Transpsoas Approach Research Articles

Lordosis restoration after anterior longitudinal ligament release and placement of lateral hyperlordotic interbody cages during the minimally invasive lateral transpsoas approach: a radiographic study in cadavers

In the surgical treatment of spinal deformities, the importance of restoring lumbar lordosis is well recognized. Smith-Petersen osteotomies (SPOs) yield approximately 10° of lordosis per level, whereas pedicle subtraction osteotomies result in as much as 30° increased lumbar lordosis. Recently, selective release of the anterior longitudinal ligament (ALL) and placement of lordotic interbody grafts using the minimally invasive lateral retroperitoneal transpsoas approach (XLIF) has been performed as an attempt to increase lumbar lordosis while avoiding the morbidity of osteotomy. The objective of the present study was to measure the effect of the selective release of the ALL and varying degrees of lordotic implants placed using the XLIF approach on segmental lumbar lordosis in cadaveric specimens between L-1 and L-5. Nine adult fresh-frozen cadaveric specimens were placed in the lateral decubitus position. Lateral radiographs were obtained at baseline and after 4 interventions at each level as follows: 1) placement of a standard 10° lordotic cage, 2) ALL release and placement of a 10° lordotic cage, 3) ALL release and placement of a 20° lordotic cage, and 4) ALL release and placement of a 30° lordotic cage. All four cages were implanted sequentially at each interbody level between L-1 and L-5. Before and after each intervention, segmental lumbar lordosis was measured in all specimens at each interbody level between L-1 and L-5 using the Cobb method on lateral radiography. The mean baseline segmental lordotic angles at L1-2, L2-3, L3-4, and L4-5 were -3.8°, 3.8°, 7.8°, and 22.6°, respectively. The mean lumbar lordosis was 29.4°. Compared with baseline, the mean postimplantation increase in segmental lordosis in all levels combined was 0.9° in Intervention 1 (10° cage without ALL release); 4.1° in Intervention 2 (ALL release with 10° cage); 9.5° in Intervention 3 (ALL release with 20° cage); and 11.6° in Intervention 4 (ALL release with 30° cage). Foraminal height in the same sequence of conditions increased by 6.3%, 4.6%, 8.8% and 10.4%, respectively, while central disc height increased by 16.1%, 22.3%, 52.0% and 66.7%, respectively. Following ALL release and placement of lordotic cages at all 4 lumbar levels, the average global lumbar lordosis increase from preoperative lordosis was 3.2° using 10° cages, 12.0° using 20° cages, and 20.3° using 30° cages. Global lumbar lordosis with the cages at 4 levels exhibited a negative correlation with preoperative global lordosis (10°, R = -0.756; 20°, -0.730; and 30°, R = -0.437). Combined ALL release and placement of increasingly lordotic lateral interbody cages leads to progressive gains in segmental lordosis in the lumbar spine. Mean global lumbar lordosis similarly increased with increasingly lordotic cages, although the effect with a single cage could not be evaluated. Greater global lordosis was achieved with smaller preoperative lordosis. The mean maximum increase in segmental lordosis of 11.6° followed ALL release and placement of the 30° cage.

Lumbarized Sacrum as a Relative Contraindication for Lateral Transpsoas Interbody Fusion at L5-6

Retrospective review. To determine if lumbarized sacra at the L5-6 level (functional L4-5) are a contraindication to a lateral transpsoas approach. Transitional vertebrae at the lumbosacral junction present mechanical and morphologic changes, though these changes have not been characterized with respect to the feasibility of a lateral transpsoas approach. Three hundred fifty-one patients were scheduled for lumbar interbody fusion using a mini-open lateral transpsoas approach (XLIF) at L4-5 from 2004 to 2008 at a single institution. In patients with 6 lumbar vertebrae, accessibility, based on neuromonitoring, of the L5-6 level (functional L4-5) was reviewed. Qualitative assessments using axial magnetic resonance imaging (MRI) were performed and compared with a sample of patients with normal anatomy treated at L4-5. Of the 351 patients scheduled for treatment at L4-5, 10 (2.8%) were determined to have 6 lumbar vertebrae with the symptomatic level at L5-6. Of those 10, 2 (20%) could be treated using a lateral transpsoas approach, and 8 (80%) were converted to another approach after a corridor through the psoas muscle was not found, based on neuromonitoring feedback. Review of axial MRI showed a teardrop-shaped psoas detached from the lateral border of the disc space in patients with transitional anatomy unapproachable at L5-6, resemblant of L5-S1 in normal anatomy. In the 2 patients who could be safely approached, the psoas anatomy at L5-6 was similar to a normal L4-5 level, with a domed/helmet shape, attached laterally to the disc space. Treating the L5-6 level using a lateral transpsoas approach in individuals with lumbarized sacra can be challenging due to anatomy more similar to the L5-S1 level in normal patients. Preoperative planning using axial MRI and intraoperative adherence to advanced neuromonitoring can aid in identifying and avoiding injury in these rare patients.

