The Bone Anchored Hearing System: Understanding and improving clinical outcomes

Hearing loss is a significant impairment affecting approximately 5% of the population. Hearing loss can usually be treated with conventional hearing aids or reconstructive ear surgery.

Unfortunately, some individuals do not benefit from these solutions. In 1977 the Bone Anchored Hearing System (BAHS) or BAHA was introduced. The BAHS consists out of a percutaneous implant which is integrated in the skull and a sound processor that is attached to the implant. This system is a proven hearing rehabilitation option with good outcomes. Nevertheless, there is room for improvement. The most common complication is inflammation of the skin around the implant. The etiology of this is believed to be multifactorial including skin movements, inflammatory responses and surgical technique. In this thesis, a new single hole technique called Minimally Invasive Ponto Surgery (MIPS) is compared to the current recommended technique in a Randomized Controlled Trial (RCT). The results show no difference in rate of inflammation between techniques. Secondary outcome measures such as esthetics, numbness adjacent to the implant and surgical timings were superior in the MIPS group. Pain scoring showed no differences. Although not significantly lower, implant loss is a concern related to MIPS surgery. Concluding, MIPS is a new technique showing promising results for bone anchored hearing surgery.

In a proof of principle study, we evaluated the use of Cone Beam CT to analyze the seating of an implant post-surgery.

To obtain further knowledge on immune responses and bacterial alterations, samples were obtained during surgery, at 12 weeks follow-up and during additional episodes of inflammations. qPCR analyses of cytokines showed that IL-1β, IL-8, MMP-9, TIMP-1 and COL1α1 were significantly higher during follow-up and IL-6 and FGF-2 were significantly down-regulated. Within individuals no differences were observed between samples obtained during surgery and during episodes of inflammation. Moreover, smoking was associated with increased MMP-9 expression. An explorative analysis showed significant higher levels of IL-1β and IL-17 in samples obtained during episodes of inflammation than samples from individuals without inflammation during follow up.

All bacteria on the implant and skin are defined as microbiome. The microbiome was evaluated using a novel molecular technique, IS-pro™. Overall bacterial diversity measured with the Shannon Diversity Index was increased post-implantation for skin bacteria, but not for all bacteria combined. No significant differences in microbiome were found during episodes of skin inflammation. Common known bacteria including Staphylococcus epidermidis, Streptococcus pneumoniae/mitisand Haemophilus parainflenzaewere observed on the skin penetrating part of implant and surrounding skin. Streptococcus pneumoniae/mitiswere significantly more present on the post-surgical samples and Propionibacterium acneswere observed significantly less often. Staphylococcus epidermidisand Staphylococcus aureuswere observed most often during episodes of inflammation.

Finally, a case report describing chronic pain post-surgery is presented. This case shows clear evidence of osseointegration. Although macroscopically no signs of bacteria or inflammation were observed, in depth analyses show evidence of chronic inflammation and invasion of the peri-implant soft tissue and bone.

This thesis might contribute to further evaluation of percutaneous devices and our understanding of implant related inflammation and infection.