Lateral Retroperitoneal Transpsoas Approach Research Articles

Minimally invasive lateral retroperitoneal transpsoas approach for lumbar corpectomy and fusion with posterior instrumentation.

In this video, the authors highlight the operative treatment of a 55-year-old man with chronic osteomyelitis discitis. The operation entailed a minimally invasive lateral retroperitoneal transpsoas approach for L3 and L4 corpectomies, L2–5 interbody fusion, and L2–5 minimally invasive posterior instrumentation. The operation proceeded in two stages, beginning in the lateral position with corpectomy of the L3 and L4 vertebral bodies and placement of a corpectomy cage. After closure of this access wound, the patient was turned to a prone position for the posterior element of the operation. Posterior instrumentation was placed with pedicle screws at L2 and L5.The video can be found here: https://stream.cadmore.media/r10.3171/2022.3.FOCVID2210

MIS lateral retroperitoneal transpsoas approach allows gross total resection of a giant L4 schwannoma.

In this surgical video, the authors present a successful minimally invasive (MIS) lateral retroperitoneal transpsoas approach for resection of an L4 nerve root schwannoma. They describe the surgical approach in detail, with special emphasis on patient positioning for an orthogonal view, as well as technical nuances throughout the procedure. Using a sequential tubular retractor, they performed a microscopic dissection of the lesion. The tumor was debulked and the tumor capsule was disconnected from the surrounding tissue. During dissection, direct stimulation identified a functional nerve root that was carefully dissected from the tumor capsule. The tumor was then removed en bloc.The video can be found here: https://stream.cadmore.media/r10.3171/2022.3.FOCVID2220

A MORPHOMETRIC STUDY OF VENTRAL NERVE ROOTS AND RETROPERITONEAL VESSELS IN RELATION TO A MINIMALLY INVASIVE LATERAL APPROACH TO DETERMINE SAFE WORKING ZONE

Background: The minimally invasive lateral retroperitoneal transpsoas approach is a new method that was designed to minimize problems related with standard or minimally invasive anterior or posterior lumbar spine techniques. The current work used magnetic resonance imaging to determine the anatomic location of the ventral root and retroperitoneal arteries in respect to the vertebral body and to establish the anatomical safe zones. We examined lumbar spine MRI in 50 individuals retrospectively (L1-L2 to L5-S Method: 1 levels). The ventral root and surrounding major arteries were identied using axial T1 and T2 scans. Axial MR scans were utilized to determine the anterior-posterior (AP) diameter of the vertebral endplate, the overlap between the ventral root and the posterior border of the vertebra, and the overlap between the retroperitoneal big vessels and the anterior edge of the vertebra. The safe zone was then determined. From L1–L2 Results: to L5–S1, the mean AP diameter of the vertebral body and the overlap of the vertebral body with the nerve roots and retroperitoneal arteries grew gradually. When we examined the extent of overlap of retroperitoneal arteries with the ventral border of the lower vertebral body endplate, we discovered that the right vascular structures were more posterior than the left vascular structures. The safe working zone was 81.86 percent of the lower endplate of the sagittal diameter of the vertebral body at L1–L2, 70.03 percent at L2–L3, 69.32 percent at L3–L4, 50.08 percent at L4–L5, and 17.92 percent at L5–S1 levels. The Conclusion: retroperitoneal transpsoas method is a less invasive and more efcient alternative to the conventional posterior, open lumbar procedures. It can be used to treat trauma, degenerative disc disease, adult degenerative scoliosis, spondylosis with instability, spondylolisthesis, lumbar stenosis, and neighboring segment failure.

