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12-02-08 0905.jpg Bent knee 12-02-08 0902.jpg Foot 12-02-08 0903.jpg Knee 12-02-08 0904.jpg Socket 12-02-08 0907.jpg Liner Snapshot 2008-12-02 09-23-20.jpg Whole leg

Proposal: The Future of Prosthetic Legs is Now

Research Paper by Travis Pollen

Motivation for Project

I myself wear an artificial leg and am very interested in learning about the future of prosthetics as it pertains to myself as well as bioengineering. (Is there a code of ethics involved?) The situation over the summer involving the sprinter Oscar Pistorius really piqued my curiosity. Could artificial limbs really work better than human ones? Taking into consideration that I’m also missing my knee, could my artificial limb (with the flex foot and hydraulic knee) eventually be as good or better than my human leg? At what price? Also, after seeing I, Robot, I want to know if the technology exists now or is in the making for prosthetic limbs to look like human ones. I’m excited to utilize Swarthmore’s online resources such as science journals to get the newest information out there on this field.

Description of project

Five to six page paper that will include -- in technical as well as lay terms -- the history of prosthetics, current technology, and what the future may hold. I will also research who is doing the most state-of-the-art work, where the work is being done, how much it is costing, and who it is benefiting.

Time line

11/20 – Collect information from various sources and in various formats. 11/24 – Begin Wiki page, inputting information such as sources and notes. 11/25-12/8 – Create outline for final paper including source information. 12/9 – Present findings to class. 12/10 – Post final paper to Wiki.



Orthopedic Prosthetics and Orthotics in Rehabilitation. Bronzino, Joseph D. The Biomedical Engineering Handbook. Hartford: CRC Press, 1995.

Prosthesis - external devise that replaces lost parts or functions of neuroskeletomotor system (skeletal frame of body with muscles and nervous system which participate in movement and stabilization of body) -2055 Necessary after disease, trauma, or even birth Body has lost weight and is no longer symmetrical and balanced Me: you can't lose or gain too much weight because that throws off the fit of the socket Engineers daunted by design requirements for prostheses In order for prosthesis to function like a human leg, it must provide structural support for upper body when standing and walking (complex joint articulations and muscular motor system), sensory feedback (pressure, length, force, position sensors) There's no foot on which to bear weight, load has to be transferred elsewhere, where depends on the individual's limb shape Strive to make limb of similar weight (ACTUALLY MUCH LIGHTER!!!) with powerful motors and sensors connected to patient's neuromuscular system OR accept loss and redefine optimal function of new unit of person+technology Interface between external environment and human body isn't natural, especially for use during all waking hours (often 16 continuous hours) and right up against skin Future of coupling: Direct transcutaneous fixation to bone leads to infection due to lack of materials biocompatibility, for now we use straps or suction-2056

THREE areas of consideration: function, structure, cosmetics FUNCTION: Kinematics, dynamics, energy Coupling: molded to contours of patient, but not an exact match, shape rectified (adjusted) to relieve areas of skin with low load tolerance Alignment: for determining moments and forces transmitted to interface when foot is flat on ground Check socket for changing alignment (can't be done once things have been connected) Components/mechanisms: hinges and dampers, motions can be driven from external power sources (gas, electric/computers) but are usually body-powered Adjustability for kids Durability - absorb repeated shock of walking and major shocks during sports of falls - 2057 Mode of failure (slow yielding to avoid injury) Life of limb, hygiene, ease of cleaning COSMETIC covers - 3-D computer-aided design, CNC machining to generate customized shapes to match remaining limb "It is possible to function fairly well with one arm, but try walking with one leg." -2058 Tryna line knees up

Materials: at first it was carved wood, shaped leather, or beaten sheet metal -2059 Now we have thermosetting fiber-reinforced pastics hand-shaped over a plaster cast of limb, substitution of thermoforming plastics that could be automatically vacuum-formed made a leap forward Polypropylene Flex foot - traditional anthropomorphic design with imitation ankle joint and metatarsal break abandoned for functional design adopted to optimize energy storage and return, based ontwo leaf springs joined together at ankle with one splaying down toward toes to form forefoot spring and other rearward to form heel spring, adaptable to rough ground and shock-absorption (athletes!) - 2060 Carbon fiber (flexible?)

