A power operated rotary knife assembly including a power operated rotary knife having an annular rotary knife blade, a trim guide, and a drive mechanism for driving the rotary knife blade about an axis of rotation. The assembly also includes a portable power unit, a vacuum assembly and a flexible shaft drive transmission coupled between the power operated rotary knife and the portable power unit. The portable power unit includes a drive motor assembly providing a rotational power source which is operatively coupled to the drive mechanism through the flexible drive transmission to rotate the rotary knife blade. The portable power unit also includes a blower assembly providing vacuum pressure at an inlet duct side, the vacuum assembly being in fluid communication with the inlet duct side to generate a vacuum pressure condition in a region of a cutting opening defined by the rotary knife blade and the trim guide.