Vertebral Osteomyelitis After Spine Surgery

In This Article

Abstract and Introduction

Abstract

Study Design: Prospective cohort study.

Objective: We aimed to determine the 2-year survival and to identify clinical and microbiological characteristics of patients with native vertebral osteomyelitis (VO) as compared to postoperative VO to find further strategies for improvement of the management of VO.

Summary of Background Data: A relevant subgroup (20%–30%) of patients with VO has a history of spine surgery. Infection in these patients might be clinically different from native VO. However, clinical, microbiological, and outcome characteristics of this disease entity have not been well studied as most trials either excluded these patients or are limited by a small cohort and short observation period.

Methods: Between 2008 and 2013, patients who presented at a tertiary care center with symptoms and imaging findings suggestive of VO were reviewed by specialists in infectious diseases, clinical microbiology, and orthopedics to confirm the diagnosis and followed prospectively for a period of 2 years. Statistical analysis for group comparisons, survival analysis, and uni- and multivariable Cox regression models were performed.

Results: Thirty percent of the patients with VO (56/189) reported a history of spine surgery in the same segment. Patients with postoperative infection had a lower ASA score (American Society of Anesthesiologists) (P = 0.01) and were less likely to suffer from comorbidities compared to native cases (P = 0.003). Infections caused by coagulase-negative staphylococci (33.3 vs. 6.5%, P < 0.001) and other bacteria of the skin flora (15.2 vs. 0%, P = 0.002) were more prevalent in postoperative patients. Suffering from native VO increased the 2-year mortality risk 3-fold, also when adjusted for the remaining risk factors ASA score and number of comorbidities (hazard ratio 2.916 [95% confidence interval 1.215 –6.999], P = 0.017).

Conclusion: Beside clear microbiological differences, the significant better 2-year survival supports the concept of postoperative VO presenting a distinct disease entity. The subtle disease presentation of patients with postoperative VO should not attenuate clinical suspicion of physicians.

Level of Evidence: 3

Introduction

Infections of the vertebrae and intervertebral disc—known as pyogenic vertebral osteomyelitis (VO) or spondylodiscitis—are rare. The increasing incidence of VO during the last years^[1,2] might be attributed to an ageing society with chronic debilitating diseases, a growing number of immunocompromised individuals, and invasive medical procedures as well as to a higher diagnostic awareness and yield.^[1–3]

A relevant subgroup of 20% to 30% of patients with VO has a history of previous spine surgery.^[4,5] Although native vertebral osteomyelitis (NVO) is typically the result of hematogenous spread of pathogens from a distant infectious focus, the direct inoculation of pathogens and a spread of infection per continuitatem seems to be the more relevant pathogenetic mechanism in patients with postoperative vertebral osteomyelitis (PVO).^[3–5] Furthermore, infection in these patients is more likely to be caused by coagulase-negative staphylococci^[3–8]—a fact prompting that other disease characteristics might also differ.

However, most reports addressing VO either excluded patients with a history of spine surgery, mix them with patients with post-traumatic infection or are limited by a small cohort and short observation period.^[4,5,9] Controversy especially exists over the outcome in these patients ranging from a good prognosis^[10] to severe and long-lasting disability.^[11]

The goal of this study was to determine the 2-year survival and to identify clinical and microbiological characteristics of patients with native as compared to postoperative VO to find further strategies for improvement of the management of VO.

Table 1. Patient Baseline Characteristics
	All n = 189	Surgery and Infection in the Same Segment (PVO) n = 56	Native Vertebral Osteomyelitis (NVO) n = 131
	Median (IQR)	Median (IQR)	Median (IQR)	P
Age, y	69 (59–77)	68 (55 –74)	70 (62–78)	0.080
Length of hospital stay, days	29 (20–40)	26 (21 –35)	30 (20–42)	0.156
BMI, kg/m² (n = 159)	26 (23–29)	26.4 (24 –29)	25.8 (22–30)	0.382
	n (%)	n (%)	n (%)
Male sex	117 (62)	38 (67.9)	78 (60)	0.326
Comorbidities (n)				0.003*
0	99 (52)	40 (71)	58 (44)
1	62 (33)	14 (25)	48 (37)
2	22 (12)	2 (4)	19 (15)
3	6 (3)	0 (0)	6 (5)
Autoimmune disease	18 (10)	5 (9)	13 (10)	>0.999
Diabetes mellitus	38 (20)	5 (9)	33 (25)	0.010**
Immunosuppression	2 (1)	0 (0)	2 (2)	>0.999
Intravenous drug abuse	6 (3)	0 (0)	6 (5)	0.181
Liver cirrhosis	2 (1)	0 (0)	2 (2)	>0.999
Malignancies	39 (21)	5 (9)	33 (25)	0.010**
Renal Insufficiency	19 (10)	3 (5)	15 (12)	0.281

BMI indicates body mass index; IQR, interquartile range.
*P ≤ 0.01.
**P &le 0.05.

