RESUMEN
BACKGROUND: Tuffier's line is often used as a landmark for lumbar puncture. When attempting to identify lumbar interspaces using Tuffier's line, the actual level often turns out to be higher or lower than presumed. The imaginary line that joins both posterior superior iliac spines on the sacrum (posterior superior iliac spine line; PSIS line) can be physically constructed. The purpose of this study was to assess the posibility that the PSIS line could be used as a marker of lumbar spine level. METHODS: After informed consent had been obtained, sixty-seven patients undergoing lumbar spine surgery were examined. The identification of the L4-5 interspinous space was performed in the prone position using a radioluscent wilson frame (RWF-1000 Model 5323, OSI, USA) after general anesthesia. In the same patients, Tuffier's line and the PSIS line were used to determine the level of needle insertion into the L4-5 interspinous space. At first, the L4-5 interspinous space was identified by palpating the interspinous space, two levels above the PSIS line, and then a mark was drawn on the skin. Second, the L4-5 interspinous space was identified and marked by streching a silk between the two iliac crests to construct Tuffier's line. Needles were inserted into the accounted spaces at each marking level. Using a radiologic imaging method, the actual levels were confirmed. RESULTS: By using the Tuffier's line method of identifying the L4-5 interspinous space, 73.1% of needles were inserted correctly, whereas using the PSIS line method of identifying the L4-5 interspinous space, 74.6% of needles were inserted into the correct space. CONCLUSIONS: We conclude that the PSIS line may be as useful as Tuffier's line for determing the lumbar spine level.