Skeletal Age for mapping the impact of fracture on mortality
Authors: Tran Thach , Ho-Le Thao , Bliuc Dana , Abrahamsen Bo , Hansen Louise , Vestergaard Peter , Center Jacqueline R. , Nguyen Tuan V. 
Published: September 2022

Objectives

to propose a novel “Skeletal Age” metric as the age of an individual’s skeleton resulting from a fragility fracture to convey the combined risk of fracture and fracture-associated mortality for an individual with specific risk profile.

Design

a retrospective population-based cohort study.

Setting

hospital records from the Danish National Hospital Discharge Register that includes the whole-country data of all contacts to health care system.

Participants

1,667,339 adults in Denmark born on or before 1 January 1950, who were followed up to 31 December 2016 for incident low-trauma fracture and mortality.

Main outcome measures

fracture and chronic diseases recorded within 5 years prior to the index fracture were identified using ICD-10 codes. Death was ascertained from the Danish Register on Causes of Death. We used Cox’s proportional hazards regression to estimate the hazard ratio of mortality following a fracture, and then used the Gompertz law of mortality to transform the hazard ratio into life expectancy for a specific fracture site. The difference between life expectancy associated with a fracture and background population life expectancy is regarded as the years of life lost. Skeletal age is then operationally defined as an individual’s current age plus the years of life lost.

Results

during a median follow-up of 16.0 years, 95,372 men and 212,498 women sustained a fracture, followed by 41,017 and 81,727 deaths, respectively. A fracture was associated with 1 to 4 years of life lost dependent on fracture site, gender and age, with the greater loss being observed in younger men with a hip fracture. Hip, proximal and lower leg fractures, but not distal fractures, were associated with a substantial loss in life expectancy. A 60-year-old man with a hip fracture is expected to have a skeletal age of 66.1 years old (95% CI: 65.9, 66.2).

Conclusion

we propose to use skeletal age as a metric to assess fracture risk for an individual and thus improve doctor-patient risk communication.

What have been known on this topic?

Fragility fracture is associated with increased mortality risk, however it is currently underdiagnosed and undermanagement globally.

Despite the excess mortality after fracture, mortality is never a part of doctor-patient communication about treatment or risk assessment, due to a lack of an intuitive method of conveying risk as the traditional probability-based risk is counter-intuitive and hard to understand.

In engineering, “effective age” is the age of a structure based on its current conditions, and, in medicine, the effective age of an individual is the age of a typical healthy person who matches the specific risk profile of this individual.

What this study adds

We advanced the concept of “Skeletal Age” as the age of an individual’s skeleton resulting from a fragility fracture using data from a nationwide cohort of 1.7 million adults aged 50+ years old in Denmark.

Unlike the existing probability-based risk metrics, skeletal age combines the risk that an individual will sustain a fracture and the risk of mortality once a fracture has occurred, making the doctor-patient communication more intuitive and possibly more effective.