Clinical survey of Oticon Medical Ponto implants and a surgical technique with tissue preservation

Percutaneous bone anchored hearing systems were introduced in 1977 and have now
been used clinically for over 30 years. Today, more than 100.000 implantations
have been made around the world. The long-term success rate is high, with a low
rate of major complications [Dun et al 2012].
The most common complication is soft tissue reactions around the
skin-penetrating coupling [Holgers et al 1988]. Recently, promising
modifications related to the surgical approach have been suggested [Hultcrantz
2011, Shin et al 2012, Singam 2010, Soo 2009]. The result is minimal scar
tissue formation and skin with natural thickness around the abutment. In
combination with recent abutment developments introduced by Oticon Medical
[Westerkull 2012] this has the potential to offer significant benefits for the
patients and the success of percutaneous bone anchored hearing devices.
The aim of the traditional surgical procedure is to achieve a thin hairless
skin that is well fixated to the underlying periosteum to hinder skin movement
around the abutment and to facilitate cleaning. The preparation is usually
performed either through a straight incision or with the help of a dermatome.
Although this approach is well established and works very well for the majority
of patients [Dun et al 2012, Holgers et al 1988], there are a number of
drawbacks such as the large amount of scar tissue formation and numbness in the
area around the abutment, and for many patients the cosmetic aspect of being
left with a bald spot [Hultzcrantz 2011] is unattractive. In addition, skin can
thicken up so that the abutment becomes too short with resulting skin
irritation [Hultzcrantz 2011]. In recent years, promising results with
modified surgical techniques with tissue preservation have been presented
[Hultzcrantz 2011, Shin et al 2012, Singam 2010, Soo 2009]. With this technique
no soft tissue reduction is performed, except in specific cases where the
longest abutments are still too short. For instance, Hultcrantz has reported
less numbness in the area around the abutment and no increase in skin
complications with tissue preservation surgery. This technique can also
significantly shorten the time of the surgery.

In the original procedure, introduced by Tjellstrom in 1977, no soft tissue
reduction (or skin graft) was performed, but surgery was a two stage procedure.
No subcutaneous tissue was removed, and in the second stage of the procedure,
only a hole was punched through the skin to allow for the attachment of the
abutment to the implant. In the discussion, they note that *a few patients
complained of minor skin irritation during the first weeks after the second
surgical procedure [the placement of the abutment]. This problem was noted
among those patients who had a thick subcutaneous layer and a skin rich in
sebaceous glands*, but no adverse skin reactions or removal of abutments was
noted. In a subsequent paper, long-term follow-up of the same patients was
published. Here it is noted that soft tissue had to be trimmed to avoid tissue
movement around the abutment in a few cases. A free skin graft is also
mentioned as a solution for cases where there are hair follicles in the area
around the implant. Again it is noted that *problems with slight skin
irritations were only found in patients with thick soft tissue layers over the
mastoid. After surgical reduction of the subcutaneous layers the problems
disappeared. This kind of surgical soft tissue reduction has, in selected
patients, since been included at the first clinical operation [in a two stage
procedure]. After this change of clinical routine there has been no skin
irritation at the abutment penetration site*. Reduction of soft tissue has
since been a part of the standard bone-anchored hearing system surgery.
It should be noted that the early abutment design had a sharp 90 degree edge
facing the skin, which possibly can have contributed to skin irritation. It
could be postulated that a thicker skin would come in contact with the sharp
edge of the abutment whereas there was no contact with the sharp edge for
patients with a thin skin. The Ponto implants and abutments does not feature a
sharp edge, and compes in a varity of different lengths to accommodate
different skin thickness.

Very recently, a number of studies have reported results using a surgical
technique with minimal soft tissue removal [Goldman et al 2013, Hawley et al
2013, Husseman et al 2013, Lanis et al 2013, Wilson et al 2013, Shin et al
2012], also called minimal invasive surgery (MIS). Allocating the result from
Hawley, Husseman, Hultcrantz, Lanis, and Shin (which all used a version on
linear incision surgery with soft tissue preservation) yields a total of 97
patients with 98 implants (of which 15 children) having their bone anchored
hearing aids installed without or with limited skin thinning. The mean
follow-up time in these studies is between 12-18.5 months (minimum 0.3 months).
Implant extrusion occurred in three patients (incidence between 0 to 2.7 %) and
revision surgeries were needed for totally four patients, all in the same study
[Hawley et al 2013] (incidence between 0 to 10.8%). The incidence of skin
reactions in four of the five reported studies ranges between 0 to 28% for
adult and 0 to 60% for children. (A single study [31] reported the highest
incidences for both children and adults
Excluding this study, reported ranges were 0 to 14.7% for adults and 0 to 10%
for children.) Skin reactions were defined as Holgers scale *2 for all but one
study, where it was defined as peri-implant infection yielding an incidence of
10% (n=1/10) [Lanis et al 2013]. These results are comparable or better than
the data reported in the systematic review by Kiringoda et. al.

