Bone Disease - Histopathology Flashcards
What are the main functions of bones?
Mechanical – support and shape body
Site for muscle attachment
Protective
Metabolic – reserve of calcium
What are the two main components of bone and what are their relative proportions?
Inorganic (65%) – calcium hydroxyapatite stores 99% of body’s Ca, 85% of the P and 65% of Na and Mg
Organic (35%) – bone cells and protein matrix
Describe the classification of bone as cortical and cancellous.
Cortical - Long bones 80% of skeleton Appendicular skeleton 80-90% calcified Mainly mechanical and protective role
Cancellous - Vertebrae and pelvis 20% of skeleton Axial 15-25% calcified Mainly metabolic Large surface
What are the indications for bone biopsy?
Evaluate bone pain or tenderness Investigate abnormality seen on X-ray Bone tumour diagnosis Determine cause of unexplained infection Evaluate therapy
What are the two types of bone biopsy?
Closed – core biopsy with Jamshidi needle
Open – surgical removal under general anaesthetic (for sclerotic or inaccessible lesions)
What are the three types of bone cell?
Osteoblast – build bone by laying down osteoid Osteoclast – multinucleate cells of the macrophage family that resorb bone
Osteocyte – osteoblast like cells, form network for signalling in bone (for repair etc.)
Where are osteocytes found?
Lacunae
What cytokine is important for stimulating the differentiation of osteoclast precursors into pre-osteoclasts?
M-CSF (produced by osteoblasts)
Which cells produce RANKL and what is its effect?
Pre-osteoblasts
It stimulates the maturation of osteoclasts
What do mature osteoblasts produce that blocks the RANK/RANKL binding?
Osteoprotegerin
How are bones classified anatomically?
Flat - E.g Ribs Long - E.g Femur Cuboid - Carpals, Tarsals Irregular bones - Very specifically shaped, e.g Pelvis Sesamoid - Inserted within a tendon
What type of ossification leads to the formation of long and flat Bones.
Long bones = Endochondral ossification
Flat bones = Intramembranous ossification
How else can bone be classified?
Trabecular (cancellous) or compact (cortical)
Woven (immature) or lamellar (mature)
What is metabolic bone disease?
Disordered bone turnover due to imbalance of various chemicals in the body (vitamins, hormones, minerals etc.)
Overall effect is usually reduced bone mass (osteopaenia) often resulting in fractures from little or no trauma
What are the three main categories of metabolic bone disease?
Related to endocrine abnormality (e.g. Vit D and PTH)
Non-endocrine (e.g. age-related osteoporosis)
Disuse osteopaenia
Describe the staining of calcified and uncalcified bone.
Calcified – green
Uncalcified – orange
What are the primary and secondary causes of osteoporosis?
Primary
Age
Post-menopause
Secondary
Drugs
Systemic disease
Describe the histology of osteoporotic bone.
Weak trabecular bridging
Holes and cysts
What is osteomalacia and what can it be caused by?
Condition of defective bone mineralisation that can be caused by Vitamin D deficiency or Phosphate deficiency (usually related to chronic renal disease)
What are the metabolic and endocrine consequences of vitamin D deficiency?
Secondary hyperparathyroidism –> increased bone resorption
Hypocalcaemia – neuronal excitability causing muscle twitching, spasms, tingling and numbness
Describe the histology of osteomalacia.
No calcification of bone
More uncalcified osteoid
Bones are very bendy and cannot carry musculature very easily
What are the clinical consequences of osteomalacia?
Bone pain/tenderness
Fracture (horizontal fractures at Looser’s zone at the neck of the femur are commonly seen)
Proximal weakness
Bone deformity
What is used to investigate mineralisation?
Fluorescent tetracycline labelling
What are the consequences of hyperparathyroidism?
Hypercalcaemia (increased Ca2+ reabsorption)
Hypophosphataemia (increased phosphate excretion in the urine)
Osteitis fibrosa cystica (due to increased osteoclast activity)
