Management of the Incus Body in Ossiculoplasty

Abstract

Objective: 1) Evaluate the sound transfer impact of removal of the incus body in ossicular chain reconstruction (OCR) utilizing an incus strut prosthesis. 2) Provide basic science data to guide clinical decision making in ossiculoplasty. Method: OCR with an incus strut prosthesis was performed on 7 human temporal bones with and without the incus body. The difference in round window membrane (RWM) peak- to-peak displacements (90-dB SPL, 250 to 8000 Hz) using single-point laser Doppler vibrometry (LDV) was compared to observed baseline, intact ossicular chain values. Results: For each of the 7 temporal bones, the average displacement decreased across most sound frequencies with OCR as compared with baseline. Median velocity differences (×10–3), with 95% confidence intervals in parentheses, from baseline for OCR with incus were 4.8 mm/s (2.1-6.4), while median differences from baseline for OCR without incus were 3.0 mm/s (1.7-4.2). A signed-rank test yielded P = .002, implying the median velocity is significantly lower when the incus body is removed. Secondarily, a variance ratio test showed no difference in variability between the 2 study arms ( P = .925). Conclusion: Removal of the incus body in OCR utilizing an incus strut prosthesis significantly reduces the sound transfer function of the middle ear relative to its preservation. The finding suggests that preserving the incus body may stabilize the malleus and the tympanic membrane.