Spondylolisthesis & Spondylolysis

INTRODUCTION

Definitions

• Spondylolisthesis:
  • Forward displacement of 1 vertebra on another
  • Usually L5-S1 in isthmic & L4-L5 in degenerative spondylolisthesis
• Spondylolysis:
  • Defect in pars interarticularis
  • Present in about 5 to 6% of adult population
• Spondyloptosis:
  • >100% slip

Classification (Wiltse)

• Type I:
  • Dysplastic
  • Congenital anomalies of upper sacral facets or inferior facets of 5^th lumbar vertebra that allow slipping of L5 on S1
  • No pars interarticularis defect is present in this type
• Type II:
  • Isthmic
  • Defect in pars interarticularis that allows forward slipping of L5 on S1 (> L4 on L5)
  • 3 subtypes
    • Lytic (stress fracture)
    • Elongated (but intact)
    • Acute fracture
• Type III:
  • Degenerative
  • Lesion results from intersegmental instability of long duration with subsequent remodelling of articular processes at level of involvement, esp L4/5
• Type IV:
  • Traumatic
  • Results from fractures in area of bony hook other than pars, such as pedicle, lamina, or facet
• Type V:
  • Pathological
  • Results from generalised or localised bone disease & structural weakness of bone such as osteogenesis imperfecta, tumour infiltration
• Type VI:
  • Iatrogenic

ISTHMIC SPONDYLOLISTHESIS

Epidemiology & Natural History

• Hereditary predisposition
• Begins during childhood, however most patients do not seek medical attention until adulthood
• 75% of defects radiographically evident by 6 years of age & 75% of patients with spondylolysis also demonstrate spondylolisthesis
• Onset of symptoms tends to occur after childhood with a mean age at presentation of 20 years
• Slip >10mm correlates positively with symptoms
• Foraminal stenosis occurs in as many as 75% of patients & may be, but is not always, associated with leg pain or radicular symptoms

Clinical Manifestations

• While subjective complaints of leg pain are common, documented neurologic deficit or radiculopathy is seen less frequently (16 to 27% of cases)
• Subjective decrease in light-touch sensation over dorsum of foot & mild weakness of EHL are most common neurologic abnormalities, correlating with L5 root irritation as seen with L5-S1 spondylolisthesis
• Straight leg raising is usually normal
• Loss of bowel & bladder function does not routinely manifest

Imaging

• Plain radiographs:
  • AP & lateral views (preferably standing)
  • Oblique projections to highlight pars & 30° caudal-tilt AP view
  • Classification (Meyerding Severity Scale – based on S1 width)
    • Grade I -               0 to 25%
    • Grade II                -               25 to 50%
    • Grade III               -               50 to 75%
    • Grade IV              -               75 to 100%
    • Grade V                -               >100% (spondyloptosis)
• CT:
  • Bony anatomy
• MRI:
  • Thecal sac compression in high grade deformity

Predictors of Progression

• Young age
• Female
• Dome shaped upper S1 end-plate
• Sacral inclination >30°
• Slip angle >10°
• High grade slip (III+)

