Radiculopathy & Herniated Lumbar Disc

Pathophysiology

In asymptomatic patients 20% of those <60 years of age & 36% of those >60 years of age have evidence of a herniated disc on MRI
2 factors required to induce radiculopathy:
- Mechanical compression of nerve root is primary pathogenic factor
- Nerve root needs also to be sensitized by bioactive molecules in order to be mechanically susceptible; mechanical compression alone is not enough
  - Bioactive molecules arise from extruded nucleus pulposus, & include interleukins & other inflammatory factors such as TNF-α

Epidemiology & Natural History

Risk factors:
- Ages of 45 to 64 years
- Sedentary lifestyle
- Frequent driving
- Chronic cough
- Pregnancy
- Smoking
- Frequent lifting of heavy objects
With activity modification & rest alone:
- 80% of patients have major improvements after 6 weeks
- 90% of patients have major improvements after 3 months
- 93% of patients have major improvements after 6 months
Majority of disc herniations diminish in size over time; 80% decreasing by >50%
Stable motor deficits (excluding those with cauda equina syndrome):
- 45% of patients have improvement with non-operative treatment
- 53% have improvement after surgery

Management

Non-operative:
- Indications
  - Absence of a progressive neurologic deficit
  - Absence of cauda equina syndrome
- Medications
  - NSAIDs
  - Corticosteroids
  - Muscle relaxants
  - Opioids
  - Antiepileptics (e.g. gabapentin)
  - Tricyclic antidepressants (e.g. amitriptyline)
- Physiotherapy
  - Important to limit bed rest to a short term only & resume ADLs as soon as possible
  - Active stretching/mobilisation & lumbar stabilisation exercises
  - Bracing with lumbar supports
  - TENS
- Epidural steroid injections
  - Transient decrease in symptoms but generally have no sustained benefits in terms of analgesia, function, or avoidance of surgery
  - Fluoroscopic guided caudal, dorsal laminar or transforaminal approaches
Operative:
- Neurological variables
  - Indicated for progressive neurologic deficit & in cauda equina syndrome, in which urgent decompression provides the best functional improvement
- Anatomic features of herniation
  - Size of disc herniation correlates poorly with pain & eventual need for surgical intervention
  - Massive annular defects have highest rate of reherniation
- Variations in surgical technique
  - Too little removal may lead to increased recurrence
  - Too much removal raises concerns about accelerated disc degeneration & increased back pain
- Patient factors adversely affecting surgical outcome
  - Most useful measure of a given operation’s success is whether patient perceives it to be successful, regardless of what surgeon-determined outcomes may demonstrate
  - Smoking
  - BMI
  - Depression
  - Frequent headaches
  - Low educational level
  - Work & disability status
  - Legal status
  - Compensation status
- Medical comorbidities affecting surgical outcome
  - Presence of >4 significantly & independently lowers improvement at 1 year post-operatively
- Operative compared with non-operative management
  - Patients treated with surgery have a significantly better result at 1 year postoperatively
  - At 4 years postoperatively, surgically treated patients have a trend toward better results
  - No difference is observed at 10 years
  - However, surgically treated patients have far fewer relapses than the non-operatively treated group in the 1^st 4 years
  - Motor weakness improves equally in both groups, as does sensory dysfunction
- Overview
  - Regardless of treatment, lumbar disc herniations usually have a favourable natural history with improvement over time, but it may take 1 to 2 years for functional improvement to plateau
  - In absence of a cauda equina syndrome or progressive weakness, best indication for surgical management is refractory radicular pain