LAUSR

OBJECTIVE Lumbar epidural lipomatosis (LEL) is a rare condition defined as the excessive accumulation of epidural fat (EF). We herein investigated the indicators of the posterior compression factors, EF and yellow ligament (YL), and to identify the clinical features of LEL. METHODS Five hundred consecutive patients who underwent posterior lumbar decompression surgery for lumbar spinal stenosis (LSS) were retrospectively reviewed. The EF/SC-L index (the ratio of the antero-posterior length of the EF to that of the spinal canal (SC)), was evaluated at the spinal level that exhibited maximum dural tube compression. The participants were divided into three groups: grade I, EF/SC-L index ≤50%; grade II, EF/SC-L index 51-74%; grade III, EF/SC-L index ≥75%. EF/SC-A (the ratio of the cross-sectional area of EF to that of SC) and YL/SC-A (the ratio of the cross-sectional area of YL to that of SC) were calculated. The clinical outcomes were assessed according to the Japan Orthopaedic Association scale for lumbar disease. RESULTS EF/SC-L exhibited a significantly positive correlation with EF/SC-A (r=0.82, p<0.001), and a negative correlation with YL/SC-A (r=-0.71, p<0.001). The JOA recovery rate was 56.7±22.6 in the case-matched control group, 34.5±31.2 in the grade II group (p<0.001) and 39.6±24.9 in the grade III group (p=0.032). CONCLUSIONS EF/SC-L index is a simple and reliable indicator to quantitatively evaluate posterior compression in patients with LSS. As the accumulation of EF is associated with worse operative outcomes, the EF/SC-L index should be considered when planning lumbar decompression surgery for patients with LSS.