FAILURE OF SYNTHES ANTERIOR CERVICAL FIXATION DEVICE BY FRACTURE OF MORSCHER SCREWS - A BIOMECHANICAL STUDY

Anterior cervical fixation using the Synthes system has become increas ingly popular. Two screw types for anchoring the plates include a ''so lid'' titanium expansion screw and a plasma-sprayed fenestrated expans ion screw that permits bony ingrowth. These screws were compared clini cally and in the laboratory. In our first 20 cases using Synthes plate s secured by Morscher fenestrated screws, 3 failures were observed, un ilaterally in 1 patient and bilaterally in 2 others. In the unilateral screw failure, the contralateral screw was ''solid'' and did not fail . In the mechanical studies, screws were secured in the Synthes plate and embedded into methylmethacrylate and subjected to a sinusoidal ben ding moment to the midshaft of the screw. Load deflection data and cyc les to failure were recorded. Fenestrated screws were found to demonst rate nearly twice as much deformation at failure and tolerated signifi cantly fewer cycles to failure than did ''solid'' screws (p < 0.05). B ecause benefits of bony ingrowth into the screw are not well identifie d, the risks of fenestrated screw failure should preclude their routin e use.