Biomechanics of Prosthetic Use

Question 1

in PTB sockets, where is the emphasis on weightbearing on pressure tolerant areas

Answer 1

• patellar tendon
• pretibialis
• posterior distal aspect of residuum
• popliteal fossa, lateral shaft of fibula and tibial flares

Question 2

what do the head, arm & trunk do while walking

Answer 2

rights itself over the weightbearing limb

Question 3

mechanical axis

Answer 3

• hip center to ankle center
• should cross the knee center
• varus angle

Question 4

anatomic axis

Answer 4

• center of femoral shaft is 6 degrees off the mechanical axis
• center of tibia is parallel to the mechanical axis
• valgus angle
• joint line is in varus relative to the mechanical axis

Question 5

medial/lateral stabilization

Answer 5

• attempt to replicate the neutral mechanical axis at the knee causing varus
• need good lateral wall support
• provide abductor contact with the socket
• points of force in proximomedial direction and distolateral direction to prevent lateral shifting in socket
• center of heel under or slightly lateral to ischial tuberosity to promote slight vlagus

Question 6

place of medial/lateral stabilization

Answer 6

place foot 1/2 inch medial to center during bench alignment

Question 7

what to avoid in medial/lateral stabilization

Answer 7

avoid valgus moment at the knee

Question 8

foot too far inset is the same as..

Answer 8

socket too far outset

Question 9

anterior/posterior stabilization

Answer 9

• place socket in 5 degrees flexion to enhance PTB
• place foot slightly posterior to center of socket
• promotes flexion in the socket –> ideal moment for quad force

Question 10

incorrect placements

too far anterior:

Answer 10

excessive anteroproximal and posterodistal pressures

Question 11

incorrect placements

too far posterior:

Answer 11

hyperflexion at the knee with posteroproximal pressures and anterodistal pressures

Question 12

transfemoral biomechanics

Answer 12

• minimize rotation of the socket
• medial/lateral stability
• sagittal plane stability

Question 13

how to minimize rotation of the socket

Answer 13

• maintain pelvis in a posterior tilt on posterior rim
• incorporate ischial/glute weigtbearing
• adductor longus tendon housed in a groove
• more surface area = more stability

Question 14

incorrect placement

foot too far medial:

Answer 14

excessive pressure in groin and distolateral

Question 15

incorrect placement

foot too far lateral:

Answer 15

excessive pressure proximolateral and distomedial

Question 16

floor reaction force must stay where..

Answer 16

• anterior to the knee joint

Question 17

keeping the floor reaction force anterior to the knee joint does what..

Answer 17

• 5 degrees flexion built into the socket
• which enhances of firing glutes
• avoids hyperlordosis

Question 18

what are the parts of the static checkout

Answer 18

• soles of feet flat
• sockets fit well
• user comfortable
• is suspension adequate
• are bony landmarks level
• vertical pylon in stance
• are tissue rolls minimal
• gapping between leg and socket
• does residuum have distal contact
• normal heel center spacing
• is knee stable