Prosthesis Structure

Structural Components

  • Socket
  • Suspension
  • Container
  • Joints -> hip, knee, ankle
  • Connectors -> tubes between joints
  • Floor interface -> foot, bung
  • Additional mobility

Overall Structure

  • Endoskeletal & Exoskeletal
  • Cosmesis – constrainted movement unless 2-part

Statistics of the Referred Population

Service Centres in the UK

  • England: 35
  • Northern Ireland: 1
  • Scotland: 5
  • Wales: 3

201011 statistics from:

Types of Data Collected

There are 2 classifications:


  • Sex
  • Site
  • Side


  • Centre
  • Years between Referral & Birth
  • Weeks between Referral & Amputation
  • Months between Amputation & Birth
  • Ethnic Background
  • Level of Amputation
  • Cause of Amputation

Lower Limb Numbers


91% lower limb absence (very little movement analysis on upper limbs)

  • 29% females
  • 71% males
  • 94% single sided
  • 6% double sided
  • 0.017% x-site, triple, quadruple


  • 10% trauma
  • 52% dysvascularity
  • 9% infection
  • 1% neurological disorder
  • 3% neoplasia
  • 5% congenital absence
  • 20% no data


  • ~0% hemiplevectomy
  • 3% hip disarticulation
  • 37% trans-femoral
  • 3% knee disarticulation
  • 54% trans-tibial
  • 1% ankle disarticulation
  • 2% partial foot
  • ~0% foot digits
  • ~0% congenital absence


  • 3% ≥ 00 & ≤ 15
  • 27% > 15 & ≤ 54
  • 20% > 54 & ≤ 54
  • 24% > 64 & ≤ 54
  • 26% > 74

Disarticulations vs Through-bone

Advantages and Disadvantages of Disarticulations

Disarticulations – e.g. hip, knee, ankle

  • distal (end) bearing
  • less need for weight distribution
  • less need for intrusive proximal socket extension
  • self-suspending
  • potentially greater range of motion
  • potentially less space for distal components
  • potentially segment length difference compared to sound side

Details on Main Prosthesis Components

Socket Shapes and Suspension

Trans Tibial

PTB Sockets Predominantly patella tendon bearing (PTB) sockets

Total Contact Sockets With e.g. roll-on liners (pin, hypobaric (suction)), sleeves (suction)

No 8 (conventional plug fit) Thigh corset with articulated side-steels

Trans Femoral

MAS Very rarely Marlo Anatomical Socket (MAS)


  • Soft suspension, pelvic band, suction, osseointegration
  • Roll-on liners (pin, lanyard, hypobaric (suction)) – as shown before



  • No knee
  • Mechanical -> mechanical, pneumatic, hydraulic friction
  • Microprocessor -> pneumatic, hydraulic, magnetorheological friction
  • Power -> motor assist

Overview of Function

Swing flexion – for swing phase AND sitting

  • allows knee flexing
  • single axis or polycentric rotation mechanism

Swing control – for swing phase

  • controls rate of swing
  • resistance, assistance

Stance control – for stance phase AND standing

  • prevents knee flexing
  • GRF anterior to knee, weight/user activated locking mechanism

Stance flexion – for stance phase

  • flexes knee without collapsing
  • rotation around secondary axis while primary axis is locked

Control in Microprocessor / Power Knees

  • Real-time control

  • Accommodation
    • force – variable stiffness
    • terrain – ROM in various positions
    • speed – variable loading
    • user specific motion – sitting & stair mode
    • gait asymmetry – stance & swing

  • Energy
    • dissipation – correct time & angle
    • return – correct time & angle

Martin J, Pollock A, Hettinger J. Microprocessor lower limb prosthetics: Review of current state of the art. Journal of Prosthetics and Orthotics. 2010;22(3):183-93.



  • Adapt to ground during stance
  • Push off at late stance
  • Ground clearance during swing

Overview of Function

  • Passive feet
    • non-energy storing & return (standard feet)
    • energy storing & return (ESR) (or dynamic response)
    • self-aligning feet (standard & ESR)

  • Active feet
    • passive power (for ground clearance)
    • active power (for ground clearance & push off)

Design Features

  • similar choice for all levels (except from long trans-tibial level downward)
  • 1-3 axes (all planes)
  • torque absorber & shock absorber
  • removable cover
  • adjustable heel height
  • definition of toes (split toe option)
  • colours (light / dark)
  • exchangeable elastic elements (vary stiffness)
  • separate ankle joint e.g. Blatchford Endolite Multiflex
  • mechanism / electronics linked to knee e.g. Hydracadence, Symbionic leg

