Hip Joint Anatomy
The hip joint is a synovial
ballandsocket joint between the head of the femur and the acetabulum of the
hip bone (Fig. 6.66).
The femoral head, covered by
hyaline cartilage, forms twothirds of a sphere and has a central pit (fovea; Fig.
6.66) giving attachment
to the round ligament (ligamentum teres). The head surmounts the femoral neck,
whose base abuts the medial side of the greater trochanter. The acetabulum is a
deep socket with a Cshaped articular area covered with hyaline cartilage and a
fat filled nonarticular area (acetabular fossa), the margins of which give
attachment to the base of the ligamentum teres (Fig. 6.67). The acetabulum is deficient inferiorly at
the acetabular notch (Fig. 6.66), where blood vessels, bridged by the
transverse acetabular ligament, enter the joint. A fibrocartilaginous labrum,
attached to the margins of the acetabulum and the transverse ligament, helps to
deepen the socket.
Medially, the fibrous capsule is
attached to the outer margin of the labrum; laterally the capsule attaches to
the intertrochanteric
line (Figs
6.66 & 6.68) at the root of the femoral neck and to the femoral shaft just
above the lesser trochanter. From the femoral attachment of the capsule,
retinacular fibres derived from the deep part of the capsule (Fig. 6.67) are
reflected medially over the neck to the margins of the head. Posteriorly, the
line of attachment of the capsule is such that only the upper (medial) half of
the femoral neck lies within the joint.
Ligaments
The iliofemoral, pubofemoral and
ischiofemoral ligaments are capsular thickenings that spiral downwards and
laterally from the hip bone to the femur. The strong iliofemoral ligament (Fig.
6.68) is an inverted
Yshape, the stem attaching to the anterior inferior iliac spine and the limbs
to the upper and lower ends of the inter trochanteric line.
The pubofemoral ligament (Fig.
6.68) passes from the
iliopubic eminence to the femoral neck just above the lesser trochanter. The
ischiofemoral ligament lies posteriorly (Fig. 6.70) and reaches the root of the
greater trochanter.
Within the joint is the ligament of
the head of the femur (ligamentum teres femoris) (Figs 6.67 & 6.69), which
has the form of a flattened cone, the base attaching to the margins of the
acetabular fossa and transverse acetabular ligament and the apex to the fovea on
the femoral head.
Synovial membrane lines the
interior of the capsule and the nonarticular surfaces of the joint, clothes
the ligament of the head of the femur and is reflected over the retinacular
fibres and the femoral neck as far as the head. The iliopsoas tendon and
anterior aspect of the capsule are separated by a large bursa (Fig. 6.68),
which often is in communication with the joint cavity.
The tendon of obturator externus is
separated from the capsule by a smaller bursa, which may also communicate with
the joint.
The hip joint is multiaxial and
permits flexion, extension, abduction, adduction, medial and lateral rotation
and circumduction.
Flexion is produced by iliopsoas,
assisted by sartorius, rectus femoris and pectineus. Gluteus maximus and the
hamstrings are extensors. Abductors of the hip include gluteus medius and
minimus, while adduction is produced by adductors longus, brevis and magnus,
pectineus and gracilis. Medial rotation is produced by iliopsoas, tensor
fasciae latae and the anterior fibres of gluteus minimus and medius. Lateral
rotation is produced by piriformis, quadratus
femoris, obturator externus and internus and the gemelli.
The hip joint is very stable,
largely because of its bony morphology and the deep fit of the femoral head
into the acetabulum. Other important factors include the ligaments and the tone
of the muscles crossing the joint. The ilio, pubo and ischiofemoral ligaments
all limit extension and medial rotation. The iliofemoral ligament, in
particular, prevents hyperextension, especially in the upright posture when
body weight acts behind the transverse axis of the hip joint and tilts the
pelvis backwards. The ligament of the head of the femur limits adduction of the
hip.
The joint is deeply placed behind
the midpoint of the inguinal ligament. Laterally, the greater trochanter covers
the neck of the femur and is palpable on the lateral side of the thigh.
Medially, only the thin bone of the acetabular fossa (Figs 6.71 & 6.72)
separates the head of the femur from structures within the pelvis that are
vulnerable following acetabular fracture accompanied by medial displacement of
the femoral head. Posteriorly lie structures of the gluteal region (Fig. 6.70),
including the sciatic nerve, which may be damaged in posterior dislocation.
Anteriorly, the joint is covered by the iliopsoas and the femoral vessels and
nerve. Obturator externus and the adductor muscles lie inferiorly (Fig.
6.72), while superiorly
are gluteus medius and minimus.
Blood supply
The arterial supply of the hip
joint, especially that of the head and neck of the femur, is of particular
clinical importance. The joint receives branches from the obturator artery, superior
and inferior gluteal arteries, and medial and lateral circumflex femoral
arteries, either directly or from the trochanteric anastomosis they form. From
this anastomosis (Fig. 6.70), nutrient arteries travel in the retinacular
fibres to enter foramina on the upper part of the femoral neck and terminate in
the head. As only the upper half of the neck is covered posteriorly by the
joint capsule, fractures at this site may be classified as either intra or
extracapsular. Intracapsular fractures that tear the retinacular fibres may
deprive the head of the femur of much of its blood supply, resulting in
avascular necrosis. Additional blood supply comes from a branch of the
obturator artery conveyed in the ligament of the head of the femur to the
femoral head, and from one of the perforating branches of the profunda femoris
artery via a nutrient artery that enters the shaft to supply the femoral neck
and head.
Nerve supply
Nerves to the joint include the
nerve to rectus femoris from the femoral nerve, branches from the anterior
division of the obturator nerve, and the nerve to quadratus femoris from the
sacral plexus.