Motor nerve injuries following the minimally invasive lateral transpsoas approach

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. A retrospective chart review of 118 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. In the period from 2007 to 2011 the lateral interbody fusion procedure was attempted on 201 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 2 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 (4.2%) had postoperative abdominal flank bulge attributable to injury to the abdominal wall motor innervation. The overall incidence of femoral nerve injury after the lateral transpsoas approach was 1.7%; 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-11 and T-12 motor nerves during exposure and closure of the abdominal wall.

Case report: incisional hernia as a complication of extreme lateral interbody fusion

Minimal access surgery is becoming more popular for spinal fusion because of a lower theoretical risk of complications and shorter postoperative recovery period, compared with the traditional open approach. The lateral approach uses retroperitoneal transpsoas access to the vertebra, obviating the need for an approach surgeon and minimizing muscular disruption, thus allowing a quicker recovery. Initial reports of the lateral transpsoas procedure described few complications. However, a number of complications have subsequently been documented. To our knowledge, there has not been a description of an incisional hernia after this approach. To report the rare complication of an incisional hernia after a minimal access lateral transpsoas approach for lumbar interbody fusion. Case report. We reviewed the hospital charts, radiographs, and intraoperative photographs of a patient who underwent a minimally invasive lateral approach lumbar spine fusion with a subsequent incisional hernia that necessitated laparoscopic repair. A 75-year-old woman with a history of low back and left lower extremity pain with radiographic evidence of foraminal stenosis and degenerative spondylolisthesis underwent a successful L4-L5 discectomy with an extreme lateral interbody fusion via a retroperitoneal transpsoas approach. This was supplemented with a posterior minimally invasive surgery instrumented fusion from L4 to L5. The patient reported significant improvement in symptoms on initial follow-up, however, complained of a prominence over her incision 4 weeks later. An incisional hernia was diagnosed and subsequently repaired laparoscopically, from which the patient recovered uneventfully. Postoperative incisional hernia after extreme lateral interbody fusion is a complication that has not been previously described in the literature but is one that spine surgeons must recognize. This case may prompt surgeons to use a more posterior approach to avoid this complication. Additionally, direct repair of the transversalis fascia is critical to avoiding this complication.

Movement of abdominal structures on magnetic resonance imaging during positioning changes related to lateral lumbar spine surgery: a morphometric study

The minimally invasive lateral interbody fusion of the lumbar spine through a retroperitoneal transpsoas approach has become increasingly used. Although preoperative imaging is performed supine, the procedure is performed with the patient in the lateral decubitus position. The authors measured the changes in location of the psoas muscle, aorta, inferior vena cava (IVC), iliac vessels, and kidneys with regard to the fixed lumbar spine when moving from a supine to a lateral decubitus position. Unenhanced lumbar MRI scans were performed using a 3T magnet in 10 skeletally mature volunteers in the supine, left lateral decubitus (LLD), and right lateral decubitus (RLD) positions. Positional changes in the aorta, IVC, iliac vessels, and kidneys were then analyzed at all lumbar levels when moving from supine to RLD and supine to LLD. Values are presented as group means. When the position was changed from supine to RLD, both the aorta and the IVC moved up to 6 mm to the right, with increased movement caudally at L3-4. The aorta was displaced 2 mm anteriorly at L1-2, and the IVC moved 3 mm anteriorly at L1-2 and L2-3 and 1 mm posteriorly at L3-4. The left kidney moved 22 mm anteriorly and 15 mm caudally, while the right kidney moved 9 mm rostrally. When the position was changed from supine to LLD, the aorta moved 1.5 mm to the left at all levels, with very minimal anterior/posterior displacement. The IVC moved up to 10 mm to the left and 12 mm anteriorly, with increased movement rostrally at L1-2. The left kidney moved 3 mm anteriorly and 1 mm rostrally, while the right kidney moved 20 mm anteriorly and 5 mm caudally. The bifurcation of the aorta was an average of 18 mm above the L4-5 disc space, while the convergence of the iliac veins to form the IVC was at the level of the disc space. The iliopsoas did not move in any quantifiable direction when the position was changed from supine to lateral; its shape, however, may change to become more flat or rounded. When the position was changed from supine to RLD, the right iliac vein moved posteriorly an average of 1.5 mm behind the anterior vertebral body (VB) line (a horizontal line drawn on an axial image at the anterior VB), while the other vessels stayed predominantly anterior to the disc space. When the position was changed from supine to LLD, the right iliac vein moved to a position 1.4 mm anterior to the anterior VB line. There was negligible movement of the other vessels in this position. The authors showed that the aorta, IVC, and kidneys moved a significant distance away from the surgical corridor with changes in position. At the L4-5 level, a left-sided approach may be riskier because the right common iliac vein trends posteriorly and into the surgical corridor, whereas in a right-sided approach it trends anteriorly.

