Anatomy of the lumbar interspinous ligament: findings relevant to epidural insertion using loss of resistance

Neuraxial initiation techniques for labor analgesia: Comparative insights on standard epidural, combined spinal-epidural and dural puncture epidural analgesia

PURPOSE OF REVIEW

In recent years, initiation techniques for neuraxial labor analgesia have focused on enhancing analgesic quality while minimizing complications. This review aims to summarize recent evidence on the standard epidural (EPL), combined spinal-epidural (CSE), and dural puncture epidural (DPE) techniques, emphasizing their benefits, risks, and relevance in contemporary obstetric anesthesia care.

RECENT FINDINGS

The DPE technique offers unique values, combining the advantages from CSE and EPL techniques. DPE and CSE, compared with EPL, techniques involve a dural puncture with a spinal needle, and the resulting epidural-intrathecal conduit enables translocation of analgesic agents, providing faster onset, earlier sacral coverage, better catheter function, and more rapid epidural extension to surgical anesthesia. Moreover, by limiting the intrathecal dose administered with the CSE technique, the DPE technique lowers the risks of fetal bradycardia and pruritus.

SUMMARY

EPL and CSE techniques are widely used for neuraxial labor analgesia. The DPE technique offers a novel alternative, delivering high-quality analgesia with minimal complications. While the benefits of the DPE technique are increasingly being recognized, additional comparative research will better support anesthesiologists in selecting the most appropriate technique across diverse clinical scenarios.

Development of a spinopelvic complex finite element model for quantitative analysis of the biomechanical response of patients with degenerative spondylolisthesis

Research on degenerative spondylolisthesis (DS) has focused primarily on the biomechanical responses of pathological segments, with few studies involving muscle modelling in simulated analysis, leading to an emphasis on the back muscles in physical therapy, neglecting the ventral muscles. The purpose of this study was to quantitatively analyse the biomechanical response of the spinopelvic complex and surrounding muscle groups in DS patients using integrative modelling. The findings may aid in the development of more comprehensive rehabilitation strategies for DS patients. Two new finite element spinopelvic complex models with detailed muscles for normal spine and DS spine (L4 forwards slippage) modelling were established and validated at multiple levels. Then, the spinopelvic position parameters including peak stress of the lumbar isthmic-cortical bone, intervertebral discs, and facet joints; peak strain of the ligaments; peak force of the muscles; and percentage difference in the range of motion were analysed and compared under flexion-extension (F-E), lateral bending (LB), and axial rotation (AR) loading conditions between the two models. Compared with the normal spine model, the DS spine model exhibited greater stress and strain in adjacent biological tissues. Stress at the L4/5 disc and facet joints under AR and LB conditions was approximately 6.6 times greater in the DS spine model than in the normal model, the posterior longitudinal ligament peak strain in the normal model was 1/10 of that in the DS model, and more high-stress areas were found in the DS model, with stress notably transferring forwards. Additionally, compared with the normal spine model, the DS model exhibited greater muscle tensile forces in the lumbosacral muscle groups during F-E and LB motions. The psoas muscle in the DS model was subjected to 23.2% greater tensile force than that in the normal model. These findings indicated that L4 anterior slippage and changes in lumbosacral-pelvic alignment affect the biomechanical response of muscles. In summary, the present work demonstrated a certain level of accuracy and validity of our models as well as the differences between the models. Alterations in spondylolisthesis and the accompanying overall imbalance in the spinopelvic complex result in increased loading response levels of the functional spinal units in DS patients, creating a vicious cycle that exacerbates the imbalance in the lumbosacral region. Therefore, clinicians are encouraged to propose specific exercises for the ventral muscles, such as the psoas group, to address spinopelvic imbalance and halt the progression of DS.

Macrophage-derived extracellular vesicles transfer mitochondria to adipocytes and promote adipocyte-myofibroblast transition in epidural fibrosis

Epidural fibrosis post laminectomy is the leading cause of failed back surgery syndrome. Little is known about the role and mechanisms of adipose tissues in epidural fibrosis. Here, we found that obese patients were more likely to develop epidural fibrosis after spine surgery. Similarly, obesity led to more progressive epidural fibrosis in a mouse model of laminectomy. Adipocyte-myofibroblast transition (AMT) occurs in epidural scarring. Mechanistically, large extracellular vesicles (EVs) from M2-type macrophages transfer mitochondria into adipocytes and promote AMT by activating the TGF-β and PAI-1 pathways. Blocking the PAI-1 pathway significantly attenuated the transition of adipocytes into myofibroblasts. We conclude that large EVs from macrophages transfer mitochondria to promote AMT in epidural fibrosis.

