Osteoporosis

Abstract

Bone is a dynamic tissue that is remodelled constantly throughout life. The arrangement of compact and cancellous bone provides strength and density suitable for both mobility and protection. Osteoporosis is defined as a reduction in the strength of bone that leads to an increased risk of fractures. The World Health Organisation operationally defined osteoporosis as a bone density also referred to as a T-score of <–2.5 and is associated with increased risk of fractures. Bone remodelling is regulated by multiple hormones, including oestrogens (in both genders), androgens, Vitamin D and parathyroid hormone (PTH), as well as locally produced growth factors, such as IGF-I, transforming growth factor β, PTH-related peptide (PTHrP), interleukins, prostaglandins and members of the tumour necrosis factor superfamily. The risk of fracture can be predicted by the Fracture Risk Assessment score. Several non-invasive techniques are available for estimating skeletal mass or bone mineral density including single energy X-ray absorptiometry, dual-energy X-ray absorptiometry, quantitative computed tomography and ultra-sound. Total daily calcium intakes <400 mg are detrimental to the skeleton. The recommended daily required intake of 1000–1200 mg for adults accommodates population heterogeneity in controlling calcium balance. For optimal skeletal health, serum 25(OH)D should be >75 nmol/L (30 ng/mL). Bisphosphonates have become the mainstay of osteoporosis treatment. Calcitonin preparations are approved by the FDA for osteoporosis in women >5 years past menopause. Denosumab was approved by the FDA in 2010. Parathormone analogues augment trabecular bone mineral density and reduce fracture occurrence. PTH (1–34) (teriparatide) produced substantial increments in bone mass. Abaloparatide is a synthetic analogue of human PTHrP, which has significant homology to PTH and also binds the PTH Type 1 receptor increasing the bone mass. Ageing is associated with progressive decline in overall muscle strength and bone loss. Resistance training increases bone strength and density, reducing the risk of fracture during a fall. Increased levels of endurance, strength and balance with exercises increase the threshold for disability and dependence as we age. Inactive and sedentary lifestyle should be discouraged. Treatment accessibility could be improved and treatment adherence should be encouraged.