Bone Anchored Hearing Solutions – Update from Scientific Meetings
Carolyn Smaka: Hi Ravi, thanks for providing us with an update from some of the scientific meetings you’ve attended recently, specifically the 117th American Academy of Otolaryngology (AAO) Meeting in September and the 29th Politzer Society in November.
Ravi Sockalingam: Yes, the AAO meeting was held in Vancouver, Canada while the Politzer Society meeting was held in Antalya, Turkey. In both meetings, there were several sessions on bone anchored hearing systems.
Carolyn: Great! What were some of the highlights?
Ravi: Some of the sessions touched on surgical techniques, and there was one particular session about loading timeframe. Loading is the time when we put the sound processor on the abutment. Patients will have surgery, and then we wait until the skin heals before we put the sound processor onto the abutment. The FDA indications say three months before loading. Many doctors feel it is safe to put the sound processor on at six to eight weeks post-op. There is now more evidence indicating that even a three-week loading does not increase the risk of an implant extrusion or adverse skin reactions. Dr Jack Wazen at Silverstein Institute in Sarasota reported no differences in outcomes between loading at three weeks and loading at six weeks. The outcomes at 3 weeks loading were reported to be good with no revision surgery or implant extrusion, and the skin reactions were either nonexistent or very minimal. Those that were considered to be very minimal were treated locally, and all resolved without any further problems
Carolyn: Is that for adults and children?
Ravi: That is only for adults with normal bone quality. There is some development on the pediatric side about whether the surgery should be done in a single-stage or two stages. Typically, surgery in children is performed in two stages because they have softer bone. Surgeons would want to put the implant in first, wait for three months, and then put on the abutment. Then they would wait for another three months or so to be fit with the sound processor. There are centers here in the United States that do the surgeries in one stage. They place the implant and the abutment at the same time, just as they do in adults, and wait for three months before they load the sound processor. It depends on the quality of the bone before the surgeon decides whether it is going to be single stage or two stages. The rule of thumb is, if a child is over 12 years old, the surgery is not staged, provided the quality of the bone is good. If the child is under 12 years of age, then surgery is staged.
There is some evidence from the University of Texas - Southwestern Medical School that it is not the age that really matters, but bear in mind that in the United States, the FDA has only cleared the surgery for a child that is five years of age or older. Researchers from UT Southwestern believe that a child who is six or seven years of age should be eligible for single-stage surgery, provided the child does not have contraindications such as craniofacial anomalies or soft bone. When they compared recipients of two-stage and single-stage surgery, they did not see a difference in complication rates between the two groups. The study at UT Southwestern was led by Dr. Peter Roland.
Carolyn: The study sounds very practical with the types of things that make a difference to patients. What else was discussed at the meeting?
Ravi: There was talk about surgical techniques. For a long time the surgical technique employed was one that involved thinning of the skin and removing tissue around the implant site. Later, a linear incision technique, whereby a small straight line incision is made, was adopted by many surgeons in Europe and in the US. More recently, more and more surgeons are using a linear incision technique with minimal or no tissue removal. These surgeons are reporting better skin outcomes with this technique.
There are also, surgeons, particularly in the US, who have been using what we call a punch technique. They make a very small, circular 5 mm punch and put the implant and abutment in. Among the surgeons who perform the “punch” technique are Dr. Wayne Shaia from Richmond, Virginia and Dr. Daniel Coelho from Virginia Commonwealth University, also in Richmond. I always joke that Richmond is the punch capital of the world now. They are reporting good outcomes with this technique.
The linear incision technique with minimal or no tissue reduction, and the “punch’ technique aim to preserve as much soft tissue as possible. Often times these techniques are collectively referred to as “Tissue Preservation technique”. Long term data indicate that this technique results in quicker healing, better cosmetics, fewer postoperative complications, and shorter surgery time.
Carolyn: What about the implant itself? What changes might we see down the road?
Ravi: The modern design of our implant itself lends itself to tissue preservation surgery very well. We have a smooth titanium surface on the abutment that adheres to the skin and supports it very well. You may have to use the longer abutment if you are using the tissue preservation technique because you are not removing any tissue. You will typically use at least a 9 mm abutment. In some cases, surgeons use a 12 mm abutment. There is an ENT professor at the Karolinska Institute in Stockholm, Sweden who has been following patients for five years using the non-skin reduction technique and a longer abutment. She has been reporting very good outcomes, even up to five years.
Carolyn: If someone was implanted with a shorter abutment years ago, can they switch to a longer one? What if a patient does not want the bone anchored hearing system anymore?
Ravi: Yes, with no problem. You may have to take them under local anesthesia and because it is considered a minor surgical procedure. It is done in either a hospital or at a day surgery center. You take the patient in, make a small incision, and unscrew the old abutment and put a longer one in.
If the patient does not want the bone anchored hearing system at all anymore, it is reversible in a sense. The implant is already fused with the bone, so it is not going to cause any problems. The abutment is removed (usually done in the doctor’s office) and the skin closes over. A small scar may remain, and depending on what surgical technique was used, it may be almost invisible.