The lateral transpsoas approach to the lumbar and thoracic spine: A review

Background:In the last several years, the lateral transpsoas approach to the thoracic and lumbar spine, also known as extreme lateral interbody fusion (XLIF) or direct lateral interbody fusion (DLIF), has become an increasingly common method to achieve fusion. Several recent large series describe several advantages to this approach, including less tissue dissection, smaller incisions, decreased operative time, blood loss, shorter hospital stay, reduced postoperative pain, enhanced fusion rates, and the ability to place instrumentation through the same incision. Indications for this approach have expanded and now include degenerative disease, tumor, deformity, and infection.Methods:A lateral X-ray confirms that the patient is in a truly lateral position. Next, a series of tubes and dilators are used, along with fluoroscopy, to identify the mid-position of the disk to be incised. After continued dilation, the optimal site to enter the disk space is the midpoint of the disk, or a position slightly anterior to the midpoint of the disk. XLIF typically allows for a larger implant to be inserted compared to TLIF or PLIF, and, if necessary, instrumentation can be inserted percutaneously, which would allow for an overall minimally invasive procedure.Results:Fixation techniques appear to be equal between XLIF and more traditional approaches. Some caution should be exercised because common fusion levels of the lumbar spine, including L4-5 and L4-S1, are often inaccessible. In addition, XLIF has a unique set of complications, including neural injuries, psoas weakness, and thigh numbness.Conclusion:Additional studies are required to further evaluate and monitor the short and long-term safety, efficacy, outcomes, and complications of XLIF procedures.

Lateral interbody fusion for treatment of discogenic low back pain: minimally invasive surgical techniques.

Low back pain is one of the most common ailments in the general population, which tends to increase in severity along with aging. While few patients have severe enough symptoms or underlying pathology to warrant surgical intervention, in those select cases treatment choices remain controversial and reimbursement is a substancial barrier to surgery. The object of this study was to examine outcomes of discogenic back pain without radiculopathy following minimally-invasive lateral interbody fusion. Twenty-two patients were treated at either one or two levels (28 total) between L2 and 5. Discectomy and interbody fusion were performed using a minimallyinvasive retroperitoneal lateral transpsoas approach. Clinical and radiographic parameters were analyzed at standard pre- and postoperative intervals up to 24 months. Mean surgical duration was 72.1 minutes. Three patients underwent supplemental percutaneous pedicle screw instrumentation. Four (14.3%) stand-alone levels experienced cage subsidence. Pain (VAS) and disability (ODI) improved markedly postoperatively and were maintained through 24 months. Segmental lordosis increased significantly and fusion was achieved in 93% of levels. In this series, isolated axial low back pain arising from degenerative disc disease was treated with minimally-invasive lateral interbody fusion in significant radiographic and clinical improvements, which were maintained through 24 months.

Lateral Transpsoas Fusion: Indications and Outcomes

Spinal fusion historically has been used extensively, and, recently, the lateral transpsoas approach to the thoracic and lumbar spine has become an increasingly common method to achieve fusion. Recent literature on this approach has elucidated its advantage over more traditional anterior and posterior approaches, which include a smaller tissue dissection, potentially lower blood loss, no need for an access surgeon, and a shorter hospital stay. Indications for the procedure have now expanded to include degenerative disc disease, spinal stenosis, degenerative scoliosis, nonunion, trauma, infection, and low-grade spondylolisthesis. Lateral interbody fusion has a similar if not lower rate of complications compared to traditional anterior and posterior approaches to interbody fusion. However, lateral interbody fusion has unique complications that include transient neurologic symptoms, motor deficits, and neural injuries that range from 1 to 60% in the literature. Additional studies are required to further evaluate and monitor the short- and long-term safety, efficacy, outcomes, and complications of lateral transpsoas procedures.

