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ULBD for lumbar canal stenosis. Fig. 1-A Central canal stenosis can be managed by a unilateral approach with undercutting of the spinous process to access the contralateral lateral recess. The dotted lines represent the bilateral access achieved using the unilateral approach. Fig. 1-B A tubular or hinged-blade retractor system can be used for ULBD.
Initial bone exposure and removal as seen on different views (A, B, and C) of the lamina. For an L4-L5 decompression, bone removal starts at the inferior aspect of the superior lamina—i.e., the L4 lamina. The lamina bone is removed using a high-speed drill up to the attachment of the ligamentum flavum, which usually represents the uppermost aspect of the canal stenosis.
Angled curets and drills are key instruments for the ULBD procedure as they assist with contralateral decompression and removal of ligament and facet hypertrophy. Angled drills can provide access under the spinous process and contralateral lamina, and angled curets can decompress “around corners” to achieve adequate decompression of the neural elements of the contralateral lateral recess.
Sequence of the procedure. Fig. 4-A Initial unilateral exposure for a right-sided approach. Fig. 4-B The inferior half of the L4 lamina has been drilled and the base of the spinous process to expose the ligamentum flavum bilaterally to the insertion point deep to the L4 lamina (arrow). LF/L = left ligamentum flavum, and LF/R = right ligamentum flavum. Fig. 4-C Decompression of the contralateral (left) side. Fig. 4-D Photograph made at the completion of the operation, demonstrating bilateral decompression from a right-sided unilateral approach. The arrows demonstrate the midline of the thecal sac.