Hip Bone

The hip bone is often referred to as the os coxae, and some textbooks continue to refer to it as the innominate bone. The most widely used term is hip bone.

The hip bone consists of the ilium, pubis, and ischium (Figs. 7-1 and 7-2). These three bones join together to form the acetabulum, the cup-shaped socket that receives the head of the femur. The ilium, pubis, and ischium are separated by cartilage in children but become fused into one bone in adults.

The hip bone is divided further into two distinct areas: the iliopubic column and the ilioischial column (see Fig. 7-2, C). These columns are used to identify fractures around the acetabulum.


The ilium consists of a body and a broad, curved portion called the ala. The body of the ilium forms approximately two fifths of the acetabulum superiorly (Fig. 7-3). The ala projects superiorly from the body to form the prominence of the hip. The ala has three borders: anterior, posterior, and superior. The anterior and posterior borders present four prominent projections:

The anterior superior iliac spine (ASIS) is an important and frequently used radiographic positioning reference point. The superior margin extending from the ASIS to the posterior superior iliac spine is called the iliac crest. The medial surface of the wing contains the iliac fossa and is separated from the body of the bone by a smooth, arc-shaped ridge, the arcuate line, which forms a part of the circumference of the pelvic brim. The arcuate line passes obliquely, inferiorly, and medially to its junction with the pubis. The inferior and posterior portions of the wing present a large, rough surface—the auricular surface—for articulation with the sacrum. This articular surface and the articular surface of the adjacent sacrum have irregular elevations and depressions that cause a partial interlock of the two bones. The ilium curves inward below this surface, forming the greater sciatic notch.


The ischium consists of a body and the ischial ramus. The body of the ischium forms approximately two fifths of the acetabulum posteriorly (see Figs. 7-2 and 7-3). It projects posteriorly and inferiorly from the acetabulum to form an expanded portion called the ischial tuberosity. When the body is in a seated-upright position, its weight rests on the two ischial tuberosities. The ischial ramus projects anteriorly and medially from the tuberosity to its junction with the inferior ramus of the pubis. By this posterior union the rami of the pubis and ischium enclose the obturator foramen. At the superoposterior border of the body is a prominent projection called the ischial spine. An indentation, the lesser sciatic notch, is just below the ischial spine.

Proximal Femur

The femur is the longest, strongest, and heaviest bone in the body. The proximal end of the femur consists of a head, a neck, and two large processes: the greater and lesser trochanters (Fig. 7-4). The smooth, rounded head is connected to the femoral body by a pyramid-shaped neck and is received into the acetabular cavity of the hip bone. A small depression at the center of the head, the fovea capitis, attaches to the ligamentum capitis femoris (Fig. 7-5; see Fig. 7-4). The neck is constricted near the head but expands to a broad base at the body of the bone. The neck projects medially, superiorly, and anteriorly from the body. The trochanters are situated at the junction of the body and the base of the neck. The greater trochanter is at the superolateral part of the femoral body, and the lesser trochanter is at the posteromedial part. The prominent ridge extending between the trochanters at the base of the neck on the posterior surface of the body is called the intertrochanteric crest. The less prominent ridge connecting the trochanters anteriorly is called the intertrochanteric line. The femoral neck and the intertrochanteric crest are two common sites of fractures in elderly adults. The superior portion of the greater trochanter projects above the neck and curves slightly posteriorly and medially.

The angulation of the neck of the femur varies considerably with age, sex, and stature. In the average adult, the neck projects anteriorly from the body at an angle of approximately 15 to 20 degrees and superiorly at an angle of approximately 120 to 130 degrees to the long axis of the femoral body (Fig. 7-6). The longitudinal plane of the femur is angled about 10 degrees from vertical. In children, the latter angle is wider—that is, the neck is more vertical in position. In wide pelves, the angle is narrower, placing the neck in a more horizontal position.

Articulations of the Pelvis

Table 7-1 and Fig. 7-7 provide a summary of the three joints of the pelvis and upper femora. The articulation between the acetabulum and the head of the femur (the hip joint) is a synovial ball-and-socket joint that permits free movement in all directions. The knee and ankle joints are hinge joints; the wide range of motion of the lower limb depends on the ball-and-socket joint of the hip. Because the knee and ankle joints are hinge joints, medial and lateral rotations of the foot cause rotation of the entire limb, which is centered at the hip joint.

The pubes of the hip bones articulate with each other at the anterior midline of the body, forming a joint called the pubic symphysis. The pubic symphysis is a cartilaginous symphysis joint.

The right and left ilia articulate with the sacrum posteriorly at the sacroiliac (SI) joints. These two joints angle 25 to 30 degrees relative to the midsagittal plane (see Fig. 7-7, B). The SI articulations are synovial irregular gliding joints. Because the bones of the SI joints interlock, movement is limited or nonexistent.


The female pelvis (Fig. 7-8) is lighter in structure than the male pelvis (Fig. 7-9). It is wider and shallower, and the inlet is larger and more oval-shaped. The sacrum is wider, it curves more sharply posteriorly, and the sacral promontory is flatter. The width and depth of the pelvis vary with stature and gender (Table 7-2). The female pelvis is shaped for childbearing and delivery.

The pelvis is divided into two portions by an oblique plane that extends from the upper anterior margin of the sacrum to the upper margin of the pubic symphysis. The boundary line of this plane is called the brim of the pelvis (see Figs. 7-8 and 7-9). The region above the brim is called the false or greater pelvis, and the region below the brim is called the true or lesser pelvis.

