Q1: Biomechanical Goals TT Flashcards
What are the biomechanical goals of a TT Prosthesis
- Maximize residual limb weight bearing capacity
- maintain ML stability through stance phase
- maintain sagittal plane stability through stance phase
What are the three ways to accoomplish goal #1 (Maximize residual limb weight bearing capacity)
- total contact socket design
- intentional loading and socket fit
- flexed alignment of the socket
Total Contact Socket Design
- increases overall surface area
- minimizes distal end edema
- increases proprioception
Pressure Tolerant Areas PTB Socket Design
- Medial Tibial Flare
- Patellar Tendon
- Shaft of fibula
- Anterior compartment
- Medial Tibial Shaft
- Medial femoral condyle
- Popliteal Fossa
- Distal End
- Gastrocnemius
Pressure Intolerant Areas PTB Socket Design
- Fibular Head
- Peroneal Nerve
- Crest of Tibia
- Distal Fibula
- Hamstring Tendons
- Distal Anterior Tibia
Equal Pressure Distribution (TSB)
- Impression technique without specifically applied pressures
- modification process does not relieve specific areas
- Use of gel liner assists in equalization of pressure
What does flexed alignment increase?
- increases the area for vertical load bearing on the anterior surface of RL
- Socket flexion for PTB: begin at 10 deg
- Socket flexion for TSB: begin at 5 deg
What are the ways to accomplish goal #2 (maintain ML stability through stance phase)
- coronal plane alignment
- transverse plane alignment
- socket fit and stability
Where should GRF line pass in relation to the knee at midstance
- should pass medial to knee joint at midstance
- slight varus thrust at midstance
What are the general guidelines for foot inset:
- short limbs: 3-6 mm inset
- Medium limbs: 6-9 mm inset
- Long Limbs: 9-12 mm inset
- Bilateral patients: 0-6 mm inset
What are the benefits of Foot Inset/Varus Moment
Narrow base of support
- provides midstance stability
- simulates NHL (normal human locomotion)
- Decreases energy expenditure
What does excessive medial placement of the foot produce
- excessive varus moment
- increased lateral distal pressure
- increased medial proximal pressure
What does excess lateral placement of the foot produce
- valgus moment
- medial distal pressure
- proximal lateral pressure
What happens if the socket is excessively ABducted
- when patient walks, socket will follow the patients anatomical presentation
- lateral leaning pylon, medial aspect of foot off ground, excessive varus moment
Increased Toe out……
Results in wider base of support at terminal stance
excessive toe out ……
results in a reduced varus moment OR valgus moment at terminal stance
insufficient toe out…..
results in an excessive varus moment at terminal stance
If socket does not fit snugly in ML dimension…..
socket will move on limb in stance phase
Ways to accomplish goal #3 (sagittal plane stability)
- sagittal plane alignment
- appropriate heel/keel properties
Heel lever goals during loading response
- weight acceptance with shock absorption through heel
- stable and controlled knee flexion
Toe lever goals in terminal stance
- sufficient forefoot leverage to maintain weight bearing until contralateral weight acceptance (long)
- prevention of excessive knee extension moment in terminal stance (short)
Sagittal Plane alignment goal
reduce knee extension moment during loading terminal stance
What is socket position determined by
sagittal plane bisector at MPT level
3 reasons for flexing the transtibial socket
- load anterior surface of RL (goal 1)
- increase knee flexion moment during early stance (goal 3)
- decrease knee extension moment during terminal stance (goal 3)
During loading response, we want the prosthesis to replace what?
anatomic eccentric dorsiflexor activity
Heel Durometer
- cushioned heel of SACH foot compresses during loading response and facilitates controlled foot flat
- simulates plantar flexion of the ankle
- improves stability as foot fully contacts the ground
increased heel stiffness results in ?
greater knee flexion moment and decreased shock absorption
What happens if there is an excessivley soft heel
- early stance phase appears delayed, like person is stuck and acannot roll forward onto the foot
- “stepping into a hole”
- knee will remain in extension
Keel properties goals in terminal stance
- sufficient forefoot leverage to maintain weight bearing until contralateral weight acceptance
- prevention of excessive knee extension moment in terminal stance
- affected by: length of keel, flexibility of keel
