274
UNIT TWO
Muscles surround the joint capsule of the hip. The artic-
ulating parts of the hip are held more closely together than
those of the shoulder, allowing considerably less freedom of
movement. The structure of the hip joint, however, still per-
mits a wide variety of movements, including fl exion, exten-
sion, adduction, abduction, rotation, and circumduction.
The hip is one of the joints most frequently replaced (Clinical
Application 8.1).
Knee Joint
The
knee joint
is the largest and most complex of the syn-
ovial joints. It consists of the medial and lateral condyles at
the distal end of the femur and the medial and lateral con-
dyles at the proximal end of the tibia. In addition, the femur
articulates anteriorly with the patella. Although the knee
functions largely as a modiF
ed hinge joint (allowing fl
ex-
ion and extension), the articulations between the femur and
tibia are condylar (allowing some rotation when the knee
is fl exed), and the joint between the femur and patella is a
plane joint.
Hip Joint
The
hip joint
is a ball-and-socket joint that consists of the
head of the femur and the cup-shaped acetabulum of the
hip bone. A ligament (ligamentum capitis) attaches to a pit
(fovea capitis) on the head of the femur and to connective
tissue in the acetabulum. This attachment, however, seems
to have little importance in holding the articulating bones
together, but rather carries blood vessels to the head of the
femur
(f g. 8.17)
.
A horseshoe-shaped ring of fibrocartilage (acetabular
labrum) at the rim of the acetabulum deepens the cavity of
the acetabulum. It encloses the head of the femur and helps
hold it securely in place. In addition, a heavy, cylindrical
joint capsule reinforced with still other ligaments surrounds
the articulating structures and connects the neck of the femur
to the margin of the acetabulum
(f
g. 8.18)
.
The major ligaments of the hip joint include the follow-
ing
(f g. 8.19)
:
1.
Iliofemoral
(il
e-o-fem
o-ral)
ligament.
This ligament
consists of a
Y
-shaped band of strong F
bers that
connects the anterior inferior iliac spine of the hip bone
to a bony line (intertrochanteric line) extending between
the greater and lesser trochanters of the femur. The
iliofemoral ligament is the strongest ligament in the
body.
2.
Pubofemoral
(pu
bo-fem
o-ral)
ligament.
The
pubofemoral ligament extends between the superior
portion of the pubis and the iliofemoral ligament. Its
F bers also blend with the F
bers of the joint capsule.
3.
Ischiofemoral
(is
ke-o-fem
o-ral)
ligament.
This
ligament consists of a band of strong F
bers that
originates on the ischium just posterior to the
acetabulum and blends with the F
bers of the joint
capsule.
Arthroscopy enables a surgeon to visualize the interior of a joint and
perform diagnostic or therapeutic procedures, guided by the image
on a video screen. An arthroscope is a thin, tubular instrument about
25 cm long containing optical F
bers that transmit an image. The sur-
geon inserts the device through a small incision in the joint capsule.
It is far less invasive than conventional surgery. Many runners have
undergone uncomplicated arthroscopy and raced just weeks later.
Arthroscopy is combined with a genetic technique called the
polymerase chain reaction (PCR) to rapidly diagnose infection. Guided
by an arthroscope, the surgeon samples a small piece of the synovial
membrane. PCR detects and ampliF
es speciF
c DNA sequences, such
as those of bacteria. ±or example, the technique can rapidly diagnose
Lyme disease by detecting DNA from the causative bacterium
Borrelia
burgdorferi
. This is valuable because a variety of bacteria can infect
joints, and choosing the appropriate antibiotic, based on knowing
the type of bacterium, is crucial for fast and complete recovery.
(a)
(b)
FIGURE 8.17
Hip joint. (
a
) The acetabulum provides the socket for
the head of the femur in the hip joint. (
b
) The pit (fovea capitis) in the
femur’s head marks attachment of a ligament that surrounds blood
vessels and nerves.
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