Lumbar plexus anatomy within the psoas muscle: implications for the transpsoas lateral approach to the L4-L5 disc

The change in lumbar lordosis from the standing to the lateral position: implications for lateral interbody fusion

PURPOSE

The purpose of this cross-sectional, observational study was to establish the relationship between standing lumbar lordosis (LL) and lateral decubitus LL.

METHODS

Forty-nine subjects, 24 male and 25 female, were prospectively enrolled. Patients with pre-existing spinopelvic pathology were excluded. Standing, relaxed-seated, and lateral decubitus lateral radiographs were obtained. Radiographic variables measured included LL and lordosis change at each lumbar level (e.g. L1-L2). The change in LL when going from a standing to a lateral decubitus position (ΔLL), the correlation between standing and sitting LL compared to lateral decubitus LL, and the correlation between ΔLL and standing pelvic incidence (PI), pelvic tilt (PT), PI-LL mismatch, pelvic femoral angle (PFA), and sacral slope (SS) were calculated.

RESULTS

Subjects had an average age of 25.7 ± 2.3 years and body mass index of 24.1 ± 3.0 kg/m2. On average, 11.9°±8.2° (range - 7° to 29°) of LL was lost when transitioning from a standing to the lateral decubitus position. Lateral decubitus LL had a higher correlation with standing LL (R = 0.725, p < 0.001) than with relaxed-seated LL (R = 0.434, p < 0.001). Standing PT and PI-LL mismatch had moderately negative correlations with ΔLL (R=-0.58 and R=-0.59, respectively, both p < 0.05). Standing PI and standing PFA had a low negative correlation with ΔLL (R=-0.31 and R=-0.44, respectively, both p < 0.05) Standing SS and LL had no correlation with ΔLL.

CONCLUSIONS

Standing LL was strongly correlated to lateral decubitus LL, although subjects lost an average of 11.9° from the standing to the lateral decubitus position. This has important implications for fusion in the lateral position.

L4-L5 anatomy classification system for lateral lumbar interbody fusion

Lateral lumbar interbody fusion (LLIF), developed by Dr. Luiz Pimenta in 2006, allows access to the spinal column through the psoas major muscle. The technique has many advantages, such as reduced bone and muscular tissue damage, indirect decompression, larger implants, and lordosis correction capabilities. However, this technique also has drawbacks, with the most notorious being the risk of spinal pathologies due to indirect injury of the lumbar plexus, but with low rates of persistent injuries. Therefore, several groups have proposed classifications to help identify patients at a greater risk of presenting with neurological deficits. The present work proposes a classification system that relies on simple observation of easily identifiable key structures to guide lateral L4-L5 LLIF decision-making. Patients aged > 18 years who underwent preoperative magnetic resonance imaging (MRI) between 2022 and 2023 were included until 50 high-quality images were acquired. And excluded as follow Anatomical changes in the vertebral body or major psoas muscles prevent the identification of key structures or poor-quality MRIs. Each anatomy was classified as type I, type II, or type III according to the consensus among the three observers. Fifty anatomical sites were included in this study. 70% of the L4-L5 anatomy were type I, 18% were type II, and 12% were type III. None of the type 3 L4-L5 anatomies were approached using a lateral technique. The proposed classification is an easy and simple method for evaluating the feasibility of a lateral approach to-L4-L5.

Comparative analysis of tubular retractors and hook retractors in oblique lumbar interbody fusion at the initial stage of the learning curve

PURPOSE

Oblique lumbar interbody fusion (OLIF) still has a steep learning curve that many spinal surgeons who want to develop are hesitant. The purpose of this study is to provide reference for beginners through the comparative analysis of the application of two kinds of retraction devices in the early stage of learning curve.

METHOD

We prospectively included the first 60 patients with lumbar degenerative diseases treated with OLIF by a surgeon in our department. According to the application of different retraction devices during the operation, the patients were divided into hook retractor group and tubular retractor group. The clinical effects and complications of the two groups were compared.

RESULT

The average age of hook retractor group was 62 years old, the average age of tubular retractor group was 65 years old. There was no significant difference in age, sex, operative segment, follow-up time and blood loss between the two groups. The operation time in hook retractor group was less than that in tubular retractor group. The incidence of complications in hook retractor group (11.8%) was significantly lower than that in tubular retractor group (38.5%).

CONCLUSION

The tubular retractor group has a higher risk of neurovascular injury in the initial stage of learning, as well as the risk of vertebral fracture. In contrast, the hook retractor group has the advantages of simple method, high fault tolerance and relatively low incidence of complications. Therefore, we believe that the application of hook retractor in the early stage of OLIF learning curve is easier to increase the operator's confidence and make OLIF more acceptable.

Variations of the extrapsoas course of the lumbar plexus with implications for the lateral transpsoas approach to the lumbar spine: a cadaveric study

BACKGROUND

Together with an increased interest in minimally invasive lateral transpsoas approach to the lumbar spine goes a demand for detailed anatomical descriptions of the lumbar plexus. Although definitions of safe zones and essential descriptions of topographical anatomy have been presented in several studies, the existing literature expects standard appearance of the neural structures. Therefore, the aim of this study was to investigate the variability of the extrapsoas portion of the lumbar plexus in regard to the lateral transpsoas approach.

METHODS

A total of 260 lumbar regions from embalmed cadavers were utilized in this study. The specimens were dissected as per protocol and all nerves from the lumbar plexus were morphologically evaluated.

RESULTS

The most common variation of the iliohypogastric and ilioinguinal nerves was fusion of these two nerves (9.6%). Nearly in the half of the cases (48.1%) the genitofemoral nerve left the psoas major muscle already divided into the femoral and genital branches. The lateral femoral cutaneous nerve was the least variable one as it resembled its normal morphology in 95.0% of cases. Regarding the variant origins of the femoral nerve, there was a low formation outside the psoas major muscle in 3.8% of cases. The obturator nerve was not variable at its emergence point but frequently branched (40.4%) before entering the obturator canal. In addition to the proper femoral and obturator nerves, accessory nerves were present in 12.3% and 9.2% of cases, respectively.

CONCLUSION

Nerves of the lumbar plexus frequently show atypical anatomy outside the psoas major muscle. The presented study provides a compendious information source of the possibly encountered neural variations during retroperitoneal access to different segments of the lumbar spine.

Feasibility of Saphenous Nerve Somatosensory-Evoked Potential Intraoperative Monitoring During Lumbar Spine Surgery: Early Results

STUDY DESIGN

Retrospective review.

OBJECTIVE

Assess the feasibility of saphenous nerve somatosensory evoked potentials (SN-SSEP) monitoring in lumbar spine surgeries.

BACKGROUND CONTEXT

SN-SSEPs have been proposed for detecting lumbar plexus and femoral nerve injury during lateral lumbar surgery where tibial nerve (TN) SSEPs alone are insufficient. SN-SSEPs may also be useful in other types of lumbar surgery, as stimulation of SN below the knee derives solely from the L4 root and provides a means of L4 monitoring, whereas TN-SSEPs often do not detect single nerve root injury. The feasibility of routine SN-SSEP monitoring has not been established.

METHODS

A total of 563 consecutive cases using both TN-SSEP and SN-SSEP monitoring were included. Anesthesia was at the discretion of the anesthesiologist, using an inhalant in 97.7% of procedures. SN stimulation was performed using 13 mm needle electrodes placed below the knee using 200-400 μsec pulses at 15 to 100 mA. Adjustments to stimulation parameters were made by the neurophysiology technician while obtaining baselines. Data were graded retrospectively for monitorability and cortical response amplitudes were measured by two independent reviewers.