Retrodural space of Okada in the posterior ligamentous complex region: clinical and anatomical findings relevant to lumbar interlaminar epidural injection

Background

The retrodural space of Okada is a potential space posterior to the ligamentum flavum that allows communication with the bilateral facet joints. However, the actual anatomy of this space has not been clearly visualized to date. We sought to investigate the characteristics of patients showing contrast spreading to the facet joint space during epidural injection and to clarify the anatomical structures of the retrodural space and adjacent ligamentous tissues in cadaveric specimens.

Methods

Fluoroscopic images of patients who underwent fluoroscopy-guided lumbar interlaminar epidural injection were assessed for contrast flow to the facet joints. Patient demographics, preprocedural imaging study findings, and epidural approaches were analyzed. The anatomical study included the sectional dissection, micro-CT imaging, and histological evaluation of lumbar spine specimens from 16 embalmed cadavers.

Results

Fluoroscopic images of 605 epidural injections were analyzed. Among them, 36 with inadvertent spread into the facet joints (5.9%) were identified. Multivariate analysis revealed that facet joint pathologies were significantly associated with inadvertent spread into the facet joints (OR 4.382; 95% CI 1.160 to 16.558; p=0.029). Micro-CT and histological findings consistently showed a retrodural space between the ligamentum flavum and interspinous ligament. Various anatomical communication routes in the posterior ligamentous complex leading to this space were observed in specimens with degenerative and pathological changes.

Conclusion

Degenerative and pathological facet joint changes were associated with a higher incidence of spread into the retrodural space during epidural injection. Our findings confirm anatomical evidence for a false loss of resistance before the needle enters the epidural space.

Cervical spine ligamentum flavum gaps: MR characterisation and implications for interlaminar epidural injection therapy

Background

Cervical epidural steroid injections are commonly performed to manage pain from cervical spine disease. Cadaveric studies have demonstrated incomplete ligamentum flavum fusion in the central interlaminar region with resultant midline gaps. We performed an MR-based characterization of cervical ligamentum flavum midline gaps to improve understanding of their prevalence and guide interventionalists in procedural planning.

Methods

Fifty patients were retrospectively reviewed following institutional review board approval. Axial T2-weighted spinecho sequences were used to evaluate ligamentum flavum integrity at the interlaminar spaces of C5–C6, C6–C7 and C7–T1. Interlaminar spaces were further subdivided into superior, middle, and inferior portions, yielding 150 interlaminar regions characterized from C5 to T1. Subsequently, a novel categorization of gap morphology was performed, highlighting gap morphology (anterior, posterior, full, or no gap).

Results

Full gaps of the ligamentum flavum, with direct epidural space exposure, were observed with variable prevalence at all three levels evaluated. The highest incidence of full ligamentum flavum gaps were observed at C7–T1, occurring in 71.4% of patients at both its middle and inferior portions. The inferior aspect of C5–C6 demonstrated the lowest observed rates of full ligamentum flavum gap (2%).

Conclusions

Ligamentum flavum gaps occur in the lower cervical spine at high rates, with the highest prevalence of full thickness ligamentum flavum gaps at C7–T1. Interventionists must be aware of these important normal variants and evaluate preprocedural MRI to plan interventions.

Neuraxial labor analgesia: Initiation techniques

The ideal technique for labor analgesia would have a quick onset, predictable quality, and adjustable depth and duration. Moreover, it would be easy to perform and have minimal maternal and fetal side effects. A catheter-based neuraxial approach encompasses these desirable characteristics and includes the epidural, combined spinal epidural, dural puncture epidural, and intrathecal catheter techniques. In this review, we outline the unique technical considerations, analgesic characteristics, and side effect profiles for each technique that can ultimately impact the maternal-fetal dyad. The selection of neuraxial analgesia techniques should consider the patient and team's goals and expectations, the clinical context, and the institutional culture. Labor analgesic techniques that initiate with an intentional dural puncture component have a faster onset, greater bilateral and sacral spread, and lower rates of epidural catheter failure. Further elucidation of the mechanisms, benefits, and risks of each neuraxial initiation technique will continue to benefit patients and care providers.