bone - anchored hearing devices of percutaneous type have been successfully used to treat conductive hearing loss ( hl ) patients that can not be corrected by surgery and single side deaf patients .
bone - anchored hearing aids ( baha ) are the most widely used percutaneous type device . but
skin penetrating abutment of baha occasionally develops soft tissue problems   and has poor aesthetic outcome .
if the cleansing is insufficient , soft tissue infection , skin overgrowth around abutment , and osseointegration failure could occur more frequently .
since 2013 , a new bone - anchored hearing device of transcutaneous type , sophono alpha 2 system ( sophono inc . ,
boulder , co , usa ) has been commercially available in korea . because sophono does not have skin penetrating abutment
, sophono is thought to have no soft tissue problem relating to abutment and to have better aesthetic outcome . on the other hand ,
transcutaneous device s output is reported to be 10 to 15 db lower than percutaneous device .
however , few reports have compared transcutaneous device with percutaneous device . therefore , we conducted a retrospective study on nine sophono patients in 2 hospitals who had implantation with sophono with alpha 2 processor and ten baha patients who had implantation with single vertical incision without skin thinning technique .
sophono and baha were compared to each other from surgical and audiological points of view .
we performed baha surgery using single vertical incision without skin thinning technique since december 2009 .
the 10 baha patients had an average age of 39.9 years ( range , 12 to 62 years ) , including six men and four women .
their mean follow - up period was 25.3 months ( range , 20 to 35 months ) .
the causes of baha surgery included bilateral congenital aural atresia ( n=4 ) , chronic ear infections ( n=3 ) , and unilateral hl ( n=3 ) .
every baha patient except two bilateral aural atresia patients used baha bp100 ( cochlear , sydney , australia ) .
sophono patients had an average age of 28.1 years ( range , 5 to 71 years ) , including 4 men and 5 women .
their mean follow - up period was 8.4 months ( range , 4 to 12 months ) .
the causes of sophono surgery included bilateral congenital aural atresia ( n=5 ) , unilateral congenital aural atresia ( n=1 ) , chronic ear infections ( n=1 ) , and unilateral hl ( n=2 ) .
and another one bilateral aural atresia patient was baha user who was included in this study .
at first , he underwent bilateral meatoplasty to restore his hearing , but the hearing was unsatisfactory .
single vertical incision without skin thinning technique was used for baha implantation as described previously .
we compared sophono with baha by the operation time , wound healing time , postoperative complications , postoperative hearing gain after switch on , and postoperative air - bone ( ab ) gap .
the operation time was calculated using operation record . the wound healing time was defined as the period from operation day to the day that regular outpatient visit for the wound care was no longer needed .
postoperative wound infection , skin overgrowth , reoperation , and other postoperative complications were investigated using medical record .
postoperative hearing gain , postoperative ab gap : mean air - conduction ( ac ) , and bone - conduction ( bc ) hearing were averaged at 4 audiometric frequencies ( 500 , 1,000 , 2,000 , and 4,000 hz ) .
postoperative hearing gain was measured as unaided mean ac hearing minus aided mean free - field ac hearing .
postoperative ab gap was measured as aided mean free - field ac hearing minus mean bc hearing of better bone conduction ear .
we compared sophono with baha by the operation time , wound healing time , postoperative complications , postoperative hearing gain after switch on , and postoperative air - bone ( ab ) gap .
the operation time was calculated using operation record . the wound healing time was defined as the period from operation day to the day that regular outpatient visit for the wound care was no longer needed .
postoperative wound infection , skin overgrowth , reoperation , and other postoperative complications were investigated using medical record .
postoperative hearing gain , postoperative ab gap : mean air - conduction ( ac ) , and bone - conduction ( bc ) hearing were averaged at 4 audiometric frequencies ( 500 , 1,000 , 2,000 , and 4,000 hz ) .
postoperative hearing gain was measured as unaided mean ac hearing minus aided mean free - field ac hearing .
postoperative ab gap was measured as aided mean free - field ac hearing minus mean bc hearing of better bone conduction ear .
the mean time required for surgery was 60 minutes ( range , 40 to 105 minutes ) for sophono and 25 minutes ( range , 20 to 30 minutes ) for baha .
but , actual switch on of sophono was started from 4 weeks after surgery . in baha cases , there were 2 patients with abutment loosening .
skin infection , skin growth over the abutment , and fixture extrusion were not observed in any of these cases during follow - up period . in sophono cases ,
2 patients complained about pain around the external base plate after processor switch - on .
