266
UNIT 2
Covering, Support, and Movement of the Body
8
Articular
capsule
Synovial
membrane
Synovial cavity
Articular cartilage
Coronoid process
Tendon of
brachialis muscle
Ulna
Humerus
Fat pad
Tendon of
triceps
muscle
Bursa
Trochlea
Articular cartilage
of the trochlear
notch
(a) Median sagittal section through right elbow (lateral view)
Humerus
Lateral
epicondyle
Articular
capsule
Radial
collateral
ligament
Olecranon
(b) Lateral view of right elbow joint
Anular
ligament
Radius
Ulna
Anular
ligament
Humerus
Medial
epicondyle
Ulnar
collateral
ligament
Ulna
Articular
capsule
Radius
Coronoid
process
(c) Cadaver photo of medial view of right elbow
Articular
capsule
Anular
ligament
Coronoid
process
(d) Medial view of right elbow
Radius
Humerus
Medial
epicondyle
Ulnar
collateral
ligament
Ulna
Figure 8.11
The elbow joint.
Elbow Joint
Our upper limbs are flexible extensions that permit us to reach out
and manipulate things in our environment. Besides the shoulder
joint, the most prominent of the upper limb joints is the elbow.
Te elbow joint provides a stable and smoothly operating hinge
that allows flexion and extension only
(Figure 8.11)
. Within the
joint, both the radius and ulna articulate with the condyles of the
humerus, but it is the close gripping of the trochlea by the ulna’s
trochlear notch that forms the “hinge” and stabilizes this joint (Fig-
ure 8.11a). A relatively lax articular capsule extends inferiorly from
the humerus to the ulna and radius, and to the
anular ligament
(an
9
u-lar) surrounding the head of the radius (Figure 8.11b, c).
Anteriorly and posteriorly, the articular capsule is thin and allows
substantial freedom for elbow flexion and extension. However, side-
to-side movements are restricted by two strong capsular ligaments:
the
ulnar collateral ligament
medially, and the
radial collateral
ligament
, a triangular ligament on the lateral side (Figure 8.11b, c,
and d). Additionally, tendons of several arm muscles, such as the
biceps and triceps, cross the elbow joint and provide security.
Te radius is a passive “onlooker” in the angular elbow
movements. However, its head rotates within the anular liga-
ment during supination and pronation of the forearm.
Hip Joint
Te
hip
(coxal)
joint
, like the shoulder joint, is a ball-and-socket
joint. It has a good range of motion, but not nearly as wide as the
shoulder’s range. Movements occur in all possible planes but are
limited by the joint’s strong ligaments and its deep socket.
Te hip joint is formed by the articulation of the spherical
head of the femur with the deeply cupped acetabulum of the hip
bone
(Figure 8.12)
. Te depth of the acetabulum is enhanced
by a circular rim of fibrocartilage called the
acetabular labrum
(as
0
ĕ-tab
9
u-lar) (Figure 8.12a, b). Te labrum’s diameter is less
than that of the head of the femur, and these articular surfaces
fit snugly together, so hip joint dislocations are rare.
Te thick articular capsule extends from the rim of the acetab-
ulum to the neck of the femur and completely encloses the joint.
Several strong ligaments reinforce the capsule of the hip joint.
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