An assembly of devices that generates a high frequency electrical current and converts it into a high frequency mechanical oscillation (ultrasonic vibration) applied to a resorbable fixation pin on a surgically-drilled bone tunnel, to create friction and then heat so that the pin will flow into the tunnel and solidify (weld) with underlying porous bone after energy removal. It typically includes an energy generator, a reusable sonotrode handpiece with cables for energy conversion, and sonotrode tips for energy application. It is typically used during oral, maxillofacial/craniofacial, neurological, or paediatric surgical procedures, including corrective surgery for Apert or Crouzon syndrome.