Key points

Introduction

The term spondylolisthesis is derived from the Greek words, spondylos, meaning “vertebrae” and olisthesis, meaning “to slip.” High-grade spondylolisthesis (HGS) is defined as greater than 50% slippage of a spinal vertebral body relative to an adjacent vertebral body as per Meyerding classification, and most often affects the alignment of the L5 and S1 vertebral bodies ( Fig. 1 ). Although more than 50% of linear translation in the sagittal plane is used to define HGS, it is the associated rotational component that often plays a greater role in prognosis and overall management. The treatment of high-grade lumbosacral spondylolisthesis differs from that of low-grade slips, and operative management remains challenging and is associated with significant controversies in terms of the optimal surgical technique. This review highlights the pathophysiology, classification, clinical presentation, and management controversies of HGS in light of recent advances in our understanding of the importance of sagittal spinopelvic alignment and technologic advancements.

Measurement of the transitional component of spondylolisthesis per Meyerding grade.

Introduction

The term spondylolisthesis is derived from the Greek words, spondylos, meaning “vertebrae” and olisthesis, meaning “to slip.” High-grade spondylolisthesis (HGS) is defined as greater than 50% slippage of a spinal vertebral body relative to an adjacent vertebral body as per Meyerding classification, and most often affects the alignment of the L5 and S1 vertebral bodies ( Fig. 1 ). Although more than 50% of linear translation in the sagittal plane is used to define HGS, it is the associated rotational component that often plays a greater role in prognosis and overall management. The treatment of high-grade lumbosacral spondylolisthesis differs from that of low-grade slips, and operative management remains challenging and is associated with significant controversies in terms of the optimal surgical technique. This review highlights the pathophysiology, classification, clinical presentation, and management controversies of HGS in light of recent advances in our understanding of the importance of sagittal spinopelvic alignment and technologic advancements.

Measurement of the transitional component of spondylolisthesis per Meyerding grade.

Pathophysiology of development of high-grade spondylolisthesis

The clinical syndrome of spondylolisthesis was first described in 1782 by the Belgian obstetrician Herbiniaux, long before an understanding of its pathophysiology, when he reported a bony prominence anterior to the sacrum that created an impediment to vaginal delivery in a cohort of his patients. Spondylolisthesis shows a strong familial association, with an incidence in first-degree or second-degree relatives of approximately 25% to 30%. A radiographic study by Wynne-Davies and Scott showed that dysplastic spondylolisthesis has a familial incidence of 33%, whereas the isthmic variant has a familial incidence of 15%, with a multifactorial autosomal dominant pattern of inheritance with incomplete penetrance. Although the etiology of the condition is not completely understood, the evidence available thus far suggests that factors beyond developmental susceptibilities may play a significant role in the development of HGS. Activities that involve hyperextension and persistent lordosis such as gymnastics, weightlifting, diving, football, and volleyball increase shear stresses at the neural arch and have been implicated as causative factors in the development of spondylolysis, with subsequent development of spondylolisthesis in a subset of patients. The majority of HGS cases are of the isthmic or dysplastic variety. The presence of a congenitally dysplastic lumbosacral segment with incompetent posterior elements cannot withstand typical forces associated with maintenance of an upright posture; this often leads to development of a slip, which over time can result in an HGS.

Variations in the cross-sectional anatomy of the pars at each level in the lumbar spine likely contribute to the increased incidence of isthmic spondylolisthesis in more caudal segments, especially at the L5/S1 level. The pars is fairly large in diameter in the upper lumbar vertebra and relatively thin at the L5 level. Fredrickson and colleagues prospectively followed 500 elementary students and found a 4.4% incidence of spondylolysis at the age of 6 years, which increased to 6% in adulthood. Of note, the same investigators also evaluated 500 newborns and found no evidence of spondylolysis/spondylolisthesis, suggesting that development of a pars defect with subsequent development of spondylolisthesis is an acquired phenomenon.

Sagittal sacropelvic morphology and orientation modulate the geometry of the lumbar spine and, consequently, the mechanical stresses at the lumbosacral junction. There have been recent attempts to quantify the relation between the lumbosacral spine and the pelvis by means of various geometric parameters in an effort to better understand the development of spondylolisthesis. These parameters include sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI). Multiple studies have demonstrated the importance of harmonious alignment among pelvic and spinal parameters with regard to standardized measures of health-related quality of life (HRQOL). Various sagittal lumbosacral spine and spinopelvic parameters are illustrated in Fig. 2 and are further described in Table 1 .

