Characteristics of LSTB
The lumbar region sustains the largest load and exhibits the greatest mobility among all spinal regions. Because of the large pressure and shear force on the lumbar segments, lumbar stability is maintained by the combined effects of the vertebrae, intervertebral discs, rich muscle groups, and tough ligaments. The local anatomical structures adjacent to the lumbar region are complex and include major blood vessels, nerves, and the ureters.
LSTB mainly involves the anterior and middle lumbar columns, potentially leading to vertebral destruction and collapse, changes in the physiological lordosis and load biomechanics, kyphosis deformity, and protrusion of the pathological tissues into the vertebral canal, seriously affecting patients’ health and quality of life. LSTB usually presents with low back pain with or without radicular leg pain and neurologic deficits secondary to compression of the cauda equina and nerve roots.
Importance of posterior-only approach
Surgical procedures in the posterior-only approach, including lesion debridement and bone grafting and fixation, can be accomplished simultaneously using one incision without changing the position; thus, this approach is much less invasive than others. Additionally, the posterior-only approach is familiar to spinal surgeons and avoids possible injury to the large blood vessels, nerves, or other anatomical structures. Furthermore, internal fixation in the posterior-only approach is more effective than that in the anterior approach with respect to kyphotic correction and the maintenance of correction [16].
However, many surgeons are concerned about the potential increase in spinal instability caused by damage to the posterior column. In our experience, the strong three-column fixation can effectively maintain short-term postoperative spinal stability. Furthermore, strong bony fusion can be obtained by the combination of interbody bone grafting and lateral bone grafting or posterior lamina reconstruction, maintaining long-term spinal stability.
The concentration of TB lesions mainly in the anterior column has given rise to controversy regarding whether the posterior approach can completely achieve focal debridement. Indeed, the posterior-only approach offers no advantage with respect to debridement. However, removal of the lamina and facet joints with moderate stretching of the nerve roots and dura mater can provide adequate surgical space in which 360° lesion debridement under direct vision can be achieved. Moreover, subsequent procedures, including saline irrigation at the lesion site with pressurized washing and negative-pressure suction and postoperative postural drainage, can effectively drain pus and eliminate residual lesions [17]. Furthermore, the cleared lesion can facilitate the penetration of anti-TB drugs, improving the efficacy of local anti-TB drugs intraoperatively and systemic anti-TB drugs postoperatively and resulting in cure through spontaneous fusion in STB lesions. Therefore, complete debridement need not be overemphasized [18].
Choice of fixation range
The choice of the fixed segment range is the focus of long-standing debate in lumbar fixation. In this study, the fixed range of mono-segment fixation was limited to the pathologic segment. Short-segment fixation is defined as limitation of the fixed range to one upper and lower vertebra adjacent to the pathologic segment, with or without inclusion of the pathologic segment according the extent of the vertebral destruction.
Short-segment fixation [19] provides strong fixation and deformity correction and is still applied by most surgeons for treatment of single-segment LSTB. The increase in the fixed segment range can distribute the longitudinal stress of the spine to longer segments, which can significantly maintain the spinal stability, improve the vertebral body height, and prevent loss of the correction angle. However, short-segment fixation also sacrifices the motion of the two normal segments, affecting the activity of the lumbar spine in the long term and leading to aggravation of adjacent segment degeneration (ASD), which may ultimately induce ASD-related diseases [20]. One study [21] showed that longer fixed segments result in greater stress concentration and exert greater loads on adjacent segments, which may accelerate ASD and cause lower back pain, pseudarthrosis, and implant rupture.
Because of the anatomical features and high requirement of activity in the lumbar region, preserving segments with normal motion is important to ensure high long-term quality of life. Thus, mono-segment rather than short-segment fixation is superior for LSTB. However, many surgeons are concerned that mono-segment fixation cannot meet the requirements of reconstruction stability in treating STB. In this study, we compared the clinical and radiological outcomes of posterior short-segment versus mono-segment fixation combined with one-stage posterior debridement and bone grafting fusion in treating single-segment LSTB.
