Since its initial description in 2006, the lateral interbody. Motor nerve injuries following the minimally invasive lateral transpsoas approach

Transcription

1 J Neurosurg Spine 7:7 3, 0 Motor nerve injuries following the minimally invasive lateral transpsoas approach Clinical article Kevin S. Cahill, M.D., Ph.D., M.P.H., Joseph L. Martinez, M.D., Michael Y. Wang, M.D., Steven Vanni, D.O., D.C., and Allan D. Levi, M.D., Ph.D. Department of Neurological Surgery and The Miami Project to Cure Paralysis, University of Miami Miller School of Medicine, Miami, Florida Object. The aim of this study was to determine the incidence of motor nerve injuries during the minimally invasive lateral interbody fusion procedure at a single academic medical center. Methods. A retrospective chart review of 8 patients who had undergone lateral interbody fusion was performed. Both inpatient and outpatient records were examined to identify any new postoperative motor weakness in the lower extremities and abdominal wall musculature that was attributable to the operative procedure. Results. In the period from 007 to 0 the lateral interbody fusion procedure was attempted on 0 lumbar intervertebral disc levels. No femoral nerve injuries occurred at any disc level other than the L4 5 disc space. Among procedures involving the L4 5 level there were femoral nerve injuries, corresponding to a 4.8% injury risk at this level as compared with a 0% injury risk at other lumbar spine levels. Five patients (4.%) had postoperative abdominal flank bulge attributable to injury to the abdominal wall motor innervation. Conclusions. The overall incidence of femoral nerve injury after the lateral transpsoas approach was.7%; however, the level-specific incidence was 4.8% for procedures performed at the L4 5 disc space. Approximately 4% of patients had postoperative abdominal flank bulge. Surgeons will be able to minimize these motor nerve injuries through judicious use of the procedure at the L4 5 level and careful attention to the T- and T- motor nerves during exposure and closure of the abdominal wall. ( Key Words complication lateral interbody fusion nerve injury lumbar fusion minimally invasive procedure Since its initial description in 006, the lateral interbody fusion technique has been used in the treatment of a variety of pathological conditions of the lumbar spine. 3 As this minimally invasive transpsoas approach has gained more widespread acceptance and increased utilization, recent interest has focused on understanding the morbidity and complication profile of the procedure. Estimates of postoperative morbidity related to psoas muscle manipulation and sensory nerve injury have varied, but it is now widely accepted that a significant percentage of patients will experience temporary sensory disturbances and hip flexion weakness related to psoas muscle retraction following the minimally invasive lateral procedure.,3, Substantially less is known regarding the frequency of motor nerve injuries during the extreme lateral approach. Anatomical studies have helped to clarify the location of Abbreviation used in this paper: EMG = electromyography. J Neurosurg: Spine / Volume 7 / September 0 the lumbosacral plexus within the psoas muscle, with an emphasis on the femoral nerve, allowing for the generation of safe working zones within this muscle., However, the risk of injury to the femoral nerve still exists, and several case reports of motor nerve injury have been published recently. 8,0 Likewise, during the surgical approach through the abdominal wall musculature, injury to the motor innervation of the abdominal wall can ultimately lead to abdominal flank bulge, which has been described following traditional open anterolateral approaches to the lumbar spine as well as with the lateral procedure. 4,9 In the present study, we estimated the frequency of femoral and subcostal motor nerve injuries during the minimally invasive lateral procedure in a single-institution, multiplesurgeon case series. This article contains some figures that are displayed in color on line but in black-and-white in the print edition. 7

