A Life Changing Procedure for Those with Conductive Hearing Loss
The world’s first transplant of middle-ear bones using 3D printed components has restored the hearing of a 40-year-old man with conductive hearing loss. The groundbreaking surgical procedure was pioneered by Mashudu Tshifularo, MD, Head of the Department of Otorhinolaryngology at the University of Pretoria’s (UP) Faculty of Health Sciences, and his medical team at Steve Biko Academic Hospital, in South Africa.
Hearing loss has long been accepted as part of the aging process. According to the National Institutes of Health, approximately one third of Americans between the ages of 65 and 74 suffer from hearing loss, and nearly half of those older than 75 have difficulty hearing. This new procedure offers hope for those suffering from one particular type of hearing impairment: conductive hearing loss, a middle ear problem caused by congenital birth defects, infection, trauma or metabolic diseases.
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 – the bones of the inner ear, and the smallest in the human body – become damaged. This patient, for example, was in a car accident that caused severe trauma to his ear.
Conductive hearing loss is traditionally treated through surgical reconstruction using patient-specific prostheses made from stainless steel and ceramic. However, this surgery has a high failure rate. "The ossicles are very small structures, and one reason the surgery fails is thought to be due to incorrect sizing of the prostheses," says Jeffrey D. Hirsch, M.D., 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."
That is exactly what Dr. Hirsch and his colleagues did. They studied 3D printing as a way to create customized prostheses for patients with conductive hearing loss. The researchers removed the middle linking bone in the ossicular chain from three human cadavers, imaged the structures with CT, and then printed cadaver-specific implants.
Four surgeons were then asked to insert each prosthesis into the corresponding middle ear, blinded to the bone from and for which each was designed. 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 Dr. Hirsch. "This study highlights the core strength of 3D printing—the ability to very accurately reproduce anatomic relationships in space to a sub-millimeter level," he says. "With these models, it's almost a snap fit."
The transplant surgery, successfully performed by Dr. Tshifularo and his colleagues in South Africa, takes Hirsh’s work one step further. It is the world’s first middle ear transplant using 3D-printed bones: It effectively replaced the hammer, anvil, and stirrup – the ossicles that make up the middle ear. Using 3D printing technology, the medical team was able to print these bones and reconstruct the ossicles in surgery. Dr. Tshifularo explains that with 3D printing his team was able to take a scan and “get the same size bone, position, shape, weight and length and put it exactly where it needs to be – almost like a hip replacement.”
He continues, "By replacing only the ossicles that aren't functioning properly, the procedure carries significantly less risk than known with prostheses and their associated surgical procedures. We used titanium for this procedure, which is biocompatible and an endoscope to do the replacement, so the transplant was quick – taking less than two hours, with minimal scarring,” Dr. Tshifularo said. Two weeks after the procedure, when his bandages were removed, the patient’s hearing had significantly improved.
The surgery further aims to simplify the reconstruction of ossicles during middle ear procedures, including ossiculoplasty and stapedectomy, because it lessens the risk of intrusion trauma.
The researchers hope to reduce the risks associated with traditional surgery, including the potential for facial nerve paralysis, which can occur if the facial nerve that passes through the middle ear space is damaged.
So far, the surgery, which can be performed on people of any age, has already been used to treat two patients. Dr. Tshifularo transplanted 3D printed ear bones into a second patient with an underdeveloped middle ear, replacing the hammer, anvil and stirrup. The process essentially rebuilt the patient’s middle ear ossicles with the help of titanium 3D printing.
Says Dr. Tshifularo, “3D technology is allowing us to do things we never thought we could.”
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