Sagittal pelvic parameters assessed from the standing lateral radiograph. The pelvic incidence (PI) is always equal to the sum of the sacral slope (SS) and the pelvic tilt (PT). LL, lumbar lordosis.

Labelle and colleagues found that PI, SS, PT, and LL (lumbar lordosis) measurements were significantly higher in subjects with spondylolisthesis than in controls. These investigators further demonstrated that the values increased with the severity of the spondylolisthesis, leading them to conclude that PI (and thus pelvic anatomy) influences the development of spondylolisthesis, and that an increased PI may be a risk factor for the development and progression of developmental spondylolisthesis. Other reports have contributed increasing evidence that in high-grade L5-S1 spondylolisthesis, the sacropelvic morphology is abnormal and that, combined with the presence of a local lumbosacral deformity and dysplasia, it can result in an abnormal sacropelvic orientation and disturbed global sagittal alignment of the spine. These findings have important implications for the evaluation and treatment of patients with HGS and have been the basis of recent spondylolisthesis classifications. These data also provide a compelling rationale to reduce and realign the deformity in order to restore global spinopelvic alignment and improve the biomechanical environment for fusion.

Classification of high-grade spondylolisthesis

The classification systems described by Wiltse and by Marchetti and Bartolozzi have remained the most commonly used classifications for spondylolisthesis over the last few decades ( Figs. 3 and 4 ). Wiltse provided a classification based on etiology. By contrast, the classification system described by Marchetti and Bartolozzi divides spondylolisthesis into two types, developmental and acquired, with the distinction between them being the presence of either a high or low amount of bony dysplasia with developmental spondylolisthesis and lack of such dysplasia with the acquired type. The vast majority of HGS seen in either pediatric or adult patients occurs in patients with developmental spondylolisthesis, particularly with a high amount of dysplasia. In general, progression of an acquired spondylolisthesis to high-grade slip is thought to be relatively uncommon. The greater the degree of dysplasia present in a developmental spondylolisthesis, the greater the amount of secondary bony changes and slippage that occur, which include a rounding off of the sacrum, angulation of the inferior endplate of L5 (trapezoid L5), increased slip angle, and verticalization of the sacrum.

Wiltse’s classification of spondylolisthesis.

Spondylolisthesis classification by Marchetti and Bartolozzi.

Although Marchetti and Bartolozzi were the first to introduce the concept of low-dysplastic and high-dysplastic developmental spondylolisthesis, they did not include strict criteria to differentiate these two subtypes. Another limitation of their classification system is a lack of consideration of spinopelvic alignment, which recently has been shown to differ significantly between high-grade and low-grade HGS, and even within HGS between the high-dysplastic and low-dysplastic cases. Although rare, acquired spondylolisthesis may progress to high grades of slippage. Most are iatrogenic following a destabilizing surgical procedure of the underlying soft tissue including the disc, facet capsules, musculature, and ligaments. This type of HGS is more similar to posttraumatic kyphosis than to the dysplastic developmental types of spondylolisthesis, and reduction of an iatrogenic postsurgical acquired spondylolisthesis seems to have a lower risk of neurologic injury than developmental types of slippage.

Although these classification systems have been popular for several years, there are substantial limitations; perhaps most notably they do not provide useful information on clinical management. Furthermore, these classifications do not take sagittal sacropelvic alignment into account, which has been found to be very important in several recent studies for the evaluation and treatment of spondylolisthesis. Mac-Thiong and colleagues recently proposed a new classification of lumbosacral spondylolisthesis that is specifically intended to guide its evaluation and treatment. This system incorporates sagittal sacropelvic alignment and morphology, and defines 8 types based on the slip grade (low-grade vs high-grade), degree of dysplasia (low-dysplastic vs high-dysplastic), and sagittal sacropelvic alignment ( Table 2 ). The Spine Deformity Study Group (SDSG) confirmed the validity of this classification and provided modifications, further dividing lumbosacral spondylolisthesis into 6 types based on 3 important characteristics that can be easily assessed from preoperative imaging studies. The SDSG-modified version of the classification has been reported to have significantly less interobserver and intraobserver variability in assessment of the grade of slip, the sacropelvic balance, and the global spinopelvic balance ( Table 3 ).

