Contraindications
No ambulation potential
Severe cardiac disease
Poor vision
Poor motivation or compliance
Poor stump - infected, ulceration, poor skin
FFD knee or hip
Indications
Young traumatic or neoplastic amputee
Motivated PVD / neuropathy amputee with cardiac reserves
Timing
Best to fit prothesis ~ day 14
- allows most stump shrinkage to occur
- IPOP tends to cause high complication rate especially with PVD
Elements of a Prosthesis
1. Socket
- transmits forces between the stump & the prosthesis in all planes
- may be proximal, distal or total bearing
2. Means of Suspension
- suction socket
- suspension belts
- neoprene sleeve
- elastic stocking
- silicone sleeve
3. Joint mechanism (knee)
A. Stance phase control
Simple
- aligns the prosthesis so the ground reaction force passes in front of the knee
- locks in hyperextension; 2 drums lock at 0-15o
- for elderly
Mechanical stabilisers
- braking mechanism activated by the weight bearing load or hydraulics
B. Swing phase control
- pneumatic cylinder
- hydraulic cylinder
- intelligent prosthesis - computer adjusts rate of swing to cadence (steps/min)
4. Terminal device / Foot
A. SACH
- Solid Ankle Cushioned Heel
- wood keel / heel cushion / rubber foot
- use for BKA
B. Single axis
- some DF/ PF possible
- makes knee stable
- use if knee stiff ie AKA or through knee
C. Multi - Axis Foot
- hindfoot eversion / inversion + DF / PF
- better for active patient
D. Dynamic Response
- "Ryan's Superfoot"
- flexible keel allows smoother roll over
- store energy via carbon fibre foot plate
- Aid toe off / more natural gait / save energy
- expensive
- not used in children as turnover too high
BKA Prosthesis
Socket
Usually firm PTB design
- can add liner for increased comfort
- definitive socket fitted 1 year (size stabilised by then)
- load patella tendon & medial / lateral flares
- most weight actually borne on medial tibial flare
- extend flares higher if unstable knee
Suspension
Suprapatellar cuff
- simplest & most common
- dacron & leather
- grips condyles
- advantage is transfers all force to residual leg below knee
Supracondylar mould
- grips above femoral condyles
- young patient or < 5cm residual tibia
Neoprene 5mm liner
- rolled over distal thigh
- frictional fit ± suction
- negative pressures in swing
AKA Prosthesis
Suspension
Difficult
- lack of bony contours
- not truly end bearing
- usually ischial bearing
Options
1. Suction with valve hole
2. Waist or hip belts - if femur too short
Requires
- surface tension
- negative pressure
- active muscles
- stable body weight / socket fits
Socket
1. Quadrilateral
- traditional socket with narrow AP diameter
- weight bear on ischium / not in socket
- difficult for the femur to sit in adduction
2. CAT - CAM
- narrow medial - lateral diameter
- femur sits in adduction
- more ovoid
- incorporate ischium into socket via flare
- more comfortable
- better femoral stability in socket
Knee Design Options
1. Single axis
- simple hinge
2. Polycentric axis
- 4 bar linkage device
- more natural
- expensive and heavy
3. Friction
- limits knee flexion
A. Constant
- cheaper
- limited to one walking speed
B. Variable friction, including with extension
- hydraulic controlled
- resist flexion in extended knee
- easy flexion in flexed knee
- allows different speeds
4. Safety knees / Stance control knee
- lock when weight applied
- good for elderly
Commonest
- Single Axis Safety Knee
Most expensive & heaviest
- Polycentric Hydraulic Controlled Knee
Through Knee Prosthesis
Socket
- endbearing socket
Suspension
- via femoral condyle flares or strap
- 4 bar linkage knee overcomes previous problems with through knee
- folds away when sitting
- knees at same level