Osteoporosis
· age-related bone disorder characterised by
· reduced bone mass
· microarchitectural deterioration of bone
· increased risk of fracture
· osteoporotic bone has
· normal ratio of mineral to organic bone mass
· reduction in trabecular bone mass in relation to total area of section
· increased porosity of trabeculae with subsequent weakness and propensity to fracture
Osteopaenia
· osteopaenia is increased radiolucency of bone seen on radiographs
· may be due to osteoporosis or osteomalacia
· osteomalacia is decreased mineralisation of bone
Type I
· post-menopausal women
· 15-20 years after menopause (50-75)
· depletion of trabecular bone
· fractures more common in
· vertebrae (crush)
· distal radius
· intertrochanteric femur
Type II
· age-related
· after age 70
· both sexes
· equal depletion of cortex and medulla
· fractures more common in
· femoral neck
· pelvis
· vertebrae (multiple wedge)
Nutritional
· malabsorption
· malnutrition
Endocrine
· thyrotoxicosis
· Cushing’s disease
· hypogonadism
Malignancy
· myeloma
· lymphoma
Connective tissue
· osteogenesis imperfecta
· Ehlers-Danlos syndrome
Inflammatory
· rheumatoid arthritis
Drugs
· corticosteroids
· alcohol
· heparin
Mechanical
· immobilisation
· weightlessness
· bone loss is age-related
· it becomes pathological when it is exaggerated and is associated with skeletal failure
· osteoporosis results from imbalance between
· bone formation
· bone resorption
· skeleton continues to accrete bone until 10 yrs after skeletal maturity
· peak bone density reached by age 30
· after this, men and women lose bone at rate of 0.3% per year
Men
· steady state of 0.3% per year maintained
Women
· rate of 0.3% per year maintained until menopause
· then rate increases 10-fold to 3% per year
· at 6-10 years after menopause, rate reverts to 0.3% per year
Causes
Oestrogen
· accelerated loss in postmenopausal women related to oestrogen concentrations
Vitamin D
· slow loss in men and women may be due to impaired vitamin D metabolism
· impaired ability of kidney to synthesise 1,25-D may lead to decreased intestinal absorption of calcium
· may lead to elevated PTH levels
Race
· increased in white women of English or northern European origin
· less common in blacks, Hispanics and Orientals
Heredity
· positive family history
Body habitus
· thin or petite
· body fat is a source of oestradiol
Menopause
· either premature or surgically induced
Smoking
· causes increased degradation of oestrogen
Alcohol
· enhances risk of osteoporosis by
· directly inhibiting osteoblast function
· affecting oestrogen metabolism
· causing calcium diuresis
Exercise
· exercise protective against bone loss
· structural integrity of bone influenced by external forces
· bone mass related to muscle mass
Diet
· chronic dietary calcium deficit
· thinning of trabeculae
· decrease in size of osteons
· enlargement of haversian and marrow spaces
· usually related to vertebral compression fractures
· localised back pain
· loss of height
· increased roundedness (dowager’s hump)
· localised vertebral tenderness
· loss of truncal height
· thoracic kyphosis
· loss of lumbar lordosis
· decreased rib cage-iliac crest distance with
· abdominal prominence
· transverse abdominal skin creases
· all investigations normal
· serum Ca++, PO4-, ALP
· urine hydroxyproline
· other tests performed to rule out secondary causes
Routine screen
· FBC (haematological disorders)
· U&Es (electrolyte imbalances and renal function)
· LFTs (hepatic function, ALP)
· 24 hr urine (calcium and phosphorus excretion, hydroxyproline)
· serum EPP (myeloma)
· TFTs (thyrotoxicosis)
Special tests
· 25-hydroxyvitamin D (osteomalacia)
· serum carotene (malabsorption)
· plasma cortisol and dexamethasone suppression test (Cushing’s)
Plain x-ray
· changes not able to be seen until >30% of trabecular bone lost
Vertebral bodies
· accentuation of end-plate shadows
· biconcave compression of one or more vertebral bodies
· expansion of intervertebral disc
· may progress to anterior wedging of vertebral body
Long bones
· thinning but relative accentuation of cortex
· accentuation of trabecular stress lines
· loss of secondary trabeculae
· increased risk of fracture of proximal femur and distal radius
· measure of bone density
· useful for
· prediction of fracture risk
· monitoring effects of treatment
· indications
· oestrogen-deficient women before starting HRT
· patients with osteopaenia before further evaluation
· limitations
· poor correlation between bone density and fracture rate in proximal femur
· bone may be of normal density but abnormal composition (eg. with fluoride treatment)
Radiogrammetry
· measures thickness of cortex of tubular bone on standard hand x-ray
· does not quantify bone mineral content
Photon absorptiometry
· uses one or two gamma ray sources, detector and electronics to measure beam attenuation through bone
