What is skeletal age?
Skeletal age is a new concept that provides a more tangible and understandable measure of the impact of fractures, particularly fragility fractures, on an individual's life expectancy. It combines a person's chronological age with the estimated reduction in lifespan associated with a fracture. For example, a 60-year-old man with a hip fracture might have a skeletal age of 66, representing an estimated 6-year reduction in life expectancy. This metric was developed to improve communication about osteoporosis risks, making the consequences of fractures more concrete.
How is skeletal age determined?
Skeletal age is calculated by analyzing large population databases to determine mortality risk for different fracture types, ages, and genders. This process involves statistically estimating the increased risk of death associated with a fracture and converting this into years of life lost (YLL). The YLL is then added to the chronological age to get the skeletal age. Researchers use statistical methods like Cox's proportional hazards model and laws of mortality such as the Gompertz law. An online tool, BONEcheck.org, is in development to facilitate these calculations.
Skeletal age vs. bone mineral density (BMD)
While both skeletal age and bone mineral density (BMD) relate to bone health, they serve different purposes.
| Feature | Skeletal Age | Bone Mineral Density (BMD) |
|---|---|---|
| Measurement | A conceptual metric; reflects the age of the skeleton based on fracture risk. | A quantitative measure of the amount of bone mineral per unit area or volume. |
| How it's calculated | Combines chronological age with estimated years of life lost following a fracture. | Typically measured via a dual-energy X-ray absorptiometry (DXA) scan. |
| Key focus | Overall mortality risk following a fracture, communicating the severity of the event. | Fracture risk based on bone mass. Low BMD is a major risk factor for fragility fractures. |
| Application | Risk communication for patients who have already experienced a fracture. | Screening for osteoporosis and predicting future fracture risk. |
| What it includes | Indirectly accounts for various factors affecting mortality, including comorbidities. | Does not directly include mortality data or account for comorbidities. |
The impact of fracture type on mortality
The location and severity of a fracture significantly influence the number of years of life lost.
- Hip fractures have the strongest association with increased mortality risk and can lead to a loss of 5 to 10 years or more, particularly in men.
- Vertebral (spine) fractures also increase mortality risk more than minor fractures.
- Major fractures at sites like the pelvis, proximal tibia, and proximal humerus also increase mortality risk, though generally less than hip and vertebral fractures.
- Minor fractures, such as those in the wrist, have a smaller impact on mortality, especially in younger individuals.
Implications of skeletal age for patient care
Skeletal age has several potential benefits for patient care and osteoporosis management. It can improve risk communication by presenting mortality risk as an intuitive age-based number, potentially enhancing patient adherence to treatments. By highlighting the increased mortality risk from specific fractures, physicians can develop more personalized treatment plans that go beyond just preventing fractures to address overall post-fracture care.
Conclusion
Skeletal age is a valuable new metric for mapping the impact of fracture on mortality, particularly for fragility fractures. By quantifying the years of life lost due to a fracture, it offers a powerful communication tool for patients and clinicians dealing with osteoporosis. This approach emphasizes that fractures have serious, long-term consequences impacting overall life expectancy. While BMD remains crucial for diagnosis, skeletal age helps prioritize care and motivate treatment by directly addressing the risk of premature death. Further research and adoption of this metric can improve geriatric and orthopedic care.
