Microbiologic profile of infections in presumed aseptic revision spine surgery

Unexpected positive culture (UPC) in adults revision spine surgery: a systematic review and meta-analysis of incidence, risk factors, and management

BACKGROUND

Without clear signs of infection, spinal implant failure is attributed to mechanical overloads and aseptic loosening. However, how low-grade infections contribute to seemingly aseptic implant failure is unclear.

PURPOSE

The systematic review examined unexpected positive cultures (UPCs) in revision spine surgery regarding prevalence, isolated pathogens, risk factors, and strategies to reduce infection among asymptomatic patients undergoing revision spine surgery.

METHODS

We followed the PRISMA guidelines and searched four main databases (PubMed, EMBASE, SCOPUS, Web of Science) comprehensively until January 2023 for articles reporting UPC after presumed aseptic adult revision spine surgery. The UPC rates were pooled, and risk factors were compared with the culture-negative control group and represented as odds ratio (OR) or mean difference (MD).

RESULTS

Fifteen studies of 1057 individuals were included in two groups: culture-positive or UPCs (n = 317) and culture-negative or control (n = 740). The overall UPC prevalence was 33.2% (317/1057, range: 0 to 53%, 95% CI = 30.2%-36.4%), and Cutibacterium acnes (43.0%, 95% CI = 37.4%-48.8%), Coagulase-negative Staphylococci (CoNS), (39.5%, 95% CI = 33.2%-46.2%), and Staphylococcus species in general (49.5%, 95%CI = 43.7%-55.4%) were reported the most common isolated microbes. 16.1% of the UPCs were polymicrobial. Risk factors associated with UPC rates were female sex (OR = 2.62, 95%CI = 1.76-3.90, P < 0.001), screw loosening (OR = 4.43, 95%CI = 1.31-15.02, P = 0.02), number of operated levels (MD = 0.77, 95%CI = 0.33-1.22, P = 0.0007), and shorter time since index surgery (MD = - 8.57 months, 95%CI = - 14.76, -2.39, P = 0.02).

CONCLUSIONS

One-third of patients undergoing spine revision surgery revealed UPC in this study. Each UPC pathogen interpretation and antibiotic use decision should be interpreted case by case.

LEVEL OF EVIDENCE

IV.

Cutibacterium acnes in spine surgery: pathophysiology, diagnosis, and treatment

Cutibacterium acnes (C. acnes) previously named Propionibacterium acnes (P. acnes) has been increasingly recognized by spine surgeons as a cause of indolent post-surgical spinal infection. Patients infected with C. acnes may present with pseudarthrosis or nonspecific back pain. Currently, microbiological tissue cultures remain the gold standard in diagnosing C. acnes infection. Ongoing research into using genetic sequencing as a diagnostic method shows promising results and may be another future way of diagnosis. Optimized prophylaxis involves the use of targeted antibiotics, longer duration of antibiotic prophylaxis, antibacterial-coated spinal implants, and evidence-based sterile surgical techniques all of which decrease contamination. Antibiotics and implant replacement remain the mainstay of treatment, with longer durations of antibiotics proving to be more efficacious. Local guidelines must consider the surge of antimicrobial resistance worldwide when treating C. acnes.

Value of 18 F-FDG PET/CT to Identify Occult Infection in Presumed Aseptic Pseudarthrosis after Spinal Fusion: Correlation with Intraoperative Cultures

Objective  Fluorine-18 fluorodeoxyglucose ( 18 F-FDG) positron emission tomography/computed tomography (PET/CT) has gained attention as an emerging tool in case of suspicion of infection on spine, whether native or instrumented. However, the diagnostic performance of 18 F-FDG PET/CT in clinically occult low-grade surgical site infection (SSI) after spinal fusion, an important risk factor for pseudarthrosis, remains unknown. Methods  We retrospectively identified all the presumed aseptic patients with pseudarthrosis confirmed by revision surgery who underwent preoperative 18 F-FDG PET/CT scans performed between April 2019 and November 2022. These patients were presumed aseptic because they did not have clinical signs or laboratory tests suggestive of SSI, preoperatively. The PET/CT images were analyzed in consensus by two nuclear medicine physicians blinded to the clinical, biological, and imaging information. Visual assessment of increased uptake around cage/intervertebral disk space (and/or hardware) higher than background recorded from the first normal adjacent vertebra was interpreted as positive. Image data were also quantitatively analyzed by the maximum standardized uptake value as an index of 18 F-FDG uptake, and the ratio between the uptake around cage/intervertebral disk space (and/or hardware) and background recorded from the first normal adjacent vertebra was calculated. The final diagnosis of infection was based on intraoperative cultures obtained during pseudarthrosis revision surgery. Results  Thirty-six presumed aseptic patients with surgically confirmed pseudarthrosis after spinal fusion underwent preoperative 18 F-FDG PET/CT scans. Cultures of samples from revisions found that 20 patients (56%) were infected. The most frequent isolated bacterium was Cutibacterium acnes ( C. acnes ) in 15 patients (75%), followed by coagulase-negative staphylococci (CNS) in 7 patients (33%). Two patients had co-infections involving both C. acnes and CNS. Of the 36 PET/CT studied in this study, 12 scans were true-negative, 10 true-positive, 10 false-negative, and 4 false-positive. This resulted in sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of 50%, 75%, 71%, 55%, and 61%, respectively. Conclusion  In presumed aseptic pseudarthrosis after spinal fusion, 18 F-FDG PET/CT offers good specificity (75%) but low sensitivity (50%) to identify occult SSI. The high prevalence (56%) of SSI, mostly caused by C. acnes (75%), found in our presumed aseptic cohort of patients supports the utility of systematic intraoperative cultures in revision cases for pseudarthrosis.

