Osteoporosis-related fracture risk refers to the increased probability that a person with osteoporosis will sustain a fracture from relatively low-energy trauma or sometimes from ordinary activities that would not normally fracture healthy bone. Osteoporosis is a skeletal disorder characterised by reduced bone strength, resulting from decreased bone mass, deterioration of bone microarchitecture and changes in the quality and organisation of bone tissue. Bone strength therefore falls even though the external appearance of the skeleton may remain normal.
The most clinically important consequence is fragility fracture, particularly involving the hip, vertebrae and distal forearm, although other bones can also be affected. Fracture risk is not determined by bone mineral density alone; age, previous fractures, falls, medications, skeletal geometry, bone quality and other clinical factors contribute.
Bone mineral density, usually measured by dual-energy X-ray absorptiometry, is an important tool for assessing osteoporosis. The measurement is commonly expressed as a T-score in postmenopausal women and men aged 50 years or older, comparing the person's bone mineral density with that of a healthy young adult reference population. A T-score at or below −2.5 at relevant measurement sites is one diagnostic criterion for osteoporosis in appropriate populations, although clinical diagnosis and treatment decisions incorporate additional information.
Bone density is generally reported at sites such as the femoral neck, total hip and lumbar spine. The measurement estimates mineral content per unit area rather than directly measuring the complete three-dimensional mechanical strength of bone. Consequently, two people with similar bone mineral density can have different fracture risks.
Osteoporosis alters both cortical and trabecular bone. Trabecular bone consists of a three-dimensional lattice of thin bony structures that contributes substantially to vertebral and other skeletal strength. With osteoporosis, trabeculae can become thinner, perforated or disconnected, reducing the efficiency of the internal load-bearing network. Cortical bone, which forms the dense outer shell of many bones, can become thinner and more porous. These changes reduce structural resistance to bending and compression.
The quality of collagen and mineralised matrix and the accumulation of microscopic damage can also influence bone strength. Bone density therefore captures only one component of skeletal integrity. Modern understanding of osteoporosis emphasises deterioration of the whole bone's structure and material properties rather than treating the skeleton simply as a store of calcium.
Vertebral fractures can occur when weakened vertebral bodies collapse under normal or relatively low forces. They may cause acute back pain, height loss or changes in spinal posture, but many vertebral fractures are clinically silent and are discovered incidentally or through imaging. Hip fractures are particularly consequential because they can lead to prolonged immobility, loss of independence and complications associated with hospitalisation and reduced physical activity. Wrist and other fractures may be the first clinical indication of skeletal fragility. A previous fragility fracture is itself an important indicator of future fracture risk because it suggests that the person's bone strength has already been insufficient to withstand relatively modest mechanical stress.
Age is a major determinant of fracture risk because bone remodelling changes over the lifespan and falls become more common with advancing age. The decline in oestrogen after menopause can accelerate bone resorption, making postmenopausal women particularly susceptible to bone loss, although osteoporosis also affects men. Low body weight, family history of hip fracture, smoking, high alcohol consumption, prolonged immobility and certain diseases can increase risk.
Long-term systemic glucocorticoid therapy is a particularly important secondary cause because it can reduce bone formation and alter calcium metabolism and bone resorption. Other endocrine, gastrointestinal, renal and haematological conditions can also contribute. Fracture-risk assessment therefore requires consideration of the underlying clinical context rather than relying on one numerical measurement.
Falls interact with bone fragility to determine whether a person actually sustains a fracture. A person may have low bone density but never experience a substantial fall, while another person with moderate skeletal fragility may fracture after repeated falls. Factors that increase fall probability include impaired balance, muscle weakness, visual impairment, certain neurological disorders, medications that cause dizziness or sedation and environmental hazards.
Muscle-strengthening and balance training can therefore reduce fracture risk through pathways that are partly independent of bone mineral density. Hip protectors, home safety modifications and appropriate management of visual and mobility problems may also be considered for selected people. Fracture prevention consequently requires both skeletal and fall-risk strategies.
Osteoporosis-related fracture risk can be estimated using clinical information and, where appropriate, validated fracture-risk tools such as FRAX. Such tools combine variables including age, sex, body measurements, previous fracture, parental hip fracture, smoking, glucocorticoid exposure, rheumatoid arthritis, secondary osteoporosis and alcohol use, with or without bone mineral density depending on the application. They provide an estimate of fracture probability over a defined period rather than predicting with certainty whether an individual will fracture. Treatment decisions may also incorporate national clinical guidelines, absolute fracture probability, previous fractures and other circumstances. A low-density result is therefore not equivalent to a guaranteed fracture, and a person without a T-score in the osteoporosis range can still have clinically important fracture risk.
Reducing osteoporosis-related fracture risk can involve exercise, adequate nutrition, fall prevention, treatment of underlying conditions and, when indicated, medicines that reduce bone loss or increase bone formation. Antiresorptive medicines such as bisphosphonates and denosumab reduce bone resorption through different mechanisms, while anabolic or bone-forming treatments can stimulate bone formation in selected high-risk patients. Treatment selection depends on fracture risk, medical history, kidney function, other medicines, previous treatments and guideline recommendations.
Calcium and vitamin D are important when intake or status is inadequate but are not substitutes for appropriate osteoporosis treatment in people at sufficiently high fracture risk. The overall objective is to reduce clinically significant fractures while maintaining a favourable balance between treatment benefits, risks and long-term skeletal health.