tables 1 and 2 are the demographic data and individual audiologic data of study population . at first , we compared the hearing improvement after switch on in bilateral aural atresia cases .
there were four bilateral aural atresia cases in baha and five bilateral aural atresia cases in sophono .
unaided mean ac hearing of baha was 62.5 db ( standard deviation [ sd ] , 1.8 ) .
aided mean free - field ac hearing of baha was 23.1 db ( sd , 8.9 ) .
aided mean free - field ac hearing of sophono was 29 db ( sd , 10.8 ) .
postoperative ab gaps of baha were 12.5 db at 0.5 khz , 6.2 db at 1 khz , 2.5 db at 2 khz , and 7.5 db at 4 khz .
postoperative ab gaps of sophono were 21 db at 0.5 khz , 10 db at 1 khz , 2 db at 2 khz , and 23 db at 4 khz .
the difference of ab gap between 2 groups was 8.5 db at 0.5 khz and 15.5 db at 4 khz .
however , the difference was not statistically significant ( 0.5 khz , p=0.17 ; 4 khz , p=0.16 )
. we compare the ab gap between the two groups , including the unilateral hl patients and other patients for measuring the actual amplification of 2 implants . in the unilateral hl patient ,
the postoperative ab gaps of baha were 10 db at 0.5 khz , 9.5 db at 1 khz , 4 db at 2 khz , and 8.5 db at 4 khz .
postoperative ab gaps of sophono were 26.6 db at 0.5 khz , 16.7 db at 1 khz , 8.3 db at 2 khz , and 26.7 db at 4 khz .
the difference of ab gap between the two groups was 16.6 db at 0.5 khz and 18.2 db at 4 khz .
the differences of postoperative ab gaps of 0.5 khz ( p=0.0024 ) and 4 khz ( p=0.02 ) between the 2 implants were statistically significant ( fig .
the audiogram of patient who was implanted with sophono and baha was shown in fig .
the mean time required for surgery was 60 minutes ( range , 40 to 105 minutes ) for sophono and 25 minutes ( range , 20 to 30 minutes ) for baha .
skin infection , skin growth over the abutment , and fixture extrusion were not observed in any of these cases during follow - up period . in sophono cases ,
2 patients complained about pain around the external base plate after processor switch - on .
tables 1 and 2 are the demographic data and individual audiologic data of study population . at first , we compared the hearing improvement after switch on in bilateral aural atresia cases .
there were four bilateral aural atresia cases in baha and five bilateral aural atresia cases in sophono .
unaided mean ac hearing of baha was 62.5 db ( standard deviation [ sd ] , 1.8 ) .
aided mean free - field ac hearing of baha was 23.1 db ( sd , 8.9 ) .
aided mean free - field ac hearing of sophono was 29 db ( sd , 10.8 ) .
postoperative ab gaps of baha were 12.5 db at 0.5 khz , 6.2 db at 1 khz , 2.5 db at 2 khz , and 7.5 db at 4 khz .
postoperative ab gaps of sophono were 21 db at 0.5 khz , 10 db at 1 khz , 2 db at 2 khz , and 23 db at 4 khz .
the difference of ab gap between 2 groups was 8.5 db at 0.5 khz and 15.5 db at 4 khz .
however , the difference was not statistically significant ( 0.5 khz , p=0.17 ; 4 khz , p=0.16 ) .
we compare the ab gap between the two groups , including the unilateral hl patients and other patients for measuring the actual amplification of 2 implants . in the unilateral hl patient ,
the postoperative ab gaps of baha were 10 db at 0.5 khz , 9.5 db at 1 khz , 4 db at 2 khz , and 8.5 db at 4 khz .
postoperative ab gaps of sophono were 26.6 db at 0.5 khz , 16.7 db at 1 khz , 8.3 db at 2 khz , and 26.7 db at 4 khz .
the difference of ab gap between the two groups was 16.6 db at 0.5 khz and 18.2 db at 4 khz .
the differences of postoperative ab gaps of 0.5 khz ( p=0.0024 ) and 4 khz ( p=0.02 ) between the 2 implants were statistically significant ( fig .
the audiogram of patient who was implanted with sophono and baha was shown in fig .
in this study , the operation time of sophono took 35 minutes longer than baha . during baha surgery with the single vertical incision without skin thinning technique , there was no need to reduce soft tissue or to elevate the flap .
it just required the 2.5-cm single post auricle incision reaching the periosteum . in the sophono surgery
in addition , sophono needed flap elevation and more drilling the skull for the internal device .
there was no major complication during surgery or postoperative period in both baha cases and sophono cases .
