CorpusHuman Anatomy
SkeletalTissue

Compact bone

Substantia compacta

Also known as: cortical bone, dense bone, lamellar bone

Dense bone that forms the outer shell of every bone and the thick wall of long-bone shafts. It is built from closely packed cylindrical osteons aligned with the long axis, resisting bending and compression.

Long Bone — Structure Synovial Joint — Structure

Overview

Porosity≈5–10%
Share of skeletal mass≈80%
Annual turnover≈2–4%

Compact bone has a porosity of only ≈5–10% and accounts for ≈80% of skeletal mass. Its structural unit is the osteon (Haversian system) — concentric lamellae around a central (Haversian) canal containing blood vessels and nerves. Osteons run roughly parallel to the long axis of the bone, matching the direction of the principal stresses. The spaces between osteons are filled by interstitial lamellae (remnants of older osteons partly resorbed during remodelling), and the whole cortex is bounded by outer circumferential lamellae beneath the periosteum and inner circumferential lamellae beneath the endosteum.

Vessels reach the central canals through transverse perforating (Volkmann) canals, which connect the periosteal, endosteal and Haversian circulations and, unlike central canals, are not surrounded by concentric lamellae. Osteocytes in lacunae communicate through a vast network of canaliculi — no osteocyte lies more than ≈0.2 mm from a capillary. Cortical thickness is greatest in the mid-shaft of long bones, where bending moments are highest.

Location

Outer layer of all bones; thickest in the diaphyses of long bones; inner and outer tables of the skull.

Parts & subdivisions

  1. Osteons (Haversian systems)
    Cylindrical units ≈200–300 µm in diameter and several mm long.
  2. Outer circumferential lamellae
    Encircle the whole bone beneath the periosteum; anchored by perforating (Sharpey) fibres.
  3. Inner circumferential lamellae
    Line the medullary cavity beneath the endosteum.
  4. Interstitial lamellae
    Fragments of old osteons between intact ones — evidence of remodelling.
  5. Perforating (Volkmann) canals
    Transverse channels linking periosteal and medullary vessels to central canals.

Anatomy

Arterial supply

Inner two-thirds of the cortex from the nutrient artery (medullary, centrifugal flow); outer third from periosteal arteries.

Histology

Ground sections show osteons as concentric rings around dark central canals with lacunae and radiating canaliculi; cement (reversal) lines mark osteon boundaries.

Function

  • Resists bending, torsion and compression; provides most of a bone’s strength
  • Protects the medullary cavity and spongy bone within
  • Provides firm attachment for tendons and ligaments via Sharpey fibres
Physiology

Remodelled by cutting cones that tunnel through the cortex, at ≈2–3% per year — much slower than trabecular bone.

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.