Computer-aided engineering - design of customized components to match to body shape, ability to produce well-fitting socket in one visit What they do for me: cast residual limb in plaster of paris, pour positive mold, rectify manually, fabricate socket over rectified cast - takes weeks OR Use advanced technology to capture limbs shape on computer, rectify it with computer algorithms, and CNC machine to produce rectified cast in a matter of minutes, vacuum-form machinery pulls socket rapidly over cast, socket ready for trial fitting in single session, shape stored digitally in computer, can be reproduced or adjusted Difficult to measure limb/trunk because the rest of the body gets in the way (resists being orientated conveniently in machines and distorts with slightest pressure) Instrumentation for body shape scanning - contact probes measuring contours of paster casts, triangulation Use "an adapted lathe with a milling head to spiral down a large cylindrical plug of a material such as a plaster of paris mix" Rectification - two options - prosthetist uses own expertise on 3D model OR computer has rectification maps/templates -2061

Describe parts (PICTURE!): liner, hard socket - 2064

Phases of walking Control of artificial lower limb most problematic during swing phase (foot lifted off ground to be guided into contact ahead of walker) Prosthesis has to be lighter than it's real counterpart Carbon fiber (and other composite materials) makes it light, pneumatic/hydraulically controlled damping mechanisms enable adjustment of swing phase to suit individual walking pattern (gait) - 2065 Swing-phase control of knee: resistance to flexion at late stance during toe-off controls tendency to heel rise at early swing, extension assist after mid-swing ensures limb's fully extended and ready for heel strike, resistance before terminal impact at end of extension swing dampens out inertial forces allowing smooth transition form flexed to extended knee position Conventional limbs - parameters determined by fixed components (springs and valves) and set to optimum for normal gait (one speed - limb leeds if walking slowly or vice versa) With a computer, built-in intelligence adjusts swing-phase automatically for cadence variations

Potentiometers, touch sensors, contact force, slip sensors -2066 Electromyographic signals (touch, hold, squeeze, and release)

Knee doesn't have a fixed axis, but it's best represented by a polycentric joint

Goal of low cost, custom product very difficult "taxes the skills of most engineers, both to design the product at reasonable up-front costs and to manufacture it economically in low volume" - 2068

Intermediate technology for 3rd world Not mass production, either

Artificial Limb. Schlager, Neil. How Products are Made: an Illustrated Guide to Product Manufacturing. Detroit: Gale Research Inc., 1994.

Me: We've come a long way since the simple peg leg. Many changes have been initiated by amputees themselves -14 J.E. Hanger Company has been around since the Civil War, when engineering student by said name designed a leg for himself and founded the company Modern plastics and pigments make prosthetics stronger and lighter and more realistic looking than those made of iron/wood Myoelectricity uses electric signals from patient's remaining muscles to move limb

Impressioning/digital imaging: CAD/CAM - design model of patient's residual limb and prepare mold from which new limb can be shaped -15 Also laser guided measuring/fitting

Parts: custom fit socket (made of polypropylene), pylon - endoskeletal part - (titanium, aluminum, carbon fiber - not steel anymore), belt that attaches to body, prosthetic socks to cushion area of contact (cotton, - not wool anymore), cover (soft polyurethane foam cover that matches shape of other leg, covered with artificial skin that matches actual color, adjustability in thickness) -16 {Soft foam liner-17} Feet made of urethane foam with wooden inner keel

Manufacturing: Feet and pylons made in factories Goal to have limb that is as comfy and useful as the real deal Plaster of paris cast of stump from which positive model (duplicate) of residual limb is made Transparent thermoplastic sheet is test socket, can be heated and formed Importance: fit/comfort, functionality, cosmetic appeal Socket often has to be replaced annually Components put together with bolts, adhesives (Loctite), and LAMINATION - which can come apart (leg breaks) Assembled with torque wrench, screwdriver

There aren't any quality control standards for prostheses in U.S. -17 Manufacturers do test products Static loads for strength test (weight until deformation, weight until failure) -18 Cyclic loads for determining limb lifetime (for examples: one load/second, two million times) Software developed that superimposes grid on CAT scan of residual limb to show amount of pressure soft tissue can endure without pain, socket designed to minimize amount of soft tissue displaced Pressure-sensitive feet - pressure transducers in feet send signals to electrodes in stump, nerves receive and interpret signals, amputees walk more normally because they can feel ground and adjust gait Also, above-knee legs that have built-in computers programmed to match wearer's gait, making walking automatic and natural

Has to be easy to learn how to use, require little repair/replacement, be comfy and easy to take on and off, strong yet light, easily adjustable, natural looking, easy to clean


We Have Always Been Bionic. Perkowitz, Sidney. Digital People: From Bionic Humans to Androids. Washington, D.C.: Joseph Henry Press, 2004.

