Orthosis

Question 1

What is an orthosis?

Answer 1

• A device that is Externally applied or Attached to a body segment and that Faciliates or Improves function by support, correcting or compensating for a skeletal deformity or weakness

Question 2

What is the regions of the body in aaos nomenclature?

Answer 2

upper limb

• S= shoulder
• E= elbow
• W= wrist
• H= Hand

Lower limb

• H= hip
• K= knee
• A= ankle
• F=foot

Spine

• C= Cervical
• T=thoracic
• L= lumbar
• S= sacroiliac

Question 3

What is the control of the designated function of Orthoses?

Answer 3

• F- free motion allowed
• A- assist
  
  • application of external force to increase range or velocity of a desire motion
• R- resist movement of a external force
• S - stop -ie static unit to deter motion
• H - hold ie elimination of all motion in a prescribed plane
• L -lock- optional lock

Question 4

What are the ideal characteristics of Orthoses ?

Answer 4

• Lightweight
• Durable
• Biomechanically effective
• Cosmetically pleasing
• Easy to don and off
• Rapid provision and replacement
• Washable
• Adjustable
• Comfortable
• Free of pressure areas

Question 5

What are the functional characteristics of Orthoses?

Answer 5

• Provisional support- prevent weak muscles/ligaments being stretched- TLO to support a collapsing osteeoporosis spine
• Limitation of motion - KO to prevent hyperextension
• Correction of deformity - force affected joint into near alignment and redirect growth e.g.a- tlso- Thoracolumbarsacral orthosis
• Assistance of motion- hkafo- hipkneeanklefoot orthosis in myelomeningocele
• Miscellaneous - warmth, placebo effect
• Combination-many combine several functions e.g.KAFO for leg with polio, gives support, limits movement at the knee, may correct ankle varus and springs assist ankle dorsiflexion

Question 6

What other ways can you define the function of orthosis?

Answer 6

• Static- has no moving parts and is used to immobilise a part of the body
• Dynamic- moving parts by movement is controlled by an energy store

Question 7

What must an orthosis have for proper control?

Answer 7

• 3 points of contact to control the joint

Question 8

What are the criteria for a supportive orthosis ?

Answer 8

• Joint must be maintained in an optimium anatomical position during rest period

Question 9

What is the purpose of a corrective orthosis ?

Answer 9

• Is to impose or control a set of forces on a body part
• Each force has magnitude and direction & the resultant worked out

Question 10

What is Newton’s 3rd law of reaction?

Answer 10

• For every reaction there is an equal and opposite reaction

Question 11

What is the ground reaction force?

Answer 11

• The force exerted by the ground on the body
• it is the magnitude but opposite in direction to the force exerted on the ground by the body
• if the GRF doesn’t pass thru the centre of the joint it creates a moment on that joint

Question 12

Where is the GRF in mid-stance?

Answer 12

• Posterior to the hip
  
  • -> hip extension moment counter balanced by the gradual tightening of the anterior hip capsule
• The GRF is anterior to the knee
  
  • -> knee extension moment that resisted by the tight posterior knee capsule
• the GFR falls anterior to the ankle
  
  • -> ankle dorsiflexion moment that is resisted by contraction os gastronemius soleus muscle complex
• ie in mid stance there is very little muscle activity required to maintain an up right position

Question 13

Where is the GRF in pre-swing?

Answer 13

• the force passes behind the knee
  
  • acts as a flexor- reducing the work requirements for knee flexion

Question 14

How do orthosese function?

Answer 14

• By application of mechanical forces to the musculoskeletal system

Question 15

How can orthosis modify the system of external forces and moments across a joint?

Answer 15

• Direct
  
  1. Control of moments about a joint
  2. control of translation forces across a joint
  3. control of axial forces across a joint
• Static
  
  1. Control of line of action

Question 16

describe how orthosis control of moments across a joint?

Answer 16

• most common reason for prescribing orthosis
• modifying the moments about a joint may partially or totally restrict the rotational movement at the joint
• -> either a decrease in ROM about a particular axis or a limitation in number of axes about which motion may occur by
• 3 point fixation
  
  • involves one force acting acting over the joint centre
  • other 2 forces acting in oppposite direction to the first, placed proximal and distal to the joint

Question 17

describe how orthosis control of translational forces across a joint?

