Round and Oval Window Anatomic Variability: Its Implication for the Vibroplasty Technique.

OBJECTIVE: The objective of this study is to evaluate the anatomical variability of round and oval window regions and its relationship with their closest structures, to determine its implication on the fitting and stabilization of the middle ear implant Vibrant Soundbridge.

METHODS: Variations of the anatomy of round and oval window regions were assessed in a total of 85 human dissected temporal bones. Afterward, we evaluated the adaptation and subsequent stabilization of the floating mass transducer (FMT) of the Vibrant Soundbridge in 67 cases in round window (RW) and in 22 cases in oval window (OW), and the influence that the variability of the different anatomical features examined had on this stabilization. We also assessed access and surgeon's view of the RW niche through the facial recess approach.

RESULTS: Stabilization of the FMT in the RW was achieved in 53 (79%) of the 67 cases; we found that the less favorable anatomical conditions for stabilization were: membrane smaller than 1.5 mm, presence of a high jugular bulb and a narrow or very narrow RW niche. Frequently, two or more of these conditions happened simultaneously. In seven cases (22%) access to the RW through facial recess approach did not allow positioning the FMT in place. OW stabilization succeeded in 18 (82%) of the 22 cases.

CONCLUSION: Round and oval window vibroplasty are difficult surgical techniques. To place the FMT directly on the OW may be easier as we do not have to drill the niche. In both regions there are some anatomical conditions that hinder fitting the FMT and even make it impossible. Once fitted, the main problem is to achieve good stabilization of the device.