Ankle Foot Mechanisms Flashcards
Single-axis ankle foot
Prior to 1950 only articulating foot
Px foot in IC=foot flat quickly
GRF vector moves forward through ankle joint=extension moment at knee- increase knee stability
Heavy though terminal end- primary used when knee stability is major concern
SACH
1950s CU developed
Post. Third of foot consists of an open cell foam rubber- compresses under load in early stance-lowering foot to ground
Rigid wooden inner keel, flexible toe permits rollover- very smooth
Still remains lightest, simplest, and lowest cost option
Popular for infants and toddlers and is often used in preparatory limbs or patients whose physical condition precludes ambulating more than a few steps
Multiaxial ankle foot
Limited range in coronal plane- inversion and eversion as well as sagittal plane PF and DF
Uneven surfaces
Increased socket comfort by absorbing impact
Most but not all have transverse plane motion
Maintenance needed- rubber bumpers wear out
Flexible-keel
Composed almost entirely of resilient polyurethane rubber except where bolt attaches
Very flexible forefoot-accommodates irregularities by bending into pro nations or supination
Facilitates rollover
Plantar surface of this design is reinforced with high- strength webbing straps analogous to the plantar fascia-shift onto forefoot the plantar straps tighten and gradually stiffen the toe allowing push off—- similar to Windlass effect in normal foot
Preparatory limbs
Pediatric px
Not good for rapid forefoot loading(sprinting) takes a moment for it to stiffen for propulsion
Dynamic response
Spring-like keel that deflects under load, stores potential energy and releases it in the latter part of stance phase
Standard foot for higher activity levels
Only contraindication if amputee is unable or unwilling to load the forefoot in which the forefoot spring would be nonfunctional
Most energy efficient option for sports and recreational activities, few studies studies demonstrated any energy advantage at normal walking speed on level surfaces
