13 Degenerative Spondylolisthesis: Does the Sagittal Balance Matter?
Abstract
This chapter focuses on the importance of considering the sagittal balance in the surgical treatment of lumbar degenerative spondylolisthesis (DS). The chapter includes epidemiology, prevalence, pathophysiology, imaging, and management of DS.
13.1 General Considerations
13.1.1 Definition
Spondylolisthesis is defined as slippage of a vertebra in relation to the vertebra below (Fig. 13‑1). The slippage may be anterior, that is, anterolisthesis; posterior, that is, retrolisthesis; lateral, that is, laterolisthesis; or rotatory, that is, rotatory subluxation. Degenerative spondylolisthesis (DS) is most often associated with arthritic changes in the facet joints at the level of the listhesis. It differs from isthmic spondylolisthesis by the absence of a pars interarticularis defect and was first described as early as 1930 by Junghanns who introduced the term “pseudo-spondylolisthesis.” 1 In 1950, MacNab 2 described spondylolisthesis “with the neural arch intact” as opposed to the spondylolisthesis of children and adolescents by isthmic lysis and, finally, Newman in 1963 3 proposed the term “degenerative spondylolisthesis” considering that DS was quasi-systematically associated with facet arthritis. In the lumbar spine, it usually occurs in patients over 50 years of age, with female predominance and ligament hyperlaxity as a predisposing factor. DS corresponds to type III according to the Wiltse 4 spondylolisthesis classification modified by the Scoliosis Research Society. 5
13.1.2 Epidemiology and Prevalence
The DS is most commonly found at the L4-L5 level (80% to 85% of cases) in opposition to isthmic spondylolisthesis, which occurs most commonly at the L5-S1 level. 6 DS is rarely observed at L5-S1 for anatomical reasons. First, the frontal orientation of S1 facets represents a solid barrier to anteroposterior (AP) slippage and, second, there is an abundance of ligament structures around the L5-S1 complex with the presence of the strong iliolumbar ligaments. Prevalence is variable according to age and sex, augmented by a factor of 4 in the female population and is estimated to be ~ 10% after 60 years old for females (up to 43% referring to population-based studies). 7 , 8 , 9
13.1.3 Imaging Findings
Positive diagnosis of DS is established on standards X-rays in a standing posture. The diagnosis is generally retained when the slippage is greater than 3 mm or when the slippage is measured to more than 10% according to the Meyerding classification. One must pay attention to the fact that around 20% of DS is undetected on magnetic resonance imaging (MRI). 10 Also, MRI typically underestimates the slippage by approximately 50%. Therefore, standing radiographs should be systematically performed for the management of lumbar degenerative disorders in addition to lying imaging modalities (computed tomography [CT] scan and/or MRI) (Fig. 13‑2).
13.2 Pathophysiology
Factors influencing the occurrence and/or progression of DS can be divided into general factors, regional factors (including the sagittal balance), and local factors.
13.2.1 General Factors
Genetic
It is unclear in the literature that genetical factors have been evoked to explain the increased frequency in certain populations and families without knowing precisely the role of posture and habitus. DS is more frequent in elderly Caucasian Americans, around 31% after 74 years old. 11 Prevalence estimates among women range from 8% in Denmark, 8.9% in Japan, 12 12% in Thailand, 13 to ~ 25% in the United States. 14
Obesity
Obesity seems to be a key factor with increasing stress on facet joints and disks. Schuller et al. 15 found a mean body mass index (BMI) in the DS group equal to 28 versus 24 in the control group without DS, and 70% of patients with DS presented with a BMI >25. The continuous high load accelerates posterior disk and zygapophyseal degeneration and may, therefore, favor the development of DS.
Hormonal Factors
DS is constantly reported more frequently in women than men younger than 50 years old. Jacobsen 16 found a prevalence of DS in women of 8.3% versus only 2.7% for men. Otherwise, Enyo et al 6 reported a risk of female slip progression 3.5 times greater than in men because of joint laxity and instability. There is also a high proportion of patients with ligament hyperlaxity; up to 65% of patients according to Postacchini. Cholewicki et al 17 found a risk of developing spondylolisthesis in women who experienced multiparity and hysterectomies.