Key to synthesis is connecting neural systems to electronic ones (neuroprosthesis) -86 Functional and virtual rehabilitation -87 First written accounts of prosthetics: An Indian poem from over 4000 years ago about a queen who lost her leg in battle, replaced it with an iron one, and came back to continue fighting Greek mythology, where one of the gods give Zeus's son an ivory shoulder Play by Aristophanes including character with wooden leg Romans used wooden peg legs and iron hooks in medieval times - don't match usefulness or look of real hand Until recently, cosmetic appearance and proper functionality were rarely combined "Natural appearance often had to be sacrificed to functionality, and power to operate a limb was hard to come by." -89 in 1800 the Anglesey Leg was created. It featured an articulating foot controlled by strings from the knee to the ankle. These cables were similar to tendons stretching from muscles in arm to control fingers. Breakthrough: artificial muscles that work like real ones Needs of knightly warriors of the past similar to those of injured war veterans today -90 Need for serious development of prostheses gained recognition after WWII, when the U.S. gained 45,000 new amputees U.S. population today has more than a million amputees and 100,000 new lower limb ones every year -91 Other parts of the world, war and land mines leave lots more without limbs Titanium and now graphite composites like tennis rackets Plastics can be formed into natural-appearing limbs Mechanical systems to articulate limbs - pneumatic or hydraulic fittings Energy storing artificial feet, springs that compresses as foot strikes ground and then extends to release stored energy and propel leg forward in stride Extremely small, battery-operated motors Future - connection between digital electronics and prosthetic science - Sensory capability to test nature of walking surface, adjust pace, and maintain balance, receive commands from brain (processing power) -92 New "smart legs" have electronic sensors and computer chips Direct neural connection between limb and brain further off but beginning to see results

Hin, Teoh Swee. Engineering Materials for Biomedical Applications. London: World Scientific, 2004.

Me: various branches of engineering: rehabilitation, bio(mechanical), computer-aided, materials y ¿qué más? Gait studies

Interface between stump and prosthesis is the socket, so is interface between man and machine -10-1 "The field of prosthetics rlies heavily on innovative use of existing materials often found in other industries," especially aerospace

Intro: Rehabilitation engineering - "application of science and technology to ameliorate the handicaps of individuals with disabilities ... and recover physical capabilities" Lower extremity amputation after car crashes, land mines, vascular diseases Trans-femoral prosthesis = above-knee, trans-tibial = below-knee -10-2 Parts: socket, knee, shank (pylon), ankle, foot 1950: wooden

        • Today (talk about each of these individually): flexible plastic socket, computer controlled knee, carbon-fiber shank, energy storing foot

Me: makes runners like Oscar Pistorius competitive with able-bodied runners

Function and Safety: 10-3 New methods and materials improve function and safety during walking Human walk has swing and stance phases Stance phase broken into heel contact, mid stance, and toe/push off

    • Components have to be optimized for all phases of gait

Me: that's why you can't have one leg that does everything - specialized legs for different activities Lightweight for swing, strong for stance -10-4 Gait analysis involves temporal-distance measurements, kinematics, kinetics (forces, pressure), energy factors, muscle activity T-D measurements are speed, stride length, step length, cadence, and gait cycle AKA walk 40% slower than normal "The combination of both kinematics and kinetics data enables the transformation of ground reaction forces to the respective anatomical joints, defining forces and moments at the various joints." Gait studies of different prosthetic feet provide quantitative measurement of gait restoration - expensive, though (FUTURE: everyone will get this done) 1996: fundamental safety requirements made official (standards to describe static and dynamic/cyclic strength tests evaluating using load carrying) Loads applied to whole leg or individual parts, relative alignment matters Tested at heel strike and toe off

