Anterior lumbar interbody fusion: changes in area of the dural tube, disc height, and prevalence of cauda equina adhesion in magnetic resonance images.

OBJECTIVE

Many investigators have reported satisfactory outcome in anterior lumbar interbody fusion (ALIF) performed for lumbar disc herniation or "multiply operated back" (MOB), but without comparing preoperative and postoperative dural tube area and cauda equina adhesion in magnetic resonance imaging (MRI). We conducted this study to determine these data in ALIF performed for lumbar disc herniation and MOB.

METHODS

Thirty-two patients who underwent ALIF, involving 38 discs, were studied. In MRI obtained before and after surgery (interval 9-48 months, mean 19.2 months), cross-sectional areas of the lumbar dural tube were measured from axial T2-weighted images using a computer-linked digitizer. At 30 disc levels operated on, the cauda was identified in images; cauda equina adhesions were classified according to Matsui et al (grade I-III). Clinical improvement was scored.

RESULTS

Bony union was observed in radiographs of all patients. Preoperative and postoperative cross-sectional areas of the lumbar dural tube were 1.32 +/- 0.4 and 1.87 +/- 0.5 cm, respectively, and expansion ratio was 1.43 +/- 0.4. Recovery did not correlate with expansion ratio. Positive correlation was noted between expansion ratio and disc height ratio. At 30 disc levels where cauda equina was identified, 22 represented grade I and 8 represented grade II. At three of the latter, prior surgery had been performed via a posterior approach.

CONCLUSIONS

No significant difference was noted in occurrence of grade II adhesions between primary ALIF and ALIF performed for MOB. Dural tube expansion was accomplished even without exposure of the tube, and cauda equina adhesion was uncommon in primary ALIF.