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Introduction
  • A condition characterized by lumbar spondylolithesis without a defect in the pars
    • absent of pars defect differentiates from adult isthmic spondylolithesis
  • Epidemiology
    • prevalence
      • ~5% in men
      • ~9% in woman
    • demographics
      • more common in African Americans, diabetics, and woman over 40 years of age
      • ~8 times more common in woman than men
        • increase in prevalence in women postulated to be due to increased ligamentous laxity related to hormonal changes
    • location
      • degenerative spondylolithesis is 5-fold more common at L4/5 than other levels
        • this is different that isthmic spondylolithesis which is most commonly seen at L5/S1
    • risk factors
      • sacralization of L5 (transitional L5 vertebrae)
      • sagittally oriented facet joints
  • Pathoanatomy
    • forward subluxation (intersegmental instability) of vertebral body is allowed by
      • facet joint degeneration
      • facet joint sagittal orientation
      • intervertebral disc degeneration
      • ligamentous laxity (possibly from hormonal changes)
    • degenerative cascade involves
      • disc degeneration leads to facet capsule degeneration and instability
      • microinstability which leads to further degeneration and eventual macroinstability and anterolithesis
      • instability is worsening with sagittally oriented facets (congenital) that allow forward subluxation
    • neurologic symptoms caused by
      • central and lateral recess stenosis  
        • a degenerative slip at L4/5 will affect the descending L5 nerve root in the lateral recess
          • caused by slippage, hypertrophy of ligamentum flavum, and encroachment into the spinal canal of osteophytes from facet arthrosis
      • foraminal stenosis  
        • a degenerative slip at L4/5 will affect the L4 nerve root as it is compressed in the foramen
        • vertical foraminal stenosis (loss of height of foramen) caused by 
          • loss of disk height
          • osteophytes from posterolateral corner of vertebral body pushing the nerve root up against the inferior surface of the pedicle
        • anteroposterior foraminal stenosis (loss of anterior to posterior area) caused by 
          • degenerative changes of the superior articular facet and posterior vertebral body
Classification
 
Myerding Classification
Grade I < 25%
  
Grade II 25 to 50%
  
Grade III 50 to 75% (Grade III and greater are rare in degenerative spondylolithesis)   
Grade IV 75 to 100%   
Grade V Spondyloptosis (all the way off)   
 
Presentation
  • Symptoms
    • mechanical/ back pain
      • most common presenting symptom
      • usually relieved with rest and sitting
    • neurogenic claudication & leg pain
      • second most common symptoms
      • defined as buttock and leg pain/discomfort caused by upright walking
        • relieved by sitting
        • not relieved by standing in one place (as is vascular claudication)
        • may be unilateral or bilateral
      • same symptoms found with spinal stenosis
    • cauda equina syndrome (very rare)
  • Physical exam
    • L4 nerve root involvement (compressed in foramen with L4/5 DS)
      • weakness to quadriceps
        • best seen with sit to stand exam maneuver
      • weakness to ankle dorsiflexion (cross over with L5)
        • best seen with heel-walk exam maneuver
      • decreased patellar reflex
    • L5 nerve root involvement
      • weakness to ankle dorsiflexion (cross over with L4)
        • best seen with heel-walk exam maneuver
      • weakness to EHL (great toe extension)
      • weakness to gluteus medius (hip abduction)
    • provocative walking test
      • have patient walk prolonged distance until onset of buttock and leg pain
        • have patient stop but remain standing upright
          • if pain resolves this is consistent with vascular claudication
        • have patient sit
          • if pain resolves this is consistent with neurogenic claudication (DS)
    • hamstring tightness
      • commonly found in this patients, and must differentiate this from neurogenic leg pain
Imaging
  • Radiographs
    • recommended views
      • weight bearing lumbar AP, lateral neutral, lateral flexion, lateral extension
    • findings 
      • slip evident on lateral xray 
      • flexion-extension studies
        • instability defined as 4 mm of translation or 10° of angulation of motion compared to adjacent motion segment
  • MRI
    • indications
      • persistent leg pain that has failed nonoperative modalities
      • best study to evaluate impingement of neural elements
    • views
      • T2 weighted sagittal and axial images best to look for compression of neurologic elements  
  • CT
    • useful to identify bony pathology
  • CT myelogram
    • helpful in patients in which a MRI is contraindicated (pacemaker)
Treatment
  • Nonoperative
    • physical therapy and NSAIDS
      • indications
        • most patients can be treated nonoperatively
      • modalities include
        • activity restriction
        • NSAIDS
        • PT
    • epidural steroid injections
      • indications
        • second line of treatment if non-invasive methods fail
  • Operative
    • lumbar wide decompression with instrumented fusion       
      • indications
        • most common is persistent and incapacitating pain that has failed 6 mos. of nonoperative management and epidural steroid injections
        • progressive motor deficit
        • cauda equina syndrome
      • outcomes 
        • ~79% have satisfactory outcomes
        • improved fusion rates shown with pedicle screws
        • improved outcomes with successful arthrodesis 
        • worse outcomes found in smokers 
        • risk of adjacent segment degeneration requiring surgery is greater than 30% at 10 years 
    • posterior lumbar decompression alone 
      • indications
        • usually not indicated due to instability associated with spondylolithesis
        • only indicated in medically frail patients who cannot tolerate the increased surgical time of performing a fusion
      • outcomes
        • ~69% treated with decompression alone are satisfied
        • ~ 31% have progressive instability
    • anterior lumbar interbody fusion (ALIF)
      • indications
        • reserved for revision cases with pseudoarthrosis
      • outcomes
        • injury to superior hypogastric plexus can cause retrograde ejaculation 
Surgical Techniques
  • Posterior decompression and posterolateral fusion (+/- instrumentation) 
    • approach
      • posterior midline approach
      • multiple parasagittal incisions for minimally invasive approaches
    • decompression  
      • usually done with laminectomy, wide decompression, and foraminotomy
    • fusion 
      • posterolateral fusion with instrumentation most common 
      • TLIF/PLIF growing in popularity and may increase fusion rates and decrease risk of postoperative slip progression
    • reduction of listhesis
      • limited role in adults
Complications
  • Pseudoarthrosis (5-30%) 
    • CT scan is more reliable than MRI for identifying failed arthrodesis 
  • Adjacent segment disease (2-3%) 
    • incidence is approximately 2.5% a year
  • Surgical site infection (0.1-2%)
    • treat with irrigation and debridement (usually hardware can be retained) 
  • Dural tear
  • Positioning neuropathy
    • LFCN
      • seen with prone positioning due to iliac bolster 
    • ulnar nerve or brachial plexopathy
      • from prone positioning with inappropriate position 
  • Complication rates increase with 
    • older age
    • increased intraoperative blood loss
    • longer operative time
    • number of levels fused
 

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