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 identification of central or foraminal stenosis Nonoperative treatment includes a trial of 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 the population increased prevalence in sports that involve repetitive hyperextension (gymnasts, weightlifters, and football linemen) Anatomic location 82% occur at L5-S1 11% occur at L4-5 due to the forces in the lumbar spine being greatest at these levels and the facets being more sagittally oriented 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 because slips are usually only grade I or II Classification Wiltse-Newman Classification Type I Dysplastic (a congenital defect in the pars) Type II-A Isthmic (pars fatigue fracture) Type II-B Isthmic (pars elongation due to multiple healed stress fractures) Type II-C Isthmic (acute pars fracture) Type III Degenerative (facet instability without a pars fracture) Type IV Traumatic (acute posterior arch fracture, other than the pars) Type V Neoplastic (pathologic destruction of pars) Meyerding 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 usually a long history with periodic episodes that vary in intensity and duration leg pain usually L5 radiculopathy 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 are 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 AP, lateral, oblique, and flexion-extension views findings AP deformity in the coronal plane lateral spondylolisthesis and pars defect flexion-extension instability defined as 4 mm of translation or 10° of angulation of motion compared to the adjacent 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 (angle X in figure above) correlates with severity of disease pelvic incidence has a 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 to the side margin of the radiograph) is drawn intersecting the center of the femoral head the angle between these two lines is the pelvic tilt (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 (angle Y in the figure above) MRI views T2 parasagittal images are best for evaluating foraminal stenosis and compression of neural elements Treatment Nonoperative oral medications, lifestyle modifications, therapy indications most patients techniques activity restriction NSAIDs role of injections is 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 can be achieved with reduction risk of stretch injury to the L5 nerve root with reduction L4-S1 decompression and instrumented fusion +/- reduction indications L5-S1 high-grade spondylolisthesis with persistent and incapacitating pain that has failed 6 months of nonoperative management ALIF indications 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 adults with leg pain below the knee usually involves Gill laminectomy and foraminal decompression removal of loose lamina and scarred pars defect allows decompression of the 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 the facets transforaminal lumbar interbody fusion (TLIF) requires facetectomy and a more lateralized 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 performed through a trans-retroperitoneal approach decompression indirect decompression of the nerve root through foraminal distraction via restoration of disc height fusion grafts used include autologous iliac crest, structural allograft, and cages of various materials pros may increase the chance of union through 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 the pars defect that are not removed with an anterior procedure alone preferred treatment is surgeon-dependent, with each technique having similar outcomes Complications Pseudoarthrosis Dural tear Prognosis Relatively few patients (5%) with spondylolysis will develop spondylolisthesis Slip progression is more common in females Slip progression usually occurs during adolescence and is rare after skeletal maturity Slip angle is the most predictive factor of slip progression and overall outcomes