The treatment of PLS includes conservative treatment and surgical treatment. Conservative treatment mainly involves broad-spectrum antibiotics or sensitive antibiotics, and can cure most cases of PLS [5]. However, some cases require surgery, and the surgical indications are as follows. 1. Failure to respond to conservative therapy. 2. Significant or progressive neurologic deficits. 3. Large paraspinal abscess with local mass effect or septic embolization. 4. Significant osseous disease with involvement of more than two vertebral bodies, or greater than 50% loss in a single vertebral body. 5. Progressive deformity with or without incapacitating spinal posture. We show a typical pyogenic spondylodiscitis case treated with XLIF (Fig. 2).
The main surgical purposes for lumbar spondylodiscitis include debridement of focal lesions, canal decompression, deformity correction and stability reconstruction [4, 23]. To improve life quality and reduce the complications caused by long-term conservative treatment, some researchers advocate early surgical intervention [24]. Several surgical approaches, including anterior, posterior or combined anterior and posterior approaches, have been proposed for treating PLS [6]. However, anterior approach is associated with massive trauma and prolonged postoperative recovery [25]. Certain complications, such as intestinal obstruction, hemangioma, retrograde ejaculation and deep venous thrombosis, are nonnegligible, especially for patients in poor conditions [4, 12, 25]. In this context, posterior approach combined with internal fixation is a considerable alternative. This approach is simple, less traumatic, and allows debridement, interbody fusion and stability reconstruction in a single incision at the same time. However, complete debridement is relatively difficult under indirect visualization, which is likely to increase the risk of dural sac tear and nerve root injury. Besides, infection may spread from anterior and middle column to non-infected posterior column and surrounding normal tissues. Therefore, the posterior approach was usually used for patients with mild infection and relatively limited lesions [26]. As for combined surgery, the main advantages include complete debridement, decompression, bony fusion and stability reconstruction. Meanwhile, the debridement area is seperated from the internal fixation, thus infection spread can be avoided. However, certain drawbacks, including long operative time, increased blood loss, massive trauma and high rate of complications, are noteworthy. In the past decade, searching for an optimized surgical approach has become the research focus.
XLIF, firstly proposed by Ozgur in 2006 [21], is one of the minimally invasive procedures for treatment of PLS. Primarily, it was used for treating lumbar degenerative disease, where advantages including little trauma, shorter operation time, less blood loss, faster postoperative recovery and fewer complications were verified [14, 15, 16]. Considering the ability of focus debridement under direct visualization, the application of XLIF has been expanded to treat PLS. Via a working channel passing through the psoas to the lateral side of target disc, this approach allows sufficient exposure of lesions located in the anterior and middle column, making complete debridement accessiable. This viewpoint has been proved by previous literature [17, 18, 19, 20]. In the present study, complete debridement was achieved in all cases and there was no recurrency, further confiming the feasibility of XLIF in treating PLS. Moreover, a large cage with lordosis (0–8 degrees) was placed into the intervertebral space intraoperatively, which was aimed to improve the sagittal alignment of spine and ensure sufficient decompression. Eventually, the global and segmental lumbar lordosis was significantly ameliorated. With the help of posterior instrumentation and the implanted cage, the stability reconstruction of spine was excellent. Besides, the symptoms were relieved immediately after surgery. Early postoperative ambulation (4.3 ± 2.4 days) was permitted and life quality was significantly improved.
Although satisfactory outcomes have been reported previously, few literature focused on the quantitative evaluation of indirect decompression. Clinical trials on treating lumbar degenerative disease with XLIF provide us with some insights. Oliveira et al. reported that the mean disc height, foraminal height, foraminal area and the central canal diameter increased by 41.9%, 13.5%, 24.7%, and 33.1% respectively in 21 cases [15]. Wang et al. found that the indirect decompression parameters were remarkably improved except for the central canal area [27]. However, PLS differs from the degenerative spinal diseases. The collapse and kyphosis are much severer due to the erosion and destruction of intervertebral space. Consequently, the fold of posterior longitudinal ligament and ligamentum flavum results in the spinal stenosis and the symptoms of nerve compression. So far, there is no report assessing the indirect decompression with regard to treating PLS with XLIF. In this study, all the indirect decompression parameters, including the disc height, foraminal height and area, central canal area and diameter, were improved postoperatively. At the final follow-up, VAS and ODI scores were notably reduced (P < 0.05) and the ASIA classification grades were improved with 100% excellent/good rate. Collectively, these findings suggested that for treating PLS, satisfactory indirect decompression results can be obtained from XLIF.
In spite of its superiority in safety, the application of XLIF is associated with certain complications. As reported by Rodgers, the overall incidence reached 6.2% in 600 cases, of which 2.5% were surgically related and 0.7% were postoperative transient nerve injury [16]. Knight declared that the incidence of major complications was 8.6% in 58 cases and path-related nerve irritation accounted for 3.4% [14]. In this study, paresthesia in the thigh or groin, hip flexion weakness, abdominal distension, urinary injury and cage subsidence were recorded, although the mobidity was low. Consitent with others, the most common complication was the transient paresthesia in the thigh /groin, which disappeared within 4–6 weeks postoperatively [14]. This could be attributed to intraoperative irritation of the lumbar plexus and psoas major. Besides, abdominal distension and constipation were primarily associated with nerve irritation and prolonged bed rest. Symptoms were alleviated within 1 week after symptomatic treatment. Cage subsidence primarily occured in patients with severe breakage of bilateral cortical bone and osteoporosis, and no related symptom was found.