For the SDSG classification system modified from that of Mac-Thiong, first the degree of slip is quantified from the lateral radiograph, to determine if it is low grade (grades 0, 1, and 2, or <50% slip) or high-grade (grades 3, 4, and spondyloptosis, or ≥50% slip). Next, the sagittal alignment is measured by determining sacropelvic and global spinopelvic alignment, using measurements of PI, SS, PT, and the C7 plumb line. In HGS, sacropelvic alignment is assessed based on the SS and PT. Each subject is classified as high SS/low PT (balanced sacropelvis) or low SS/high PT (unbalanced sacropelvis) ( Fig. 5 ). Patients with low-grade spondylolisthesis can be subdivided into 3 types based on their sacropelvic balance : type 1, the nutcracker type, a subgroup with low PI <45°; type 2, a subgroup with normal PI (between 45°, and 60°); and type 3, the shear type, a subgroup with high PI (≥60°) (see Table 3 ). Patients with a high PI have a high shear stress across the lumbosacral junction and a higher likelihood of their spondylolisthesis progressing to a high grade. Patients with a low PI, on the other hand, have low shear stress across the lumbosacral junction and less chance of progression of their spondylolisthesis to a high grade. Finally, global spinopelvic alignment is determined using the C7 plumb line. If this line falls over or behind the femoral heads the spine is aligned, whereas if it lies in front of both femoral heads the spine is malaligned.

Schematic figure demonstrating balanced versus unbalanced spinopelvis.

( Reprinted from Mac-Thiong JM, Labelle H, Parent S, et al. Reliability and development of a new classification of lumbosacral spondylolisthesis. Scoliosis 2008;3:19; with permission from SpringerOpen.)

Clinical presentation

Although HGS can often be asymptomatic, those who do become symptomatic usually present with back pain, leg pain, or a combination of these. Complaints of back pain with activity that are relieved with recumbency are often described. The leg pain, which may also include numbness or paresthesias, described by symptomatic patients is predominately dermatomal in distribution, and often related to the nerve(s) being compressed in the lateral recess at the level of the pars defect. The leg symptoms are described as sclerodermal if they are referred into the broad region of the buttock or posterior thigh, which usually occurs as a result of the disc degeneration that often accompanies the pars defect. In addition, the postural changes associated with HGS in adults can lead to low back pain, tight hamstrings, and postural deformity.

On clinical examination, palpation of the spine may elicit midline tenderness, and a step-off of the spinous processes may be felt above the level of the slip. There will often be limited flexion of the lumbar spine caused by paraspinal spasm as those muscles attempt to prevent shear forces across the affected segment. There can be presence of trunk foreshortening, and hamstring tightness may be noted, with compensatory hyperlordosis above the slip and a waddling gait. Patients may have a classically described Phalen-Dickson sign (ie, a knee-flexed, hip-flexed gait). Neurologically, deficits may include motor weakness and/or sensory deficits depending on the degree of nerve compression in the lateral recess, which typically occurs as a result of the fibrocartilaginous mass or Gill lesion. Cauda equina syndrome is rare because of a relative enlargement of the canal that occurs as the cephalad vertebra slips anterior to the caudal vertebra, leaving the separated posterior elements of the cephalad vertebra in a posterior position. Unlike low-grade slips, whose manifestations are typically limited to painful segmental instability or neural compromise at the affected level, high-grade slips invariably provoke secondary changes in the regional pelvic anatomy, and thus contribute to global sagittal deformity. Historically the cosmetic deformity of HGS has been underappreciated or considered to be of secondary importance to symptoms of pain. The local deformity of the high-grade slip invariably induces compensatory changes in the regional pelvic anatomy, forcing the patient into positive sagittal malalignment. The body’s attempts to restore alignment via tonic activation of the paraspinous (eg, erector spinae) muscles, and progressive retroversion of the pelvis (increased PT) is typically accompanied by clinical sequelae of low back pain (presumably caused by chronic paraspinous muscle activation and/or segmental instability), tight hamstrings, and postural deformity. The presence of this global deformity contributes to the complexity of surgical management of HGS.

