One in 10,000 to 15,000 babies are born with aural atresia—an extremely narrow or absent external ear canal, often accompanied by microtia, a malformed auricle. Options for these children historically consisted of a bone conduction implant with a soft exterior band until age five, followed by either three to four reconstructive procedures to open the ear canal and rebuild the auricle, or a percutaneous implant for those who were not reconstructive surgery candidates.
Computer-assisted robotic canalplasty has the potential to optimize the complex surgical procedure, lowering the risk of damage to critical structures in the region and increasing odds that the ear canal will remain unobstructed. At Vanderbilt University Medical Center, Alejandro Rivas, M.D., director of endoscopic ear surgery, and Robert Labadie, M.D., vice chair of research, are developing a customizable drill technology for robotic canalplasty to refine this approach.
Rivas and Labadie are also working under an industry grant to investigate a transcutaneous active bone transmission device, the Bonebridge®, that received de novo FDA clearance in July 2018 for ages 12 and up. The implant requires only one procedure and resides under the skin—surgically attached to the mastoid bone. The Bonebridge® is magnetically bound to an external processor, and offers hearing outcomes comparable to those of percutaneous devices.
Making Atresia Repair Safer
Atresia is correctable by surgery in many, but not all, patients. “As long as the child has functional hearing ossicles, a middle ear space and inner ear, we can usually attempt the surgery,” Rivas said. The risk level hinges primarily on whether the patient already has a small channel that ends in a blind pouch, or no ear canal whatsoever. Other considerations include the position of the facial nerve and other soft tissues (e.g. blood vessels, brain) as well as the body’s attempt to close the channel as part of healing.
To lower surgical risks, Labadie and Rivas are developing a patient-customized drill template for use with robotic canalplasty. When used with CT imaging, the device is intended to provide a more precise guide for extending or creating an ear canal.
“Using CT guidance, the software maps the location of the facial nerve and other tissues to be avoided and charts the best path from the outside to the location of the new ear drum,” Labadie said. “We can then mount a drill on the customized drill guide to follow that path.”
Rivas and Labadie are testing this technology on cadavers and expect to compile the data for an FDA Investigational Device Exemption submission.
Many children with atresia who aren’t candidates for ear canal surgery can still attain near-natural hearing through implants. Percutaneous passive implants entail an abutment protruding through a permanent hole in the skin and a processor that snaps on and off. Transcutaneous passive devices are entirely under the skin and conduct acoustic signals through magnets on either side of the skin barrier.
While transcutaneous options avoid an external wound, thicker skin can impede hearing quality. The newly FDA-approved Bonebridge® (transcutaneous active) device solves this issue in a novel way. It retains the magnetic contact on either side of the skin, but adds an amplifier to the implant, compensating for amplitude lost in transit through the skin.
Vanderbilt is working with three other centers on a clinical trial of hearing outcomes in adults with the Bonebridge®. Because active bone conduction implants optimize both hearing and cosmetics, Rivas and Labadie are enthusiastic about their prospects for expanding patient benefits.
“Choice of treatment options is so important.”
“Choice of treatment options is so important because there are so many malformation variations and different options for them,” Rivas said. “A child who plays physical sports might need the percutaneous device that won’t slip off. Another child who loves to swim might do better with transcutaneous devices they can take off when they go in the pool.”
Rivas and Labadie are also planning a study investigating the Bonebridge® device for children as young as five years old. “If we can provide this procedure to a younger child, we may be able to avoid complications like skin infections from the percutaneous devices, while providing optimal hearing and good cosmetic results,” Rivas said.