Clinical Outcome and Fusion Rates after the First 30 Extreme Lateral Interbody Fusions

Introduction. The lateral transpsoas approach for lumbar interbody fusion (XLIF) is gaining popularity. Studies examining a surgeon's early experience are rare. We aim to report treatment, complication, clinical, and radiographic outcomes in an early series of patients. Methods. Prospective data from the first thirty patients treated with XLIF by a single surgeon was reviewed. Outcome measures included pain, disability, and quality of life assessment. Radiographic assessment of fusion was performed by computed tomography. Results. Average follow-up was 11.5 months, operative time was 60 minutes per level and blood loss was 50 mL. Complications were observed: clinical subsidence, cage breakage upon insertion, new postoperative motor deficit and bowel injury. Approach side-effects were radiographic subsidence and anterior thigh sensory changes. Two patients required reoperation; microforaminotomy and pedicle screw fixation respectively. VAS back and leg pain decreased 63% and 56%, respectively. ODI improved 41.2% with 51.3% and 8.1% improvements in PCS and MCS. Complete fusion (last follow-up) was observed in 85%. Conclusion. The XLIF approach provides superior treatment, clinical outcomes and fusion rates compared to conventional surgical approaches with lowered complication rates. Mentor supervision for early cases and strict adherence to the surgical technique including neuromonitoring is essential.

Early Outcomes of Minimally Invasive Anterior Longitudinal Ligament Release for Correction of Sagittal Imbalance in Patients with Adult Spinal Deformity

The object of this study was to evaluate a novel surgical technique in the treatment of adult degenerative scoliosis and present our early experience with the minimally invasive lateral approach for anterior longitudinal ligament release to provide lumbar lordosis and examine its impact on sagittal balance. Methods. All patients with adult spinal deformity (ASD) treated with the minimally invasive lateral retroperitoneal transpsoas interbody fusion (MIS LIF) for release of the anterior longitudinal ligament were examined. Patient demographics, clinical data, spinopelvic parameters, and outcome measures were recorded. Results. Seven patients underwent release of the anterior longitudinal ligament (ALR) to improve sagittal imbalance. All cases were split into anterior and posterior stages, with mean estimated blood loss of 125 cc and 530 cc, respectively. Average hospital stay was 8.3 days, and mean follow-up time was 9.1 months. Comparing pre- and postoperative 36′′ standing X-rays, the authors discovered a mean increase in global lumbar lordosis of 24 degrees, increase in segmental lumbar lordosis of 17 degrees per level of ALL released, decrease in pelvic tilt of 7 degrees, and decrease in sagittal vertical axis of 4.9 cm. At the last followup, there was a mean improvement in VAS and ODI scores of 26.2% and 18.3%. Conclusions. In the authors' early experience, release of the anterior longitudinal ligament using the minimally invasive lateral retroperitoneal transpsoas approach may be a feasible alternative in correcting sagittal deformity.

Complications of lateral plating in the minimally invasive lateral transpsoas approach

The aim of this study was to review the authors' experience with 101 cases over the past 3 years with minimally invasive lateral interbody fusion using a lateral plate. Their main goal was to specifically look for hardware-associated complications. Three cases of hardware failure and 3 cases of vertebral body (VB) fractures associated with lateral plate placement are reported. The authors also review the literature pertaining to lateral plates and related complications. This study is a retrospective review of a database of patients who underwent minimally invasive lateral interbody fusion in the thoracolumbar spine during a 3-year period. Six complications were identified, resulting in an incidence of 5.9%. Three hardware failures, 2 coronal plane VB fractures, and 1 lateral VB fracture were identified. All complications occurred in multilevel cases. All cases presented with recurrent back pain except one, which was identified incidentally. Minimally invasive lateral interbody fusion is a safe and direct technique that is practical, especially when trying to avoid other approaches for hardware insertion, and it also avoids the complications associated with other types of instrumentation such as pedicle screws. Careful consideration during patient selection and during the operation will aid in the avoidance of complications.