Table 2. Disease Presentation
	No Data n	All n = 189	Surgery and Infection in the Same Segment (PVO) n = 56	Native Vertebral Osteomyelitis (NVO) n = 131
		n (%)	n (%)	n (%)	P
Symptoms
Fever >38°C	17	24 (14)	5 (10)	19 (16)	0.469
Back pain	0	187 (99)	54 (96)	131 (100)	0.089
Leg pain	1	78 (41)	26 (46)	51 (39)	0.418
Neurological deficit	4	58 (32)	18 (32)	40 (31)	0.864
Abscess formation
Epidural	0	30 (16)	8 (14)	21 (16)	0.829
Paravertebral	0	22 (12)	11 (20)	11 (8)	0.045*
- psoas	0	39 (21)	12 (21)	27 (21)	>0.999
No. of spinal levels involved	0			0.494
1	0	130 (69)	41 (73)	89 (68)
≥2	0	57 (30)	15 (27)	42 (32)
Duration of symptoms until diagnosis	20				0.103
<1 mo		40 (24)	4 (7)	36 (32)
1–2 mo		39 (23)	14 (26)	25 (22)
3–6 mo		55 (33)	20 (37)	35 (31)
7–12 mo		12 (7)	7 (13)	5 (4)
13–24 mo		5 (3)	3 (6)	2 (2)
>24 mo		16 (8)	6 (11)	10 (9)
ASA score¹	4				0.01*
1		10 (5)	5 (9)	5 (4)
2		56 (30)	22 (39)	33 (26)
3		100 (54)	26 (46)	73 (58)
4		16 (9)	2 (4)	14 (11)
5		3 (2)	1 (2)	2 (2)
		All n = 189	Surgery and infection in the same segment (PVO) n = 56	Native vertebral osteomyelitis (NVO) n = 131	p-value
Management	0				0.683
Conservative treatment (antibiotics only)		35 (19)	9 (16)	26 (20)
Surgical treatment (and antibiotics)		154 (81)	47 (84)	105 (80)
		Median (IQR)	Median (IQR)	Median (IQR)
Antimicrobial therapy in days	0	98 (63 –115)	101 (71– 111)	98 (70 –116)	0.723

ASA score indicates American Society of Anesthesiologists; IQR, interquartile range.
*P ≤ 0.05

Table 3. Microbiological Characteristics
	Culture-positive Patients n = 112 (59%)	Surgery and Infection in the Same Segment (PVO) - Culture-positive Cases Only n = 33	Native Vertebral Osteomy- elitis (NVO) - Culture-positive Cases Only n = 77
	n (%)	n (%)	n (%)	P
Staphylococcus aureus	56 (50)	10 (30)	45 (58)	0.012*
Coagulase-negative staphylococci	17 (15)	11 (33)	5 (7)	<0.001**
Gram-negative bacteria	12 (11)	2 (6)	10 (13)	0.505
Skin flora bacteria^† (other than staphylococci)	5 (5)	5 (15)	0 (0)	0.002**
Streptococcus species	5 (5)	1 (3)	4 (5)
Mycobacterium tuberculosis complex	5 (5)	1 (3)	4 (5)
Others^‡	12 (11)	3 (9)	9 (12)

*P ≤ 0.05.
**P ≤ 0.01.
^†Skin flora bacteria: Propionibacterium acnes (n = 4) and Corynebacterium simulans (n = 1).
^‡Others: Enterococcus faecalis (n 5), Brucella melitensis (n = 2), Peptococcaceae (n = 1), Candida albicans (n = 1), Bacteroides fragilis (n = 1), Fusobacterium nucleatum (n = 1), Abiotrophia defectiva (n = 1).

Table 4. Multivariable Cox-Regression for 2-year Mortality Risk
Multivariable Cox-Regression for 2-year Mortality Risk
	Hazard Ratio	95% CI for Hazard Ratio		P
		Lower	Upper
Native vs. postoperative VO	2.916	1.215	6.999	0.017*
ASA score (continuous)	2.791	1.852	4.206	<0.001**
Number of comorbidities				0.026 (Overall)*
1 vs. 0	1.985	1.022	3.854	0.043*
>1 vs. 0	0.701	0.261	1.879	0.480

CI indicates confidence interval.
*P ≤ 0.05.
**P ≤ 0.01.

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Vertebral Osteomyelitis After Spine Surgery

A Disease With Distinct Characteristics

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