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Implications of Lumbar Plexus Anatomy for Removal of Total Disc Replacements Through a Posterior Approach

Study Design. An anatomic study in which the lumbar plexuses of 14 embalmed cadavers were dissected bilaterally and measured using a posterior approach. Objective. To determine the cephalocaudal (root-to-root) distances and the mediolateral (root-to-tether) distances within the lumbar plexus and determine the feasibility for removal of a lumbar total disc replacement (TDR) through these anatomic spaces using a posterior approach. Summary of Background Data. Currently, lumbar TDRs are implanted primarily through an anterior retroperitoneal or transperitoneal approach. However, revision surgeries through these approaches can be complicated by significant adhesions, with potential injuries to intra- and retroperitoneal contents. Advancements in accessing anterior column structures through a posterior lumbar extracavitary approach suggest that posterior removal of TDRs may be an alternative. Unlike the thoracic extracavitary approach in which ligation of the thoracic nerve rarely leaves significant morbidity, the lumbar extracavitary approach cannot rely on the analogous ligation of the lumbar root to achieve access. Therefore, feasibility of the lumbar extracavitary approach depends on the presence of sufficient anatomic space between the tethered nerves of the lumbar plexus. Methods. Fourteen adult cadavers (5 M/9F) were dissected through a posterior approach to expose the lumbar plexus bilaterally. The root-to-root distances at levels L2–S1 and corresponding root-to-tether distances at levels L3–L5 were measured bilaterally. Results. Root-to-root distance was smallest at the male L5–S1 interval (11.7 ± standard deviations 4.1 mm). Root-to-tether distance was smallest at the female L5 (43.1 ± standard deviations 8.4 mm). These plexus measurements compare favorably with the CHARITÉ TDR components, in which the thickest sliding core is 11.0 mm in height and the largest endplate is 42.0 mm in width. Conclusion. This anatomic study suggests that posterior TDR removal is possible in the lumbar spine without undue risk to the surrounding nervous structures.