RADIOLOGICAL FOLLOW UP OF PATIENTS AFTER ANTERIOR CERVICAL FUSION WITH CONVENTIONAL AND POLYAXIAL LOCKING PLATES

Abstract

Introduction Locking plates are the most used devices for achieving anterior cervical spinal fusion and offer considerable advantages such as faster and easier implantation and fewer implant-related failures than older plate systems. Recently polyaxial locking screws were introduced to make the implantation of these plates even easier by facilitating the implantation of the screw in all directions. However polyaxial screws may have the disadvantage of losing the angular stability with subsequent failure of the plate. The aim of this study was the radiological follow up of the patients with polyaxial screw and to compare them with the conventional looking plates.

Methods Patients underwent anterior cervical discectomy and fusion in which either ventral cervical locking plates or a polyaxial locking screw were used for indications including cervical spondylotic radiculopathy, disc herniation, trauma, and myelopathy. Patients underwent anterior cervical discectomy and interbody fusion and / or corpectomy. Preoperative and postoperative radiographic data included sagittal angle, translation, and settling of the graft.

Results One hundred and forty patients were investigated (mean age of 49 years) with an average follow up period of 21.5 months (range from 4 to 50 months). All underwent anterior cervical plate fusion as a component of the surgical treatment for symptomatic degenerative cervical spinal disease (55%) or for vertebral destruction caused by trauma (45%).100 (71%) of patients were treated with a conventional locking plate and 29 % with a plate with polyaxial screw fixation. Besides plate fixation, 4 of the 140 patients had a combined ventrodorsal fusion. In 46 cases (25%), one or more vertebral bodies were removed and replaced with either iliac bone graft (two levels, 21% of all cases) or fibula strutgraft (4%). In the group with conventional locking plates no patient had to be revised, 3 showed a subluxation (up to 1/3 of the vertebral body diameter) and 2 screw back out posteriorly without clinical relevance. In the group with the plate with polyaxial screw fixation two patient had to be revised (posterior stabilisation) because of subluxation due to loss of angular stability of the screws and one patient developed subluxation of 1/3 of the vertebral body also due to loss of angular stability.

Discussion The complication rate and the revision rate for anterior cervical discectomy and fusion with plates with and without polyaxial screw fixation were similarly low. Polyaxial screw may have the theoretical disadvantage of loosening with loss of the angular stability and subsequent failure necessitating revision.