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 login to view 3 more bullets lateral recess stenosis login to view 1 more bullet central stenosis login to view 1 more bullet 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 login to view 1 more bullet lateral login to view 1 more bullet flexion-extension login to view 1 more bullet measurements pelvic incidence login to view 6 more bullets pelvic tilt login to view 4 more bullets sacral slope login to view 4 more bullets MRI views T2 parasagittal images are best for evaluating foraminal stenosis and compression of neural elements Treatment Nonoperative oral medications, lifestyle modifications, therapy indications login to view 1 more bullet techniques login to view 4 more bullets Operative L5-S1 decompression and instrumented fusion +/- reduction indications login to view 4 more bullets reduction login to view 2 more bullets L4-S1 decompression and instrumented fusion +/- reduction indications login to view 1 more bullet ALIF indications login to view 2 more bullets outcomes login to view 1 more bullet 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 login to view 2 more bullets fusion posterolateral fusion is standard interbody fusion (PLIF/TLIF) commonly performed login to view 2 more bullets 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