Thoracic Discectomy

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Chapter 77 Thoracic Discectomy

It has been estimated that up to 20% of the population has a thoracic disc herniation, as evidenced by MRI.1,2 However, the need for discectomy is relatively rare. Surgery for removal of thoracic disc herniations is thought to constitute less than 4% of all disc operations.3,4 Historically, these operations have been associated with suboptimal outcomes for various reasons, in part because of diagnostic delays. These delays are a result of the rarity of symptomatic thoracic discs and the lack of a characteristic presentation pattern. It is hoped that a growing awareness of this disorder will lead to better outcomes as a result of earlier treatment. Additionally, there is uncertainty about the natural history of this disease. There is no consensus regarding the indications for disc removal. Most surgeons generally avoid prophylactic surgery for disc herniation; however, this practice has not been based on prospective studies. Generally, surgery is reserved for patients with severe, intractable radicular pain or for those with myelopathy, especially when it is progressive or severe. Finally, there are numerous operations for the removal of these lesions. Regrettably, no universally accepted selection criteria exist to help determine the best operation for each individual situation. Recently, surgical selection guidelines were proposed based on a large series of ventrolateral and lateral operations, the well-documented success of groups using the transpedicular approach, and preliminary experience with newer procedures, including transthoracic thoracoscopy, retropleural thoracotomy, and transfacet pedicle-sparing approaches (Table 77-1).59

TABLE 77-1 Surgical Approaches for Herniated Thoracic Discs

Surgical Approach General Indications
Ventral
   Transsternal Upper thoracic spine
Densely calcified centrolateral
Ventrolateral
   Transthoracic/ thoracoscopic Densely calcified centrolateral
Selected mildly calcified centrolateral
   Retropleural Selected high-medical-risk static severe myelopathy
Lateral
   A. Extracavitary  
   B. Costotransversectomy A and B, selected densely calcified centrolateral
Mildly calcified centrolateral
   C. Parascapular C, upper thoracic spine calcified centrolateral
Dorsolateral
   Transfacet pedicle-sparing/transpedicular All soft herniated discs
Calcified lateral
Mildly calcified centrolateral
All high-medical-risk except densely calcified centrolateral

Until the 1950s, laminectomy, with or without disc removal, was the treatment of choice for the surgical management of this disorder. Logue’s historical review in 1952 revealed the poor results achieved using laminectomy.10 Consequently, other methods of performing discectomy were developed. These operations were intended to improve the exposure to the ventral spinal canal throughout the thoracic spine. Although these approaches were successful at improving access to the disc space, they were technically formidable and associated with considerable morbidity. Each of these approaches has a unique set of potential complications; it is important to be aware of them so that they can be avoided. This chapter emphasizes these other methods and focuses on the advantages and disadvantages of each procedure. Fourteen contemporary thoracic disc series are summarized, with special attention given to the reported complications. In closing, a new management paradigm for the treatment of symptomatic thoracic discs is presented.

Surgical Approaches for Thoracic Discectomy

Dorsal Approaches

Laminectomy

The initial approach used for thoracic disc herniation was laminectomy, either with or without disc removal. In 1952, Logue10 reviewed the thoracic discectomy literature and found that the results were poor. A significant percentage of patients were left paraplegic. Although the precise reasons for these results were not known, it was postulated that laminectomy alone did not significantly reduce the ventral forces created by a thoracic disc herniation acting on the spinal cord.4 Additionally, when discectomy was performed, spinal cord manipulation was generally poorly tolerated. The limited space available for the spinal cord, as well as the comparatively tenuous blood supply, was thought to increase the susceptibility of the thoracic spinal cord to injury during disc removal (Fig. 77-1).

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FIGURE 77-1 Laminectomy approach. The lamina and spinous process are removed, often extending above and below the level of disc herniation. This approach has been associated with suboptimal outcomes. It may be used for the management of thoracic spondylosis.

(From Stillerman CB, Weiss MH: Principles of surgical approaches to the thoracic spine. In Tarlov EC, editor: Neurosurgical topics: neurosurgical treatment of disorders of the thoracic spine, Park Ridge, IL, 1991, AANS, pp 1–19.)

Dorsolateral Approaches

Transpedicular Approach

Patterson and Arbit13 first reported the transpedicular approach in 1978. It was initially performed on three patients with thoracic disc herniations. Two of the patients had complete resolution of their symptoms, and the third markedly improved. Subsequently, several other series have also reported excellent results (Fig. 77-2).

Disadvantages

Critics of this procedure point out the limited ability to visualize across the spinal canal, making decompression of the central and contralateral portions of the disc a relatively blind procedure. Sometimes, difficulty is encountered in managing calcified and intradural disc fragments. We8,13,16 believe that safety is enhanced by using specially designed thoracic microdiscectomy instrumentation (Fig. 77-3) and endoscopic techniques.4,8,16 Although some report being able to remove intradural fragments and central, densely calcified discs using the dorsolateral techniques,5,13,16,19,22 we4 have not had success with these entities. Dense calcifications involving the dorsal margin of the disc space tend to adhere strongly to the ventral dura mater.4,17 The possibility of significant dural adherence may lead one to use one of the ventrolateral or lateral procedures in those situations.4,17

image

FIGURE 77-3 A selection of the Manny-Mark Stillerman thoracic microdiscectomy instruments. These were developed to facilitate disc removal during a dorsolateral approach without damaging the medially situated spinal cord.

