A new surgical treatment for post-tubercular thoracic kyphosis, a retrospective study.

Background: In the late stage of Spinal tuberculosis, the bony destruction and vertebral collapse often leads to significant kyphosis, presenting clinically as a painful gibbus deformity, with increased instability, vertebral body translations. Deformity more commonly occurs and rapidly progresses in the thoracic spine. The surgical treatment of deformity in the thoracic region poses a challenge to the spine surgeon because its high neurological risk. Vertebral column decancellationa new spinal osteotomy technique, is thought to be suitable for most patients with severe rigid kyphosis. In the current study, we report VCD technique as another surgical strategy for correction of post-tubercular thoracic kyphosis and evaluate the clinical and radiographic patient results. Methods: Between January 2016 and January 2018, 16 patients with post-tubercular thoracic kyphosis underwent the Vertebral column decancellation. Preoperative and postoperative Konstam’s angle were measured. Oswestry Disability Index(ODI) ,Visual analog scale(VAS) and American Spinal Injury Association(ASIA) were documented. The mean follow-up was 31.4 months Results: The average operation time was 226 minutes (range, 200–260 minutes) with a mean intraoperative blood loss of 466 mL (range, 400–580 mL).The Konstam’s angles decreased from 88.8°(range, 76°– 103°)preoperatively to 19.0°(range, 9°–32°)at the final follow-up (P<0.01). The mean VAS score was reduced from preoperative 7.0(range, 6–8) to 1.7 (range, 1–3, P<0.01) and the ODI improved from 67.6% (range, 59%– 77%) to 20.7% (range, 15%–33%, P<0.01). At final follow-up, there was radiographic evidence of solid fusion at the osteotomy site and fixed segments in all patients. Neurological function improved from ASIA scale D to E in 6 patients, C to D in 3 patients. Conclusion: Our results suggest that VCD is a safe and effective treatment option for post-tubercular


Background
Spinal tuberculosis is the most common form of the extra-pulmonary tuberculosis. It accounts for nearly half of the musculoskeletal tuberculosis cases. Delayed diagnosis is common and patients treated with anti-TB chemotherapy alone or with simple surgical debridement without fusion may result in disease reactivation. [1] In the late stage, the bony destruction and vertebral collapse often leads to significant kyphosis, presenting clinically as a painful gibbus deformity, with increased instability, vertebral body translations and increased risk of neurologic involvement [2,3]. Deformity more commonly occurs and rapidly progresses in the thoracic spine [4]. The surgical treatment of deformity in the thoracic region poses a challenge to the spine surgeon because its high neurological risk [5].
Anterior, posterior, or combined anterior and posterior (AP) procedures that show various degrees of success for correcting kyphosis of TB [6][7][8] .The late correction of stiff and sharp angular deformities (more than 60°) is only feasible with three-column osteotomies or vertebral column resection (VCR) [9]. Pedicle subtraction osteotomy (PSO) (Fig. 1A), recommended 30-40°as a safe range [10,11], is usually insufficient to correct severe kyphosis. Despite VCR (Fig. 1B) is considered as the most powerful tool for the correction of spinal deformity, this technique is a formidable last resort technique for severe fixed sagittal and coronal deformity due to its technical difficulty and potential for complications [12].
Vertebral column decancellation (VCD) (Fig. 1C), a combination of the eggshell technique, Smith-Petersen osteotomy (SPO), PSO and VCR, is thought to be suitable for most patients with severe rigid kyphosis [13].In the current study, we report VCD technique as another surgical strategy for correction of post-tubercular thoracic kyphosis and evaluate the clinical and radiographic patient results.

Materials And Methods
23 patients with post-tubercular thoracic kyphosis were admitted to our department from January 2016 to January 2018. Diagnosis was made based on radiographic examination, laboratory tests and histopathology. This study was conducted with approval from the Ethics Committee of Our Hospital and was performed in accordance with the Declaration of Helsinki. Written informed consent was obtained from all participants. The indications for surgery were as follows: (1) low back pain refractory to conservative treatment; (2) being not able to lie down in dorsal position; (3) increasing neurological deficit. Patients with active infection and who cannot tolerate surgery due to poor cardiopulmonary function were excluded. Anteroposterior, lateral spine radiographs, CT 3-D reconstruction, Magnetic Resonance Imaging (MRI) were available for all patients (Fig. 2).
Then, VCD was performed. The pedicle probe and drill were used to create and enlarge the relatively normal pedicle holes of the fused vertebras with both sides of the pedicles. These fused vertebras were treated as one targeted vertebra. Through the pedicle holes, the cancellous bone of the posterior half of osteotomy column was adequately removed using rongeur and curette. A high-speed drill was used to make thinning of the anterior cortex and lateral walls of vertebral body and linear fractures of the anterior cortex achieved using an osteotome. Then the spinal canal was opened laterally, and the posterior elements including the spinous process, bilateral lamina, transverse process, and the adjacent facet joints were removed. After removing the posterior cortical bone of the osteotomised vertebra, the kyphotic spine is corrected using gentle manual force stabilized by a temporary rod. The operating table and the position of the patient were adjusted for the correction.
During the correcting procedure, an anterior opening wedge was created and the middle column was preserved as the hinge. The posterior interlaminar fusion was completed over the fixed segments with residual autogenous bone. After confirmation of absent soft or bony compression, a drainage tube was placed in the surgical field, and the wound was closed in layer sequence.