Further, other positive outcomes reported were:
* Better cosmetic outcomes were mentioned in all studies including a control
* Shorter surgery time was reported in all studies including a control
* Faster wound healing was mentioned in three studies considering MIS
[Hultzcrantz et al 2011, Husseman et al 2013, Lanis et al 2013], two of which
were controlled
* Less numbness was mentioned in three [Hultzcrantz et al 2011, Hawley et al
2013, Lanis et al 2013] of the five studies, two of which were controlled
studies.

The risk of losing an implant due to adverse skin reaction when using a tissue
preservation technique at installation of the system is in the same region or
better than the general data previously reported in the literature. The
incidence of skin reactions is better or equal to the data previously reported
in the literature and an increased risk for trauma resulting in loss of implant
has not been reported. In addition, new risk factors and other potential
effects (beneficial and harming) have not been reported in the currently
published studies.
Another weakness of these studies is that they often mix different types of
implant and/or abutment geometries. Further, several of the studies are either
retrospective in nature, or controlled studies but with a limited number of
patients. The follow-up times are generally relatively short.
The justification for this study is therefore to collect data in a prospective
study, including a larger number of patients. We will use a single abutment
geometry and surface, so that the results only reflect the difference in
surgical techniques. With this study, we will further collect long-term (three
year) data. Focus will be on numbness, which has been stated as an area where
tissue preservation has a positive patient impact, but where reproducible
measurements have lacked until today, as well as surgery time, complications
needing treatment and skin-related issues. We will further investigate the
effect of this modified technique on audiometric thresholds. We will also
investigate the safety of the tissue preservation surgical technique with
regard to implant survival and stability data.

The primary objective of the study is to investigate the difference in numbness
around the implant between after a surgical procedure with soft tissue
preservation (test) and a surgery with soft tissue reduction (control) for
implanting using Oticon Medical Ponto implants and abutments with regard to:
- Numbness around implant

The primary hypothesis is that there is less numbness is lower, surgery time is
shorter, and there is little to no loss of sound quality after surgery with
soft tissue preservation than after surgery with a procedure with soft tissue
reduction.

The secondary objectives are
- Compare the Surgical time between test and control group
- Investigate the effect of soft tissue around the abutment on audiometric
thresholds
- Investigate and compare the number of unplanned visits, unplanned surgical
procedures and other treatments for the test and control group.
- Investigate and compare the rate of adverse skin reactions
- Investigate implant loss and implant stability
- Investigate and compare healing time after surgery
- Investigate and compare subjective benefit as measured by APHAB, GBI and GHSI
questionnaires
- Investigate and compare scar assessment.

Patient inclusion for the test group of this clinical investigation will be
performed among patients that already have been audiologically and otologically
evaluated and found suitable candidates for treatment with a bone anchored
hearing aid. The test group will be consecutively included in the study, and
includes 25 patients. The control group will consist of the last 25 patients
(all patients for which 12 month follow-up visit takes place after Jan 1st ,
2014) that have already undergone surgical intervention in the prospective
clinical study C33 (CMO 2011/497), and that have received the same wide Ponto
implant with 6 mm abutment and soft tissue reduction as a part of that study.
The test group will come for check-ups at 7 days, 21 days, 12 weeks, 6, 12, 24
and 36 months following implant insertion, approximately the same amount number
of follow-up moments visits patients undergo in regular clinical practice. At
each visit a clinical evaluation will be made where implant stability is
measured using resonance frequency analysis, and a range of outcome measured
related to skin status are collected including the standardized Holgers score.
Three weeks after surgery the patients will be fitted with the sound processor.
The control group has undergone an extensive follow-up programme with special
focus on implant stability measures. For the last 25 participants of this
study, a few study variables need to be added at the 1, 2, and 3 year follow-up
visits for comparative reasons .

All data is to be registered in the paper based Case Report Forms.

The risk of participating in the study is low and comparable to corresponding
rehabilitation outside the study. The implant and abutment are identical to the
ones used in a regular surgery and will not contribute to any additional risk.
The patients will be fitted with their sound processor at 3 weeks, which is
nowadays regular practice and will speed up the rehabilitation. No type of
complications other than those that might occur when rehabilitating patients
with a bone anchored hearing aid outside the study is anticipated. Treatment of
possible complications for patients in the study will be the same as for
regular implant patients. All adverse events will be registered and taken into
consideration when compiling the final report.
The subcutaneous tissue reduction, that is a part of the standard surgical
technique, is omitted in this study. The reports published so far indicate
positive patient benefits in terms of less numbness around the implant, faster
healing time after surgery and a cosmetically more attractive result.
If long-term results are not as anticipated, subcutaneous tissue reduction can
be performed after the initial surgery if needed. This will require an
additional surgery, but the end result should be the same as for patients
undergoing the regular surgery. (Two-stage surgeries are already today used is
some patients, and revision surgeries are a possible treatment for patients
suffering from e.g. skin overgrowth.)
Participation in the study requires follow-upvisits for the patient with
approximately the same frequency, but with longer duration, than what is
normally required. This will require an extra effort for the patient however
the patient will have the opportunity to interact more with the treating
physician.
We conclude that the risks of this modified surgical technique are acceptable
when weighted against the user benefits of the technique and the gain in terms
of research results in a field important for long-term patient outcomes.