Minimally invasive spine surgery in lumbar spondylodiscitis: a retrospective single-center analysis of 67 cases

The incidence of spondylodiscitis is increasing due to an aging population, immune-compromising diseases, and frequent spine procedures [1]. It is a life-threatening and serious disease with high mortality rates [2]. Surgery for lumbar spondylodiscitis is indicated for neurological deficits, instability, deformity, medically intractable pain, or disease progression [3, 4]. The surgical goal in lumbar spondylodiscitis is the debridement of infection, identification and reduction of pathogens, stabilization of deformed and instable segments, and decompression of neural structures [3‐7].

Lumbar pedicle screw fixation with transforaminal lumbar interbody fusion (TLIF) is an established, safe, and effective surgical technique in patients with infective spondylodiscitis. It provides an adequate surgical debridement and enables immediate stabilization, if necessary [6]. Nevertheless, open pedicle screw fixation with TLIF is an invasive surgical intervention that may be associated with several risks [8]. Therefore, minimally invasive techniques have been developed for degenerative diseases and have been applied in infected cases to minimize tissue damage, reduce narcotic requirements, decrease blood loss, and, therefore, potentially avoid prolonged immobilization [9‐12]. This is of great interest especially in spondylodiscitis patients who frequently suffer from severe comorbidities.

Thus, the purpose of the present retrospective study was to detect the safety and efficacy of a minimal invasive posterior approach with transforaminal lumbar interbody debridement and fusion plus pedicle screw fixation in lumbar spondylodiscitis in comparison to an open surgical approach. Based on these data, treatment decisions tailored to the patient´s general condition were analyzed.

A retrospective review of patients who underwent surgical treatment for lumbar spondylodiscitis at our department was performed. 67 consecutive patients were identified between 2000 and 2016 and their data were retrospectively investigated. The patients were categorized into two groups based on the operative procedure: group (MIS) minimally invasive lumbar spinal fusion; group (OPEN) open lumbar spinal fusion. The two groups were compared at the time of initial diagnosis, the day of admission, on the third postoperative day, before discharge, and after 3 month follow-up. Data were collected using the patients´ health records and magnetic resonance imaging (MRI). MRI was read by an independent neuroradiologist, blinded to the patients´ clinical data. C-reactive protein (CRP), hemoglobin, and complete white cell count were analyzed routinely. Patients with neurological deficits, progressive pain, or progression on MRI despite conservative treatment underwent surgical treatment. Each treatment option was accompanied by broad spectrum antibiotic therapy or antibiotics according to the antiobiogram when available. Patients were treated with intravenous broad spectrum antibiotics for 2–6 weeks followed by oral antibiotics for a total period of 3 months.

The demographic details and patients’ characteristics are presented in Table 1. Sixty-seven consecutive patients who underwent lumbar fusion surgery for lumbar spondylodiscitis have been identified between 2000 and 2016 and their data were retrospectively investigated. Thereby, the proportion of patients who underwent minimal invasive surgery was 28.4% (group MIS, n = 19) versus 71.6% (group OPEN, n = 48) with open surgical procedures. Altogether, 43 (64.2%) patients were female. The most common ASA score was ASA 3° in the OPEN group, whereas ASA 2° and 3° have been mostly detected in MIS group (p > 0.05). There have been no differences in comorbidities or addiction between groups (p > 0.05).

Preoperative MRI showed higher rates of paraspinal abscess (35.5 vs. 5.6%, p = 0.016) and multilocular location in the OPEN group (20 vs. 0%, p = 0.014). There were trends that epidural abscesses and paraspinal enhancement occurred more frequently in the OPEN group than in the MIS group, but this was not statistically significant (p > 0.05). No differences could be revealed in disc or vertebral bone destruction between the two groups (p > 0.05) (Fig. 2). Mean disc height of the affected discs was 5.8 ± 2 mm in the OPEN group and 5.3 ± 2 mm in the MIS group (p > 0.05).

1.8 ± 1 lumbar levels in the OPEN group and 1.3 ± 0.8 levels in the MIS group were fused (p > 0.05). The intraoperative amount of blood transfusion was higher in the OPEN group (472.3 ± 555 vs. 110.5 ± 205 ml, p = 0.015). No differences occurred in duration of surgery between the two groups: OPEN 208.8 ± 86 min vs. MIS 173.4 ± 71 min (p > 0.05).