(From Stillerman CB, Chen TC, Day JD, et al: The transfacet pedicle-sparing approach for thoracic disc removal: cadaveric morphometric analysis and preliminary clinical experience. J Neurosurg 83:971–976, 1995.)

The final disadvantage of this procedure relates to the removal of the facet-pedicle complex, without the ability to place an interbody graft. It has been reported that patients operated on using the transpedicular approach have somewhat disappointing results from the standpoint of localized back pain.8,13,16,19,23 The desire to improve these results led to the development of the transfacet pedicle-sparing approach.4,8,18 It was postulated that the avoidance of pedicle removal should minimize postoperative back pain. The preliminary experience has suggested that this, in fact, may be the case.

Recent Experience

Bilsky reviewed 20 cases performed between 1982 and 1992 at New York Hospital in which the transpedicular approach was used for thoracic discs (lateral or centrolateral calcified or soft discs). No postoperative instrumentation was used for stabilization; however, no patient suffered from postoperative spinal instability-related pain or delayed kyphosis.15 Levi et al. have published a contemporary series of 35 patients operated upon via a unilateral transpedicular approach. Good results were obtained in 15 patients, fair results in 11 patients, and no improvement in 8 patients, and 1 patient was paraplegic after surgery. They also did not find evidence of clinical or radiographic instability.24 Chi et al. describe a mini-open transpedicular thoracic discectomy in which tubular retractors and microscope visualization are used in performing a transpedicular thoracic discectomy. Eleven patients were operated on using the mini-open disectomy approach versus four patients operated on using an open dorsolateral approach. Patients operated on using the mini-open approach had less blood loss and a greater improvement in their modified Prolo score compared with the open procedure. At long-term follow-up, the modified Prolo score was similar for both groups of patients.25 Jho published a series of endoscopic transpedicular thoracic discectomies in 25 patients. A 1.5-cm trocar is placed at the junction of the lamina and facet via a paramedian incision. The medial portion of the facet, the very lateral portion of the lamina, and the rostral one third of the pedicle are removed using a high-speed drill. A limited amount of spinal cord dura and nerve root are exposed, and then a 70-degree lens endoscope is introduced, allowing for a discectomy to be performed under direct visualization. This surgery was able to be performed on an outpatient or overnight stay basis; no surgery-related complications were reported.26

Transfacet Pedicle-Sparing Approach

The transfacet pedicle-sparing approach was developed as a simpler alternative to the formidable ventrolateral and lateral operations for the treatment of thoracic disc disease.4,8 Initially, morphometric studies were carried out and improved the authors’ orientation to the disc space and ventral spinal canal, thereby aiding discectomy. Cadaveric studies demonstrated that a keyhole facetectomy alone, without associated pedicle or lamina removal, did not sacrifice the exposure achieved with the transpedicular approach.4,8 Although the safety and overall effectiveness of the transpedicular approach have been well documented,13,16 it was hoped that avoidance of pedicle removal and limiting the amount of facet resected would improve localized back pain results.8

Technique

The operation is performed with the patient in the prone position on a radiolucent frame and spinal table. The arms are placed at the sides, and the patient is taped to the table. Anteroposterior (AP) fluoroscopic imaging is used to identify the appropriate disc space. A 4-cm linear skin incision is centered over the disc space. The paraspinal muscles are subperiosteally reflected laterally, exposing the ipsilateral spinous process, lamina, facet joint, and transverse processes above and below the disc space. A small, self-retaining retractor is placed, and the fluoroscope is introduced to verify the correct level and the precise location of the underlying disc relative to the facet joint. Once this relationship is ascertained, a high-speed drill is used to facilitate a partial facetectomy (Fig. 77-4A). Care is taken to preserve the lateral margin of the inferior and superior articular processes of the facet joint and the entire pedicle directly caudal to the disc. When the partial facetectomy is completed, the underlying neuroforaminal fat is coagulated with bipolar cautery. The nerve root, which exits the spinal canal under the more rostral pedicle, is rarely encountered, except in the upper thoracic spine (Fig. 77-4B). The underlying anulus is coagulated and incised. The disc herniation is removed using conventional microdiscectomy techniques (Fig. 77-4C). As with the transpedicular approach, no fusion is required.8

Disadvantages

The disadvantages are the same as for the transpedicular approach.13,16 Specially designed thoracic microdiscectomy instrumentation8 and, on occasion, open endoscopic visualization of the disc and ventral dural mater have been helpful in enhancing safety during the disc removal.8,16

Minimally Invasive Approaches

A number of minimally invasive microendoscopic discectomy techniques have been advocated, all using a dorsolateral approach and an endoscope for visualization. Although the series are not large, they have all demonstrated adequate access and visualization with removal of the thoracic discs with decreased morbidity compared with open approaches.22

