Bone conduction implants are hearing devices that require osseointegration to create a stable and reliable interface between the hearing device and the skull to deliver sound to the cochlea. This article reviews the physiology of osseointegration, factors that may lead to failure of this and what we could do as clinicians to avoid failure of osseointegration in patients. Osseointegration occurs between the implant, which is pure titanium compositions for otological implants, and bone. There is an initial inflammatory response to trauma, followed by fibrin matrix aggregation; mesenchymal cells differentiation into osteoblasts and subsequently mineralisation of the implant-bone interface. The key with osseointegration is that, once completed, the titanium oxide layer of the implant is permanently incorporated within the bone such that any removal will require fracture of the bone.

A meta-analysis found higher rate of failure of osseointegration in the paediatric population and patients older than 60 years. Unsurprisingly, patients with osteoporosis are more likely to have implant failures but if the patients are on bisphosphonates, implant stability seemed to improve. Other preoperative considerations include patient’s nutritional status, smoking status, radiotherapy and systemic illness such as rheumatoid arthritis.

In such patients, a two-staged procedure may be indicated. Intraoperatively, continuous cooling with irrigation and low speed drilling is key to reduce the risk of bone necrosis. The authors also found meticulous postoperative care of avoiding any trauma to the implant key as repetitive micromotion of the implant can lead to formation of fibrous tissue disrupting the bone-implant contact and subsequent loosening of implant.

Physiology of osseointegration.
Lee JWY, Bance ML.
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Wai Sum Cho

Queens Medical Centre, Nottingham, UK.

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