Illustrated Encyclopedia of Human Anatomic Variation: Opus V: Skeletal Systems: Lower Limb

Pelvis

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

The hip bone or os coxae is not subject to great variation: however, relatively few pelves are easily classified as male or female.

A canal may groove the iliac fossa, transmitting a vein that connects the external pelvic and internal pelvic veins.

Conversion of the obturator sulcus (or groove) into a bony foramen has been reported.

Defect or nonunion of the pubic and ischial rami is occasionally observed.

There are reports of accessory articular surfaces on the ilium in the region of the posterior superior spine and tuberosity, which articulate with accessory facets on the sacrum at the level of the first and second posterior sacral foramina. The first anatomical description of these variations was by the Dutch anatomist Anton Albinus in 1753. In 1801, the Italian Caldanus also reported them in his "Icones Anatomicae." They vary in diameter from 0.59 to 1.2 cm and are found in 10-50% of all pelves. In one study of 56 skeletons, 9 had accessory sacroiliac joints. In three cases the joint was bilateral and in five, unilateral. In one case, the contralateral side was missing. Of 100 CT examinations of the pelvis, accessory joints were present in 13 cases, and were bilateral in 3. In 1100 plain radiographs the reported incidence was 14%. Trotter gives the incidence of accessory sacroiliac joints to be 36% (958), the highest value in the literature. Derry finds 10.4% (195 skeletons), the lowest value in the literature.

The acetabular notch may be absent.

Extra joint surfaces have also been reported to increase with age.

The dimension of the greater sciatic notch is variable.

An accessory ischial spine may project from the ilium/ischium synchrondrosis, separating the greater sciatic foramen into two compartments.

An accessory spine behind the ileopectineal eminence occasionally provides an attachment site for the psoas minor muscle.

Sex differences in size and form of the pelvis are related to its function in parturition although variation in size and form are not always gender specific. Agenesis of the os pubis and duplication of the ischium have been reported.

The sacral canal os the continuation of the vertebral canal. The subdural and subarachnoid spaces extend within the canal as far as the middle third of the body of the second sacral vertebra in 46% of 56 cadavers examined (Lanier, McKnight and Trotter).

References

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