Chapter 8: Proximal Femur & Pelvis

Detailed Chapter Overview

Chapter 8 provides a critical examination of the pelvis and proximal femur, a central region of the skeleton that is fundamental to weight-bearing, locomotion, and the protection of vital abdominopelvic organs. Radiography of this area is essential for diagnosing a wide range of conditions, particularly fractures in elderly and trauma patients, as well as congenital and degenerative diseases. The chapter begins with a detailed exploration of the pelvic girdle's complex anatomy, including the three fused bones of the os coxae (ilium, ischium, pubis) and their significant landmarks. A major focus is placed on understanding the orientation of the proximal femur, specifically the natural anteversion of the femoral necks, and how internal rotation of the lower limbs is a non-negotiable step in positioning to achieve a true AP relationship. The chapter meticulously differentiates between the male and female pelvis, a key consideration in both radiographic interpretation and clinical practice. It provides detailed, step-by-step instructions for routine and trauma projections, with a strong emphasis on the axirolateral inferosuperior (Danelius-Miller) method as a life-saving tool in trauma settings. For each projection, stringent evaluation criteria are presented, focusing on symmetry, landmark visualization (e.g., lesser trochanters), and the clear demonstration of joint spaces, ensuring that radiographers can produce images of the highest diagnostic quality for this anatomically complex and clinically vital area.

In-Depth Study Guide

Anatomy of the Pelvic Girdle

The pelvic girdle serves as the basin-shaped connection between the trunk and the lower limbs. It is composed of two hip bones (ossa coxae or innominate bones), the sacrum, and the coccyx.

Hip Bone (Os Coxae):

Each hip bone is formed by the fusion of three bones during development, which meet at the acetabulum.

• Ilium: The largest and most superior part. Key landmarks include the **iliac crest** (superior border), the **anterior superior iliac spine (ASIS)**, the **posterior superior iliac spine (PSIS)**, and the wing-like portion called the **ala**.
• Ischium: The posteroinferior part. Its major feature is the large **ischial tuberosity**, which bears the body's weight when sitting. The **ischial spine** is a posterior projection located just superior to the tuberosity.
• Pubis: The anteroinferior part. The two pubic bones meet at the midline to form the **pubic symphysis**, a cartilaginous joint.
• Acetabulum: The deep, cup-shaped socket on the lateral surface of the hip bone that articulates with the head of the femur. All three bones (ilium, ischium, pubis) contribute to its formation.
• Obturator Foramen: The large opening formed by the ischium and pubis, through which nerves and blood vessels pass.

True and False Pelvis:

• Greater (False) Pelvis: The general area above the oblique plane that passes through the pelvic brim. It is formed laterally by the alae of the ilia.
• Lesser (True) Pelvis: The cavity completely surrounded by bone, located inferior to the pelvic brim. It forms the actual birth canal in females.

Anatomy of the Proximal Femur

• Head: A rounded, smooth structure that articulates with the acetabulum. It has a small depression called the **fovea capitis**, where a major ligament attaches.
• Neck: A strong, pyramidal process of bone that connects the head to the body (shaft). It projects superiorly and medially from the shaft at an angle of about 125 degrees.
• Trochanters: Large eminences for muscle attachment. The **greater trochanter** is a large, palpable prominence on the superolateral aspect. The **lesser trochanter** is a smaller, conical eminence projecting medially and posteriorly from the junction of the neck and shaft.
• Intertrochanteric Crest: A thick ridge of bone connecting the two trochanters posteriorly.

Positioning, Orientation, and Landmark Localization

Femoral Neck Orientation:

The femoral head and neck do not lie on the same plane as the femoral shaft. They are angled anteriorly by about 15 to 20 degrees relative to the body of the femur. This is called **anteversion**.

• Critical Positioning Step: To overcome this natural anteversion and place the femoral necks parallel to the image receptor for a true AP projection, the lower limbs and feet must be **internally rotated 15 to 20 degrees**.
• How to Verify Rotation: Correct internal rotation is confirmed radiographically when the lesser trochanters are either not visible at all or only very slightly visible. The greater trochanters should be fully seen in profile laterally.

Landmark Localization:

Palpation of key landmarks is essential for accurate centering.

• Hip Joint Localization: The femoral head can be located by finding the ASIS and the superior margin of the pubic symphysis. The femoral head lies 1.5 inches distal to the midpoint of a line drawn between these two landmarks.

Routine and Special Projections

AP Pelvis

• Purpose: A survey image of the entire pelvic girdle, including both hip joints, for assessment of fractures, dislocations, or degenerative joint disease.
• Positioning: Patient is supine. CR is directed perpendicularly to a point midway between the level of the ASIS and the pubic symphysis. Both legs are internally rotated 15-20 degrees.
• Evaluation Criteria: Entire pelvis is visualized. No rotation is evident (iliac wings and obturator foramina are symmetric). The lesser trochanters should not be visible. Sacrum and coccyx are aligned with the pubic symphysis.

AP Unilateral Hip ("AP Spot")

• Purpose: A more focused view of a single hip joint.
• Positioning: Similar to AP Pelvis, but centered specifically to the affected hip joint (using the localization method described above). Internal rotation of the affected leg is still required.
• Evaluation Criteria: The acetabulum, femoral head, neck, and greater trochanter are clearly demonstrated. The femoral neck should be seen in its full length without foreshortening.

Unilateral "Frog-Leg" Lateral (Modified Cleaves Method)

• Purpose: A nontraumatic lateral view of the femoral head and neck.
• Positioning: Patient is supine. The knee of the affected side is flexed, and the femur is abducted 45 degrees from the vertical plane. This places the femoral neck parallel to the IR.
• Evaluation Criteria: The acetabulum and femoral head and neck are seen in a lateral profile. The lesser trochanter is seen in profile on the medial aspect of the femur.

Axiolateral Inferosuperior (Danelius-Miller Method) - Trauma Cross-Table Lateral

• Purpose: To obtain a lateral view of the hip without moving the patient or their affected leg. This is the required projection for suspected hip fractures.
• Positioning: Patient is supine. The IR is placed vertically in the crease above the iliac crest, angled so it is parallel to the femoral neck. The CR is directed horizontally, perpendicular to the IR and the femoral neck. The unaffected leg must be flexed and lifted out of the path of the x-ray beam.
• Evaluation Criteria: The entire femoral head, neck, and acetabulum are visible. The ischial tuberosity is seen posterior to the femoral head. Any orthopedic hardware should be fully visualized.