Introduction
Bone-anchored hearing systems have been proven successful for hearing rehabilitation in patients unable to wear conventional hearing aids, such as those suffering from recurrent aural discharge.Reference Arunachalam, Kilby, Meikle, Davison and Johnson1, Reference Hakansson2 Additionally, bone-anchored hearing systems have been demonstrated to improve the quality of life of patients with unilateral profound hearing loss via contralateral cochlea stimulation.Reference Saroul, Mohamed, Yoann, Laurent and Thierry3 Bone-anchored hearing systems work by transforming an auditory stimulus into a vibratory stimulus; this is transmitted to the cochlea via a titanium fixture within the temporal bone. For this process to be successful, osseointegration of the titanium prosthesis into the temporal bone is required.Reference George, Coulson, Ross and De4
Satisfaction rates with bone-anchored hearing systems have been reported to be as high as 98 per cent.Reference Battista and Ho5 Although implants are generally well tolerated, a recent study with an 18-year follow up of bone-conducting implants revealed that 70 per cent of patients reported annoyance with wind noise.Reference Rasmussen, Olsen and Nielsen6 Bone-anchored hearing systems have developed rapidly in the past few years with the introduction of fitting software and signal processing enhancements, such as directional microphones, digital feedback cancellation, and noise and wind noise reduction. Studies have shown increased speech intelligibility and improved subjective patient satisfaction ratings.Reference Olsen, Glad and Nielsen7
There is still debate regarding the optimum time for processor loading; a balance between ensuring osseointegration has occurred and minimising the patient's wait to use the bone-anchored hearing system has to be made. There appears to be little difference in the risk of osseointegration failure for those patients loaded at less than 6 weeks or more than 12 weeks, or even at 4 weeks post-operatively.Reference Zeitler, Snapp, Angeli, Heman, Plum and Telischi8–Reference Dun, Faber, de Wolf, Mylanus, Cremers and Hol10 Recent advances in fixture technology include a wider diameter fixture to increase the bone-fixture contact area and novel fixture coatings to speed up osseointegration.Reference Marsella, Scorpecci, D'Eredita, Della Volpe and Malerba11 Both of these may permit earlier loading than has traditionally been performed.
The Ponto implant system (Oticon Medical, Askim, Sweden) consists of fixtures with two different widths and a range of abutment lengths. In this study, the Ponto 3.75 mm fixture with a 6 mm abutment was used together with the Xpress coupling. The Oticon Medical Xpress external component is attached to the abutment via a clip-on mechanism, without the usual lever action required to attach and remove a classic sound processor (Figures 1 and 2). It is hypothesised that the lever action of coupling and decoupling the bone-anchored hearing system to the abutment may compromise the integrity of fixture fixation during the initial crucial period of osseointegration, and lead to extrusion of the implant. The Xpress fitting system was developed to permit early loading of bone-anchored hearing systems without compromising the integrity of osseointegration. In this study, 20 bone-anchored hearing systems were fitted with the intention of early loading with the Oticon Xpress external component.
Fig. 1 Mechanism of the Oticon Medical Xpress bone-anchored hearing system attachment.
Fig. 2 The Oticon Medical Xpress bone-anchored hearing system attachment.
Materials and methods
Ethical approval for the study was prospectively granted by our institutional ethics board.
Surgical procedure
All procedures were performed under local anaesthetic and involved single-stage insertion of fixture and abutment. A split skin graft was harvested with an electric dermatome, and the soft tissues were appropriately undermined. Loose periosteum was removed and a punch performed in the periosteum at the intended location of the implant. A standard 4 mm guide drill and countersink were used before the implant was inserted, with up to 40 Ncm torque. The split skin graft was secured in place with size 4.0 Vicryl sutures (Ethicon, Somerville, New Jersey, USA). Jelonet (Smith and Nephew, Hull, UK), Inadine (Johnson and Johnson, New Brunswick, New Jersey, USA) and gauze dressings were then applied before the healing cap was attached. All patients wore a head bandage overnight; this was removed at home the following day.
Patients
Fifteen adult patients (6 males and 9 females, aged 16–70 years) were initially recruited via the out-patient otology service at the Queen Elizabeth Hospital, Birmingham (a regional teaching hospital). Twenty implants were subsequently implanted into these 15 patients. Demographic data are shown in Table I. All patients were implanted with the intention of using the Oticon Medical Xpress coupling system (Oticon Medical).
