Vertebral Osteomyelitis: A Comparison of Associated Outcomes in Early Versus Delayed Surgical Treatment

INTRODUCTION

Vertebral osteomyelitis (VO) is a rare spine infection often developing from open spinal trauma, infections in adjacent anatomic structures, or hematogenous spread of bacteria or as a postoperative complication to spinal surgery.^1–4 Although VO remains uncommon, with yearly rates of 5 to 20 cases per million in the United States, its incidence is increasing.^3,5–7 This is believed to be attributed to the increase of patients with advanced age, diabetes mellitus, chronic renal or liver disease, intravenous drug use, HIV infection, chronic corticosteroid use, chemotherapy, and severe trauma—all predisposing factors to VO.^8,9 Since 1974, the incidence has nearly doubled from 0.2 to 2 cases per 10 000 hospital admissions to 2 to 3 cases per 10 000 hospital admissions,^10–12 with a 20-fold-higher incidence in older patients.¹³ If left untreated, VO can lead to irreversible spinal cord injury, deformity, neurologic deficits, septicemia, and mortality (mortality rates ranges 4%–29%).^4,14 VO is traditionally treated conservatively with antimicrobial therapies, but up to 40% to 50% of VO patients suffering will eventually require surgical intervention.^4,15

VO surgical intervention is indicated when patients express progressive loss of motor and/or neurological functions, cauda equine syndrome, progressive deformities, spinal instability, abscess formation, and delayed diagnosis. Failure of conservative treatment categorized as persistent pain, residual neurologic deficits, and systemic inflammation/infection also warrants surgical intervention. While clinicians have agreed on surgical indications for VO, a persistent area of controversy is the optimal timing of surgery that most benefits the patient.¹⁴ Prior studies report conflicting findings: Ghobrial et al¹⁶ in 2014 and Connor et al¹⁸ in 2013 reported a relative advantage to earlier surgical intervention with regard to discharge neurological status, while Adogwa et al¹⁷ in 2014 and Karikari et al¹⁰ in 2009 reported no statistical benefit from early surgical intervention on postoperative outcomes. While these studies present relative insight into the timing of surgical intervention, they are limited by small sample sizes (82–104 patients), minimal subgroup analysis, and institutional bias.

This study evaluates the outcomes of early (< 24 hours) versus delayed surgical treatment of VO using a large nationwide inpatient database. Our study also aimed to investigate the demographics, comorbidities, socioeconomics, and prevalence of multiple complications associated with variant surgical timing of the VO patient population.

MATERIALS AND METHODS

RESULTS

Trends of Surgical Timing

Since 1998, the incidence of patients undergoing surgical treatment has drastically increased. In 1998, 1243 patients underwent surgical intervention. Since then, there has been an incremental increase to 3155 patients undergoing surgical treatment in 2013. The prevalence of VO patients undergoing same-day-admission surgeries decreased from 61.5% in 1998 to 42.5% in 2013, while the prevalence of VO patients undergoing surgical delays has increased. In 1998, patients with 3 to 6 days of surgical delay had a rate of 8.4%, which increased to 17.7% in 2013 (Figure 1). Of all years examined, 2013 showed the highest prevalence of patients undergoing surgery with a 1-day delay (14%), 2-day delay (9.2%), and 3- to 6-day delay (17.7%) (Figure 1).

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Figure 1

Trends in same-day surgeries and surgical delays for vertebral osteomyelitis (VO) patients from 1998 to 2013. The y-axis percentages represent the prevalence of patients in a specified surgical group in relation to the total amount of surgical VO patients for each corresponding x-axis year.

DISCUSSION

Trends over the past 2 decades have shown a progressive increase of incidence in VO.^3,5–7 Elderly patients are particularly at risk,¹³ and with the US annual increase in life expectancy,²⁰ VO has become an increasingly relevant concern for health care providers. VO's high operative and mortality rates^4,14,15 pose a need for more information concerning surgical treatment and perioperative outcomes. Currently, the recommended timing of surgical intervention for VO patients is very controversial.

This study found that VO patients who underwent surgery after 24 hours of admission had higher chances of mortality, being discharged with an impaired neurologic status, and having any type of perioperative complication. Specifically, there were higher rates of sepsis, anemia, and recurrent infection in surgically delayed patients. These patients were also more likely to have a combined anterior-posterior surgery and less likely to undergo an anterior approach. Surgeries were more likely to be performed at the thoracic than cervical level in surgically delayed patients. Demographically, our results indicate that surgically delayed VO patients were more likely to be older, male, black or Hispanic, and on Medicare or Medicaid and to have increased total hospital charges. Patients experiencing surgical delays predictably had higher Deyo-Charlson scores and increased comorbidity rates. While the Deyo-Charlson score was shown to be a significant predictor of adverse outcomes, controlled regression models showed that surgical delay of any degree most greatly predicted mortality, impaired neurologic status, and the chance of developing any complication. This reduces the confounding nature of the association between the Deyo-Charlson score and surgical delay, further justifying our findings.

