The biomechanics concept of hip will be given this ppt and the clear picture of weight bearing concept will help you to understand easily......

2.  Internal architecture of pelvis and femur
relies on mechanical stress and transmission
of forces between pelvis and femur.
 The line of weight-bearing is through the
vertebrae of the spinal column to the sacral
promontary and on through the Sacroilliac
joint.
 From the sacroilliac joint it is transmitted to
the acetabulum.

3.  Cancellous bone, also
known as Spongy/
Trabecular bone, is one
of the 2 types of bone
tissue found in the
human body.
 It is found at the ends of
long bones, as well as in
the pelvis,ribs,skull,and
the vertebrae of the
spinal column.

4.  Shaft of femur is not vertical, it is oblique.
 Anteriorly or forward bending of shaft of
femur.(because, the vertical loading on
the oblique femur results in bending
stresses in the shaft).
 Medial condyle is larger than the lateral
condyle.
 These are all the changes,important for
weight-bearing of the upper body.

5.  In standing or upright weight-bearing
activities, atleast half of the weight of the
HAT*(the gravitational force) passes
down through the pelvis to the femoral
head.
 The ground Reaction force travels up to
the shaft.
 These 2 forces act on the articular
surface of Hip joint, femoral head and
neck & also the femoral shaft.
 (Note:- HAT= H-Head, A-Arm, T-
Trunk)*

6.  These 2 forces are nearly parallel
and in opposite directions create a
force couple with an moment
arm(MA).
 These forces create a bending
movement of the femoral neck.

7.  The bending stress creates
› Tensile force on the superior
aspect of the femoral neck,
› And compressive stress on the
inferior aspect of the femoral
neck.
 USE- A complex set of forces
prevents the rotation and resist
the shear force.

8.  These follow for the shaft of Femur,
› Compressive stresses in the medial
shaft,
› Tensile stresses in the lateral shaft.

9.  Trabeculae- calcified plates of
tissue within the cancellous
bone.
 The trabeculae are quite
evident on bony cross-
section.
 The force couple causes and
creates the structural
resistance of 2 major and 3
minor trabecular systems.

10. 1) Medial/ principle compressive system
2) Lateral/ principle tensile sysytem
3) Secondary/accessory system
i. Secondary tensile system
ii. Secondary compressive system
4) Zone of weakness

11.  Presence:- medial cortex
of the upper femoral shaft
and radiates through the
cancellous bone to cortical
bone of the superior
aspect of the femoral
head.
 It responds to Vertical
compressive force

12.  Presence:- lateral cortex of
the upper femoral shaft &
after crossing the medial
system, terminate in the
cortical bone on the inferior
aspect of the femoral head.
 It is Oblique.
 It responds to parallel force
of weight of HAT and
GRF(ground reaction force).

13.  There are 2 accessory
trabecular system,
i. Compressive
ii. Tensile
 Presence:- trochanteric
area of femur.
 It responds to
compressive and tensile
stresses.

14.  Used data from instrumented in vivo Hip
prostheses and mathematical modeling to
conclude that,
› The loading environment in the femur during
activity was largerly compressive with relatively
small shear forces.

15.  Area at which 2 different
trabecular systems crosses
each other and offers the
Greatest resistance to
Stress and Strain.

16.  There is an area in the femoral
neck in which the trabeculae
are relatively thin and do not
cross each other, this is known
as “zone of weakness”.
 It has less reinforcement and
thus more potential for failure.
 Bending forces across this
area can lead to femoral neck
fracture

17.  Study by Crabtree and Colleagues from Hip
fracture patient and cadavers.
 They concluded that the cortical bone in the
femoral neck support atleast 50% of load
placed on the proximal femur.
 They suggested that compromise of cortical
bone may be more of a factor in fracture
than is diminished cancellous bone.

18. 1) Acetabulum:-
I. The primary weight-bearing surface of
acetabulum(Dome of acetabulum) is loacted on
the superior portion of the lunate surface.
II. In normal Hip, the dome lies directly over the
femoral head.

19. I. During unilateral standing, the contact
pressure located is near the dome.
II. Degenerative changes- pressure on the
dome of the acetabulum.

20.  FEMUR:-
I. The primary weight-bearing area of the femoral
head is correspondingly its superior portion.
II. Degenerative changes- femoral head includes
loss of ball shape and flattening of superior
portion also noted near the attachment of
ligamentum teres. (because of primary weight-
bearing area is superior portion of femoral
head & lunate surface in contact while
bearing).

21. 2) Full loading of Hip joint is presumably
necessary to achieve congruence and
optimize load distribution between the larger
Femoral head & Acetabulum.
3) The superior femoral head receives
compression not only from the dome in
standing,
› But also from posterior Acetabulum while
standing,
› Anterior Acetabulum in Extension of Hip.

22. 4) More frequent and complete compression of
the cartilage of the superior femoral head,
according to this premise, leads to better
nutrition within the cartilage.
› It must be remembered, however, that Avascular
cartilage is depended on both compression and
release to move nutrition through the tissue; both too
little compression and excessive compression can
lead to compromise of the cartilage structure.