The Safe Entry Zones through the Transpsoas Approach to Lumbar Discs: A Cadaver Study

Abstract Background Data: Low back pain (LBP) is a common musculoskeletal disorder. In Egypt, patients with LBP constitute a high percentage of patients seeking medical care at outpatient clinics. Spinal fusion is a common treatment for spinal disorders such as disc degeneration, deformity, spondylolisthesis, or fracture. The minimally invasive lateral retroperitoneal transpsoas approach is a recent technique developed to avoid complications associated with traditional or minimally invasive anterior or posterior approaches to the lumbar spine. This technique provides a small incision that avoids significant abdominal muscle injury and lateral access to the disc space from L1-L2 to L4-L5. Purpose: To define a safe entry zone in the psoas muscle to prevent lumbar plexus injury during the transpsoas approach. Study Design: A descriptive cadaveric study. Material and Methods: A total of 30 cadavers were used in this study where each cadaver was dissected from both sides. Each cadaver was placed in lateral decubitus and a skin incision in the midaxillary line from the last rib to iliac crest was made. Then, the peritoneum was dissected, psoas muscle was exposed, and nerve roots were identified and reported at each disc space from L1-L2 to L4-L5. The safe entry zone was defined by the absence of crossing of a lumbar plexus branch. Results: Each disc space was divided into four zones: zone 1, the posterior quadrant; zone 2, the middle anterior quadrant; zone 3, the middle posterior quadrant; zone 4, the posterior quadrant. The safe working zone includes zones 2 and 3 at level L1-L2, zone 3 at level L2-L3, zone 3 at level L3-L4, and zone 2 at level L4-L5. There was no variance observed between either side regarding the relationships between the lumbar plexus and the intervertebral disc. Conclusion: Knowledge of the anatomy of lumbar plexus roots in psoas muscle is mandatory to prevent injury to lumbar plexus roots during entry of dilator through psoas muscle. This anatomical study suggests that there are certain safe zones at the lumbar disc spaces that allow passage of dilator inside psoas muscle to reduce direct nerve injury of the lumbar plexus. (2020ESJ200) Background data: Low back pain (LBP) is a common musculoskeletal disorder. In Egypt, patients with LBP constitutes a high percentage of patients seeking medical care at outpatient clinics. Spinal fusion is a common treatment for spinal disorders such as disc degeneration, deformity, spondylolisthesis or fracture. The minimally invasive lateral retroperitoneal transpsoas approach is a recent technique developed to avoid complications associated with traditional or minimally invasive anterior or posterior approaches to the lumbar spine. This technique was popularized by Pimenta and Ozgur. This technique provides small incision that avoids significant abdominal muscle injury and provides lateral access to the disc space from L1–L2 to L4–L5. Purpose: This study aims to define safe entry zone in psoas muscle to prevent lumbar plexus injury during transpsoas approach. Study design: This study is descriptive cadaveric study. Methods: Cadavers number: 10 cadavers, each cadaver was dissected from both sides. Each cadaver is placed in lateral decubitus, skin incision in midaxillary line from last rib to iliac crest. Incision of abdominal muscle then retraction of peritoneum, psaos muscle exposed. The psoas muscle is dissected, and nerve roots are identified and reported at each disc space from L1_2 to L4_5. The safe entry zone is defined by the absence of crossing of a lumbar plexus branch. Results: Our results are comparable to previous anatomical studies. Each disc space divided into four zones; zone 1 the posterior quadrant, Zone 2 the middle anterior quadrant, Zone 3 the middle posterior Quadrant, Zone 4 the posterior quadrant. 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. There is no variance was observed between either side as regards the relationships between the lumbar plexus and the intervertebral disc. Conclusion: The tranpsoas approach is minimally invasive approach developed to prevent major complications of traditional approaches. However, the proximity of lumbar plexus is the main limitation of the approach. Knowledge of anatomy of lumbar plexus roots in psoas muscle is mandatory to prevent injury to lumbar plexus roots during entry of dilator through psoas muscle.

Femoral nerve and lumbar plexus injury after minimally invasive lateral retroperitoneal transpsoas approach: electrodiagnostic prognostic indicators and a roadmap to recovery.

Injury to the lumbosacral (LS) plexus is a well-described complication after lateral retroperitoneal transpsoas approaches to the spine. The prognosis for functional recovery after lumbosacral plexopathy or femoral/obturator neuropathy is unclear. We designed a retrospective case-control study with patients undergoing one-level lateral retroperitoneal transpsoas lumbar interbody fusion (LLIF) between January 2011 and June 2016 to correlate electrodiagnostic assessments (EDX) to physiologic concepts of nerve injury and reinnervation, and attempt to build a timeline for patient evaluation and recovery. Cases with post-operative obturator or femoral neuropathy were identified. Post-operative MRI, nerve conduction studies (NCS), electromyography (EMG), and physical examinations were performed at intervals to assess clinical and electrophysiologic recovery of function. Two hundred thirty patients underwent LLIF. Six patients (2.6%) suffered severe femoral or femoral/obturator neuropathy. Five patients (2.2%) had immediate post-operative weakness. One of the six patients developed delayed weakness due to a retroperitoneal hematoma. Five out of six patients (83%) demonstrated EDX findings at 6weeks consistent with axonotmesis. All patients improved to at least MRC 4/5 within 12months of injury. In conclusion, neurapraxia is the most common LS plexus injury, and complete recovery is expected after 3months. Most severe nerve injuries are a combination of neurapraxia and variable degrees of axonotmesis. EDX performed at 6weeks and 3, 6, and 9months provides prognostic information for recovery. In severe injuries of proximal femoral and obturator nerves, observation of proximal to distal progression of small-amplitude, short-duration (SASD) motor unit potentials may be the most significant prognostic indicator.

Lateral lumbar retroperitoneal transpsoas approach in the setting of spondylodiscitis: A technical note

Thoracolumbar spondylodiscitis is a morbid disease entity, impacting a sick patient population with multiple comorbidities. Wherever possible, surgical measures in this population should limit the extent of soft tissue disruption and overall morbidity that is often associated with anteroposterior thoracolumbar decompression and fusion. The authors describe the rationale, technique, and use of the lateral lumbar transpsoas retroperitoneal approach in tandem with posterior decompression and instrumented fusion in the treatment of circumferential thoracolumbar spondylodiscitis with or without epidural abscesses. The authors have routinely implemented the lateral lumbar transpsoas retroperitoneal approaches to address all pyogenic vertebral abscesses, spondylodiscitis, and ventral epidural abscesses with anterior column debridement and reconstruction with iliac crest autograft, posterior decompression, and pedicle screw instrumentation. In five consecutive patients, the mean blood loss and operative duration was 275mL and 259min, respectively. There were no instances of major vascular injury as this corridor obviates the need for retraction of inflamed retroperitoneal structures. The use of the lumbar lateral retroperitoneal transpsoas approach to the lumbar spine for the treatment of destructive and pyogenic spondylodiscitis is a potential alternative to the traditional anterior lumbar retroperitoneal approach in tandem with posterior spinal decompression and instrumented stabilization.

A new extensile anterolateral retroperitoneal approach for lumbar interbody fusion from L1 to S1: a prospective series with clinical outcomes

Background ContextA variety of surgical approaches have been used for cage insertion in lumbar interbody fusion surgery. The direct anterior approach requires mobilization of the great vessels to access the intervertebral disc spaces cranial to L5/S1. With the lateral retroperitoneal transpsoas approach, it is difficult to access the L4/L5 intervertebral disc space due to the lumbar plexus and iliac crest, and L5/S1 is inaccessible. We describe a new anterolateral retroperitoneal approach, which is safe and reproducible to access the disc spaces from L1 to S1 inclusive, obviating the need for a separate direct anterior approach to access L5/S1. PurposeThis paper had the following objectives: first, to report a reproducible novel single-incision, muscle-splitting, anterolateral pre-psoas surgical approach to the lumbar spine from L1 to S1; second, to highlight the technical challenges of this approach and highlight approach-related complications; and third, to evaluate clinical outcomes using this surgical technique in a prospective series of L1 to S1 anterior lumbar interbody fusions (ALIFs) performed as part of a 360-degree fusion for adult spinal deformity correction. Study DesignThis report used a prospective cohort study. Patient SampleA prospective series of patients (n=64) having ALIF using porous tantalum cages as part of a two-stage complex spinal reconstruction from L1 to S1 were studied. Outcome MeasuresData collected included blood loss, operative time, incision size, technical challenges, perioperative complications, and secondary procedures. Clinical outcome measures used included visual analogue scale (VAS) Back Pain, VAS Leg Pain, EuroQoL-5 Dimensions (EQ-5D), EQ-5D VAS, Oswestry Disability Index (ODI), and Scoliosis Research Society-22 (SRS-22). MethodsPre- and postoperative radiographic parameters and clinical outcome measures were assessed. Mean follow-up time was 1.8 years. ResultsMean blood loss was 68±9.6 mL. The mean VAS Back Pain score improved from 7.5±1.25 preoperatively to 2.5±1.7 at 3 months (p=.02), 1.2±0.5 at 6 months (p=.01), and 1.4±0.6 at 1 year (p=.02). The mean ODI improved from 64.3±31.8 preoperatively to 16.6±14.7 at 3 months (p>.05), 10.7±6.0 at 6 months (p=.02), and 6.7±6.1 at 1 year (p=.01). There were no permanent neurologic, vascular, or visceral injuries. One revision anterior procedure was required on a patient with rheumatoid arthritis and advanced systemic disease that sustained a sacral fracture and required revision ALIF at L5/S1. ConclusionsThe technique described is a safe, new, muscle-splitting, psoas-preserving, one-incision approach to provide access from L1 to S1 for multilevel anterior or oblique lumbar interbody fusion surgery.

Anterior Longitudinal Ligament Release From the Minimally Invasive Lateral Retroperitoneal Transpsoas Approach: Technical Note.

The technique for minimally invasive anterior longitudinal ligament release is a major advancement in lateral access surgery. This method provides hypermobility of lumbar segments to allow for aggressive lordosis restoration while maintaining the benefits of indirect decompression and minimally invasive access. To provide video demonstration of the lateral retroperitoneal transpsoas approach with anterior longitudinal ligament sectioning. A detailed surgical technique of the minimally invasive anterior column release is described and illustrated in an elderly patient with adult spinal deformity and low back pain (visual analog scale, 8 of 10) refractory to conservative measures. The 3-foot standing radiographs demonstrated a lumbar lordosis of 54.4°, pelvic incidence of 63.7°, and pelvic tilt of 17.5°. Computed tomography and magnetic resonance imaging showed generalized lumbar spondylosis and degenerative disc changes from L2 to L5. The patient underwent a multilevel minimally invasive deformity correction with an anterior longitudinal ligament release at the L3/L4 level through the lateral retroperitoneal transpsoas approach. Lumbar lordosis increased from 54.4° to 77° with a global improvement in sagittal vertical axis from 4.37 cm to 0 cm. Total blood loss was less than 25 mL, and there were no major neurological or vascular complications. The anterior longitudinal ligament release using the minimally invasive lateral approach allows for deformity correction without the morbidity and blood loss encountered by traditional open posterior approaches. However, the risk of major vascular/visceral complication warrants only experts in minimally invasive lateral surgery to attempt this technique.

Femoral Neurogram Before Transpsoas Spinal Access at L4–5 Intervertebral Disk Space

Observational study. To illustrate the variability of the course of the femoral nerve across the L4-5 disk space, and to present a novel application of transforaminal epidural steroid injections (TFESI) in the visualization of femoral nerve roots. A concern regarding the lateral retroperitoneal transpsoas approach is the proximity of the lumbar plexus. Current techniques of assessing the proximity of neural tissue to the L4-5 disk space have limited capabilities. A total of 100 patients were selected for L4-5 TFESI (L4 selective nerve root blocks) because of lumbar radiculopathy. L4 neurograms were obtained while performing L4-5 TFESI under flouroscopic guidance, using a retroneural technique. The course of the L4 root/femoral nerve was then evaluated under fluoroscopy in the anteroposterior and lateral planes. Images were then reviewed by a radiologist, physiatrist, and 2 orthopedic spine surgeons. Fluoroscopic evaluation revealed that the pattern of location of the femoral nerve was highly variable. In males, it was located 4.7% in zone 2, 32.5% in zone 3, 53.5% in zone 4, and 9.3% in zone P. In female patients, it was located 7.0% in zone 2, 14% in zone 3, 54.4% in zone 4, and 24.6% in zone P. An L4 neurogram will provide an accurate trajectory of L4 root/femoral nerve as it crosses the L4-5 intervertebral disk space. An accurate assessment is essential to help minimize the increasing frequency of thigh pain, paresthesias, and weakness associated with the lateral access to the L4-5 intervertebral disk space. Femoral nerves that fall within zones 2 and 3 will require more manipulation during retraction and may be better suited with a different surgical approach.

Neural anatomy, neuromonitoring and related complications in extreme lateral interbody fusion: video lecture

The lateral retroperitoneal transpsoas approach to the lumbar spine requires passage in close proximity to both superficial and deep neural structures [1, 2]. While the majority of nerves that are at risk for injury in the lateral approach are located on and within psoas major (e.g., femoral and genitofemoral nerves), the subcostal, lateral femoral cutaneous, ilioinguinal, and iliohypogastric nerves are all located outside of the psoas muscle and may be encountered prior to passage through the psoas muscle (superficial nerves). Given the less-invasive nature of the approach adjacent to these structures, a clear understanding of the relevant anatomy with respect to neural architecture, followed by close adherence to intraoperative neuromonitoring and surgical technique may reduce the risk of neurologic injury.

Fusion via transpsoas lateral approach: considerations and initial results

OBJECTIVE: To present some technical considerations about interbody fusion by direct lateral retroperitoneal transpsoas approach and its initial results. METHODS: Non-randomized prospective study of 14 patients undergoing interbody fusion via lateral approach, with evaluation of initial results and complications. RESULTS: We collected and analyzed data from 14 patients with a total of 27 levels operated. The average operative time was 146 minutes and blood loss was on average less than 50 ml. Ten patients required supplemental percutaneous fixation with pedicle screws. VAS scores for the lumbar region and lower limbs and ODI had significant improvement in the postoperative period. There was an associated case of postoperative infection and thromboembolism that required reoperations. CONCLUSION: This technique has revolutionized the care of patients requiring fusion of T6-7 to L4-5. Following the five basic steps and using intraoperative monitoring, this technique is safe and reproducible with encouraging clinical results and low rate of serious complications.

MRI Assessment of the Psoas Muscle and Its Relationship with Lumbar Plexus and the Lumbar L4-L5 Disc: A Guideline in Surgical Planning for Patient with Indication of Lateral Approach: A Prospective Study

The minimally invasive lateral retroperitoneal transpsoas approach (LRTA) is being increasingly employed to treat common spinal disorders. We sought to describe the locations of relevant neural structures based on MRI with respect to this approach. We assessed prospectively a series of lumbosacral spine MRI scans in 42 patients and its concordance with the use of intraoperative real-time nerve monitoring (Concordance rate). MRI scans were independently reviewed by two readers to identify the location of the psoas muscle and lumbar plexus.

Functional recovery of severe obturator and femoral nerve injuries after lateral retroperitoneal transpsoas surgery

The minimally invasive lateral retroperitoneal transpsoas approach is a popular fusion technique. However, potential complications include injury to the lumbar plexus nerves, bowel, and vasculature, the most common of which are injuries to the lumbar plexus. The femoral nerve is particularly vulnerable because of its size and location; injury to the femoral nerve has significant clinical implications because of its extensive sensory and motor innervation of the lower extremities. The authors present an interesting case of a 49-year-old male patient in whom femoral and obturator nerve functional recovery unexpectedly occurred 364 days after the nerves had been injured during lateral retroperitoneal transpsoas surgery. Chronological video and electrodiagnostic findings demonstrate evidence of recovery. Classification and mechanisms of nerve injury and nerve regeneration are discussed.

Analysis of lumbar plexopathies and nerve injury after lateral retroperitoneal transpsoas approach: diagnostic standardization

The minimally invasive lateral transpsoas approach has become an increasingly popular means of fusion. The most frequent complication is related to lumbar plexus nerve injuries; these can be diagnosed based on distribution of neurological deficit following the motor and/or sensory nerve injury. However, the literature has failed to provide a clinically relevant description of these complications. With accurate clinical diagnosis, spine practitioners can provide more precise prognostic and management recommendations to include observation, nerve blocks, neurodestructive procedures, medications, or surgical repair strategies. The purpose of this study was to standardize the clinical findings of lumbar plexopathies and nerve injuries associated with minimally invasive lateral retroperitoneal transpsoas lumbar fusion. A thorough literature search of the MEDLINE database up to June 2012 was performed to identify studies that reported lumbar plexus and nerve injuries after the minimally invasive lateral retroperitoneal transpsoas approach. Included studies were assessed for described neurological deficits postoperatively. Studies that did attempt to describe nerve-related complications clinically were excluded. A clinically relevant assessment of lumbar plexus nerve injury was derived to standardize early diagnosis and outline prognostic implications. A total of 18 studies were selected with a total of 2310 patients; 304 patients were reported to have possible plexus-related complications. The incidence of documented nerve and/or root injury and abdominal paresis ranged from 0% to 3.4% and 4.2%, respectively. Motor weakness ranged from 0.7% to 33.6%. Sensory complications ranged from 0% to 75%. A lack of consistency in the descriptions of the lumbar plexopathies and/or nerve injuries as well as a lack of diagnostic paradigms was noted across studies reviewed. Sensory dermal zones were established and a standardized approach was proposed. There is underreporting of postoperative lumbar plexus nerve injury and a lack of standardization of clinical findings of neural complications related to the minimally invasive lateral retroperitoneal transpsoas approach. The authors provide a diagnostic paradigm that allows for an efficient and accurate classification of postoperative lumbar plexopathies and nerve injuries.

Anterior longitudinal ligament release using the minimally invasive lateral retroperitoneal transpsoas approach: a cadaveric feasibility study and report of 4 clinical cases

Traditional procedures for correction of sagittal imbalance via shortening of the posterior column include the Smith-Petersen osteotomy, pedicle subtraction osteotomy, and vertebral column resection. These procedures require wide exposure of the spinal column posteriorly, and may be associated with significant morbidity. Anterior longitudinal ligament (ALL) release using the minimally invasive lateral retroperitoneal approach with a resultant net lengthening of the anterior column has been performed as an alternative to increase lordosis. The objective of this study was to demonstrate the feasibility and early clinical experience of ALL release through a minimally invasive lateral retroperitoneal transpsoas approach, as well as to describe its surgical anatomy in the lumbar spine. Forty-eight lumbar levels were dissected in 12 fresh-frozen cadaveric specimens to study the anatomy of the ALL as well as its surrounding structures, and to determine the feasibility of the technique. The lumbar disc spaces and ALL were accessed via the lateral transpsoas approach and confirmed with fluoroscopy in each specimen. As an adjunct, 4 clinical cases of ALL release through the minimally invasive lateral retroperitoneal transpsoas approach were reviewed. Operative technique, results, complications, and early outcomes were assessed. In the cadaveric study, sectioning of the ALL proved to be feasible from the minimally invasive lateral retroperitoneal transpsoas approach. The structures at most immediate risk during this procedure were the aorta, inferior vena cava, iliac vessels, and sympathetic plexus. The mean increase in segmental lumbar lordosis per level of ALL release was 10.2°, while global lumbar lordosis improved by 25°. Each level of ALL release took 56 minutes and produced 40 ml of blood loss on average. Visual analog scale and Oswestry Disability Index scores improved by 9 and 35 points, respectively. There were no cases of hardware failure, and as of yet no complications to report. This initial experience suggests that ALL release through the minimally invasive lateral retroperitoneal transpsoas approach may be feasible, allows for improvement of lumbar lordosis without the need of an open laparotomy/thoracotomy, and minimizes the tissue disruption and morbidity associated with posterior osteotomies.

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.

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.

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.

Safe working zones using the minimally invasive lateral retroperitoneal transpsoas approach: a morphometric study

The minimally invasive lateral retroperitoneal transpsoas approach is a recent technique developed for lumbar interbody fusion and discectomy. The proximity of the retroperitoneal vessels and ventral nerve roots to the surgical pathway increases the risk of injury to these anatomical structures. A precise knowledge of the regional anatomy of the lumbar plexus is required for safe passage through the psoas muscle. Preoperative examination of the axial MRI images will allow the surgeon to observe the neural structures at the operative levels and confirm that abdominal vessels do not obstruct the lateral disc space. The objective of this study was to determine the anatomic position of the ventral nerve roots and the retroperitoneal vessels in relation to the vertebral body in the degenerative spine and to delineate a safe working zone using magnetic resonance imaging (MRI). We retrospectively evaluated lumbar spine MRI in 78 patients (from L1-L2 to L4-L5). The total number of lumbar vertebrae measured was 304 levels. Sagittal MRI sections were used to measure disc height (anterior, middle, posterior). Axial MRI sections were used to measure the sagittal and transversal vertebral endplate diameters, the overlap between ventral nerve roots and the posterior border of the lower endplate of the vertebral body, and the overlap between the retroperitoneal vessels and the anterior border of the lower endplate of the vertebral body. The safe zone was subsequently calculated. It was defined as the relative lower endplate vertebral body sagittal diameter that is anterior to the nerve root and is posterior to the retroperitoneal vessels. The safe working zone was 75.3% of the lower endplate of the vertebral body sagittal diameter at L1-L2, 59.5% at L2-L3, 51.9% at L3-L4 and 37.8% at L4-L5 levels. This area significantly decreases from L1-L2 to L4-L5 (p<0.05). Compared with L1-L2, L2-L3 levels, the more anterior position of the nerve root and the more posterior position of the retroperitoneal vessels at the L4-L5 level causes a significant reduction of this area. Compared with the L3-L4 level, we observed that the safe zone decrease was simply secondary to the more anterior position of the nerve roots at the L4-L5 level. Preoperative planning and safe zone delineation are a simple method to assess the relative position of neural and vascular anatomic structures in relation to the surgical area. This method can help spine surgeons to prevent perioperative complications.

Trajectory of the main sensory and motor branches of the lumbar plexus outside the psoas muscle related to the lateral retroperitoneal transpsoas approach

The minimally invasive lateral retroperitoneal transpsoas approach is increasingly used to treat various spinal disorders. Accessing the retroperitoneal space and traversing the abdominal wall poses a risk of injury to the major nervous structures and adds significant morbidity to the procedure. Most of the current literature focuses on the anatomy of the lumbar plexus within the substance of the psoas muscle. However, there is sparse knowledge regarding the trajectory of the lumbar plexus nerves that travel along the retroperitoneum and abdominal wall muscles in relation to the lateral approach to the spine. The objective of this study is to define the anatomical trajectories of the major motor and sensory branches of the lumbar plexus that are located outside the psoas muscle. Six adult fresh frozen cadaveric specimens were dissected and studied (12 sides). The relationship between the retroperitoneum, abdominal wall muscles, and the lumbar plexus nerves was analyzed in reference to the minimally invasive lateral retroperitoneal approach. Special attention was given to the lumbar plexus nerves that run outside of psoas muscle in the retroperitoneal cavity and within the abdominal muscle wall. The skin and muscles of the abdominal wall and the retroperitoneal cavity were dissected and analyzed with respect to the major motor and sensory branches of the lumbar plexus. The authors identified 4 nerves at risk during the lateral approach to the spine: subcostal, iliohypogastric, ilioinguinal, and lateral femoral cutaneous nerves. The anatomical trajectory of each of these nerves is described starting from the spinal column until their termination or exit from the pelvic cavity. There is risk of direct injury to the main motor/sensory nerves that supply the anterior abdominal muscles during the early stages of the lateral retroperitoneal transpsoas approach while obtaining access to the retroperitoneum. There is also a risk of injury to the ilioinguinal, iliohypogastric, and lateral femoral cutaneous nerves in the retroperitoneal space where they travel obliquely during the blunt retroperitoneal dissection. Moreover, there is a latent possibility of lesioning these nerves with the retractor blades against the anterior iliac crest.