Evaluation of the efficacy of OLIF combined posterior internal fixation for single-segment lumbar tuberculosis: a single-center retrospective cohort study

Osteoarticular tuberculosis (TB) is the most common form of extrapulmonary TB, with about 50% of cases occurring in the spine [1]. Lumbar TB is the most common spine TB, often resulting in vertebral destruction, collapse, spinal instability, deformity, and even neurological dysfunction in severe cases [2]. The treatment of spinal TB mainly includes anti-TB chemotherapy and surgery. It is currently considered that anti-TB chemotherapy is the cornerstone of spinal TB treatment and surgery is mainly used for patients with severe spinal instability, spinal deformity, or impaired neurological function [3].

At present, the surgical methods for lumbar TB include anterior approach surgery, posterior approach surgery, and combined anterior and posterior approach surgery, among which the posterior approach is the most common used [4]. Application of posterior approach surgery in lumbar TB has been showed satisfactory clinical efficacy and safety, including improvement in clinical symptoms, high bone fusion rate and good deformity correction effect [5]. However, cases of chronic back pain or lower limb weakness are not rarely reported after the posterior approach surgery which may be due to the stripping of unilateral or bilateral parvertebral muscles and the opening of the spinal canal during the surgical procedure [6, 7]. Thus, spinal surgeons have been trying to find more minimally invasive surgical methods for the treatment of lumbar TB.

Oblique lateral interbody fusion (OLIF) is a minimally invasive surgical technique, which has been widely used in the treatment of lumbar diseases in recent years. During the OLIF procedure, the surgeon enters the target intervertebral space through the anatomical gap between the anterior edge of the psoas major muscle and the abdominal aorta to perform discectomy, dural sac decompression, and also realize effective indirect decompression by placing a large cage [8]. OLIF technique has shown satisfactory clinical efficacy in the treatment of lumbar spinal stenosis and lumbar disc herniation [9, 10]. However, at present, few scholars have applied OLIF in the treatment of spinal TB. In our previous study, we found that OLIF combined posterior internal fixation in the treatment of degenerative lumbar spondylolisthesis has the advantages of less surgical invasion, better decompression effect and faster postoperative recovery (including back pain and lumbar function) compared with the posterior approach surgery [11]. Thus, we wanted to know whether these positive results of OLIF could be extended to patients with lumbar TB.

Therefore, we conducted this retrospective cohort study to evaluate the clinical efficacy of OLIF combined posterior internal fixation for single-segment lumbar TB.

Our present study was approved by the Ethics Committee of the First Affiliated Hospital of Chongqing Medical University (2017-067). Written informed consent was got from each included patient. This research was conducted in accordance with the Declaration of Helsinki (as revised in 2013) and reported in line with the STROBE criteria [12].

A total of 39 patients were finally included in this study (Fig. 1), including 17 males and 22 females. Preoperative American Standards Association (ASA) classification showed that 25 cases were Grade I, 12 cases were Grade II, and 2 cases were Grade II. The mean age, body mass index (BMI), operative time, operative blood loss, and hospital stay were 44.3 ± 11.2 years, 21.3 ± 2.1 kg/m², 135.8 ± 19.2 min, 239.4 ± 84.7 ml, and 9.5 ± 2.7 days, respectively (Table 1).

The mean follow-up time was 26.3 ± 7.5 months. Compared with preoperative, postoperative VAS score and ODI showed a trend of gradual decline (Fig. 2a). VAS score and ODI were significantly improved at all follow-up time points (1, 3, 6, 12 months, and the last follow-up) after surgery compared with those before surgery (all P < 0.001). Cobb angle was significantly corrected at 1 month postoperative (P < 0.001), however, from 1 month postoperative to the last follow-up, Cobb angle showed a trend of gradual loss (Fig. 2b). The correction and loss of Cobb angle were 11.6 ± 4.8° and 6.8 ± 2.2°, respectively. Bone graft fusion rate at 3 months, 6 months, 1 year postoperative, and the last follow-up were 66.67%, 87.18%, 94.88%, and 100%, respectively (Fig. 2b). ESR and CRP were both showed a trend of gradual decline after surgery compared with preoperative, postoperative ESR and CRP were significantly decreased at different follow-up time points (1, 6 months, and the last follow-up) (all P < 0.001) (Fig. 2c). Compared with preoperative, the ASIA grade at the last follow-up of all patients showed significant improvement (Z = − 3.578, P < 0.001), with 1 case of Grade A, 1 case of Grade B, 3 cases of Grade C, 10 cases of Grade D, and 24 cases of Grade E before surgery, and 1 case of Grade C, 2 cases of Grade D, and 36 cases of Grade E at the last follow-up (Fig. 2d).

Six patients were found with postoperative complications with the rate of 15.38%, including 1 case of neurological injury, 1 case of vascular injury, 1 case of instrument failure, a1 case of incision infection, and 2 cases of lower limb weakness and numbness (Table 2). All complications were cured after active treatment.

Typical cases Figs. 3 and 4.

