Artificial Limbs 1

Why do arms and legs enable someone to do

enable movement, fine motor skills, provide support & maintaining balance, moving, engaging with the surrounding environment

what are the 3 distinct features of a limb

bones, muscles and joints

What is bone

bone is a composite tissue consisting of mineral, matrix (collagen and non-collagenous proteins), cells and water

what are the 5 main functions of the bones

1. support of the body

2. protection of soft organs

3. storage of minerals and fats

4. blood cell formation (hematopoiesis)

5. movement thanks to the attached skeletal muscles

what are joints

joints are the areas where two or more bones meet. Most joints are mobile, allowing the bones to move, creates the flexibility of the human body, types of joints according to the movement they allow

what are the 3 types of muscles

1. smooth muscle- found in the internal organs and blood vessels → involuntary

2. cardiac muscle- found only in the heart

3. skeletal muscle- attached to the skeleton → voluntary

what is the result of a muscle contraction

is always tension; a muscle can only exert a pull, muscles cannot exert a push

movement of the human body segments is achieved as

a result of forces generated by skeletal muscles

antagonistic muscle pairs

the muscle is contracting is called the agonist and the muscle that is relaxing or lengthening is called the antagonist

what happens during a bicep curl

• the biceps will be the agonist

• the triceps will eb the antagonist

what are ligaments

• connect bones to bones directly

• limit joint movement and stabilize joints

• in physiological conditions, experience low loads which increase with range of motion

what are tendons

• attach muscle to bones

• loaded in series with the muscles

• experience high loads

lower limbs anatomy

1. quadriceps femoris group

2. hamstring group

3. gluteal muscles

4. adductors

5. abductors

6. calf muscles

7. tibialis anterior

isometric contractions

generate force without changing the length of the muscle

Isotonic contractions

generate force by changing the length of the muscle and can be concentric or eccentric contractions

Isotonic concentric contraction

causes muscles to shorten, thereby generating force

Isotonic eccentric contractions

allow a controlled elongation in response to a greater opposing force

what are the two phases of a normal step

stance and swing

stance phase

Stance phase occupies 60% of the gait cycle, during which one leg and foot are bearing most or all of the body weight

swing phase

Swing phase occupies only 40% of it, during which the foot is not touching the walking surface

double-support phase

both feet are in contact with the floor at the same time for about 20% of the time. This part of the cycle is called the double-support phase

orthosis

medical apparatus designed to support, align, or enhance the function of a person's musculoskeletal system.

• address various orthopaedic issues

• correct deformities

• provide stability to an affected body part.

prostheses

artificial device that replaces a missing body part, such as a limb, joint, or even a tooth. restore functionality and improve the quality of life for individuals who have lost a part of their body due to injury, disease, or congenital conditions.

what are the two type of limb prostheses

artificial limbs and joint prostheses

what are the differences between orthosis and prosthesis

orthosis: support and improve function

prosthesis: replace missing part

what medical conditions can prostheses help

amputations, replacements, birth abnormalities

what may create a situation of incapable of exercising their physiological action

in a pathological situation, however one or more tissues may be weakened or damaged and therefore incapable of exercising their physiological action

how can normal functionality be re-established through the use of orthoses

the use of orthoses that modify the system of forces and moments acting on one or more joints of the body, compensating for the inadequacy of the compromised tissues

what is the function of orthotic design

function, comfort, cosmesis, fabrication, cost

what is the function of orthotic design (FUNCTION)

• meets the individuals mobility needs and goals

• maximises stance phase stability

• minimizes abnormal alignment

• minimally compromises swing clearance

• effectively prepositions the limb for initial contact

• is energy efficient

what is the function of orthotic design (COMFORT)

• can be worn for long periods without damaging skin or causing pain

• can be easily donned and doffed

what is the function of orthotic design (COSMESIS)

meets the individuals need to fit in with peers

what is the function of orthotic design (FABRICATION)

• Can be made in the shortest period of time

• Uses a minimally complex design

• Has some degree of adjustability to enhance initial fitting

• For children, responds to growth or change over time

• Is durable: stands up to stresses/strains of daily activity

what is the function of orthotic design (COST)

can be made with minimal initial cost, and minimal cost for maintenance

How is orthosis manufactured

Once the orthotist has determined the configuration and orientation of the subject's anatomy for corrective measures, the limb shape is captured by wrapping a sock and casting the leg (Figure A,B)

Once the cast has set it is cut away along the anterior contour (Figure C).

Plaster is poured into the leg cavity. Key surfaces are built outwards with plaster by embedding staples corresponding to surface markers (Figure D).

Pre-heated thermoplastic is vacuum formed around the plaster (Figure E). Once cool, the unwanted plastic is cut away, and edges on the AFO are ground down & smoothed (Figure F).

Due to warehousing considerations, most leg busts in clinics are not kept for more than typically 2 months, so for each patient refitting (typically occurring every other year), the whole process must start from the beginning

Manufacturing of orthosis using CAD

a. The patient is positioned; a 3D scanner capable of creating a full 3D point cloud of the ankle-foot complex is used to record the anatomical surface

b. the point cloud is processed and manipulated to create the computer model of the desired orthosis according to the clinical needs

c. RP is used to fabricate the orthosis

ankle foot orthosis (rigid or solid)

characterized by stiff shells preventing ankle movement in the three anatomical planes

ankle foot orthosis (dynamic)

flexible in the sagittal plane, allow for some dorsi/plantarflexion movement

how can flexibility be provided for AFO

Flexibility can be provided by a deformable shell (non articulated: e.g. posterior leaf spring or ventral shell spring) or via a fixed-stiffness hinge joint (articulated: spring-hinged posterior or ventral shell).Flexibility can be provided by a deformable shell (non articulated: e.g. posterior leaf spring or ventral shell spring) or via a fixed-stiffness hinge joint (articulated: spring-hinged posterior or ventral shell).

What is the purpose of AFO- Fixed

• provide a rigid structure around the foot and ankle, promoting healing

• stop the foot from dropping during walking

What is the design considerations of AFO- Fixed

• standardised sizing

• level of affixation (neurological or orthopaedic)

• comfort

• length of wear

• cost

What is the human factors of AFO- Fixed

• will the user be able to don and off themselves

• can it be put on wrong

• will overuse cause damage

• how much walking will they be doing

What is the design considerations of AFO- Hinged/Spring

• Semi Custom

• User comfort

• Cost low/high

What is the purpose of AFO- Hinged/Spring

• lift the foot during walking (neurological conditions)

• maintain energy through gait

What is the human factors of AFO- Hinged/Spring

• more active users

• complex conditions

What is AFO designed to control and improve

AFO is designed to control the motion of the ankle joint, and to improve the gait function of patients with motor impairments

what is the three point pressure system

Three point pressure system helps manage the deformities such as excessive pronation and valgus angles

F1 is applied to the proximal-posterior calf

F2 to the foot sole

F3 to the dorsal foot

This system limits the motion around the joint axes and therefore rotations around the joint axes could be managed and joint stabilizations could be provided