Tuberculosis is an internal medicine disease, and its treatment is primarily based on anti-tuberculosis drugs that can achieve good therapeutic effects.[7, 8] A long-term follow-up study showed that although conservative treatment achieved good outcomes, residual low back pain and kyphosis were more common in late stages. Currently, it is generally believed that patients should be treated with surgical intervention as long as there is progressive aggravation of neurological dysfunction, massive paraspinal abscess and sequestrum formation, severe pain not significantly relieved with medication, or significant bone destruction that affects spinal stability.[10, 11] The purpose of the operation is complete lesion removal, spinal canal decompression, correction of deformity, and re-establishment of spine stability through bone grafting and stable internal fixation. After the operation, patients can quickly return to normal life as a consequence of rehabilitation exercise.[4, 12] However, the methods to achieve these goals are controversial.[3, 4]
Since Hodgson first reported the treatment of spinal tuberculosis using the “Hong Kong operation” in 1960, tuberculosis debridement and internal fixation through an anterior approach has become the preferred surgical approach for spinal tuberculosis. The advantages of the anterior-approach surgery are as follows: (1) direct access to the lesion for complete debridement and direct spinal canal decompression.[4, 14] (2) anterior vertebral column stability can be reestablished immediately through intervertebral bone grafting, and the compressive stress is conducive to postoperative bone fusion.(3)it can appropriately improve kyphosis. Nevertheless, the disadvantages of anterior-approach surgery are that the bone graft bears high compressive stress after anterior-approach lesion debridement alone, and the bone graft is prone to collapse and absorption, causing insufficient support for the lumbosacral segment. Furthermore, the lumbosacral segment is an inflection point of biomechanical change where the local stresses are large. Without internal fixation, long-term bed rest after surgery is required, and the bone graft can be displaced or even become detached due to excessive stretching or torsion of the waist. Selection of anterior-approach internal fixation therefore requires greater exposure, increasing the risks of surgery, and has greater requirements on the residual vertebral bone. It has been reported that the complication rate increased by 50% as the scope of surgical exposure was increased and internal fixation was placed on normal vertebral bodies. Weinstein pointed out that the pedicle itself provides 60% of the total pedicle screw anti-pullout strength; cancellous bone accounts for approximately 15–20%, and the anterior cortical bone accounts for approximately 20–25%. Sun et al. reported that the average improvement in lumbosacral angle after posterior-approach surgery was 44.3°. whereas the average improvement in lumbosacral angle after anterior-approach surgery was only approximately 9.5°. Therefore, the anti-pullout strength, the ability to correct kyphosis, and the ability to maintain corrective effect with posterior-approach fixation is better than with anterior-approach fixation. Nevertheless, posterior-approach tuberculous lesion debridement alone is often incomplete and is prone to recurrences after surgery, especially in patients with significant bone destruction of the anterior vertebral column and large abscesses in the psoas major muscle or iliac fossa. Moreover, the stability of the anterior vertebral column is not easily reestablished by structural bone grafting via posterior-approach surgery alone; this leads to loss of lumbosacral height and the effect of kyphosis correction.[15, 21]Therefore, the first choice for L5-S1 spinal tuberculosis with severe bone destruction is a combined anterior-posterior approach.[4, 11, 21]
With respect to the order, Zeng et al. believe that because performing posterior-approach fixation leads to stiffness of the fixed segment, it will be difficult for anterior bone graft to support the anterior vertebral column after anterior-approach surgery. Therefore, performing anterior-approach surgery first is recommended for patients with severe bone destruction in L5-S1 spinal tuberculosis. For anterior-approach bone grafting, the size of the iliac bone graft should be appropriately larger than the measured height in order to be conducive to reducing dislocation of the bone grafting interface under compressive stress and to promoting bone graft fusion. For posterior-approach bone grafting with autologous iliac cancellous bone, the cartilage surface of the facet joints in the lumbosacral region should be removed, including the L5-S1 spinal facet joint articular surface, and full decortication of the transverse process and the residual lamina can be performed to improve postoperative bone graft fusion and maintain the effect of kyphosis correction.
In order to improve postoperative bone graft fusion rate and reduce surgical complications, it is necessary to preserve as many of the residual vertebrae as possible and to place screws on the residual vertebrae to reduce the fixed segments. Since Steinmann et al. first reported successful placement of pedicle screws by image-based technique in 1993, this technology has been developed into computer navigation technology and has been widely used in spinal surgery. Studies have shown that the success rates of screw placement with traditional positioning based on anatomical landmarks combined with surgeon’s experience and intraoperative imaging or nerve monitoring were 90.3–94.1%.[23, 24] Wood et al implanted 627 pedicle screws in 150 patients at the same institution under computer navigation, and the overall complication rate (including poor pedicle screw placement and pedicle screws requiring adjustment) was 3.83%. Siasios et al. suggested that the accuracy of screw placement under computer navigation was 95.3–100%. It can be seen that screw placement under computer navigation is more accurate than the traditional method. Especially for residual vertebrae, the screws successfully placed at one time can increase the anti-pullout strength. In the present study of 24 patients, only 4 of 112 screws slightly broke through the medial wall of the pedicle, and the accuracy of screw placement was 96.43%. The possible causes are that the navigational device placement was not tight, resulting in intraoperative deviation, or that there were operational errors by the surgeon during screw placement.
We achieved good surgical outcomes in 24 patients with severe bone destruction in L5-S1 spinal tuberculosis. There were no vascular injuries, ureteral injuries or new nerve injury complications, and intraoperative screw placement under computer navigation was accurate. In all patients, ESR, CRP, VAS, and lumbosacral angles significantly improved one month postoperatively and at the last follow-up compared with the values before surgery. Although local bone resorption of iliac bone graft were identified in 1 case, solid posterolateral fusion was achieved at the final follow-up, and no correction loss occurred.There were no other complications such as bone graft displacement, tuberculosis recurrence, internal fixation loosening or fracture occurred during the follow-up period, and fusion was achieved in all cases at the final follow-up.
Several limitations should be considered while interpreting the results of this study. This was a retrospective analysis of patients from a single-center, which limits generalizability of study findings. The small sample size of our study (n=24) decreases the power of the results. Some prospective randomized control trial studies with larger sample sizes are needed to validate our results.