In this study, all lumbar TB patients underwent OLIF combined posterior internal fixation, which was similar to traditional combined anterior and posterior spinal TB surgery. However, we did not find large surgical trauma in this study. On the contrary, the operative time and operative blood loss reported in this study were both lower than those of only posterior approach surgery for lumbar TB as we previously reported [14]. We thought there may be the following reasons: (1) During OLIF surgery, the surgeon could reach the lesion segment and perform the procedures such as TB lesion debridement, bone grafting and fusion under the direct vision [15]; however, in the traditional posterior approach surgery, these above procedures were all conducted in a blind field of vision especially the opposite side of the TB lesion [16]. (2) In OLIF combined posterior internal fixation surgery, the surgeon did not need to open the spinal canal [17]; but in posterior surgery, the surgeon need to remove at least one side of the lamina and facet articular process to create a window for operations such as debridement of TB lesions [18]. (3) In our present study, posterior pedicle screw internal fixation instrument was inserted via the bilateral Witlse approach, the surgeon did not need to dissection the posterior paravertebral muscles; but in traditional posterior approach surgery, at least one side of paravertebral muscles should be completely dissected from the lamina [19]. Moreover, this study also found that lumbar TB patients treated with OLIF combined posterior internal fixation had a significantly shorter hospital stay than those patients treated by posterior surgery as we previously reported. This may be related to the smaller surgical trauma of the surgical method in our present study.

In our present study, VAS score and ODI both showed significant improvement at each follow-up time points postoperatively compared with those before surgery. This result confirmed that OLIF combined posterior internal fixation in the treatment of lumbar TB was effective in alleviating clinical symptoms. Possible reasons were as follows: (1) Radical debridement and effective anti-TB chemotherapy were helpful to TB control and thus beneficial to pain relief and lumbar function recovery [20]. (2) Paravertebral muscle was an important factor affecting low back pain and lumbar function [21]. In OLIF combined posterior internal fixation surgery, surgeon inserted pedicle screws via the bilateral Witlse approach, and did not strip the paravertebral muscles [17]. (3) Implantation of the titanium cage and pedicle screw restored the height and stability of the diseased segments.

During the follow-up, a high and satisfactory bone graft fusion rate was also found. In this study, we used a titanium cage filled with granular bone for anterior column reconstruction, and our previous study had confirmed that the fusion time of granular bone graft was shorter [14, 18]. Compared with preoperative, Cobb angle was significantly corrected at 1 month postoperative, and the correction ability was larger than that reported in the posterior approach surgery. This maybe due to the following reasons: (1) In the OLIF procedure, a large titanium cage with a certain inclination angle can be placed in the diseased segment, which facilitates the reconstruction of the anterior column, correction of the kyphosis deformity, and recovery of the lordosis of the lumbar spine [22, 23]. (2) In this study, we combined the posterior pedicle screw internal fixation on the basis of OLIF, which was beneficial to the correction and maintenance of Cobb angle [24]. During the follow-up, Cobb angle showed a trend of gradual loss, but the loss was similar to that reported in posterior approach surgery. The possible reasons were as follows: (1) In this study, titanium cage was used to reconstruct the anterior column. Titanium cage had large elastic modulus and sharp edge, and thus was easy to subside [25]. (2) Posterior fixation system could not only help maintain Cobb angle correction but also reduce its loss. (3) Wearing a lumbar brace for 3 months after surgery was also conducive to reducing the Cobb angle loss [26]. The Cobb angle loss was related to the bone graft fusion condition. In this study, most patients (87.18%) had achieved bone graft fusion at 6 months, and small Cobb angle loss and significant VAS score and ODI improvement were also found at 6 months postoperatively. This result confirmed our previous findings that once the bone graft fusion was achieved, the Cobb angle loss was slight and did not affect the relief of patient's clinical symptoms [27].

The ESR, CRP and ASIA grade (neurological function) were all showed significant decrease during the follow-up. This was mainly related to the standardized anti-TB chemotherapy, radical debridement of TB lesions, effective spinal canal decompression, anterior column reconstruction, and spinal stability maintenance [28]. It was reported that segmental artery injury, transient thigh numbness were the common complications of OLIF surgery [29], because the lumbar plexus, lumbar sympathetic trunk and segmental artery are all located laterally in front of the lumbar vertebrae and susceptible to being irritated or injured. In this study, we found the complication rate was 15.38% which was similar to previous studies. All complications were cured after active treatment, this also indicated the safety of OLIF combined posterior internal fixation surgery for lumbar TB.

In our opinion, the operative indications of OLIF combined posterior internal fixation for lumbar TB were as follows: (1) Severe back pain, conservative treatment was ineffective or had poor effect; (2) Progressive neurological impairment or paralysis; (3) Progressive-aggravated spinal instability or severe deformity; (4) Single-segment lumbar TB (L2–L5); (5) TB lesion i\was mainly located in the anterior column of the vertebral body, with little involvement in the posterior column; (6) Preoperative CT or MRI showed an appropriate surgical window between the psoas major muscle and the abdominal aorta [30].

Based on our preliminary experience, in the treatment of lumbar tuberculosis with OLIF combined posterior internal fixation, we recommend the followings: (1) During the debridement of TB lesion via the lateral anterior approach, the sclerotic bone and the bone bridge between the anterior edge of the vertebral bodies should be preserved as much as possible. (2) The posterior internal fixation should be performed via the bilateral Witlse approach or by the percutaneous pedicle screw fixation to reduce the iatrogenic injury to the posterior paravertebral muscle and ligament complex. (3) Posterior rigid fixation with minimal or no intervertebral distraction.

The present study also has several limitations. First, it was a single-center retrospective study. Secondly, this study was a cohort study without setting a control group, so it was hardly to compare the efficacy of OLIF and other surgical methods. Third, the sample size was small and the follow-up time was short.

In conclusion, OLIF combined posterior internal fixation is safe and effective in the treatment of single-segment lumbar TB, with satisfactory pain relief, improvement of lumbar and neurological function, and deformity correction. However, due to the limitations of this study, the above conclusions need to be further validated by high-quality prospective controlled study with large sample and long follow-up.