A bone to speak and to swallow

June 23, 2016
Adityarup “Rup” Chakravorty

Only one out of the more than 200 bones in our bodies is free-floating, with no local attachment to other bones, but it’s no freeloader. The hyoid bone is located in the front of the neck, just below the lower jaw, carrying the weight of the tongue and playing a vital role in speech and swallowing.

At birth, the hyoid bone is made up of three unconnected bones. Over time, these bones may—or may not—fuse to form a crescent-shaped structure. But exactly when these bones fuse or how often they remain unfused throughout life is inconclusive.

Houri K. Vorperian, PhD
Houri K. Vorperian, PhD

In a recent study, led by Houri K. Vorperian, PhD, researchers in the Vocal Tract Development Laboratory at the Waisman Center used an extensive medical imaging database to precisely and accurately measure hyoid bone fusion; they also created three-dimensional models to measure bone density throughout the lifespan.

Knowing more about how the hyoid bone develops may help us better understand how we speak and how we swallow. The hyoid bone is part of a functional system providing attachments for the muscles of the tongue, the larynx (voice-box), the mandible (lower jaw) and other structures in the mouth and throat — “if only one of them grows or fails to grow, growth in all neighboring structures, as well as the functions the system supports, such as speech and swallowing, can be affected,” says Vorperian.

She hopes that understanding hyoid bone development in typically developing individuals will also provide new insight into the speaking and swallowing challenges faced by individuals with some developmental disabilities.

For example, individuals with Down syndrome often have problems with speech and swallowing. Vorperian has observed that in some cases the hyoid bone looks different in children with Down syndrome compared to typically-developing children.

Could these differences in hyoid bone structure and position play a role in some of the swallowing and speech challenges faced by individuals with Down syndrome?

Vorperian says it’s possible but too soon to draw any conclusions. “There is no doubt that there’s an interplay of structure and function,” says Vorperian. “For example, when you swallow, your tongue applies pressure to the roof your mouth and that pressure permits the function of swallowing while also shaping the palate (roof of the mouth).”

The differences in how the hyoid bone looks in children with Down syndrome compared to typically developing children may be a clue, but more research is needed.

And this research needs to be quantitative and precise because of the natural variability in how humans develop, says Vorperian. “What we consider typical versus atypical is along a continuum—it’s not one or the other.”

To precisely measure the hyoid bone in individuals of different ages, Vorperian and her colleagues have established a lifespan medical imaging database of head and neck CT scans obtained mostly from the University of Wisconsin Hospital and Clinics.

CT scans use X-rays to create highly-detailed images of our bodies and are used widely to screen or diagnose patients. The researchers in Vorperian’s lab subjected the medical images in their database to advanced visualization and analysis software to render three-dimensional models and measure the hyoid bones’ density.

“This is the first study that has looked at hyoid bone density,” says Vorperian. “Our findings on hyoid bone fusion and bone density has important implications for the field of forensic science, where such information on changes in the hyoid bone during the lifespan may be used to determine the age of unidentifiable human remains.”

The detailed hyoid bone images derived from CT scans of individuals ranging in age from about a year old to 94 years old produced some surprises.

“The assumption is that the hyoid bones fuse with age in most people, but we see that’s not always the case,” says Vorperian. In fact, only 34% of adults over the age of 75 had full hyoid bone fusion.

Vorperian is curious to learn whether the fusion—or lack thereof—of the hyoid bone in the elderly might affect their speech and swallowing. “We know that some individuals have issues with swallowing as they get older, likely due to the additional descent of the hyoid bone” she says, “but I wish we could also explore whether hyoid bone fusion plays a role.”

Sophisticated analysis methods are allowing the researchers to continue to precisely track how the hyoid bone develops during childhood. One approach is to place virtual ‘landmarks’ on images of the hyoid bone to quantify the growth of each of the three bones that make up the hyoid bone, and its descent from a high to lower position in the throat during development; other approaches include surface and volume-based analyses. Such approaches will allow researchers to calculate not only which regions of the hyoid bone are growing but also how much growth is taking place in children of various ages.

That’s important because of the teamwork behind a successful swallow or shout—the hyoid working with the voice box, the lower jaw and other structures. “My hope is that we will eventually be able to quantify how the hyoid bone grows in relation to its surrounding structures,” says Vorperian.

Animation showing the position of the hyoid bone in the human body
The position of the hyoid bone (shown in red) in the body (Animation courtesy of the Vorperian lab)

– See more at: http://www.waisman.wisc.edu/news2016-Vorperian.htm#sthash.AVDfGId3.dpuf