CRP and leucocytes differed significantly preoperatively (p < 0.05; Fig. 3). Overall pain at discharge was less in the MIS group: NRS 2.4 ± 1 vs. NRS 1.6 ± 1 (p = 0.036). No differences were present after 3 months follow-up (p > 0.05). 51.1% in the OPEN vs. 18.8% in the MIS cohort suffered from a motor deficit at first diagnosis (p = 0.026). For more details, see Fig. 4. The hospital stay was longer in the OPEN than the MIS group (19.1 ± 12 vs. 13.7 ± 5 days, p = 0.018). No differences occurred in postoperative complications (Table 2).

The authors present a retrospective study comparing patients with lumbar spondylodiscitis that underwent either a minimally invasive or an open transpedicular lumbar spinal fusion. Motor deficits were more common as well as higher inflammatory blood values could be detected in patients in which the open approach was performed. Patients who underwent minimally invasive spine surgery showed less pain at discharge. After 3 months of follow-up, improvement of pain and motor function was equally distributed in both groups.

Lumbar pedicle screw fixation with transforaminal lumbar interbody fusion (TLIF) is an established, safe, and effective surgical technique in patients with infective spondylodiscitis. It provides an adequate surgical debridement and enables immediate stabilization, if necessary [6]. However, a TLIF is still associated with major risks, especially in elderly or immunocompromised patients and patients with multiple comorbidities [8]. Thus, minimally invasive surgical techniques have been developed to avoid and reduce tissue damage. The treatment goal of MIS in lumbar spondylodiscitis is to decrease muscle crush injuries during retraction and to avoid disruption of the osseotendinous complex of the paraspinal muscles. In addition, although MIS uses a smaller skin incision, adequate surgical debridement is necessary to achieve good clinical results [6, 12].

An appropriate access to the spinal canal was attained in both surgical techniques. When a medial facet resection was done to decompress the ipsilateral side of the spinal canal, a hemilaminectomy could be performed. Furthermore, if the tube was angled toward the contralateral side, the contralateral side of the spinal canal could also be reached [14]. Epidural abscess formation was detected on preoperative MRI in both groups and could be removed adequately by the surgical technique mentioned above.

According to the recent published literature [15], no differences were found in the duration of surgery in our study population. These results are likely attributed to the local surgical expertise. Minimal invasive surgery for spondylodiscitis in our department is exclusively undertaken by neurosurgeons who are already experienced with tubular surgical techniques for lumbar decompression. Nevertheless, in the MIS group, the percentage of misplaced screws was 5.3%, which may due to the loss of visual anatomic landmarks and reduced tactile feedback [16].

Patients who underwent MIS showed significantly lower pain scores at discharge compared to patients undergoing the open surgical technique, whereas no differences could be revealed 3 months after surgery. The differences between groups found proved to be statistically significant, but do not seem to be clinically relevant according to the recent literature on the minimal clinical important difference of NRS [17].

Furthermore, titanium cages were preferably used in our study group to achieve adequate stability and to avoid pseudoarthrosis. Titanium has been successfully proven to provide sufficient resistance to microbial adherence and showed good radiological results in pyogenic spondylodiscitis [18, 19]. Poly-ether-ether-ketone (PEEK) cages as biocompatible alternatives to titanium implants have been used in spinal fusion surgery, but still have been an issue of debate in pyogenic spondylodiscitis. Recent published data could show favorable results on the application of PEEK cages, but prospective randomized controlled trials are lacking [20, 21].

There is still controversy regarding the indication of MIS in lumbar spondylodiscitis. Decision-making is predominantly based on the individual surgeon´s preference and skill. In our study group, the open procedure was favored especially in patients with abscess formation and in the presence of a motor deficit, whereas comorbidities or age did not seem to influence a surgeon’s treatment decision. In severe cases with high inflammatory values, surgery was performed earlier in the infectious cascade. In addition, the delay from the first diagnosis until surgery was significantly shorter in the OPEN group. These facts may be contributed to the evidently sicker patients in this group. On the contrary, the levels to be treated did not seem to influence the decision for an open or minimal invasive surgery.

Additional studies with greater patient numbers are required for definitive confirmation. However, beside the low number of patients, we have to mention the retrospective character of our study results and the short follow-up period as further limitations.

Both the MIS and the open technique were used in this retrospective study. The patients who were treated by the open approach were evidently sicker. Less postoperative pain before discharge was detected in the MIS group. The open technique is effective in all varieties of spondylodiscitis inclusive in epidural abscess formation. MIS can be applied safely and effectively as well in selected cases, even with epidural abscess. Nevertheless, prospective randomized controlled clinical trials will be mandatory to develop evidence-based treatment recommendations.