Maida et al. [22] compared the clinical and radiological outcomes of mono-segment fixation with bi-segment fixation in treating thoracolumbar spine fractures. They found no statistically significant difference in vertebral body height restoration or correction of the kyphotic deformity between the two groups, confirming the validity of mono-segment fixation. Wei et al. [23] demonstrated that both mono-segment fixation and short-segment fixation are effective and reliable for thoracolumbar burst fractures. Mono-segment fixation significantly shortened the operative time and decreased the amount of blood loss, thus offering better clinical results. Li et al. [24] reported that the mean postoperative VAS score and vertebral kyphotic angle were similar in the mono-segment fixation group and short-segment fixation group. These clinical studies have demonstrated that mono-segment fixation can meet the stability requirements necessary for spinal fracture reconstruction, which has also been confirmed in biomechanical experiments and finite element analysis [25, 26].
Various degrees of reactive new bone formation can be seen in the involved vertebrae in most patients with STB. The vertebrae involved by Mycobacterium tuberculosis form sclerotic bone walls, resulting in abnormally high bone density of the pathological vertebrae. This pathologic feature of STB brings stronger holding forces of the pedicle screws to the involved vertebrae than in spinal fracture, making mono-segment fixation more feasible for treating STB than spinal fractures. Wang et al. [27] reported that after bone fusion, mono-segment fixation was effective in restoring and maintaining spinal stability and retained normal-motion segments more than did short-segment fixation.
In the present study, the mean local angle correction rate and correction loss were 66.9% ± 6.2% and 0.9° ± 0.3° in Group Bk and 48.1% ± 19.2% and 0.6° ± 0.2° in Group Bl, respectively. There were no differences in the deformity angle correction rate or correction loss between Groups A and B (P > 0.05). These findings indicate that mono-segment fixation can achieve satisfactory effectiveness in restoring and maintaining spinal stability, similar to short-segment fixation.
Mono-segment fixation has several advantages in treating single-segment LSTB. Above all, the lumbar segments with normal motion can be retained, which may slow the degeneration of adjacent segments to some extent. Additionally, the surgical field of exposure in mono-segment fixation is relatively smaller and less invasive. Furthermore, the need for fewer fixation materials reduces the operation time and hospitalization costs, which can ease the burden on patients and may be more suitable for patients in developing countries and poorer areas. In the present study, the mean operative time, amount of blood loss, and hospitalization duration in Group B were 137.4 ± 22.6 min, 665.3 ± 111.9 ml, and 13.6 ± 2.3 days respectively, all of which were lower than those in Group A (P < 0.05).
The application of mono-segment fixation in treating single-segment LSTB also has some limitations. Because of the irregular destruction created by LSTB, the degree of vertebral destruction varies among different patients. The choice for mono-segment fixation should be based on the extent of vertebral destruction. Wang et al. [28] considered that the remaining one- to two-thirds of the vertebral height is enough to accommodate a conventional transpedicular screw after debridement, which is consistent with our experience. In addition, the structural integrity, including the pedicle in the diseased vertebrae, the upper endplate of the upper pathologic vertebra, and the lower endplate of the lower pathologic vertebra, are important for screw implantation.
Therefore, mono-segment fixation can be chosen when the following two conditions are fulfilled: a major lesion involving one motion unit of the lumbar spine is present, and enough space is available for screw implantation in the vertebrae adjacent to the lesion (more than one-third the vertebral height, with structural integrity of the pedicle and endplates in the pathologic vertebrae). Furthermore, mono-segment fixation is unsuitable for patients with severe kyphosis deformity or osteoporosis. Short-segment fixation is more suitable when the pathologic vertebral height is less than one-third.
This study has two main limitations. First, its retrospective nature may have resulted in biased outcomes. Second, the sample size was relatively small and the follow-up duration was relatively short. Therefore, prospective studies with larger samples and longer follow-up periods are needed.