RESULTS

Ninety-eight percent of TN-SSEPs and 92.5% of SN-SSEPs were monitorable at baseline, with a mean response amplitude of 1.35 μV for TN-SSEPs and 0.71 μV for SN-SSEPs. A significant difference between the stimulation parameters used to obtain reproducible TN and SN-SSEPs at baseline was observed, with SN-SSEPs requiring greater stimulation intensities. Body mass index is not associated with baseline monitorability. Out of 20 signal changes observed, 11 involved SN, while TN-SSEPs were unaffected.

CONCLUSION

With adjustments to stimulation parameters, SN-SSEP monitoring is feasible within a large clinical cohort without modifications to the anesthetic plan. Incorporating SN into standard intraoperative neurophysiological monitoring protocols for lumbar spine procedures may expand the role of SSEP monitoring to include detecting injury to the lumbar plexus.

LEVEL OF EVIDENCE

3.

A retrospective case-control study on the effectiveness of preoperative diffusion tensor imaging for mitigating nerve injury in extreme lateral interbody fusion surgery

BACKGROUND CONTEXT

Extreme Lateral Interbody Fusion (XLIF) has been established as an effective treatment for degenerative disorders of the lumbar spine. Nevertheless, there is a potential risk of lumbar plexus damage associated with XLIF, especially during surgeries at the L4-5 segment. Diffusion Tensor Imaging (DTI) evaluates the directional diffusion of water molecules in tissue, providing a more intricate depiction of internal tissue microstructure compared to conventional MRI techniques. The capability of DTI sequences to elucidate the 3-dimensional interplay between lumbar nerve pathways and adjacent musculoskeletal structures, potentially reducing the incidence of nerve injury complications related to XLIF, remains to be established.

PURPOSE

This study evaluates the effectiveness of preoperative Diffusion Tensor Imaging (DTI) in reducing neurological complications after Extreme Lateral Interbody Fusion (XLIF) surgeries at the L4-5 level, focusing on the interaction between lumbar nerves and the psoas major muscle.

STUDY DESIGN

Retrospective case-control study.

PATIENT SAMPLE

The study included 128 patients undergoing XLIF surgery for degenerative disorders at the L4-5 segment: 68 in the traditional group and 62 in the DTI group.

OUTCOME MEASURES

The study assessed Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) scores, along with complication rates. It also documented psoas major muscle morphology and its correlation with nerve pathways.

METHODS

A retrospective analysis of 128 patients undergoing XLIF surgery for degenerative disorders at the L4-5 segment between February 2020 and August 2022 was conducted. The cohort was divided into a traditional group (68 patients) receiving presurgery MRI scans to identify surgical entry points at the intervertebral space midpoint (Zones II-III junction) and a DTI group (62 patients) who additionally underwent preoperative DTI to customize entry points. The study evaluated VAS and ODI scores, complication rates, psoas major muscle morphology, and its interaction with nerve pathways.

RESULTS

The traditional group uniformly chose the Zone II-III junction for entry. In contrast, the DTI group's entry points varied. Postoperative follow-up revealed significant improvements in VAS and ODI scores in both groups. However, the DTI group experienced fewer immediate postoperative complications such as thigh pain, numbness, and motor disturbances. The study also noted a ventral shift in nerve positioning in patients with elevated psoas muscles.

CONCLUSIONS

Preoperative DTI effectively maps the relationship between the psoas major muscle and lumbar nerves. Tailoring surgical entry points based on DTI results significantly reduces the risk of nerve damage in XLIF surgeries. The study underscores the importance of recognizing variability in lumbar nerve pathways due to differing psoas muscle morphologies, highlighting a higher risk of nerve injury in patients with elevated psoas muscles during XLIF procedures.

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.

Location of the Femoral Nerve in the Lateral Decubitus Versus Prone Position

STUDY DESIGN

Cadaveric study.

OBJECTIVE

To compare the position of the femoral nerve within the lumbar plexus at the L4-L5 disc space in the lateral decubitus vs prone position.

METHODS

Seven lumbar plexus specimens were dissected and the femoral nerve within the psoas muscle was identified and marked with radiopaque paint. Lateral fluoroscopic images of the cadaveric specimens in the lateral decubitus vs prone position were obtained. The location of the radiopaque femoral nerve at the L4-L5 disc space was normalized as a percentage of the L5 vertebral body (0% indicates posterior location and 100% indicates anterior location at the L4-L5 disc space). The location of the femoral nerve at L4-L5 in the lateral decubitus vs prone position was compared using a paired t test.

RESULTS

In the lateral decubitus position, the femoral nerve was located 28% anteriorly from the posterior edge of the L4-L5 disc space, and in the prone position, the femoral nerve was relatively more posterior, located 18% from the posterior edge of the L4-L5 disc space (P = .037).

CONCLUSIONS

The femoral nerve was on average more posteriorly located at the L4-L5 disc space in the prone position compared to lateral decubitus. This more posterior location allows for a larger safe zone at the L4-L5 disc space, which may decrease the incidence of neurologic complications associated with Lateral lumbar interbody fusion in the prone vs lateral decubitus position; however, further studies are needed to evaluate this possible clinical correlation.

Postoperative clinical outcomes in patients undergoing MIS-TLIF versus LLIF for adjacent segment disease

PURPOSE

Few studies examine the clinical outcomes in patients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) versus lateral lumbar interbody fusion (LLIF) for adjacent segment disease (ASD). We aim to compare the postoperative clinical trajectory through patient-reported outcome measures (PROMs) and minimum clinically important difference (MCID) in patients undergoing MIS-TLIF versus LLIF for ASD.

METHODS

Patients were stratified into two cohorts based on surgical technique for ASD: MIS-TLIF versus LLIF. PROMs of 12-Item Short Form Physical Component Score (SF-12 PCS), visual analog scale (VAS) back, VAS leg, and Oswestry Disability Index (ODI) were collected at preoperative and postoperative 6-week/12-week/6-month/1-year time points. MCID attainment was calculated through comparison to established thresholds. Cohorts were compared through nonparametric inferential statistics.

RESULTS

Fifty-four patients were identified, with 22 patients undergoing MIS-TLIF after propensity score matching. Patients undergoing MIS-TLIF for ASD demonstrated significant postoperative improvement up to 1-year VAS back, up to 1-year VAS leg, and 6-month through 1-year ODI (p ≤ 0.035, all). Patients undergoing LLIF demonstrated significant postoperative improvement in 6-month SF-12 PCS, 6-month through 1-year VAS back, 12-week through 6-month VAS leg, and 6-month to 1-year ODI (p ≤ 0.035, all). No significant differences were calculated between surgical techniques for PROMs or MCID achievement rates.

CONCLUSION

Patients undergoing either MIS-TLIF or LLIF for adjacent segment disease demonstrated significant postoperative improvement in pain and disability outcomes. Additionally, patients undergoing LLIF reported significant improvement in physical function. Both MIS-TLIF and LLIF are effective for the treatment of adjacent segment disease.

Lateral lumbar interbody fusion - clinical outcomes, fusion rates and complications with recombinant human bone morphogenetic protein-2

BACKGROUND

The authors report an Australian experience of lateral lumbar interbody fusion (LLIF) with respect to clinical outcomes, fusion rates, and complications, with recombinant human bone morphogenetic protein-2 (rhBMP-2) and other graft materials.

METHODS

Retrospective cohort study of LLIF patients 2011-2021. LLIFs performed lateral decubitus by four experienced surgeons past their learning curve. Graft materials classified rhBMP-2 or non-rhBMP-2. Patient-reported outcomes assessed by VAS, ODI, and SF-12 preoperatively and postoperatively. Fusion rates assessed by CT postoperatively at 6 and 12 months. Complications classified minor or major. Clinical outcomes and complications analysed and compared between rhBMP-2 and non-rhBMP-2 groups.