Technique

The basic underlying instrumentation used in all approaches involves a dorsolateral approach, endoscope, and tubular dilators. The patient is usually placed in a prone position; however, Jho has placed the patient in a lateral position for an endoscopic transpedicular thoracic discectomy.26 The approach used by Fessler et al. involves a prone position on a radiolucent Wilson frame.28 A localizing radiograph is obtained to determine the level of the thoracic disc. A paramedian skin incision is made at the level of the disc, approximately 3 to 4 cm lateral to the midline. A series of tubular muscle dilators are then placed, and the tubular retractor is placed to form a working port for the endoscope. The endoscope is passed down the center of the tubular retractor. Under endoscopic visualization, the muscle and soft tissue is cleaned off at the level of the transverse process and lateral aspect of the facet. A drill then excises the junction of the transverse process and lateral facet, allowing access to the disc. The pedicle is identified, and drilling of the superior aspect of the caudal pedicle is performed to allow access to the thoracic disc. The disc anulus is identified and cut, and the endoscope is tilted for a 30-degree visualization similar to a transforaminal-type approach. The disc is removed, and a down-going curet or a Woodson elevator is used to push down the disc fragment away from the spinal cord. After the discectomy is performed, the tubular retractor is removed and the wound closed.

Recent Experience

Two main series using this approach have been published.22,26 Perez-Cruet et al. have a series of seven patients operated on using a minimally invasive thoracic microendoscopic discectomy (TMED).22 Results demonstrated no morbidity with this approach, good access, and quick return to work. No case required conversion to an open procedure. Jho reported a series of endoscopic transpedicular approaches also with excellent results. His series is based on a more extensive pedicle takedown, coming in more medially than Perez-Cruet. Results were also excellent for visualization, disc removal, and quick return to work.26

Lateral Approaches

Lateral Extracavitary Approach

LECA was developed and refined by Larson.29 It was first performed for the management of Pott disease. It provides the best exposure to the ventral spinal canal of all lateral operations. Large thoracic discectomy series have documented its safety and efficacy17,30 (Fig. 77-5).

image

FIGURE 77-5 Lateral extracavitary approach. A hockey-stick–shaped incision centered over the level of disc herniation is generally used. A, Caudally, the incision is curved off the midline to maximize the amount of rib that can be exposed and removed. Shorter portions of rib resections create a more dorsolateral orientation to the disc space. Conversely, extensive removal of rib facilitates a more lateral approach to the disc space. The skin, subcutaneous tissue, and fascia are rotated laterally. B, The erector spinae muscles are then flapped medially, exposing the underlying rib(s), which are resected flush with the vertebral body. C, Removal of the proximal rib head, transverse process, and pedicle directly caudal to the disc space enables exposure of the neural foramen and lateral dura mater. D, The intercostal nerve is identified and traced into its respective foramen. This is tagged and cut. Care must be taken to avoid traction on this nerve. E, The lateral anulus is incised, and a portion of nucleus is removed, enabling drilling through the disc to the contralateral side. The dorsal portion of the disc, posterior longitudinal ligament, and disc herniation are left intact. A cavity is created by removing a portion of the rostral and caudal vertebral bodies. F, The remaining disc and posterior longitudinal ligament are then depressed into this cavity. G, Once the ventral dura and spinal canal are directly inspected for retained fragments, the rib that was removed during the exposure is fashioned into struts and gently impacted across the defect.

(From Stillerman CB, Weiss MH: Management of thoracic disc disease. Clin Neurosurg 38:325–352, 1992.)

Technique

The procedure is performed with the patient prone and taped to the table with arms at the side. The skin incision consists of a hockey-stick incision, with the vertical portion centered over the area of pathology11,18,29,30 (see Fig. 77-5A). Caudally, the incision is gently curved off the midline for 8 to 12 cm, enabling the skin, subcutaneous tissue, and fascial flap to be rotated far laterally. Alternatively, a paramedian lunar-shaped incision may be used. The erector spinae muscles are subperiosteally dissected off the dorsal ribs and transverse processes and flapped medially.31 The erector spinae muscle complex may be wrapped in a moistened laparotomy pad and gently retracted medially. Intraoperative imaging helps ensure removal of the rib that articulates with the correct disc space (see Fig. 77-5B). Once the proximal 8 to 12 cm of rib is resected, the underlying intercostal nerve is identified and traced into the neural foramen (see Fig. 77-5C). The pedicle caudal to the disc is identified and removed, exposing the lateral aspect of the dura mater (see Fig. 77-5D). At this point, the dorsal third of the disc space is removed. Care is taken to leave intact the dorsal-most margin of disc and the posterior longitudinal ligament (see Fig. 77-5E). The dorsal-caudal quarter of the rostral vertebra is drilled out, as is the dorsal-rostral quarter of the caudal vertebra. This creates a cavity so that the remaining dorsal disc and posterior longitudinal ligament can be gently depressed away from the spinal cord (see Fig. 77-5

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