How old is your skeleton
A bone fracture signals a systemic skeletal deterioration, resulting in an increased mortality risk. A new tool has been developed to estimate one’s skeletal age.
Fracture increases mortality risk
From the age of 50, one out of 8 women will sustain a hip fracture during their remaining lifetime. This lifetime risk is equivalent to or higher than the risk of invasive breast cancer. More importantly, those with a hip fracture have a high risk of premature mortality, with 30% of patients dying within a year of their fracture.
Several factors such as the severity of the fracture, pre-existing medical conditions, and the impact of immobilization and surgery on the patient's overall health are believed to contribute to the elevated risk of premature mortality. However, even after controlling for all these factors and assuming everything else remains constant, hip fracture patients still have an increased risk of premature death.
In addition to hip fracture, our research has revealed that the risk of premature mortality is increased in several other types of fractures, including those that occur in the vertebrae, ribs, femur, pelvis, and even the forearm. Although the extent of risk is relatively lower than that of hip fracture, this suggests that any fracture, regardless of the bone affected, signifies a reduction in the individual's life expectancy.
Individuals who do not have a fracture can still be at a higher risk of mortality if they have a low bone mineral density, a critical risk factor for fractures, or experience rapid bone loss over time. Recent studies found that those with osteoporosis, a condition characterized by low bone mass, exhibit a 20% heightened risk of mortality, irrespective of whether they have sustained a fracture or not.
These facts collectively indicate that the skeletal system of individuals who have suffered a fracture or are at an elevated risk of fracture (due to low bone mass) appears to be older than their chronological age.
What is skeletal age?
We have developed a new metric called 'Skeletal Age' to quantify the fragility of the skeleton. Conceptually, skeletal age is the age of our skeleton because of a fracture or being exposed to risk factors that elevate the risk of fracture.
The determination of skeletal age exploits a well-known but underappreciated law of mortality: from the age of 35 years, the annual mortality risk increases by an average of ~10%. The probability of mortality increases by 10% for individuals who are 36 years old compared to those who are 35 years old. Similarly, the probability of mortality is 10% higher for those who are 37 years old than for those who are 36 years old, and this pattern continues for subsequent age groups. This law is universally applicable to both men and women across populations worldwide.
In accordance with this law, if a risk factor raises the probability of mortality beyond the anticipated 10%, then the number of years lost (or gained) associated with a risk factor can be readily determined. As a result, the concept of skeletal age is operationally defined as the sum of an individual's actual age and the years of life lost associated with a fracture or exposure to risk factors that put an individual at a greater risk of fracture.
Skeletal age as a risk communication tool
Skeletal age, as defined, is a measure of both fracture vulnerability and mortality risk. Therefore, if an individual's skeletal age surpasses their chronological age, it indicates that the individual is at a greater risk of fracture and mortality when compared to other people of the same age and gender.
Currently, doctor-patient communication of fracture risk involves the use of probability. However, a major disadvantage of probability is that it can be difficult for people to understand. Moreover, people perceive the probability depending on the context in which it is presented, such as whether it is seen as likely or unlikely. For instance, patients often perceive a 5% risk of hip fracture over a 5-year period, which is a significant risk, as a 95% chance of not sustaining a hip fracture. Consequently, the use of risk probability may not be as successful in motivating patients to adopt treatment or positive lifestyle changes.
Our proposal is to inform patients of their skeletal age, rather than their absolute probability of experiencing a fracture. Instead of simply informing a 60 years old patient about her 5% probability of hip fracture, an alternative approach is to convey that her skeletal age is 65, and that by taking an effective treatment or adopting a healthy lifestyle, it is possible to reduce her skeletal age from 65 years to 61 years.
Skeletal age has an important advantage over the traditional probabilistic metric. It is intuitive and easy to understand because skeletal age uses the reference point of actual age to estimate the number of years of life lost; therefore, it can be beneficial for people who don't fully understand probabilistic metrics.
In the cardiovascular field, informing heart age to patients is an effective tool for motivating individuals to make positive lifestyle changes such as quitting smoking, improving their diet, and increasing physical activity. Similarly, it is expected that by providing patients with a concrete estimate of their skeletal age, healthcare providers can help patients understand the impact of their lifestyle choices on their bone health.
Globally, hip fracture is a significant public health issue, with an annual incidence of approx 1.6 million cases and a resulting of ~500,000 deaths. At least 30% of hip fractures and deaths can be prevented if patients take treatment and modify their lifestyle. Knowing one's skeletal age can be a motivating factor for patients to take treatment and make positive lifestyle changes to reduce their fracture risk and mortality risk.
Reference
The paper that describes the concept of Skeletal Age has just been published by eLife: Tran TS, Ho-Le TP, Bliuc D, Abrahemsen B, Hansen L, Vestergaard P, Center JR, Nguyen TV. Skeletal age for mapping the impact of fracture on mortality. eLife 16/5/2023.
Website and app
A skeletal age calculator has been developed and implemented on the website www.BONEcheck.org or BONEcheck app available in Apple Store and Google Play.