RESULTS

A cohort of 343 patients underwent 437 levels of LLIF. Mean age 67 ± 11 years (range 29-89) with a female preponderance (65%). Mean BMI 29kg/m2 (18-56). Most common operated levels L3/4 (36%) and L4/5 (35%). VAS, ODI and SF-12 improved significantly from baseline. Total complication rate 15% (53/343) with minor 11% (39/343) and major 4% (14/343). Ten patients returned to OR (2-wound infection, 8-further instrumentation and decompression). Most patients (264, 77%) received rhBMP-2, the remainder a non-rhBMP-2 graft material. No significant differences between groups at baseline. No increase in minor or major complications in the rhBMP-2 group compared to the non-rhBMP-2 group respectively; (10.6% vs 13.9% [p = 0.42], 2.7% vs 8.9% [p < 0.01]). Fusion rates significantly higher in the rhBMP-2 group at 6 and 12 months (63% vs 40%, [p < 0.01], 92% vs 80%, [p < 0.02]).

CONCLUSION

LLIF is a safe and efficacious procedure. rhBMP-2 in LLIF produced earlier and higher fusion rates compared to available non-rhBMP-2 graft substitutes.

Multimodality Intraoperative Neuromonitoring in Lateral Lumbar Interbody Fusion: A Review of Alerts in 628 Patients

STUDY DESIGN

Retrospective review of private neuromonitoring databases.

OBJECTIVES

To review neuromonitoring alerts in a large series of patients undergoing lateral lumbar interbody fusion (LLIF) and determine whether alerts occurred more frequently when more lumbar levels were accessed or more frequently at particular lumbar levels.

METHODS

Intraoperative neuromonitoring (IONM) databases were reviewed and patients were identified undergoing LLIF between L1 and L5. All cases in which at least one IONM modality was used (motor evoked potentials (MEP), somatosensory evoked potentials (SSEP), evoked electromyography (EMG)) were included in this study. The type of IONM used and incidence of alerts were collected from each IONM report and analyzed. The incidence of alerts for each IONM modality based on number of levels at which at LLIF was performed and the specific level an LLIF was performed were compared.

RESULTS

A total of 628 patients undergoing LLIF across 934 levels were reviewed. EMG was used in 611 (97%) cases, SSEP in 561 (89%), MEP in 144 (23%). The frequency of IONM alerts for EMG, SSEP and MEPs did not significantly increase as the number of LLIF levels accessed increased. No EMG, SSEP, or MEP alerts occurred at L1-L2. EMG alerts occurred in 2-5% of patients at L2-L3, L3-L4, and L4-L5 and did not significantly vary by level (P = .34). SSEP and MEP alerts occurred more frequently at L4-L5 versus L2-L3 and L3-L4 (P < .03).

CONCLUSIONS

IONM may provide the greatest utility at L4-L5, particularly MEPs, and may not be necessary for more cephalad LLIF procedures such as at L1-L2.

A modified oblique lumbar interbody fusion: A better way to establish an exposure under direct microscopic vision

Study design

This is a retrospective study.

Objective

To demonstrate a modified oblique lumbar interbody fusion (OILF) technique for L1-L5.

Methods

The modified technique splits anterior portion of psoas belly to access the oblique corridor (OC) anteroinferior to psoas, minimizing psoas manipulation and retraction and avoiding nerve injury while offering excellent microscopic visualization. Psoas weakness and neurovascular complication rates in patients treated with traditional OLIF (T-OLIF) or anteroinferior psoas OLIF (AP-OLIF) were retrospectively reviewed. Clinical outcomes were also reviewed.

Results

A total of 162 cases treated with T-OLIF (n = 73) and AP-OLIF (n = 89) for degenerative lumbar disease were included. The mean operative time and blood loss were less with AP-OLIF (P < 0.01). Approach related complications were 14 (19.1%) with T-OLIF and 4 (4.5%) with AP-OLIF. Postoperative visual analog scale (VAS) and Oswestry Disability Index (ODI) scores improved in both T-OIF and AP-OIF groups (P < 0.01).

Conclusion

The modified OLIF technique (AP-OLIF) is characterized by an easy exposure of the lumbar spine under direct microscopic vision, resulting in less psoas weakness and neurovascular injury.

Psoas weakness following oblique lateral interbody fusion surgery: a prospective observational study with an isokinetic dynamometer

BACKGROUND CONTEXT

Although the surgical corridor used for oblique lateral interbody fusion (OLIF) protects the intrapsoas nerves by causing minimal compression, transient weakness remains the most commonly reported postoperative complication.

PURPOSE

Using a dynamometer to evaluate how the hip flexor strength changes following OLIF.

STUDY DESIGN/SETTING

A prospective observational study.

PATIENT SAMPLE

Forty-six patients who underwent single or multi-level OLIF for lumbar spondylolisthesis.

OUTCOME MEASURES

Isokinetic dynamometer values (peak torque, total work, average power), visual analogue scale (VAS) scores for leg pain, hypoesthesia, subjective weakness of the left hip flexor muscle, Oswestry disability index, body mass index, bone mineral density, radiologic findings of the psoas muscle (cross-sectional area, Hounsfield unit (HU), fat portion grade), and psoas retraction time.

METHODS

The isokinetic muscle strength of the hip flexor was measured five times (preoperatively and postoperatively at 2 days, 1 week, 1 month, and 3 months) for both legs. The peak torque was defined as the postoperative strength of the left hip flexor muscles, and was compared to the preoperative baseline value. The strength of the left and right hip flexor muscles were also compared at each time point. For logistic regression analysis, when the peak torque was below the median value, it was defined as lower peak torque.

RESULTS

Up to 1 week after surgery, the strength of the left hip flexor muscle decreased significantly (paired difference in peak torque was 22.6%, p<.001). In the results of multivariate logistic regression analysis, diabetes (odds ratio [OR]=8.43, p=.020) and the HU of the psoas muscle (OR=0.916, p=.034) were associated with lower peak torque 1 week after surgery. From 1 month after surgery, postoperative weakness of the psoas muscle was not significant. In the questionnaire survey, subjective left hip flexion weakness was reported in 8.5% (4/47) of patients 1 week after surgery, and it remained in only 2.1% (1/47) of patients after 3 months of operation. The frequency of left anterior thigh pain and hypoesthesia decreased from 85.1% (40/47) at 1 week to 2.1% (1/47) at 3 months after surgery. The mean VAS score for left anterior thigh or groin pain decreased significantly at 1 month after surgery (PO2D: 4.04±1.84, PO1M: 1.67±1.10, p<.001).

CONCLUSIONS

Dynamometer measurement showed that psoas strength declined significantly up to 1 week after OLIF surgery. Patients with diabetes or lower HU of the psoas muscle showed delayed recovery from postoperative weakness of the psoas muscle. However, the weakness was insignificant from 1 month after surgery. At 3 months after surgery, the other psoas-related problems (left anterior thigh pain and hypoesthesia) also disappeared.

L4 Corpectomy: Surgical Approaches and Mitigating the Risk of Femoral Nerve Injuries

OBJECTIVE

Because of the challenging anatomic location, corpectomies are performed less often at the fourth lumbar vertebral body than at other levels. Our objective was to review the literature of L4 corpectomy and anterior column reconstruction.

METHODS

A literature search in the Medline/PubMed database was conducted following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines to identify all relevant cases and cases series describing corpectomies of the L4 vertebral body using "lumbar" AND "corpectomy" as search terms. We present an illustrative case to describe the technique.

