The incudostapedial joint angle: Implications for stapes surgery prosthesis selection and crimping

Objective: To evaluate the role of the incudostapedial joint (ISJ) angle in stapes prosthesis size selection and crimping. Methods: The ISJ of 13 cadaveric human temporal bones were photographed, then measured using computer-aided design software. The relationship of ISJ angle to prosthesis length was modeled. A literature review evaluated factors contributing to stapedectomy failure. Results: The mean ISJ angle was 93.0degrees (SD = 8.3degrees) (range, 75.0degrees - 104.0degrees). The mean ISJ angle deviation from 90 was 7.35degrees (SD = 4.45degrees) (range, 0.3degrees -15.0degrees). The mean distance along the incus accessible for prosthesis placement was 3.21 mm (SD = 0.55 mm) (range, 2.00-4.00 mm). Conclusions: Significant deviation of the ISJ angle from 90degrees was found (P < .0001). The length along the incus accessible for prosthesis placement was sufficient to result in errors in prosthesis size selection and crimping with only small variations in the ISJ angle. Incorrect prosthesis sizing and crimping are frequently associated with stapedectomy failure. Variations in ISJ anatomy should be considered when selecting stapes prostheses lengths and may affect crimping technique.