Postprocedural discitis of the vertebral spine: challenges in diagnosis, treatment and prevention

Optimal microbiological sampling for the diagnosis of osteoarticular infection

Infection is a dire complication afflicting every field of orthopaedics and traumatology. If specific clinical, laboratory and imaging parameters are present, infection is often assumed even in the absence of microbiological confirmation. However, apart from confirming infection, knowing the exact infecting pathogen(s) and their antimicrobial susceptibility patterns is paramount to help guide treatment. Every effort should therefore be undertaken with that goal in mind.Not all microbiological findings carry the same relevance, and knowing exactly how and where a sample was collected is key. Several different sampling techniques are available, and one must be aware of both advantages and limitations. Microbiological sampling alternatives in some of the most common clinical scenarios such as native and prosthetic joint infections, osteomyelitis and fracture-related infections, spinal and diabetic foot infections will be discussed.Orthopaedic surgeons should also be aware of basic laboratory sample processing techniques as they have a direct impact on the way specimens should be dealt with and transported to the laboratory. Only by knowing these basic principles will surgeons be able to participate in the multidisciplinary discussion and decision making around how to interpret microbiological findings in each specific patient. Cite this article: EFORT Open Rev 2021;6:390-398. DOI: 10.1302/2058-5241.6.210011.

Microbiologic Diagnosis of Pyogenic Spondylitis

Pyogenic spondylitis requires long-term antibiotics treatment and identification of the etiologic microorganism is essential. The first test in the microbiologic diagnosis of pyogenic spondylitis is a blood culture. Any microorganisms that grow in blood culture are highly likely to be the etiological microorganisms of pyogenic spondylitis. If the microbial etiology cannot be defined by the blood culture, a needle biopsy is performed on the inflamed tissues. Here, it is recommended that paraspinal tissues, rather than spinal tissues, are collected to increase the positive rate in tissue culture. If the microbial etiology cannot be defined by the first needle biopsy, another needle biopsy may be performed. The collected tissue sample is used in culture tests on bacteria and mycobacteria as well as pathological tests. If tuberculous spondylitis is suspected, polymerase chain reaction is carried out to detect Mycobacterium tuberculosis. In the case that the etiological microorganisms cannot be identified, the data of the patient regarding age, sex, vertebrae involved, history of spinal surgery or procedure, previous or concurrent urinary tract or intra-abdominal infection are analyzed. Based on this the most probable microbial etiology is determined to select the antibiotics to be used in the empiric treatment.

Clinical presentation and diagnosis of acute postoperative spinal implant infection (PSII)

Acute postoperative infections after surgical interventions on the spinal column are associated with prolonged treatment duration, poor patient outcomes, and a high socioeconomic burden. In the field of joint replacement, guidelines have been established with recommendations for the diagnosis and treatment of such complications, but in spinal surgery there are no definitions permitting distinction between early and late infections and no specific instructions for their management. Various factors increase the risk of acute postoperative infection, including blood transfusions, leakage of cerebrospinal fluid, urinary tract infection, injury of the dura mater, an American Society of Anesthesiologists (ASA) score >2, obesity, diabetes mellitus, and surgical revision. We suggest defining all infections occurring within the first 4 weeks after spinal surgery as early infections. The symptoms are pain at rest, on motion, and/or pressure pain, abnormal warmth, local erythema, circumscribed swelling of the wound, and newly occurring secretion. Together with laboratory parameters such as C-reactive protein (CRP) and leukocytes, a central role is played by imaging in the form of magnetic resonance imaging (MRI), although diagnosis can be hampered by the presence of postoperative fluid collections such as edema or hematoma or by artifacts from an implant. Once an infection has been confirmed, immediate wound revision with debridement and rinsing (sodium hypochlorite) is essential. Intraoperatively it may prove advantageous to use jet lavage and administer vancomycin. We recommend leaving the implant in place in cases of acute postoperative infection. Patients who are not conditional for surgery can first receive antibiotic suppression treatment before surgery at a later date. In such cases initial computed tomography (CT)-guided aspiration or drain insertion can take place.