Direct Lateral Transpsoas Approach to Interbody Fusion—May Be Risky After All

Abstract of Reviewed ArticleAnatomic Mapping of Lumbar Nerve Roots During a Direct LateralTranspsoas Approach to the Spine: A Cadaveric StudyBanagan K, Gelb D, et al.Spine 2011;36:E687–E691610.1097/BRS.1090b1013e3181ec5911Study design: Cadaveric study.Objective: Identifying anatomic structures at ri

Erratum to: Minimally invasive lateral transpsoas approach with advanced neurophysiologic monitoring for lumbar interbody fusion

The online version of the original article can be found under doi:10.1007/s00586-011-1997-x.

The lumbosacral plexus: anatomic considerations for minimally invasive retroperitoneal transpsoas approach

The minimally invasive transpsoas approach can be employed to treat various spinal disorders, such as disc degeneration, deformity, and lateral disc herniation. With this technique, visualization is limited in comparison with the open procedure and the proximity of the lumbar plexus to the surgical pathway is one limitation of this technique. Precise knowledge of the regional anatomy of the lumbar plexus is required for safe passage through the psoas muscle. The primary objective of this study was to determine the anatomic position of the lumbar plexus branches and sympathetic chain in relation to the intervertebral disc and to define a safe working zone. The second objective was to compare our observations with previous anatomical studies concerning the transpsoas approach. A total of 60 lumbar plexus in 8 fresh cadavers from the Department of Anatomy were analyzed in this study. Coronal and lateral X-Ray images were obtained before dissection in order to eliminate spine deformity or fracture. All cadavers were placed in a lateral decubitus position with a lateral bolster. Dissection of the lumbar plexus was performed. All nerve branches and sympathetic chain were identified. Intervertebral disc space from L1L2 to L4L5 was divided into four zones. Zone 1 being the anterior quarter of the disc, zone 2 being the middle anterior quarter, zone 3 the posterior middle quarter and zone 4 the posterior quarter. Crossing of each nervous branch with the disc was reported and a safe working zone was determined for L1L2 to L4L5 disc levels. A safe working zone was defined by the absence of crossing of a lumbar plexus branch. No anatomical variation was found during blunt dissection. As described previously, the lumbar plexus is composed of the ventral divisions of the first four lumbar nerves and from contributions of the sub costal nerve from T12. The safe working zone includes zones 2 and 3 at level L1L2, zone 3 at level L2L3, zone 3 at level L3L4, and zone 2 at level L4L5. No difference was observed between right and left sides as regards the relationships between the lumbar plexus and the intervertebral disc. We observed some differences concerning the safe working zone in comparison with other cadaveric studies. The small number of cadaveric specimens used in anatomical studies probably explains theses differences. The minimally invasive transpsoas lateral approach was initially developed to reduce the complications associated with the traditional procedure. The anatomical relationships between the lumbar plexus and the intervertebral disc make this technique particularly risky a L4L5. Alternative techniques, such as transforaminal interbody fusion (TLIF), posterior lumbar interbody fusion (PLIF) or anterior interbody fusion (ALIF) should be used at this level.

Minimally invasive lateral lumbar interbody fusion and transpsoas approach–related morbidity

Recently, the minimally invasive, lateral retroperitoneal, transpsoas approach to the thoracolumbar spinal column has been described by various authors. This is known as the minimally invasive lateral lumbar interbody fusion. The purpose of this study is to elucidate the approach-related morbidity associated with the minimally invasive transpsoas approach to the lumbar spine. To date, there have been only a couple of reports regarding the morbidity of the transpsoas muscle approach. A nonrandomized, prospective study utilizing a self-reported patient questionnaire was conducted between January 2006 and June 2008 at Northwestern University. Data were collected in 53 patients with a follow-up period ranging from 6 months to 3.5 years. Only 2 patients were lost to follow-up. Thirty-six percent (19 of 53) of patients reported subjective hip flexor weakness, 25% (13 of 53) anterior thigh numbness, and 23% (12 of 53) anterior thigh pain. However, 84% of the 19 patients reported complete resolution of their subjective hip flexor weakness by 6 months, and most experienced improved strength by 8 weeks. Of those reporting anterior thigh numbness and pain, 69% and 75% improved to their baseline function by the 6-month follow-up evaluations, respectively. All patients with self-reported subjective hip flexor weakness underwent examinations during subsequent clinic visits after surgery; however, these examinations did not confirm a motor deficit less than Grade 5. Subset analysis showed that the L3-4 and L4-5 levels were most often affected. The minimally invasive, transpsoas muscle approach to the lumbar spine has a number of advantages. The data show that a percentage of the patients undergoing the transpsoas approach will have temporary sensory and motor symptoms related to this approach. The majority of the symptoms are thought to be related to psoas muscle inflammation and/or stretch injury to the genitofemoral nerve due to the surgical corridor traversed during the operation. No major injuries to the lumbar plexus were encountered. It is important to educate patients prior to surgery of the possibility of these largely transient symptoms.