2 K. S. Cahill et al. Methods The institutional review board at the University of Miami approved the study protocol. Patient Population A retrospective chart review was performed to identify all patients 8 years of age and older who had undergone the minimally invasive lateral procedure for lumbar interbody fusion in the period from 007 to 0 at the Jackson Memorial Hospital (University of Miami). The senior authors (S.V., A.D.L., and M.Y.W.) performed all surgeries. Operative Techniques The surgical technique used for all of the procedures has been described in detail elsewhere. All procedures were performed with continuous EMG monitoring. Initially, the midportion of the intervertebral disc is targeted. If during the transpsoas approach the lumbosacral nerve is positioned anteriorly, a new, more anterior target is attempted. If no safe working channel through the muscle is available, that level is aborted and a posterior transforaminal interbody fusion is performed. Postoperative Outcomes Postoperative femoral nerve injuries were identified by the presence of new postoperative quadriceps muscle weakness. The presentation is distinctly different from the more common psoas muscle weakness related to manipulation of the muscle and is limited to hip flexion. Postoperative abdominal wall motor nerve injuries were identified by inspecting the surgical site and abdominal wall during follow-up evaluation in the outpatient clinic. The pseudohernia is distinctly different from a true abdominal hernia related to the incision in that it affects the ipsilateral abdominal wall distal to the incision. Results In the period from 007 to 0, 8 patients underwent the minimally invasive lateral fusion procedure. These cases represent fusions attempted at 0 disc levels. The distribution of single and multilevel cases is featured in Table. Approximately half of the cases were singlelevel fusion procedures, 37% were -level procedures, and the remaining cases were multilevel procedures. The mean patient age was 6 ± years, and the primary diagnoses included lumbar spondylolisthesis, pseudarthrosis, postlaminectomy kyphosis, adjacent-segment disc degeneration, and degenerative lumbar scoliosis. Posterior instrumentation was performed in 96 patients (8%). The distribution of disc levels of attempted minimally invasive lateral fusion procedures is provided in Table. Forty-one of the 8 cases included the L4 5 disc level. Among the 0 disc levels at which fusion was attempted, the procedure could not be completed at 5 levels given the anterior location of the motor nerve in the psoas muscle (Table 3). Two aborted procedures were at the L3 4 disc space and 3 were at the L4 5 disc space. Thus, the overall success rate for the minimally invasive TABLE : Distribution of surgical cases according to number of disc levels attempted and primary indication for surgery* Factor No. of Cases (%) disc levels attempted 56 (47) 44 (37) 3 6 (4) 4 () reason for surgery degenerative scoliosis 46 (39) adjacent-level disc disease 4 (0) degenerative disc disease 4 () disc herniation 9 (8) postlaminectomy deformity 7 (6) pseudarthrosis 5 (4) degenerative spondylolisthesis 5 (4) lumbar stenosis 5 (4) discitis 3 (3) * One hundred eighteen patients underwent lateral interbody fusion. lateral fusion procedure at the L3 4 level was 98% and at the L4 5 level was 9%. Injury to the lumbosacral plexus, specifically the femoral nerve, was identified in patients. Both of these injuries occurred during dilation of the psoas muscle for the approach to the L4 5 disc space. While the overall risk of femoral nerve injury among all cases was.7%, the risk associated with the L4 5 level in particular was 4.8%. The first case with a femoral nerve injury occurred in a 46-year-old male who underwent an attempted 3-level minimally invasive lateral fusion from L- to L-5. During the approach to the L4 5 disc space, a safe working zone could not be defined despite positioning the dilators in the anterior third of the disc space. During the attempted fusion at the L 3 and L3 4 levels, EMG evoked potential monitoring indicated that the retractors were safely positioned. Postoperatively, the patient was noted to have new weakness in the iliopsoas and quadriceps muscles on the operative side, which was graded 3/5 in the iliopsoas muscle and /5 in the quadriceps muscle. On discharge from the hospital the patient was ambulatory with a walker and required inpatient and outpatient rehabilitation. The weakness was persistent on 6- and 9-month follow-up visits. The patient was also TABLE : Distribution of cases according to individual disc level* Disc Level No. of Cases T L L 0 L 3 6 L L4 5 4 * Two hundred one disc levels were subjected to lateral interbody fusion. 8 J Neurosurg: Spine / Volume 7 / September 0

