SPINE Volume 33, Number 9, pp E274 –E278 ©2008, Lippincott Williams & Wilkins Implications of Lumbar Plexus Anatomy for Removal of Total Disc Replacements Through a Posterior Approach David B. Bumpass, BS,* Thomas C. Keller, BS,* Elliot P. Robinson, BA,* Ian Marks, MSc, PA-C,† Michael Iwanik, PhD,‡ Vincent Arlet, MD,† and Francis H. Shen, MD† Study Design. An anatomic study in which the lumbar plexuses of 14 embalmed cadavers were dissected bilat- erally and measured using a posterior approach. Objective. To determine the cephalocaudal (root-to- root) distances and the mediolateral (root-to-tether) dis- tances within the lumbar plexus and determine the feasi- bility for removal of a lumbar total disc replacement (TDR) through these anatomic spaces using a posterior ap- proach. Summary of Background Data. Currently, lumbar TDRs are implanted primarily through an anterior retro- peritoneal or transperitoneal approach. However, revi- sion surgeries through these approaches can be compli- cated by significant adhesions, with potential injuries to intra- and retroperitoneal contents. Advancements in ac- cessing anterior column structures through a posterior lumbar extracavitary approach suggest that posterior re- moval of TDRs may be an alternative. Unlike the thoracic extracavitary approach in which ligation of the thoracic nerve rarely leaves significant morbidity, the lumbar ex- tracavitary approach cannot rely on the analogous liga- tion of the lumbar root to achieve access. Therefore, fea- sibility 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 dis- sected through a posterior approach to expose the lum- bar plexus bilaterally. The root-to-root distances at levels L2–S1 and corresponding root-to-tether distances at lev- els 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 mea- surements compare favorably with the CHARITE ´ 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 poste- rior TDR removal is possible in the lumbar spine without undue risk to the surrounding nervous structures. Key words: CHARITE ´ , posterior approach, feasibility, surgical technique, extracavitary, lumbosacral plexus. Spine 2008;33:E274 –E278 Artificial lumbar total disc replacements (TDRs) have been performed in thousands of patients in the United States since the 2004 U.S. Food & Drug Administration approval of the prosthesis. 1,2 Unfortunately, approxi- mately 9% of these patients eventually require replace- ment or removal of their prosthetic discs. 3 Current indi- cations for revision surgery include malposition or migration of the device, vertebral body fracture, infec- tion, and premature wear of the prosthesis. 4,5 Initial placement of the prosthetic lumbar disc is ac- complished through an anterior retroperitoneal ap- proach from a midline laparotomy, which requires care- ful manipulation of the abdominal viscera and great vessels. 6 Within 2 weeks, however, prominent adhesions develop among the aorta, iliac vessels, ureters, and the anterior column of the spine. 2,4,5 Thus, a second anterior approach for revision of lumbar arthroplasty is techni- cally more difficult for the surgeon and carries additional risk to the patient. There are 2 surgical strategies currently being used to access the anterior column and retrieve TDRs. One method is to use the same midline laparotomy incision and retroperitoneal approach that was used for initial placement, removing the TDR from the side contralat- eral to the adhesions that developed after initial inser- tion. 2,7,8 Occasionally, a transperitoneal modification is used if the adhesions have caused considerable scar- ring. 7,8 Precautions include preoperative placement of ureteral stents and the assistance of a vascular surgeon familiar in this type of surgical approach. 2,7 The second method is to approach the spine from a lateral abdomi- nal incision and a transpsoas approach, thereby elimi- nating some risk to the great vessels. 2,5 One shortcoming of this approach is that it cannot provide access to the L5–S1 disc. 2 Unfortunately, with the aforementioned approaches to accessing the lumbar spine, the amount of mobiliza- tion required of the surrounding structures in order to obtain sufficient visualization and working space to re- trieve the implant can be problematic. Many of the com- plications described after revision lumbar TDR surgery can be directly attributed to the challenges associated with anterior access and have included great vessel in- jury, bowel perforation, prolonged postoperative ileus, small bowel obstruction, symptomatic retroperitoneal From the *University of Virginia School of Medicine, Charlottesville, Virginia; †Department of Orthopedic Surgery, University of Virginia Health System, Charlottesville, Virginia; and ‡Department of Anat- omy, University of Virginia School of Medicine, Charlottesville, Vir- ginia. Acknowledgment date: October 4, 2007. Revision date: November 28, 2007. Acceptance date: December 3, 2007. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. All authors have contributed to the preparation of this manuscript. Address correspondence and reprint requests to Francis H. Shen, MD, Department of Orthopedic Surgery, University of Virginia Health Sys- tem, PO BOX 800159, Charlottesville, 22908 VA; E-mail: fhs2g@ virginia.edu E274