The patients underwent surgery between March 2009 and January 2012 in a single UK teaching hospital. All procedures were performed by one of two surgeons experienced in bone-anchored hearing systems. Patients were followed up at one week by a bone-anchored hearing system clinical nurse specialist for removal of dressings, and patient and relative abutment care education. The patients were seen at two weeks by an audiologist for potential fitting of sound processors. If suitable, fitting occurred at two weeks post-surgery; if not, patients were reviewed weekly until fitting was appropriate. The interval between the operation and time of processor loading was recorded for all patients, along with the cause of any delays. Late complications were also recorded, regardless of whether or not these resulted in the removal of the bone-anchored hearing system. Patients were seen by their surgeon in the out-patient department, at four weeks post procedure.
Surgical procedure and out-patient follow-up data were retrospectively retrieved from the electronic note system and cross-referenced with clinical records from the audiological service.
Results
Two patients were fitted with a total of three implants at seven and nine weeks because of administrative errors; no skin problems were reported by these patients. Of the remaining 17 implants, 8 processors (47.1 per cent) were fitted at 2 weeks post procedure, 1 at 3 weeks (5.9 per cent), 4 at 4 weeks (23.5 per cent), 3 at 7 weeks (17.6 per cent) and 1 at 8 weeks (5.9 per cent). In those (non-administration error) patients who were fitted later than two weeks, the delay was due to incomplete skin healing. The devices were loaded as soon as complete skin healing had occurred.
Two implants were subsequently removed because of complications. One implant was removed as a result of persistent skin site inflammation. This implant had been loaded at seven weeks; the delay was due to on-going skin inflammation. The other implant became loose during subsequent revision mastoid surgery and was removed; the implant had originally been loaded at four weeks and had caused no problems before the mastoid surgery. Further details are shown in Table I.
Table I Results
Pt no = patient number; y = years; post-op = post-operation; M = male; L = left; F = female; R = right
Discussion
Skin site complications are a recognised cause of processor loading delay following bone-anchored hearing system implantation. Skin complications occur with greater frequency in people of African origin, though there appears to be no correlation with diabetes mellitus, immunosuppression or tobacco usage.Reference Zeitler, Herman, Snapp, Telischi and Angeli12 Initial skin problems may be reduced by utilising a linear incision rather than a split skin graft.Reference Bovo13 The feasibility of early loading protocols for a variety of bone-conducting hearing aids appears to be increasing, with new wider implant designs and less invasive surgical procedures.
The results of a recent study using linear incision and a wide implant (Cochlear BAI300) suggested complete skin healing in an average of 8 days, with a steady implant stability quotient at 3 weeks, implying that osseointegration had occurred.Reference D'Eritida, Caroncini and Saetti14 Use of the same implant processor with loading at four weeks has also been shown to be viable.Reference McLarnon, Johnson, Davisson, Hill, Henderson and Leese9 In a study of a linear incision surgical technique with no skin thinning, using both Cochlear and Oticon Medical implant systems, healing time was reported to be significantly shorter for the test group than for a control group who underwent surgery with a dermatome procedure. The skin of all patients in the test group healed within 10 days.Reference Hultcrantz15
Our study demonstrated that the Oticon Xpress system enables the loading of sound processors as soon as two weeks after insertion of the titanium implant. In this study, approximately half of the patients were loaded two weeks after surgery. In common with other implanted bone-conducting systems, prolonged skin healing time was the main reason for the delay in fitting sound processors. We were reluctant to load the processor before complete healing, and it may well be the case that many of the patients who waited longer than two weeks could have been fitted sooner. All patients in the study underwent sound processor fitting within the three months traditionally allowed according to national standard practice (nearly all patients had the fitting within two months, which is the standard practice at our institution).
• Bone-anchored hearing systems are effective for hearing rehabilitation in a variety of conditions
• A new sound processor system attachment (Oticon Medical Xpress) can be loaded as early as two weeks after surgery
• Problems with skin healing are the main reason for delayed loading of sound processors
In one of the two patients whose implant was extruded or removed, the delayed loading of the Xpress system was due to skin problems. We do not believe that the use of the early loading system was a factor in the implant loss. Interestingly, this patient requested the continued use of the Xpress system at two months (when the patient was to be converted to a classical fitting system) as they found it simpler to attach and remove. This patient was elderly, with reduced dexterity. The alternative attachment mechanism of the Xpress system may therefore benefit patients struggling with a conventional device.
Conclusion
Whilst our series is of modest size, it does illustrate the feasibility of early sound processor fitting using the Oticon Medical Xpress system. This system allows processor loading as soon as two weeks after the surgical procedure, provided skin healing is adequate. All patients were fitted within the three months traditionally allowed. Prolonged skin healing was the major reason for the delayed fitting of sound processors.
