3. BIOMECHANICS – Science that deals with the
study of forces (internal or external ) acting on
the living body
The hip is a true ball-and-socket joint
surrounded by powerful and well-balanced
muscles
Mobile as well as stable
9. To maintain stable hip, torques produced by the
body weight is countered by abductor muscles
pull. Abductor force X lever arm1 = weight X
leverarm2
10. FORCES ACTING ACROSS HIP JOINT
Body weight
Abductor muscles force
Joint reaction force
11. JOINT REACTION FORCE
force generated within a joint in response to
forces acting on the joint
in the hip, it is the result of the need to balance
the moment arms of the body weight and
abductor tension
maintains a level pelvis
12. BILATERAL LIMB STANCE
the centre of gravity is located between the two
hips, with an equal force exerted on both hips.
13. SINGLE LEG STANCE
Centre of gravity moves distally and away from
the supporting leg
The non-supporting leg becomes a part of the
body mass .
The abductors resisting the rotation of the
femoral head
The lever of the abductors is shorter than the
lever arm of body weight. Therefore, the
combined force of the abductors must be
multiples of body weight (typically three times
body weight),
14. CLINICAL IMPLICATIONS
Actions that decrease joint reaction force include
acetabular side
moving acetabular component medial, inferior, and
anterior
femoral side
increasing offset of femoral component
long stem prosthesis
patient's gait
shifting body weight over affected hip this results in
Trendelenburg gait
cane in contralateral hand
reduces abductor muscle pull and decreases the moment
arm between the center of gravity and the femoral head
Strong bones • Powerful muscles • Strongest ligaments • Depth of acetabulum , narrowing of mouth by acetabular labrum • Length and obliquity of neck of femur
, including the upper fibres of the gluteus maximus, the tensor fascia latae, the gluteus medius and minimus, the piriformis and obturator internus