TB spondylitis is still a tricky problem in both developing and developed countries, 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. 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. Pedicle subtraction osteotomy (PSO), the most popular osteotomy technique, has been applied for progressive tubercular thoracic and thoracolumbar kyphosis. Kalra et al 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. Some modifications of PSO are reported that could obtain a greater correction angle without postoperative complications and Wu SS et al. claimed that they obtain a maximum correction angle of 60° at a single level. However, it 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, 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. Zheng et al. 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, 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. It should be noticed that TBWO could effectively reconstruct regional alignment than many other posterior osteotomy techniques. 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 with upper 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. Secondly, collapse of anterior cortex of the osteotomy vertebra facilitates the correction of a rigid kyphosis, and larger bony contact surface could provide better fusion rates and additional spinal stability. Thirdly, TBWO could allow greater correction angles for its sufficient decompression of posterior elements, especially for upper thoracic and cervical segments. When angular kyphosis deflexed, dura sac expanded and folded backwards, without obvious axial shortening. In our study, the average correction angle was 54.1°, and the maximum correction angle was 88.6°. One quadriceps paralysis was observed and recovered 3 months later postoperatively. 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, satisfactory rehabilitation and no permanent neurological complications occurred.
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 [24–26]. 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.