Bone histology and histopathology for clinicians

Bone Histology and
Histopathology for Clinicians
A Primer
Stephen F. Hodgson M.D., M.A.C.E, F.A.C.P.
Bart L. Clarke M.D., F.A.C.E., F.A.C.P.
Robert Wermers M.D., F.A.C.E.
Theresa Hefferan, Ph.D.
Michael Yaszemski. M.D., Ph.D.


Presented By

Mayo Clinic
Divisions of Endocrinology
and Orthopedic Research
and

The American College
of Endocrinology


Supported by an Educational Grant
from:

The American
College of Endocrinology


The authors acknowledge the many
valuable contributions of others
•

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•
•
•
•
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Julie Burgess
Glenda Evans
Dr. Lorraine Fitzpatrick
Dr. Hunter Heath
Dr. Dan Hurley
Donna Jewison
Dr. Ann Kearns
Dr. Kurt Kennel
Dr. Sundeep Khosla

•
•
•
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Dr. Rajiv Kumar
Dr. James McCarthy
Dr. B.L. Riggs
Dr. Jean Sibonga
Peter Steiner,

Illustration & Design

• Dr. Peter Tebben
• Dr. Robert Tiegs
• Dr. Russell Turner


Bone Histology and
Histopathology for Clinicians©
This presentation provides basic
instruction in bone histology, and in the
histopathology of metabolic bone
diseases and related disorders. It was
prepared primarily for endocrine fellows,
endocrinologists, osteologists, and other
physicians and scientists interested in
metabolic and related bone diseases.
©2007 Mayo Foundation for Medical Education and Research and licensed to
The American College of Endocrinology.


• Normal Bone Microanatomy and
Histology

• Bone Cells and Bone
Remodeling

• Basic Bone Histomorphometry

Normal Bone Microanatomy
Cortical
bone

Cancellous
bone

From Gray’s Anatomy

All bones of the human skeleton, though widely variable in function and
shape, share a common anatomic organization. Grossly, they are
composed of dense outer cortical bone which encloses an irregular
medullary space containing cancellous bone,
bone bone that is composed of
branching networks of interconnecting bony trabecular elements.


Normal Bone Microanatomy
Cortical
bone

Cancellous
bone

Undecalcified transiliac bone biopsies (right) are considered to be
representative of all skeletal bone and are suitable for examining,
measuring, and analyzing the microscopic features of cortical and
cancellous bone. Also, with the appropriate use of absorbable
fluorochrome agents, the dynamic changes that occur in bone can be
assessed.

Normal Bone Microanatomy
Variable cortical
thickness

Trabecular orientation differs

Note that cortical thickness varies within individual bones. Also, note that
trabeculae in the vertebral body are oriented vertically along lines of
mechanical stress, whereas in the ilium they appear to be randomly
oriented and are therefore said to be isotropic.


Anatomic Features of a Normal
Transiliac Bone Biopsy

Cortex

Hematopoietic
and fatty marrow

7.5
mm

Trabeculae


Normal Bone Microanatomy
Differential Tissue Stains

Mineralized bone

Unmineralized bone

A number of differential stains can be used to examine undecalcified
tissue. Toluidine Blue stain (left) and Goldner Trichrome stain (right)
will be used throughout this presentation, except as otherwise indicated.
Each stain has characteristics that favor, or disfavor, its use. Either may
be used for histomorphometric analysis.


Normal Bone Microanatomy and Histology
Cortical Bone
Cortical bone forms a relatively thick and dense outer wall and makes up
about 80% of total skeletal mass.


Normal Bone Microanatomy and Histology
Periosteum
The outer cortical surface is enveloped in the periosteum,
periosteum a connective
tissue covering that contains cells that maintain, change, and repair the
external cortical surface.