RESULTS

We identified 18 articles with 30 patients who met the search criteria. Including our case illustration, the most common approach used was the lateral retroperitoneal approach (n = 17, 54.8%), of which 8 (26.7%) were performed via a transpsoas approach. Seven (23%) patients underwent corpectomy through a posterior approach, 4 (12.9%) through an anterior retroperitoneal approach, and 3 (10%) through combined anterior and lateral retroperitoneal. The overall complications rate was 19.3% including 1 case each of femoral nerve injury and iatrogenic lumbar nerve root injury.

CONCLUSIONS

Corpectomies of the L4 vertebral body are challenging. None of the various approaches described clearly demonstrates any superiority in mitigating the risk of neural complications. Decision making about which surgical approach to use should be based on patient-specific characteristics.

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.

Application of Offset Dingo Instruments in Anterior to Psoas (ATP)/Oblique Lumbar Interbody Fusion (OLIF) Procedure: A Retrospective Study of 80 Patients

OBJECTIVE

Oblique lumbar interbody fusion (OLIF) is a minimally invasive lumbar fusion procedure that has flourished in recent years. However, complications related to the anterior-to-psoas (ATP) approach have been reported. The purpose of this study was to assess the OLIF technique using offset design "Dingo" instruments for the treatment of degenerative lumbar disorders.

METHODS

A retrospective review was performed to identify patients between March 2018 and November 2020 who underwent OLIF with conventional or modified instruments with a minimum follow-up of 12 months. Demographic data were recorded. Operation time, intraoperative blood loss, and length of hospital stay were compared between cohorts. Imaging parameters were measured and compared between cohorts before and after surgery. Clinical outcomes were assessed at each follow-up visit. All complications were reviewed.

RESULTS

A total of 80 consecutive patients were included. The mean follow-up times for the conventional group and modified group were 14.5 months and 16.3 months, respectively. The incidence of hip flexion weakness was 27.5% and 7.5% for the conventional cohort and modified cohort, respectively. The modified group was associated with a shorter operation time, shorter length of hospital stay, higher postoperative disk height and better cage position. The symptoms of all patients improved after surgery. At 1-week follow-up, the modified group showed significantly better clinical scores.

CONCLUSIONS

OLIF with modified instruments and techniques shows promising outcomes in reducing approach-related complications. Additionally, the modified technique is associated with a better cage position, shorter length of hospital stay and less postoperative pain in the early period.

Oblique Lumbar Interbody Fusion Using a Stand-Alone Construct for the Treatment of Adjacent-Segment Lumbar Degenerative Disease

Objective

Adjacent-segment disease (ASD) is common in patients undergone previous lumbar fusion. A typical revision treatment from posterior approach requires management of postoperative scar tissue and previously implanted instrumentation. An oblique lumbar interbody fusion (OLIF) approach allows surgeon to reduce the potential risk of posterior approach. This study aimed to analyze the clinical and radiographic efficacy of stand-alone OLIF for the treatment of lumbar adjacent-segment disease.

Methods

A total of 13 consecutive patients who underwent stand-alone OLIF for the treatment of adjacent-segment disease from December 2016 to January 2019 were reviewed. Visual analog scale (VAS) of back pain and leg pain and the Oswestry Disability Index (ODI) before surgery and at last postoperative clinic visits were obtained. Radiography, CT and MRI before and at last follow-up after surgery was evaluated in all patients.

Results

During the study period, 13 cases were successfully treated with stand-alone OLIF. The mean follow-up was 17.7 ± 8.3 months. The back pain VAS improved from 6.2 ± 1.0 to 2.0 ± 1.1 (P < 0.01), and the leg pain VAS improved from 7.0 ± 1.9 to 1.0 ± 0.9 (P < 0.01). ODI improved from 28.0 ± 7.5 to 10.8 ± 4.0 (P < 0.01). The disc height (DH) increased from 9 ± 2 to 12 ± 2 mm (P < 0.01), the cross-sectional area (CSA) of spinal canal increased from 85 ± 26 to 132 ± 24 mm² (P < 0.01), the foraminal height increased from 17 ± 2 to 21 ± 3 mm (P < 0.01) and the CSA of foramen increased from 95 ± 25 to 155 ± 36 mm² (P < 0.01). Cage subsidence was observed in 2 cases.

Conclusions

Stand-alone OLIF provides a safe and effective alternative way to treat ASD.

Femoral nerve neuromonitoring for lateral lumbar interbody fusion surgery

BACKGROUND CONTEXT

The transpsoas lateral lumbar interbody fusion (LLIF) technique is an effective alternative to traditional anterior and posterior approaches to the lumbar spine; however, nerve injuries are the most reported postoperative complication. Commonly used strategies to avoid nerve injury (eg, limiting retraction duration) have not been effective in detecting or preventing femoral nerve injuries.

PURPOSE

To evaluate the efficacy of emerging intraoperative femoral nerve monitoring techniques and the importance of employing prompt surgical countermeasures when degraded femoral nerve function is detected.

STUDY DESIGN/SETTING

We present the results from a retrospective analysis of a multi-center study conducted over the course of 3 years.

PATIENT SAMPLE

One hundred and seventy-two lateral lumbar interbody fusion procedures were reviewed.

OUTCOME MEASURES

Intraoperative femoral nerve monitoring data was correlated to immediate postoperative neurologic examinations.

METHODS

Femoral nerve evoked potentials (FNEP) including saphenous nerve somatosensory evoked potentials (snSSEP) and motor evoked potentials with quadriceps recordings were used to detect evidence of degraded femoral nerve function during the time of surgical retraction.

RESULTS

In 89% (n=153) of the surgeries, there were no surgeon alerts as the FNEP response amplitudes remained relatively unchanged throughout the surgery (negative group). The positive group included 11% of the cases (n=19) where the surgeon was alerted to a deterioration of the FNEP amplitudes during surgical retraction. Prompt surgical countermeasures to an FNEP alert included loosening, adjusting, or removing surgical retraction, and/or requesting an increase in blood pressure from the anesthesiologist. All the cases where prompt surgical countermeasures were employed resulted in recovery of the degraded FNEP amplitudes and no postoperative femoral nerve injuries. In two cases, the surgeons were given verbal alerts of degraded FNEPs but did not employ prompt surgical countermeasures. In both cases, the degraded FNEP amplitudes did not recover by the time of surgical closure, and both patients exhibited postoperative signs of sensorimotor femoral nerve injury including anterior thigh numbness and weakened knee extension.

CONCLUSIONS

Multimodal femoral nerve monitoring can provide surgeons with a timely alert to hyperacute femoral nerve conduction failure, enabling prompt surgical countermeasures to be employed that can mitigate or avoid femoral nerve injury. Our data also suggests that the common strategy of limiting retraction duration may not be effective in preventing iatrogenic femoral nerve injuries.

Intraoperative Neuromonitoring During Lateral Lumbar Interbody Fusion

Objective

To review the evidence for the use of electromyography (EMG), motor-evoked potentials (MEPs), and somatosensory-evoked potentials (SSEPs) intraoperative neuromonitoring (IONM) strategies during lateral lumbar interbody fusion (LLIF), as well as discuss the limitations associated with each technique.

Methods

A comprehensive review of the literature and compilation of findings relating to clinical studies investigating the efficacy of EMG, MEP, SSEP, or combined IONM strategies during LLIF.

Results

The evidence for the use of EMG is mixed with some studies demonstrating the efficacy of EMG in preventing postoperative neurologic injuries and other studies demonstrating a high rate of postoperative neurologic deficits with EMG monitoring. Multimodal IONM strategies utilizing MEPs or saphenous SSEPs to monitor the lumbar plexus may be promising strategies based on results from a limited number of studies.