Principles of Management

• Non-operative:
  • Simple analgesics & NSAIDs
  • Activity modification
  • Physiotherapy
    • Strengthening exercises
    • Postural retraining& correct lifting techniques
  • Smoking cessation
  • Anti-lordotic bracing
  • 83% good to excellent results at 7 years
• Operative:
  • Indications
    • Persistent or intolerable leg or back pain
    • Progressive deformity 
    • Worsening motor deficit, including foot-drop & bowel or bladder dysfunction (extremely rare)
  • Arthrodesis
    • For patients who have persistent complaints of lower back pain, with or without radiculopathy, & who have not responded satisfactorily to non-operative management, arthrodesis may be indicated
    • Patients with spondylolisthesis tend to fare better than patients who undergo arthrodesis for other reasons (>90% success)
  • Surgical approach
    • Wiltse approach (parasagital between multifidus & longisimus; enables direct line for pedicle screw insertion)
    • Posterolateral fusion with bone graft in lateral gutters & pedicle-screw & rod instrumentation
    • For patients with a slip of <50% & a normal or near-normal adjacent disk, single-level fusion is used
    • If spondylolisthesis is >50%, or if there is significant disc degeneration just above level of slip, extension of fusion to next level is undertaken
    • Full return to strenuous work & recreational activity is usually not possible before 6 months, i.e slow post-op course
  • Decompression
    • Neural foraminal narrowing with associated nerve-root compression & leg pain is common in adults with isthmic spondylolisthesis
    • Gill procedure (excision of the loose posterior arch) + lateral nerve-root release by foraminotomy to adequately decompress affected root
    • Limited decompression, consisting of generous foraminotomy, with resection of interposed fibrocartilaginous material from pars defect while retaining the lamina is an alternative
    • Indication for formal decompression
      • Presence of an objective neurologic deficit, including significant radicular pain or nerve-root dysfunction nerve-root irritation (pain, numbness, or sensory loss without associated motor involvement) or nerve-root compression (radiculopathy &/or motor loss)
      • Patients with leg pain, but without objective deficit, benefit from fusion without decompression
  • Reduction
    • Indications
      • High-grade spondylolisthesis with significant lumbosacral kyphosis (increased slip angle) resulting in an unacceptable deformity &/or a mechanically unfavourable position of L4 relative to sacrum for fusion
    • Mean obtainable slip correction 90%
    • Complications
      • Loss of reduction
      • Failure of fusion (up to 33%)
      • Neurologic deficit, most commonly L5 root injury which is manifested clinically as foot-drop (up to 20%); thorough root decompression, slow reduction of slippage, & intra-operative neurologic monitoring lessen risk of neurologic injury

DEGENERATIVE SPONDYLOLISTHESIS

Epidemiology & Aetiology

• Women more commonly affected than men
• Prevalence increases with age
• Diabetic patients & women who have undergone oophorectomy at greater risk

Pathophysiology

• Most important requisite for degenerative spondylolisthesis is relative immobility of lumbar segment below lesion
• Immobility most commonly due to hemi-sacralisation (Bertolotti’s syndrome) but can also result from advanced disc degeneration at the L5-S1 level
  1. This finding is thought to have etiologic significance because immobility of L5-S1 level shifts mechanical stresses to adjacent L4-5 level
• An iatrogenic cause for immobility is spinal fusion
  1. Forward slip occurs many years after original fusion; surprisingly, many patients are asymptomatic despite the deformity

Differential Diagnosis

• Osteoarthritis of hip
• Sacroiliac pathology
• Degenerative scoliosis:
  • In these patients neurologic complaints may be more diffuse, consistent with multi-level involvement
• Diffuse idiopathic skeletal hyperostosis (DISH):
  • Characterised by multi-level bridging osteophytes
  • Commonly affects middle-aged & older men
  • Diabetes & hyperuricaemia
• Cervical spinal stenosis
• Intrinsic neurologic disorders
• Primary or metastatic disorders
• Peripheral vascular disease:
  • A useful differentiation is that patients with a spinal cause usually are relieved of symptoms only by cessation of walking & sitting down or flexing the spine
  • In contrast, patients with a vascular cause have only to stop walking & symptoms disappear in normal upright standing position