Additional Mobility


  • Torque and/or shock absorber
  • Rotators

Amputee Gait Analysis

Prosthesis Simulator

Help to recruit from typical healthy population instead of from limbless population for research purposes

Marker Location

  • Segements are rigid & small surface area can be extended
  • Take care with polycentric (instantaneous CoR) designs
  • see Miller & Childress, May 2005, Robotica;23(03):329-35

Segment Properties

Prosthetic foot & shank (for trans-tibials) - Mass – scales (incl. water bag inside the socket for residuum mass - Lengths - ruler (in 3 directions) - CoM - knife edge - RoG - pendulum

Anatomic foot & shank (for trans-tibials) - Subtract prosthesis mass (incl. water bag) from body mass (incl. prosthesis) - to obtain body mass as if amputated through knee

  • From anthropometric data, calculate body mass if not amputated
    • to obtain more accurate anatomic segment mass

What is a prosthesis?

A prosthesis is a device that replaces a part of a body that was either absent from birth or has been lost due to injury, illness and / or deformity

First Major Improvements

  • 1912 when an aluminium prosthetic leg was created by Marcel and Charles Desoutter after Marcel lost a leg in an aviation accident. The aluminium leg weight about 1.8 kg instead of the usual 3.5 to 4.5 kg at the time.

  • Lots of materials and techniques borrowed from the aviation industry.

  • 1969 – Otto Bock invents the first modular prosthetic system, facilitating ease of changing components and alignment of the prosthesis

Conventional Prosthesis


Most of these were still common in the UK in the late 1980’s

Modular Systems


  • Add/change components that give you available features for each joint being replaced

  • Adjustable – easier to change socket, length and alignment

  • Easier to make and repair if parts are available

Key Considerations

  • The ‘Fit’ (the prosthetic interface with the residual limb)

  • The Function-how useful it is

  • Biomechanics is central to comfort and function

  • The Cosmesis-its appearance

The Residuum

  • The residual limb has been described as an outer envelope of the skin and soft tissue surrounding a central strut, the skeletal shaft.

  • The soft tissue which covers the residuum is not designed for weightbearing

  • Trans-tibial has no horizontal weightbearing surface.

  • The qualities of the skin coverage and the amount and consistency of soft tissues is variable.

  • The difficulties with fluctuation

  • Differing amputation techniques – the quality of the residuum has a huge impact on rehabilitation!

Weightbearing, Stability & Suspension

  • The socket has to stabilize bone structure in all planes of motion through soft tissue in a manner which is comfortable and causes no damage or detriment to the soft tissue.

  • The socket has to act as a mechanical junction or coupling between the soft tissue and skeleton of the residual limb and the rigid structure of the prosthesis during non-weight-bearing situations. The aim is to have minimum longitudinal displacement between weight bearing and non-weight bearing phases.



If the bone structure is not stable then the socket will be able to move causing instability and there will be lessened control at joints


  • Mechanical – Utilisation of a bony structure that they hook over such as the femoral condyles or iliac crests or radial compression and coefficient of friction

  • Suction – The creation of a situation where negative pressure creates a vacuum – Active vacuum

A Good Socket

  • “A Good fit is not Primarily defined by a particular shape of socket, but by the accommodation of the forces or pressures between the stump and socket to provide for comfortable and harmless weight-bearing, stabilisation and suspension.” Klasson B 1995

  • Cosmetics & Range of movement.

  • Revisiting theories/techniques as materials and technology changes

Redheads, R., (1979) - total surface bearing socket really came into play with ICEROSS and other liners

Names of Socket Types


  • Quadrilateral
  • ‘H’ for health
  • ‘C’ for conventional
  • Ischial containment sockets
  • Marlo Anatomical socket
  • Hifi
  • Hybrid
  • Ossur trans-femoral Socket
  • Sub ischial sockets


  • Patella tendon bearing
  • Patella tendon bearing with
  • supracondylar
  • Patella tendon bearing with supracondylar and supra patella
  • Total surface bearing

Evidence for which is the Best Socket?

  • Not enough and often small scale (extraneous variables)

  • Still many issues

  • ICS more comfortable than quadrilaterals (Hachisuka et al, 1999)

  • Or perhaps not (Boonstra et al.,1994)

  • MAS sockets have also been reported to improve gait efficiency, ease ascending slopes and sitting in soft chairs (Traballesi, et al, 2011) and provide greater ischial containment and medio-lateral stability than other sockets and that it also reduces trim lines which improves hip range of motion, (Trower, 2006; Perry, 1992; Flandry et al, 1989; Klotz, 2011).

