Drill-free Screws

Klaus Louis Gerlach and Wolfgang Heidemann

Introduction

In craniomaxillofacial surgery, the use of self-tapping bone screws is now virtually universal in osteosynthesis to stabilize most skeletal and mandibular fractures and deformities. The requirement of drilling a pilot hole to use conventional self-tapping screws is a time-consuming extra step, which has some potential disadvantages. These include damage to nerves, tooth roots or germs, thermal bone necrosis, screw stripping due to an overdrilled pilot hole especially in thin cortical or soft cancellous bone, drill bit breakage, improper drill-bit size selection and, finally, the extra cost of single-use drill bits.

Normally, self-tapping screws (Champy et al., 1976b) have asymmetric threads with sharp edges to the screw shaft. The surface of the threads is nearly perpendicular to the direction of pull-out force, to provide maximum load transmission. The thread spirals around a cylindrical core with a pitch (the distance between the threads) of 0.75 mm or 1 mm. A cutting flute is engraved at the leading end of the threaded portion of the screw (Fig. 28.1).