29th April 2024

Osteoporosis

Background

Osteoporosis implies low bone mass leading to skeletal fragility, resulting in decreased bone strength and an increased risk of fracture. If the trabecular bone is affected, vertebral crush fractures are common; if the cortical bone is affected, long bone fractures are more likely, for instance, neck or femur fractures.  Around the world, one in three women and one in five men over the age of 50 will suffer a fracture due to osteoporosis according to the International Osteoporosis Foundation.

Risk factors

• Early menopause
• Low testosterone in men (i.e. hypogonadism or anti-androgen treatment for prostate cancer)
• Prolonged steroid use (i.e. >5mg/day of prednisolone)
• Alcohol or tobacco use
• Endocrine diseases (i.e. hyperthyroidism, hyperparathyroidism, hypercalciuria & type 1 diabetes)
• Erosive/ inflammatory bone disease (i.e. multiple myeloma or rheumatoid arthritis)
• Dietary (i.e. reduced calcium intake or malabsorptive conditions
• Sedentary lifestyle
• Low BMI (< 18.5)
• Renal or liver failure

Clinical manifestation

There are no specific clinical manifestations of osteoporosis until a fracture occurs. Vertebral fractures are the most common clinical manifestation of osteoporosis. However, most of these fractures are asymptomatic and diagnosed as an incidental finding on chest or abdominal X rays. Colles’ fractures are more common in women shortly after menopause, and the risk of hip fracture increases with age.

Diagnosis

The World Health Organization (WHO) has defined diagnostic thresholds for low bone mass and osteoporosis based upon Bone mineral density (BMD) measurements. A patient’s BMD is compared with a young-adult reference population. Values are quantified using a T-score.

Clinical diagnosis of osteoporosis can be made based on the presence of:

• Fragility fracture, particularly at the spine, hip, wrist, humerus, rib or pelvis OR
• T-score ≤ -2.5 standard deviations (SDs) at any site based upon BMD measurement by dual-energy X-ray absorptiometry (DXA)

Alternatively, fracture risk can be assessed using the FRAX (Fracture Risk Assessment Tool), which is a computer-based calculator that estimates the 10-year probability of major osteoporotic fracture or hip fracture. A diagnosis of osteoporosis may be made if the 10-year probability of major osteoporotic fracture is ≥20% or the 10-year probability of hip fracture is ≥3%.

Measurements taken of the spine or hip are recommended as fractures are more likely at these sites. Spine BMD can be more useful if pharmacological therapy is planned as it shows less variability than other sites, and response to therapy can be detected earlier in the spine.

A T-score that is 1 to 2.5 SD below the young adult mean is termed low bone mass (osteopenia). Normal bone density is defined as a value within 1 SD of the mean value in the young adult reference population

Treatment

Non-pharmacological measures

• Adequate calcium and vitamin D intake
• Weight bearing exercises to increase bone mineral density
• Balance exercises to reduce falls risk
• Smoking cessation
• Reduction of alcohol consumption
• Home based fall prevention programmes

Pharmacological therapy

Who to treat:

• Patients with a history of fragility fracture or osteoporosis (BMD T score ≤-2.5)
• Patients with a T score between -1.0 and -2.5 with high risk on FRAX, i.e. a 10-year probability of hip fracture or combined major osteoporotic fracture of ≥3.0 or ≥20 percent, respectively.

Types of pharmacological therapy

• Bisphosphonates: Alendronate, Risedronate, Zoledronate, Ibrandonate
• Targeted monoclonal antibodies: Denosumab
• Selective oestrogen receptor modulators – Raloxifene, Tamoxifen
• Anabolic agents – Teriparatide, Abaloparatide, Romosozumab
• Others – Calcitonin, Strontium ranelate, Androgens

References

• Rosen HN, Drezner MK. Clinical manifestations, diagnosis, and evaluation of osteoporosis in postmenopausal women. In: UpToDate, Post TW (Ed), UpToDate, Waltham, MA.
• Wilkinson IE, Raine T, Wiles K, Goodhart A, Hall C, O’Neill H. Oxford Handbook of Clinical Medicine (10ᵗʰ ed.). Oxford (UK): Oxford University Press; 2017