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Surgical Outcomes Research

Anterior Single-Rod Instrumentation of the Thoracic and Lumbar Spine: Saving Levels

Lowe, Thomas G. MD*; Betz, Randal MD*; Lenke, Lawrence MD†; Clements, David MD‡; Harms, Jürgen§; Newton, Peter MD¶; Haher, Thomas MD∥; Merola, Andrew MD§; Wenger, Dennis MD¶

Study Design. To evaluate the ability of single-rod anterior instrumentation to save or preserve fusion levels and improve thoracic hypokyphosis in patients with adolescent idiopathic thoracic, thoracolumbar, or lumbar scoliosis.

Objective. To provide indications for single anterior rod instrumentation for the treatment of adolescent idiopathic scoliosis and demonstrate effectiveness in properly selected cases.

Summary of Background Data. Posterior multisegmented dual rod instrumentation is the most commonly used instrumentation for the surgical treatment of adolescent idiopathic scoliosis. The issue of longer fusion levels and inability to correct hypokyphosis with posterior instrumentation continues to be debated in the literature. Anterior instrumentation has the ability in certain curve patterns to preserve distal and proximal levels as well as correct thoracic hypokyphosis.

Methods. A brief discussion of the Lenke adolescent idiopathic scoliosis classification system is presented. Surgical treatment options for each of the curve types are discussed in detail.

Results. Single-rod anterior instrumentation for adolescent idiopathic scoliosis will predictably save levels in Type I curves without hyperkyphosis as well as Type 5 curves; however, it is usually contraindicated in Type 2, Type 4, and Type 6 curves. Single-rod anterior instrumentation can occasionally be utilized in Type 3 curves if the magnitude of the lumbar curve is significantly less than the thoracic curve and the flexibility of the lumbar curve approaches 25° on the side-bending radiograph.

Conclusions. Single-rod anterior instrumentation will often saved one to three distal fusion levels when treating isolated major thoracic, thoracolumbar, or lumbar curves. Fusion levels should include upper to lower Cobb levels. Additionally, anterior single-rod instrumentation because its kyphogenic nature will predictably correct hypokyphosis of the thoracic spine.

The major surgical goals in the treatment of adolescent idiopathic scoliosis (AIS) include obtaining maximum safe correction of the components of the deformity and providing for coronal and sagittal balance with inclusion of as few motion segments as is necessary. Since its inception in the mid 1980s, posterior multisegmented dual-rod systems have remained the most commonly used instrumentation for the surgical correction of AIS.

Excellent results have been published with regards to clinical outcomes, percentage and maintenance of coronal plane correction, and, in most instances, the sagittal plane as well. 1–3 Correction of hypokyphosis of the thoracic spine and correction of the rotational component of the deformity have not been affected significantly with posterior instrumentation. 4,5 The early problems of imbalance and worsening of 1C curves (King II curves) related to rod rotation and attempts at maximum correction of the thoracic curve have largely been overcome by current surgical principles. 2,6,7

The issue of longer fusion levels with posterior instrumentation compared to anterior instrumentation levels continues to be debated in the literature and at international meetings. 3,6,8 Anterior instrumentation has the ability in certain curve patterns to preserve both proximal and distal levels that would normally be instrumented when posterior instrumentation was selected. 9–13

A recent paper by Ginsburg et al has advocated fusing as few lumbar segments as possible because of the increasing incidence of low back pain in patients with fusion extending into the lumbar spine. 14 This study with a mean follow-up of 28 years found that by the fifth decade, back pain resulting from fusions to L1–L3 approached pain similar to fusions extending to L4 or L5.

Dwyer and Schaeffer were the first to report on the use of flexible anterior instrumentation for thoracolumbar and lumbar curves in 1974, followed by Zielke and several others in the mid 1980s. Each of these authors had noted the ability to save distal levels with this technique. Both Dwyer and Zielke reported on the use of anterior instrumentation for thoracic curves although their experience was very limited.

Harms in 1988 modified the flexible rod-screw system of Zielke making it stronger and somewhat stiffer and began to define the indications and fusion levels for selective anterior instrumentation of thoracic curves. He noted that by disc removal and compressing the convexity of the curve that hypokyphosis could be nicely corrected, better derotation of the deformity could be achieved and that the instrumentation only needed to include the upper and lower Cobb levels.

In 1991, the Harms Anterior Spine Study Group was formed to retrospectively and prospectively compare patients undergoing anterior fusion with Harms anterior instrumentation in patients undergoing the more traditional posterior dual rod systems for adolescent idiopathic thoracic scoliosis. From the 2-year data generated by the flexible threaded rod cases compared with posterior dual rod multisegmented hook-screw instrumentation, there was noted to be equal instrumented curve correction (58%) in each group but better correction of hypokyphosis and 2.5 distal levels saved in the anterior group. 9 Also, 97% of the patients in the anterior group had selective thoracic fusions, whereas in the posterior group, 82% included a significant portion of the lumbar curve. Lenke et al further noted that when selective anterior thoracic instrumentation was compared to posterior thoracic instrumentation for 1C curves (King II), better spontaneous lumbar curve correction occurred following anterior instrumentation even though posterior instrumentation generally extended one or two levels lower distally. 10 However, a number of instrumented related complications occurred. Forty percent of the patients in the anterior group developed hyperkyphosis >40° when the preoperative kyphosis (T2–T12) was between 20° and 40°. There was also a rod breakage rate of 31% in the anterior group as opposed to 1% in the posterior group, although only 5% were felt to have pseudoarthroses. Twenty-three percent of the anterior group lost ≥10° correction.

In an attempt to decrease the high rate of hyperkyphosis and rod breakage with the flexible rod, in 1997, the Harms Study Group began using a solid 4.0 and 5.0 mm Moss-Miami rod along with structural interbody support (Harms cages) at instrumented levels below T9. Although long-term follow-up data are not yet available, it appears that rod breakage is at a rate of about 2%.

The purpose of this paper is to discuss specific adolescent idiopathic curve patterns where selective anterior instrumentation and fusion can often save fusion levels. Specific curve patterns discussed in this chapter will be classified based on the “Lenke Treatment Based Classification System for Adolescent Idiopathic Scoliosis.”15,16

It should be noted that anterior instrumentation is not indicated for curve patterns in which there is hyperkyphosis of the thoracic spine >40° or where more than one structural curve requires treatment or for any curve greater than 80°. 9,15

 

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Spine: 15 October 2003 – Volume 28 – Issue 20S – pp S208-S216