Sanderson and Fraser 18 found an association between nulliparous and parous women and DS (28% vs. 16%) and the incidence of DS increased in parallel with the number of pregnancies. Many physiological changes during pregnancy, including relaxation of the pelvic and increase of the flexion moment on the lower back, play an essential role in the progression of listhesis.
Hyperlaxity
In the presence of hyperlaxity, Matsunaga et al 19 reported that the prevalence of DS was augmented by a factor of 8.
Age
Age represents one of the main factors in the natural history of DS, with a clear progressive increase in incidence after the age of 50 years old, which is greater in women than in men. 20
13.2.2 Regional Anatomical Factors
Spinopelvic Alignment
We previously reported in 2004 21 , 22 , 23 that patients with DS were associated with a greater pelvic incidence (PI) compared to the normal population. Roussouly’s spinopelvic morphotypes 3 and 4 represented more than 85% of DS patients versus only 60% in the control group. In our study, mean PI was measured at 60° versus only 52° for the control group.
PI and high lumbar lordosis represent important risk factors for the development of DS caused by stresses on the posterior elements and to the inclination of the L5 upper endplate. Since our work, many studies have confirmed the association between high PI and DS patients 21 , 22 , 24 , 25 , 26 with a mean PI of ~ 58°–60° in DS patients.
We assume that a high PI represents a risk factor for three main reasons:
High PI is associated with a high sacral slope (SS) and high inclination of the sacral plate and L5 endplates (inferior and superior L5 endplates). Because of gravity, the higher the slope, the higher the risk of slippage.
High PI is associated with hyperlordosis and stresses on the posterior structures of the lumbar spine, especially on posterior facets, which may favor degenerative changes of L4-L5 facets, making them less resistant to slippage.
Finally, high PI and hyperlordosis influence the geometry of the lumbar spine, reducing the space available for the posterior elements and making them more compact. By limiting the craniocaudal development of posterior arches, hyperlordosis reduces their ability to resist AP shear forces.
Further considerations about spinopelvic alignment and DS will be discussed in Section 3 of this chapter.
Sacralization of L5
Lumbosacral transition vertebra is the most common congenital anomaly of the lumbosacral spine with 8.1% in the general population, 27 but observed at high rates in DS at L4-L5 (up to 70% according to Kong et al. 28 ). Sacralization of L5 leads to a higher concentration of stresses on the L4-L5 segment with the risk of hypermobility.
Degenerative Ankylosis of L5-S1
For the same reasons as above, degenerative evolution of L5-S1 segment will result in hypermobility of the upper adjacent segment with the risk of developing a DS at this level. 7
13.2.3 Local Factors
Local factors are represented by some specific anatomical variations of the involved vertebra at the index level.
Sagittal Orientation of the Facets
The facet joints play an essential role in segment balance and stability. The orientation of the facets may limit the amount of axial rotation and increase torsion resistance. Many authors 29 , 30 , 31 , 32 , 33 assume that the sagittal orientation of the facets at the index level is associated with a reduction of resistance to shear forces in the AP direction and may favor the occurrence of anterolisthesis. Sato et al 30 found that the sagittal orientation of the facet joints led to an increased risk of slippage as a result of greater and inadequately distributed stresses. Liu et al 29 in a literature review found a significant association between sagitalization of facets and the appearance of DS. The transverse facet angle of more than 50° represents a significative factor of listhesis. This angle was found to be around 60° in the DS population versus 40° in the normal population.
Horizontalization of the Posterior Arch
Another anatomical variation that may favor the slippage is represented by a horizontal orientation of the posterior arch of the index vertebra. Once again, horizontalization of the posterior elements (lamina, facets) offers less resistance to AP shear forces with the risk to favor AP translation of the vertebra. 19 , 34
Controversy
There is some controversy regarding the role played by the local anatomy in the development of DS as some authors 35 consider that these anatomical variations result mainly from the degenerative changes. They are mostly the consequence of the DS and not the primary cause.