· makes use of difference in photon absorption between bone and soft tissue
Single energy photon absorptiometry (SPA)
· uses single gamma ray source
· requires constant soft tissue density
· performed on distal radius or calcaneus
· small radiation dose
· good precision and accuracy
· does not measure trabecular bone
· does not assess spine or proximal femur
Dual photon absorptiometry (DPA)
· uses radioisotope that emits photons at two energy levels
· eliminates need for constant soft tissue density
· allows use of spine and proximal femur
· measures both cortical and trabecular bone
Dual x-ray energy absorptiometry (DEXA)
· x-ray beam rather than photon source used
· uses lateral beam
· eliminates
· artifact of calcified great vessels
· effect of posterior elements
· less radiation (5% of CXR)
· more rapid (5 min)
· more precision and accuracy
Quantitative CT scan
· of vertebral body or proximal femur
· allows measurement of isolated trabecular bone
· more expensive
· higher radiation dose
· less precise and accurate
· indications
· confirm osteomalacia or hyperparathyroidism
· elucidate cause of osteopaenia with inconclusive biochemistry
· transiliac biopsy
· preprocedure administration of tetracycline label
· 3 cm posterior and inferior to ASIS
· cylindrical specimen 6 mm dia
· both cortices and intervening cancellous bone
· role of orthopaedic surgeon is
· encouraging preventative measures
· establishing diagnosis and referral to endocrinologist
· maximisation of peak bone mass
· prevention of loss of peak bone mass
· promotion of bone formation in established osteoporosis
· treatment of fractures
Adequate dietary calcium intake
· main role of calcium is in childhood and adolescence
· maintain minimum daily requirement
Adequate exercise
· toning rather than specific
· weight-bearing (walking) rather than weightless (swimming)
· may also decrease incidence of falls
Risk avoidance
· avoidance of
· smoking
· excessive alcohol
Efficacy
· prevents postmenopausal loss of bone mass
· decreases hip and vertebral fractures by 50%
Mechanism of action
· oestrogen receptor identified on osteoblasts
· may be effects on PTH and calcitonin
Indications
· premature menopause
· overt osteoporosis with fractures
Commencement
· within 6 years of menopause
Form
· oestrogen for days 1-25 of month with
· progestagen for days 16-25 of month
· continued for at least 5 years
Disadvantages
· causes recurrence of monthly bleeding
· increases risk of endometrial carcinoma
· eliminated with addition of progestagen
· unclear effect on risk of breast carcinoma
· increases risk of venous thromboembolism
· causes sodium retention
Contraindications
· breast carcinoma
· history of pulmonary embolism
· history of hypertension or congestive heart failure
Precautions
· annual mammogram
· investigation of any abnormal vaginal bleeding
Mechanism of action
· inhibits osteoclast function and decreases bone resorption
Efficacy
· prevents post-menopausal bone loss when there is high bone turnover
· no better than oestrogen and no additive effect
· no data on effect on fracture rate
Disadvantages
· expensive
· side-effects of nausea and flushing
· only available as injectable form
Indications
· as alternative to oestrogen
· ie. where oestrogen indicated but contraindications exist
· supplementation controversial
· does not protect against osteoporosis in premenopausal women
· conflicting evidence regarding protection against bone loss with post-menopausal supplementation
· current recommendation is use of physiological doses
· 1500 mg calcium/day
· 800 mg vitamin D/day
Mechanism of action
· promotes hydroxyapatite crystal growth and stability
Effect
· increases bone mass rather than just preventing loss
· produces abnormal bone
· increases mineralisation of trabecular bone at expense of cortical bone
· bone more brittle (weaker per unit mass)
Efficacy
· conflicting evidence regarding risk of fractures
Disadvantages
· side-effects of nausea and lower limb arthralgias
Indications
· routine use not justified
· alter physicochemical properties of bone like fluoride
· etidronate not effective
· newer drugs may be more useful
· exclude secondary causes
· physiological doses of calcium and vitamin D
· encourage lifestyle modification (exercise, smoking, alcohol)
· oestrogen for women with
· early menopause
· documented osteoporosis with fractures
· no contraindications
· calcitonin for women with
· above indications but contraindication to oestrogen
Principles
· fracture healing not impaired
· prolonged immobilisation should be avoided
Spine
· vast majority stable
· treat with
· analgesia
· physiotherapy
· temporary corset or brace may help
Long bones
· skeleton has difficulty holding plates and screws
· use load-sharing devices
· intramedullary nail
· tension band wire
· sliding nail-plate
· can use PMMA to enhance fixation