Lower-extremity prosthetics Prosthesis

1 lower-extremity prosthetics

1.1 socket
1.2 shank , connectors
1.3 foot
1.4 knee joint

1.4.1 microprocessor control

lower-extremity prosthetics

a prosthetic leg worn ellie cole

lower-extremity prosthetics describes artificially replaced limbs located @ hip level or lower. concerning ages ephraim et al. (2003) found worldwide estimate of all-cause lower-extremity amputations of 2.0–5.9 per 10,000 inhabitants. birth prevalence rates of congenital limb deficiency found estimate between 3.5–7.1 cases per 10,000 births.

the 2 main subcategories of lower extremity prosthetic devices trans-tibial (any amputation transecting tibia bone or congenital anomaly resulting in tibial deficiency), , trans-femoral (any amputation transecting femur bone or congenital anomaly resulting in femoral deficiency). in prosthetic industry trans-tibial prosthetic leg referred bk or below knee prosthesis while trans-femoral prosthetic leg referred ak or above knee prosthesis.

other, less prevalent lower extremity cases include following:

socket

this important part serves interface between residuum , prosthesis, allowing comfortable weight-bearing, movement control , proprioception. fitting 1 of challenging aspects of entire prosthesis. difficulties accompanied socket needs have perfect fit, total surface bearing prevent painful pressure spots. needs flexible, sturdy, allow normal gait movement not bend under pressure.

shank , connectors

this part creates distance , support between knee-joint , foot (in case of upper-leg prosthesis) or between socket , foot. type of connectors used between shank , knee/foot determines whether prosthesis modular or not. modular means angle , displacement of foot in respect socket can changed after fitting. in developing countries prosthesis non-modular, in order reduce cost. when considering children modularity of angle , height important because of average growth of 1.9 cm annually.

foot

providing contact ground, foot provides shock absorption , stability during stance. additionally influences gait biomechanics shape , stiffness. because trajectory of center of pressure (cop) , angle of ground reaction forces determined shape , stiffness of foot , needs match subject s build in order produce normal gait pattern. andrysek (2010) found 16 different types of feet, varying results concerning durability , biomechanics. main problem found in current feet durability, endurance ranging 16–32 months these results adults , worse children due higher activity levels , scale effects.

knee joint

in case of trans-femoral amputation there need complex connector providing articulation, allowing flexion during swing-phase not during stance.

microprocessor control

to mimic knee s functionality during gait, microprocessor-controlled knee joints have been developed control flexion of knee. examples otto bock’s c-leg, introduced in 1997, ossur s rheo knee, released in 2005, power knee ossur, introduced in 2006, plié knee freedom innovations , daw industries’ self learning knee (slk).

the idea developed kelly james, canadian engineer, @ university of alberta.

a microprocessor used interpret , analyse signals knee-angle sensors , moment sensors. microprocessor receives signals sensors determine type of motion being employed amputee. microprocessor controlled knee-joints powered battery housed inside prosthesis.

the sensory signals computed microprocessor used control resistance generated hydraulic cylinders in knee-joint. small valves control amount of hydraulic fluid can pass , out of cylinder, regulating extension , compression of piston connected upper section of knee.

the main advantage of microprocessor-controlled prosthesis closer approximation amputee’s natural gait. allow amputees walk near walking speed or run. variations in speed possible , taken account sensors , communicated microprocessor, adjusts these changes accordingly. enables amputees walk down stairs step-over-step approach, rather 1 step @ time approach used mechanical knees.

however, have significant drawbacks impair use. can susceptible water damage , great care must taken ensure prosthesis remains dry.