Conclusion

The use of traditional EMG during LLIF remains without consensus. There is a growing body of evidence utilizing multimodal IONM with MEPs or saphenous SSEPs demonstrating a possible decrease in postoperative neurologic injuries after LLIF. Future prospective studies, with clear definitions of neurologic injury, that evaluate different multimodal IONM strategies are needed to better assess the efficacy of IONM during LLIF.

Pararectus approach combined with three-dimensional printing for anterior plate fixation of sacral fractures

BACKGROUND

Surgical treatment of sacral fractures is difficult, both for reduction and stabilization. Traditional surgical reduction and internal fixation require a long duration of operation leading to extra blood loss, extensive tissue damage, and increased risk of post-operation complications. The purpose of this study was to evaluate the feasibility of a minimally invasive technique that could be more effective, more tissue sparing, and lead to less bleeding. We hypothesized that a Pararectus approach for anterior fixation of unstable sacral fractures would be reliable and more advantageous and significantly improve the outcome of sacral fracture repair.

METHODS

Twelve patients with unstable sacral fractures were recruited and examined by CT scanning. A 3D model of each sacral fracture was reconstructed. The computer-assisted 3D image of the reduced pelvis was 3D printed for surgery simulation and plate pre-bending. All cases were treated operatively with the anterior anatomical reduction and internal fixation via a minimally invasive Pararectus approach. VAS, Matta, and Majeed scores were used to evaluate outcomes of the operation.

RESULTS

Pre-operations were consistent with the actual surgeries in all cases. The pre-bent plates had an anatomical shape specifically fit to the individual pelvis without further adjustment at the time of surgery, and fracture reductions were significantly improved with little invasive tissue damage. The average operation time was 110 min. The intraoperative blood loss and incision length averaged 695 ml and 6.7 cm, respectively. A high percentage of all cases achieved a diaplasis with an excellent or good score according to the Matta and Majeed standards (83.33% and 91.67%, respectively).All patients achieved clinical healing with an average healing time of 8 weeks.

CONCLUSION

3D printing-assisted anterior fixation of unstable sacral fractures via a minimally invasive Pararectus approach is feasible. This new surgical strategy minimizes trauma damage and bleeding and produces satisfactory reduction and therapeutic efficacy.

Efficacy and radiographic analysis of oblique lumbar interbody fusion in treating adult spinal deformity

Adult spinal deformity (ASD) is usually rigid and requires a combined anterior–posterior approach for deformity correction. Anterior lumbar interbody fusion (ALIF) allows direct access to the disc space and placement of a large interbody graft. A larger interbody graft facilitates correction of ASD. However, an anterior approach carries significant risks. Lateral lumbar interbody fusion (LLIF) through a minimally invasive approach has recently been used for ASD. The present study was performed to evaluate the effectiveness of oblique lumbar interbody fusion (OLIF) in the treatment of ASD. We performed a retrospective study utilizing the data of 74 patients with ASD. The inclusion criteria were lumbar coronal Cobb angle > 20°, pelvic incidence (PI)–lumbar lordosis (LL) mismatch > 10°, and minimum follow–up of 2 years. Patients were divided into two groups: ALIF combined with posterior spinal fixation (ALIF+PSF) (n = 38) and OLIF combined with posterior spinal fixation (OLIF+PSF) (n = 36). The perioperative spinal deformity radiographic parameters, complications, and health-related quality of life (HRQoL) outcomes were assessed and compared between the two groups. The preoperative sagittal vertical axis (SVA), LL, PI–LL mismatch, and lumbar Cobb angles were similar between the two groups. Patients in the OLIF+PSF group had a slightly higher mean number of interbody fusion levels than those in the ALIF+PSF group. At the final follow–up, all radiographic parameters and HRQoL scores were similar between the two groups. However, the rates of perioperative complications were higher in the ALIF+PSF than OLIF+PSF group. The ALIF+PSF and OLIF+PSF groups showed similar radiographic and HRQoL outcomes. These observations suggest that OLIF is a safe and reliable surgical treatment option for ASD.

Treatment of Degenerative Lumbar Scoliosis with Oblique Lumbar Interbody Fusion in Conjunction with Unilateral Pedicle Screw Fixation via the Wiltse Approach

Objective

To evaluate the clinical outcomes of oblique lumbar interbody fusion (OLIF) in conjunction with unilateral pedicle screw fixation (UPSF) via the Wiltse approach in treating degenerative lumbar scoliosis (DLS).

Methods

The article is a retrospective analysis. Twelve patients with DLS who underwent combined OLIF and UPSF between July 2017 and December 2018 were included. The study included 2 male and 10 female patients, with a mean age at the time of the operation of 67.2 ± 9.1 years. The surgical characteristics and complications were evaluated. The clinical and radiological data such as the correction of deformity, coronal and sagittal profile were analyzed.

Results

The mean follow‐up time of the study was 26.8 ± 1.8 months. At the final follow‐up, all patients who underwent combined OLIF and UPSF achieved statistically significant improvements in coronal Cobb angle (from 19.6° ± 4.8° to 6.9° ± 3.8°, P < 0.01), distance between the C7 plumb line and central sacral vertebral line (from 2.5 ± 1.7 cm to 0.9 ± 0.6 cm, P < 0.01), sagittal vertebral axis (from 4.3 ± 4.3 cm to 1.5 ± 1.0 cm, P = 0.03), lumbar lordosis (from 29.4° ± 8.6° to 40.8° ± 5.8°, P < 0.01), pelvic tilt (from 27.6° ± 10.8° to 18.3° ± 7.0°, P < 0.01), pelvic incidence‐lumbar lordosis mismatch (from 23.3° ± 10.5° to 11.9° ± 8.4°, P < 0.01), and cross‐sectional area of the dural sac (from 87.33 ± 39.41 mm² to 124.70 ± 39.26 mm², P < 0.01). The visual analogue score for back and leg pain and Oswestry Disability Index of all patients significantly improved postoperatively (P < 0.01). One case of lumbar plexus injury was found after surgery. During the follow‐up period, one patient had cage subsidence. A fusion rate of 100% and good positioning of the pedicle screws were achieved in all patients at the final follow‐up.

Conclusion

OLIF in conjunction with UPSF is a safe and effective minimally invasive procedure for correcting both coronal and sagittal deformities, as it results in an improved quality of life in patients with DLS.

Transpsoas Lumbar Interbody Fusion Without Psoas Stimulated Electromyography

STUDY DESIGN

This is a retrospective case review.

OBJECTIVE

The objective of this study was to present an anatomic approach to transpsoas interbody fusion without psoas stimulated electromyography (sEMG) and to evaluate the rate of neurological and approach-related complications.

BACKGROUND

The transpsoas approaches have become commonly utilized for lumbar interbody fusion and may have certain advantages compared with other methods of interbody stabilization. Traditionally, transpsoas approaches have been performed utilizing sEMG as it has been purported to reduce the risk of injury to the lumbar plexus; however, an anatomic approach to transpsoas surgery is also possible as cadaveric studies have demonstrated the anatomy of the psoas muscle and lumbar plexus.

METHODS

Patients who underwent transpsoas interbody fusion using an anatomic approach without psoas sEMG between 2005 and 2018 were enrolled in this study. The preoperative and postoperative medical records for this cohort were carefully reviewed to identify any new or persistent radicular symptoms, neurological deficits or approach-related complications.