The brim forms the superior aperture, or inlet, of the true pelvis. The inferior aperture, or outlet, of the true pelvis is measured from the tip of the coccyx to the inferior margin of the pubic symphysis in the anteroposterior direction and between the ischial tuberosities in the horizontal direction. The region between the inlet and the outlet is called the pelvic cavity (Fig. 7-10).

When the body is in the upright or seated position, the brim of the pelvis forms an angle of approximately 60 degrees to the horizontal plane. This angle varies with other body positions; the degree and direction of the variation depend on the lumbar and sacral curves.

Localizing Anatomic Structures

The bony landmarks used in radiography of the pelvis and hips are as follows:

Most of these points are easily palpable, even in hypersthenic patients (Fig. 7-11). Because of the heavy muscles immediately above the iliac crest, care must be exercised in locating this structure to avoid centering errors. Having the patient inhale deeply is advisable; while the muscles are relaxed during expiration, the radiographer should palpate for the highest point of the iliac crest.

The highest point of the greater trochanter, which can be palpated immediately below the depression in the soft tissues of the lateral surface of the hip, is in the same horizontal plane as the midpoint of the hip joint and the coccyx. The most prominent point of the greater trochanter is in the same horizontal plane as the pubic symphysis (see Fig. 7-11).

The greater trochanter is most prominent laterally and more easily palpated when the lower leg is medially rotated. When properly used, medial rotation assists in localization of hip and pelvis centering points and avoids distortion of the proximal end of the femur during radiography. Improper rotation of the lower leg can rotate the pelvis. Consequently, positioning of the lower leg is important in radiographing the hip and pelvis; the feet must be immobilized in the correct position to avoid distortion of the image. Traumatic injuries or pathologic conditions of the pelvis or lower limb may rule out the possibility of medial rotation.

The pubic symphysis can be palpated on the midsagittal plane and on the same horizontal plane as the greater trochanters. By placing the fingertips at this location and performing a brief downward palpation with the hand flat, palm down, and fingers together, the radiographer can locate the superior margin of the pubic symphysis. To avoid possible embarrassment or misunderstanding, the radiographer should advise the patient in advance that this and other palpations of pelvic landmarks are part of normal procedure and necessary for an accurate examination. When performed in an efficient and professional manner with respect for the patient’s condition, such palpations are generally well tolerated.

The hip joint can be located by palpating the ASIS and the superior margin of the pubic symphysis (Fig. 7-12). The midpoint of a line drawn between these two points is directly above the center of the dome of the acetabular cavity. A line drawn at right angles to the midpoint of the first line lies parallel to the long axis of the femoral neck of an average adult in the anatomic position. The femoral head lies 1½ inches (3.8 cm) distal, and the femoral neck is 2½ (6.4 cm) distal to this point.

For accurate localization of the femoral neck in atypical patients or in patients in whom the limb is not in the anatomic position, a line is drawn between the ASIS and the superior margin of the pubic symphysis, and a second line is drawn from a point 1 inch (2.5 cm) inferior to the greater trochanter to the midpoint of the previously marked line. The femoral head and neck lies along this line (see Fig. 7-12).


Bello1 described an alternative positioning landmark for the pelvis and hip.


Condition Definition
Ankylosing spondylitis Rheumatoid arthritis variant involving the SI joints and spine
Congenital hip dysplasia Malformation of the acetabulum causing displacement of the femoral head
Dislocation Displacement of a bone from the joint space
Fracture Disruption in the continuity of bone
Legg-Calvé-Perthes disease Flattening of the femoral head owing to vascular interruption
Metastases Transfer of a cancerous lesion from one area to another
Osteoarthritis or degenerative joint disease Form of arthritis marked by progressive cartilage deterioration in synovial joints and vertebrae
Osteopetrosis Increased density of atypically soft bone
Osteoporosis Loss of bone density
Paget disease Thick, soft bone marked by bowing and fractures
Slipped epiphysis Proximal portion of femur dislocated from distal portion at the proximal epiphysis
Tumor New tissue growth where cell proliferation is uncontrolled
 Chondrosarcoma Malignant tumor arising from cartilage cells
 Multiple myeloma Malignant neoplasm of plasma cells involving the bone marrow and causing destruction of the bone

Pelvis and Upper Femora


Position of part:

• Center the midsagittal plane of the body to the midline of the grid, and adjust it in a true supine position.

• Unless contraindicated because of trauma or pathologic factors, medially rotate the feet and lower limbs about 15 to 20 degrees to place the femoral necks parallel with the plane of the image receptor (IR) (Figs. 7-15 and 7-16). Medial rotation is easier for the patient to maintain if the knees are supported. The heels should be placed about 8 to 10 inches (20 to 24 cm) apart.

• Immobilize the legs with a sandbag across the ankles, if necessary.

• Check the distance from ASIS to the tabletop on each side to be sure that the pelvis is not rotated.

• Center the IR midway between ASIS and pubic symphysis. In average-sized patients, the center of the IR is about 2 inches (5 cm) inferior to ASIS and 2 inches (5 cm) superior to pubic symphysis (Fig. 7-17).

• If the pelvis is deep, palpate for the iliac crest and adjust the position of the IR so that its upper border projects 1 to 1½ inches (2.5 to 3.8 cm) above the crest.

• Shield gonads.

• Respiration: Suspend.

Structures shown: The image shows an AP projection of the pelvis and of the head, neck, trochanters, and proximal one third or one fourth of the shaft of the femora (Fig. 7-18).

Mar 4, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on PELVIS AND UPPER FEMORA
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