Posterolateral transforaminal interbody fusion for thoracic disc herniation: a retrospective study of 38 cases

Abstract

Objective:  To evaluate the clinical results of posterolateral transforaminal interbody fusion (PTIF) for the treatment of thoracic disc herniation (TDH).

Methods:  Thirty‐eight patients with TDH were treated with PTIF in our hospital from November 1999 to November 2003. The mean follow‐up period was 5.8 years (range, 4.2 to 6.5 years). There were 24 men and 14 women, ranging from 30.5 to 67.5 years, with an average of 46.5 years. The interval between onset of symptoms and surgery ranged from 5 to 12 months with an average of 9 months. In this group, the disc herniation involved T_9‐10 or T_10‐11 in 26 (68.5%) patients, T_8‐9 in 4 (10.5%), T_11‐12 in 4 (10.5%) and T₁₂L₁ in 4 (10.5%). All patients underwent X‐ray and magnetic resonance imaging (MRI) examination. Twenty‐two patients underwent myelography, while 25 patients underwent computer tomography (CT) or CT myelography (CTM) examination. The clinical results were evaluated using the Otani scoring system.

Results:  The outcome according to the Otani scoring system was excellent in 16 patients, good in 18, fair in 2 and poor in 2. No neurological symptoms, wound infection or clinical or radiographic evidence of instability were found; and the fusion rate was 100% by final follow‐up. An excellent or good outcome was achieved in 89.5% of patients.

Conclusion:  PTIF is an effective strategy for the treatment of TDH.

Introduction

TDH is an uncommon disease, accounting for only 0.2% to 0.3% of disc herniations, although it may account for as many as 5% of all symptomatic protrusions of the intervertebral disc. Late or missed diagnosis of the condition often occurs because there is no characteristic clinical presentation. Once a diagnosis is established, surgery is the optimal method of treatment. Various procedures and approaches for the treatment of TDH have been reported, all of which have been associated with numerous intraoperative complications and postoperative morbidities ¹ . The aim of this study was to evaluate the clinical results of posterolateral transforaminal interbody fusion (PTIF) for the treatment of TDH.

Materials and methods

General information

This study was approved by the ethics board of the Third Affiliated Hospital of Hebei Medical University. From November 1999 to November 2003, a total of 38 patients (24 men and 14 women; aged 30.5–67.5 years, with an average of 46.5 years) who had been diagnosed with TDH in our hospital were retrospectively reviewed in this study. Four patients had a trauma history, and two who had already undergone a laminectomy in other hospitals were admitted to our hospital because of weakness in both legs and sphincter disturbance. All these patients had severe neurologic deficits (Table 1).

Table 1.

Clinical signs and symptoms in the 38 patients

Symptoms	Proportion	cases
Complete paralysis	10.53%	4
Weakness of the lower extremities	60.53%	23
Paresthesias and numbness	60.53%	23
Difficulty walking	5.26%	2
Urinary dysfunction	36.84%	14
Positive pyramidal tract symptoms	5.26%	2
Muscle atrophy	15.79%	6
Radicular pain in the lower extremities	10.53%	4

Imaging examination

TDH can occur in any segment, but is commonest at T_9‐10 and T_10‐11, which accounted for 26 (68.5%) of our cases. T_8‐9, T_11‐12, and T₁₂‐L₁ were each involved in 4 cases (10.5%). All patients underwent examination by X‐ray and magnetic resonance imaging (MRI) preoperatively. Twenty‐two patients underwent myelography, while 25 patients underwent examination by computer tomography (CT) or CT myelography (CTM).

According to these preoperative imaging studies, vertebral canal compression was divided into three grades: small (<10% of the canal compromised), medium (10%–20% of the canal compromised), large (>20% of the canal compromised). There were 3 (7.89%) of small, 26 (68.42%) of medium and 9 (23.69%) of large grade.

Surgical technique

Under general anesthesia, the patients were placed in the prone position. A 9–12 cm vertical skin incision centered over the lesion was made along the midline. Subperiosteal dissection, including the spinous processes, hypertrophic articular facets, transverse processes, and capitulum costae was performed, and then the laminae on either side of the affected disc were removed. Where the ligamentum flavum (OLF) or posterior longitudinal ligament (OPLL) were ossified, these structures were also excised.