Radiology of high-grade spondylolisthesis

Radiographic evaluation should consist of anteroposterior and lateral flexion-extension radiographs. This combination allows the determination of translational instability. However, radiologic evaluation of HGS is no longer limited to assessment of the degree of translational slip alone. Long cassette scoliosis radiographs should also be evaluated to assess for overall sagittal alignment. Computed tomography scans provide excellent bony details of the pathologic status, and magnetic resonance imaging can give much better delineation of the soft-tissue abnormalities. Table 1 summarizes key radiographic parameters used to characterize HGS. In spondylolisthesis, there are 2 primary components involved in the underlying deformity: translational and angular. The diagnosis of HGS is overt even on plain radiographs, obviating any need of oblique radiographs to demonstrate the pars defect seen in spondylosis. Measurement of slip grade as per Meyerding classification clearly confirms the diagnosis of high-grade spondylolisthesis by grading the translational component of the deformity (see Fig. 1 ). By contrast, there are multiple techniques to measure angular deformity. Normally the junction between the fifth lumbar and the first sacral vertebrae is lordotic. However, as the degree of slip progresses to higher grades, this relationship tends to become kyphotic in nature. Studies have suggested a role of lumbosacral kyphosis (LSK) in determining the risk of slip progression, and have also suggested the importance of correcting LSK because this helps to restore global spinal alignment, enhances the biomechanics of fusion, and can protect against stretch of the L5 nerve root. The Boxall slip angle and lumbosacral angle (LSA) provide assessment of the angular component of deformity associated with HGS ( Fig. 6 ). With progression of slippage, the inferior endplate of L5 tends to become dysplastic and the L5 vertebral body may adopt a trapezoidal shape. Moreover, remodeling of the S1 endplate can occur, referred to as sacral doming or rounding. These changes can make the identification of the inferior endplate of L5 and superior endplate of S1 difficult, as can be observed in the radiograph shown in Fig. 6 , favoring evaluation of the LSK based on the LSA rather than the slip angle. Positive and negative values of the sagittal vertical axis reflect cases whereby the C7 plumb line falls anterior or posterior, respectively, to the posterosuperior corner of the S1 vertebral body ( Fig. 7 ).

Schematic diagram and lateral radiograph demonstrating measurement of Dubousset lumbosacral angle ( upper and lower right ) and Boxall slip angle ( upper and lower left ).

Measurement of spinal vertical axis. The sagittal vertical axis is measured as the distance from the posterior superior corner of the sacrum to a vertical plumb line dropped from the C7 centroid (C7 plumb line).

Natural history: to operate or not to operate?

Symptomatic high-grade isthmic spondylolisthesis in children and adolescents has an unfavorable natural history, with a high risk of progression and low likelihood of symptomatic relief. Conservative treatment is generally not recommended in symptomatic patients, who constitute the majority of patients with high-grade slips in this age group. Pizzutillo and colleagues found that only 1 of 11 symptomatic patients treated conservatively had significant pain relief at long-term follow-up. Asymptomatic patients can be treated with observation, and if symptoms do develop surgery is generally recommended. Some investigators have recommended surgical treatment for these patients regardless of symptoms, because of the high risk of progression. However, Harris and Weinstein reported that 10 of 11 patients with high-grade slips who were treated nonoperatively remained active and required only minor modifications in activity.

In contrast to children or adolescents, adults with high-grade slips have often reached a stable position and typically do not experience progression, making slip progression less of a concern. Autofusion or ankylosis of the slipped level can occur. Some of these patients are asymptomatic or minimally symptomatic, and can be successfully treated with physical therapy and selective nerve-root injections if radicular symptoms are present. If conservative treatment fails, surgery is recommended in adult patients who have high-grade slips with back pain and/or radicular symptoms. Unlike low-grade slips, whose manifestations are typically limited to painful segmental instability or neural compromise at the affected level, high-grade slips invariably provoke secondary changes in the regional pelvic anatomy and can thus produce global sagittal deformity with clinical manifestations of intractable back pain or deformity, which might be another indication for surgery.