RESULTS

A total of 133 patients (48 males, 85 females) underwent transpsoas interbody fusion at 222 levels in this cohort-which had a mean age of 63 (61, 65) years and body mass index of 28.8 (27.8, 29.9). New neurological complications were seen in 5 patients (3.8%) and 5 patients (3.8%) were found to have new postoperative radicular pain, up to 3 months postoperatively. The total number of perioperative, approach-related complications was 7 (5.3%) for the entire cohort.

CONCLUSION

An anatomic transpsoas approach to the interbody space without psoas sEMG demonstrated a rate of neurological and approach-related complications that was comparable or superior to the rate of complications reported using the traditional transpsoas approach with sEMG.

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.

Magnetic Resonance Imaging Study of Oblique Corridor and Trajectory to L1-L5 Intervertebral Disks in Lateral Position

OBJECTIVE

This study investigated the retroperitoneal oblique corridor and trajectory of L1-L5 as the lateral surgical access to the intervertebral disks in the Chinese population and detected the potential relationship between the corridor or trajectory and vertebral parameters, including disk axis, psoas muscle, and retroperitoneal vessel.

METHODS

Seventy magnetic resonance imaging studies performed from January 2017 to January 2019 were investigated. The oblique corridor was defined as the distance between the left lateral border of the retroperitoneal vessel and the anterior border of psoas. The trajectory was defined as the distance between the retroperitoneal vessel and lumbar plexus.

RESULTS

The oblique corridor analysis to L1-L5 disks have the following mean distances: L1-2 13.36 mm, L2-3 13.36 mm, L3-4 12.37 mm, and L4-5 10.36 mm. There was no difference in the L1-L5 corridor between genders. And the position of retroperitoneal vessel was negatively correlated with the corridor width. The trajectory measurements to L1-L5 disks have the following mean distances: L1-2 27.44 mm, L2-3 30.86 mm, L3-4 30.73 mm, and L4-5 24.36 mm. Moreover, the vertebral parameters, including the disk axis and psoas muscle, were positively correlated with the trajectory width. Otherwise, the position of retroperitoneal vessel was negatively correlated with the trajectory width.

CONCLUSIONS

Compared with previous studies, the safe surgical area of the Chinese is generally smaller than that of Caucasian. The position of the retroperitoneal vessel is the vital potential to limit the corridor and trajectory. Preoperative assessment of vertebral parameters, especially vascular structure, is essential for planning surgical process.

Does the hip positioning matter for oblique lumbar interbody fusion approach? A morphometric study

PURPOSE

To evaluate whether left hip positioning widened the access corridor using oblique lateral interbody fusion (OLIF) approach during right lateral decubitus (RLD).

METHODS

Ten healthy adult volunteers underwent a T2 lumbosacral MRI (1.5 T) in the supine position, RLD position with left hip in extension and then in flexion. L2-L3 to L5-S1 disc spaces were identified. At each level, left psoas surface (in cm²), access corridor (in mm) and vessel movement were calculated in the three positions. Paired t test was used for comparison.

RESULTS

The mean surface of the left psoas ranged from 7.83 to 17.19 cm² in the three positions (p > 0.05). From L2-3 to L4-5, in RLD, when the left hip shifted from extension to flexion, nor the access corridor nor vessel movements were significantly different. When the volunteers shifted from supine to RLD position with hip in extension, arteries moved 3.66-5.61 mm to the right (p < 0.05 at L2-3, L3-4 and L5-S1), while the venous structures moved 0.92-4.96 mm (p < 0.05 at L2-3) to the right. When the position shifted from supine to RLD with hip in flexion, the arterial structures moved 0.47-4.88 mm (p < 0.05 at L2-3 and L3-4) to the right, while the venous structures moved - 0.94 to 4.13 mm (p < 0.05 at L2-3 and L3-4) to the right.

CONCLUSION

Hip positioning was not associated with a significant widening of the surgical corridor. To perform OLIF, we advocate for RLD position with left hip in extension to move away the vascular structures and reduce the psoas volume. These slides can be retrieved under Electronic Supplementary Material.

The Anatomic Characteristics of the Retroperitoneal Oblique Corridor to the L1-S1 Intervertebral Disc Spaces

STUDY DESIGN

This is a cross-sectional study.

OBJECTIVE

To investigate the oblique corridor to the L1-S1 intervertebral disc space between the psoas muscle and the great vessels in cadaveric specimens bilaterally and the location of genitofemoral nerve and the diaphragmatic crura relative to the oblique corridor.

SUMMARY OF BACKGROUND DATA

Although use of oblique lumbar interbody fusion is rapidly expanding, the morphometric data related to the procedure are limited.

METHODS

Twelve fresh-frozen full-torso cadaveric specimens were dissected to examine the oblique corridor to access the L1-S1 space in a static state and with mild retraction of the psoas. The level at which the genitofemoral nerve pierces from the psoas major and the diaphragmatic crura originate from the lumbar vertebral body was also investigated.

RESULTS

The mean width of oblique corridor in the static state and with mild psoas retraction, respectively, were as follows: on the right side: (L1-2) 13.33 and 16.75 mm; (L2-3) 15.42 and 21.42 mm; (L3-4) 16.58 and 22.67 mm; (L4-5) 12.75 and 21.17 mm; (L5-S1) 5.92 and 12.00 mm; on the left side: (L1-2) 16.75 and 19.67 mm; (L2-3) 18.50 and 25.33 mm; (L3-4) 20.58 and 28.00 mm; (L4-5) 18.17 and 26.08 mm; and (L5-S1) 5.83 and 12.00 mm. The level at which the genitofemoral nerve pierces from the psoas major was between L2 and L4. The diaphragmatic crura originates from L1 to L3.

CONCLUSION

The oblique corridor allows access to the L1-L5 discs from both sides, but it is larger on the left side. The corridor between the iliac vessels and the psoas for L5-S1 is difficult to be applied clinically. Mild psoas retraction can moderately enlarge the oblique corridor. The genitofemoral nerve and diaphragmatic crura may be encountered in this approach and should be carefully observed.

LEVEL OF EVIDENCE

5.

Neural decompression in challenging cases: advantages and disadvantages

The peculiarity of extreme lateral interbody fusion (LLIF) is the achievement of indirect neural decompression of the spinal canal while distracting the intervertebral disc space using an interbody cage. In this manuscript we will review the potentials and limitations of this technique when treating degenerative disc disease of the lumbar spine. A literature search of the PubMed-National Library of Medicine was performed. Only articles in English were included. The current available literature demonstrates that LLIF is an effective method to decompress foraminal and central canal stenosis. Based on the current available literature LLIF effects on lateral recess stenosis are less consistent. The aim of this review is to provide with a thorough overview of the latest literature available and provide the audience with targeted-oriented published results that will eventually improve the decision-making process when using the LLIF technique.

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.

Outcomes of direct lateral interbody fusion (DLIF) in an Australian cohort

Background

Direct lateral interbody fusion (DLIF) mitigates many of the vascular complications and bony resections associated with other interbody fusion techniques. However, there are concerns regarding postoperative neural complications and that indirect decompression of the foramen has not been consistently demonstrated. This study prospectively assessed the clinical and radiological outcomes and the complication rates of the DLIF approach.

Methods

A prospective review was conducted of the first 50 consecutive DLIF cases of a single neurosurgeon between 2010 and 2014. Clinical outcomes were assessed using Visual Analogue Scale (VAS), Oswestry Disability Index (ODI) and Roland Morris Disability Questionnaire (RMDQ) surveys. Radiological outcomes, including spondylolisthesis, disc height, local disc angle, lumbar lordosis and foraminal height and width, were measured using Surgimap Spine software at the preoperative, 6 weeks, 6 months, and 12 months postoperative follow-up. Complication rates were also reported.