13.3 Spinopelvic Alignment
Roussouly et al 36 (Fig. 13‑3) described a classification into four morphotypes of back depending on PI and SS. Type 1 is characterized by a SS of less than 35°, low PI, and, consequently, short lumbar lordosis, which predispose to arthritis of posterior elements (facets, spinous processes). Type 2, “flat” back, is characterized by low SS (<35°), low PI, and low lumbar lordosis that is longer and more harmonious and predisposes to premature disk degeneration. The type 3 back is the most common in the general population and is characterized by harmonious curves. The SS is between 35° and 45° and PI is around 50°–52°. Type 4 lordosis is characterized by a high PI with a pronounced SS (>45°) and by a compensation effect of marked sagittal curvatures that may cause spondylolisthesis or lumbar stenosis.
In the DS population, 85% of patients present with a morphotype 3 or 4 and mean PI ~ 60° (Barrey), which is significantly different from the normal population. Also, it has been reported that the lordosis was slightly reduced with a mean lack of lordosis ~ 10°. It was noted that the L1-S1 lordosis was not so reduced but that the lordosis was generally significantly reduced at the L4-S1 segment with compensation in the upper lumbar spine. 15 , 22 The disk degeneration associated with the anterior slippage at the index level results in a local loss of lordosis, which is needed for compensation in the upper lumbar spine (extension of L1-L4 segments). In most cases, the local loss of lordosis because of DS is limited, and the compensation provided by a slight extension of the adjacent spine above works very well.
The global balance is typically preserved even if some amount of pelvic compensation may be noted with increased PT and decreased SS. Most of the variations were regional except in the cases of multilevel DS with severe and global lumbar kyphosis (Fig. 13‑4).
It is also important to analyze the sagittal orientation of the slippage (Fig. 13‑4). This may occur in a neutral direction with the slippage progressing parallel to the superior endplate of L5. The slippage may be in extension, permitting local compensation of the lack of lordosis and thus limiting the consequences of the DS on the sagittal balance. The drawback of DS in extension is the risk of inducing canal stenosis and foraminal stenosis with the development of radicular symptoms. The latter situation is represented by the slippage in flexion, which is the worst situation regarding balance and generally associated with global sagittal imbalance. On the other hand, the slippage in flexion permits opening the canal, increasing the foramen size, and decompressing the neurological structures. In the end, there is no perfect situation; both have consequences on balance on one side and the risk of canal stenosis on the other side. DS represents a degenerative disk disease (DDD) of the spine that exposes the patient to the risk of kyphosis and stenosis.
Finally, we must underline the situation of multilevel DS, which induces an important lack of lordosis in the lumbar spine because of multilevel slippages and multilevel DDD in the lumbar spine (Fig. 13‑5). They represent ~ 5%–8% of DS patients. 19 In this situation, the surgical strategy must restore adequately the lumbar lordosis and sagittal alignment and generally requires extensive instrumentation of the lumbar spine.
Similarly, when DS is associated with multilevel DDD, there is an additive effect of the segmental loss of lordosis, and, in the end, the deficit of lumbar lordosis is great even if not only a result of the DS. In the case of DS associated with multilevel DDD, especially at the level below (L5-S1) and above (L3-L4), the disease presents more as a degenerative lumbar kyphosis than a simple “one-level disease” with DS.
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15 Scheuermann’s Kyphosis
16 Cervical Sagittal Alignment and Cervicarthrosis
14 The Degenerative Aging Spine: A Challenge for Contemporaneous Societies
12 Isthmic Lytic Spondylolisthesis—The Physiopathology, Classification, and Treatment Better Explained by the Sagittal Balance
23 Techniques for Spine Osteotomies and Clinical Applications
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