Anatomic considerations in lumbar posterolateral percutaneous procedures

Study Design. Intervertebral foraminal anatomy of L2-S1 was investigated by the anatomic dissection of 96 foraminal levels in 12 human cadaveric spines. Objectives. The goal of this study was to determine the dimensions of th "safe zone" and a safe point of insertion in percutaneous intradiscal procedures and the largest safe working cannula diameter. Summary of Background Data. Working cannulas are used in percutaneous lumbar procedures. The dimensions of the safe zone of insertion and determination of the optimal cannula size based on these measurements and point of insertion are unclear from the literature. Methods. Safe zone dimensions from L2-L3 to L5-S1 were determined as were two cannula diameters, C1 and C2.C1 was the maximal cannula size that can be placed within the safe zone.C2 is the maximal size allowable when the point of insertion lies in the midline of the pedicle. Results. The average triangular safe zone was 18.9 mm wide and 12.3 mm high; the hypotenuse measured 23.0 mm.The maximum C1 diameter ranged 5.0-10.0 mm. The corresponding safe point of insertion lay along the medial one third of the pedicle. The maximum C2 diameter ranged 4.0-8.9 mm. The corresponding safe point of insertion lay in the midline of the pedicle. Conclusions. Either a 7.5-mm cannula placed in line with the medical one third of the pedicle or a 6.3-mm cannula located in the midline of the pedicle appears safe.