. however , hultcrantz   and soo et al .   reported that a simple vertical incision without skin thinning could reduce soft tissue complications . in this study , there was no soft tissue complication during the follow - up period .
baha in this study had only two abutment loosening cases that were solved by tightening the abutment in outpatient clinical setting .
in transcutaneous device , siegert reported a 4% rate of temporary pressure marks as the only complication in more than 100 patients .
however , oniel et al .   reported the skin complication rate was 35.7% , including skin breakdown ( n=2 ) and a patient younger than 5 years required a revision surgery . among our sophono cases ,
meticulous care is required when patient report pain around the baseplate , especially in young children because their skin and soft tissue is thin . in bilateral aural atresia cases of sophono ,
postoperative hearing gains in other reports were 29.7- to 43-db hl [ 9 - 12 ] .
it may be caused by the age of study group and previous operation history . in our sophono study ,
the average age of bilateral aural atresia patients was 19.4 years ( range , 5 to 33 years ) .
it was reported that postoperative hearing gain was 29.7 db in 10 subtotal petrosectomy patients . in that study , patients were adults with several operation histories .
when we compared the postoperative hearing gain between baha and sophono in bilateral aural atresia cases , baha was better than sophono .
postoperative hearing gains of baha and sophono were 39.4 db and 25.5 db , respectively .
the difference became clear when we compared all patients results at each frequency for comparing the actual amplification of two implants .
the difference of ab gap between 2 groups was 16.6 db at 0.5 khz and 18.2 db at 4 khz . despite limited number and diverse causes of patients comprised in the series , the difference of postoperative ab gap at 0.5 khz and 4 khz was statistically significant .
direct bone oscillation of baha could be thought to improve signal transmission . in comparative study between baha implant and baha headband ,
a 5 to 20 db increase in gain with baha implant compared to baha headband at 1 to 4 khz levels was reported .
although sophono fits the external processer better than headband , skin and soft tissue interference could influence signal transmission . it was reported that baha users exhibited 5 to 10 db better aided thresholds than sophono users in higher frequencies ( i.e. , 2,000 and 4,000 hz ) .
however , 500 and 1,000 hz aided hearing thresholds were similar to each other , which was slightly different from our result according to the frequency . this difference might be due to external sound processor .
they used baha divino ( cochlear ) and sophono alpha 1 system ( sophono inc . ) . in this study , baha bp100 , baha bp110 , and sophono alpha 2 were used .
another problem was that sophono patients complained of acoustic feedback when we gave more gain in low frequency . and follow - up period of each implant can influence the result .
this study is the comparative clinical study of postoperative aided hearings between baha and sophono with sound processor that is the most widely used at present .
 objectives bone - anchored hearing aids ( baha ) occasionally cause soft tissue problems due to abutment . because sophono does not have abutment penetrating skin 
 , it is thought that sophono has no soft tissue problem relating to abutment . on the other hand , 
 transcutaneous device s output is reported to be 10 to 15 db lower than percutaneous device . 
 therefore , in this study , sophono and baha were compared to each other from surgical and audiological points of view.methods we retrospectively reviewed the medical records of 9 sophono patients and 10 baha patients . in baha cases , 
 single vertical incision without skin thinning technique was done . 
 we compared sophono to baha by operation time , wound healing time , postoperative complications , postoperative hearing gain after switch on , and postoperative air - bone gap.results the mean operation time was 60 minutes for sophono and 25 minutes for baha . 
 the wound healing time was 14 days for sophono and 28 days for baha . 
 no major intraoperative complication was observed . 
 skin problem was not observed in the 2 devices for the follow - up period . 
 postoperative hearing gain of bilateral aural atresia patients was 39.4 db for baha ( n=4 ) and 25.5 db for sophono ( n=5 ) . 
 however , the difference was not statistically significant . in all patients included in this study , 
 the difference of air - bone gap between two groups was 16.6 db at 0.5 khz and 18.2 db at 4 khz . 
 baha was statistically significantly better than sophono.conclusion considering the audiologic outcome , baha users were thought to have more audiologic benefit than sophono users . however , sophono had advantages over baha with abutment in cosmetic outcome . 
 sophono needed no daily skin maintenance and soft tissue complication due to abutment would not happen in sophono . 
 therefore , a full explanation about each device is necessary before deciding implantation . 
INTRODUCTION
MATERIALS AND METHODS
Comparison parameters in this study
RESULTS
Operation time and healing time
Postoperative complications
Hearing improvement after switch on
DISCUSSION