Normal Bone Microanatomy and Histology
Periosteum
The periosteum also contains blood vessels, sensory nerves, and dense
fibrous tissue that is contiguous with the connective tissue elements of
tendons, ligaments, and joint capsules

Cortex

Periosteum


Normal Bone Microanatomy and Histology
Bone Structural Units (BSU)

Both cortical and trabecular bones are composed of an assembly of individual
bone structural units (BSU), also called osteons, each of which represents
the structural end result of a focus of bone renewal (remodeling).
Architecturally, cortical and trabecular BSUs are distinct. In cortical bone
(left), BSUs may appear in cross section as concentric rings (lamellae),
forming cylindrical - shaped structures. In cancellous bone (right), the
lamellae are flat and appear stacked in saucer shaped depressions.


Normal Bone Microanatomy and Histology
Cancellous Bone
Cancellous bone accounts for the remaining 20% of skeletal mass and
consists of interconnecting trabecular plates that share the medullary
space with hematopoietic and fatty marrow.


Normal Bone Microanatomy and Histology
Endosteum
The inactive or resting trabecular surface is covered by a thin endosteum which,
like the contiguous cortical endosteum, has widely spaced flat lining cells that are
believed to have osteogenic potential, and form a barrier between marrow and bone.

Lining cells

Endosteum


Normal Bone Microanatomy and Histology
Cortical BSUs

Cortical BSUs are laminated bony cylinders (seen in cross section above) that have
central (Haversian) canals enclosing vascular structures, nerves, and a thin
membranous lining (cortical endosteum) containing flat, inactive appearing lining
cells. Cortical BSUs arise from Haversian and other communicating channels
called Volkman’s canals. They are about 0.4 mm in width and are several mm in
length. They are oriented in a branching pattern and lie perpendicular to the long
access of bone.
(Cortex above (left) under incandescent and (right) polarized light)


Cortical (Haversian) BSU

Viewed in cross section under Polarized light


Trabecular BSUs
Trabecular BSUs are laminated saucer-shaped structures that, though appearing
somewhat variable in two-dimensional view, contain a relatively uniform volume of
bone, each BSU representing a “quantum” of bone.

Bone Cells and Bone Remodeling
All normal adult human bone undergoes renewal and
repair through a process called bone remodeling.
Teams of bone resorbing and bone forming cells
form basic multicellular units (BMU) that function at
discrete sites throughout the skeleton in a highly
coordinated sequence of cellular activity. At any
given remodeling site, bone resorption always
precedes bone formation, resulting in the removal
and subsequent replacement of a quantum of bone
at each site.
Under normal steady state conditions, the amount
of bone removed is precisely replaced and there is
no net change in bone mass. Only bone architecture
is changed.


Bone Remodeling
Sequence of Bone Cell Activity
The sequential events of the bone remodeling cycle are
driven by an evolution of cellular events that occurs over a
time period of three to six months:
• Activation – a quiescent bone surface becomes
populated with cells that have been recruited from
osteoclast precursors and are destined to become bone
resorbing osteoclasts
• Resorption – osteoclasts mature and remove a finite
quantum of mineralized bone
• Reversal – osteoclast activity and numbers decline and
are replaced by pre-osteoblasts (bone forming cell

precursors)
• Formation – preosteoblasts become mature osteoblasts
and secrete bone matrix, which subsequently undergoes
mineralization


Bone
Remodeling
Activation
Lining cells produce
collagenase, which exposes
the mineralized bone surface
for bone resorption


Bone
Remodeling
Resorption
(Mineralized bone)
Osteoclast

Sealed
micro-environment

Ruffled membrane

(Marrow)

Cells
derivedsurface

from circulating
mononuclear
phagocyte
are recruited
The basal
of the osteoclast
is rich
in HClprecursors
and cathepsin
transferto
become
boneand
resorbing
pre-osteoclasts,
which cannot be visually identified by
organelles
is called
the ruffled membrane.
standard microscopy. Pre-osteoclasts mature to become osteoclasts and attach
to the exposed mineralized bone surface, to form an isolated and sealed microenvironment that is rich in both HCl and lysozomal enzymes (cathepsin).


Bone Remodeling
Resorption
Resorption (Howship’s) lacunae

Mature osteoclasts move over the surface, removing mineral and organic
components of mature bone simultaneously, leaving serrated footprints, or
Howship’s lacunae, on the surface