3 Motor nerve injuries from transpsoas approach TABLE 3: Success of lateral interbody fusion according to disc level TABLE 4: Distribution of disc levels in cases with permanent postoperative abdominal flank bulge Disc Level Success Rate (no. of levels aborted*) Case No. No. of Disc Levels Fused Levels Fused T L L L 3 L3 4 L4 5 00% 00% 00% 98.3% () 9.3% (3) L, L 3, L3 4 L 3, L3 4 L3 4 L 3 L 3, L3 4 * In all 5 aborted cases, a posterior transforaminal interbody fusion was subsequently performed. noted to have a persistently decreased patellar reflex. Atrophy and persistent weakness of the quadriceps muscle is shown in Fig.. The second patient was a 55-year-old male who had undergone an attempted L4 5 single-level minimally invasive lateral fusion. The procedure was aborted after a safe working zone could not be established given the anterior position of the nerve. Postoperatively, the patient was noted to have new quadriceps weakness initially graded 3/5. Iliopsoas muscle strength was normal. The patient s quadriceps muscle strength improved to 4/5 by the time of discharge, and he was ambulatory by then. The patient had normal strength by the 3-month follow-up visit. Five patients (4.%) had new postoperative abdominal wall bulges on the operative side of the abdomen. This abdominal wall finding was detected in single-level as well as multilevel cases. The distribution of levels fused in patients with the postoperative abdominal bulge is featured in Table 4. One patient had a transient abdominal bulge that gradually resolved on subsequent follow-up but is not included in this analysis. A patient with a permanent postoperative abdominal bulge is featured in Fig.. Figure 3 consists of immediate postoperative and -year follow-up CT scans. As shown by the differences in thickness of the abdominal musculature on the side of the surgical approach, the abdominal bulge is not a true hernia in that there is no defect in the abdominal musculature. Fig.. Photograph showing new postoperative left-sided abdominal flank bulge in a patient who underwent a left-sided minimally invasive lateral interbody fusion. J Neurosurg: Spine / Volume 7 / September 0 Discussion We previously documented the rate of postoperative sensory disturbances in our institutional series of minimally invasive lateral fusion cases and estimated that approximately 60% of patients experienced new thigh sensory disturbances following the procedure. In an effort to further clarify the overall morbidity and complication profile of the procedure, we focused on the frequency of motor nerve injuries in a series of 8 patients in the current study. In this retrospective analysis, we estimated that the overall rate of femoral nerve injury for the minimally invasive lateral fusion procedure at the L4 5 level was 4.8%, while no femoral nerve injuries occurred during fusions at any other levels. Additionally, we reported a 4.% incidence of postoperative abdominal wall bulge related to permanent injury to the motor nervous supply to the lateral abdominal wall. It is important to note that our study is a retrospective case series and has the limitations associated with such analyses. For example, it is possible that we underestimate the true risk of these motor nerve injuries if the injuries were not identified during regular clinical examination at follow-up appointments. This scenario is unlikely for a femoral nerve injury since all patients undergo formal motor strength testing postoperatively. For abdominal flank bulges, however, subtle bulges may not have been clinically diagnosed. Fig.. Photograph of a representative patient with persistent left quadriceps muscle weakness and atrophy. 9

4 K. S. Cahill et al. Fig. 3. Immediate postoperative (A C) and -year postoperative (D F) abdominal CT scans obtained in a patient who demonstrated a permanent postoperative abdominal flank bulge. The patient underwent a 3-level minimally invasive lateral interbody fusion from L- to L-4 via a left-sided approach. Arrows indicate significant thinning and dilation of the abdominal musculature that extends anteriorly from the surgical site. The average thickness of the abdominal wall musculature on the surgical approach side is approximately 5 mm less than on the contralateral side. Anatomical safe zones have been identified from cadaveric dissections of the psoas muscle and were developed to represent areas of the psoas muscle that could be dissected without nerve injury during endoscopic anterior and lateral approaches to the lumbar spine. It was believed that no nerves are at risk from exposures of the L 3 disc space and above, whereas between the body of L-3 and the L4 5 disc space, the genitofemoral nerve is superficially and anteriorly located on the psoas muscle. We and others have reported that the lumbar contribution to the lumbosacral plexus migrates dorsally to ventrally from L- to L-5.,5 At the L4 5 disc space the ventral migration is most significant, with the trunk found in the center of the disc space in 5% of specimens in one cadaveric study. 5 Others have confirmed that the femoral nerve can be located as far anteriorly as the midpoint of the disc space at L4 5, while sensory branches such as the genitofemoral nerve are often located even farther anteriorly. 