Abstract: The instrument connected to an ultrasonic oscillations source is provided with a knife to perform longitudinal mechanical oscillations at ultrasonic frequency during tissue separation. The working portion of the knife is essentially a plate made of a titanium alloy and having a pentogonal cross-section, a smooth rounding at the end thereof and two rows of teeth of triangular and wave-like shapes for separating osseous and cartilaginous tissue, respectively. A specific dimensional geometry of the instrument knife is described.