The aim of this study was to retrospectively review clinical outcomes of posterolateral fusion for 50 consecutive patients with unstable lumbar spine and to determine which radiological factors affect clinical results. Patients with poor outcomes were older and had a greater number of fused segments than did those with good outcomes. Except for these, there were no relationships between clinical preoperative factors and outcomes on follow-up examination. At follow-up, decrease in lordosis and increases in slippage and L1 axis S1 distance (LASD) (which was measured as the distance along the perpendicular axis from the center in the L1 body to the posterior superior edge of the S1 body) were found in patients with poor surgical outcomes. The slippage on follow-up examination was significantly greater in patients with LASDs above 35 mm, preoperatively, than in those whose LASD was less than 35 mm. The lesions of adjacent segments and bony union rate did not influence the clinical results. A preoperative radiological risk factor is LASD greater than 35 mm, which was associated with an increase in the slippage at follow-up. Maintenance of lumbar lordosis and an LASD below 35 mm and after the surgery, may improve clinical outcomes.
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Kawakami et al. (1998) studied this question.