Introduction

Spondylolisthesis is the common cause of low back pain in adolescents. ¹ The incidence of scoliosis in patients with spondylolysis or spondylolisthesis has been well reported in the literature, with the percentage ranging from 15% to 48%. ² , ³ Conversely, the incidence of spondylolisthesis in idiopathic scoliosis patients was documented to be 6.2%, ³ which is appreciably higher than that found in the general population, ranging from 4.4% at the age of 6 years to 6% in adulthood. ⁴ Most of the existing investigations focused on the relationship between adult scoliosis and lumbar degenerative spondylolisthesis, whereas only a few studies reported the association of scoliosis with spondylolisthesis in the adolescent population. ² , ³ , ⁵ – ⁷ As highlighted in the literature, the true incidence of the two deformities occurring concomitantly in one patient is difficult to determine, and there is no consensus on the optimal management strategy. ⁶ , ⁸ , ⁹ This chapter discusses how spondylolisthesis associated with scoliosis influences decision making in the treatment of adolescent patients.

Etiology of Scoliosis Associated with Spondylolisthesis

Fisk et al ³ were the first to conduct a study on scoliosis associated with spondylolisthesis in adolescents. They found that 48% of the patients with spondylolisthesis had concomitant scoliosis. Several studies ⁶ , ⁷ , ¹⁰ , ¹¹ focusing on adolescent scoliosis associated with spondylolisthesis were then performed, and scoliosis associated with spondylolisthesis has been divided into three main categories ⁵ :

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  Type I: idiopathic scoliosis in the upper spine (thoracic or thoracolumbar curve), which is not considered to be related to the olisthetic defect ( Fig. 11.1 )

  
  
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  Type II: scoliosis resulting from the olisthetic defect and rotational displacement of the lumbar vertebra in relation to the sacrum ( Fig. 11.2 )

  
  
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  Type III: “sciatic” scoliosis, which is considered secondary to nerve root compression and muscle spasm induced by spondylolisthesis ( Fig. 11.3 )

In type I, idiopathic scoliosis with concomitant spondylolisthesis, patients usually have a typical thoracic or thoracolumbar curve and a positive family history. ³ They usually present initially with scoliosis because of their cosmetic concerns; they are otherwise asymptomatic. ³ , ¹² They typically have a right thoracic curve or a left lumbar curve, with a wellbalanced spine. ⁶ , ¹³ Generally, the spondylolisthesis is an accidental finding on radiography. It is generally believed that the two pathologies are not dependent on each other. ⁶ However, some authors suggest that thoracolumbar or lumbar idiopathic scoliosis can induce spondylolysis because of asymmetrical stress and strain during the growth period. ¹¹ I believe that the lumbar idiopathic curve should be considered as an independent spinal deformity, if it complies with the features mentioned above and if the apical lumbar vertebral rotation is larger than that of the slipped vertebra. Based on these criteria, it would be reasonable to conclude that idiopathic scoliosis and spondylolisthesis occur independently in these patients and neither one affects the occurrence of the other ( Fig. 11.1 ).

In type II, scoliosis resulting from an olisthetic defect, several features distinguish patients from those with an idiopathic scoliosis. The curve associated with an asymmetric olisthetic defect is usually more rotated than an idiopathic scoliosis curve that is of a similar severity. ¹³ Unlike idiopathic scoliosis, in which the apical vertebra rotates the most, the spondylolytic vertebra has the maximal rotation in scoliosis secondary to an olisthetic defect. ¹³ , ¹⁴ A possible mechanism is that the asymmetric olisthesis creates an asymmetric foundation, which may cause the upper spine to rotate into a torsional lumbar scoliosis ( Fig. 11.2 ). The etiopathogenesis was first explained by Tojner. ¹⁴ According to his theory, in a spine with bilateral spondylolysis, the lytic vertebra may slip and rotate on the narrower spondylolisthesis gap. Then the rotation can cause the lateral shift of the olisthetic vertebra and exert traction on the intervertebral disk, especially on the side opposite the axis of rotation, leading to vertebral body sinking on that side. This “sinking” of an olisthetic vertebral body can create an asymmetric foundation of the upper spine, and can further induce the loss of static balance and the development of a compensatory scoliosis. However, there are several controversies about this theory. Schlenzka ¹⁵ questioned whether the rotational slip was the first event leading to the development of a scoliosis above the vertebra, or whether the rotation of the spondylolytic vertebra developed secondarily as in an ordinary idiopathic lumbar curve. In particular, unlike “sciatic” scoliosis, olisthetic scoliosis usually has no coronal shifting ( Fig. 11.2 ). In short, “olisthetic” scoliosis usually presents with an asymmetric olisthetic defect (unstable asymmetric foundation and torsion scoliosis), and the maximum rotation occurs at the olisthetic defect rather than at the curve apex. These patients may complain of leg pain.

Type III, “sciatic” scoliosis, is characterized by coronal decompensation caused by foraminal nerve root compression and muscle spasm in patients with symptomatic spondylolisthesis. Sciatic scoliosis is a functional (nonstructural) secondary deformity and is usually characterized by having little or no vertebral rotation, hamstring tightness, and coronal imbalance (thoracic trunk shift). This is similar to lumbar scoliosis caused by nerve root compression and muscle spasm in other spine diseases (e.g., lumbar disk herniation, osteoid osteoma) ( Fig. 11.3 ). The clinical features of sciatic scoliosis are as follows: (1) low back pain as the presenting complaint; (2) trunk shifting with a small curve angle but a long curve span; and (3) back muscle spasm as an additional presenting complaint.

In my center, 30 cases of adolescent spondylolisthesis were treated surgically between 2002 and 2014. Of these patients, 14 (46.7%) had concomitant scoliosis, of whom eight patients were diagnosed as spondylolisthesis-associated adolescent idiopathic scoliosis (AIS) (type I).