Answer 17

• Translational forces arise only when there is significant shear forces acting across the joint
• achieved by 4 point fixation across joint
• can be hinged to allow rotation
• e.g. KO used to prevent translation in the transverse plane in PCL rupture

Question 18

decribe how orthosis control of axia forces across a joint?

Answer 18

• load sharing between the anatomical structures and the orthotic exoskeleton
• useful for reducing pain in arthritic joints

Question 19

decribe how orthosis control of line of action of GRF?

Answer 19

• involves modification of the point of application and line of action of the GRF during either static or dynamic weight bearing
• particulary useful in modifying abnormally high moments about a joint but also chnage alignment of a joint
• e.g. lateral heel wedge, transfer GRF from medial aspect of a varus degenerate knee to the intercondylar eminence or lateral joint line

Question 20

name the materials used in orthotics?

Answer 20

1. **Thermosetting plastics **
2. Thermoforming plastics
3. Self generating polyurethane foam

Question 21

What are the thermosetting plastics?

Answer 21

• Polyester resins
• can be moulded into permanent shape after heating
• don’t return to original consistency even after being reheated
• Formed by pouring liquid resins into moulds, mixed with a catalyst the polymerisation reaction of resin to set in a rigid form
• often used in prosthetics cf orthotics - where greater ridigity required

Question 22

What are thermoforming plastics?

Answer 22

• these soften when heated allowing reshaping by application of pressure
• harden when cool
• they can be **reshaped many times **
• subdivided into their moulding temperatures

1. High temperature thermoplastics
   
   • require moulding between 120-190oC
   • great skill required for manufacturing
   • Ideal for high stress activities
   • made by heating a sheet of polyethylene or polypropylene in a hot oven.
   • final product is in either vacuum formed or moulded over a positive POP cast
   • made for AFO/TLSO
2. Moderate temperature thermoplastics
   
   • require moulding temp 100-120oC
   • e.g.Plastozote foam made from polyethylene of closed cell construction
   • very lightweight
   • after heating in a hot-air oven it can be moulded directly on the patient as it has low heat conductivity & its sufaces cool rapidly
   • commonly used for custom cervical collars, pressure distribution pads
3. Low temperature thermoplastics
   
   • require moulding 80oC
   • can be moulded in water bath ot hot air oven
   • ideal for acute splinting
   • moulded directly to the patient with minor modifications made using a gun/hair dryer
   • less rigid and less durable
   • cheaper, less time and skill for fabrication
   • e.g. polycaprolactone (Polyform) to which synthetic rubber can be added

Question 23

What is the self generating polyurethane foam

Answer 23

• used in “neofract” for corset and braces
• freshly prepared foam is poured into a cotton pattern and distributed evenly with a roller
• the filled pattern is allowed to harden directly over the patient
• the custom-made cast is prepared in minutes and donned and doffed by using a zip fastener.
• polyurethane foam is used to make moulded cushions for wheelchairs adn can be as a filler in KAFO’s a nd shoes

Question 24

Name the types of insoles?

Answer 24

1. Simple
   
   • off the shelf/fabricated w cast
   • provide poor surface area contact
   • little mechanical control
2. Total contact insoles
   
   • made- initally imprint of pt foot & then casting of imprint w POP.
   • A thermoplastic then moulded from the positive pop cast.
   • most common type foot orthosis
3. Functional/biomechanical orthoses
   
   • corrective insoles
   • foot held in corrected position when cast is taken
   • insole obtained therefore acts to correct underlying foot deformity when the deformity is flexible
   • fixed deformities- require accomodative insole

Question 25

When the limits of insoles are reached what is available?

Answer 25

• Custom made shoes
• corrective or accommodative

Question 26

What are the heel modifications that can be made to shoes?

Answer 26

• altering heels; can be..

1. Cushioned
   
   • wedge of compression rubber used to absorb impact at heel strike or w rigid ankle plantarflexion by reducing the knee flexion moment
2. Flared
   
   • medial to resist eversion and lateral to resist inversion
3. Wedged
   
   • medial to promote inversion and lateral to promote eversion
4. extended
   
   • thomas heel projects anteriorly on the medial side to provide support to medial longitudinal arch
5. Elevated
   
   • shoe lift to compensate for fixed equinus deformity or LLD of > 0.65cm

Question 27

what can modifications can soles have?