Abdominal wall paresis as a complication of minimally invasive lateral transpsoas interbody fusion

The minimally invasive lateral transpsoas approach for interbody fusion has been increasingly employed to treat various spinal pathological entities. Gaining access to the retroperitoneal space and traversing the abdominal wall poses a risk of injury to the major nervous structures. Nerve injury of the abdominal wall can potentially lead to paresis of the abdominal musculature and bulging of the abdominal wall. Abdominal wall nerve injury resulting from the minimally invasive lateral retroperitoneal transpsoas approach has not been previously reported. The authors describe a case series of patients presenting with paresis and bulging of the abdominal wall after undergoing a minimally invasive lateral retroperitoneal approach. The authors retrospectively reviewed all patients who underwent a minimally invasive lateral transpsoas approach for interbody fusion and in whom development of abdominal paresis developed; the patients were treated at 4 institutions between 2006 and 2010. All data were recorded including demographics, diagnosis, operative procedure, positioning, hospital course, follow-up, and complications. The onset, as well as resolution of the abdominal paresis, was reviewed. The authors identified 10 consecutive patients in whom abdominal paresis developed after minimally invasive lateral transpsoas spine surgery out of a total of 568 patients. Twenty-nine interbody levels were fused (range 1-4 levels/patient). There were 4 men and 6 women whose mean age was 54.1 years (range 37-66 years). All patients presented with abdominal paresis 2-6 weeks postoperatively. In 8 of the 10 patients, abdominal wall paresis had resolved by the 6-month follow-up visit. Two patients only had 1 and 4 months of follow-up. No long-term sequelae were identified. Abdominal wall paresis is a rare but known potential complication of abdominal surgery. The authors report the first case series associated with the minimally invasive lateral transpsoas approach.

Complications of the Lateral Transpsoas Approach for Lumbar Interbody Arthrodesis: A Case Series and Literature Review

The lateral transpsoas approach to the lumbar spine was developed to eliminate the need for an anterior-approach surgeon and retraction of the great vessels and has the potential for shorter operative times. However, the reported complications associated with this approach vary. We identified the incidence of complications associated with the lateral transpsoas approach to the lumbar spine. We retrospectively reviewed 45 patients who underwent a lateral transpsoas approach to the spine for various diagnoses between January 1, 2006, and October 31, 2010. The patients' average age was 63.3years. Sixteen (35.6%) patients had prior lumbar spinal surgery. Twenty-one patients (46.7%) underwent supplemental posterior instrumentation. Minimum followup was 0months (mean, 11months; range, 0-34months). Eighteen of the 45 patients (40%) had complications: 10 (22.2%) developed postoperative iliopsoas weakness, three had quadriceps weakness, and one experienced foot drop. Eight patients (17.8%) developed anterior thigh hypoesthesia, which did not fully resolve in seven of the eight patients at an average of 9months' followup. Three patients had postoperative radiculopathies, one a durotomy, and one died postoperatively from a pulmonary embolism. We found a 40% incidence of complications and a nontrivial frequency and severity of postoperative weakness, numbness, and radicular pain in patients who underwent a lateral transpsoas approach to the spine. Given the expanding use of the approach, a thorough understanding of the risks associated with it is essential for patient education, medical decision making, and identifying methods of reducing such complications. Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Lateral Lumbar Trans-Psoas Interbody Fusion

The lateral lumbar trans-psoas approach has gained increasing attention as an approach to achieve interbody fusion. The lateral approach offers several distinct advantages over the traditional anterior and posterior approaches. Specifically, it has demonstrated short hospital stays, low complication rates, and improved interbody graft placement and associated indirect decompression when used for several degenerative and deformity applications. The lateral approach is associated with thigh symptoms and irritation of the hip flexors which occurs in a minority of patients and typically is transient. There are several subtle aspects of the surgical technique which can minimize approach-related complications, optimize exposure, facilitate interbody graft placement, and indirect decompression, which may improve overall patient outcomes and recovery.

