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  • Defined as spondylolisthesis in an adult caused by a defect in the pars interarticularis (spondylolysis)
    • pars defects usually acquired and caused by microtrauma 
  • Epidemiology
    • incidence
      • spondylolysis is seen in 4-6% of population
      •  increased prevalence in sports that involve repetitive hyperextension (gymnasts, weightlifters, football linemen)
    • location
      • 82% occur at L5/S1
      • 11% occurs  L4/5 (11%)
      • due to forces in the lumbar spine being greatest at these levels and the facet being more coronal
  • Pathophysiology
    • foraminal stenosis
      • adult isthmic spondylolisthesis at L5/S1 often leads to radicular symptoms caused by compression of the exiting L5 nerve root in the L5-S1 foramen
      • compression can be caused by
        • hypertrophic fibrous repair tissue of the pars defect
        • uncinate spur formation of the posterior L5 body
        • bulging of the L5/S1 disc
      • lateral recess stenosis
        • caused by facet arthrosis and hypertrophic ligamentum flavum
      • central stenosis
        • rare due to fact that these slips are usually only Grade I or II
  • Prognosis
    • relatively few patients (5%) with spondylolysis with develop spondylolisthesis
    • slip progression more common in females
    • slip progression usually occurs in adolescence and rare after skeletal maturity
Wiltse-Newman Classification
 Type I  • Dysplastic: a congenital defect in pars  
 Type II-A  • Isthmic - pars fatigue fx
 Type II-B  • Isthmic - pars elongation due to multiple healed stress fx
 Type II-C  • Isthmic - pars acute fx   
 Type III  • Degenerative: facet instability without a pars fx  
 Type IV  • Traumatic: acute posterior arch fx other than pars  
 Type V  • Neoplastic: pathologic destruction of pars  
Myerding Classification
 Grade I  • < 25%
 Grade II  • 25-50%
 Grade III  • 50-75%  
 Grade IV  • 75-100%  
 Grade V  • spondyloptosis  
Physical Exam
  • Symptoms
    • axial back pain
      • most common presentation
      • pain usually has a long history with periodic episodes that vary in intensity and duration
    • leg pain
      • usually a L5 radiculopathy usually caused by foraminal stenosis at the L5-S1 level
    • neurogenic claudication
      • caused by spinal stenosis
      • characterized by buttock and leg pain worse with walking
      • symptoms of neurogenic claudication rare because these slips rarely progress beyond Grade II
    • cauda equina syndrome
      • rare because these slips rarely progress beyond Grade II
  • Physical exam
    • L5 radiculopathy
      • ankle dorsiflexion and EHL weakness
  • Radiographs
    • recommended views
      • obtain AP, lateral, obliques, and flexion-extension views
    • findings
      • AP
        • deformity in coronal plane
      • lateral
        • will see spondylolisthesis and pars defect
      • flexion-extension
        • instability defined as 4 mm of translation or 10° of angulation of motion compared to adjacent motion segment
    • measurements
      • pelvic incidence    
        • pelvic incidence = pelvic tilt + sacral slope
        • a line is drawn from the center of the S1 endplate to the center of the femoral head
        • a second line is drawn perpendicular to a line drawn along the S1 endplate, intersecting the point in the center of the S1 endplate
        • the angle between these two lines is the pelvic incidence (see angle X in figure above)
        • correlates with severity of disease 
        • pelvic incidence has direct correlation with the Meyerding–Newman grade  
      • pelvic tilt    
        • sacral slope =  pelvic incidence - pelvic tilt
        • a line is drawn from the center of the S1 endplate to the center of the femoral head
        • a second vertical line (parallel with side margin of radiograph) line is drawn intersecting the center of the femoral head
        • the angle between these two lines is the pelvic tilt (see angle Z in figure above)
      • sacral slope    
        • pelvic tilt = pelvic incidence - sacral slope
        • a line is drawn parallel to the S1 endplate
        • a second horizontal line (parallel to the inferior margin of the radiograph) is drawn
        • the angle between these two lines is the sacral slope (see angle Y in the figure above)
  • MRI
    • views
      • T2 parasagittal images are best study to evaluate for foraminal stenosis and compression of neural elements
  • Nonoperative
    • oral medications, lifestyle modifications, therapy 
      • indications
        • most patients can be treated nonoperatively
      • techniques
        • activity restriction
        • NSAID
        • role of injections unclear
        • bracing may be beneficial especially in the acute phase
  • Operative
    • L5-S1 decompression and instrumented fusion +/- reduction
      • indications
        • L5-S1 low-grade spondylolisthesis with persistent and incapacitating pain that has failed 6 months of nonoperative management (most common)
        • progressive neurologic deficit
        • slip progression
        • cauda equina syndrome
      • reduction
        • improved sagittal balance with reduction
        • risk of stretch injury to L5 nerve root with reduction 
    • L4-S1 decompression and instrumented fusion +/- reduction 
      • indications
        • L5-S1 high-grade spondylolithesis with persistent and incapacitating pain that has failed 6 months of nonoperative management
    • ALIF
      • indications
        • can be used successfully to treat low-grade isthmic spondylolisthesis even when radicular symptoms are present
        • cannot be used to treat high grade isthmic spondylolisthesis due to translational and angular deformity
      • outcomes
        • studies have shown good to excellent results in 87-94% at 2 years
Surgical Techniques
  • L5/S1 wide decompression and instrumented fusion
    • approach
      • posterior midline 
    • decompression
      • indicated in adult with leg pain below knee
      • usually involves Gill laminectomy and foraminal decompression
        • removal of loose lamina and scared pars defect allows decompression of nerve root
        • a Gill decompression is destabilizing and should be combined with fusion
    • fusion
      • posterolateral fusion is standard
      • interbody fusion (PLIF/TLIF) commonly performed
        • posterior lumbar interbody fusion (PLIF) involves insertion of device medial to facets
        • transforaminal lumbar interbody fusion (TLIF) requires facetectomy and more lateralized and transforaminal approach to the disc space
    • cons
      • interbody fusion has increased operative time with greater blood loss and longer hospitalizations
  • Anterior Lumbar Interbody Fusion (ALIF)
    • approach
      • usually done through trans-retroperitoneal approach 
    • decompression
      • decompression of nerve root done indirectly by foraminal distraction via restoration of disc height
    • fusion
      • grafts used include autologous iliac crest, structural allograft, and cages of various materials
    • pros
      • may increase chance of union by more complete discectomy and endplate preparation
      • allows improved restoration of disc height
    • cons
      • retrograde ejaculation and sexual dysfunction
      • persistent radiculopathy due to inadequate indirect foraminal decompression
      • persistent low back pain may be caused by nociceptive pain fibers in pars defect that are not removed in an anterior procedure alone
  • Psuedoarthrosis
  • Dural Tear

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