Retooling the Sound System: How a Middle Ear Prosthesis Helps Patients Hear Again
A surgeon at Wake Forest University School of Medicine has invented a tiny medical device that helps to restore hearing loss, a recently published study demonstrates. Dr. Eric M. Kraus’s K-Helix Prosthesis helps surgeons reconnect middle ear bones separated by infections or tumors. We caught up with Dr. Kraus to learn more about how the medical device works and to dig into some recent research showing that the device holds fast and continues to provide stable hearing over the long term.
The Middle Ear’s Tiny Tools
So why do patients need to have a middle ear prosthesis anyway? It all comes down to the smallest bones in the human body: the ossicles. (Fun fact: The anatomical term “ossicles” comes from the Latin word for “small bone.”) In addition, the ossicles are adult size at birth and never become larger. Together, the malleus (hammer), the incus (anvil), and the stapes (stirrup) take up a space about the size of an orange seed. When sound vibrations strike the eardrum and cause it to vibrate, the three ossicles transmit the vibrations to the nearby inner ear (cochlea). Once within the cochlea, the vibrations are changed into auditory nerve signals that are sent to our brains to interpret as hearing sounds.
When the delicate ossicles become damaged or degraded because of chronic ear infections, trauma, age, tumors, fluid buildup, or other factors, they no longer conduct vibrations between the eardrum and the cochlea. A condition called conductive or mixed hearing loss results. To remedy this kind of hearing loss, surgeons place prosthetic devices to take the place of the ossicles within the middle ear so that the ossicular chain can transmit vibrations once again to the cochlea, and in turn, improve hearing. With Dr. Kraus’s technique, the K-Helix prostheses are used as connectors to reconnect the damaged hearing bones and to stabilize the connection with a special glass ionomer cement “to increase long-term stability and to improve hearing outcomes, particularly in the high frequencies,” Dr. Kraus says.
Surgeons working to treat conductive and mixed hearing loss often find themselves working on the long process of the incus, the end of the second hearing bone. “The part of the incus that extends down to the stapes has the weakest blood supply among the bones in the middle ear,” Dr. Kraus explains. As a result, “the long process of the incus is the weakest part of the hearing bone chain, which makes it “particularly vulnerable to erosion and breakdown,” he adds.
(Image: Blausen.com staff (2014). “Medical Gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2).)
The K-Helix Crown Is Surgeon-Friendly
The K-Helix is coiled, which permits straightforward implantation over the incus. The coils allow the surgeon to customize the prosthesis to fit each individual patient’s anatomy. “The surgeon is able to easily slide the coils over the eroded incus like a finger-in-a-glove,” Dr. Kraus explains. In contrast to conventional ossicular prostheses, no crimping or special surgical instruments are required. Surgeons can compress, stretch, or remove coils to accommodate any length of the remaining long process of the incus as they repair the ossicular chain. Surgeons can use the K-Helix Crown to connect an eroded incus to the stapes. Or, if turned 90 degrees, to connect the malleus to the stapes.
‘Rebar’ for the Middle Ear
Another advantage of the helical coil design? The coils help to guide the flow of the glass ionomer cement that surgeons use to secure the prosthesis to the ossicular chain. The coils permit the cement to bond more securely than it would otherwise.
To understand how the K-Helix works, imagine a tiny version of those steel rods you see amidst the concrete in construction sites. Builders embed these rods–rebar–in concrete to make it stronger. Similarly, the K-Helix strengthens the glass ionomer cement’s bonding in the middle ear.
‘One Size Fits All’ Saves Time and Money in the OR
The device’s coiled design and ability to be adjusted around three different axes solves a significant prosthetic challenge for operating rooms, Dr. Kraus says. Because every patient’s damaged incus is different, conventional ossicular replacement prostheses, or PORPs, require ORs to keep prostheses of multiple lengths and sizes in their inventory to ensure that surgeons have the correct size and length of prosthesis for an effective fit.
The K-Helix’s universal, one-size-fits-all design helps operating rooms with inventory control. Supply managers need only keep one size of K-Helix in inventory rather than multiple sizes. In fact, ORs need to keep only two prostheses in inventory–one to implant and one to serve as a backup.
The Kraus K-Helix Crown Helps Patients Hear Better, Even after Nine Years
Between 2008 and 2018, Dr. Kraus’s research team measured hearing capabilities in 38 patients before and after the eOCR surgeries that deployed the K-Helix Crown prosthesis with glass ionomer cement. All patients who underwent ossicular chain reconstructions during the study were missing the long process of the incus prior to their operations, and most had other ear pathologies that were weakening their hearing. All patients had chronic ears.
The team measured preoperative and postoperative hearing results for up to nine years to gauge how well the procedure improved patients’ hearing over the long term. They looked at the following elements to assess hearing health:
Data from the study show that eOCR procedures that deployed the K-Helix Crown prosthesis improved patients’ hearing both in the short term and in the long term. Here’s a peek at Table 3 from the research article, which summarizes the results:
The study demonstrates that “eOCR using the K-Helix Crown prosthesis, incus to stapes, and glass ionomer cement can significantly improve hearing at one year and maintain stable hearing over nine years. Both prosthesis and cement are safe.” More studies are needed to confirm these results in larger pools of patients and among multiple surgeons.