Results

A total of 50 patients (84 levels) were treated with DLIF. The mean patient age was 68.2±9.8 years and 62.0% were female. At latest follow-up, mean VAS pain score improved from 7.7±1.5 to 1.9±0.9 (P<0.0001), mean ODI improved from 42.1±14.5 to 16.9±6.7 (P<0.0001) and mean RMDQ score improved from 12.1±5.2 to 6.2±4.7 (P<0.0001). Mean spondylolisthesis reduced from 7.5%±6.5% to 1.3%±1.1% at 6 weeks (P<0.0001), 0.95%±0.74% at 6 months (P<0.0001) and recurred to 1.9%±1.7% at 12 months postoperatively (P=0.0006). Mean anterior disc height improved from 7.3±3.2 to 11.6±2.5 mm at 6 weeks (P<0.0001), 12.2±3.3 mm at 6 months (P<0.0001) and 9.8±2.1 mm at 12 months (P=0.0032) postoperatively. Mean posterior disc height improved from 4.4±2.0 to 6.8±2.1 mm at 6 weeks (P<0.0001), 6.6±2.5 mm at 6 months (P=0.0003), and 5.9±1.4 mm at 12 months (P=0.0039) postoperatively. Mean local disc angle improved from 7.0°±3.7° to 9.2°±3.3° at 6 weeks (P=0.0072), 10.4°±3.9° at 6 months (P=0.0013) and 8.2°±2.9° at 12 months (P=0.2487) postoperatively. No significant postoperative changes in lumbar lordosis were observed. Mean foraminal height improved from 18.3±3.5 to 21.5±3.9 mm at 6 weeks (P=0.0004), 20.6±3.4 mm at 6 months (P=0.0266), and 18.7±1.9 mm at 12 months (P=0.8021) postoperatively. Mean foraminal width improved from 7.9±2.0 to 10.2±2.8 mm at 6 weeks (P=0.0001), 9.4±2.6 mm at 6 months (P=0.0219) and 8.3±1.6 mm at 12 months (P=0.5734) postoperatively. Fusion rate at 6 and 12 months was 62.2% and 89.2%, respectively. A total of 6 patients (12%) had postoperative complications. Three patients (6%) had pain-related psoas muscle weakness and 3 patients (6%) had sensory neural complications that had resolved entirely by 8 and 16 weeks postoperatively, respectively.

Conclusions

The study provides encouraging short and medium-term clinical and radiological results for DLIF. In this patient series, there was a low complication rate with no permanent neural injury reported.

COMPARATIVE STUDY OF LUMBAR PLEXUS PATH ON THE LEFT AND RIGHT SIDES THROUGH THE PSOAS MUSCLE

ABSTRACT Objective: Spine surgery with a minimally invasive lateral approach and validate possible anatomical differences between the right and left sides. Methods: Four measurements (cm) were taken on 38 cadavers: the distance between the lumbar plexus and the transverse process (L4-L5) and the distance between the lumbar plexus and the midline of the lumbar spine, both on the right and left sides. Results: The mean distance between the lumbar plexus and the transverse process of L4-L5 was 1.03 cm and the distance to the midline was 3.99 cm for the right side. The averages of the left side were 1.13 cm and 3.38 cm, respectively. There is statistical difference between the sides (p<0.05) using the non-parametric Wilcoxon test. Conclusions: The authors suggest that the transverse process might be used as an anatomical landmark to define the surgical approach through the psoas muscle. Level of Evidence IV; Cadaveric study.

Use of motor evoked potentials during lateral lumbar interbody fusion reduces postoperative deficits

BACKGROUND CONTEXT

Intraoperative neurophysiological monitoring (IONM) has gained rather widespread acceptance as a method to mitigate risk to the lumbar plexus during lateral lumbar interbody fusion (LLIF) surgery. The most common approach to IONM involves using only electromyography (EMG) monitoring, and the rate of postoperative deficit remains unacceptably high. Other test modalities, such as transcranial electric motor-evoked potentials (tcMEPs) and somatosensory-evoked potentials, may be more suitable for monitoring neural integrity, but they have not been widely adopted during LLIF. Recent studies have begun to examine their utility in monitoring LLIF surgery with favorable results.

PURPOSE

This study aimed to evaluate the efficacy of different IONM paradigms in the prevention of iatrogenic neurologic sequelae during LLIF and to specifically evaluate the utility of including tcMEPs in an IONM strategy for LLIF surgery.

STUDY DESIGN/SETTING

A non-randomized, retrospective analysis of 479 LLIF procedures at a single institution over a 4-year period was conducted. During the study epoch, three different IONM strategies were used for LLIF procedures: (1) surgeon-directed T-EMG monitoring ("SD-EMG"), (2) neurophysiologist-controlled T-EMG monitoring ("NC-EMG"), and (3) neurophysiologist-controlled T-EMG monitoring supplemented with MEP monitoring ("NC-MEP").

PATIENT SAMPLE

The patient population comprised 254 men (53.5%) and 221 women (46.5%). Patient age ranged from a minimum of 21 years to a maximum of 89 years, with a mean of 56.6 years.

OUTCOME MEASURES

Physician-documented physiological measures included manual muscle test grading of hip-flexion, hip-adduction, or knee-extension, as well as hypo- or hyperesthesia of the groin or anterolateral thigh on the surgical side. Self-reported measures included numbness or tingling in the groin or anterolateral thigh on the surgical side.

METHODS

Patient progress notes were reviewed from the postoperative period up to 12 months after surgery. The rates of postoperative sensory-motor deficit consistent with lumbar plexopathy or peripheral nerve palsy on the surgical side were compared between the three cohorts.

RESULTS

Using the dependent measure of neurologic deficit, whether motor or sensory, patients with NC-MEP monitoring had the lowest rate of immediate postoperative deficit (22.3%) compared with NC-EMG monitoring (37.1%) and SD-EMG monitoring (40.4%). This result extended to sensory deficits consistent with lumbar plexopathy (pure motor deficits being excluded); patients with NC-MEP monitoring had the lowest rate (20.5%) compared with NC-EMG monitoring (34.3%) and SD-EMG monitoring (36.9%). Additionally, evaluation of postoperative motor deficits consistent with peripheral nerve palsy (pure sensory deficits being excluded) revealed that the NC-MEP group had the lowest rate (5.7%) of motor deficit compared with the SD-EMG (17.0%) and NC-EMG (17.1%) cohorts. Finally, when assessing only those patients whose last follow-up was greater than or equal to 12 months (n=251), the rate of unresolved motor deficits was significantly lower in the NC-MEP group (0.9%) compared with NC-EMG (6.9%) and SD-EMG (11.0%). A comparison of the NC-MEP versus NC-EMG and SD-EMG groups, both independently and combined, was statistically significant (>95% confidence level) for all analyses.

CONCLUSIONS

The results of the present study indicate that preservation of tcMEPs from the adductor longus, quadriceps, and tibialis anterior muscles are of paramount importance for limiting iatrogenic sensory and motor injuries during LLIF surgery. In this regard, the inclusion of tcMEPs serves to compliment EMG and allows for the periodic, functional assessment of at-risk nerves during these procedures. Thus, tcMEPs appear to be the most effective modality for the prevention of both transient and permanent neurologic injury during LLIF surgery. We propose that the standard paradigm for protecting the nervous system during LLIF be adapted to include tcMEPs.

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.