Rabbit model of Staphylococcus aureus implant-associated spinal infection

Post-surgical implant-associated spinal infection is a devastating complication commonly caused by Staphylococcus aureus. Biofilm formation is thought to reduce penetration of antibiotics and immune cells, contributing to chronic and difficult-to-treat infections. A rabbit model of a posterior-approach spinal surgery was created, in which bilateral titanium pedicle screws were interconnected by a plate at the level of lumbar vertebra L6 and inoculated with a methicillin-resistant S.aureus (MRSA) bioluminescent strain. In vivo whole-animal bioluminescence imaging (BLI) and ex vivo bacterial cultures demonstrated a peak in bacterial burden by day 14, when wound dehiscence occurred. Structures suggestive of biofilm, visualized by scanning electron microscopy, were evident up to 56 days following infection. Infection-induced inflammation and bone remodeling were also monitored using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) and computed tomography (CT). PET imaging signals were noted in the soft tissue and bone surrounding the implanted materials. CT imaging demonstrated marked bone remodeling and a decrease in dense bone at the infection sites. This rabbit model of implant-associated spinal infection provides a valuable preclinical in vivo approach to investigate the pathogenesis of implant-associated spinal infections and to evaluate novel therapeutics.

Summary: A model of post-surgical methicillin-resistant Staphylococcus aureus implant-associated spinal infection was created in rabbits, recapitulating acute infection as well as chronic low-burden infection, with structures suggestive of biofilm formation and bone remodeling.

Comparison of pyogenic postoperative and native vertebral osteomyelitis

BACKGROUND CONTEXT

Postoperative vertebral osteomyelitis (PVO) after spinal surgery is a clinical challenge. However, there is a paucity of evidence regarding the most likely etiologic organisms to guide the choice of empirical antibiotic therapy, and previous reports of treatment outcomes for PVO are scarce.

PURPOSE

To compare the microbiology, clinical characteristics, and outcomes of pyogenic PVO with native vertebral osteomyelitis (NVO).

STUDY DESIGN

Retrospective comparative study.

PATIENT SAMPLE

Patients with microbiologically proven vertebral osteomyelitis from three university-affiliated hospitals in South Korea between January 2005 and December 2015 with follow-up of at least 12 months after completion of antibiotics or until the patient was transferred. Patients who had a spine operation in the same location within 1 year of diagnosis, and all patients with remnant implants at the time of the vertebral osteomyelitis diagnosis, were defined as having PVO. The remainder of the patients was considered to have NVO. Spinal operations included discectomy, laminectomy, arthrodesis, and instrumentation for stabilization of the spine.

OUTCOME MEASURES

Overall mortality, neurologic outcomes, treatment failure, and relapse of infection.

METHODS

Demographic data, comorbidities, presenting symptoms, microbiological data, radiographic characteristics, laboratory data (including white blood cell counts, erythrocyte sedimentation rate, and C-reactive protein), surgical treatment, and neurologic outcomes for each patient were reviewed from electronic medical records and analyzed. Mortality rate, treatment failure, and relapse of infection were calculated for the two groups. Factors associated with treatment outcome were evaluated using univariate and multivariate logistic regression analyses.

RESULTS

The study evaluated 104 patients with PVO and 441 patients with NVO. In PVO, the most common isolate was Staphylococcus aureus (34%, n=35), followed by coagulase-negative staphylococci (31%, n=32). In NVO, the most common isolates were S. aureus (47%, n=206) and streptococci (21%, n=94). Of the staphylococci, the proportion of methicillin-resistant strains was significantly higher in PVO than that in NVO (75% vs. 39%, p<.001). The proportion of patients with gram-negative bacilli was 14% in PVO and 20% in NVO. Pre-existing or synchronous nonspinal infection was observed more frequently in NVO than in PVO (33% vs. 13%, p<.001). Although the duration of antibiotic use was similar in both groups, surgery for infection control was performed more frequently in PVO. The mortality rate was similar in both groups. However, the treatment failure and relapse rates at 12 months were higher in the PVO group (23% vs. 13%, p=.009; 14% vs. 7%, p=.028, respectively). Methicillin-resistant S.aureus was significantly associated with treatment failure or relapse via logistic regression (odds ratio 3.01, 95% confidence interval [1.71-5.32], p<.001; odds ratio 2.78, 95% confidence interval [1.40-5.49], p=.003).

