Haversian System (Secondary Osteon)
Definition
The basic structural unit of mature cortical bone: a cylinder of 4-20 concentric lamellar rings around a central Haversian canal carrying blood vessels. In cross-section, secondary osteons appear as rounded laminated structures. Their count increases with age, forming the biological basis of histological age estimation.
- Structural unit
- 4-20 concentric lamellae around a central canal
- Appearance
- Rounded, laminated in cross-section
- Age relation
- Count increases with age
- Application
- Histological age-at-death estimation
- Distinguished from
- Primary osteons, which lack a cement line
Common questions
Why does secondary osteon count rise with age instead of falling?+
Bone continually remodels through life: osteoclasts resorb old tissue and osteoblasts lay down new concentric lamellae, and each remodeling event adds a new secondary osteon, so the cumulative count in a cross-section climbs across decades.
What limits the accuracy of osteon counting for age estimation?+
Remodeling rate varies with bone loading, health, hormonal status and skeletal site, so counts from a single field support a probabilistic age range rather than a precise year, and published regression formulas are population-specific.
Related terms
- Cortical (Compact) Bone
- The dense outer shell of long bones and the tables of flat bones. Approximately 80% of skeletal mass. High mineral density (65-70%...
- Epiphyseal Growth Plate (Physis)
- The cartilaginous zone between the epiphysis and metaphysis where endochondral ossification occurs during growth. Closes (fuses) at puberty under the influence of...
- Interstitial Lamellae
- The angular remnants of older osteons left behind after a BMU has partially resorbed them. Their relative area decreases with age as...
- Kerley Method
- A histological age estimation method published by Ellis Kerley in 1965, based on counting secondary osteons, osteon fragments, circumferential lamellar bone, and...
- Lacuna
- A small lens-shaped cavity within bone lamellae that houses an osteocyte cell body. Lacunae are connected by canaliculi radiating toward the Haversian...
- Osteoclast
- The large, multinucleated bone-resorbing cell responsible for excavating the resorption tunnel in a BMU. Activated by the RANKL/OPG cytokine axis. Creates the...
- Plexiform Bone
- A microstructural pattern found in the cortical bone of large rapid-growth mammals (bovids, horses, deer) characterised by alternating layers of woven bone...
- Trabecular (Cancellous) Bone
- The porous, lattice-like interior bone occupying epiphyses, metaphyses, and flat bones. High surface area and metabolic activity but rapidly lost in taphonomic...
- Wolff's Law
- The principle that bone is deposited and resorbed in response to mechanical loading history. Cortical thickness and trabecular orientation follow principal stress...