11 Lumbar Disk Disease • Axial back pain extremely common: – Most common cause is muscle strain, followed by degenerative disease of spine. • Natural aging and genetic predisposition lead to lumbar disk degeneration: – Decreased water content and blood supply to annulus of disk: ∘ Results in acidic changes and degeneration of intervertebral disk. ∘ After birth, the nucleus pulposus decreases in size and cellularity in proportion to the intervertebral disk. • Lumbar disk degeneration can result in a mixture of pathologies: – Disk herniation characterized by herniated nucleus pulposus (HNP). – Spondylosis characterized by degeneration of intervertebral disk and osteophyte formation. – Spondylolisthesis characterized by slippage of vertebral body. • Mean age of onset is 35 years: – Over 50% of individuals over 60 years of age exhibit degenerative changes on imaging. • Background and etiology – 90% of herniated disks occur at L4/L5: ∘ Increased risk for herniation from aging and disk degeneration. – Chronic or significant acute stress on annulus of intervertebral disk: ∘ Leads to annular tears and HNP. ∘ Results in direct compression of neural elements. • Characteristics of herniation (see Chapter 11: Cervical Disk Disease). – Protrusion: ∘ Herniation remains within annular margin. – Extrusion: ∘ Herniation tears through annular margin but contained by posterior longitudinal ligament: ▪ Extends into spinal canal. ▪ Can displace cranially or caudally. – Sequestration: ∘ Separation of herniated disk fragment from intervertebral disk. • Symptoms and clinical findings: – Axial back pain: ∘ Controversial etiology. ∘ Recurrent torsional strain may also lead to outer annulus tears. ∘ Worse pain with lumbar flexion in the absence of lumbar spinal stenosis. – Radiculopathy: ∘ Radiating pain in distribution of affected nerve root dermatome: ▪ Can be associated with sensory or motor deficits of compressed nerve root. ▪ Decreased reflexes of involved nerve root. ∘ Herniation impinging of exiting nerve roots: ▪ In neuroforamen (neuroforaminal stenosis): ❖ Far-lateral herniation. ❖ Affects exiting nerve root. ❖ Nerve roots exit below pedicle (L4 exits at L4–L5 disk). ∘ Herniation of traversing nerve roots (Fig 11.1): ▪ In spinal canal (spinal stenosis): ▪ Paracentral/posterolateral herniation. ▪ Affects nerve root traversing to exit at next disk level (L4–L5 paracentral herniation affects L5): ❖ Improvement of leg pain with bending forward due to increased space within spinal canal: ◊ Known as neurogenic claudication due to the intermittent symptomology. ◊ Distinguish from vascular claudication: pain is not relieved by standing still. – Cauda equina and conus syndromes (Table 11.1): ∘ Orthopaedic emergencies. ∘ Herniation compressing multiple lumbar and sacral nerve roots within the thecal sac or the conus medullaris (T12–L1): ▪ Large central herniation. Fig. 11.1 (a) Left paracentral L5–S1 disk herniation affecting traversing S1 nerve root. (b) Extruded disk L5–S1 herniation migrating inferiorly, compressing the S1 nerve root. (c) Sequestered disk herniation migrating superiorly, impinging both L5 and S1 nerve roots. Table 11.1 Conus medullaris versus cauda equina syndromes
11.1 Background
11.2 Lumbar Disk Herniation
| Conus medullaris syndrome | Cauda equina syndrome |
Vertebral level | L1–L2 | L2 sacrum |
Spinal level | Sacral cord segment and roots | Lumbosacral nerve roots |
Presentation | Sudden and bilateral | Gradual and unilateral |
Radicular pain | Less severe | More severe |
Low back pain | More | Less |
Motor strength | Symmetrical, less marked hyperreflexic distal paresis of LL fasciculation | More marked asymmetric areflexic paraplegia, atrophy more common |
Reflexes | Ankle jerks affected | Both knee and ankle jerks affected |
Sensory | Localized numbness to perianal area, symmetrical, and bilateral | Localized numbness at saddle area, asymmetrical, and unilateral |
Sphincter dysfunction | Early urinary and fecal incontinence | Tend to present late |
Impotence | Frequent | Less frequent |
• Imaging:
– X-ray:
∘ Initial evaluation for bony deformities.
∘ Often first line for evaluating general degenerative lumbar pathology:
▪ Assess for disk space narrowing.
▪ Unable to determine disk pathology from plain radiographs.
∘ AP and lateral for examining alignment.
∘ Flexion/extension for examining instability.
– MRI:
∘ Modality of choice for assessing nerve root or spinal cord compression along with disk and ligamentous pathology:
▪ Loss of T2 signal within disk nucleus (Fig. 11.2).
∘ Modic’s changes:
▪ Describes vertebral degeneration seen on MRI:
❖ Associated changes on T1- and T2-weighted MRIs with progressive degeneration (Table 11.2).
– Computed tomography (CT) scan:
∘ Limited use:
▪ If MRI contraindicated.
• Treatment:
– Conservative therapy:
∘ Majority of patients will improve with nonoperative management.
