Background and Aims A freely available visual guide with optimal angles for paramedian approaches, depending on the skin-dural sac distance (S-DS-d) (http://diposit.ub.edu/dspace/handle/2445/179594 ) and viable paths for needle insertions, perpendicular to the back, below the upper spinous process in a given interspinous space, had been described. Our aim was now to verify needle location applying the guide in ex-vivo samples.
Methods Random selection of ex-vivo samples with flexed lumbosacral spines (n=7), determination of S-DS-d in the interspinous spaces by ultrasound, needle insertions at axial 0°, below the upper spinous process at different interspinous spaces, from L4-L5 to L1-L2 [n=42; median (n=21), 1cm paramedian (n=16) or individualized paramedian, previsualizing the longest interlaminar height, pre-estimating the angle by means of a protractor (n=5)], computed tomography, three-dimensional reconstruction and verification of needle location (figure 1).
Results When osteoporotic compression fracture was found (38%), the contact between adjacent spinous process impeded the median approach (figure 2), but most needle insertions were located within the spinal canal in the other cases (85.7% median or 81% 1cm paramedian) (figure 3). In 23% the needle remained within the canal beside the dural sac. In 13% a certain bone penetration occurred. Individualization of the paramedian approach led to successful insertions at very variable angles and distances (up to 32,2° and 2,64 cm paramedian, respectively).
Conclusions Ultrasound may indicate if the interspinous space is visible. Then, the insertion of needles at 0° regarding the axial plane, taking the upper process as reference, is viable. If not, the alternative optimal paramedian approach must be individualized in fractured or rotated spines.
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