Once the laminectomy had been completed, the articular processes close to the disc were nibbled away to expose the dural sac fully, explore the location and extent of the protruded disc and allow punch forceps (which have to be passed in front of the theca in order to remove the disc materials) to be introduced, as closely as possible, parallel to the backs of the vertebral bodies. This surgery had to be extremely gentle; one usually had to be content to remove only very small pieces of disc materials and osteophytes with each bite of the forceps. The residual disc and osteophytes were then curetted with a curet, taking care to protect the nerve root and surrounding blood vessels (Fig. 1). After performing foraminotomy and discectomy, graft materials, consisting of cancellous auto‐bone harvested from the lamina mixed with cancellous allograft, were used to fill the intervertebral space, then pedicle screw fixation was performed under C‐arm guidance. The wound was then closed and Hemovac (Shengyuan Medical Equipment, Shijiazhuang, China) drains inserted. The Hemovac drains were removed 48 hr postoperatively.

Figure 1.

A schematic representation of the posterolateral approach: (a) Full exposure of the articular processes, transverse process and capitulum costae; (b) Excision of the articular processes close to the lesion; (c) Removal of the disc materials transforaminally; (d) The extent of excision with the posterolateral transforaminal approach.

Results

All patients were followed up in the out‐patient clinic at three or six month intervals for periods ranging between 4.2 and 6.5 years, with an average of 5.8 years. No aggravation of neurological symptoms, wound infection, cerebrospinal fluid leakage or fracture of the fixation system was detected postoperatively. The fusion rate was 100% by final follow‐up (Fig. 2).

Figure 2.

A 45‐year‐old male had gradually developed a gait disorder, bilateral numbness of lower limbs and muscle strength of grade 2 according to the Medical Research Council (MRC) scale. (a, b) Five months later, an MRI scan revealed thoracic disc herniation with spinal cord compression at T₁₂‐L₁. (c, d) A posterolateral transforaminal approach was performed followed by bone graft interbody fusion and transpedicular fixation. The patient's neurological deficit improved rapidly postoperatively, and he had achieved a normal gait by the second year follow‐up.

The Otani scoring system includes severity of overall pain, capacity to work and/or activity level, ability to walk, use of analgesics and overall patient satisfaction with postoperative results (Table 2) ² . The results showed an excellent outcome in 16 patients, who recovered fully and participated in unrestricted outdoor activities; good in 18, who had slight weakness or spasticity and were able to return to their previous work; fair in 2, who had definite improvement but still had reflex pain and moderate fatigue; and poor in 2 patients, who showed no improvement postoperatively. The combined excellent and good rate was 89.47%.

Table 2.

Results according to the Otani scoring system

Criteria	Numbers
Severity of pain
Severe	2
Moderate	6
None	30
Capacity to work
Restricted indoor activities	2
Unrestricted indoor activities	8
Partially restricted outdoor activities	19
Unrestricted activities	9
Ability to walk
Less than 100 m	2
100–500 m	16
More than 500 m	20
Use of analgesics
Daily	2
Weekly	10
Never	26
Satisfaction
Dissatisfied	2
Somewhat satisfied	9
Satisfied	27

Discussion

The incidence of disc herniation in the thoracic spine is much lower than in the cervical or lumbar spine. It has been reported to make up between 0.15% and 0.80% of all disc herniations ³ . With improved imaging techniques, including MRI, more cases have been diagnosed. TDH is particularly prevalent in middle‐aged and elderly patients. In these patients, calcification and osteophytes tend to form consequent to degeneration of the thoracic disc, resulting in what is defined as a rigid intervertebral disc. In the young, disc herniation is mainly caused by trauma; the resultant pathology is defined as a soft intervertebral disc ⁴ . TDH can occur in each segment, but is commonest in the lower thoracic spine. In our group, the TDH was at T_9‐10 and T_10‐11 in 68.5% of patients, which is similar to that reported in the literature ⁵ . It can also occur simultaneously in other segments of the lower thoracic spine ⁶ , ⁷ , the higher incidence at the lower levels may result from their increased mobility due to free ribs at these levels ⁸ .