This study is the first to review a large VO cohort, derived from a nationwide database, to delineate associated effects of surgical delay. Comparatively, the majority of papers investigating surgical indications and treatment outcomes for VO patients have cohorts ranging between 10 and 300 patients. Previous studies by Miller et al,²¹ Adogwa et al,¹⁷ Kothari et al,²² Arnold et al,²³ and Mavrogenis et al²⁴ all had cohort sizes of 50, 82, 16, 94, and 13 patients, respectively. Of the few studies that did use large database cohorts, such as Akiyama et al²⁵ (n = 7118), none investigated the effects of delayed surgical treatment. Previous studies focusing on the timing of surgical intervention, such as Ghobrial et al,¹⁶ reported that surgical evacuation of abscess within 24 hours of admission showed a relative advantage to discharge neurologic grade in comparison to delayed surgical patients. The findings of Connor et al¹⁸ strongly support immediate surgical decompression, combined with appropriately tailored antibiotic therapy for optimal neurologic outcomes. Alternatively, studies such as those by Karikari et al¹⁰ and Adogwa et al¹⁷ reported no benefit to early surgical intervention for abscess removal.

Despite the controversial nature of our findings, the mortality rates presented in our cohort (which range between 0.3% and 5.5%) seem to be relatively more consistent than the majority of reports in the literature. Akiyama et al,²⁵ McHenry et al,²⁶ Grammatico et al,⁷ Hutchinson et al,²⁷ and Mylona et al¹ reported in-hospital mortality rates of 6%, 11%, 3%, 27%, and 6%, respectively. The slightly lower rates observed in our cohort may be an implication of our VO patient population being limited to surgical candidates only. Miller et al²¹ (n = 50) reported a mortality rate of 2% within the 30-day postoperative period, while Matsui et al²⁸ (n = 38) reported a postoperative mortality rate of 0%.

For the majority of patients, anterior vertebral elements are most commonly involved with infection, while posterior elements are affected mainly in patients with advanced infection. In general, most authors advocate anterior procedures for extensive disc and vertebral body debridement in that early surgical patients, who may be in better health and of higher bone quality, may not need the additional stabilization provided by the posterior approach.⁵ Arnold et al²³ observed that in patients with successful surgical treatments, 32% had an anterior approach, 24% had a posterior approach, and 44% had a combined approach. Pourtaheri et al²⁹ observed that in patients with instrumented surgical treatment, 58% had an anterior approach, 13% had a posterior approach, and 29% had a combined approach. While our rates for the anterior approach seem to align with previous literary reports, our high posterior-approach rates seem to be discrepant. This may be explained by the belief that the posterior approach is associated with fewer overall postoperative complications³⁰ regardless of higher wound infection rates.³¹ Cohort size differences and/or surgeon preference of smaller studies may also be to blame. Our data also showed that combined surgical approach rates incrementally increased with further delay of surgery. This may be attributed to the complexity of the procedure that typically requires a 2-stage operation with extensive planning.¹⁴

We also found a higher prevalence of surgically delayed VO patients with Medicare and Medicaid insurance. Previous studies have indicated that patients on Medicaid have a hindered access to health care,³² longer and more costly hospitalizations,³³ and higher rates of delayed cancer diagnosis, resulting in higher mortality rates,^34,35 and are less likely to receive cancer-directed surgery³⁶ in comparison to privately insured patients. If these trends hold true for patients with VO, delay of diagnosis and health care providers' reluctance to provide surgical care is extremely detrimental to a patient suffering from VO. Timely diagnoses and earlier surgical care may reduce inpatient length of stay, decrease total hospital costs, lower mortality rates, and improve a patient's overall quality of care. Effectively, Furlan et al³⁷ provided an economic cost-utility analysis for patients undergoing early versus delayed surgical spinal cord decompression. They found that early surgical decompression was more cost effective and resulted in improved patient's quality of life in comparison to delayed surgical decompression.

Information is needed with regard to the causative factors that are at play in patients receiving surgical treatment for VO. While the NIS is one of the largest health care databases available, there are confounding variables that are neither identifiable nor controlled for. For example, patient frailty may play a significant role in surgical decision making and influence the decision to delay a surgical procedure. While frailty indexes have been developed for other large databases, such as the National Surgical Quality Improvement Program,³⁸ to the best of our knowledge, no previous frailty measures have been validated for use on the NIS, most likely due to a lack of specificity among clinical metrics. The use of ICD-9 codes also limits our ability to determine causation of outcomes. Further, the NIS includes only inpatient data, without outpatient claims, follow-up, and patient-reported outcomes. This is an important limitation to consider, specifically with the usage of the Deyo-Charlson Index. The Deyo-Charlson Index, which includes only data from the inpatient setting, may not include important comorbidities that are recorded on outpatient claims, creating a misrepresentation of a patient's true comorbidity severity.³⁹ The NIS database also lacks specific information regarding the patient's clinical course and operation. Finally, this paper does not detail the varying organisms responsible for infection, which may have a profound effect on outcomes. Further information on patient history, clinical course, and follow-up outcomes is needed to create a complete understanding with regard to the management of VO.

CONCLUSION

This study explores the associated effects of surgical delays in patients with VO. Using a nationwide database, the prevalence of various outcomes in VO patients who underwent early versus delayed surgical procedures was compared. Patients with surgical delays were more likely to have higher mortality rates, develop any complication, or discharge with neurologic deficits. Surgically delayed patients were also more likely to have a greater length of stay and higher total hospital charges. Medically fit patients may benefit from earlier surgical management in order to reduce risk of postoperative complications, improve outcomes, and reduce overall hospital costs.