Stapedectomy in Sheep: An Animal Model for Surgical Training

Hypothesis and Background: Stapedectomy is a surgical technique that requires progressive training. The external and middle ear of sheep have a close resemblance to the human and have been previously used as surgical training models. In our project we describe the anatomy of the middle and external ear in sheep focusing on surgical landmarks and technique in order to determine whether the sheep's ear is an adequate model for stapedectomy training. Materials and Methods: We reviewed the literature on sheep anatomy and use of sheep as an otologic surgical model. Macroscopic sections as well as temporal bone computed tomography were obtained. Stapedectomy was performed on 40 sheep, using 4 mm platinum piston prosthesis, by first year residents. Results: Most of the structures in the sheep's middle ear are similar to those in humans although their size is about two thirds smaller. Incus long process is shorter, thicker, and closer to the malleus body, making the piston insertion and adjustment more difficult. The median surgical time of stapedectomy was reduced from 70 (52,5-100,3) minutes to 39,5 (35,5-48) minutes after completing training. There was also a reduction in rate of complications (flap disruption, incus dislocation, and footplate mobilization). Conclusion: Sheep ears constitute a cheap, easy to obtain and anatomically adequate model for stapedectomy training.