Published 6/1/2014
Laura M. Bruse Gehrig, MD

The Importance of Sexual Dimorphism Research

Laura M. Bruse Gehrig, MD

The AAOS Women’s Health Issues Advisory Board (WHIAB) seeks to advocate, advance, and serve as a resource for research on sex and gender differences in musculoskeletal health for a variety of audiences, including orthopaedic surgeons, policymakers, and the general public. The WHIAB has several ongoing initiatives to promote awareness of sex differences in the diagnosis, treatment, and outcomes of orthopaedic conditions.

Significant efforts to prioritize research to include sexual dimorphism are imperative to improve patient care and healthcare delivery. Yet many orthopaedists continue to ask, “Why should musculoskeletal research direct resources to sexual dimorphism?”

More women than men
According to the 2010 U.S. Census, of 308.7 million people in the United States, 157 million were female (50.8 percent) and 151.8 million were males (49.2 percent). Life expectancy for a woman is currently 81.2 years, while life expectancy for men is 75.9 years. If more of the population is female, and women live longer than men, shouldn’t the musculoskeletal research reflect this sexual dichotomy?

Economic impact of musculoskeletal diseases
Based on the World Health Organization’s (WHO) Disability Adjusted Life Expectancy (DALE) calculations, the United States ranks 24th among 191 nations. Under this system, which estimates the average number of years that a person can expect to live in “full health” by taking into account years lived in less than full health due to disease and/or injury, men in the United States can expect 67.5 years of full health, while women can expect to have 72.6 years of healthy life.

This has been interpreted, according to Christopher Murray, MD, PhD, professor of global health at the University of Washington and director of the Institute for Health Metrics and Evaluation (IHME), as “basically you die earlier and spend more time disabled if you’re an American rather than a member of most other advanced countries.”

The leading cause of disability in the United States is musculoskeletal disorders and diseases, which account for more than half of all chronic conditions in people older than age 50 in developed countries. The economic impact of these conditions is staggering.

For the years 2004–2006, the sum of direct expenditures in healthcare costs and indirect expenditures in lost wages in the United States has been estimated at $950 billion annually, or 7.4 percent of the national gross domestic product. The aging “baby boomer” generation accounts for an increasingly greater proportion of total musculoskeletal disease treatment cost and lost wages, a trend that will continue for the next several decades. One in two adults reported a chronic musculoskeletal condition in 2008, nearly twice the rate of reported chronic circulatory or respiratory conditions.

The impact of sexual dimorphism
Musculoskeletal health is one of the areas of medicine in which the differences between males and females are most striking. Although males have a higher incidence of traumatic injuries, females are disproportionately disabled by musculoskeletal conditions. For example, compared to males, females have significantly higher incidences of the following musculoskeletal conditions:

  • adolescent spinal deformities
  • adolescent anterior cruciate ligament (ACL) injuries
  • stress fractures during adulthood
  • osteoarthritis
  • rotator cuff tears
  • osteoporotic fragility fractures

Differences in injury mechanisms, pain sensation, drug handling, and healing response have known biologic bases. How these biologic processes are affected by sex is not yet well understood.

Responses to surgery, anesthesia, medications, and rehabilitation also differ by sex. Yet, in most cases, understanding of disease processes and therapeutic modalities has been based on studies of male populations or young adult male animals, or the studies do not specify the sex of the population. As a result, understanding of these conditions as they occur throughout the human life span is limited with respect to sex.

Improved healthcare delivery
An approach tailored to the separate biologic needs of females and males continues to be investigated in many clinical scenarios. Genomic sex-based medicine is also the wave of the future and ideally will help improve care. Consideration of age-related changes in each sex is critical because many of the conditions that affect musculoskeletal tissues are age dependent.

As the armamentarium of treatment options increases, recognition of sex differences will enable healthcare providers to address each patient based on his or her personal biologic needs. Interventions, therapeutic modalities, and best practices based on sexual dimorphism will improve healthcare delivery for all patients.

Fostering research
The AAOS WHIAB encourages orthopaedic specialty societies to help increase awareness of sex differences, particularly in sponsored education venues, by taking the following steps to ensure these differences are acknowledged:

  • Any paper accepted for presentation at a society’s specialty day or annual meeting should include acknowledgement/recognition of sex differences when appropriate.
  • Any poster accepted for display at the AAOS poster exhibits should include discussion of sex differences when appropriate.
  • All presenters invited to speak during a specialty day or annual meeting should be asked to include information on sex-specific differences in their subject material as appropriate to the presentation.
  • Any article accepted for publication in a society’s journal (if applicable) should be examined by the reviewers to ensure that sex differences are addressed as appropriate.
  • Each presenter included in society-sponsored webinar should be charged to include sex-specific differences in all educational discussions.
  • Any symposium presentation on Specialty Day at the AAOS Annual Meeting should acknowledge sex differences in the literature. If none is known or it has not been studied, that should also be noted.

The AAOS WHIAB is sponsoring a symposium to help identify the most promising research directions for exploring sex differences, with the goal of improving bone and joint care for both males and females throughout their lives. The Musculoskeletal Sex Differences Throughout the Lifespan Research Symposium will be held July 30–Aug. 1, 2014, in Rosemont, Ill., and is sponsored by the AAOS, the Orthopaedic Research Society, Clinical Orthopaedics and Related Research, the Center for Musculoskeletal Health at University of California Davis, and the Society for Women’s Health Research.

With continued efforts of the WHIAB to help ensure that sexual dimorphism is considered a priority within the spectrum of orthopaedic research, clinical practice will continue to advance women’s health and improve health for both men and women throughout the lifespan.

Laura M. Bruse Gehrig, MD, chairs the AAOS Women’s Health Issues Advisory Board.

Putting sex in your orthopaedic practice
This quarterly column from the AAOS Women’s Health Issues Advisory Board and the Ruth Jackson Orthopaedic Society provides important information for your practice about issues related to sex (determined by our chromosomes) and gender (how we present ourselves as male or female, which can be influenced by environment, families and peers, and social institutions). It is our mission to promote the philosophy that male and female patients experience and react to musculoskeletal conditions differently; when it comes to patient care, surgeons should not have a one-size-fits-all mentality.

Additional Information: