The rising psoas sign: an analysis of preoperative imaging characteristics of aborted minimally invasive lateral interbody fusions at L4–5

Anterior Column Realignment Using an Anterior-To-Psoas Approach: A Radiographic-Anatomic Feasibility Study at L1-L5

STUDY DESIGN

Cross-sectional radioanatomic study.

OBJECTIVE

To determine the feasibility of performing an anterior column realignment (ACR) using an anterior-to-psoas (ATP) approach at L1-L5.

METHODS

Axial magnetic resonance images (MRI) of the L1-L5 disc levels obtained at a single institution were obtained and analyzed. The feasibility of performing an ACR was assessed using a combination of the size of the left oblique corridor (OC), the psoas morphology using the modified Moro classification, and the anterior disc edge to great vessel distance.

RESULTS

Three hundred MRI studies obtained from 300 patients were included. All patients had a measurable left OC at the L1-L4 levels. Twenty patients (6.7%) had no measurable OC at the L4-L5 level. According to the modified Moro's classification, a high-rising psoas was seen in 4 patients (1.3%) at the L3-L4 level and 57 patients (19.0%) at the L4-L5 level. An ALL release was considered high risk due to no measurable space between the anterior disc edge and the great vessels in 54 patients (18.0%) at the L1-L2 level, 39 patients (13.0%) at the L2-L3 level, 119 patients (39.7%) at the L3-L4 level, and 226 patients (75.3%) at the L4-L5 level.

CONCLUSION

ACR using an ATP approach is the most radioanatomically feasible at L2-L3. The L4-L5 level has the highest risk with regards to both the ATP approach and the ALL release for an ACR due to high rates of unmeasurable left OC and space between the anterior disc edge and the great vessels.

Female Sex and Supine Proximal Lumbar Lordosis Are Associated With the Size of the LLIF "Safe Zone" at L4-L5

STUDY DESIGN

Retrospective chart review.

OBJECTIVE

Identify demographic and sagittal alignment parameters that are independently associated with femoral nerve position at the L4-L5 disk space.

SUMMARY OF BACKGROUND DATA

Iatrogenic femoral nerve or lumbar plexus injury during lateral lumbar interbody fusion (LLIF) can result in neurological complications. The LLIF "safe zone" is the anterior half to two third of the disk space. However, femoral nerve position varies and is inconsistently identifiable on magnetic resonance imaging. The safe zone is also narrowest at L4-L5.

METHODS

An analysis of patients with symptomatic lumbar spine pathology and magnetic resonance imaging with a visibly identifiable femoral nerve evaluated at a single large academic spine center from January 1, 2017, to January 8, 2020, was performed. Exclusion criteria were transitional anatomy, severe hip osteoarthritis, coronal deformity with cobb >10 degrees, > grade 1 spondylolisthesis at L4-L5 and anterior migration of the psoas.Standing and supine lumbar lordosis (LL) and its proximal (L1-L4) and distal (L4-S1) components were measured. Femoral nerve position on sagittal imaging was then measured as a percentage of the L4 inferior endplate. A stepwise multivariate linear regression of sagittal alignment and LL parameters was then performed. Data are written as estimate, 95% CI.

RESULTS

Mean patient age was 58.2±14.7 years, 25 (34.2%) were female and 26 (35.6%) had a grade 1 spondylolisthesis. Mean femoral nerve position was 26.6±10.3% from the posterior border of L4. Female sex (-6.6, -11.1 to -2.1) and supine proximal lumbar lordosis (0.4, 0.1-0.7) were independently associated with femoral nerve position.

CONCLUSIONS

Patient sex and proximal LL can serve as early indicators of the size of the femoral nerve safe zone during a transpsoas LLIF approach at L4-L5.

Antepsoas Approaches to the Lumbar Spine

Lumbar interbody fusion (LIF) is a well-established approach in treating spinal deformity and degenerative conditions of the spine. Since its inception in the 20th century, LIF has continued to evolve, allowing for minimally invasive approaches, high fusion rates, and improving disability scores with favorable complication rates. The anterior to the psoas (ATP) approach utilizes a retroperitoneal pathway medial to the psoas muscle to access the L1-S1intervertebral disc spaces. In contrast to the transpsoas arppoach, its primary advantage is avoiding transgressing the psoas muscle and the contained lumbar plexus, which potentially decreases the risk of injury to the lumbar plexus. Avoiding transgression of the psoas may minimize the risk of transient or permanent neurological deficits secondary to lumbar plexus injury. Indications for ATP approaches may expand as it is shown to be a safe and effective method of achieving spinal arthrodesis.

Robotic-Assisted Single-Position Prone Lateral Lumbar Interbody Fusion: Indications, Techniques, and Outcomes

Background

Lateral lumbar interbody fusion (LLIF) is a widely utilized minimally invasive surgical procedure for anterior fusion of the lumbar spine. However, posterior decompression or instrumentation often necessitates patient repositioning, which is associated with increased operative time and time under anesthesia1-3. The single-position prone transpsoas approach is a technique that allows surgeons to access both the anterior and posterior aspects of the spine, bypassing the need for intraoperative repositioning and therefore optimizing efficiency4. The use of robotic assistance allows for decreased radiation exposure and increased accuracy, both with placing instrumentation and navigating the lateral corridor.

Description

The patient is placed in the prone position, and pedicle screws are placed prior to interbody fusion. Pedicle screws are placed with robotic guidance. After posterior instrumentation, a skin incision for LLIF is made in the cephalocaudal direction, orthogonal to the disc space, with use of intraoperative (robotic) navigation. Fascia and abdominal muscles are incised to enter the retroperitoneal space. Under direct visualization, dilators are placed through the psoas muscle into the disc space, and an expandable retractor is placed and maintained with use of the robotic arm. Following a thorough discectomy, the disc space is sized with trial implants. The expandable cage is placed, and intraoperative fluoroscopy is utilized to verify good instrumentation positioning. Finally, posterior rods are placed percutaneously.

Alternatives

An alternative surgical approach is a traditional LLIF with the patient beginning in the lateral position, with intraoperative repositioning from the lateral to the prone position if circumferential fusion is warranted. Additional alternative surgical procedures include anterior or posterior lumbar interbody fusion techniques.

Rationale

LLIF is associated with reported advantages of decreased risks of vascular injury, visceral injury, dural tear, and perioperative infection5,6. The single-position prone transpsoas approach confers the added benefits of reduced operative time, anesthesia time, and surgical staffing requirements7. Other potential benefits of the prone lateral approach include improved lumbar lordosis correction, gravity-induced displacement of peritoneal contents, and ease of posterior decompression and instrumentation8-11. Additionally, the use of robotic assistance offers numerous benefits to minimally invasive techniques, including intraoperative navigation, instrumentation templating, a more streamlined workflow, and increased accuracy in placing instrumentation, while also providing a reduction in radiation exposure and operative time. In our experience, the table-mounted LLIF retractor has a tendency to drift toward the floor-i.e., anteriorly-when the patient is positioned prone, which may, in theory, increase the risk of iatrogenic bowel injury. The rigid robotic arm is much stiffer than the traditional retractor, thereby reducing this risk.

Expected Outcomes

Compared with traditional LLIF, with the patient in the lateral and then prone positions, the single-position prone LLIF has been shown to have several benefits. Guiroy et al. performed a systematic review comparing single and dual-position LLIF and found that the single-position surgical procedure was associated with significantly lower operative time (103.1 versus 306.6 minutes), estimated blood loss (97.3 versus 314.4 mL), and length of hospital stay (1.71 versus 4.08 days)17. Previous studies have reported improved control of segmental lordosis in the prone position, which may be advantageous for patients with sagittal imbalance18,19.

Important Tips

Adequate release of the deep fascial layers is critical for minimizing deflection of retractors and navigated instruments.The hip should be maximally extended to maximize lordosis, allowing for posterior translation of the femoral nerve and increasing the width of the lateral corridor.A bolster is placed against the rib cage to provide resistance to the laterally directed force when impacting the graft.The cranial and caudal limits of the approach are bounded by the ribcage and iliac crest; thus, surgery at the upper or lower lumbar levels may not be feasible for this approach. Preoperative radiographs should be evaluated to determine the feasibility of this approach at the intended levels.When operating at the L4-L5 disc space, posterior retraction places substantial tension on the femoral nerve. Thus, retractor time should be minimized as much as possible and limited to a maximum of approximately 20 minutes20-22.A depth of field (distance from the midline to the flank) of approximately 20 cm may be the limit for this approach with the current length of retractor blades19.In robotic-assisted surgical procedures, minor position shifts in surface landmarks, the robotic arm, or the patient may substantially impact the navigation software. It is critical for the patient and navigation components to remain fixed throughout the operation.In addition to somatosensory evoked potential and electromyographic monitoring, additional motor evoked potential neuromonitoring or monitoring of the saphenous nerve may be considered22.In the prone position, the tendency is for the retractor to migrate superficially and anteriorly. It is critical to be aware of this tendency and to maintain stable retractor positioning.

Acronyms and Abbreviations

LLIF = lateral lumbar interbody fusionMIS = minimally invasive surgeryPTP = prone transpsoasy.o. = years oldASIS = anterior superior iliac spinePSIS = posterior superior iliac spineALIF = anterior lumbar interbody fusionTLIF = transforaminal lumbar interbody fusionMEP = motor evoked potentialSSEP = somatosensory evoked potentialEMG = electromyographyCT = computed tomographyMRI = magnetic resonance imagingOR = operating roomPOD = postoperative dayIVC = inferior vena cavaA. = aortaPS. = psoas.

Psoas Major Swelling Grade Affects the Clinical Outcomes after OLIF: A Retrospective Study of 89 Patients

OBJECTS

Oblique lumbar interbody fusion (OLIF) has gained increasing popularity recently. However, complications resulting from intraoperative retraction of psoas major (PM) sometimes occur. The aim of this study is to evaluate the degree of PM swelling by developing a scoring system called the Psoas Major Swelling Grade (PMSG), and to investigate the correlation between the PMSG and clinical outcomes after OLIF.

METHODS

Patients who underwent L4-5 OLIF at our hospital from May 2019 to May 2021 were reviewed and all data were recorded. The extent of postoperative PM swelling was determined by calculating the percentage of change in the PM area before and after surgery on MRI and divided into three grades subsequently. Swelling within the range of 0% to 25% was defined as grade I, 25%-50% was grade II, and more than 50% was grade III. All patients were grouped into the new grade system and followed up for at least 1 year, during which the visual analog scale (VAS) and Oswestry disability index (ODI) scores were recorded. Categorical data were analyzed using chi-square and Fisher's exact tests, while continuous variables were assessed with one-way ANOVA and paired t-tests.

RESULTS

Eighty-nine consecutive patients were enrolled in this study, with a mean follow-up duration of 16.9 months. The proportion of female patients in the PMSG I, II, and III groups was 57.1%, 58.3%, and 84.1%, respectively (p = 0.024).  Furthermore, the total complication rate was 43.2% in the PMSG III group, significantly higher than 9.5% and 20.8% in the PMSG I and II groups (p = 0.012). The incidence of thigh paraesthesia was also considerably higher in the PMSG III group at 34.1% (p = 0.015), compared to 9.5% and 8.3% in the PMSG I and II groups. Among the patients, 12.4% exhibited a teardrop-shaped PM, with the majority (90.9%) belonging to the PMSG III group (p = 0.012). Additionally, the PMSG III group demonstrated a higher estimated blood loss (p = 0.007) and significantly worse clinical scores at the 1-week follow-up assessment (p < 0.001).

CONCLUSION

PM swelling adversely affects the OLIF prognosis. Female patients with teardrop-shaped PM are more likely to develop swelling after OLIF. A higher PMSG is associated with a higher complication rate of thigh pain or numbness and worse short-term clinical outcomes.

Elimination of Lumbar Plexus Injury by Changing the Entry Point and Traction Direction of the Psoas Major Muscle in Transpsoas Lateral Lumbar Spine Surgery

Background and Objectives: The lateral approach is commonly used for anterior column reconstruction, indirect decompression, and fusion in patients with lumbar degenerative diseases and spinal deformities. However, intraoperative lumbar plexus injury may occur. This is a retrospective comparative study to investigate and compare neurological complications between the conventional lateral approach and a modified lateral approach at L4/5. Materials and Methods: Patients with a lumbar degenerative disease requiring single-level intervertebral fusion at L4/5 were included and categorized into group X and group A. Patients in group X underwent conventional extreme lateral interbody fusion, while those in group A underwent a modified surgical procedure that included splitting of the anterior third of the psoas muscle, which was dilated by the retractor on the anterior third of the intervertebral disc. The incidence of lumbar plexus injury, defined as a decrease of ≥1 grade on manual muscle testing of hip flexors and knee extensors and sensory impairment of the thigh for ≥3 weeks, on the approach side, was investigated. Results: Each group comprised 50 patients. No significant between-group differences in age, sex, body mass index, and approach side were observed. There was a significant between-group difference in intraoperative neuromonitoring stimulation value (13.1 ± 5.4 mA in group X vs. 18.5 ± 2.3 mA in group A, p < 0.001). The incidence of neurological complications was significantly higher in group X than in group A (10.0% vs. 0.0%, respectively, p < 0.05). Conclusions: In our modified procedure, the anterior third of the psoas muscle was entered and split, and the intervertebral disc could be reached without damaging the lumbar plexus. When performing lumbar surgery using the lateral approach, lumbar plexus injury can be avoided by following surgical indication criteria based on the location of the lumbar plexus with respect to the psoas muscle and changing the transpsoas approach to the intervertebral disc.

Approach-related anatomical differences in patients with lumbo-sacral transitional vertebrae undergoing lumbar fusion surgery at level L4/5

INTRODUCTION

Lumbo-sacral transitional vertebrae (LSTV) are accompanied by changes in soft tissue anatomy. The aim of our retrospective study was to evaluate the effects of LSTV as well as the number of free lumbar vertebrae on surgical approaches of ALIF, OLIF and LLIF at level L4/5.

MATERIAL AND METHODS

We assessed the CTs of 819 patients. Of these, 53 had LSTV from which 11 had six (6LV) and 9 four free lumbar vertebrae (4LV). We matched them for sex and age to a control group.

RESULTS

Patients with LSTV had a higher iliac crest and vena cava bifurcation, a greater distance between the common iliac veins and an anterior translation of the psoas muscle at level L4/5. In contrast, patients with 6LV had a lower iliac crest and aortic bifurcation, no differences in vena cava bifurcation and distance between the iliac veins compared to the control group.

CONCLUSIONS

For patients with LSTV and five or four free lumbar vertebrae, the LLIF approach at L4/5 may be hindered due to a high riding iliac crest as well as anterior shift of the psoas muscle. Whereas less mobilization and retraction of the iliac veins may reduce the risk of vascular injury at this segment by ALIF and OLIF. For patients with 6LV, a lower relative height of the iliac crest facilitates lateral approach during LLIF. For ALIF and OLIF, a stronger vessel retraction due to the deeper-seated vascular bifurcation is necessary during ALIF and is therefore potentially at higher risk for vascular injury.

Long-Term Motor versus Sensory Lumbar Plexopathy After Lateral Lumbar Interbody Fusion: Single-Center Experience, Intraoperative Neuromonitoring Results, and Multivariate Analysis of Patient-Level Predictors

BACKGROUND

Although lateral lumbar interbody fusion (LLIF) is an effective surgical option for lumbar arthrodesis, postoperative plexopathies are a common complication. We characterized post-LLIF plexopathies in a large cohort and analyzed potential risk factors for each.

METHODS

A single-institutional cohort who underwent LLIF between May 2015 and December 2019 was retrospectively reviewed for postoperative lumbar plexopathies. Plexopathies were divided based on sensory and motor symptoms and duration, as well as by laterality relative to the surgical approach. We assessed these subgroups for associations with patient and surgical characteristics as well as psoas dimensions. We then evaluated risk of developing plexopathies after intraoperative neuromonitoring observations.

RESULTS

A total of 127 patients were included. The overall rate of LLIF-induced sensory or motor lumbar plexopathy was 37.8% (48/127). Of all cases, 42 were ipsilateral to the surgical approach (33.1%); conversely, 6 patients developed contralateral plexopathies (4.7%). Most (31/48; 64.6%) resolved with a follow-up interval of 402 days in the plexopathy group. Of ipsilateral cases, 24 patients experienced persistent (>90 days) postoperative sensory symptoms (18.9%), whereas 20 experienced persistent weakness (15.7%). More levels fused predicted persistent sensory symptoms (odds ratio, 1.714 [1.246-2.359]; P = 0.0085), whereas surgical duration predicted persistent weakness (odds ratio, 1.004 [1.002-1.006]; P = 0.0382). Psoas anatomic variables were not significantly associated with plexopathy. Nonresolution of intraoperative evoked motor potential alerts was a significant risk factor for developing plexopathies (relative risk, 2.29 [1.17-4.45]).

CONCLUSIONS

Post-LLIF plexopathies are common but usually resolve. Surgical complexity and unresolved neuromonitoring alerts are possible risk factors for persistent plexopathy.

Different Moro Zones of Psoas Major Affect the Clinical Outcomes after Oblique Lumbar Interbody Fusion: A Retrospective Study of 94 Patients

Oblique lumbar interbody fusion (OLIF) has been driven to the maturity stage in recent years. However, postoperative symptoms such as thigh paresthesia resulting from intraoperative retraction of the psoas major (PM) have sometimes occurred. The aim of this study was to assess the different positions and morphology of PM muscles and their relationship with clinical outcomes after OLIF by introducing the Moro zones. Patients who underwent L4-5 OLIF at our institution between April 2019 and June 2021 were reviewed and all data were recorded. All patients were grouped by Moro zones into a Moro A cohort and a Moro I and II cohort based on the front edges of their left PM muscles. A total of 94 patients were recruited, including 57 in the Moro A group and 37 in the Moro I and II group. Postoperative thigh pain or numbness occurred in 12 (21.1%) and 2 (5.4%) patients in the Moro A group and the Moro I and II group, respectively. There was no difference in the psoas major transverse diameter (PMTD) between groups preoperatively, while longer PMTD was revealed postoperatively in the Moro A group. The operating window (OW) and psoas major sagittal diameter (PMSD) showed significant differences within and between groups. Thirteen patients had teardrop-shaped PM muscles, with 92.3% in the Moro A group showing significantly worse clinical scores at 1-week follow-up. The Moro zones of the PM affected the short-term outcomes after OLIF. Preoperative measurements and analysis of OW, PMSD and PM morphology should be performed as necessary to predict short-term outcomes.

Anterior spinal fusion (ALIF/OLIF/LLIF) with lumbosacral transitional vertebra: A systematic review and proposed treatment algorithm

•Key anterior approaches differences in LSTV include vascular (aortic bifurcation/iliocaval confluence), muscular (psoas) and osseus anatomy (inter-crestal tangent/pubic symphysis), when compared to non-LSTV.•There are increased surgical deviations but not significantly greater complications for anterior approaches in LSTV.•Vascular awareness while accessing L45 will be in the presence of a more cephalad ABF and ICC with sacralized L5, and access to the deeper L56 level will be in the presence of a more caudal ABF and ICC in lumbarized S1.

Multilevel tandem spondylolisthesis associated with a reduced "safe zone" for a transpsoas lateral lumbar interbody fusion at L4-5

OBJECTIVE

The aim of this study was to investigate the effect of degenerative spondylolisthesis (DS) on psoas anatomy and the L4-5 safe zone during lateral lumbar interbody fusion (LLIF).

METHODS

In this retrospective, single-institution analysis, patients managed for low-back pain between 2016 and 2021 were identified. Inclusion criteria were adequate lumbar MR images and radiographs. Exclusion criteria were spine trauma, infection, metastases, transitional anatomy, or prior surgery. There were three age and sex propensity-matched cohorts: 1) controls without DS; 2) patients with single-level DS (SLDS); and 3) patients with multilevel, tandem DS (TDS). Axial T2-weighted MRI was used to measure the apical (ventral) and central positions of the psoas relative to the posterior tangent line at the L4-5 disc. Lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and PI-LL mismatch were measured on lumbar radiographs. The primary outcomes were apical and central psoas positions at L4-5, which were calculated using stepwise multivariate linear regression including demographics, spinopelvic parameters, and degree of DS. Secondary outcomes were associations between single- and multilevel DS and spinopelvic parameters, which were calculated using one-way ANOVA with Bonferroni correction for between-group comparisons.

RESULTS

A total of 230 patients (92 without DS, 92 with SLDS, and 46 with TDS) were included. The mean age was 68.0 ± 8.9 years, and 185 patients (80.4%) were female. The mean BMI was 31.0 ± 7.1, and the mean age-adjusted Charlson Comorbidity Index (aCCI) was 4.2 ± 1.8. Age, BMI, sex, and aCCI were similar between the groups. Each increased grade of DS (no DS to SLDS to TDS) was associated with significantly increased PI (p < 0.05 for all relationships). PT, PI-LL mismatch, center psoas, and apical position were all significantly greater in the TDS group than in the no-DS and SLDS groups (p < 0.05). DS severity was independently associated with 2.4-mm (95% CI 1.1-3.8 mm) center and 2.6-mm (95% CI 1.2-3.9 mm) apical psoas anterior displacement per increased grade (increasing from no DS to SLDS to TDS).

CONCLUSIONS

TDS represents more severe sagittal malalignment (PI-LL mismatch), pelvic compensation (PT), and changes in the psoas major muscle compared with no DS, and SLDS and is a risk factor for lumbar plexus injury during L4-5 LLIF due to a smaller safe zone.

Lumbar plexus safe working zones with lateral lumbar interbody fusion: a systematic review and meta-analysis

PURPOSE

Significant risk of injury to the lumbar plexus and its departing motor and sensory nerves exists with lateral lumbar interbody fusion (LLIF). Several cadaveric and imaging studies have investigated the lumbar plexus position with respect to the vertebral body anteroposterior plane. To date, no systematic review and meta-analysis of the lumbar plexus safe working zones for LLIF has been performed.

METHODS

This systematic review was conducted according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Relevant studies reporting on the position of the lumbar plexus with relation to the vertebral body in the anteroposterior plane were identified from a PubMed database query. Quantitative analysis was performed using Welch's t test.

RESULTS

Eighteen studies were included, encompassing 1005 subjects and 2472 intervertebral levels. Eleven studies used supine magnetic resonance imaging (MRI) with in vivo subjects. Seven studies used cadavers, five of which performed dissection in the left lateral decubitus position. A significant correlation (p < 0.001) existed between anterior lumbar plexus displacement and evaluation with in vivo MRI at all levels between L1-L5 compared with cadaveric measurement. Supine position was also associated with significant (p < 0.001) anterior shift of the lumbar plexus at all levels between L1-L5.

CONCLUSIONS

This is the first comprehensive systematic review and meta-analysis of the lumbar neural components and safe working zones for LLIF. Our analysis suggests that the lumbar plexus is significantly displaced ventrally with the supine compared to lateral decubitus position, and that MRI may overestimate ventral encroachment of lumbar plexus.

Lateral Interbody Fusion at L4/5: Management of the Transitional Psoas

OBJECTIVE

Managing retraction of the lumbar plexus is critical to safely perform lateral lumbar interbody fusion (LLIF) via the transpsoas approach. Occasionally, a transitional psoas is encountered at L4/5 and has been postulated to be a contraindication to transpsoas LLIF. A case series of patients with transitional psoas who underwent L4/5 LLIFs is presented.

METHODS

This retrospective review assessed 79 consecutive patients who underwent L4/5 LLIF during a 24-month period. Preoperative imaging was reviewed, and patients were classified into 2 groups: normal psoas or transitional psoas. Intraoperative features and outcomes were compared between groups.

RESULTS

Seventy-nine patients underwent L4/5 LLIFs, of whom 23 had transitional psoas anatomy and 56 had normal psoas anatomy. Among patients with transitional psoas, the center of the psoas was a mean (range) of 11.2 (5.2-26.6) mm in front of the center of the vertebral body compared with 2.0 (0-4) mm in the normal psoas group. The mean (range) retraction time was similar between groups (10.8 [6.7-14.9] minutes in the transitional psoas group vs. 11.0 [7.8-15.0] minutes in the normal psoas group). No permanent motor injuries occurred in either group, and no differences in length of stay or preoperative or postoperative Oswestry Disability Index scores were found between the groups. The protocol for L4/5 LLIF in patients with transitional psoas anatomy is described.

CONCLUSIONS

Transitional psoas anatomy is frequently encountered in surgical candidates for L4/5 LLIF. Through careful identification of the lumbar plexus and judicious retraction, the transpsoas LLIF can safely be performed in these patients.

Contraindication of Minimally Invasive Lateral Interbody Fusion for Percutaneous Reduction of Degenerative Spondylolisthesis: A New Radiographic Indicator of Bony Lateral Recess Stenosis Using I Line

Study Design

Retrospective cohort study.

Purpose

This study aimed to evaluate aggravated lateral recess stenosis and clarify the indirect decompression threshold by combined lateral interbody fusion and percutaneous pedicle screw fixation (LIF/PPS).

Overview of Literature

No previous reports have described an effective radiographic indicator for determining the surgical indication for LIF/PPS.

Methods

A retrospective review of 185 consecutive patients, who underwent 1- or 2-level lumbar fusion surgery for degenerative spondylolisthesis (DS). According to their symptomatic improvement, they were placed into either the “recovery” or “no-recovery” group. Preoperative computed tomography (CT) images were evaluated for the position of the superior articular processes at the slipping level, followed by a graded classification (grades 0–3) using the impingement line (I line), a new radiographic indicator. All 432 superior articular facets in 216 slipped levels were classified, and both groups’ characteristics were compared.

Results

There were 171 patients (92.4%) in the recovery group and 14 patients in the no-recovery group (7.6%). All patients in the no-recovery group were diagnosed with symptoms associated with deteriorated bony lateral recess stenosis. All superior articular processes of the lower vertebral body in affected levels reached and exceeded the I line (I line-; grade 2 and 3) on preoperative sagittal CT images. In the recovery group, most superior articular processes did not reach the I line (I line+; grade 0 and 1; p=0.0233).

Conclusions

In DS cases that are classified as grade 2 or greater, the risk of aggravated bony lateral recess stenosis due to corrective surgery is high; therefore, indirect decompression by LIF/PPS is, in principle, contraindicated.

Lateral Lumbar Interbody Fusion: Review of Surgical Technique and Postoperative Multimodality Imaging Findings

The lateral lumbar interbody fusion (LLIF) approach is a minimally invasive surgery that can be used as an alternative to traditional lumbar interbody fusion techniques. LLIF accesses the intervertebral disk through the retroperitoneum and psoas muscle to avoid major vessels and visceral organs. The exposure of retroperitoneal structures during LLIF leads to unique complications compared with other surgical approaches. An understanding of the surgical technique and its associated potential complications is necessary for radiologists who interpret imaging before and after LLIF. Preoperative imaging must carefully assess the location of anatomic structures, including major retroperitoneal vasculature, lumbar nerve roots, lumbosacral plexus, and the genitofemoral nerve, relative to the psoas muscle. Multiple imaging modalities can be used in postoperative assessment including radiographs, CT, CT myelography, and MRI. Of these, CT is the preferred modality, because it can assess a range of complications relating to both the retroperitoneal exposure and the spinal instrumentation, as well as bone integrity and fusion status. This article describes surgical approaches for lumbar interbody fusion, comparing the approaches' indications, contraindications, advantages, and disadvantages; reviews the surgical technique of LLIF and relevant anatomic considerations; and illustrates for interpreting radiologists the normal postoperative findings and potential postsurgical complications of LLIF.

Complications associated with L4-5 anterior retroperitoneal trans-psoas interbody fusion: a single institution series

Background

Lateral lumbar interbody fusion (LLIF), first described in the literature in 2006 by Ozgur et al., involves direct access to the lateral disc space via a retroperitoneal trans-psoas tubular approach. Neuromonitoring is vital during this approach since the surgical corridor traverses the psoas muscle where the lumbar plexus lies, risking injury to the lumbosacral plexus that could result in sensory or motor deficits. The risk of neurologic injury is especially higher at L4-5 due to the anatomy of the plexus at this level. Here we report our single-center clinical experience with L4-5 LLIF.

Methods

A retrospective chart review of all patients who underwent an L4-5 LLIF between May 2016 and March 2019 was performed. Baseline demographics and clinical characteristics, such as body mass index (BMI), medical comorbidities, surgical history, tobacco status, operative time and blood loss, length of stay (LOS), and post-op complications were recorded.

Results

A total of 220 (58% female and 42% male) cases were reviewed. The most common presenting pathology was spondylolisthesis. The average age, BMI, operative time, blood loss, and LOS were 64.6 years, 29 kg/m², 214 min, 75 cc, and 2.5 days respectively. A review of post-operative neurologic deficits revealed 31.4% transient hip flexor weakness and 4.5% quadricep weakness on the approach side. At 3-week follow-up, 9.1% of patients experienced mild hip flexor weakness (4 or 4+/5), 0.9% reported mild quadricep weakness, and 9.5% reported anterior thigh dysesthesias; 93.2% of patients were discharged home and 2.3% were readmitted within the first 30 days post discharge. Female sex, higher BMI and longer operative time were associated with hip flexor weakness.

Conclusions

LLIF at L4-5 is a safe, feasible, and versatile approach to the lumbar spine with an acceptable approach-related sensory and motor neurologic complication rates.

Localization of the Lumbar Plexus in the Psoas Muscle: Considerations for Avoiding Lumbar Plexus Injury during the Transpsoas Approach

Introduction

Transpsoas lumbar spine surgery is minimally invasive and has very good corrective effects. However, approach-side nerve complications delay post-operative rehabilitation. We anatomically investigated the localization of the lumbar plexus running in the psoas muscle.

Methods

We examined 27 formalin-fixed cadavers. The left-sided psoas muscle was extracted and cut parallel to the intervertebral disc at the L2/3, L3/4, and L4/5 disc levels. Using digitized photographs, we calculated the ratio of the distance from the front edge of the psoas muscle to the center of the lumbar plexus in the anteroposterior diameter of the psoas muscle (%). Then, we calculated the ratio of the distance from the lateral edge of the psoas muscle to the center of the lumbar plexus in the lateral diameter of the psoas muscle (%).

Results

The anterior-posterior lumbar plexus localization was 74.5 at L2/3, 74.7 at L3/4, and 81.2 at L4/5. There was a significant difference between L2/3 and L4/5 and between L3/4 and L4/5, but not between L2/3 and L3/4 (P=0.02, 0.01, and 0.94, respectively). The lateral and medial lumbar plexus localization was 85.4 at L2/3, 83.9 at L3/4, and 77.7 at L4/5. There was a significant difference between L2/3 and L4/5 and between L3/4 and L4/5, but not between L2/3 and L3/4 (P=0.01, 0.04, and 0.41, respectively).

Conclusions

The lumbar plexus was localized in the posterior one-third and medial one-third of the psoas muscle and moved to a posterolateral location at L4/5. To avoid neuropathy, consider the psoas muscle's position relative to that of the intervertebral disc. It is essential to understand lumbar plexus localization in the psoas muscle when looking directly at this muscle to enter the pricking point or route with a lower risk of nerve damage.

The spontaneous restoration of the course of psoas muscles after corrective surgery for adult spinal deformity

BACKGROUND

A previous study demonstrated that spinopelvic alignment and morphology influence a deviation in the course of psoas muscle (PM). However, it is unknown whether such deviations might be caused by a decrease in lumbar lordosis (LL) or the lateral deviation of the lumbar spine following scoliosis. The purpose of this study was to elucidate the close relationship between the coronal and sagittal lumbar alignment and a deviation in the course of PM.

METHODS

We investigated the preoperative and postoperative spinopelvic parameters and the morphology of PM at L4/5 level in 30 patients treated with corrective surgery for adult spinal deformity who were diagnosed with "rising psoas sign" before surgery. Spinopelvic parameters were measured on X-ray films. Investigation of the morphology of PM and the morphological measurements were performed using computed tomography (CT) images. The "rising psoas sign" was classified as bilateral- or unilateral-type as defined in the previous study.

RESULTS

Among 18 patients who had bilateral-type rising psoas sign before surgery, 11 patients remained bilateral-type after surgery despite an increase in LL. The pelvic incidence of these 11 patients was significantly larger than that of the other 7 patients (53.5 ± 10.2° vs 43.2 ± 5.8°) (p = 0.037). The magnitude of postoperative increase in LL positively correlated with that of the posterior shift of PM (r = 0.41, p = 0.025). The degree of restoration of the lumbar spine following scoliosis was positively correlated with that of the medial shift of PM (r = 0.66, p = 0.025).

CONCLUSION

The decrease in LL and the lateral deviation of lumbar spine following scoliosis caused a deviated course of the PM, which was spontaneously corrected by the restoration of lumbar alignment. However, the bilateral-type deviation in patients with higher pelvic incidence was considered to be within the range of normal variation.

Mini-Open Access for Lateral Lumbar Interbody Fusion: Indications, Technique, and Outcomes

Background

Lateral lumbar interbody fusion (LLIF) is a relatively new procedure. It was established as a minimally invasive alternative to traditional open interbody fusion. LLIF allows the surgeon to access the disc space via a retroperitoneal transpsoas muscle approach. Theoretical advantages of the LLIF technique include preservation of the longitudinal ligaments, augmentation of disc height with indirect decompression of neural elements, and insertion of large footprint cages spanning the dense apophyseal ring bilaterally^1,2. The original 2-incision LLIF technique described by Ozgur et al., in 2006, had some inherent limitations³. First, it substantially limited direct visualization of the surgical field and may have endangered nerve and vascular structures. Additionally, it often required multiple separated incisions for multilevel pathologies. Finally, for surgeons with experience in traditional open retroperitoneal surgery, utilization of their previously acquired skills may have been difficult with this approach. To overcome these limitations, we adopted the mini-open lateral approach, which allows for visualization, palpation, and electrophysiologic neurologic confirmation during the procedure⁴.

Description

As detailed below, the patient is positioned in the lateral decubitus position and a single incision is carried out centered between the target discs. For single-level LLIF, the incision spans approximately 3 cm and can be lengthened in small increments for multilevel procedures. After blunt dissection, the retroperitoneal space is entered. The psoas muscle is split under direct visualization, carefully avoiding the traversing nerves with neurosurveillance⁵. A self-retaining retractor is used, and after thorough discectomy, the disc space is sized with trial components. The implant is filled with bone graft materials and is introduced using intraoperative fluoroscopy.

Alternatives

The 2-incision LLIF technique or traditional anterior or posterior lumbar spine interbody fusion techniques might be used instead.

Rationale

LLIF offers the reported advantages of minimally invasive surgery, such as reduced tissue trauma during the approach, low blood loss, shorter length of stay, decreased recovery time, and less postoperative pain. LLIF allows for the placement of a relatively larger interbody cage spanning the dense apophyseal ring bilaterally. The lateral approach preserves the anterior longitudinal ligament and posterior longitudinal ligament. These structures allow for powerful ligamentotaxis and provide extra stability for the construct. Compared with other approaches, LLIF has a reduced risk of visceral and vascular injuries, incidental dural tears, and perioperative infections. Although associated with approach-related complications such as motor and sensory deficits, LLIF can be a safe and versatile procedure^1,2.

Lateral Approaches for the Surgical Treatment of Lumbar Spondylolisthesis

Spondylolisthesis is a common cause of lower back pain in people of all ages. When nonsurgical management is unsuccessful in treatment for lumbar spondylolisthesis, surgical treatment algorithms can be used. This article focuses on lateral lumbar interbody fusion (LLIF). It represents a minimally invasive approach that affords surgeons an increased ability to restore disc height, indirectly decompress the neural elements, and affect global spinal alignment. As the role for circumferential minimally invasive spine surgery continues to expand, the use of LLIF in the setting of spondylolisthesis-and other pathologies-will continue to represent a robust fusion option.

Anatomic Considerations in the Lateral Transpsoas Interbody Fusion: The Impact of Age, Sex, BMI, and Scoliosis

STUDY DESIGN

This is a retrospective case series.

OBJECTIVE

Define the anatomic variations and the risk factors for such within the operative corridor of the transpsoas lateral interbody fusion.

SUMMARY OF BACKGROUND DATA

The lateral interbody fusion approach has recently been associated with devastating complications such as injury to the lumbosacral plexus, surrounding vasculature, and bowel. A more comprehensive understanding of anatomic structures in relation to this approach using preoperative imaging would help surgeons identify high-risk patients potentially minimizing these complications.

MATERIALS AND METHODS

Age-sex distributed, naive lumbar spine magnetic resonance imagings (n=180) were used to identify the corridor for the lateral lumbar interbody approach using axial images. Bilateral measurements were taken from L1-S1 to determine the locations of critical vascular, intraperitoneal, and muscular structures. In addition, a subcohort of scoliosis patients (n=39) with a Cobb angle >10 degrees were identified and compared.

RESULTS

Right-sided vascular anatomy was significantly more variant than left (9.9% vs. 5.7%; P=0.001). There were 9 instances of "at-risk" vasculature on the right side compared with 0 on the left (P=0.004). Age increased vascular anatomy variance bilaterally, particularly in the more caudal levels (P≤0.001). A "rising-psoas sign" was observed in 26.1% of patients. Bowel was identified within the corridor in 30.5% of patients and correlated positively with body mass index (P<0.001). Scoliosis increased variant anatomy of left-sided vasculature at L2-3/L3-4. Nearly all variant anatomy in this group was found on the convex side of the curvature (94.2%).

CONCLUSIONS

Given the risks and complications associated with this approach, careful planning must be taken with an understanding of vulnerable anatomic structures. Our analysis suggests that approaching the intervertebral space from the patient's left may reduce the risk of encountering critical vascular structures. Similarly, in the setting of scoliosis, an approach toward the concave side may have a more predictable course for surrounding anatomy.

LEVEL OF EVIDENCE

Level 3-study.

Leg Muscle Strength After Lateral Interbody Fusion Surgery Recovers Over Time After Temporary Muscle Weakness

STUDY DESIGN

Case-control study.

OBJECTIVE

The objective of this study was to reveal the changes of leg muscle strength after lateral interbody fusion (LIF).

SUMMARY OF BACKGROUND DATA

Muscle trauma and damage to intermuscular nerves due to dissection of the psoas are recognized perioperative complications of LIF. Although reduced leg strength is temporary in many cases, the underlying changes have not been studied in detail.

METHODS

Leg muscle strength was measured quantitatively before LIF surgery and 1 week, 2 weeks, 3 weeks, 4 weeks, 8 weeks, and 12 weeks after surgery (n=38). Reduced muscle strength was defined as <80% of the preoperative measurement. The psoas position (PP%) was calculated from axial T2-weighted magnetic resonance images and compared with the degree of psoas and quadriceps muscle strength reduction at 1 week after surgery on the approach side. Twenty cases that underwent a posterior lumbar approach (posterior group) acted as controls.

RESULTS

The proportion of patients with reduced psoas muscle strength 1 week after LIF was 60.5% on the approach side and 39.5% on the healthy side, versus 30.0% in the posterior group. The corresponding results for the quadriceps were 34.2%, 39.5%, and 25.0%, respectively. All cases had strength improvement on the approach side by 12 weeks postsurgery in the psoas and by 4 weeks postsurgery for the quadriceps. Psoas muscle strength and quadriceps strength at 1 week after surgery were correlated (ρ=0.57, P<0.001). There was a low inverse correlation between PP% and quadriceps strength at 1 week (ρ=-0.31, P<0.001).

CONCLUSIONS

Muscle strength declined in both the psoas and quadriceps muscle groups after LIF; however, the effect was temporary and strength recovered over time. Reduced postoperative quadriceps muscle strength may relate the position of the psoas muscle via increased irritation of the lumbar plexus during the splitting maneuver.

Diffusion tensor tractography of the lumbar nerves before a direct lateral transpsoas approach to treat degenerative lumbar scoliosis

OBJECTIVE

The purpose of this study was to determine the relationship between vertebral bodies, psoas major morphology, and the course of lumbar nerve tracts using diffusion tensor imaging (DTI) before lateral interbody fusion (LIF) to treat spinal deformities.

METHODS

DTI findings in a group of 12 patients (all women, mean age 74.3 years) with degenerative lumbar scoliosis (DLS) were compared with those obtained in a matched control group of 10 patients (all women, mean age 69.8 years) with low-back pain but without scoliosis. A T2-weighted sagittal view was fused to tractography from L3 to L5 and separated into 6 zones (zone A, zones 1-4, and zone P) comprising equal quarters of the anteroposterior diameters, and anterior and posterior to the vertebral body, to determine the distribution of nerves at various intervertebral levels (L3-4, L4-5, and L5-S1). To determine psoas morphology, the authors examined images for a rising psoas sign at the level of L4-5, and the ratio of the anteroposterior diameter (AP) to the lateral diameter (lat), or AP/lat ratio, was calculated. They assessed the relationship between apical vertebrae, psoas major morphology, and the course of nerve tracts.

RESULTS

Although only 30% of patients in the control group showed a rising psoas sign, it was present in 100% of those in the DLS group. The psoas major was significantly extended on the concave side (AP/lat ratio: 2.1 concave side, 1.2 convex side). In 75% of patients in the DLS group, the apex of the curve was at L2 or higher (upper apex) and the psoas major was extended on the concave side. In the remaining 25%, the apex was at L3 or lower (lower apex) and the psoas major was extended on the convex side. Significant anterior shifts of lumbar nerves compared with controls were noted at each intervertebral level in patients with DLS. Nerves on the extended side of the psoas major were significantly shifted anteriorly. Nerve pathways on the convex side of the scoliotic curve were shifted posteriorly.

CONCLUSIONS

A significant anterior shift of lumbar nerves was noted at all intervertebral levels in patients with DLS in comparison with findings in controls. On the convex side, the nerves showed a posterior shift. In LIF, a convex approach is relatively safer than an approach from the concave side. Lumbar nerve course tracking with DTI is useful for assessing patients with DLS before LIF.

Malposition of Cage in Minimally Invasive Oblique Lumbar Interbody Fusion

Introduction

Minimally invasive oblique lumbar interbody fusion is one of the novel lateral lumbar interbody fusion techniques for which the successful early results have been reported. However, new complications were increasingly reported from ongoing studies.

Case Presentation

We report a case of an unusual complication of minimally invasive oblique lumbar interbody fusion associated with contralateral nerve root compression due to deep and posterior position of polyetheretherketone cage and discussion of the operating technique for repositioning polyetheretherketone cage.

Conclusion

Malposition of polyetheretherketone cage can cause contralateral nerve root compression and neurological complication. The surgical technique to proper pull the polyetheretherketone cage back into the acceptable position should be considered and well prepared.

Relationship between Displacement of the Psoas Major Muscle and Spinal Alignment in Patients with Adult Spinal Deformity

Study Design

Cross sectional study.

Purpose

To clarify the difference in position of the psoas muscle between adult spinal deformity (ASD) and lumbar spinal stenosis (LSS).

Overview of Literature

Although it is known that the psoas major muscle deviates in ASD patients, no report is available regarding the difference in comparison with LSS patients.

Methods

This study investigates 39 patients. For evaluating spinal alignment, pelvic tilt (PT), pelvic incidence (PI), sacral slope, lumbar lordosis (LL), PI–LL, Cobb angle, and the convex side, the lumbar curves were measured. For measuring the position of the psoas major at the L4/5 disk level, magnetic resonance imaging was used. The displacements of psoas major muscle were measured separately in the anterior–posterior and lateral directions. We examined the relationship between the radiographic parameters and anterior displacement (AD) and lateral displacement (LD) of the psoas major muscle.

Results

AD was demonstrated in 15 cases with ASD and nine cases with LSS (p>0.05). LD was observed in 13 cases with ASD and no cases with LSS (p<0.01). The Cobb angle was significantly greater in cases with AD than in those without AD (p=0.04). PT, LL, PI–LL, and Cobb angle were significantly greater in cases with LD (p<0.05). All cases with LD had AD, but no case without AD had LD (p<0.001). The side of greater displacement at L4/5 and the convex side of the lumbar curve were consistent in all cases.

Conclusions

Despite AD being observed in LSS as well, LD was observed only in the ASD group. Radiographic parameters were worse when LD was seen, rather than AD.

Integrated anatomy of the neuromuscular, visceral, vascular, and urinary tissues determined by MRI for a surgical approach to lateral lumbar interbody fusion in the presence or absence of spinal deformity

Introduction

To comprehensively investigate the anatomy of the neuromuscular, visceral, vascular, and urinary tissues and their general influence on lateral lumbar interbody fusion (LLIF) surgery in the presence or absence of spinal deformity.

Methods

We retrospectively reviewed 100 consecutive surgery cases for lumbar degenerative disease of patients aged on average 70.5 years and of which 67 were women. A sagittal vertical axis deviation of more than 50 mm was defined as adult spinal deformity (ASD: 50 patients). The degenerative disease of the other patients was defined as lumbar spinal stenosis (LSS: 50 patients). We analyzed the relative anatomical position of the psoas major muscle, lumbar plexus, femoral nerves, inferior vena cava, abdominal aorta and its bifurcation, ureter, testicular or ovarian artery, kidney and transverse abdominal muscle in patients with ASD or with LSS, using preoperative magnetic resonance imaging (MRI).

Results

For patients with ASD, the L4-5 intervertebral disk was closer to the lumbar nerve plexus than it was in those with LSS (p < 0.0001), and a rising psoas sign at the L4-5 disk was significantly more frequent in patients with ASD than in those with LSS (p < 0.05). The aortic bifurcation frequently appeared at the level of L4-5 in patients with either degenerative disease, so the common iliac artery may pass near the disk. The inferior vena cava passed closer to the center of the L4-5 disk in patients with ASD than it did in those with LSS (p < 0.05). The transverse abdominal muscle at L2-3, L3-4, and L4-5 was closer to and less than 3 mm from the kidneys in many more patients with ASD than was the case for patients with LSS (p = 0.3, p < 0.05, p = 0.29, respectively).

Conclusions

We recommend careful preoperative MRI to determine the location of organs to help to avoid intraoperative complications during LLIF surgery, especially for patients with ASD.

Radiographic Analysis of Psoas Morphology and its Association With Neurovascular Structures at L4-5 With Reference to Lateral Approaches

STUDY DESIGN

Retrospective imaging review.

OBJECTIVE

Utilize magnetic resonance imaging (MRI) to expand the anatomical description of psoas morphology and its association with neurovascular structures at L4-5.

SUMMARY OF BACKGROUND DATA

Anatomical psoas muscle variants may present a greater risk of neurovascular injury at the L4-5 level during lateral transpsoas approaches.

METHODS

Axial L4-5 sections of consecutive patients who obtained lumbar MRIs were analyzed. Teardrop psoas morphology was assessed qualitatively. MRI described psoas morphology and proximity of neurovascular structures, whereas plain radiographs were evaluated for lumbosacral transitional vertebrae (LSTV). Teardrop morphology was tested for associations with radiographic measurements using t tests and χ analysis.

RESULTS

Fifty teardrop and 476 nonteardrop psoas muscles were identified. Teardrop morphology was associated with greater longitudinal length (53.1 vs. 49.3 mm, P = 0.012), and shorter transverse length (34.9 vs. 44.8 mm, P < 0.001) compared with nonteardrop. Teardrop morphology was associated with anterior and lateral migration of the psoas with greater distance between the anterior borders of the psoas and disc (13.5 vs. 6.3 mm, P < 0.001), and greater distance between the medial border of the psoas to the lateral disc border (1.6 vs. 0.5 mm, P < 0.001). Teardrop morphology was associated with a higher incidence of the lumbar plexus migrating anteriorly adjacent to the middle-third of the disc (43.4% vs. 17.6%, P < 0.001) and the iliac vasculature being more laterally and posteriorly located, adjacent to the anterior-third of the disc (43.4% vs. 30.0%, P = 0.047). Teardrop morphology was not associated with presence of LSTV (3.8% vs. 7.6%, P = 0.306).

CONCLUSION

The current study provides detailed metrics of teardrop psoas muscles and surrounding structures. The study confirms that the presence of teardrop anatomy on L4-5 axial imaging is associated with anterior migration of the lumbar plexus and posterolateral migration of the iliac vasculature which may increase the risk of neurovascular injury during direct and oblique-lateral lumbar spine procedures.

LEVEL OF EVIDENCE

3.

Influence of spinopelvic alignment and morphology on deviation in the course of the psoas major muscle

BACKGROUND

In some people, the psoas major rises laterally or anteriorly at the L4/5 disc level and detaches from the most posterior aspect of the disc despite the absence of transitional vertebrae; this is called the "rising psoas sign." There are no reports of the relationship between spinopelvic parameters and rising psoas sign. The objective of this study was to investigate the relationship between spinopelvic parameters and deviations in the location and shape of psoas major muscle at the L4/5 disc level.

METHODS

We investigated the preoperative location and shape of both psoas major muscles in 64 patients treated with lateral lumbar interbody fusion. Spinopelvic parameters were measured on X-ray films. The morphology of psoas major at the L4/5 disc level was investigated with magnetic resonance images. The morphological measurements were normalized by the anteroposterior diameter of the center of the L4 vertebral body, which was measured by computed tomography. The rising psoas sign was classified into 2 types: bilateral or unilateral.

RESULTS

The pelvic incidence (PI) was significantly larger for the bilateral type than the others (normal and unilateral types) (60.2 ± 11.0 vs. 46.7 ± 8.7, p < 0.001). The PI correlated significantly with the normalized anteroposterior diameter of the pelvis (R = 0.66, p < 0.001). The receiver-operator characteristic curve showed an optimal cutoff value of PI = 54, with 75% sensitivity and 78.5% specificity. The coronal L1-4 Cobb angle was significantly larger in the unilateral type than the others (normal and bilateral types) (p < 0.0001). In the unilateral type, the Cobb angle in the recumbent position correlated significantly with the normalized distance of the lateral deviation of psoas major (R = 0.60, p = 0.0085).

CONCLUSION

The rising psoas sign was related to a higher PI and lumbar scoliosis. It was firstly elucidated that the spinopelvic alignment and morphology influence the deviation of the course of the psoas major muscle.

STUDY DESIGN

A retrospective morphological study.

Lateral Lumbar Interbody Fusion-Outcomes and Complications

PURPOSE OF REVIEW

Lateral lumbar interbody fusion (LLIF) is a relatively new, minimally invasive technique for interbody fusion. The goal of this review is to provide a general overview of LLIF with a special focus on outcomes and complications.

RECENT FINDINGS

Since the first description of the technique in 2006, the indications for LLIF have expanded and the rate of LLIF procedures performed in the USA has increased. LLIF has several theoretical advantages compared to other approaches including the preservation of the anterior and posterior annular/ligamentous structures, insertion of wide cages resting on the dense apophyseal ring bilaterally, and augmentation of disc height with indirect decompression of neural elements. Favorable long-term outcomes and a reduced risk of visceral/vascular injuries, incidental dural tears, and perioperative infections have been reported. However, approach-related complications such as motor and sensory deficits remain a concern. In well-indicated patients, LLIF can be a safe procedure used for a variety of indications.

Complications Associated With Lateral Interbody Fusion: Nationwide Survey of 2998 Cases During the First 2 Years of Its Use in Japan

STUDY DESIGN

Retrospective nationwide questionnaire-based survey of complications.

OBJECTIVE

To elucidate the incidence of complications and risk factors associated with lateral interbody fusion (LIF).

SUMMARY OF BACKGROUND DATA

After its introduction to Japan in February 2013, the numbers of LIF cases have increased substantially because of the advantages of this minimally invasive procedure. However, LIF has the potential risk of several complications unique to the procedure. Although there are many reports of complications, no nationwide survey has been conducted.

METHODS

Questionnaires were sent to all Japanese Society for Spine Surgery and Related Research (JSSR) members. Questionnaires requested information about surgical procedures (XLIF or OLIF), patient characteristics, preoperative diagnosis, complications, salvage procedures, final outcomes, and the surgeon's experience of LIF. The data from replies received between March 2013 and April 2015 were recorded on a web site and the details of complications were analyzed by a JSSR research team.

RESULTS

Seventy-one institutions (12.3%) answered "yes" to LIF experience and 2998 cases (1995 XLIF and 1003 OLIF) were enrolled in this study. The response rate was 86.1%. A total of 540 complications were reported, of which 474 (84.8%) could be further analyzed. The overall complication rate was 18.0%. The most frequent complications were sensory nerve injury (5.1%) and psoas weakness (4.3%) and the majority resolved spontaneously. The rates of major vascular injury, bowel injury, and surgical site infection were 0.03%, 0.03%, and 0.7%, respectively. The overall reoperation rate was 2.2%. Higher rates of sensory nerve injury and psoas weakness were reported for XLIF and higher rates of peritoneal laceration and ureteral injury were reported for OLIF.

CONCLUSION

A nationwide survey of complications associated with LIF was conducted. Although the majority of complications were minor, a relatively high rate of complications was reported. Approach-related specific features of the two procedures were identified.

LEVEL OF EVIDENCE

4.

Variation in Psoas Muscle Location Relative to the Safe Working Zone for L4/5 Lateral Transpsoas Interbody Fusion: A Morphometric Analysis

BACKGROUND

The safe working zone for lateral access to the L4/5 disc space has been said to lie in the anteroposterior (AP) midpoint of the disc space due to the location of the femoral nerve at that level. However, the AP location of the psoas muscle (and thus the lumbosacral plexus within) at L4/5 is variable. A psoas muscle lying excessively anteriorly at the L4/5 disc space may preclude safe access to the L4/5 disc space from a lateral transpsoas approach.

METHODS

Lumbar spine magnetic resonance imaging (MRI) for 300 consecutive patients at the authors' institution were reviewed retrospectively. The AP distance between the ventral aspect of the thecal sac and the dorsal aspect of the psoas muscle at L4/5 was measured, as was the AP diameter of the L4/5 disc space.

RESULTS

The dorsal aspect of the psoas muscle at L4/5 was most commonly found dorsal to the ventral aspect of the thecal sac (zone P, N = 145; 48.3%), whereas it was found at the junction of zones IV/P in 37 patients (12.3%), in zone IV in 85 patients (28.3%), in zone III in 29 patients (9.7%), and in zone II in 4 patients (1.3%).

CONCLUSIONS

The location of the psoas muscle in relation to the L4/5 disc space is somewhat variable. In 11% of patients, the dorsal-most aspect of the psoas muscle was located within zones II or III, likely precluding safe access to the L4/5 disc space from a lateral transpsoas approach.

Resolution of the more anteriorly positioned psoas muscle following correction of spinal sagittal alignment from spondylolisthesis: case report

Several studies have described the radiographic, histological, and morphological changes to the paraspinal muscle in patients with chronic low-back pain due to degenerative diseases of the spine. Gross anatomical illustrations have shown that the psoas muscle lies lateral to the L4–5 vertebrae and subsequently thins and dissociates from the vertebral body at L5–S1 in a ventrolateral course. A “rising psoas” may influence the location of the lumbar plexus and result in transient neurological injury on lateral approach to the spine. It is postulated that axial back pain may be exacerbated by anatomical changes of paraspinal musculature as a direct result of degenerative spine conditions. To their knowledge, the authors present the first reported case of a more anteriorly positioned psoas muscle and its resolution following correction of spondylolisthesis in a 62-year-old woman. This case highlights the dynamic nature of degenerative spinal disorders and illustrates that psoas muscle position can be affected by sagittal balance. Normal anatomical positioning can be restored following correction of spinal alignment.

Anatomical differences in patients with lumbosacral transitional vertebrae and implications for minimally invasive spine surgery

OBJECTIVE

The objective of this study was to investigate the neurovascular and anatomical differences in patients with lumbosacral transitional vertebrae (LSTV) and the associated risk of neurovascular injury in minimally invasive spine surgery.

METHODS

The authors performed a retrospective study of CT and MR images of the lumbar spine obtained at their institution between 2010 and 2014. The following characteristics were evaluated: level of the iliac crest in relation to the L4–5 disc space, union level of the iliac veins and arteries in relation to the L4–5 disc space, distribution of the iliac veins and inferior vena cava according to the different Moro zones (A, I, II, III, IV, P) at the L4–5 disc space, and the location of the psoas muscle at the L4–5 disc space. The findings were compared with findings on images obtained in 28 age- and sex-matched patients without LSTV who underwent imaging studies during the same time period.

RESULTS

Twenty-eight patients (12 male, 16 female) with LSTV and the required imaging studies were identified; 28 age- and sex-matched patients who had undergone CT and MRI studies of the thoracic and lumbar spine imaging but did not have LSTV were selected for comparison (control group). The mean ages of the patients in the LSTV group and the control group were 52 and 49 years, respectively. The iliac crest was located at a mean distance of 12 mm above the L4–5 disc space in the LSTV group and 4 mm below the L4–5 disc space in the controls. The iliac vein union was located at a mean distance of 8 mm above the L4–5 disc space in the LSTV group and 2.7 mm below the L4–5 disc space in the controls. The iliac artery bifurcation was located at a mean distance of 23 mm above the L4–5 disc space in the LSTV group and 11 mm below the L4–5 disc space in controls. In patients with LSTV, the distribution of iliac vein locations was as follows: Zone A, 7.1%; Zone I only, 78.6%; Zone I encroaching into Zone II, 7.1%; and Zone II only, 7.1%. In the control group, the distribution was as follows: Zone A only, 17.9%; Zone A encroaching into Zone I, 75%; and Zone I only, 7.1%. There were no iliac vessels in Zone II in the control group. The psoas muscle was found to be rising away laterally and anteriorly from the vertebral body more often in patients with LSTV, resulting in the iliac veins being found in the “safe zone” only 14% of the time, greatly increasing the risk of vascular injury.

CONCLUSIONS

In patients with LSTV, the iliac crest is more likely to be above the L4–5 disc space, which increases the technical challenges of a lateral approach. The location of the psoas muscle rising away laterally and ventrally in patients with LSTV compared with controls and with the union of the iliac veins occurring more often above the L4–5 disc space increases the risk for iatrogenic vascular injury at the L4–5 level in this patient population.

A radiographic analysis of cage positioning in lateral transpsoas lumbar interbody fusion

Direct Lumbar Interbody Fusion (DLIF) and eXtreme Lateral Interbody Fusion (XLIF) are the most common surgical platforms available for performing transpsoas spinal fusion but no study has been carried out to compare them. We evaluated 21 DLIF and 22 XLIF cage positions by measuring the distance between the posterior vertebral border and the centre of the cage normalised to the midsagittal length of the inferior end plate. We found that DLIF cages were significantly more anteriorly located than XLIF (0.65 vs 0.52, p = 0.001) at L4-5, suggesting that XLIF would permit implantation of wider cages than DLIF.

Prevention of neurological complications using a neural monitoring system with a finger electrode in the extreme lateral interbody fusion approach

OBJECTIVE

Extreme lateral interbody fusion (XLIF) is a minimally disruptive surgical procedure that uses a lateral approach. There is, however, concern about the development of neurological complications when this approach is used, particularly at the L4–5 level. The authors performed a prospective study of the effects of a new neural monitoring system using a finger electrode to prevent neurological complications in patients treated with XLIF and compared the results to results obtained in historical controls.

METHODS

The study group comprised 36 patients (12 male and 24 female) who underwent XLIF for lumbar spine degenerative spondylolisthesis or lumbar spine degenerative scoliosis at L4–5 or a lower level. Using preoperative axial MR images obtained at the mid-height of the disc at the treated level, we calculated the psoas position value (PP%) by dividing the distance from the posterior border of the vertebral disc to the posterior border of the psoas major muscle by the anteroposterior diameter of the vertebral disc. During the operation, the psoas major muscle was dissected using an index finger fitted with a finger electrode, and threshold values of the dilator were recorded before and after dissection. Eighteen cases in which patients had undergone the same procedure for the same indications but without use of the finger electrode served as historical controls. Baseline clinical and demographic characteristics, PP values, clinical results, and neurological complications were compared between the 2 groups.

RESULTS

The mean PP% values in the control and finger electrode groups were 17.5% and 20.1%, respectively (no significant difference). However, 6 patients in the finger electrode group had a rising psoas sign with PP% values of 50% or higher. The mean threshold value before dissection in the finger electrode group was 13.1 ± 5.9 mA, and this was significantly increased to 19.0 ± 1.5 mA after dissection (p < 0.001). A strong negative correlation was found between PP% and threshold values before dissection, but there was no correlation with threshold values after dissection. The thresholds after dissection improved to 11 mA or higher in all patients. There were no serious neurological complications in any patient, but there was a significantly lower incidence of transient neurological symptoms in the finger electrode group (7 [38%] of 18 cases vs 5 [14%] of 36 cases, p = 0.047).

CONCLUSIONS

The new neural monitoring system using a finger electrode may be useful to prevent XLIF-induced neurological complications.

Risk Management for Avoidance of Major Vascular Injury due to Lateral Transpsoas Approach

STUDY DESIGN

A retrospective study using 323 contrast-enhanced, multi-planner three-dimensional computed (3D-CT) scans.

OBJECTIVE

The aim of this study was to identify risk factors for injury to the major vessels in the lateral transpsoas approach.

SUMMARY OF BACKGROUND DATA

To avoid critical complications such as major vessel injury, it is essential to examine anatomical information related to preoperative risk management that is specific to the lateral transpsoas approach.

METHODS

The abdominal contrast-enhanced, multi-planner 3D-CT scans of 323 consecutive subjects (203 males and 120 females, 15-89 years old) were retrospectively reviewed. The true axial views were used for evaluation of the locations of the major vein and artery at L3 to L4 and L4 to L5. According to the Moro system, the axial view was divided into 6 zones from the front side (A, I II, III, IV, P) and the locations of the dorsal tangential line of the major vessels were evaluated.

RESULTS

At the L3 to L4 level, the dorsal tangential line of the major vein located in zone A was found in 18% of subjects, in zone I in 74%, and in zone II in 8%. The line of the major artery was located in zone A in 92.6% of subjects and in zone I in 7.1%. At the L4 to L5 level, the line of the major vein was located in zone A in 5% of subjects, in zone I in 75%, in zone II in 20%, and in zone III in only 1 subject. The line of the major artery was identified in zone A in 87% of subjects, in zone I in 12%, and in zone II in 1%. Women had significant dorsal-migrated veins and arteries at both spinal levels (P < 0.01).

CONCLUSION

To avoid critical complications in extreme lateral lumbar interbody fusion, careful preoperative radiological evaluation of the major vessels and intraoperative care are important.

LEVEL OF EVIDENCE

3.

Magnetic Resonance Neurography of the Lumbar Plexus at the L4-L5 Disc: Development of a Preoperative Surgical Planning Tool for Lateral Lumbar Transpsoas Interbody Fusion (LLIF)

STUDY DESIGN

Observational study.

OBJECTIVE

To demonstrate use of magnetic resonance (MR) neurography to visualize the course of the lumbar plexus at the L4-L5 disc space.

SUMMARY OF BACKGROUND DATA

Risk of injury to the lumbar plexus during lateral transpsoas approach for lumbar interbody fusion (LLIF) is significant. We describe a new technique for preoperative mapping using magnetic resonance neurography to directly visualize the course of the plexus relative to the L4-L5 disc space.

METHODS

Consecutive lumbar plexus MR neurograms (n=35 patients, 70 sides) were studied. Scans were obtained on a Siemens 3-Tesla Skyra magnetic resonance imaging scanner. T1- and T2-color-coded fusion maps were generated along with 3-dimensional models of the lumbosacral plexus with attention to the L4-L5 interspace. The position of the plexus and the shape of the psoas muscle at the L4-L5 interspace were evaluated and recorded.

RESULTS

Direct imaging of the lumbar plexus using MR neurography revealed a substantial variability in the position of the lumbar plexus relative to the L4-L5 disc space. The left-side plexus was identified in zone 2 (5.7%), zone 3 (54.3%), and zone 4 (40%) (P = 0.0014); on the right, zone 2 (8.6%), zone 3 (42.9%) or zone 4 (45.7%), and zone 5 (2.9%) (P = 0.01). Right-left symmetry was found in 18 of 35 subjects (51.4%) (P = 0.865). There was no association between the position of the plexus and the shape of the overlying psoas muscle identified. In patients with an elevated psoas (n = 12), the lumbar plexus was identified in zone 3 in 75% and 66% (left and right) compared with patients without psoas elevation (n = 23), 30.4% and 43.5% (left and right).

CONCLUSION

The course of the lumbosacral plexus traversing the L4-L5 disc space may be more variable than has been suggested by previous studies. Magnetic resonance neurography may provide a more reliable means of preoperatively identifying the plexus when compared with current methods.

LEVEL OF EVIDENCE

3.