Unexpected intraoperative positive culture (UIPC) in presumed aseptic revision spine surgery: a systematic review and meta-analysis

BACKGROUND CONTEXT

Unexpected intraoperative positive culture (UIPC) has recently become increasingly common in revision spine surgery, being implicated as an etiological factor in revision spine surgery indications such as implant failure or pseudoarthrosis.

PURPOSE

Utilizing the available literature, this study aimed to investigate the prevalence of UIPC, and its clinical importance in patients following presumed aseptic revision spine surgery.

STUDY DESIGN

Meta-analysis and systematic review.

METHODS

Multiple databases and reference articles were searched until May 2022. The primary outcome was the pooled rate of UIPC, and the secondary outcomes were the microbiological profile of UIPC, the risk factors of UIPC, and the clinical fate of UIPC.

RESULTS

Twelve studies were eligible for meta-analysis, with a total of 1,108 patients. The pooled rate of UIPC was 24.3% (95% CI=15.8%-35.5%) in adult patients, and 43.2% (95% CI=32.9%-54.2%) in pediatric patients. The UIPC rate was higher when both conventional wound culture and sonication were used together compared to sonication alone or conventional wound culture alone. The rates were 28.9%, 23.6%, and 15.5 %, respectively. In adult and pediatric patients, the most commonly cultured organism was Cutibacterium acnes (42.5% vs 57.7%), followed by coagulase-negative Staphylococcus (39.9% vs 30.5%). Male patients had a higher rate of UIPC (OR= 2.6, 95% CI=1.84-3.72, p<.001), as did patients with a longer fusion construct (MD=0.76, 95% CI=0.27-1.25, p<.001).

CONCLUSIONS

The pooled rate of UIPC in aseptic spine revision surgery was 24.3% and 43.2% in adult and pediatric patients respectively. The most common organisms were C. acnes and coagulase-negative Staphylococcus. The impact of UIPC on patients` clinical outcomes is not fully understood. We are not able to recommend routine culture in revision spine surgery, however, adding sonication may aid in the diagnosis of UIPC. There is not enough evidence to recommend specific treatment strategies at this time, and further studies are warranted.

A high prevalence of Cutibacterium acnes infections in scoliosis revision surgery, a diagnostic and therapeutic dilemma

PURPOSE

To investigate if serum inflammatory markers or nuclear imaging can accurately diagnose a chronic spinal instrumentation infection (SII) prior to surgery.

METHODS

All patients who underwent revision of spinal instrumentation after a scoliosis correction between 2017 and 2019, were retrospectively evaluated. The diagnostic accuracy of serum C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR), ¹⁸F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) and Technetium-99m-methylene diphosphonate (99mTc-MDP) 3-phase bone scintigraphy (TPBS) to diagnose infection were studied. Patients with an acute infection or inadequate culture sampling were excluded. SII was diagnosed if ≥ 2 of the same microorganism(s) were isolated from intra-operative tissue cultures.

RESULTS

30 patients were included. The indication for revision surgery was pseudoarthrosis in the majority of patients (n = 15). 22 patients (73%) were diagnosed with SII. In all infected cases, Cutibacterium acnes was isolated, including 5 cases with a polymicrobial infection. The majority of patients had low inflammatory parameters preoperatively. For CRP > 10.0 mg/L, the sensitivity was 9.1% and specificity 100%; for ESR > 30 mm/h, the sensitivity was 9.1% and specificity 100%. The diagnostic accuracy for nuclear imaging was 64% for the FDG-PET/CT and 67% for the TPBS to diagnose infection.

CONCLUSIONS

The prevalence of SII in patients undergoing revision spinal surgery is high, with Cutibacterium acnes as the main pathogen. No diagnostic tests could be identified that could accurately diagnose or exclude SII prior to surgery. Future studies should aim to find more sensitive diagnostic modalities to detect low-grade inflammation.

Clinical relevance of occult infections in spinal pseudarthrosis revision

Background

Occult infections in spinal pseudarthrosis revisions have been reported in the literature, but the relevance of such an infection on patient outcomes is unknown. We aimed to elucidate clinical outcomes and re-revision risks between patients with and without occult infections in spinal revision surgery for pseudarthrosis.

