1. Biomechanics of Walking for People with Lower Extremity Amputations
Dave Thompson PT
Update on Lower Extremity Amputations
September 28, 2006

2. Update on Lower Extremity Amputations
Objectives
List the gait deviations that are most common in people who wear prostheses, and explain their most frequent causes.
Explain how changes in prosthetic alignment alter the position of the ground reaction force and affect prosthetic joint movement during gait.
Explain how prosthetic foot alignment affects the alignment of a person's residual limb inside a prosthetic socket.
Update on Lower Extremity Amputations
September 28, 2006

3. When is someone ready for a prosthesis?
when he or she can control the knee joint well enough to walk safely.
Update on Lower Extremity Amputations
September 28, 2006

4. Controlling the knee joint:
Forces that affect joint position and movement during stance:
ground reaction
muscles
joint reaction
Update on Lower Extremity Amputations
September 28, 2006

5. Ground reaction force (GRF)
GRF is equal in magnitude and opposite in direction to sum of gravitational and inertial forces
Assess GRF’s effect on joint movement in customary way, by evaluating its location with respect to joint axis.
Update on Lower Extremity Amputations
September 28, 2006

6. Update on Lower Extremity Amputations
A useful simplification: Moments produced by GRF and muscles are equal and opposite.
Mmm = -Mgrf
Update on Lower Extremity Amputations
September 28, 2006

7. Moments produced by GRF and muscles are equal and opposite.
During loading response, GRF’s sagittal plane location is:
posterior to ankle axis
posterior to knee axis
anterior to hip axis
Update on Lower Extremity Amputations
September 28, 2006

8. Update on Lower Extremity Amputations
To preserve stability, people with amputations can compensate for absent or weak muscles by:
1. substituting another muscle in a closed chain
2. moving joint axis to  GRF’s moment about joint.
3. moving GRF to  its moment about joint.
Update on Lower Extremity Amputations
September 28, 2006

9. Controlling the knee joint during loading response:
People with amputations can activate muscles to control residual and prosthetic joints:
Knee extensors (in TT prosthesis)
Hip extensors
Hip abductors / rotators
Update on Lower Extremity Amputations
September 28, 2006

10. A less useful way to control the knee joint during loading response:
reposition knee joint axis posteriorly to  GRF’s moment about joint
by posterior rotation of pelvis
Update on Lower Extremity Amputations
September 28, 2006

11. Update on Lower Extremity Amputations
Prosthetic alignment can help control knee joint during loading response:
Position prosthetic foot so origin of GRF is more anterior.
Update on Lower Extremity Amputations
September 28, 2006

12. Moments produced by GRF and muscles are equal and opposite.
During preswing, GRFV’s sagittal plane location is:
anterior to ankle axis
posterior to knee axis
posterior to hip axis
Update on Lower Extremity Amputations
September 28, 2006

13. Initiation of knee flexion during preswing
GRF initiates prosthetic knee flexion if it is posterior to knee joint axis.
Heel must rise.
Pelvis must rotate forward, moving the femur.
Body weight must transition smoothly from trailing to forward limb.
Update on Lower Extremity Amputations
September 28, 2006

14. Poor preswing initiation of knee flexion
Four probable causes
 GRF
 fwd pelvic rotation
 hip flexor action
Prosthetic alignment that delays heel rise.
Update on Lower Extremity Amputations
September 28, 2006

15. Moments produced by GRF and muscles are equal and opposite.
During loading response, GRF’s frontal plane location is:
lateral to subtalar axis
medial to knee
medial to hip axis
Update on Lower Extremity Amputations
September 28, 2006

16. Hip abductors counter GRF’s adductor moment
Figure from Gottschalk et al. (1989). Does socket configuration influence the position of the femur in above-knee amputation? Journal of Prosthetics and Orthotics, 2,
Update on Lower Extremity Amputations
September 28, 2006

17. Lateral trunk lean reduces GRF’s hip adductor moment
Update on Lower Extremity Amputations
September 28, 2006

18. Update on Lower Extremity Amputations
Objectives
List the gait deviations that are most common in people who wear prostheses, and explain their most frequent causes.
Update on Lower Extremity Amputations
September 28, 2006

19. Update on Lower Extremity Amputations
Objectives
Explain how changes in prosthetic alignment alter the position of the ground reaction force and affect prosthetic joint movement during gait.
Explain how prosthetic foot alignment affects the alignment of a person's residual limb inside a prosthetic socket.
Update on Lower Extremity Amputations
September 28, 2006