Clinical Signs & Symptoms

• Back pain:
  • Episodic & recurrent for many years
  • Worsens over course of day
  • Radiation into posterolateral thighs
• Mono-radiculopathy is less common type of leg pain:
  • When present, it is result of entrapment of L5 root in lateral recess.
• More common pain presentation is that of neurologic claudication:
  • Pain may be diffuse in lower extremities, involving L5 &/or L4 roots unilaterally or bilaterally
  • Accentuated by walking & relieved by forward flexion of spine
• Additional complaints include cold feet, altered gait, & “drop episodes,” where patient unexpectedly falls while walking
• With extreme stenosis, interference with bladder & bowel control can occur
  • Unlike acute & often devastating bladder & bowel symptoms of cauda equina syndrome in lumbar disc herniation, spinal stenosis often has an insidious & subtle presentation
  • Stenotic symptoms are result of mechanical & vascular factors
  • As slip progresses, facet hypertrophy, buckling/infolding of ligamentum flavum, & diffuse disc bulging contribute with forward displacement to compression of cauda equine
  • Relief of symptoms that follows forward spinal flexion is thought to be related to increase in AP dimensions of spinal canal
  • At extreme, patients may report need to sleep in foetal position to relieve leg symptoms
  • Significant vascular component in complaints of leg pain may lead to another manifestation, restless legs syndrome
    • In this condition, patients are awakened by aching pain in calves, restlessness, an irresistible urge to move legs, & fasciculations
  • Exacerbated by congestive heart failure

• Numbness & weakness, are variably present
• Some patients present with degenerative spondylolisthesis above a spinal fusion
  • A long symptom-free interval is followed by onset of nerve-root symptoms & stenosis emanating from level above their previous fusion

Physical Examination

• ·         Loss of lumbar lordosis
• When stenotic symptoms are severe, a fixed forward-flexed posture, sometimes accompanied by hip-flexion contractures, can be observed
• Except in very thin patients, step deformity usually is not palpable
• Normal spinal mobility or hypermobility
• Commonly, neurologic findings are nonspecific & may include bilaterally absent reflexes, spotty sensory losses, & muscle atrophy without frank weakness
• When bladder symptoms are reported, sensory loss may be present in perineal area, accompanied by a decrease in rectal sphincter tone

Imaging

• Plain radiographs:
  • Disc-space narrowing, vacuum sign, endplate sclerosis, peridiscal osteophytes, & facet sclerosis & hypertrophy +/- hemi-sacralisation of L5
  • Dynamic flexion-extension radiographs
    • Instability in flexion-extension is displacement exceeding 5 mm.
• CT:
  • Use of reverse gantry imaging to exclude any possible pars defect
• MRI:
  • Indications
    • Significant & progressing neurologic claudication or radiculopathies
    • Clinical suspicion that another condition, such as metastatic disease, may be causative
    • Bladder or bowel complaints
  • Findings
    • Constriction of cauda equina associated with a diminished cross-sectional area & diameter
    • Facet degeneration & hypertrophy with subarticular entrapment of L5 nerve roots
    • Apparent thickening & buckling of ligamentum flavum, & diffuse disk bulging

Management

• Non-operative:
  • NSAIDs
  • Physiotherapy
  • Weight reduction
  • Management of osteoporosis
  • Epidural blocks
• Operative:
  • 10 to 15% of patients are surgical candidates
  • Indications
    • Cauda equina dysfunction, accompanied by evidence of a complete block at affected level
    • Progressive muscular weakness of functional significance, such as a dropped foot or quadriceps dysfunction
    • Progressive & incapacitating radicular pain or claudication, particularly when it causes sleep disturbance
    • Failure of non-operative management
  • Procedure
    • Decompressive laminectomy
    • Disc should not be excised unless it is frankly ruptured (excising disc increases risk of later instability)
    • Following decompression, patency of dural sac is established by presence of dural pulsations & absence of nerve-root tension

• Fusion
  • Indicated when adequate decompression requires sacrifice of >50% of facets or when pars has been breached
  • May be necessary to extend fusion to L5-S1 level in patients, unless that level is stabilised by bone abnormalities or marked disc degeneration
• Results
  • 70 to 85% success rate for treatment of radiculopathy or claudication
  • Relief of low back pain is less predictable
  • Predictors of failure are increased age, associated comorbidities (e.g. cardiac disease), & a longer duration of surveillance