summary Adult Isthmic Spondylolisthesis is a common adult spinal condition characterized by subluxation of one vertebral body anterior to the adjacent inferior vertebral body, caused by a defect in the pars interarticularis. Diagnosis is made with lateral radiographs. Flexion and extension lateral lumbar radiographs can identify the degree of instability. MRI studies can be helpful for central or foraminal stenosis. Treatment is a trial of nonoperative management with NSAIDs and physical therapy. Surgical management is indicated for progressive disabling pain that has failed nonoperative management, and/or progressive neurological deficits. Epidemiology Incidence spondylolysis is seen in 4-6% of population increased prevalence in sports that involve repetitive hyperextension (gymnasts, weightlifters, football linemen) Anatomic 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 Etiology 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 Classification 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 Imaging 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 Treatment 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 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 preferred treatment is surgeon dependent with each technique having similar outcomes Complications Psuedoarthrosis Dural Tear 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