Thoracic Discectomy: Posterior Transpedicular Tubular Approach

26 Thoracic Discectomy: Posterior Transpedicular Tubular Approach

Christopher D. Witiw, Brian T. David, and Richard G. Fessler

Summary

The posterior transpedicular tubular approach is one among the several options available for treatment of a symptomatic thoracic disc herniation. It serves as an effective minimally invasive corridor of access through a trajectory that is very familiar to spinal surgeons. It may be performed using a microscope or an endoscope for visualization. This chapter describes the procedure in a detailed step-by-step manner.

Keywords: thoracic disc herniation posterior minimally invasive transpedicular

26.1 Introduction

The surgical management of thoracic disc herniations presents a substantial clinical challenge. Owing to the lesser incidence of thoracic disc herniations compared with those of the cervical or lumbar spine, surgeons typically have less familiarity with this pathology. Moreover, surgery is technically challenging because of the anatomical constraints imposed by the narrow thoracic spinal canal, the need to avoid spinal cord manipulation, and the frequently calcified nature of the disc herniations.

Multiple corridors of access have been described. These include anterior thoracotomy or thoracoscopy-based approaches, lateral retropleural approaches, or any of a contingent of posterior-lateral approaches. Of these posterior-lateral approaches, two in particular are highly amenable to minimally invasive tubular retractor-based access. One is the microendoscopic thoracic discectomy starting lateral to the facet joint,1 which will be described in Chapter 29. This chapter will focus on the posterior transpedicular approach to the thoracic disc.

The transpedicular approach was initially described by Patterson and Arbit in 1978.² This involves accessing the posterior-lateral aspect of the spinal dura via hemilaminotomies and a medial facetectomy (Fig. 26.1a) followed by a partial resection of the pedicle, thereby providing the surgeon exposure to the disc space and allowing decompression of the disc fragment without undue spinal cord manipulation (Fig. 26.1b). Traditionally, the exposure was provided via a midline incision and lateral retraction of the paraspinal muscles. However, with the advancement of minimally invasive techniques, the exposure has been adapted to incorporate tubular muscle dilation and visualization with either a microscope or endoscope.³^,⁴ This chapter will serve to provide an overview of the indications, surgical considerations, and techniques for those planning to perform a minimally invasive, tubular retractor based transpedicular approach to a herniated thoracic disc.

Fig. 26.1 (a) Posterior view of the thoracic spinal column. Dashed lines represent the posterior bone decompression performed via hemilaminotomy and medial facetectomy. (b) Partial resection of the pedicle permits access to the herniated disc. (Adapted from Bilsky et al. Neurosurg Focus. 2000 Oct 15;9(4):e3.)

26.2 Indications

The primary indication for a posterior transpedicular thoracic discectomy is a symptomatic midline or paramedian thoracic disc herniation.

26.3 Contraindications

Most thoracic disc herniations are accessible with a unilateral posterior tubular approach. However, certain broad-based herniations resulting in bilateral compression of the spinal cord may necessitate a bilateral transpedicular approach with instrumented fusion. Additionally, in rare cases of an intradural thoracic disc herniation an anterior or lateral extracavitary approach might be considered to ensure the appropriate trajectory to retrieve the disc fragment.

26.4 Preoperative Planning

A detailed clinical history and physical examination are critical prior to any plan for surgical intervention. Patients with a symptomatic thoracic disc herniation will present with complaints consistent with a radiculopathy localizable to a thoracic level, a myelopathy involving the lower extremities, or a combination of both. In cases without strong clinical–radiographic correlation, an alternative source of the neurological dysfunction should be ruled out prior to proceeding to surgical intervention at the thoracic level.

As part of a comprehensive presurgical workup, all patients should have magnetic resonance (MR) and computed tomography (CT) imaging of the thoracic spine. The MR imaging serves to assess the degree and direction of spinal cord deformation from the disc herniation, while the CT images serve to identify any evidence of calcification within the herniated fragment.

These images should include either the sacrum or the second cervical vertebrae to ensure accurate localization of the level of the pathology. All patients must also have a preoperative chest radiograph to account for the possibility of an additional rib, as well as lumbosacral radiographs to assess for the presence of a lumbosacral transitional vertebra. Taking these steps prior to surgery will serve to mitigate the risk of operating at an incorrect thoracic level.

26.5 Patient Positioning

The patient should be positioned prone on a Jackson table. This permits unencumbered access for C-arm fluoroscopy both in the anteroposterior (AP) and lateral orientations. The choice of frame may be based on the surgeon’s preference. The patient can be positioned on either an open Jackson frame with chest and hip bolsters or on a traditional Wilson frame. An open Jackson frame ensures maximal decompression of the abdomen, which may reduce epidural venous plexus bleeding during the surgery and also ensures full AP radiographic visualization of all thoracic levels. A Wilson frame matches the natural kyphotic contour of the thoracic spine and may provide a more anatomic configuration of the thoracic levels. However, one should be aware of the position of any radiopaque components of the Wilson frame as these may obstruct AP fluoroscopic images intraoperatively.

Once the patient is positioned, the accurate localization of the level of pathology is of paramount importance; this is particularly true in the thoracic spine, where the risk of wrong-level surgery is particularly high. Fluoroscopic localization with multiple cues from AP and lateral images should be utilized. An upward count from the sacrum is preferred because intraoperatively it is easier to count in a cranial direction from the sacrum or from the lowest rib because the pectoral girdle can obstruct fluoroscopy of the lower cervical and upper thoracic spine.

There are multiple options available to the spine surgeon faced with the management of a symptomatic thoracic disc herniation. The posterior transpedicular tubular approach described in this chapter provides an effective minimally invasive access corridor to the pathology. This procedure can be performed using either microscopic or endoscopic visualization. In the editor’s experience, the use of intraoperative CT guidance can be helpful for localization and for final intraoperative confirmation of successful decompression.

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