[Bone union after lumbar postero-lateral fusion: comparative evaluation by x-ray and CT]

As yet there has been no report on a uniform and precise method for evaluating bone union after lumbar postero-lateral fusion (PLF). Here we report and compare the roentgenogram (X-P) and computerized tomography (CT) methods to evaluate the union and non-union of PLF. PLF without internal fixation was undertaken in 252 patients between 1978 and 1991. Of these, 125 patients underwent both X-P and CT scanning and were followed up for more than one year (mean 4 years and 2 months, range 1 to 14 years). In the cases of complete union, X-P demonstrated that the solid fusion mass showed a continuous trabecular pattern along the grafted segment, while CT demonstrated that the solid fusion mass appeared as a long bone with the mass incorporated into the transverse process and the superior facet. In such cases, there was no micromotion on stress roentgenograms. In the cases of incomplete union, the status of the non-union was classified into three types as; Type I showing atrophy and resorption of the grafted bone, Type II showing a lack in trabecular continuity of the fusion mass, and Type III showing a gap either cranially or caudally between the fusion mass and lumbar matrix (which includes the transverse process and superior facet). X-P could easily diagnose Type I and Type II, but could not clearly diagnose Type III. CT, however, could easily diagnose Type III. Therefore, the use of only X-P might lead to a misdiagnosis in cases of Type III. The application of CT was more uniform and precise method to evaluate the state of PLF in the lumbosacral spine.