Structural spinal pathology and neuraxial anaesthesia

When assessing the feasibility of and approach to neuraxial analgesia in a patient with abnormal spinal anatomy, several key factors should be considered:

Are anatomical landmarks abnormal or missing, and does a specific vertebral level need to be avoided?
Does the patient have an intact ligamentum flavum and will a loss-of-resistance technique be feasible?
Is there tissue, such as scar tissue, bone graft or surgical spinal implants in the path of the needle that could preclude needle insertion or be damaged by needle or catheter insertion?
Is there significant disruption to the epidural space that would preclude local anaesthesia spread or catheter insertion?

Pathology and clinical features	Risks/Patient counselling	Techniques
Mechanical low back pain •Dull lumbar region pain •Exacerbated by forward flexion, erector spinae palpation •Lumbar movement may be limited •May radiate into leg, but usually not below the knee	•Neuraxial anaesthesia will not increase risk of postpartum back pain2 •Patients who have pre-existing back pain are at increased risk of having postpartum back pain3	•Epidural and spinal anaesthesia/analgesia can be used
Herniated lumbar disc/spinal stenosis •Back pain and unilateral leg pain that radiates below the knee •Numbness, paraesthesia, weakness and/or loss of tendon reflexes in nerve root distribution. •Pain on straight leg raise •Pain is relieved by lying down and exacerbated by prolonged walking/sitting	•Extremely rare reports of worsening neurological impairment in obstetric patients with existing spinal stenosis or disc herniation when neuraxial is used4–8	•Epidural and spinal anaesthesia/analgesia can be used •Currently no compelling evidence to avoid neuraxial anaesthesia at the level of disc herniation in asymptomatic disc disease •If known severe disease, or symptoms suggestive thereof, consider risk–benefit of neuraxial •Consider avoiding affected level, and have increased vigilance for postoperative neurological impairment9 •Ultrasound may be helpful for localising unaffected levels
Spinal stenosis •Low back, buttock or leg pain exacerbated by standing, walking, lumbar extension. Relieved by forward flexion, sitting, lying flat. May be burning or cramping in nature •Gradual onset pain, numbness and weakness after walking a predictable distance. Less pain walking uphill.
Spondylolysis and spondylolisthesis •Low back pain, exacerbated by extension	•No contraindication or increased risk with neuraxial in spondylolysis •There may be a slightly increased risk of dural puncture in spondylolisthesis if epidural is attempted at the level of pathology	•Epidural and spinal anaesthesia/analgesia can be used •Consider avoiding affected level in spondylolisthesis. •Ultrasound may be useful for localising unaffected levels
Uncorrected scoliosis •History of diagnosed scoliosis •Physical evidence of spinal curvature on exam	•Success rates for epidural and spinal anaesthesia in uncorrected scoliosis are almost comparable to those without spinal deformity, but the procedure may take longer and may require more attempts10–12 •Unilateral block is more common, but is usually manageable with positioning/additional local anaesthetic	•Epidural and spinal anaesthesia/analgesia can be used •Consider a paramedian approach on the convex side of the curve, or needle direction towards the convex side from the apparent midline •Positioning and higher volumes of local anaesthetic may be required to overcome unilateral block
Corrected scoliosis •History of scoliosis with corrective surgery	Anterior fusion: •There should be no increased risk of complications or difficulty with neuraxial anaesthesia/analgesia Posterior fusion: •Neuraxial anaesthesia may not be possible in certain patients (lumbar/lumbosacral fusions) •In those in whom neuraxial anaesthesia is possible, scar tissue and anatomical distortion may make the procedure more difficult. Both epidural and spinal may take longer and may require more attempts •Scar tissue may also result in unpredictable analgesia. Patchy or unilateral analgesia can often be overcome with positioning and/or additional local anaesthetic •Ultimately, analgesia is usually achievable, although rescue techniques (e.g. spinal anaesthesia) may be required13	•Epidural and spinal anaesthesia/analgesia can be used in unfused segments •Imaging and medical notes should be reviewed to ascertain which level may be suitable •Ultrasound may be helpful for localising suitable levels •Positioning and higher volumes of local anaesthetic may be required to overcome unilateral block •Spinal anaesthesia can be used as a rescue technique where epidural has failed
Previous spinal surgery •History	•No contraindication to neuraxial technique •Scar tissue from previous surgery may make analgesia unpredictable •Depending on nature of surgery, if neuraxial is attempted at the operative level, there may be an increased risk of dural puncture	•Epidural and spinal anaesthesia/analgesia can be used safely in unoperated segments •Because of variability in ligamentum flavum resection in various surgeries, it is prudent to avoid insertion at operative level •Ultrasound may be useful to localise appropriate level
Spinal dysraphism •History of operative repair •History of close spinal dysraphism, may have neurological impairment	Previous repair •There is a risk of damage to the spinal cord if epidural or spinal anaesthesia is performed at the level of a previous repair or where there is spinal cord tethering •Epidural anaesthesia may be possible above the level of repair, although it may be suboptimal owing to scar tissue and abnormality of the epidural space •Spinal anaesthesia has been successfully used above the level of the repair Closed isolated bony defects •No contraindication to neuraxial anaesthesia •Theoretical increased risk of dural puncture	•Epidural and spinal techniques can be used in some patients •If used, imaging/medical notes should be carefully reviewed to ascertain at which level such techniques are safe (e.g. where there is no spinal cord tethering and the epidural anatomy is normal) •Ultrasound may be useful to localise the suitable levels at the bedside •Epidural anaesthesia, if used, may be unpredictable as a result of abnormal epidural anatomy •Low-dose spinal anaesthesia at low thoracic levels can be considered

Mechanical LBP

Low back pain may accompany radicular pain with associated motor and sensory deficits, which should be examined and clearly documented. Back pain accompanied by red flag symptoms such as saddle anaesthesia, major motor weakness, incontinence and fevers should prompt further investigation.

