The present study shows a significant pain reduction as well as improved QoL in surgically treated VO patients after 1 year. Improvement remained nearly constant over the 2-year observation time, but levels were markedly below QoL data published for general population. The 1-year mortality of 20% illustrates the severity and life-threatening nature of this clinical entity.
Although the optimal choice of therapy for this heterogeneous clinical entity cannot be uniformly determined, the goal of VO therapy is to cure the underlying infection to restore function and reduce pain. High-quality studies with information regarding the effectiveness of individual therapy options are lacking, especially considering that QoL is of particular importance for evaluating success, along with functional aspects [6, 20]. Even though conservative treatment is the choice for the majority of the patients, it can be estimated that 20–40% of affected patients will undergo surgery .
The current study is the first prospective evaluation of QoL and the mortality rates of surgically treated VO patients over a 2-year period.
The older patients and patients with comorbidities are particularly susceptible to this disease. In this study, the average age was 69 years, with 66% of patients being male. A pathogen was identified in 71% of cases, the most common pathogen being Staphylococcus aureus (49%). The lumbar spine was most often affected (56%). Baseline characteristics in this study were typical and did not differ from other studies [2, 3, 16]. Average hospital inpatient stay of 30–49 days was reported in the literature and confirmed with our average stay of 33 days . Recent retrospective evaluations of a Danish registry show the high mortality of this disease with rates of 20% and 21% in the first year after diagnosis [5, 9]. These findings were also reproduced in our patient collective with a total mortality of 23% over a 2-year follow-up. The course of our Kaplan–Meier curve mirrors Kehrer et al.’s hypothesis that VO shows a dramatic course especially in the first year because of its inflammatory nature in patients with multiple comorbidities . Our study shows not only a high overall mortality but a high 1-year mortality with 20%. The significantly lower mortality rate of 4% after the first year has also been confirmed by published reports. After the first year of disease onset, patients no longer die from the infection itself but from comorbidities [5, 8, 9, 21].
Retrospective studies have already suggested that the exclusive consideration of functional aspects (e.g., neurological deficits) in the treatment of VO is not sufficient to reflect the complexity of the disease. Further long-lasting negative effects such as pain and reduction in QoL even after healing should be considered . The available studies on QoL are mostly retrospective and primarily concerned with QoL comparison in patients undergoing surgery versus conservatively treated patients or between various operative strategies. Looking at these studies, there is a trend toward increased patient satisfaction and quality of life with surgical versus conservative treatment [12, 13]. In a comparison of operative versus conservative therapy for VO patients over 65, Sobottke et al.  found no significant differences in QoL scores of COMI, ODI, and SF-36. Nasto et al.  also compared both forms of therapy for VO (operative versus conservative) by using the QoL scores SF-12 and EQ-5D. They found increased satisfaction of patients who had undergone surgery, based on significantly higher QoL up to 6 months post-surgery. After another 3 months, this difference was no longer evident. The review article by Rutges et al.  points out that many fundamental aspects of VO therapy remain unclear because prospective long-term studies are lacking. They state that VO presents a dramatic clinical picture associated with high rates of orthopedic and neurological complications and significant worsening in QoL.
To the best of our knowledge, this is the first prospective study showing significant improvements in the QoL scores COMI, ODI, SF-36, and EQ-5D over the clinical course after successful surgical treatment of VO. The VAS values for back and/or leg pain were significantly reduced at 1 and 2 years compared to baseline values. In long-term follow-up (FU), i.e., 2 years after surgery, this was still observed for all parameters, although there was no significant difference between the first- and second-year values. A QoL plateau was reached that remained stable over the 2 years. However, despite the significant increase in QoL, values of the ODI, SF-36, and EQ-5D were below published values of both a general population and a chronic back pain population. These data coincide with the published retrospective reports. In 2008, O’Daly et al.  reported that the QoL of successfully treated VO patients was improved but remained significantly reduced compared to normal populations, regardless of whether they were treated conservatively or surgically.
In 2017, Dragsted et al.  first analyzed mortality and QoL using ODI and EQ-5D only in patients undergoing surgery. The 1-year mortality of 6.5% in that study is markedly less than the 1-year mortality in our study. The reason for this might be the lower average age of 60 years, but also the lower patient number (n = 65). This group also confirmed significantly reduced QoL for these patients compared to general population using the ODI and EQ-5D. All of the QoL data we collected showed significant improvements compared to baseline. VAS values for pain were significantly reduced. Our mean ODI values (T1 = 29 and T2 = 29) correspond to the retrospectively determined mean values in VO patients as reported in the literature . They are above the values of Fairbank et al.  for healthy patients and above those of Tonosu et al.  with an age-standardized cutoff value (ODI = 22) for restrictive back pain. Comparing the mean values of MCS and PCS of the SF-36 with those for an age-matched general German population published by Bullinger et al. , the mean PCS value (T1 = 50 and T2 = 45) is not only below the comparative value of a healthy person (PCS = 92) but also well below that of a back pain patient (PCS = 54). The mean MCS values (T1 = 43and T2 = 54) were also well below the mean value of a healthy person (MCS = 71), and at 2 years it was comparable with QoL of a back pain patient (MCS = 55). Also, the EQ-5D index value for the German general population (0.9) lies above our mean EQ-5D index values (T1 = 0.6 and T2 = 0.5) .
The strengths of the current study include a high number of patients, prospective design with a long FU over 2 years, and a “Lost to Follow-Up” (LFU) of only 9.7%, which is low for a clinical study. In addition to the back pain-specific QoL score ODI, we included the established QoL scores of SF-36/EQ-5D. A VAS was used to achieve adequate pain assessment. The ODI has high validity for severe illnesses, the SF-36 for moderately severe illnesses, and the EQ-5D for mild illnesses [22, 26,27,28]. In our opinion, the use of these appropriate tools enabled the successful capture of the entire QoL spectrum for this very heterogeneous patient population.
Limitations of this study may be a possible selection bias, since this is a tertiary care facility primarily treating referred complicated cases from other hospitals. Due to the high mortality in the first year, data from the most severe patients are missing. More pre- and postoperative factors (e.g. severity of neurological deficit, comorbidities, duration of antibiotics, extent of vertebral destruction, etc.) need to be collected prospectively to perform a subgroup analysis of the QoL scores in patients after surgical treatment for VO.