains, slopes and steps (Joint design with an electrically controlled hydraulic damper, Therefore, in flexion the damper will contract and thus the piston will be driven downwardly in the cylinder by body load. In extension, the damper lengthens and the piston is pulled upwardly by body action)

what can a butterfly valve be used for

The butterfly valve is able to vary flow port areas and fluid flow rates to thereby vary resistance to knee joint rotation in either flexion or extension at the same time

Electromyography (EMG)

Electromyography (EMG) measures muscle response or electrical activity in response to a nerve’s stimulation of the muscle

lower limb prosthetics control

• The MIT agonist-antagonist myoneural interface (AMI) allows for direct mind control of the prosthesis by surface EMG sensors.

• Using various artificial sensing modalities, the AMI muscle dynamics are measured, and these sensory data are communicated using neural communications to an external prosthetic computer

• For every robotic degree-of freedom to be controlled within the external prosthesis, at least one AMI muscle pair is constructed

• The use of muscles through AMI will reduce the atrophy effect of the muscles possible leading to further socket fit issues.

• The communication is one way, but feedback from positional change simulates two way communication.

• This is due to native contractile mechanoreceptors within the natural tendon