Contralateral lumbosacral plexopathy following lumbar microdiscectomy

We describe the unique case of a 51-year-old lady who developed a contralateral lumbosacral plexopathy two days after a lumbar microdiscectomy. This is the first report to date of this complication occurring following this procedure. We review the literature regarding lumbosacral plexopathy and discuss the evidence base behind investigating and managing this condition and the potential pathophysiological mechanisms which underlie its development. We draw comparisons with the more widely recognised post-operative brachial neuritis, characterised by delayed onset brachial plexopathy developing after cervical decompression, and propose an immune-mediated inflammatory mechanism linking the two conditions.

Morphometric MRI Imaging Study of the Corridor for the Oblique Lumbar Interbody Fusion Technique at L1-L5

BACKGROUND

Anterior lumbar interbody fusion and lateral lumbar interbody fusion are associated with approach-related disadvantages. Oblique lumbar interbody fusion (OLIF) is the proposed solution, especially for upper lumbar levels. We analyzed the size and regional anatomy of the corridor used in the OLIF technique between levels L1 and L5.

METHODS

This is a morphometric study of 200 randomly selected magnetic resonance imaging (MRI) studies with features of lumbar degenerative disease. On MRI, the oblique corridor was defined as the smallest distance between the psoas major muscle and aorta or inferior vena cava (or common iliac artery) and measured at the L1/L2, L2/L3, L3/L4, and L4/L5 disc levels on both the left and right on the axial images at the mid-disc level.

RESULTS

Mean distances of the oblique corridor on the left side were L1/L2 = 18.90 mm, L2/L3 = 15.50 mm; L3/L4 = 12.75 mm, and L4/L5 = 8.92 mm; on the right side, they were L1/L2 = 14.80 mm, L2/L3 = 5.50 mm, L3/L4 = 3.00 mm, and L4/L5 = 1.46 mm. For both sides, the corridor size was not significantly affected by sex, and it increased with age and decreased at the inferior lumbar disc levels. The L1/L2 and L2/L3 levels may be obstructed by the ipsilateral kidney and renal vasculature on both sides and the liver on the right side.

CONCLUSIONS

A left-sided OLIF approach is viable for both sexes. Oblique access to the L1/L2 and L2/L3 disc levels is feasible regardless of age, whereas the L3/L4 and L4/L5 levels may be more suitable in older patients, especially for male patients. The right-sided approach is less likely to be performed effectively.

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.

Morphometric anatomy of the lumbar sympathetic trunk with respect to the anterolateral approach to lumbar interbody fusion: a cadaver study

BACKGROUND

An approach to lateral lumbar interbody fusion (LLIF) utilizing an oblique corridor anterior to the psoas muscle was first described by Mayer in 1997 and subsequently by other authors. The only consistent structure of note in this corridor is the lumbar sympathetic trunk (LST), which at times must be mobilized in order to perform a discectomy and interbody fusion, thereby placing the LST at risk. This study was designed to describe the morphometric anatomy of the LST in relation to surgically relevant landmarks for the anterolateral approach to the lumbar spine at L3/L4 to L5/S1.

METHODS

Twenty-four embalmed cadavers (13 males, 11 females, age range, 50-89) were dissected to expose the LST. Bilateral measurements were recorded using a calliper under direct visualization, using the midsagittal plane of the lumbar spine as the reference landmark. The points were then marked with radio-opaque needles, and 14 cadavers were scanned with CT to validate the measurements.

RESULTS

Of 48 LSTs, there was minimal difference in the direction of its course between sides; 14/24 specimens had concordant directions. The majority (n=28) had a medial to lateral cephalocaudal course. If osteophytes were present at the L4/L5 level, the majority of LSTs (n=7, of 8) were displaced lateral to the osteophyte. At the L5/S1 level, half of the cases with osteophytes (n=3, of 6) stretched the LST over the top of the osteophyte. The LST was adherent to the L4/L5 disc space bilaterally in 93% of cases.

CONCLUSIONS

With the development of lumbar fusion techniques which utilize an oblique corridor and the retraction of psoas muscle, LST has become an important neural structure to define, protect and mobilize. In our morphometric analysis of 24 specimens, the position has been identified and quantified, and this paper notes variations, particularly distortions caused by degenerative processes. In this study, the LST ran in a medial to lateral direction from L3 to S1, and osteophytes typically displace and adhere to the LST.

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.

Injury to the Lumbar Plexus and its Branches After Lateral Fusion Procedures: A Cadaver Study

INTRODUCTION

Neurologic deficits from lumbar plexus nerve injuries commonly occur in patients undergoing lateral approaches. However, it is not yet clear what types of injury occur, where anatomically they are located, or what mechanism causes them. We aimed to study 1) the topographic anatomy of lumbar plexus nerves and their injuries in human cadavers after lateral transpsoas approaches to the lumbar spine, 2) the structural morphology of those injuries, and 3) the topographic anatomy of the lumbar plexus throughout the mediolateral approach corridor.

METHODS

Fifteen adult fresh frozen cadaveric torsos (26 sides) underwent lateral approaches (L1-L5) by experienced lateral spine surgeons. The cadavers were subsequently opened and the entire plexus dissected and examined for nerve injuries. The topographic anatomy of the lumbar plexus and its branches, their injuries, and the morphology of these injuries were documented.

RESULTS

Fifteen injuries were found with complete or partial nerve transections (Sunderland IV and V). Injuries were found throughout the mediolateral approach corridor. At L1/2, the iliohypogastric, ilioinguinal, and subcostal nerves were injured within the psoas major muscle, the retroperitoneal space, or the outer abdominal muscles and subcutaneous tissues. Genitofemoral nerve injuries were found in the retroperitoneal space. Nerve root injuries occurred within the retroperitoneal space and psoas muscle. Femoral nerve injuries were found only within the psoas major muscle. No obturator nerve injuries occurred.

CONCLUSIONS

Lateral approaches can lead to structural nerve damage. Knowledge of the complex plexus anatomy, specifically its mediolateral course, is critical to avoid approach-related injuries.

Preoperative assessment of the ureter with dual-phase contrast-enhanced computed tomography for lateral lumbar interbody fusion procedures

BACKGROUND

Performing the minimally invasive lateral lumbar interbody fusion (LIF), such as the extreme lateral interbody fusion (XLIF) and oblique lateral interbody fusion (OLIF), through a retroperitoneal approach has become increasingly popular. Although urological injury is a major complication of LIF, the anatomical location of the ureter and its risk of injury have not been assessed. The purpose of this study was to evaluate the efficacy of dual-phase contrast-enhanced computed tomography for assessing the location of the ureter and risk of its injury in consecutive LIF cases.

METHODS

27 cases (12 men and 15 women) were enrolled in the study. Dual-phase contrast-enhanced CT was performed preoperatively, and the risk of ureteral injury was assessed. The location of the ureter was classified using the psoas muscle and vertebral body as reference structures for OLIF and XLIF procedures, respectively. During the OLIF procedures, the location of the ureter was additionally assessed with direct vision and manual palpation in all cases. Simultaneously, potential vascular anomalies were assessed with both 3D and axial images of CT.

RESULTS

A total of 125 among 162 ureters, excluding 13 with insufficient enhancement and 24 (44.4%) within the kidney at the L2-L3 level, were assessed preoperatively; 113 ureters (90.4%) were classified as anatomically close to the surgical corridor for OLIF, and 20 ureters (16.0%) as having a potential risk of injury during XLIF. In one case, OLIF was converted to a conventional posterior procedure because of a vascular anomaly. Intraoperative findings showed that ureters moved anteriorly with the peritoneum in all cases, as assessed by manual palpation under direct vision.

CONCLUSIONS

Dual-phase contrast-enhanced CT is useful in assessing the location of the ureter, kidney, and vascular structures simultaneously. Both OLIF and XLIF have a potential risk of urological injury.