Answer 27

• Rocker bars
  
  • convex structure placed posterior to MT head shifting rollover point from head to shaft
  • used for ulcers over MT in DM- see pic
• Metatarsal bars
  
  • bar with flat surface placed posterior to MT head to relive pressure on heads
• Wedges
  
  • medial to promote supination
  • lateral to promote pronate
• Flares
  
  • medial to resist eversion
  • lateral to resist inversion

Question 28

What modifications can be made to internal shoe heel modifications?

Answer 28

• Cushion relief
  
  • soft pad with excavation placed under the painful point of the heel
• Cups
  
  • rigid plastic inserts covering the plantar surface of the heel and extending posteriorly, medially and laterally to prevent lateral calcaneal shift in the flexible flat foot
• Universty of Berkley labortatory insert
  
  • rigid prefabricated over a cast of the foot hled in max manual correction and encompassing the heel,midfoot with rigid posterior, medial and lateral walls. Used to control hindfoot valgus and midfoot pronation

Question 29

Describe the internal modifications for insoles?

Answer 29

• Metatarsal pads
  
  • domed pads designed to reduce stress from MT heads by transferring load to MT shafts in metatarsalgia
• Inner sole excarvations
  
  • soft pad filled with compressed material placed under MT heads
• Arch supports
  
  • medial arch support extending form half inch posterior to first MT head to anterior tubercle of the os calcis

Question 30

what is the benefits of ankle foot orthosis?

Answer 30

• Used to prevent or correct deformities and reduce weight bearing
• Shown to reduce the energy costs of ambulation in wide variety of conditions- spastic diplegic cerebral palsy and lower motor weakness of poliomyelitis

Question 31

What do plastic AFO consist of?

Answer 31

• Shoe inserts
• calf shell
• heel retaining strap
• calf strap attached more proximally

Question 32

Can you name some AFO examples?

Answer 32

• Posterior leaf spring
  
  • narrow calf shell adn narrow ankle behind malleloi to allow some flexibility
  • used to compensate for weak ankle DF 9 prevents excessive equinus during heel strike or foot drop during swing
• Solid AFO
  
  • wider calf shell with trim ant to malleoli
  • prevents ankle DF/PF/varus/valgus
• HInged AFO
  
  • adjustable ankle hinges used to desired range of DF/PF.
  • prevents PF but allow DF during stance phase of gait
• Ground reaction force
  
  • made with solid ankle at neutral. upper portion straps around ant tibia proximally to provide strong ground reaction support for pt weak triceps surae. Prevents knee hyperextension by creating a flexion moment at the knee
• Dynamic AFO/ tone reducing afo
  
  • borad foot plate provides suppost sround most of foot, extending distally under the toes adn up over the medial and lateral aspect of the foot in order to maintain the subtalar joint in normal alignment
  • in CP pts able to reduce tone in muscle groups above the brace so reduce tone and improve function- inhibition casting

Question 33

what do metal and metal and plastic afo consist of?

Answer 33

• Shoe or foot attachment, ankle joint and 2 upright metal and lateral with a calf band connected proximally
• the mechanical ankle can control or assist ankle DF or PF by means of stop ( pins) or assist ) spring)

Question 34

what do knee ankle foot orthosis consist of?

Answer 34

• AFO with metal uprights
• mechanical knee joint
• 2 thigh bands
• used in quads paralysis or weakness to maintain knee stability and control genu valgum or varum
• manufactured from metal - double upright metal KAFO most common

Question 35

What does a trunk, hip knee ankle foot orthosis consist of?

Answer 35

• Spinal orthosis in addition to a HKAFO ( a hip joint andpevic band in addition to KAFO)

Question 36

Name some paediatric orthoses?

Answer 36

• Denis brown spint - congential talipes equinovarus
• Pavlik harness for DDH

Question 37

What are the complications of orthosis?

Answer 37

• **Psychosocial **
• Physical
  
  • compression phenoma
    
    • tight orthosis encircle limbs-> compression of nerves/arteries/veins-> pain/parathesia/imparied distal circulation and oedema
  • Heat and water retention
    
    • leading to maceration of skin, impaired wound healing, skin infection
  • Pt-orthosis interfacial effects
    
    • interface is defined as the junction between the body tissue and the orthosis and/or the support surface thru which forces transmitted
    • -> tissue necrosis/skin breakdown
    • extrinisc over bony landmarks or due to intrinsic pt factors- paralysis, insensate, pvd
    • reduce
      
      • by contouring - prevent orthosis falling to the ground
      • good mechanical design- leverage to reduce the amount of force exterted on the ground
      • adequate padding and large contact areas over which forces can act