Thach Tran, MD, and colleagues introduced the concept of “skeletal age” in a recently published paper that aims to incorporate the impact of fragility, or low trauma, fractures – which can occur in patients with osteoporosis – on mortality risk.
They defined “skeletal age” as the age of the skeleton following a fragility fracture. This is calculated as the chronological age of the individual plus the number of years of “life lost” as a consequence of the specific fracture.
The risk for premature death following fragility fractures is concerning, with 22%-58% of patients with hip fracture dying within a year (Brauer et al.; Rapp et al.). Thus, it’s important to treat osteoporosis in a timely fashion to reduce the risk for such fractures and the excess mortality risk associated with them.
Implementation and uptake of such treatment, however, either before or after a fragility fracture, is far from optimal (Solomon et al). This may be because patients don’t fully understand the consequence of such a fracture, and outcomes measures currently in use (such as relative risk or hazard of mortality) are difficult to communicate to patients.
In the recent paper by Dr. Tran and colleagues, the authors examined the association between fractures and mortality based on sex, age, associated comorbidities, and fracture site. They pooled this information to create a “skeletal age” for each fracture site, using data from the Danish National Hospital Discharge Registry, which documents fractures and related mortality for all Danish people.
They examined mortality over a period of at least 2 years following a fragility fracture in individuals aged 50 or older, and reported that occurrence of any fragility fracture is associated with a 30%-45% increased risk for death, with the highest risk noted for hip and femur fractures (twofold increase). Fractures of the pelvis, vertebrae, humerus, ribs, clavicle, and lower leg were also associated with increased mortality risk, but no increase was seen with fractures of the forearm, knee, ankle, hand, or foot.
The number of years of life lost at any age depending on the fracture site is represented as a linear graph of skeletal age for any chronological age, for specific fracture sites, separated by sex.
For example, the skeletal age of a 50-year-old man who has a hip fracture is 57 years (7 years of life lost as a consequence of the fracture), while that for a 70-year-old man with the same fracture is 75 years (5 years of life lost because of the fracture). Similarly, the skeletal age of a 50-year-old man with a fracture of the pelvis, femur, vertebrae, and humerus is 55 years (5 years of life lost). Fractures of the lower leg, humerus, and clavicle lead to fewer lost years of life.
The authors are to be commended for creating a simple strategy to quantify mortality risk following low-impact or fragility fractures in older individuals; this could enable providers to communicate the importance of osteoporosis treatment more effectively to patients on the basis of their skeletal age, and for patients to better understand this information.
The study design appears reasonably robust as the authors considered many factors that might affect mortality risk, such as sex, age, and comorbidities, and the results are based on information from a very large number of people – 1.6 million.
However, there’s a major issue with the concept of “skeletal age” as proposed by Dr. Tran and colleagues. The term is already in use and defines the maturity of bones in children and adolescents, also called “bone age” (Greulich and Pyle 1959; Skeletal Age, Radiology Key). This is a real oversight and could cause confusion in interpreting “skeletal age.”
Skeletal age as currently defined in children and adolescents is influenced by chronological age, exposure to certain hormones, nutritional deficiencies, and systemic diseases, and is a predictor of adult height based on the skeletal age and current height. This concept is completely different from that being proposed by the authors in this paper. Dr. Tran and colleagues (and the reviewers of this paper) are probably not familiar with the use of the terminology in youth, which is a major oversight; they should consider changing the terminology given this overlap.
Further, fragility fractures can occur from osteoporosis at any age, and this study doesn’t provide information regarding years of life lost from occurrence of fragility fractures at younger ages, or the age at which mortality risk starts to increase (as the study was performed only in those aged 50 or older).
While the study takes into account general comorbidities in developing the model to define years of life lost, it doesn’t account for other factors that can influence fracture risk, such as lifestyle factors, activity level, and genetic risk (family history of osteoporosis, for example). Of note, the impact of additional fractures isn’t considered either and should be factored into future investigations.
Overall, the study is robust and important and provides valuable information regarding mortality risk from a fragility fracture in older people. However, there are some flaws that need to be considered and addressed, the most serious of which is that the term “skeletal age” has been in existence for decades, applied to a much younger age group, and its implications are completely different from those being proposed by the authors here.
A version of this article first appeared on Medscape.com.