1. Lower Limb Prostheses
May 3rd, 2012
Emily Harnden

2. After AKA, what type of prosthesis do you
CASE
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?

3. MAJOR COMPONENTS Socket Suspension mechanism Knee joint Pylon
Terminal device

4. SOCKET 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

5. SOCKET Quadrilateral design Ischial containment socket
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

6. SOCKET

7. SUSPENSION MECHANISM Attaches prosthesis to residual limb
Belts, straps, cuff, sleeve, thigh-lacer, suction, shuttle- lock, 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
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

8. Shuttle-lock System

9. KNEE JOINT Support during stance phase Control during swing phase
Unrestricted motion for sitting, walking, running

10. KNEE JOINT Single vs. polycentric axis Fixed vs. variable cadence
Single axis: simple hinge with single pivot point
Polycentric axis: multiple centers of rotation
Fixed vs. variable cadence
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
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

11. PYLON 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
Endoskeleton: internal metal frame + cosmetic soft covering
Allow for adjustment and realignment of components
Important in pediatric patients

12. PYLON
Endoskeleton Prosthetic
Exoskeleton Prosthetic

13. TERMINAL DEVICE The foot 3 categories: Functions:
Non-articulated vs. Articulated
Single axis vs. Multiaxis
Non-dynamic response vs. Dynamic response
Functions:
Stable weight bearing surface
Absorbs shock
Replaces lost muscle function
Replicates the anatomic joint
Restores cosmetic appearance

14. TERMINAL DEVICE 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
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

15. TERMINAL DEVICE
SACH Foot
Dynamic Response Foot

16. WHICH PROSTHESIS TO USE?
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

17. METABOLIC COST OF AMPUTATION
Type of Amputation
% increase in energy consumption above baseline
BKA, unilateral
10-20%
BKA, bilateral
20-40%
AKA, unilateral
60-70%
AKA, bilateral
>200%

18. Functional Classification
Level 1
Level 2
Level 3
Level 4
Level 5
Non-ambulator
Household ambulator
Limited community ambulator
Unlimited community ambulator
Exceeds basic skills
Gait
Non-ambulatory, 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
Non-dynamic response foot
Dynamic response foot; energy-storing foot

19. PEDIATRIC CONSIDERATIONS
Staging
Age at fitting
Growth
Activity level
Psychosocial factors

20. Staging
Prosthetics should be staged based on child’s developmental readiness

21. Age at Fitting 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

22. 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

23. 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

24. 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

25. What kind of prosthesis would you choose for our 14 year-old patient with a new AKA?

26. REFERENCES
Friel, K. Componentry for lower extremity prostheses. J Am Acad Orthop Surg. 2005 Sep;13(5):
Datta D, Howitt J. Conventional versus microchip controlled pneumatic swing phase control for trans-femoral amputees: User’s verdict. Prosthet Orthot Int. 1998;22:
Cummings DR; Kapp SL. Lower-limb pediatric prosthetics: General considerations and philosophy. Journal of Prosthetics and Orthotics. 1992;4(4):
Keenan MA, Smith DG. Orthoses, amputations, and prosthesis, in Lieberman JR (ed): AAOS Comprehensive orthopedic review. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2009:
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