Researchers using CT scans and 3-D printing have created accurate, custom-designed prosthetic replacements for damaged parts of the middle ear, according to a study presented at the annual meeting of the Radiological Society of North America (RSNA) in Chicago. The technique has the potential to improve a surgical procedure that often fails because of incorrectly sized prosthetic implants, researchers say.
Hearing works partly through the transmission of vibrations from the ear drum to the cochlea, the sensory organ of hearing, via three tiny bones in the middle ear known as ossicles. Ossicular conductive hearing loss occurs when the ossicles are damaged, such as from trauma or infection.
“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,” says study author Jeffrey D. Hirsch, MD, assistant professor of radiology at the University of Maryland School of Medicine (UMSOM) in Baltimore. “If you could custom-design a prosthesis with a more exact fit, then the procedure should have a higher rate of success.”
Hirsch and colleagues studied 3-D printing as a way to create customized prostheses for patients with conductive hearing loss. The technology has been used successfully to solve a number of other medical prosthesis problems, including in the areas of joint replacement and facial reconstruction surgery.
The researchers removed the middle linking bone in the ossicular chain from three human cadavers and imaged the structures with CT. They employed an inexpensive 3-D printer to create prostheses to restore continuity for each of the middle ears. The prostheses were made from a resin that hardens when exposed to ultraviolet laser light. Each of the prostheses had unique measurements.
Four surgeons then performed insertion of each prosthesis into each middle ear, blinded to the bone from and for which each was designed. The researchers then asked the surgeons to match each prosthesis to its correct source.
All four surgeons were able to correctly match the prosthesis model to its intended temporal bone — the bone containing the middle and inner parts of the ear. The chances of this occurring randomly are 1 in 1,296, according to Hirsch.
“This study highlights the core strength of 3-D printing — the ability to very accurately reproduce anatomic relationships in space to a submillimeter level,” Hirsch says. “With these models, it’s almost a snap fit.”