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 • • • • • • • • • Julie Burgess Glenda Evans Dr Lorraine Fitzpatrick Dr Hunter Heath Dr Dan Hurley Donna Jewison Dr Ann Kearns Dr Kurt Kennel Dr Sundeep Khosla • • • • • 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 Bone Histomorphometry Mineral Apposition Rate (MAR) MAR MAR = Interlabel distance Label Label interval interval The average distance between visible labels, divided by the labeling interval, is the mineral apposition rate (MAR) MAR in µm/day, the avarage rate at which new bone mineral is being added on any actively forming surface MAR is the basic measurement and calculation on which all dynamic estimates of bone formation are based It is usually expressed as the adjusted appositional rate ((Aj.Ar) or MAR (MS/BS ) – see next slide Bone Histomorphometry Mineralizing Surfaces (MS) Total mineralizing surfaces (MS) include all double and ½ of single-labeled surfaces MS is expressed relative to total bone surface or, MS = total labeled surface / BS Bone Histomorphometry Mineralizing Surface (MS) MS is used in the calculations for bone formation rates, ( BFR), BFR activation frequency (Ac.F), Ac.F and mineralization lag time (MLT) MLT Bone Histomorphometry Osteoid Thickness (O.Th) Osteoid thickness (O.Th) O.Th is the mean thickness, in µm, of osteoid seams on cancellous surfaces Bone Histomorphometry Osteoid Thickness (O.Th) O.Th is normally [...]... 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... 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. .. 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. .. 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... 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... 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... 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... Osteoid forms the organic matrix of bone Bone Formation Osteoblasts – Effects of Cell Age …but flatten as they complete bone formation to eventually become lining cells Young osteoblasts appear cuboidal and robust… Type I Collagen Type I collagen is a triple helical structure composed of two α1 chains and one α2 chain Collagen α chains are characterized by Gly-X-Y repeating triplets where X and Y are... are considered to be “markers” of bone resorption Bone Remodeling Reversal Preosteoblasts As the resorptive phase wanes and is replaced by the reversal phase, resorption lacunae become populated by mononuclear pre-osteoblasts (cells that may be derived from recruited monocytes and circulating bone- forming cell precursors) Preosteoblasts are destined to become bone- forming osteoblasts Osteoclasts ultimately... to the resorption surface, clear cytoplasm, single nuclei, and (+)stain for alkaline phosphatase They mature into osteoblasts (right), which appear as mononuclear cells with prominent nucleoli and deeply stained cytoplasm Osteoblasts form a cellular monolayer on the resorption surface previously abandoned by osteoclasts Bone Remodeling Bone Formation Unmineralized Unmineralized osteoid osteoid Osteoblasts