Biomechanical analysis of medialized hip implant

1. Mini Project 3: Orthobullets
Jensen Williams, Natalie Ivey,
Timothy Lindquist

2. Question

3. Summarize the problem…
What is J when the acetabulum is moved
medially on a patient standing on their right leg
given the information on the next slide?

4. Collect Information
• Non-medial
• Distance A = 50 mm =
0.05 m
• Distance B = 100 mm =
0.1 m
• J = Resultant Hip Joint
Force = 1800 N
• AT = Abductor Tension =
1200 N
• FBW = Body weight at
pubis = 5/6 x BW = 5/6 x
720 N = 600 N
• Medial
• Distance A = 50 mm =
0.05 m
• Distance B = 50 mm =
0.05m
• J = Resultant Hip Joint
Force = UNKNOWN
• AT = Abductor Tension =
UNKNOWN
• FBW = Body weight at
pubis = 5/6 x BW = 5/6 x
720 N = 600 N

5. Assumptions?
• Assumptions for this problem include:
• 1) This material exhibits ideal behavior for the models
used. This is termed a LEHI material.
• 2) 2D problem: this simplifies calculation of forces
• 3) Ignore all other forces: just focusing on the hip.
• 4) Hip in static equilibrium: allows for calculations to be
set to zero.
• 5) Forces are perpendicular to moment arm: this
eliminates the need for force calculations regarding
different angles, although some problems might
contain angles this one does not.

6. Isolate the area to be analyzed before drawing the free body diagram

7. Draw the free body diagram

8. Pick a point to take moment about

9. Visualize the moments

10. Solve for equilibrium of moments

11. Continue to solve for J

12. Alternate Way OR A Great Checking
Mechanism

13. Isolate the spot to analyze moment

14. Visualize the moments

15. Write moment equilibrium equations

16. Continue to solve the equations

17. Equilibrium in y direction

18. Looking Back
Eliminating Answers…
M = r x F
M = r x F
Fc
J
M = r x F
Red – Medial hip body weight moment
Green – Medial and nonmedial hip moment from J
Dark Blue – Nonmedial hip moment from body weight
Fc