This topic follows on from the page on (generic) back pain.
The 2023 CRQ on back pain (74% pass rate) saw candidates lose marks on the definition of radicular pain and knowledge of duration of symptoms before starting treatment.
13-40% of people experience an episode of lumbar radicular pain during their lifetime
Radiculopathy is a generic term which encompasses a range of clinical features resulting from pathology of the nerve roots
Lumbar radiculopathy is a neuropathic pain caused by pathology of the sensory lumbar nerve roots, resulting in radiating pain in a lumbar dermatomal pattern
Sciatica also refers to neuropathic pain radiating in a lumbar dermatomal pattern, with or without motor deficit
It is often used synonymously with lumbar radiculopathy
Risk Factors
Male gender
Obesity
Smoking
Depression
Frequent, heavy, manual labour with flexion-based lifting
Changes to the normal anatomical structures surrounding the nerve root cause lumbar radicular pain:
Intervertebral discs
Bones and bony articulations
Ligaments
The typical common endpoint of all processes is a narrowing of the space for the nerve root to travel, either in the spinal canal or intervertebral foramen
This causes mechanical and/or biochemical insult
Nerve roots are more susceptible to damage than peripheral nerves on account of:
Lack of perineurium, leading to reduced tensile strength and less barrier to diffusion (of noxious substances)
Diminished epineurium, diminishing the defence against compression
Poorer lymphatic drainage of inflammatory mediators, exposing the nerve to greater risk of damage from fibroblasts and intraneural fibrosis
Lumbar disc herniation i.e. discogenic radiculopathy
Is the most common aetiology of lumbar radicular pain, particulary in those <50yrs old
A damaged annulus fibrosus allows the inner nucleus pulposus to herniate, leading to:
Disc protrusion - nucleus material out-pouches but the annulus is intact, may be symptom-free (27% of asymptomatic patients have at least 1 disc protrusion)
Disc extrusion - more severe, with material exiting entirely
Disc sequestration - free fragments of disc material separates from the disc entirely; can migrate and cause symptoms distal to original vertebral level
Disc herniation can occur in various directions; centrally, laterally, paramedian or posterolaterally
Lateral herniation can impact on a nerve root and radicular symptoms
Central herniation can cause bilateral symptoms and cauda equina syndrome
Compression on the nerve root, or placing it under tension, results in an inflammatory response
Various inflammatory mediators are involved: PLA2, PGE2, leukotrienes, IL-1, IL-6, TNFɑ
These increase the sensitivity of the nerve and decrease the threshold for ectopic firing
Even as little as 10-15% stretch from resting length is enough to cause neurophysiological dysfunction
Lumbar spinal stenosis
Is the second commonest cause of lumbar radicular pain, particularly in those >50yrs old
Can arise due to a number of disease processes, including spondylolisthesis, age-related degenerative changes or ankylosing spondylitis
Leads to narrowing in the central canal, lateral recesses or intervertebral (exit) foramina
Typically causes a radicular pain exacerbated by standing and walking but relieved by leaning forward
Non-musculskeletal causes of radicular pain
Neoplasm
Herpes zoster
Lyme's disease
Epidural abscesses
Features depend on which nerve fibres are affected; sensory and/or motor symptoms can be present
Nerve root
Sensory symptoms
Motor weakness
Reflexes affected
L1/2
Inguinal area
Hip flexion
Cremasteric
L3/4
Anterior thigh and knee
Hip adduction
Knee extension
Patellar
L5
Posterolateral thigh and leg
Hip extension Knee flexion Dorsiflexion
-
S1
Posterior thigh and leg
Lateral foot
Plantarflexion
Ankle
Sensory symptoms predominate
A sharp, shooting, lancinating, stabbing or shock-like pain
Radiates from lower back to buttock, groin or leg
May be unilateral or bilateral
± Sensory loss
± Paraesthesia: a tingling, burning or prickling sensation
Motor fibres in the ventral nerve may be affected, leading to weakness, fatigue or cramping in a myotomal distribution
Facet joint pain
Facet joint issues are the second commonest cause of back pain
Facet joint pain may cause back pain without necessarily causing radiculopathy
The pain can radiate into buttocks and legs and mimic lumbar radicular pain
There is persistent point tenderness over the inflamed facet joints
Exclude sinister causes
Full history and examination, including neurological examination, are essential to exclude 'red flag' symptoms which may point to more sinister aetiology:
CES : acute, or progression to, bilateral sciatica | severe, progressive neurological deficit | saddle-area anaesthesia or paraesthesia | urinary retention/faecal incontinence
Spinal fractures: sudden onset, severe, central spinal pain associated with trauma, relieved by lying down | point tenderness of vertebral body
Cancer: age >50yrs | gradual onset of severe, unremitting pain | weight loss | previous cancer
Infection (discitis, osteomyelitis, epidural abscess): fever | recent UTI | diabetes mellitus | history of IVDU, TB, HIV or other immunosuppression
Examination
Examination techniques attempt to stretch the nerve root and induce the patient's symptoms, confirming radicular pain
These include:
Passive straight leg raise test
Positive if SLR induces or exacerbates patient's radicular pain
Sensitivity 91% / specificity 26%
Crossed SLR test
SLR test performed on contralateral lower extremity in the same way