6 There has been a relative paucity of reports on lumbosacral motor nerve injuries during the minimally invasive lateral fusion procedure in the neurosurgical literature, especially as compared with those on postoperative sensory disturbances. Thus, it is difficult to compare our rate of motor nerve injury with those of other groups. A study of 58 patients focusing on complications of the direct lateral approach documented femoral nerve injuries. 0 Patients in both of these cases had residual motor deficits at year postsurgery; however, the rate of injury per disc level cannot be determined, as the specific levels of surgery were not reported for these patients. Recently, cases of motor nerve injuries were described by Houten et al. 8 It is interesting to note that both of these injuries also occurred during the minimally invasive lateral fusion procedure at the L4 5 disc space; however, intraoperative EMG monitoring with a 0-mA threshold did not indicate proximity of the nerve. This scenario is probably different from the nerve injuries reported in our study. In our cases, the nerve was clearly detected on attempted dilation of the psoas muscle, and then the procedure was aborted in both cases when a safe working zone could not be established. Therefore, we speculated that the mechanism of injury in our patients was direct injury to the nerve by the dilators, whereas injury in the Houten et al. study occurred after the initial approach. Perhaps injury in the latter study occurred because of prolonged retraction of the nerves due to posterior migration of the retractors. In addition to approach-related lumbosacral nerve injury, contralateral femoral nerve injury has been reported in patients following the minimally invasive lateral fusion procedure. 4 One of the injuries resulted from aggressive mobilization of the contralateral osteophyte leading to compression of the femoral nerve by an endplate fragment. In the second patient a far-lateral disc fragment was produced by insertion of the interbody cage. Both cases were successfully treated with operative removal of the fragments. Although we did not have any contralateral lumbosacral nerve injuries in our series, it is important for the surgeon to be cognizant of this potentially treatable complication. Recent work has highlighted postoperative abdominal wall motor nerve injuries, as the surgical approach through the lateral abdominal wall can be a source of temporary or permanent morbidity from the minimally invasive lateral fusion procedure. Abdominal wall paresis or flank bulge has been reported following laparoscopic abdominal surgery, anterolateral approaches for vascular surgery, and thoracoabdominal spine surgical approaches. 6,7,9,7 While we documented an approximately 4% incidence of this complication, authors of a large multicenter case series of over 500 patients who had undergone the 30 J Neurosurg: Spine / Volume 7 / September 0

5 Motor nerve injuries from transpsoas approach minimally invasive lateral fusion procedure identified this postoperative complication in.8% of patients. 4 We showed that this complication can occur in single as well as multilevel procedures. Understanding the motor innervation of the abdominal wall may help to limit this complication. It has been shown that the majority of the abdominal wall musculature is innervated by the T- and T- intercostal nerves. 6 The subcostal nerves arise from T- and T- and travel underneath the transversus abdominis muscle and penetrate the muscle layers to supply the muscles of the anterior abdominal wall. 5 Zones of injury to the intercostal nerves have been proposed. 6 Zone III injuries are distal to the tip of the rib and can occur during exposure to the heat of electrocautery or by direct transection. Likewise, during closure the nerve can be injured while suturing the abdominal wall. 6 Based on the anatomical location of the T- and T- nerves, we would expect injury to these nervous structures to be more common during lateral exposures for the upper lumbar vertebrae. Likewise, an incision that parallels the subcostal nerve may lessen the risk of injury. In this series all of the injuries involved surgical exposure at the L3 4 disc level or higher. No cases of abdominal wall weakness occurred when only L4 5 level fusions were performed. Conclusions In summary, based on this series of 8 patients representing 0 attempted fusion levels, we report that approximately 5% of minimally invasive lateral fusion procedures performed at the L4 5 disc space were complicated by femoral nerve injury. Importantly, no injuries occurred at any other levels. We anticipate that surgeons could minimize this complication through judicious use of the minimally invasive lateral fusion procedure at the L4 5 level and careful attention to the location of the femoral nerve during the