SACRUM ANATOMY

GENERAL STRUCTURE

Composition

• Formed by five sacral vertebrae and intervertebral disks between them
• Base positioned superiorly facing final lumbar vertebra
• Apex directed inferiorly toward coccyx

Surface Configuration

• Pelvic surface - exhibits concave anterior orientation
• Posterior surface - demonstrates convex configuration

SURFACES AND FEATURES

Pelvic Surface

• Concave curvature with non-uniform pattern
  • Maximum depth at approximately third vertebral level
• Anterior sacral foramina - four paired arrangements
  • Exit points for ventral rami of spinal nerves
  • Located adjacent to sacral canal
• Transverse ridges between bilateral anterior foramina
  • Result from fusion of adjacent vertebral surfaces and intervertebral disks

Posterior Surface

• Uniform convex curvature
• Five longitudinal ridges from fused vertebral processes:
  • Median sacral crest - midline prominence from fused spinous processes
  • Intermediate sacral crest - lateral to median crest, medial to posterior sacral foramina, represents fused articular process remnants
  • Lateral sacral crest - lateral to posterior foramina, composed of transverse process remnants
• Superior articular processes at cranial end
  • Upper terminus of intermediate sacral crest
  • Articulate with final lumbar vertebra
• Posterior sacral foramina - eight in total
  • Exit points for dorsal rami of spinal nerves
• Sacral hiatus - inferior aperture of vertebral canal
  • Located at fourth sacral vertebra level
  • Bounded laterally by two sacral horns
  • Median sacral crest terminates superior to hiatus

Sacral Canal

• Located within sacrum interior
• Shape corresponds to overall sacral morphology
• Lateral channels correspond to intervertebral foramina
  • Formed from fused superior and inferior vertebral notches
  • Open laterally from sacral canal
• Sacral foramina open from short channels
  • Anterior openings present
  • Posterior openings present

ANATOMICAL VIEWS

Superior View

• Base - central contact surface
  • Interface point for intervertebral disk with final lumbar vertebra
  • Most prominent point designated as promontory
• Sacral alae - flank base bilaterally
  • Form upper surface of pars lateralis
  • Composed of transverse processes
• Sacral canal entrance - lies posterior to base
• Superior articular processes - positioned lateral to canal entrance, articulate with final lumbar vertebra

Lateral View

• Auricular surface - articulation site for connection with hip bone
• Sacral tuberosity - positioned posterior to auricular surface
  • Roughened area for ligament attachment

SEXUAL DIMORPHISM

The sacrum exhibits distinct morphological differences between males and females:

Male Characteristics

• Greater length
• Increased curvature

Female Characteristics

• Reduced length
• Increased width