If it causes pain, it indicates a SOL within the IT space e.g. herniated disc
Imaging
Imaging is typically only required if there are red flag signs present, in which case urgent MRI is required
If symptoms persistent beyond 4-6 weeks, further investigation may be required:
XR typically of limited value but may highlight scoliosis, spondylolisthesis or trauma
MRI is the imaging of choice, with high sensitivity (but low specificity) for nerve injury
CT may be useful if MRI is contraindicated
Myelography may be used where CT/MRI are not possible
Contrast is injected intrathecally and plain XR are taken to visualise spinal cord and nerve roots
Electrodiagnostic studies
Patients with radiculopathic clinical features, but without explanatory pathology on imaging, may benefit from nerve conduction studies or EMG
These are used to exclude peripheral entrapment neuropathies, plexopathies or polyneuropathies
Nerve conduction studies in radiculopathy typically show:
Normal compound muscle action potentials
Normal sensory nerve action potentials (despite a clinical sensory deficit), because the lesion is proximal to the dorsal root ganglion
Abnormal spontaneous activity in muscles in a myotomal pattern on EMG
Conservative management
Encourage normal activity and return to work, as normal movements are not harmful even if painful and bed rest is not recommended
Exercise
Weight loss
TENS/massage/hot or cold therapy
CBT | group exercise programmes | manual therapy e.g. massage, mobilisation
Consider referral to pain specialist for pain management programme in those with refractory symptoms
The majority of patients with disc herniation will see improved or resolved symptoms within 4 - 6 weeks with conservative management
Pharmacological management
Simple analgesics in combination, such as paracetamol and one of:
NSAIDs, at lowest effective dose for shortest possible duration
Weak opioids, only if NSAID is contraindicated or not tolerated
Opioids should not routinely be offered
There is no overall evidence that gabapentinoids, anti-epileptic drugs, anti-depressants, oral steroids or benzodiazepines provide benefit (but they do not have evidence of harm)
Minimally invasive therapies
May be warranted in patients with pain persisting beyond 4-6 weeks despite conservative management
Neuraxial injections
E.g. Inter-laminar epidural or caudal epidural or foraminal root block
Provide short-to-moderate term analgesia for acute pain, which may facilitate participation in other elements of rehabilitation
Is most successful in those with fewer than 6 months of symptoms and when the pathophysiology is herniated disc (less effective if spinal stenosis)
Targeting the relevant root with a transforaminal epidural steroid injection (TFESI) improves outcome vs. interlaminar injections
TFESI is less costly and similarly effective at reducing pain/disability as microdiscectomy
Do not offer intrathecal injections for managing low back pain
Coblation nucleoplasty
A minimally invasive technique to manage intra-discal herniation by removing part of the nucleus pulposus using energy
A reduction of disc volume by 10-20% decompresses the herniated disc and relieves nerve root pressure
Pulse radiofrequency at the DRG; median branch of dorsal ramus block (MBB)
Only perform in those who've had a positive response to a diagnostic medial branch block
Needle placed next to DRG under fluoroscopic guidance and high-voltage electrical pulses are applied to prevent conduction of pain
The current is applied in a pulsatile fashion with a maximum temperature of 42°C to avoid coagulation of nervous tissue
Surgical interventions
Should be considered for pain or function is refractory to non-surgical methods
The choice of surgery depends on the aetiology:
Microdiscectomy is the primary surgical intervention for lumbar radiculopathy due to disc herniation; 1yr outcome equivalent to conservative care
Laminectomy is the main surgical intervention in spinal stenosis
Interbody fusion or cage implantation may be indicated in the presence of deformity e.g. spondylolisthesis or scoliosis, but not for generic low back pain
Spinal cord stimulators
Spinal cord stimulators are an option for those with chronic (>6months), neuropathic pain despite appropriate conventional management and consultation with a pain specialist
It is superior to repeat spinal surgery in patients with lumbar radicular pain and failed back surgery syndrome
Perioperative management of the patient with lumbar radicular pain (in brief)
Patients with lumbar radiculopathy may present for surgery unrelated to their symptoms
A second insult to the nerve with an existing lesion can synergistically worsen or trigger symptoms, and care must be taken to minimise these risks
Pre-operative
Pre-existing pain should prompt a pre-operative neurological examination to establish a baseline state
Patients should be provided written information before surgery regarding the risks of position-related nerve injury
In those undergoing lumbar radicular surgery, pre-operative education can improve post-operative pain cognition and health-related quality of life
Intra-operative
Patients should be positioned to minimise the risk of nerve injury
Pre-existing spinal pathologies are potentially a risk factor for post-neuraxial complications, which may inform anaesthetic technique
Mechanisms include local ischaemia, mechanical trauma from compression and LA toxicity
Post-operative
Patients may be on long-term opioid or non-opioid analgesics, which may need to be incorporated into post-operative analgesic regimens