Evaluation of a new monocortical screw for anterior cervical fusion and plating by a combined biomechanical and clinical study.

The purpose of this combined study was to evaluate the stability and safety of a new monocortical screw-plate system for anterior cervical fusion and plating (ACFP) according to Caspar in comparison with classical bicortical fixation. In the biomechanical part of the study two groups, each comprising six fresh human cadaveric spines (C4-C7), matched for bone mineral density, additionally resulting in almost the same mean age, were used. Range of motion and neutral zone were analyzed in flexion-extension, rotation (left, right) and lateral bending (left, right) using pure moments of +/- 2.5 Nm for each specimen in the intact state, after discectomy at C5/6 and after discectomy at C 5/6 followed by bone grafting plus plating (Caspar plates), with either monocortical or bicortical screws. For all three motion planes, no significant difference could be found between the new monocortical and the bicortical fixation techniques. The clinical part of the study was performed as a prospective study on 30 patients suffering from symptomatic degenerative cervical disc disease in one segment. At the latest follow-up, no hardware- or graft-related complications were seen in any of the patients. Following these findings monocortical screw fixation can be recommended for the majority of anterior cervical fusion and plating procedures in degenerative disease, making the procedure quicker, easier, and safer. Bicortical screw fixation still has specific indications for multilevel stabilization, poor bone quality (osteoporosis, rheumatoid disease - as bicortical oversized rescue screw), unstable spines (trauma, tumour) and in particular for the realignment of kyphotic deformities (restoration of the normal lordotic curve). Due to the design of the study the results apply only to surgical treatment of monosegmental degenerative disc disease at the time.