Download bio-mechanics of hip joint

BIO-MECHANICS OF HIP
JOINT
Hip joint
Introduction
• The hip joint, or coxofemoral joint, is the
articulation of the acetabulum of the pelvis
and the head of the femur
• These two segments form a ball-andsocket joint with three degrees of freedom:
– flexion/extension in the sagittal plane,
– abduction/adduction in the frontal plane, and
– Medial/lateral rotation in the transverse plane.
• The primary function of the hip joint is to
support the weight of the head, arms, and
trunk (HAT) both in static erect posture
and in dynamic postures such as
ambulation, running, and stair climbing.
• The hip joint, like the other joints of the
lower extremity is structured primarily to
serve its weight-bearing functions.
Structure of Hip Joint
Proximal Articular Surfaces
• The cuplike concave socket of the hip joint
is called the acetabulum and is located on
the lateral aspect of the pelvic bone
(innominate or os coxa).
• Three bones form the pelvis: the ilium, the
ischium, and the pubis. Each of the three
bones contributes to the structure of the
acetabulum
• The pubis forms one fifth of the
acetabulum, the ischium forms two fifths,
and the ilium forms the remainder.
• Until full ossification of the pelvis occurs
between 20 and 25 years of age, the
separate segments of the acetabulum may
remain visible on radiograph
• The acetabulum appears to be a hemisphere,
but only its upper margin has a true circular
contour, and the roundness of the
acetabulum as a whole decreases with age.
• In actuality, only a horseshoe-shaped portion
of the periphery of the acetabulum (the lunate
surface) is covered with hyaline cartilage and
articulates with the head of the femur
• The inferior aspect of the lunate surface (the base of
the horseshoe) is interrupted by a deep notch called
the acetabular notch. The acetabular notch is
spanned by a fibrous band, the transverse
acetabular ligament, that connects the two ends of
the horseshoe.
• The transverse acetabular ligament also spans the
acetabular notch to create a fibro-osseous tunnel,
called the acetabular fossa, beneath the ligament,
through which blood vessels may pass into the
central or deepest portion of the acetabulum.
• The acetabulum is deepened by the
fibrocartilaginous acetabular labrum, which
surrounds the periphery.
• The acetabular fossa is nonarticular; the
femoral head does not contact this surface
• The acetabular fossa contains fibroelastic
fat covered with synovial membrane.
Center Edge Angle of the
Acetabulum
• Each acetabulum, in addition to its obvious
lateral orientation, is oriented on each
innominate bone some-what inferiorly and
anteriorly.
• The magnitude of inferior orientation is
assessed on radiograph by using a line
connecting the lateral rim of the
acetabulum and the center of the femoral
head. This line forms an angle with the
vertical known as the center edge (CE)
angle or the angle of Wiberg and is the
amount of inferior tilt of the acetabulum.
• Using computed tomography (CT), Adna
and associates found CE angles in adults
to average 38° in men and 35° in women
(with ranges in both sexes to be about 22°
to 42°).
Acetabular Anteversion
• The acetabulum faces not only somewhat inferiorly but
also anteriorly. The magnitude of anterior orientation
of the acetabulum may be referred to as the angle of
acetabular anteversion.
• Adna and associates found the average value to be
18.5° for men and 21.5° for women, although
Kapandji cited larger values of 30° to 40°.
• Pathologic increases in the angle of acetabular
anteversion are associated with decreased joint
stability and increased tendency for anterior
dislocation of the head of the femur.
Acetabular Labrum
• The entire periphery of the acetabulum is rimmed
by a ring of wedge-shaped fibrocartilage called the
acetabular labrum
• The labrum is attached to the periphery of the
acetabulum by a zone of calcified cartilage with a
well-defined tide-mark.
• The acetabular labrum deepens the socket and
increases the concavity of the acetabulum and
grasps the head of the femur to maintain contact
with the acetabulum.
• Although the labrum appears to broaden the
articular surface of the acetabulum,
experimental evidence suggests that load
distribution in the acetabulum is not affected by
removal of the labrum.
• Histological examination demonstrated free
nerve endings and sensory receptors in the
superficial layer of the labrum, as well as
vascularization from the adjacent joint capsule
only in the superficial third of the labrum.
• The transverse acetabular ligament is
considered to be part of the acetabular
labrum, although, unlike the labrum, it
contains no cartilage cells.
• Although it is positioned to protect the blood
vessels traveling beneath it to reach the
head of the femur, experimental data do not
support the role of the transverse acetabular
ligament as a load-bearing structure.
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