CONCLUSIONS

Coverage of methicillin-resistant staphylococci should be considered when prescribing empirical antibiotics for PVO. Although surgery was performed more often in PVO than NVO, the treatment failure and relapse rates at 12 months were higher in PVO.

Postoperative Surgical Site Infection After Spine Surgery: An Update From the Scoliosis Research Society (SRS) Morbidity and Mortality Database

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

Analyze the Scoliosis Research Society (SRS) Morbidity & Mortality (M&M) database to assess the incidence and characteristics related to postoperative surgical site infection (SSI) after spinal deformity surgery.

SUMMARY OF BACKGROUND DATA

Infections involving spinal instrumentation are associated with greater rates of disability. Rates of postoperative SSI after spinal deformity surgery range from 1.9% to 4.4%. Postoperative SSI rates of 4.2% for adult kyphosis, 2.1% for adult spondylolisthesis, and 3.7% for adult scoliosis have been reported.

METHODS

The SRS M&M database was evaluated to define patient demographics, perioperative factors, and infection characteristics of spinal deformity patients with postoperative spine infections after deformity surgery in 2012.

RESULTS

Of the 47,755 procedures reported to the SRS in 2012, there were 578 (1.2%) diagnosed SSIs. Infection rates for patients with kyphosis were significantly higher compared with patients with scoliosis (2.4% vs. 1.1%, p < .0001) or spondylolisthesis (2.4% vs. 1.1%, p < .0001). Spinal fusions were performed in 86.3% of patients, 75.1% of which were performed posteriorly. Osteotomies were performed in 30.1% of patients. Deep infections below the fascia accounted for 68.0% of infections. Methicillin-sensitive (41.9%) and methicillin-resistant (17.0%) Staphylococcus aureus were the most commonly isolated pathogens, whereas gram-negative bacteria accounted for 25.4% of cases. Long-term antibiotic suppression was required in 18.9% of patients, and overall complications from antibiotics occurred in 4.5% of patients. Operative treatment was required in 81.8% of SSI cases.

CONCLUSION

SSIs occur in 1.2% of spine deformity patients, with a rate significantly higher in patients with kyphosis. Approximately 25% of these infections are secondary to gram-negative species. Antibiotic complications occur in 4.5% of patients being treated for SSI. Despite advancements in surgical technique and infection prophylaxis, postoperative SSI remains one of the most common complications in spinal deformity surgery.

LEVEL OF EVIDENCE

Level III.

Locally Used Antibiotics for Spinal Infection Prophylaxis and Their Effects on Epidural Fibrosis: an Experimental Laminectomy Study in Rats Using Rifamycin and Gentamycin

The study aims to assess the effects of antibiotics (ABs), which are typically used in spinal infection prophylaxis, on the formation of epidural fibrosis (EF). Specifically, we investigated the effect of rifamycin and gentamycin on EF formation in laminectomized rats. Thirty-two rats were randomly and equally divided into four groups as follows: laminectomy and physiological saline (0.9% NaCl) solution (control); laminectomy and rifamycin; laminectomy and gentamicin; and laminectomy and a mixture of rifamycin and gentamicin. Laminectomy was performed on L1 and L2 vertebrae in all rats. One month after spinal surgery, spinal tissue samples surrounding the laminectomy were cut with a microtome and stained with hematoxylin-eosin and Masson's trichrome. The histopathological analysis included examining the extent of EF, fibroblast cell density, and cartilage and bone regeneration. Statistical analysis was performed using the IBM SPSS Statistics 22 program (SPSS IBM, Turkey). A value of p < 0.05 was considered statistically significant. EF value differences between the AB treatment groups and the control group were statistically significant (p = 0.030). Specifically, binary comparisons indicated that the EF value was significantly higher in the rifamycin group than that in the control group (p = 0.003; p < 0.05). Our study suggests that locally applied ABs, especially rifamycin, should be diluted before administration to the epidural space.

