Transcript Lower Limb Prostheses

LOWER LIMB PROSTHESES
May 3rd, 2012
Emily Harnden
CASE
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14 yo F presents w/ BLE NSTI and septic shock
Requires BLE fasciotomies, significant skin, muscle, soft
tissue debridement and ultimately a unilateral AKA
Additional diagnoses include high-risk ALL, renal failure,
period of respiratory failure, and period of depressed
cardiac function
In your social history you note she likes to play soccer
and to dance
After AKA, what type of prosthesis do you
choose?
MAJOR COMPONENTS
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Socket
Suspension mechanism
Knee joint
Pylon
Terminal device
SOCKET
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Connection between the remaining limb & prosthesis
Protects limb
Transmit forces between prosthetic & limb assoc with
standing/ambulation
PROS
CONS
Hard
Socket
Direct contact  decr
friction, no liner bulk
Easy to clean
More durable
Difficult to fit
Difficult to adjust in
response to residual
limb changes
Soft Socket
Liner serves as cushion
 added protection
Increased friction, bulk
SOCKET
 Quadrilateral
design
4
walls of socket each apply forces to residual limb,
distribute pressures
 WB through ischial tuberosity & gluteal muscles
 Ischial
containment socket
 Current
standard
 More of pelvis within socket  improved force distribution,
stability
 Flexible
above-knee socket
 Flexible
inner socket supported by rigid outer frame
 Minimizes pressure within the socket on residual limb
SOCKET
SUSPENSION MECHANISM
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Attaches prosthesis to residual limb
Belts, straps, cuff, sleeve, thigh-lacer, suction, shuttlelock, or combination of these
 Suction:
Socket held to limb via negative pressure, surface
tension
Intimate fit improves proprioception, muscular control
 Less appropriate for users with poor balance
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 Shuttle-lock
(pin-lock) system: liner with locking pin
inserts into shuttle lock inside socket
 Allows
shock absorption, torsion control, cushioning
 Good option for all functional users
Shuttle-lock System
KNEE JOINT
Support during stance phase
 Control during swing phase
 Unrestricted motion for sitting, walking, running
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KNEE JOINT
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Single vs. polycentric axis
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Fixed vs. variable cadence
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Single axis: simple hinge with single pivot point
Polycentric axis: multiple centers of rotation
Fixed: Swing rate set within knee unit; knee does not flex during stance
Variable: range of swing rates; allows flexion and lowered center of
mass during stance
Microprocessor control systems
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Variable cadence knee mechanism
Senses position + velocity of pylon relative to thigh  adjusts cadence
to accommodate to speed of user
Control for more complex movements
Expensive
PYLON
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Tube or shell that attaches the socket to the terminal
device
Dynamic devices that allow axial rotation, absorb,
store, and release energy
Exoskeleton: internal soft foam contoured to match
other limb + hard, laminated shell
More durable
 Heavier, fixed alignment
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Endoskeleton: internal metal frame + cosmetic soft
covering
Allow for adjustment and realignment of components
 Important in pediatric patients
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PYLON
Endoskeleton Prosthetic
Exoskeleton Prosthetic
TERMINAL DEVICE
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The foot
3 categories:
Non-articulated vs. Articulated
 Single axis vs. Multiaxis
 Non-dynamic response vs. Dynamic response
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Functions:
Stable weight bearing surface
 Absorbs shock
 Replaces lost muscle function
 Replicates the anatomic joint
 Restores cosmetic appearance
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TERMINAL DEVICE
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SACH foot (solid ankle/cushioned heel):
 Compressible
heel + rigid wooden keel that cannot
dorsiflex  material simulates plantar flexion to
allow smooth gait
 Non-articulated, non-dynamic response
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Dynamic response:
 Can
be articulated or non-articulated
 Single axis or multi-axis
 Elastic keel deforms under pressure  returns to
original shape once load removed  returns energy
to user
TERMINAL DEVICE
SACH Foot
Dynamic Response Foot
WHICH PROSTHESIS TO USE?
