Metabolic bone disease Flashcards
Bone functions
- Structure (gives the body structure and shape)
- Mechanical (sites for mechanical attachment, allowing movement)
- Protective (for soft tissues, vital organs and bone marrow)
- Metabolic ( reserve of calcium and other minerals)
Osteoclasts
Multinuclear cells that resorb/remove bone
Osteoblasts
Produce osteoid to form new bone
Osteocytes
Mechanosensory network embedded in mature bone
Bone biopsy types
- Closed ( bone core biopsy using Jamshidi needle)
- Open (surgical option used for osteosclerosis, inaccessible lesions or larger bone samples)
Osteoamalacia
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Hyperparathyroidism symptoms
Stones, bones, abdominal groans and psychic moans
- Stones= calcium oxalate renal stones
- Bones= osteitis fibrosa cystica, bone resorption)
- Abdominal groans= acute pancreatitis
- Psychic moans= psychosis and depression
Cortical (compact) bone classification
Abundant in: long bones Skeleton: 80% Calcified: 80%-90% Function: mainly structural, mechanical and protective Appendicular
Cancellous (trabecular) bone classification
Abundant in: vertebrae and pelvis Skeleton: 20% Calcified: 15%-25% Function: Mainly metabolic Axial
Bone composition
Inorganic (65%)
- Form of calcium hydroxyapatite crystals
- mineral reserve storing 99% of total body calcium (also 85% of phosphorus, 65% of sodium and magnesium and lesser amounts of other minerals)
Organic (35%)
-bone cells, extracellular matrix proteins, collagen fibres and linking proteins
Bone organisation
- articular surface at joint
- small articular surfaces known as facet joints/fovea
- Knuckle shaped articular surfaces known as condyles
- articular surface resembling/grooved like a pully known as trochlea
- end region of the bone known as the epiphysis
- end region has articular surface which moves up to subchondral bone
- epiphysis region separated from main bulk of bone by epiphyseal line
- main portion of the bone is known as the diaphysis
- diaphysis has medulla (containing bone marrow) surrounded on both sides by cortical bone in cortex with periosteum on outside
- region joining the diaphysis to the epiphysis is known as the metaphysis
- metaphysis contains growth plate during growth and contains bulk of trabecular bone in long bones
Bone on an X-ray
Has to be 50% mineralised
Different bone types
- Anatomical bones
- Macroscopic structures (found in anatomical bone)
- Microscopic structure (found in macroscopic structures)
Macroscopic structures
- trabecular/cancellous
- cortical/compact
Microscopic structures
- woven bone
- lamellar bone
Anatomical bones
- Flat bones (eg: cranial bones, ribs etc=protect internal organs)
- Long bones (eg: femur, tibia etc=support weight and facilitate movement)
- Short/cuboid bones (eg: carpals, tarsals etc=stabilise and facilitate movement)
- Irregular bones (eg: vertebrae, pelvis etc=complex shape to protect organ/organs)
- Sesamoid bones (eg: patella=embedded in tendons with protective function )
Metabolic Bone Disease
A group of diseases that cause reduced bone mass and reduced bone strength
- due to chemical imbalance
- causes altered bone cell activity, mineralisation rate or changes in bone structure
Common metabolic bone diseases
- Osteoporosis
- Osteomalacia/Rickets
- Primary hyperparathyroidism
- Renal osteodystrophy=secondary hyperparathyroidism
- Paget’s disease
Osteomalacia types
- Vit D deficiency (causing hypocalcaemia)
- Phosphate deficiency (phosphate wasting syndromes)
Osteomalacia
Defective mineralisation of normally synthesised bone matrix leading to bone softening
Osteomalacia sequelae
- bone pain/tenderness
- fracture
- proximal weakness
- bone deformity
Hyperparathyroidism causes
Primary
- parathyroid adenoma (most common=85%-90%)
- chief cell hyperplasia
Secondary
- chronic renal deficiency
- vit D deficiency
Renal oesteodystrophy
Comprises all the skeletal changes resulting from chronic kidney disease
Paget’s disease
Disorder of bone turnover
- Divided into 3 stages (osteolytic, osteolytic-osteosclerotic and quiescent osteosclerotic)
- Onset >40 years old
- Males > females
- Rare in Asians and Africans
Clinical features of Paget’s disease
- pain
- microfractures
- nerve compression
- skull changes (risk to medulla?)
- deafness
- +/- haemodynamic changes
- cardiac failure
- hypercalcaemia
- sarcoma development in area involved
Commonly affected sites of Paget’s disease
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Paget’s disease causes
- unknown aetiology
- genetic aspect with autosomal pattern of inheritance with incomplete penetrance (mutations in SQSTM1 or RANK)
- theory of parvomyxovirus type particles seen on EM in Pagetic bone could be responsible (doubt as to whether contamination or mis-identification)
- possible theory of disease resulting from overuse or previous bone injury
What makes bones strong?
4 M’s
- Mass
- Material properties
- Micro-architecture
- Macro-architecture
Pathology
A disease process that gives rise to symptoms, signs, biochemical disturbances and changes in imaging appearance
Radiological sign
A change in imaging appearance, whether structural or functional, that may point towards a pathology
Imaging for density
X-rays
CT
Bone densitometry
MRI
For biochemical composition
Radionuclide bone scans
For bone turnover
Looser’s zones
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Codfish vertebrae
Biconcave deformity of vertebrae
-Seen in osteoporosis and osteomalacia
Rickets
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Primary hyperparathyroidism
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Secondary hyperparathyroidism
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Tertiary hyperparathyroidism
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Brown tumour
-bone lesion arising with excess osteoclast activity
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Osteoporosis radiology
- Loss of cortical bone (thinning of cortex)
- Loss of trabeculae
- Insufficiency fractures
T score -1.5 to -2.5
Osteopenia
T score less than -2.5
Osteoporosis
Osteoporosis diagnosis
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