Methods and Materials: 10-6 Each amputee's stump is unique "A successful fitting is still highly dependent on the skill and experience of the prosthetist" Computer-Aided Design (CAD) and Computer-Aided Manufacturing (CAM) increase productivity and quality Comprised of a computer and a carving/milling machine (carves on plaster, foam, or wax) Three steps: measure body contours (non-contact laser scanning) and convert to digital data for computer, generate and manipulate/rectify (decrease/add volume) shape, realize physical socket (vacuum formed by draping heated thermoplastics over positive model) Newest processes have cut out need for (plaster of paris) positive model and go straight to fabrication of socket by controlled layering of molten polypropylene (can take as little as half an hours!) -10-7

Intelligent CAD/CAM: "a good fit is primarily not defined by a particular shape of socket, but by the accommodation of forces of pressure between the stump and the socket, to provide for comfortable and harmless weight bearing, stabilization and suspension." Stump/socket interface pressure is a quantitative way to evaluate the fit of the socket Soft tissue displacement, ideal pressure distribution calculated Me: problem is that pressure points are different during each phase of gait Combining pressure software (much like that which comes with SolidWorks) with CAD/CAM could results in giving it intelligence - iterative loop formed in which CAD software recreates socket, system calculates pressure distribution, and repeat until distribution is satisfactory-10-8

Socket design: 10-11 Factors affecting acceptability of socket fit: Stump geometry, tissue viability (pain, vascular response, skin temperature, skin abrasion), stump/socket interface mechanics from external loading (walking, running, standing) Different sockets results in different comfort levels and varying gait patterns Me: a poor gait really screws you up later in life Socket must encourage muscle usage Inconsistency is a problem for prosthetists (i.e. it doesn't always work and sometimes one has to start all over) Me: When you cast by hand you have to act like you're weight bearing and you have to have the angle exactly right New methods of pressure casting using and air pressure chamber eliminate the need for rectification -10-14

Foot: Energy storing (and returning) prosthetic feet - store energy during stance and release it during pus off, reduces fatigue and improves comfort Strong, flexible, spring-like materials - carbon fiber and Kevlar Allow stiffness tuning to adjust to body weight and activity Built-in shock pylons Incorrect foot stiffness can have big effect on overall fit of leg

Perspectives on How and Why Feet are Prescribed. Journal of Prosthetics and Orthotics > 2005 Vol. 17, Num. 4S > pp. 18-22

"Prosthetic components often emulate shock absorption functions of the physiologic foot, but usually have far fewer mechanisms to do so." "Prosthetic feet do not yet offer the degree of variable stiffness provided by the physiologic foot. Designs often compromise between the softness at the second rocker and the stiffness required at terminal stance. Usually designers seem to err toward stiffness, because drop off at terminal stance is undesirable, and even potentially hazardous for the transfemoral user if it causes knee instability." "One disadvantage in foot designs with a cushion type heel is the prolonged "heel-only" contact. ... Prolonged heel loading can also result in more falls when patients walk on low-friction surfaces such as wet tile or ice." "Dynamic-response feet can simulate progression by flexing with the load and carrying the arc of motion to the toes." There are quantitative studies, but... "Currently, prosthetists use a process based primarily on empirical observation. This includes functional assessment and patient feedback concerning the transition in rollover during stance." Sliding and tilting (altering component alignment) affects rollover shape "foot selection factors including cadence speed, uneven terrain, stability and balance, amputation level, weight, size of foot, special functions, effect of alignment, product warranty and maintenance, and cost." COST ESPECIALLY

      • Bumpers in knee add/take away stiffness

Foot has to be light but it can't be too light because amputee has to be able to feel it move through space "Combining an understanding of the normal human foot with knowledge of how prosthetic feet try to emulate those functions assists in the design, evaluation, prescription, and use of a prosthetic foot and ankle system."

Ergas, Enrique. "Prosthesis". AccessScience@McGraw-Hill. DOI 10.1036/1097-8542.YB990745.

Kinematics, stability, normal alignment, balance, distribution of forces through weight distribution in a variety of positions Materials have to be resistant to friction and wear Early prostheses considered knee as simple hinge, flexion and extension limited to single axis Knee actually multicentered with polyaxial movements Load applied to knee while walking = three times body weight, 4 to 7 for stair climbing and running!

Inside leg: Biocompatible Alloys based cobalt, titanium, iron, chrome Ultrahigh-molecular-weight polyethylene is plastic with some flexibility under load, very resistant to wear Fix to bone by... special cement, porous coated metal surface + bony ingrowth into implant, or press-fit (bone altered, prosthesis jammed in, risk of fracture) Problematic when things loosen