Imaging of TDH

Myelography was performed in 22 cases. In the orthotopic views of the myelograms, eight cases showed a complete block which often had a convex border to it. In these eight cases, there was clearly true compression as a result of hypertrophy and ossification of the ligamentum flavum and hyperplasia of the articular processes, which compressed the cord backwards. In the lateral views, all cases revealed the dural sac to have a narrow anteroposterior diameter, and compression of the spinal cord at the corresponding levels. However, because of difficulties in establishing the diagnosis, and a high incidence of adverse reactions, melography has now been replaced by CTM and MRI.

The application of CTM has increased the diagnostic accuracy and specificity, especially in the diagnosis of lateral disc herniation. Meanwhile, CTM also gives clear evidence concerning the levels at which spinal stenosis has developed.

Diagnosis of, and selection of surgical methods for, TDH

The difficulty in making a diagnosis of TDH is due to the non‐specificity of the presenting symptoms. The symptoms which have previously been reported, in descending order of frequency, include: (i) non‐specific pain in the back, chest, or lower limb; (ii) increasing weakness in the lower limb with numbness; (iii) ataxia; (iv) bowel and bladder problems; (v) paresthesias ⁹ . Rohde and Kang reported three cases of TDH in which the manifestation was abdominal pain; they used an anterolateral surgical treatment and gained good clinical results ¹⁰ .

When symptomatic compression of the spinal cord has occurred, surgery is considered to be the best option ¹¹ . Many techniques for surgical management have been proposed, especially a lateral approach, which includes the anterolateral transthoracic and posterolateral approaches. As for the anterolateral transthoracic approach, although satisfactory results have been achieved, many complications, such as pneumonia, pneumothorax, atelectasis, chest infection and chylothorax have been reported ¹ . Furthermore, when an acute prolapse has occurred, this approach is difficult to perform. However, the posterior approach also has disadvantages. Firstly, removing the protruded disc presents some difficulties and risks, because the anatomical relationship of the cord to the protruded disc makes access extremely difficult. Secondly, long term compression causes inflammation and ischemia of the spinal cord, rendering it vulnerable to even the slightest surgical trauma. Under these circumstances, posterior decompression, which is liable to cause spinal cord injury, may result in aggravation of the situation ¹² . Microdiscectomy has shown a tendency to minimize the complications that are associated with the traditional approaches, but its high incidence rate of re‐herniation and vertebral re‐stenosis should be noted ¹³ .

Halm et al. ¹⁴ and Belmont et al. ¹⁵ have reported that, after transpedicle fixation, there is a high rate (14%–34%) of the pedicle screw becoming misplaced or loose, accompanied by a marked increase in the rate of paraplegia. In our group, we have taken a posterolateral transforaminal approach, which maximally favors segmental stability and prevents further iatrogenic destabilization. No cases of paraplegia were found during postoperative follow‐up in our series. Grisolia et al. have indicated that when TDH is combined with thoracic fracture, which may exacerbate the function of the nervous system, laminectomy should be urgently performed to relieve pain and neurological symptoms ¹⁶ .

Advantages and disadvantages of the posterolateral transforaminal approach

The posterolateral transforaminal approach provides a direct view of the lesion, and the ability to remove the disc easily; even when the disc has prolapsed and is adhering to the dural sheath. Furthermore, the operation is relatively simple with a low relapse rate. There is no need to retract the spinal cord, thus this approach minimizes the risk of paraplegia. Dommisse has reported that pressure from retraction may alter the blood supply, with potential spinal cord injury and other complications ¹⁷ . Malawski has made a comparison of etiology, pathology, clinical symptoms and signs, and postoperative recovery in patients with TDH, and concluded that the posterolateral approach is more effective and safer than other approaches ¹² . The indications for the posterolateral transforaminal approach plus interbody fusion are summarized thus: (i) TDH; (ii) TDH combined with OPLL or OLF; (iii) TDH combined with thoracic fracture; (iv) severe calcified disc embedded into cord; (v) thoracic disc prolapse.

Therefore, PTIF with complete decompression and no retraction on the cord has become the favored option for treatment of TDH. Excellent and good results in our group have demonstrated its effectiveness. However, there is some concern about the impact on the spinal stability of destruction of the articular processes.

Disclosure

This article does not contain information about medical device(s)/drug(s). No benefits in any form have been, or will be, received from a commercial party related directly or indirectly to the subject of this article.