The lumbosacral spine is at the junction of a lordotic motion segment and a kyphotic fixed end, an area where the stress of the entire torso is concentrated. The intact facet joints and intervertebral discs of the lumbosacral segment are the main structures that resist the shear force of the L5 vertebral body forward. Hence, spondylolisthesis of the lumbosacral region can easily bring about force imbalance, such that firm internal fixations are usually required. Lumbosacral TB is relatively rare, and has an insidious onset and atypical symptoms. Individuals with the condition often report nonspecific symptoms, which are easily mistaken for spinal degenerative disease at the initial stage . As the disease progresses, M. tuberculosis erodes the vertebrae to the point of sequestrum and abscess formation, leading to spinal instability or deformity. Additionally, nerve compression from TB lesions that invades the spinal canal potentially cause radicular pain, and even acute paralysis, which has deleterious effects on the patient's overall quality of life .
Standard systemic anti-TB chemotherapy remains the basic strategy throughout the entire treatment period [18, 19]. In our study, normative anti-TB treatments were carried out on all patients for two weeks preoperatively and for 12–18 months postoperatively. Common indications for surgery in lumbosacral junction TB are ineffective conservative measures, persistent pain unrelieved by chemotherapy, progressive neurological deficits, relatively massive cold abscesses, and extensive vertebrae destruction with instability or deformity. The surgery is specifically carried out with the goal of removing the lesion, relieving nerve compression and rebuilding spinal stability, all of which aid the maintenance of normal lumbar lordosis and sacral kyphosis. This also ensures that the normal physiological line of force transduction is preserved. For patients who require surgery, the key techniques for surgical treatment of spinal TB include complete debridement, adequate bone grafting and firm internal fixation.
The surgical method for the treatment of TB in the lumbosacral junction is still controversial [20–22]. An anterior approach has been conventionally preferred since most TB lesions involve the vertebral body and intervertebral discs. The anterior approach allows for direct access where thorough debridement of the affected tissue and intervertebral reconstruction can be performed [23, 24]. Nevertheless, the anterior approach is associated with anteriorly related complications. In particular, the lumbosacral region is an area with complex local anatomical structures and is adjacent to numerous vital organs, including major blood vessels, nerve plexi, and ureters . Tribus et al.  reported that the distance from the bifurcation of iliac vessels to the top of the L5-S1 disc averaged 18 mm, and the average space available between the left common iliac vein and the right common iliac artery is 33.5 mm, a result they surmised from studying 37 human cadavers. This means that it is too risky to perform the surgery via the anterior approach, due to the close proximity of the vasculatures that this approach exposes. In addition, anterior instruments may be inadequate since the presence of the TB infection is associated with osteoporosis that renders the vertebrae increasingly fragile, thereby potentially causing graft failure and loss of correction after surgery . These existing objective factors pose significant challenges to anterior fixation of the lumbosacral segment, while carrying the risk of damage to major neurovascular structures. Some surgeons report that anterior debridement combined with posterior instrumentation in the management of lumbosacral TB can obtain favorable clinical efficacy [27, 28]. This approach overcomes the stability-related shortcoming when the anterior approach is used alone and encompasses a broader surgical vision and higher bone graft fusion rate. However, it also results in superimposed surgical trauma and increased complications. Taking the above factors into account, we favor the posterior approach for treating lumbosacral junction TB when surgery is indicated.
With the widespread application of pedicle screw-rod internal fixation systems, the satisfactory safety and clinical efficacy of the posterior-only approach for the treatment of lumbosacral TB has increasingly attracted the attention of orthopedic surgeons for many reasons [7, 17, 26, 29, 30]. Firstly, the posterior approach is less invasive and avoids damage to vital nerves and blood vessels. In addition, pedicle screws provide better holding force, and are thus superior to the anterior approach in correcting severe kyphosis. Zeng et al.  successfully treated 15 cases of lumbosacral TB with paraspinal abscess using the posterior approach. Similarly, Xu et al.  also reported that kyphotic deformity significantly improved with complete recovery of neurological function by interbody fusion and posterior lumbopelvic fixation for lumbosacral TB. In this study, all 38 cases showed complete resolution from TB infection by the last follow-up. The patients who suffered preoperative neurological deficit had satisfactory recovery at the final follow-up. In terms of spinal stability, over the five years of the observation period, patients presented an average loss of the correction angle of only 1.2° ± 0.7° with a 22.3% ± 6.2% correction rate after surgery. Pain intensity as measured by VAS dropped by over 80%, while at the last follow-up, 21 patients (55.3%) reported excellent status, and 16 patients (42.1%) reported good status based on Kirkaldy-Willis criteria.
The surgical treatment of lumbosacral TB should follow an individualized protocol. A routine CT scan and MRI examination are essential before surgery to map out the details of the lesion. When the S1 vertebral body is severely damaged, the use of sacral pedicle screws cannot obtain sufficient bony support. The physiological force transmission line in the lumbosacral region is subsequently affected, which brings challenges to surgical reconstruction. The sacrum forms the posterior wall of the pelvis and is connected to the ilium through the sacroiliac joints. Physiologically, gravitational force is transmitted from the lumbosacral joint to the upper part of the sacrum, and then to the pelvis through the bilateral sacroiliac joints. Due to the special role it plays in pressure bearing and force transduction, the sacrum is considered the keystone of the pelvic ring . For cases when S1 is severely damaged, lumbopelvic fixation can effectively relieve the stress on the diseased vertebra and promote its healing. In addition, iliac screw fixation can immediately stabilize the lesion and restore the normal lumbosacral angle . For patients with an S1 vertebral body lesion that is not serious and with an intact pedicle channel, sacral pedicle screw fixation can effectively reconstruct local stability and cross spinopelvic fixation can be avoided.
M. tuberculosis tends to infect the anterior and middle column of the spine. The controversy with regard to surgical treatment of lumbosacral TB with the posterior approach mainly centers around whether this approach can allow for complete debridement given its limited field of view. Indeed, the posterior approach offers no advantage in lesion clearance. Nonetheless, resection of both sides of the lamina and facet joints, and moderate stretching of the dura mater and nerve roots can provide enough operating space for the removal of the lesion. Then, through intraoperative pressure washing, negative pressure suction and postoperative postural drainage, the sequestrum, necrotic tissue and most abscesses can be removed. The remaining small areas of infection can be resolved by standardized anti-TB chemotherapy after surgery . Some surgeons are concerned that this surgical method destroys the posterior column and may cause spinal instability. However, pedicle screws, which allow for three-column fixation, can effectively restore the normal physiological curvature of the spine, and overcome the instability caused by column damage within a short time period. Sufficient intervertebral and transverse bone grafting provide long-term bone support for spine stability . During the postoperative follow-up of this study, there were no cases of TB recurrence from incomplete lesion removal. In terms of structural recovery, all patients achieved satisfactory bone fusion at an average of 12.8 ± 1.9 months after surgery without a single incidence of instrument failure.
This study has some limitations. Firstly, this is a retrospective study, which may lead to biased results. Furthermore, this study is a single-center study with a relatively small sample size. Prospective studies with larger sample sizes are required to confirm the findings, although given the rarity of this condition, it may take considerable time and coordination for such studies to take place.