Disc disease & spinal stenosis

In recent years, some evidence has emerged to suggest that there may be an increased risk of new or worsening neurological impairment in patients with existing spinal stenosis when neuraxial anaesthesia is used

This may be related to a compressive–ischaemic effect because of reduced cross-sectional area of the vertebral canal, direct trauma, haematoma, or enhanced neurotoxic effects of local anaesthetics resulting from limited distribution in the smaller space.

→ these data are almost entirely derived from older, non-obstetric patients, with very few cases reported in parturients

no firm linkage to injury if spinal stenosis is at a site distant from the level of neuraxial block placement, and if possible, the neuraxial block can be performed at an alternative level to the one affected by disc herniation or stenosis.

Scoliosis

Scoliosis is defined as a ≥10° lateral curvature of the spine in the standing position on a coronal radiographic image

idiopathic scoliosis is the most common aetiology with adolescent idiopathic scoliosis (AIS) encompassing 80% of cases

Operative management is indicated when progressive scoliosis exceeds 45° in patients with an immature skeleton or when progression or pain occurs after skeletal maturity.

Uncorrected scoliosis

The epidural injectate has been shown to initially flow towards the concave side of the curve in approximately 80% of cases. As such analgesia may be unilateral and higher volumes may be required.

Corrected scoliosis

In anterior fusion, the vertebral column is accessed anteriorly with screw and rod placement lateral to the vertebral bodies. The spinous processes remain intact and no bone graft or scar tissue should be present posteriorly to inhibit needle placement. Neuraxial analgesia in these patients should be straightforward.

Posterior fusion entails the placement of multiple bilateral pedicle screws, hooks or both, followed by rod insertion and compression/distraction of the convex and concave aspects of the curve. Spinal osteotomies may be required for release before compression/distraction, and the procedure is completed with placement of extensive bone graft to encourage fusion of the involved segments. As a result, access to the neuroaxis in the region of the fusion may be impossible

distraction/compression, bone grafting and spinal osteotomies may cause epidural space distortion and fibrosis, which may affect catheter passage and spread of local anaesthetic.

Epidural catheterisation may be challenging in women who have had posterior fusion, with catheter placement taking longer and failed or repeated attempts being more common than in healthy controls. Reassuringly, despite these difficulties, successful analgesia in this group has been reported in up to 88% of cases.

In corrected scoliosis, neuraxial analgesia below the level of instrumentation is an option and the use of ultrasound for vertebral level localisation is recommended. Common inadequacies in analgesia such as unilateral or patchy block may be overcome through repositioning and additional doses of local anaesthetic as required. In the event of epidural failure, primary or repeat spinal anaesthesia may be a rescue option with or without the use of a spinal catheter.

Previous spinal surgery

Scar tissue-mediated distortion of anatomical landmarks and epidural fibrosis may be an issue for neuraxial anaesthesia in these patients

if the ligamentum flavum has been resected, a loss-of-resistance technique at the surgical level will not be reliable

Spinal dysraphism

Spinal dysraphisms are broadly divided into open and closed abnormalities. Open spinal dysraphisms are characterised by exposure of the nervous tissue, the meninges or both to the environment through a congenital bony defect. Closed spinal dysraphisms are covered by skin such that there is no exposure of the neural/meningeal tissues, although there may be overlying cutaneous stigmata such as skin dimples or hypertrichosis.

The underlying spinal cord and associated structures are abnormal; there may be low-lying or tethered spinal cord and conus medullaris, split cord or lipomata.

Sensory impairment is extremely variable and may be asymmetric or demonstrate perineal sparing.

Coexistent scoliosis and Chiari malformation with hydrocephalus may be present

Such patients also may have severe latex allergy

posterior spinal cord tethering may be present, even in the context of prior detethering at the time of surgery, leaving it vulnerable to needle trauma

A posterior tethered cord with intact sensation is considered an absolute contraindication to neuraxial anaesthesia for this reason

Women with a sensory level above T10 may not require labour analgesia, although anaesthesia above T4 is required for Caesarean delivery

Autonomic dysreflexia is rare in this population as the majority of lesions occur in the lumbosacral region. In those with a sensory level above T6, consideration should be given to provision of anaesthesia to avoid provoking autonomic dysreflexia

PDPH

Image-guided epidural blood patch has been described in postspinal surgery patients with complex anatomy and may be an effective and safe option

References

Neuraxial Anaesthesia in the Parturient With Pre-Existing Structural Spinal Pathology - BJA Ed