Pelvis

Published on 01/04/2015 by admin

Filed under Radiology

Last modified 01/04/2015

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13

Pelvis

The standard radiograph

AP view.

Abbreviations

AIIS, anterior inferior iliac spine; AP, anterior-posterior; ASIS, anterior superior iliac spine; RTA, road traffic accident; SI joint, sacro-iliac joint.

Normal anatomy

Normal AP view

The pelvis comprises three bone rings:

The robust sacro-iliac joints and the pubic symphysis are part of the main bone ring. The sacro-iliac joints are the strongest joints in the body and resist the normal vertical and anterior-posterior displacement forces; the pubic symphysis is the weakest link in the pelvic ring14.

Arcuate lines are visible as smooth curved borders on the radiograph. They outline the roofs of the sacral formina.

image

Developing skeleton: Synchondroses

In children the synchondrosis (cartilaginous junction) between each ischial and pubic bone can sometimes appear confusing. In early childhood these unfused junctions may simulate fracture lines. Subsequently, between the ages of five and seven years, they may mimic healing fractures.

image

Developing skeleton: Pelvic bone apophyses57

In adolescents and young adults the pelvis shows several small secondary centres (the apophyses). These should be radiographically identical on the two sides.

Apophyses are secondary centres that contribute to the eventual shape, size, and contour of the bone but not to its length. These centres are traction epiphyses as muscles originate from or insert into them. They are vulnerable to severe and acute muscle contraction, and also to repetitive forceful muscle pulls when jumping, hurdling, turning suddenly, or—occasionally—when dancing.

Age of appearance and fusion of apophyses at the hip and pelvis (years)5,7

Apophysis First seen on radiograph Fuses to skeleton
Innominate bone
AIIS 13–15 16–18
ASIS 13–15 21–25
Ischial tuberosity 13–15 20–25
Iliac crest 13–15 21–25
Femur
Lesser trochanter 11–12 16–17
Greater trochanter 2–3 16–17

Note that some apophyses remain unfused and normal, but are still vulnerable into the early 20s, well after the growth of the long bones has been completed.