Mobility provocation radiostereometry in anterior cervical spine fusions

This study aimed to evaluate the use of mobility-provocation radiostereometry (RSA) in anterior cervical spine fusions and compare the results to deformation studies on the same patients and plain flexion-extension radiographs. Mobility-provocation RSA was used to evaluate anterior cervical spine fusions in 45 patients. The motions recorded at 3 and 12 months postoperatively were compared to RSA measurements of deformation of the fusion over time and to plain flexion-extension radiographs in the same patients taken 3 months postoperatively. Studies of rotations from right to left revealed ten cases with significant motion at 3 months, and three at 12 months. With motion from flexion to extension, ten cases showed significant motion at 3 months and three at 12 months. In only three cases was the mobility-provocation RSA considered to add any information on the stability of the fusions compared to that obtained with the deformation studies. In 37 patients mobility-provocation radiography in flexion-extension using conventional technique was done to evaluate the accuracy. The mean difference between angular motions recorded on plain radiographs and rotations around the transverse axis in flexion to extension recorded with RSA was 1.6° (range 0.04°–8.04°, SD 2.1°). The corresponding 95% and 99% confidence limits for the difference between the two methods were 5.8° and 7.2°. The study showed that the use of mobility-provocation RSA did not add any information over that obtained by deformation RSA studies. Conventional radiography is too inaccurate to measure inducible displacement in this patient population.