Osteoporosis
Description
- Skeletal disease of low bone mass and microarchitectural deterioration -> increased fracture risk with minimal trauma
- Silent until a fragility fracture occurs - the first presentation is often the fracture itself
Epidemiology
- ~1 in 2 women and ~1 in 3 men over 60 will have an osteoporotic fracture
- Prevalence rises steeply with age; F>M (post-menopausal oestrogen loss)
- Hip fracture incidence doubles roughly every 5-7 years after age 60
- Under-diagnosed and under-treated - <20% of fragility-fracture patients are started on treatment without a dedicated pathway
Aetiopathogenesis
Primary
- Post-menopausal (Type I) - oestrogen deficiency -> inc RANKL, dec OPG -> inc osteoclast activity -> trabecular bone loss
- Age-related (Type II) - reduced osteoblast function, dec calcium absorption, secondary hyperparathyroidism
Secondary causes - screen for these in every case
- Endocrine: hyperthyroidism, hyperparathyroidism, hypogonadism, Cushing syndrome, diabetes
- Drugs: glucocorticoids (dose- and duration-dependent, no safe threshold), aromatase inhibitors, ADT, PPIs (long-term), anticonvulsants, heparin, excess thyroxine
- GI: coeliac disease, malabsorption, bariatric surgery, IBD
- Renal: CKD-mineral bone disease
- Haematological: myeloma (always exclude with vertebral fracture or disproportionate bone pain), mastocytosis
- Lifestyle: immobility, alcohol excess, smoking, low BMI, vitamin D/calcium deficiency
Diagnosis
A. Fragility fracture (clinical diagnosis regardless of DEXA)
- Fracture from a fall from standing height or less, at a typical site (hip, vertebra, wrist, proximal humerus, pelvis)
- Diagnostic of osteoporosis on its own in a patient >50 - treat, do not wait for DEXA
B. DEXA (dual-energy X-ray absorptiometry)
- T-score <=-2.5 at hip or spine = osteoporosis; -1.0 to -2.5 = osteopenia
- Use Z-score (age-matched) in premenopausal women and men <50
C. Fracture risk tools
- FRAX (+/- femoral neck BMD) - estimates 10-year major osteoporotic and hip fracture probability; the 2024 RACGP/Healthy Bones Australia guideline anchors treatment decisions on FRAX-based risk category (low/moderate/high/very high) rather than T-score alone
- Very high risk: recent fragility fracture (especially multiple or vertebral), fracture on treatment, very low T-score, or high FRAX score with additional risk factors
D. Work-up in every new diagnosis
- Secondary cause screen: calcium, phosphate, ALP, vitamin D, TFT, UEC, LFT, PTH (if calcium abnormal), coeliac serology, testosterone (men), EPG/serum free light chains if vertebral fracture or atypical picture
- Lateral spine imaging (or VFA on DEXA) if height loss, kyphosis, or unexplained back pain - most vertebral fractures are asymptomatic and missed without imaging
Management
A. Risk stratification drives treatment (not a flat drug list)
- Very high risk (recent/multiple fragility fracture): anabolic-first strategy
- Romosozumab - sclerostin inhibitor; PBS first-line listing from November 2024 for very-high-risk treatment-naive patients; 12 months, then sequence to an antiresorptive
- Teriparatide - anabolic, up to 24 months, then sequence to antiresorptive
- Anabolic therapy builds bone; must always be followed by an antiresorptive to "lock in" the gain
- High risk: antiresorptive first-line
- Oral bisphosphonates (alendronate, risedronate) - first-line for most; weekly dosing, take fasting, remain upright 30 min
- IV zoledronic acid - annual infusion, useful where adherence/absorption is a concern
- Denosumab - 6-monthly SC injection; useful in renal impairment (bisphosphonates renally cleared)
B. Denosumab-specific rule - do not stop without a plan
- *Discontinuation or delay >4 months causes rebound bone resorption and clusters of multiple vertebral fractures*
- Must transition to a bisphosphonate (oral or IV) on ceasing denosumab - never simply stop
C. All patients
- Vitamin D and calcium correction (not high-dose calcium supplementation as monotherapy)
- Falls risk assessment, weight-bearing exercise, smoking cessation, alcohol moderation
- Treat any identified secondary cause
D. Drug holiday
- Consider after 5 years oral / 3 years IV bisphosphonate in patients now low-risk
- Not appropriate for very-high-risk patients - continue or switch to denosumab/anabolic instead
E. Monitoring
- Repeat DEXA ~2 years to assess response
- Bone turnover markers can guide bisphosphonate holidays
Associations
- Fragility fractures - hip, vertebral, wrist, proximal humerus, pelvis
- Falls and frailty
- Glucocorticoid use, aromatase inhibitor/ADT therapy
- Rheumatoid arthritis and other inflammatory disease
- Malabsorption syndromes, coeliac disease
- Hypogonadism, early menopause
Natural history & complications
- Progressive bone loss without treatment; fracture risk compounds - one fragility fracture roughly doubles risk of the next
- Hip fracture carries ~20-30% 1-year excess mortality and major loss of independence
- Vertebral fractures - kyphosis, height loss, restrictive lung impairment, chronic pain
- Secondary fracture prevention (fracture liaison services) reduces refracture and mortality - the single highest-yield systems intervention
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