Spondylolisthesis is a forward slippage (listhesis) of one vertebral body (spondylo) over the next lower vertebral body. There are a variety of causes and classification schemes but most can be described as either degenerative (due to chronic inter-segmental instability involving degenerative disc and facet joints) or isthmic (due to developmental lesions involving the posterior arch of the vertebra).
Degenerative spondylolisthesis usually affect older patients, more frequently involve women and the L4/5 level, and have relatively small slips (<30%) with associated stenosis. In contrast, isthmic spondylolisthesis usually affect patients younger than 50, primarily involves the L5 level, and may have quite severe progression and associated structural abnormalities.
Illustration demonstrating the pathology of both degenerative and isthmic spondylolisthesis
The prevalence of spondylolisthesis ranges from 6-9% of the population depending on the etiology studied and screening tools employed (1-2). Spondylolisthesis has not been reported in in utero, in non-ambulatory patients, or mammals other than humans implicating weight bearing forces unique to the upright bipedal spine. Spondylolisthesis and spondylolysis is seen in 4% of those at 6 years of age, 6% at maturity, and as many as 47% of athletes in high risk sports such as gymnastics (1, 2, 3). Back pain is the most common complaint but neurologic involvement may be seen with associated stenosis or progression and deformity. Those diagnosed prior to skeletal maturity or with slips greater than 50% are most likely to progress (4).
Isthmic spondylolisthesis (grade III) with PI 62 degrees and lumbar lordosis of 40 degrees. The PI-LL mismatch of 22 degrees indicates the presence of a sagittal malaalignment in addition to the slip and associated stenosis contributing to chronic back and leg pain.
Many patients with spondylolisthesis have no symptoms and most likely do not require any significant treatment or intervention. Symptomatic patients are most frequently treated non-operatively with NSAID’s, activity modification, physical therapy, and possibly epidural steroid injections. Bracing may be appropriate in some patients, particularly children with acute lesions (5, 6). Surgical treatment is indicated when patients have significant disabling pain despite 6 months of adequate non-operative care or, less commonly, a progressive lesion and treatment typically involves a posterior lumbar fusion (PLF, TLIF). Instrumentation is thought to improve the fusion rate and clinical outcome (7) and decompression (laminectomy, foraminotomy) is included for associated stenosis with radicular symptoms. Reduction of high grade slips remains controversial but is thought to correct kyphosis and global sagittal balance, decrease the length of fusion, and protect against adjacent segment degeneration (8-9), figure 2 and 3.
Lateral xray following reduction, decompression, and interbody fusion of the spondylolisthesis. Physiologic lumbar lordosis has been restored (65 degrees with PI-LL less than 10) the L5 nerve roots decompressed and slip reduced with resolution of preop back and leg pain.
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7) Zdeblick TA: A prospective, randomized study of lumbar fusion: Preliminary results. Spine 1993;18(8):983-991.
8) Transfeldt EE, et al. Evidenced based medicine analysis of isthmic spondylolisthesis treatment including reduction versus fusion in situ for high grade slips. Spine 2007;32(19 suppl):S126-S129.
9) Hu SS, Bradford DS, Transfeldt EE, Cohen M: Reduction of high grade spondylolisthesis using Edwards instrumentation. Spine 1996;21(3):367-371.