Statistical analysis
All statistical analysis was performed with SPSS v19.0 software (SPSS Inc., Chicago, Illinois). Students' t-test was used for all analyses, and a p-value < 0.05 was considered statistically significant.  Table 2. The mean VAS score was reduced from preoperative 7.0(range, 6-8) to 1.7 (range, 1-3, P < 0.01) and the ODI improved from 67.6% (range, 59-77%) to 20.7% (range, 15-33%, P < 0.01). At final follow-up, there was radiographic evidence of solid fusion at the osteotomy site and fixed segments in all patients. Neurological function improved from ASIA scale D to E in 6 patients, C to D in 3 patients.

Result
Dural tears with transient cerebrospinal fluid leakage were encountered in one case who underwent an initial debridement, The tear was covered intraoperatively by muscle and fat grafts, lumbar drainage was placed and removed after seven days. No deep wound infection was identified. One patient suffered transient partial neurological deficit post-operatively and resolved completely within 8 weeks.

Discussion
TB spondylitis can lead to a significant osteolysis and collapse of the vertebral bodies, which results in hyperkyphosis and tethering of the spinal cord [15]. Late stages of rigid hyperkyphosis are difficult to treat [9]. The sharp angular hyperkyphosis often requires complex three-column osteotomies. Currently, the one-stage posterior approach is most often used for minimizing the risk of injury to anterior vascular and visceral structures. Pedicle subtraction osteotomy (PSO), the most popular osteotomy technique, has been applied for progressive tubercular thoracic and thoracolumbar kyphosis. Kalra et al [16] used Pedicle subtraction osteotomy to treat 15 patients with healed tuberculosis of the spine and a resultant kyphosis. They obtained a mean correction of 44.2°. The mean pre-operative kyphosis was 58.8° and the mean post-operative kyphosis was 13.7°. The mean operative time was 210 min (110-220 min) and the mean blood loss was 940 ml (550-1550 ml). Of the 15 patients, 2 complained of mild residual pain which settled with analgesics. There was a superficial wound infection in two patients and one deep infection that required debridement. The osteotomy is described as closing wedge osteotomy and correction of the deformity is achieved by the shortening of posterior column. However, the technique should be limited to 30°-40° as a safe range of single segment osteotomy; otherwise, the spinal cord is excessively shortened and distorted [17]. Some modifications of PSO are reported that could obtain a greater correction angle .Wu SS et al. [18] claimed that they obtain an average angle of correction was 38.8°(25°-60°) without postoperative complications. However, it is not suitable to correct a severe kyphotic deformity with a Konstam's angle beyond 90°.
Although VCR or Posterior-only VCR could provide the greatest amount of surgical correction when compared to all other spinal osteotomy types [19], it is restricted owing to its high inherent neurological risk related to the instability induced during correction of the malformation [20]. The complication rate has been estimated as high as 59% for posterior VCR [21]. Zheng et al. [22] described Posterior-only multilevel modified vertebral column resection for extremely severe Pott's kyphotic deformity, and the spinal sagittal Konstam's angle was corrected from a preoperative kyphosis 100.3° to a postoperative angle of 15.9°. The mean duration of surgery was 285 min (246-400 min), the average intraoperative blood loss was 2933 ml (2000-6000 ml). a neurological deficit occurred in 1 patient in their study. This procedure, however, was recommend to be performed at or below lower thoracic spine. In our study, The Konstam's angles decreased from pre-operative 88.8°(76°-103°) to 19.0°(9°-32°)at the final follow-up. The mean operation time was 226 min (200-260 min) with a mean intraoperative blood loss of 466 mL (400-580 mL). No permanent neurological deficit or other major complications occurred. VCD technique is a simpler and safer osteotomy procedure than VCR, and at the same time it allows a greater correction angle than PSO.
For those with upper post-tubercular thoracic kyphosis, we prefer the VCD technique. First, post-tubercular fused vertebras were treated as one targeted vertebra so that one-level osteotomy could obtain satisfactory outcomes. Second, Osteoclasis of anterior cortex of the osteotomy vertebra facilitates the correction of a rigid kyphosis [13].Third, Compared to PSO, a kind of closing wedge osteotomy (CWO), VCD technique could open the anterior column of the targeted vertebrae when posterior column closing that allows greater correction angles. In our study, the average correction angle was 69.9°, and the maximum correction angle was 81°; In addition, VCD preserves the middle column as the hinge providing greater stability and better fusion than VCR. All of the 16 patients with post-tubercular thoracic kyphosis who underwent VCD technique achieved satisfactory rehabilitation and no permanent neurological complications occurred.

Conclusion
Our results suggest that VCD is a safe and effective treatment option for post-tubercular thoracic kyphosis. This technique achieves higher correction and fusion rates with adequate decompression of neurological elements.