Minimally invasive lateral transpsoas approach with advanced neurophysiologic monitoring for lumbar interbody fusion

The online version of the original article can be found under doi:10.1007/s00586-011-1997-x.

Cadaveric Study Suggests Femoral Nerve at Risk During Transpsoas Approach to L4-L5 Disc

Commentary All surgical approaches to the lumbar discs are associated with morbidity and some risk of neurovascular injury. Surgeons choose the approach on the basis of their training, experience, and the pathology to be treated. The lateral retroperitoneal approach has the advantage of minimizing or eliminating manipulation of the large anterior vessels and the contents of the spinal canal. It places the psoas muscle and the adjacent neural structures at risk. A number of surgeons have developed less-invasive techniques to take advantage of this surgical approach, aided by retractors specific to the approach, fluoroscopy, and neuromonitoring. Clinical experience with this procedure is large, as reflected in the burgeoning literature. The range of reported complications varies widely in magnitude and scope. Among the more common neuromuscular complaints are thigh hypesthesia and paresthesias as well as hip flexor and knee extensor weakness. Both transient and permanent neurological deficits can occur. Rodgers et al. reported a series of 600 cases and noted only four instances (0.7%) of transient quadriceps weakness, attributed to nerve root dysfunction1. In contrast, Isaacs et al. noted thirty-six cases of weakness in a series of 107 patients2. Seven patients had persistent weakness for at least six months or were diminished by more than two motor grades at any time. Twenty-nine patients had hip flexor weakness, which was attributed to the psoas muscle itself. Weakness could not be correlated to the number of spinal levels treated or to the specific disc treated. In a series of eighty-four patients, Youssef et al. reported that one patient had transient psoas weakness, but their literature review demonstrated that the prevalence of inclusive but nonspecific “thigh symptoms” ranged from 1% to 60.1%3. Perhaps it was this wide variation in reported neuromuscular dysfunction that prompted Davis et al. to perform their cadaveric study. It is a carefully performed and well-described anatomic investigation. The investigators dissected eighteen specimens, with the cadaver in the lateral decubitus position, in an effort to mimic the clinical situation. Spinal needles were placed with fluoroscopic guidance into the midcoronal plane of the L2-L3, L3-L4, and L4-L5 discs. Careful blunt dissection through the psoas muscle showed the femoral nerve and not the nerve roots to be at risk at the L4-L5 level. In three specimens, the L4-L5 spinal needle was in close proximity to this nerve. In ten cadavers, the needle was between the femoral nerve and the posterior margin of the disc. In the remaining five specimens, the nerve was posterior to the disc margin. The femoral nerve was formed at the level of the L4-L5 disc in thirteen specimens and caudal to that disc in the remaining five. The authors logically speculate that further dissection with tube dilators and retractor expansion could injure the femoral nerve at L4-L5 by traction or compression against the L5 transverse process. If the nerve were transfixed by the initial guidewire, direct injury could occur. The authors are to be commended for a well-done investigation that gives spine surgeons good anatomical data. The strengths of the study include a relatively large number of cadavers, compared with other reports of anatomic dissections, and the use of the lateral decubitus position. It was internally funded, eliminating the potential bias of industry support. However, there are limitations and weaknesses. Spinal needles were placed, but then the dissection deviated from that used in surgery. Detachment of the posterior psoas attachments could have resulted in anterior migration of muscle and the nerves within it. The authors countered that the lateral decubitus position eliminated the effect of gravity, but some distortion of the anatomy likely occurred. Of course, this would be expected to increase the measured femoral nerve proximity. Furthermore, the blunt dissection of the psoas may have changed the position of the femoral nerve and other nearby nerves. The study design does not provide any information on what happens with dilation and retractor deployment. The study does not address clinical variables such as body-mass index, age, sex, and deformity that potentially could alter the nerve's size, location, and susceptibility to injury. Finally, the authors’ statistics concerning femoral nerve location are useful but cannot predict where the nerve location is in any given patient. One cannot make a direct correlation between their anatomic data and the prevalence of femoral nerve dysfunction found in the current literature. Despite these limitations, Davis and coworkers have provided the spine surgeon with valuable data. They have clearly demonstrated the femoral nerve to be a structure at risk when approaching the L4-L5 disc via a transpsoas approach. It may inform preoperative counseling and increase intraoperative vigilance at L4-L5. Kudos to the authors.