Cervical spondylodiscitis following an invasive procedure on the neopharynx after circumferential pharyngolaryngectomy: a retrospective case series

PURPOSE

To highlight cervical spondylodiscitis as an infrequent complication following an invasive procedure on the neopharynx in patients previously treated with circumferential pharyngolaryngectomy with pectoralis major myocutaneous flap reconstruction.

METHODS

Patients diagnosed with cervical spondylodiscitis after circumferential pharyngolaryngectomy between 2001 and 2013 were retrospectively studied using a questionnaire sent to the French head and neck tumour study group. Medical history; tumour management; clinical symptoms; biological, microbiological and imaging results; and management of the infection were collected for each patient.

RESULTS

Six men aged 51-66 years were diagnosed with spondylodiscitis on average 5.6 years after circumferential pharyngolaryngectomy, and a mean 2 months following an invasive procedure on the neopharynx (oesophageal dilatation, phonatory prosthesis insertion). The patients presented with cervical pain and increased CRP level. MRI showed epidural abscess and communication between the pharynx and vertebral bodies in most cases. Microbiological samples yielded bacteria from the pharynx flora. Infection was managed using antibiotics adjusted according to the culture results and spinal immobilisation for duration of 6-12 weeks. No surgical treatment was required. During follow-up, no patient experienced recurrence or residual disability.

CONCLUSIONS

Cervical spondylodiscitis is a rare but potentially severe complication following an invasive procedure on the neopharynx after circumferential pharyngolaryngectomy. Therefore, the onset of nonspecific symptoms should not be overlooked, and MRI must be performed if infection is suspected. Microbiological confirmation is critical in optimising treatment, which should be aggressive, even if overall prognosis seems to be good.

Vertebral osteomyelitis in adults: an update

INTRODUCTION

The incidence of vertebral osteomyelitis is increasing, attributed to an ageing population with inherent co-morbidities and improved case ascertainment.

SOURCES OF DATA

References were retrieved from the PubMed database using the terms 'vertebral osteomyelitis' and 'spondylodiscitis' between January 1, 2009 and April 30, 2014 published in English as checked in May 2014 (>1000 abstracts checked).

AREAS OF AGREEMENT

Blood cultures and whole spine imaging with magnetic resonance imaging are essential investigations. Thorough debridement is the mainstay of surgical management, although placing metalwork in active infection is becoming increasingly common.

AREAS OF CONTROVERSY

The extent of pursuing spinal biopsies to determine aetiology, antimicrobial choices and duration, monitoring the response to treatment, and surgical techniques and timing all vary widely in clinical practice with heterogeneous studies limiting comparisons. Surgery, rather than conservative approaches, is being proposed as the default management choice, because it can, in carefully selected patients, offer faster reduction in pain scores and improved quality of life.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further studies are needed to define the most effective technique for spinal biopsies to maximize determining aetiology. High-quality trials are required to provide an evidence base for both the medical and surgical management of vertebral osteomyelitis, including challenging medical management as the default option.

Overview: the role of Propionibacterium acnes in nonpyogenic intervertebral discs

Propionibacterium acnes (P. acnes), an important opportunistic anaerobic Gram-positive bacterium, causes bone and joint infections, discitis and spondylodiscitis. Accumulated evidence suggested that this microbe can colonise inside intervertebral discs without causing symptoms of discitis. Epidemiological investigation shows that the prevalence ranges from 13 % to 44 %. Furthermore, colonisation by P. acnes inside nonpyogenic intervertebral discs is thought to be one pathogen causing sciatica, Modic changes and nonspecific low back pain. Specially, patients can attain significant relief of low back pain, amelioration of Modic changes and alleviation of sciatica after antibiotic therapy, indicating the role of P. acnes in these pathological changes. However, until now, there were hypotheses only to explain problems such as how P. acnes access intervertebral discs and what the exact pathological mechanism it employs during its latent infection period. In addition, research regarding diagnostic procedures and treatment strategies were also rare. Overall, the prevalence and possible pathological role that P. acnes plays inside nonpyogenic intervertebral discs is summarised in this paper.

