Clinical Outcomes of Soft Tissue Preservation Surgery With Hydroxyapatite-Coated Abutments Compared to Traditional Percutaneous Bone Conduction Hearing Implant Surgery-A Pragmatic Multi-Center Randomized Controlled Trial

Abstract

Background: Soft tissue preservation using a hydroxyapatite-coated abutment in bone conduction hearing implant surgery may lead to improved clinical outcomes over the short (1 year) and long term (3 years). Methods: In this open multi-center, randomized (1:1), controlled clinical trial, subjects with conductive, mixed hearing loss or single-sided sensorineural deafness were randomly assigned to receive the conventional intervention, a titanium abutment with soft tissue reduction surgery (control), or a new intervention, a hydroxyapatite-coated abutment with soft tissue preservation surgery (test). The primary efficacy outcome was the combined endpoint of numbness, pain, peri-abutment dermatitis, and soft tissue thickening/overgrowth after 1 and 3 years. Results: The Intention-to-treat (ITT) population consisted of 52 control subjects and 51 test subjects. The difference between the groups after 1 year of follow-up as measured by the primary efficacy outcome was not statistically significant (p = 0.12) in the ITT population (n = 103), but did reach statistical significance (p = 0.03) in the per-protocol (PP) population (n = 96). It showed an advantage for the test group, with over twice as many subjects (29%) without these medical events during the first year compared to the control group (13%). After 3 years, the difference between the two groups had declined and did not reach statistical significance (24 vs. 10%, ITT p = 0.45). Secondary outcome measures which showed a statistical significant difference during the first year, such as surgical time (15 vs. 25 minutes, p < 0.0001), numbness (90 vs. 69% of subjects experienced no numbness at 1 year, p < 0.01), neuropathic pain at 3 months (p = 0.0087) and the overall opinion of the esthetic outcome (observer POSAS scale at 3 months, p < 0.01) were favorable for the test group. More soft tissue thickening/overgrowth was observed at 3 weeks for the test group (p = 0.016). Similar results were achieved for the long term follow up. Conclusions: Soft tissue preservation with a hydroxyapatite-coated abutment leads to a reduction in the combined occurrence of complications over the first year which is not statistically significant in the ITT population but is in the PP population. This effect decreased for the long-term study follow up of 3 years and did also not reach statistical significance.

Keywords: BAHA; RCT - randomized controlled trial; hydroxyapatite; soft tissue preservation; surgery.

Figure 1

Overview of the abutment design and soft tissue status after surgery. (A) The hydroxyapatite-coated titanium abutment is placed in full thickness skin in the test group. (B) The all-titanium abutment is placed in skin where subdermal tissue has been removed using soft tissue reduction in the control group. Both abutments connect to the same implant fixture, which is placed in the skull bone behind the ear.

Figure 2

Randomization, treatment and follow-up of subjects during the study. *Due to wrong device allocation in the control group, one subject (randomized to the control group) is considered in the safety population of the test group.

Figure 3

The primary combined endpoints. (A) Stacked bar chart showing the percentage of subjects presenting with 0, 1, 2, 3, or 4 of the four important medical events (Holgers Index > 1, soft tissue thickening/overgrowth > 1, Pain > 2 or the presence of numbness) comprised in the combined primary variable at any point over the first year and until the end of the study. Every event is counted only once per subject. (B) Time of onset of these events presented per patient, which enables an individual and group analyses over time. The stepwise increase in intensity (in green) illustrates an incremental amount of experienced medical events (a blank bar representing 0 events). The graph does not show the duration of the events. The last day of data collection in the study for the first year is indicated by a vertical line.

Figure 4

Numbness severity per visit. Paired bar chart of the percentage of numbness around the abutment in the test and control group per study visit. P-values for the difference between groups are presented. *Denotes a significance level of p < 0.05.

Figure 5

Pain severity per visit. Paired bar chart of the percentages of (A) neuropathic pain and (B) direct pain surrounding the abutment and/or scar. P-values for the difference between groups are presented. *Denotes a significance level of p < 0.05.

Figure 6

Soft tissue thickening/overgrowth and visible abutment length. (A) Paired bar chart of the Soft tissue thickening/overgrowth scale of the test group and control group. P-values for the difference between groups are presented. (B) Mean visible abutment length over time (linearly interpolated between visits). Dashed lines represent the 95% confidence intervals for the mean. *Denotes a significance level of p < 0.05.

Figure 7

Peri-abutment dermatitis measurements. (A) Paired bar chart of the percentages of the Holgers index per scheduled visit. (B) Mean Holgers score over time recorded at scheduled study visits and unscheduled extra visits (adverse event). As there are more subjects with a Holgers Index of 0 at any point in time, the mean Holgers Index is lower than the lowest state of inflammation (Holgers Index of 1). Dashed lines indicate 95% confidence intervals for the mean. (C) Changes in Holgers index between scheduled visits for the test group. (D) Changes in Holgers index between scheduled visits for the control group. The numbers in the circles show the percentage and number of subjects per Holgers state at each time point. The numbers on the lines describe the numbers of subjects that undergo a state change between time points. The number in the squares represents the number of subjects that are a lost to follow up. Some connections do not sum due to missing data.