The next hot topic is a transcutaneous solution. Before Cochlear, there was a company called Sophono, which has a transcutaneous system. That system today and the system that Cochlear has brought to the market just recently is called passive transcutaneous. With transcutaneous solutions, you do not have an abutment. You have to have a way of transmitting the signal across the skin to the other side without an abutment. With a passive solution, the vibrator sits on the outside with the sound processor. It is like the Ponto vibrator, but you are not putting that Ponto onto an abutment, so you would have a magnet on the outside of the head over the skin, and then you will have another magnet underneath the skin. The two magnets with opposite polarity hold the hearing system together.
Carolyn: Like a cochlear implant?
Ravi: Exactly right. In this case, the battery and other components are on the outside. You have to use the power to transmit the signal. Implanted inside are magnets and a receiver. The receiver will transmit the vibrations to the bone. You are still going to lose some energy across the skin. It will never be better than the bone conduction vibrator that you would use to measure bone conduction thresholds, because that oscillator is in tight contact against the head.
For children who are under the age of five and cannot have the surgery, we put a processor on a soft band. You try to make it as tight as possible. If it is too tight, there will be an indention in the skin, and that can be painful after a while. That is what transcutaneous solutions do. They have different magnet strengths, and they will choose the one with the lowest strength that will keep the device together. There are also MRI compatibility concerns; it is compatible up to 1.5 Tesla right now, but not 3 like percutaneous solutions are. Cosmetically, it is appealing, but you are not going to have the same amount of output and gain that you would from a percutaneous system.
Percutaneous systems directly stimulate the bone through the abutment. When you transmit across the skin, however, you can lose up to 20 dB, particularly in the higher frequencies. You do need a lot of gain for conductive losses. Once you can get the sound across to the bone, you do not really need any gain.
The transcutaneous solutions that exists in the market today, might work for purely conductive hearing losses. In spite of the signal attenuation that happens during transmission across the skin, the signal may still be adequate enough to reach and stimulate the healthy cochlea. However, this may not be the case in mixed hearing loss and in single sided deafness where higher gain particularly in the higher frequencies is required. So there is a tradeoff between cosmetics and audibility. It is comparable to the high-power BTEs versus CICs. Those issues are almost identical in bone anchored solutions, too.
MED-EL has an active solution. It is called the Vibration Bone Bridge. It is not yet FDA cleared so is not available in the United States. It is available in Europe and Canada. In the passive solution, you have the vibrator outside and you are transmitting that vibration across the skin. In the Bone Bridge, the transducer that drives the vibration is located under the skin and closer it is to the cochlea, the better the output will be.
This is a neat solution because you have the battery power outside, and so it transmits the power as well as the signal. The signal has to span an extended speech bandwidth, and then you also have to drive a power source across the skin to power the transducer inside. You could either have the power for the transducer inside or outside. If you have it outside, you are going to lose some of the power through the skin and inductive link. Just as in the passive solution, you will lose some of the signal as well. The transducer, because it is inside and close to the cochlea, will recover some of the signal that you may lose. Because it is near the cochlea, you do not need a lot of power to drive it.
The Vibration Bone Bridge is limited because the transducer is large and can be difficult to place very near the cochlea. It still needs quite a bit of power. The sound processor that sits outside is fairly big.
There is another device that was invented by Bo Hakansson, who is widely considered the “Guru” of bone conduction technologies. He was the original inventor of the bone anchored hearing system and is with Chalmers University in Gothenburg, Sweden. He has come up with an active transcutaneous solution. The processor looks small, and the transducer is also quite small that it could be implanted closer to the cochlear, compared to the Vibration Bone Bridge from MED-EL. You also do not need a lot of power to drive this one. They are testing it in patients now in Sweden. I think they have done about 10 patients to date. The results are still pending, but preliminary findings have been positive. I am coordinating a scientific meeting for the company in Copenhagen that will take place in January. The ENT surgeon who is involved in the trial in Gothenburg is going to present the data for this new technology.
This is the direction technology is moving right now, cosmetics are still such a present issue. Even parents want children to have Sophono or any of the passive transcutaneous solutions for cosmetics. If we can come up with an active solution, I think it will be very attractive to a lot of patients.
Carolyn: Let me ask you, with all the advances, even before the transcutaneous solutions, are you seeing more of an uptake with bone anchored solutions? There is so much more opportunity now, so we are penetrating the market with this technology?
Ravi: One thing for sure is there is more public awareness. We are reaching out to consumers directly through social media. We also have patient advocacy weekends and retreats, picnics, and so forth. The consumers are becoming more knowledgeable about bone anchored hearing systems, and they are educating other potential consumers.
Carolyn: They are probably educating their professionals in a lot of cases.
Ravi: That is the way the whole field of bone conduction hearing is moving. I work closely with some of the surgeons and they say some of the patients show up saying, “I need a Ponto. Do you do that? What is the price? When can you do it?” They are not coming for an evaluation or opinion from the doctor. More and more of that is happening, especially with the baby boomers, who are better educated, particularly those living in urban areas. This is, in fact, a topic that is being discussed in current conferences.
Carolyn: This has been a great update. It seems like the research and options in this field are gaining momentum, which is a good thing for patients who can benefit from the technology. Thanks, Ravi. We will talk to you again soon.
Ravi: Always a pleasure. Thanks, Carolyn.