Surgical site infections following spine surgery: eliminating the controversies in the diagnosis

Surgical site infection (SSI) following spine surgery is a dreaded complication with significant morbidity and economic burden. SSIs following spine surgery can be superficial, characterized by obvious wound drainage or deep-seated with a healed wound. Staphylococcus aureus remains the principal causal agent. There are certain pre-operative risk factors that increase the risk of SSI, mainly diabetes, smoking, steroids, and peri-operative transfusions. Additionally, intra-operative risk factors include surgical invasiveness, type of fusion, implant use, and traditional instead of minimally invasive approach. A high level of suspicion is crucial to attaining an early definitive diagnosis and initiating appropriate management. The most common presenting symptom is back pain, usually manifesting 2–4 weeks and up to 3 months after a spinal procedure. Scheduling a follow-up visit between weeks 2 and 4 after surgery is therefore necessary for early detection. Inflammatory markers are important diagnostic tools, and comparing pre-operative with post-operative levels should be done when suspecting SSIs following spine surgery. Particularly, serum amyloid A is a novel inflammatory marker that can expedite the diagnosis of SSIs. Magnetic resonance imaging remains the diagnostic modality of choice when suspecting a SSI following spine surgery. While 18F-fluorodeoxyglucose-positron emission tomography is not widely used, it may be useful in challenging cases. Despite their low yield, blood cultures should be collected before initiating antibiotic therapy. Samples from wound drainage should be sent for Gram stain and cultures. When there is a high clinical suspicion of SSI and in the absence of superficial wound drainage, computed tomography-guided aspiration of paraspinal collections is warranted. Unless the patient is hemodynamically compromised, antibiotics should be deferred until proper specimens for culture are secured.

Antibiotic penetration into rabbit nucleus pulposus with discitis

OBJECTIVE

To assess the penetration into nucleus pulposus (NP) of cephazolin and clindamycin in a discitis model.

MATERIALS AND METHODS

Twenty New Zealand white rabbits were inoculated with 103 Staphylococcus aureus at lumbar disc space. The rabbits with discitis confirmed by MRI 10 days after inoculation were divided into two groups. One was given cephazolin by intravenous (IV) at 80 mg/kg/day at 1.5 h interval for 5 half-lives; the other was given clindamycin by IV at 30 mg/kg/day at 2.5-h interval for 5 half-lives. Thirty minutes after completion of the last dose, NP and serum were sent to measure antibiotic concentration.

RESULTS

Two rabbits died during inoculation. After 10 days, 18 rabbits were confirmed discitis in the inoculated levels. The cephazolin and clindamycin can diffuse throughout the infected, sham-infected and normal NP. The serum concentration of cephazolin and clindamycin was 251.3 ± 40.5 and 21.6 ± 4.71 mg/l, respectively. The cephazolin concentration in infected NP (1.93 ± 0.84 mg/l) was higher than that in sham-infected (1.73 ± 0.61 mg/l) and normal NP (1.68 ± 0.65 mg/l), but the difference showed no statistically significant (P > 0.05). The cephazolin penetration into NP averaged 0.68-0.77 % of serum level. The clindamycin concentration in infected NP (4.32 ± 1.54 mg/l) was higher than that in sham-infected NP (2.63 ± 1.26 mg/l) and normal NP (2.59 ± 1.01 mg/l) (P < 0.05). The penetration into NP averaged 11.9-20 % of serum level. There was no significance difference between sham-infected and normal NP in clindamycin and cephazolin concentration (P > 0.05).

CONCLUSIONS

This study demonstrates cephazolin and clindamycin can penetrate the infected and normal NP. The antibiotics charge influences the delivery. Furthermore, infection condition selectively promotes antibiotic distribution within NP.