approach. Moreover, we report an approximately 4% rate of postoperative abdominal flank bulge resulting from the minimally invasive lateral fusion approach through the abdominal wall. Attention to the T- and T- motor nerves during exposure and closure of the abdominal wall may help to minimize this complication. Disclosure Dr. Wang is a consultant for, receives royalties from, and holds a patent with DePuy Spine and is a consultant for Aesculap Spine and Biomet Spine; Dr. Vanni is a consultant for NuVasive and DePuy and receives teaching honoraria from DePuy. Dr. Levi has received research grants from the NIH and teaching honoraria from DePuy, Medtronic, and Synthes. Author contributions to the study and manuscript preparation include the following. Conception and design: Levi, Cahill, Wang, Vanni. Acquisition of data: all authors. Analysis and interpretation of data: Cahill. Drafting the article: Levi, Cahill. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Levi. Statistical analysis: Levi, Cahill. Administrative/technical/material support: Cahill, Martinez. Study supervision: Levi. References J Neurosurg: Spine / Volume 7 / September 0. Benglis DM, Vanni S, Levi AD: An anatomical study of the lumbosacral plexus as related to the minimally invasive transpsoas approach to the lumbar spine. Laboratory investigation. J Neurosurg Spine 0:39 44, 009. Cummock MD, Vanni S, Levi AD, Yu Y, Wang MY: An analysis of postoperative thigh symptoms after minimally invasive transpsoas lumbar interbody fusion. Clinical article. J Neurosurg Spine 5: 8, 0 3. Dakwar E, Cardona RF, Smith DA, Uribe JS: Early outcomes and safety of the minimally invasive, lateral retroperitoneal transpsoas approach for adult degenerative scoliosis. Neurosurg Focus 8(3):E8, Dakwar E, Le TV, Baaj AA, Le AX, Smith WD, Akbarnia BA, et al: Abdominal wall paresis as a complication of minimally invasive lateral transpsoas interbody fusion. Neurosurg Focus 3(4):E8, 0 5. Dakwar E, Vale FL, Uribe JS: Trajectory of the main sensory and motor branches of the lumbar plexus outside the psoas muscle related to the lateral retroperitoneal transpsoas approach. Laboratory investigation. J Neurosurg Spine 4:90 95, 0 6. Fahim DK, Kim SD, Cho D, Lee S, Kim DH: Avoiding abdominal flank bulge after anterolateral approaches to the thoracolumbar spine: cadaveric study and electrophysiological investigation. Laboratory investigation. J Neurosurg Spine 5: , 0 7. Gardner GP, Josephs LG, Rosca M, Rich J, Woodson J, Menzoian JO: The retroperitoneal incision. An evaluation of postoperative flank bulge. Arch Surg 9: , Houten JK, Alexandre LC, Nasser R, Wollowick AL: Nerve injury during the transpsoas approach for lumbar fusion. Report of cases. J Neurosurg Spine 5:80 84, 0 9. Jagannathan J, Chankaew E, Urban P, Dumont AS, Sansur CA, Kern J, et al: Cosmetic and functional outcomes following paramedian and anterolateral retroperitoneal access in anterior lumbar spine surgery. Clinical article. J Neurosurg Spine 9: , Knight RQ, Schwaegler P, Hanscom D, Roh J: Direct lateral lumbar interbody fusion for degenerative conditions: early complication profile. J Spinal Disord Tech :34 37, 009. Moller DJ, Slimack NP, Acosta FL Jr, Koski TR, Fessler RG, Liu JC: Minimally invasive lateral lumbar interbody fusion and transpsoas approach-related morbidity. Neurosurg Focus 3(4):E4, 0. Moro T, Kikuchi S, Konno S, Yaginuma H: An anatomic study of the lumbar plexus with respect to retroperitoneal endoscopic surgery. Spine (Phila Pa 976) 8:43 48, Ozgur BM, Aryan HE, Pimenta L, Taylor WR: Extreme Lateral Interbody Fusion (XLIF): a novel surgical technique for anterior lumbar interbody fusion. Spine J 6: , Papanastassiou ID, Eleraky M, Vrionis FD: Contralateral femoral nerve compression: An unrecognized complication after extreme lateral interbody fusion (XLIF). J Clin Neurosci 8:49 5, 0 5. Park DK, Lee MJ, Lin EL, Singh K, An HS, Phillips FM: The relationship of intrapsoas nerves during a transpsoas approach to the lumbar spine: anatomic study. J Spinal Disord Tech 3:3 8, Uribe JS, Arredondo N, Dakwar E, Vale FL: Defining the safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: an anatomical study. Laboratory investigation. J Neurosurg Spine 3:60 66, van Ramshorst GH, Kleinrensink GJ, Hermans JJ, Terkivatan T, Lange JF: Abdominal wall paresis as a complication of laparoscopic surgery. Hernia 3: , 009 Manuscript submitted January 5, 0. Accepted May 4, 0. Please include this information when citing this paper: published online June 9, 0; DOI: 0.37/0.5.SPINE88. Address correspondence to: Allan D. Levi, M.D., Ph.D., Department of Neurological Surgery, University of Miami Miller School of Medicine, Lois Pope LIFE Center, nd Floor, 095 NW 4th Terrace (D4-6), Miami, Florida ALevi@med.miami.edu. 3