Metallurgical Considerations in Shape-Memory Nitinol Middle Ear Prosthetics

Abstract

Objectives:

At the conclusion of this presentation, the participants should be able to 1) describe how the metallurgical phenomenon of creep may be involved in the failure of nitinol middle ear devices, and 2) describe how other metallurgical phenomena such as microfractures can also be involved.

Methods:

Retrospective literature review of nitinol middle ear device failure; retrospective literature review of known metallurgical properties of nitinol such as creep and microfractures; and prospective survey of otologic surgeons. Study period: January 2001 to present (literature review), and 2011 to present (survey). Condition studied: Delayed conductive hearing loss after stapes surgery. Subjects studied: Patients with otosclerosis described in previous studies who underwent surgery with nitinol shape-memory devices. Surgeons who implanted such devices. Interventions: Analysis of known metallurgical properties of nitinol applied to results obtained with such devices.

Results:

A comprehensive literature review revealed many instances of delayed conductive hearing loss after middle ear surgery with nitinol shape-memory devices. A survey of otologic surgeons by the author revealed 50% of surgeons reporting “loose-wire” syndrome as a delayed complication of such surgeries, signifcant to P < 0.05 confidence level (94 surgeons).

Conclusions:

1) “Loose-wire” syndrome is a frequent complication encountered by surgeons performing middle-ear surgery with nitinol shape-memory devices. 2) Metallurgical properties of nitinol such as creep (deformation over time as a result of stress) and microfractures may theoretically be responsible. 3) Additional metallurgical laboratory analysis of nitinol is indicated in order to explain and prevent such complications.