Lower Limb Prostheses May 3rd, 2012 Emily Harnden

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?

MAJOR COMPONENTS Socket Suspension mechanism Knee joint Pylon Terminal device

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

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

SOCKET

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

Shuttle-lock System

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

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

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

PYLON Endoskeleton Prosthetic Exoskeleton Prosthetic

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

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

TERMINAL DEVICE SACH Foot Dynamic Response Foot

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

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%

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

PEDIATRIC CONSIDERATIONS Staging Age at fitting Growth Activity level Psychosocial factors

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

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

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

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

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

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

REFERENCES 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