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.”
Interested in learning more about
how 3D printing is powering new innovations in healthcare? Take a closer look
at the way Stratasys is driving medical innovation HERE.
