An in vitro comparison of hollow ground and trocar points on threaded positive-profile external skeletal fixation pins in canine cadaveric bone

Objective-To compare the microstructural damage created in bone by pins wit h lathe-cut and rolled-on threads, and to determine the peak tip temperatur e and damage created by positive-profile external fixator pins with either hollow ground (HG) or trocar (T) tips during insertion. Study Design-An acute, in vitro biomechanical evaluation. Sample Population-Twenty-seven canine tibiae. Methods-Lathe-cut thread design with T point (LT-T), rolled-on thread desig n with T point (RT-T), and rolled-on thread design with HG point (RT-KG) pi ns were evaluated. Twenty pins of each type were inserted under constant dr illing pressure into 12 canine tibiae (12 diaphyseal and 8 metaphyseal site s per pin type). Peak pin tip temperature, drilling energy, end-insertional pin torque, and pullout force were measured for each pin. For the histolog ic study, five pins of each type were inserted into cortical and cancellous sites in 15 additional tibiae. Entry and exit damage, and thread quality w ere assessed from 100 micron histologic sections by using computer-interfac ed videomicroscopy. Results-T-tipped pins reached higher tip temperature in both diaphyseal and metaphyseal bone compared with HG-tipped pins. RT-T pins had higher pullou t strength (diaphyseal) and end-insertional torque compared with other comb inations. No differences in drilling energy or insertional bone damage was found between the three pin types (P < .05). Conclusions-T-tipped pins mechanically outperformed HG-tipped pins. Pin tip and thread design did not significantly influence the degree of insertiona l bone damage. Clinical Relevance-T-tipped pins may provide the best compromise between th ermal damage and interface friction for maximizing performance of threaded external fixator pins. (C)Copyright 1999 by The American College of Veterin ary Surgeons.