Hip biomechanics

1. Biomechanics of hip joint
Dr. Md. Mahbub Hasan
Resident, D-ortho, SZMC

25. Hip Free Body Analysis
W = gravitational force
weight of the body minus weight of ipsilateral extremity (or 5/6 body weight)
M = abductor muscle force
R = joint reaction force can reach 3 to 6 times body weight
Solving for joint reaction force (R)
step 1: calculate My
principle
sum of all moments equals 0
in this case, the moments are created by My and W
step 2: calculate Ry
step 3: calculate R

26. • Solving for joint reaction force (R)
– step 1: calculate My
• (A x My) + (B x W) = 0
– assume A = 5cm and B = 12.5cm
– My = 2.5W
– step 2: calculate Ry
• Ry = My + W
• Ry = 2.5W + W
• Ry = 3.5W
– step 3: calculate R
• R = Ry / (cos 30°)
– R = 3.5W / (cos 30°)
– R = ~4W