  • Limited Hip flexion Hagberg (2005)


  • No need for a socket
  • Improved control of prosthesis
  • Improved range of motion
  • Increased sensation of external world.
  • Risk of infection
  • Still need to consider alignment
  • Needs of surgery
  • Need for the removal of the abutment
  • Need for quality bone to implant into


  • The relationship between the socket and the remaining elements of the prosthesis is key

  • The relationship between each joint in the lower limb is also key

  • Symmetry is often (but not always) sought

  • Primary (new) patients will often need a number of re-adjustments, to both socket and prosthetic componentry

  • These factors will influence prescription

Gait Cycle

Energy Consumption and the Impact on Muscular Skeletal Structure.

  • Is energy consumption as high as previously thought?
  • Alignment
  • Socket fit
  • Level of amputation
  • Componentry

Thermal discomfort.

  • Sweating

  • Environmental component – where you live

  • Increase risk of infection

  • Increase risk of tissue damage when the skin is damp

  • Individual differences in level of sweating

  • Decreased surface area increased sweating

  • Surrounded in an insulator

Solution - Assessment & Prescription

  • Finding out what is the best choice for the patient’s needs

  • Identifying the best generic component for the patient

  • Communicating the ideas for prescription to the patient

  • Identifying means of support, and discussing options and rehabilitation plans with other members of the MDT

  • Producing the first stage of the socket


  • Hips
  • Knees
  • Feet
  • Torque Absorbers
  • Shock absorbers
  • Rotators



2 types:

  • Acts to assist the hip in terms of stability and function.
  • Used as a functional replacement for those who have undergone a hip disarticulation or trans-pelvic amputation

No Changes for Half a Century!

  • 1% to 2% of amputee population

  • Conventional Hip Disarticulation

  • 1954 – Canadian Hip Disarticulation – McLaurin

  • 2008 – Otto Bock Helix Hip 7E10

  • 2014 – Otto Bock 7E9 (Baby Helix)

Hip Joints



  • Locked

  • Free

  • Single axis and polycentric

  • Stance phase controls – alignment, polycentric, weight activated friction brake, Hydraulics and MPK (hydraulic and magnetorheological)

  • Swing phase controls – friction, pneumatic, hydraulic, extension assist and MPKs

Knee Prescription - Stability

Knee Prescription - Swing

Key prescription options: Micro Processor Knees (MPK’s)mark>



  • SACH (Solid Ankle Cushioned Heel)

  • Single axis

  • Multi-axial

  • Running

  • Energy storing / response –Can also be have ground compliance

  • Auto-adaptive –microprocessor ankles

  • Hydraulic ankles

  • Height adjustable

Factors Affecting Children

  • Cause of limb absence and its impact – Congenital/trauma/illness

  • When do we start rehabilitation?

  • Available componentry

  • Amputation type – retention of growth plates, end bearing

  • Bony growths

  • Changes in height

  • Body image/self esteem

  • The Parents

  • Funding for sports prosthesis (2016 further announcement 2018)


  • Body image
  • Changes in attitude to cosmesis
  • Impact on function
  • Social anxiety


Differs in different parts of UK – Postcode lottery


  • Reaction to amputation

  • Factors that impact on adaptation to amputation

  • Compliance

  • Living with a chronic disease

  • Psychological well being and outcomes

  • Paralympics

  • Positive growth

  • Economics

Phantom Limb Pain

  • Painful feeling associated with an absent limb through amputation

  • Differs from phantom limb sensation which does not include pain and residual pain which is within the residuum.

  • Variable findings of the percentage who experience phantom limb pain

  • Hampers quality of life (Trevelyan, Turner, & Robinson, 2016)

  • Little evidence for one effective treatment (Collins, 2018)


  • Improvement of general health – cardiovascular, core strength, Muscle strength, fixed flexion contractures.

  • Care of chronic conditions – diabetes, rheumatoid arthritis etc

  • Learning to use the prosthesis

  • MPKs – we need to train out bad habits that were previous strategies.

Outcome Measures


  • Prosthetic Evaluation Questionnaire – self reported quality of life and functional outcomes

  • Psychosocial outcomes

  • Socket comfort score – self reported 1 – 10 scale

  • Two-Minute Walk Test

  • Six-Minute Walk Test

  • Timed “Up & Go” Test

  • Activity monitors

  • Self reported falls

  • Hospital Anxiety and depression scale

  • Changes in K levels 0-4/Sigam A-F

Areas for the Future

  • Brain based control?

  • Muscle based control?

  • Increase in powered movement?

  • Increased control of individual segments?

  • Increased use of osseo-integration?

  • New manufacture techniques?

  • Different shape capture techniques?