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Things to consider:
 Level
of amputation
 Patient’s functional needs and physiologic level
 Prosthetic skills
 Unique pediatric considerations
 Staging
 Age
at fitting
 Growth
 Activity level
 Psychosocial factors
METABOLIC COST OF AMPUTATION
Type of Amputation
BKA, unilateral
BKA, bilateral
% increase in energy
consumption above baseline
10-20%
20-40%
AKA, unilateral
AKA, bilateral
60-70%
>200%
Functional Classification
Level 1
Level 2
Level 3
Level 4
Level 5
Nonambulator
Household
ambulator
Limited
community
ambulator
Unlimited
community
ambulator
Exceeds basic
skills
Gait
Nonambulatory,
needs
assistance w/
transfers
Fixed cadence;
level surfaces
Fixed cadence,
small
environmental
barriers (curbs,
stairs, uneven
surfaces)
Variable
cadence;
negotiates
environment
freely
Variable
cadence; high
energy,
impact, &
stress
activities
Knees
Not
candidate
Fixed-cadence swing rate
Variable-cadence swing rate;
computer assisted
Feet
Not
candidate
Non-dynamic response foot
Dynamic response foot;
energy-storing foot
PEDIATRIC CONSIDERATIONS
Staging
 Age at fitting
 Growth
 Activity level
 Psychosocial factors
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Staging
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Prosthetics should be staged based on child’s
developmental readiness
Age at Fitting
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Age determines type of prosthetic required
Components & suspension generally become more
sophisticated as child matures physically & psychologically
Birth-6 mos
No prosthetic
7-14 mos
First fit when almost ready to pull to stand
No knee
15-36 mos
Limb growth is the most evident change
3-6 yrs
Kids are active  Simple, rugged, durable prosthesis
Functional knee
Non-articulated foot
7-12 yrs
Developing interests have impact on prosthetic choice and
design
13-18 yrs
Cosmesis more significant
Growth
Kids grow longitudinally,
circumferentially, and undergo
alignment changes
 Prosthesis must accommodate growth
and other physiologic changes
 Frequent follow up: every 3-4 months
 Modular systems: component
interchangeability, alignment
adjustability
 Adjustable suspension mechanisms
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Activity Level
Prostheses for kids subjected to diverse and
high degrees of stress
 Gear towards physically active, athletic lifestyle
 Protect other joints in residual limb from injury
 Reinforce prosthesis
 Minimize weight
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Psychosocial
Kids are generally less responsible, more
emotionally immature than adults
 Child’s reaction to prosthetic and limb loss often
depends on parents reaction
 Rehab in pediatrics unique: goals of training and
fittings evolve as the child grows and changes
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What kind of prosthesis would you
choose for our 14 year-old patient
with a new AKA?
REFERENCES
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Friel, K. Componentry for lower extremity prostheses. J Am Acad Orthop Surg. 2005
Sep;13(5):326-35.
Datta D, Howitt J. Conventional versus microchip controlled pneumatic swing phase control for
trans-femoral amputees: User’s verdict. Prosthet Orthot Int. 1998;22:129-135
Cummings DR; Kapp SL. Lower-limb pediatric prosthetics: General considerations and
philosophy. Journal of Prosthetics and Orthotics. 1992;4(4):196-211
Keenan MA, Smith DG. Orthoses, amputations, and prosthesis, in Lieberman JR (ed): AAOS
Comprehensive orthopedic review. Rosemont, IL, American Academy of Orthopaedic Surgeons,
2009:171-188
Fisk JR. Introduction to the child amputee in Bowker HK, Michael JW (eds): Atlas of Limb
Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles. Rosemont, IL, American Academy
of Orthopaedic Surgeons, 2002: ch 31
Tooms RE. Acquired amputations in children in Bowker HK, Michael JW (eds): Atlas of Limb
Prosthetics: Surgical, Prosthetic, and Rehabilitation Principles. Rosemont, IL, American Academy
of Orthopaedic Surgeons, 2002: ch 32
Oglesby DG, Tablada C. Lower-limb deficiencies: prosthetic and orthotic management in
Bowker HK, Michael JW (eds): Atlas of Limb Prosthetics: Surgical, Prosthetic, and Rehabilitation
Principles. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2002: ch 35B