TB spondylitis is still a challenging problem in both developing and developed countries [12], which can lead to a significant bone destruction and collapse of the vertebral bodies, resulting in hyper-kyphosis and tethering of the spinal cord [3, 11].For patients with neurological deficits, spinal instability or severe kyphotic deformity, surgery should be considered [3]. The sharp angular hyper-kyphosis 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 [13]. Pedicle subtraction osteotomy (PSO), the most popular osteotomy technique, has been applied for progressive tubercular thoracic and thoracolumbar kyphosis. Kalra et al. [10] used pedicle subtraction osteotomy to treat patients with healed tuberculosis of the spine and a resultant kyphosis. 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 [14]. Some modifications of PSO are reported that could obtain a greater correction angle without postoperative complications [15]. Wu SS et al. [16] claimed that they obtain a maximum correction angle of 60° at a single level. However, this modified procedure is not suitable to correct a severe kyphotic deformity with a kyphotic angle beyond 90°.
Although Posterior VCR provides adequate amount of surgical correction when compared to all other spinal osteotomy types [17], it is restricted owing to its inevitable neurological risk related to the instability induced during correction of the malformation [18, 19]. The complication rate has been estimated as high as 59 % for posterior VCR [20]. Zheng et al. [21] described Posterior-only bilevel modified vertebral column resection for extremely severe Pott’s kyphotic deformity, and the spinal sagittal kyphotic angle was corrected from a preoperative kyphosis 100.3° to a postoperative angle of 15.9° in their study. This procedure, however, was recommend to be performed at or below lower thoracic spine for security concerns. Transpedicular bi-vertebrae wedge osteotomy (TBWO) was first applied for fixed sagittal deformity of ankylosing spondylitis by Wang et al. [9], and they achieved an average correction of 65.2°. Same technique was applied in Zhao’s research and achieved a 76.8 % correction of the sagittal imbalance [22]. It should be noticed that TBWO could effectively reconstruct regional alignment than many other posterior osteotomy techniques, with a postoperative TK of 31.3°, TLK of 17.7° and LL of 5.4°. And this technique allows spacious room for neural elements and direct vision during osteotomy procedure, thus it can be safely applied in cervical or cervicothoracic area.
For those patients with post-tubercular spinal deformity, we prefer the TBWO in several aspects. First, most post-tubercular fused vertebras were angular deformity, which were treated as one targeted vertebra so that one-level osteotomy could obtain satisfactory outcomes, so it could reasonably reduce operation time and blood loss. The maximal correction angle was 88.6° in lumbar spine (44.3° per segment), which is consisting with previous study. The average operative time was 305 min with a mean intraoperative blood loss of 425 ml. Without corpectomy of deformed vertebrae, correction could be gained from transpedicular procedure and osteotomy site closure, which is time saving and manageable for spine surgeon. Secondly, collapse of anterior cortex of the osteotomy vertebra facilitates the correction of a rigid kyphosis [23], and larger bony contact surface could provide better fusion rates and additional spinal stability. In our study, the average correction rate was 84.3 % in lumbar spine, 69.0 % in thoracolumbar spine and 55.6 % in thoracic spine. The relative low rate of correction in thoracic spine could owning to restriction of the rib cage, but we would not recommend over correcting angular kyphosis in the thoracic spine with high risk of complications such as hemopneumothorax and spinal cord shock. When performing decompression and electrocoagulation in thoracic spine, it is noteworthy that artery of Adamkiewicz is located at this region. Preoperative angiogram is mandatory if the target vertebra located at T7 to L2. And we avoid rhizotomy if a preoperative angiogram has not been performed. During TBWO procedure, consideration should be given during electrocautery near the thoracic foramen or nerve dissection at the left side. However, literature has shown that the artery can be ligated safely as long as the collateral circulation is preserved [24], and we hardly have experienced a vascular spinal cord injury in our center. But as the literature mentioned, it remains a theoretical risk. Thirdly, TBWO could allow greater correction angles for its sufficient decompression of posterior elements, especially for upper thoracic and cervical segments. Neurologic complication is one of the main risks of extensive kyphotic correction by posterior osteotomy. TBWO procedure started with a decancellization procedure along the pedicles. Then osteotomized segments were gently closed with cantilever procedure under monitoring of somatosensory-evoked potentials, transcranial motor-evoked potentials, and free-running electromyography. When angular kyphosis deflexed, dura sac expanded and folded backwards, without obvious axial shortening. the distance of osteotomy closure could larger than substantial dural sac shortening distance. Based on the experience of our center, < 12 mm of substantial posterior shortening distance could be a safe range of shortening and central canal enlargement is critical. The perioperative neurological complication rate is 11.1 % in our study, with 2 of the 18 patients having neural monitoring changing intraoperatively. One patient regained the signals after standard procedures. One quadriceps paralysis was observed and recovered 3 months later postoperatively. No permanent neurological deficit due to TBWO procedure were observed. And there was one dura tears case with no postoperative infection. All of the 18 patients with post-tubercular spinal deformity who underwent TBWO achieved steady fusions with satisfactory rehabilitation. It should be noticed that several of 18 patients had initial poor neurological status and relative younger age, which indicated TBWO procedure demands rather strict patient selection.
In a decade ago, high-speed drill was commonly used in bone removing. However, when close to dura and nerve roots, a downward pressure of drill could be dangerous and disastrous neurological complications could happen. Especially in angular kyphosis, dura was stretched and high-tension, which closely clung to bony structure, and epidural space is extremely narrow. UBS applied in spine surgery has a huge advantage in time saving, minimizing soft tissues injury and could precisely finish bone cutting [25,26,27]. Utilization of UBS in osteotomy procedure can be safe and compatible in transpedicular bone removing, and leaves a smooth surface, which give less chance of dura tear and nerve injury. However, further research is needed to investigate the impact of UBS heat effect during osteotomy on bony fusion.
To best of our knowledge, there is no literature further discuss the subtype of post-tubercular kyphotic deformity. Our study firstly reviewed three different types of post-tubercular kyphotic deformity. And we carried out the point that a same technique managing post-tubercular kyphotic deformity in different spinal region with different correction ability. Our study had not compared the loss of correction and pelvic morphology. And as the number of the cases are small and this is a single center study, the larger sample research is needed for further study.