Custom 3D Printed Ossicular Prostheses Could Improve Treatment for Patients with Conductive Hearing Loss

Today is the last day of this year’s Radiological Society of North America (RSNA) Annual Meeting, and we’ve been hearing a lot of announcements regarding 3D printing technology from the event, including Fovia’s new F.A.S.T. Cloud Development platform and the University of Utah Hospitals and Clinics health system launching TeraRecon’s 3D Print Pack Portal. Researchers from the University of Maryland School of Medicine (UMSOM) are presenting their study at the RSNA Annual Meeting, which details how they used CT scans and 3D printing technology to create accurate, custom prosthetic replacements for damaged parts of the middle ear, which could majorly improve treatment for patients with hearing loss.

 

Inside the middle ear are three tiny bones, called ossicles (see video above), which help transmit ear drum vibrations to the cochlea – the sensory hearing organ. When the ossicles are damaged, through incidents like infection or trauma, ossicular conductive hearing loss occurs. Prostheses can be used to restore continuity to the middle ear, but because the current prosthetic implants are often made from ceramic cups and stainless steel struts and don’t fit properly, there has been a high failure rate of using surgical reconstruction to treat conductive hearing loss.

Jeffrey D. Hirsch, M.D.

Jeffrey D. Hirsch, M.D., assistant professor of radiology at UMSOM and one of the study’s authors, explained, “The ossicles are very small structures, and one reason the surgery has a high failure rate is thought to be due to incorrect sizing of the prostheses. If you could custom-design a prosthesis with a more exact fit, then the procedure should have a higher rate of success.”

That phrasing – custom design a prosthesis – is where 3D printing technology comes into play. Dr. Hirsch and fellow study co-authors David Eisenman, M.D., and Richard Vincent, M.D., used 3D printing technology to create customized prostheses for patients with conductive hearing loss.

According to the abstract for their paper, “Surgical reconstruction of the ossicular chain with custom 3D printed ossicular prosthesis“:

“Conductive hearing loss due to ossicular abnormalities occurs from many causes, including trauma, infection, cholesteatoma, surgery and congenital anomalies. Surgical reconstruction of the ossicular chain is a well-established procedure for repair of ossicular defects, but is still plagued by high failure rates. Underlying disease and proper sizing of prostheses are two challenges that lead to component failure. Three-dimensional (3D) printing has been used successfully to solve a number of medical prosthesis problems. Custom 3D printing an individualized ossicular prosthesis would be a potential solution for the wide range of anatomic variation encountered in the pathological middle ear, and could decrease the rate of post-operative prosthesis displacement by increasing the likelihood of a proper fit, in addition to decreasing surgical time.”

In their study, the researchers wanted to see if data from commercially available CT scanners could be used to design a custom ossicular prosthesis, and if 3D printing technology could be used to create one that has a proper fit. Additionally, they wanted to see if surgeons would be able to detect the differences in the prostheses.

The team worked with three human cadavers, removing the middle linking bone in their ossicular chains, then used a CT scanner to capture the imaging data. Materialise Mimics Innovation Suite software was used to design custom prostheses, which were then 3D printed out of resin on a Formlabs Form 2 SLA 3D printer. Then came the final step – matching each prosthesis with the correct middle ear. According to an RSNA press release, four surgeons inserted the prostheses “blinded to the bone from and for which each was designed.”

The surgeons were all successful at matching the prosthesis model to the correct temporal bone, which contains the ear’s middle and inner parts, and according to Dr. Hirsch, this was no accident, because the “chances of this occurring randomly are 1 in 1,296.”

“This study highlights the core strength of 3-D printing — the ability to very accurately reproduce anatomic relationships in space to a sub-millimeter level. With these models, it’s almost a snap fit,” said Dr. Hirsch.

The results of the study, which the researchers presented this morning at the RSNA Annual Meeting, show that commercial CT scanners are in fact able to detect major differences in the anatomy of normal middle ear ossicles, and furthermore, that 3D printing technology can be used to represent these differences, which will help decrease the time spent in surgery and increase the chances of making a properly fitted custom prostheses.

The team will now focus on using biocompatible materials to make custom prostheses, as well as potentially combining 3D printed prostheses with stem cells.

Dr. Hirsch said, “Instead of making the middle ear prosthesis solid, you could perforate it to be a lattice that allows stem cells to grow onto it. The stem cells would mature into bone and become a permanent fix for patients with hearing loss.”

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[Images: University of Maryland School of Medicine]