MT: Transfemoral Biomechanics

Question 1

Coronal Plane: Biomechanical Objectives

Answer 1

• provide ML stability of the pelvis during midstance on prosthesis
• conserve energy by minimizing excessive lateral displacement

Question 2

Sagittal Plane: Biomechanical Objectives

Answer 2

• enable a symmetric step with contralateral leg
• provide prosthetic knee stability during loading response

Question 3

ML Stability & Energy Conservation

Socket Geometry

Answer 3

• AP dimension
• ML dimesion
• Adduction Angle
• lateral wall contour (support femur)
• medial brim height/contours

Question 4

ML Stability & Energy Conservation

Alignment

Answer 4

• Narrow base = conserves energy
• Wider base = requires less strength & balance

Question 5

Hip Abductors: Normal Gait

Answer 5

abductors of stance limb activate to stabilize the pelvis keeping it from dropping toward swing limb

Question 6

Weak Hip Abductors

Answer 6

most effective way to reduce the forces causing the pelvis to drop to the swing side is to shift the center of gravity toward the stance limb

Question 7

Trendelenburg Gait

Uncompensated gait

Answer 7

pelvis drops toward non-weight bearing side (swing limb)

Question 8

Trendelenburg Gait

Comensated Gait

Answer 8

• exaggerated trunk lean towards the weight-bearing side
• caused by: hip abductor weakness, lack femoral stabilty, pain TF prosthetic

Question 9

What can have the same effect as weak abductors

Answer 9

abducted femur within the prosthetic socket

Question 10

How can Hip Abductor weakness be corrected

Answer 10

• cane in contralateral hand
• hip joint/pelvic band
• alignment - long line
• socket shape
• proper surgical techniques

Question 11

Cane in contralateral hand

Answer 11

• redirects force across hip
• without cane resultant force across hip is about three times body weight
• effective and inexpensive

Question 12

Hip joint and pelvic band

Answer 12

• provides femoral support in the coronal plane by extending the lever arm proximal to hip joint
• trade off: eliminates voluntary hip ab/adduction

Question 13

Correcting Coronal Plane Instability

Surgical Technique

Answer 13

• adductor magnus provides 70% of adduction force
• preserve AM insertion by myodesis to lateral femur
• quality of surgery limits femoral adduction in TFA

Question 14

Step Length on Contralateral Side

Answer 14

• normal step length requires 15 deg of hip extension from trailing limb
• socket flexion angle: place socket in patients max extended position plus 5 deg
• lumbar motion: 10 deg

Question 15

Knee stability strategies

Answer 15

• voluntary control
• alignment
• foot function
• knee design

Question 16

Voluntary control

Answer 16

• use creates internal hip extension moment during LR
• residual limb factors: muscular strength, neurological control
• ROM at hip
• boney lever arm RL length

Question 17

Alignment - Knee Component

Answer 17

• sagittal knee position effects stability and efficiency
• knee posterior to TA line = stable
• Knee unit anterior to TA line = unstable

Question 18

Foot Function

Answer 18

• soft heel increases knee stability
• single axis foot should be used when the patient needs max stability

Question 19

Primary Consideration

*

Answer 19

• functional level: motivation, cognitive ability, physical capabilites
• biomechanical needs: stance stability and swing responsiveness
• voluntary control
• reliability, effectiveness, weight, cost,
• component design and alignment

Question 20

Swing phase control

knee joint resistance

Answer 20

• resists knee flexion & knee extension when unloaded
• early in swing: limits excessive heel rise
• late in swing: prevents terminal impact

Question 21

Stance Phase control

knee joint resistance

Answer 21

• resists knee flexion and extension when loaded
• prevents knee collapse in stance