Methods

In this matched case-control study, we identified 128 patients who underwent thoracolumbar revision surgery from 2014–2019 for pseudarthrosis of the spine. Among them, 13 (10.2%) revealed an occult infection (defined by at least two positive intraoperative tissue samples with the same pathogen), and nine of these 13 were available for follow-up. We selected 18 of the 115 controls using a 2:1 fuzzy matching based on fusion length and length of follow-up. The patients were followed up to assess subsequent re-revision surgeries and the following postoperative patient-reported outcome measures (PROMs): overall satisfaction, Oswestry Disability Index, 5-level EQ-5D, and Short Form 36.

Results

Patient characteristics, surgical data, and length of follow-up were equal between both study groups. The rate of re-revision free survival after the initial pseudarthrosis revision surgery was higher in the occult infection group (77.8%) than the non-infectious controls (44.4%), although not significantly (0.22). The total number of re-revision surgeries, including re-re-revisions, was thirteen (in ten patients) in the control and two (in two patients) in the occult infection group (p = 0.08) after a median follow-up of 24 months (range 13-75). Four cases in the control group underwent re-revision for pseudarthrosis compared to none in the infected group. Satisfactory scores were recorded in all PROMs, with similar scores between the two groups.

Conclusions

The presence of an occult infection accompanying spinal pseudarthrosis revision was not inferior to non-infected pseudarthrosis revisions in a matched, small sample size cohort study. This may be explained due to the possibility of targeted treatment of the identified cause of pseudarthrosis.

Does Postoperative Spine Infection Bacterial Gram Type Affect Surgical Debridement or Antibiotic Duration?

STUDY DESIGN

This is a retrospective cohort study.

OBJECTIVE

The aim was to evaluate differences in readmission rates, number of debridements, and length of antibiotic therapy when comparing bacterial gram type following lumbar spinal fusion infections.

SUMMARY OF BACKGROUND DATA

Surgical site infections (SSIs) after spinal fusion serve as a significant source of patient morbidity. It remains to be elucidated how bacterial classification of the infecting organism affects the management of postoperative spinal SSI.

METHODS

Patients who underwent spinal fusion with a subsequent diagnosis of SSI between 2013 and 2019 were retrospectively identified. Patients were grouped based on bacterial infection type (gram-positive, gram-negative, or mixed infections). Poisson regressions analyzed the relationship between the type of bacterial infection and the number of irrigation and debridement (I&D) reoperations, and the duration of intravenous (IV) antibiotic therapy. Significance was set at P <0.05.

RESULTS

Of 190 patients, 92 had gram-positive (G+) infections, 57 had gram-negative (G-) infections, and 33 had mixed (M) infections. There was no difference in 30 or 90-day readmissions for infection between groups (both P =0.051). Patients in the M group had longer durations of IV antibiotic treatment (G+: 46.4 vs. G-: 41.0 vs. M: 55.9 d, P =0.002). Regression analysis demonstrated mixed infections were 46% more likely to require a greater number of debridements ( P =0.001) and 18% more likely to require an increased duration of IV antibiotic therapy ( P <0.001), while gram-negative infections were 10% less likely to require an increased duration of IV antibiotic therapy ( P <0.001) when compared with G- infections.

CONCLUSION

Spinal SSI due to a mixed bacterial gram type results in an increased number of debridements and a longer duration of IV antibiotics required to resolve the infection compared with gram-negative or gram-positive infections.

LEVEL OF EVIDENCE

Level III.

18F-NaF PET/CT in Presumed Aseptic Pseudarthrosis after Spinal Fusion: Correlation with Findings at Revision Surgery and Intraoperative Cultures

Background Conventional imaging is useful to assess interbody fusion by showing complete trabecular bony bridging, but has a low positive predictive value for pseudarthrosis. Because alterations of bone metabolism may precede structural anatomical changes on computed tomography (CT), we aimed to investigate the ability of fluorine 18 sodium fluoride positron emission tomography/computed tomography (18F-NaF PET/CT) to identify pseudarthrosis after spinal fusion using surgical revision as the reference standard.

Methods We retrospectively reviewed 18F-NaF PET/CT scans performed between February 2019 and September 2020 in patients experiencing pain after spinal fusion. We included the 18 patients who underwent revision surgery for suspicion of pseudarthrosis. Five consecutive patients who were clearly fused on CT served as the control group.

Results In the revision surgery group (n=18), visual assessment by 18F-NaF PET/CT revealed that all 22 cages with an increased 18F-NaF uptake around intercorporal fusion material had mobility at revision surgery, whereas none of the fused patients (n=5) showed uptake around cage/intervertebral disk space. Among the 18 patients with presumed aseptic pseudarthrosis, intraoperative cultures revealed surgical site infection (SSI) caused by Cutibacterium acnes (C. acnes) in seven patients (38.9%). There was a statistically significant difference in standardized uptake values and uptake ratios between the revision surgery and control groups (p=5.3× 10−6 and p=0.0002, respectively).

Conclusions 18F-NaF PET/CT imaging appeared as a useful tool to identify pseudarthrosis following spinal fusion. The unexpectedly high prevalence (38.9%) of SSI caused by C. acnes found in presumed aseptic patients supports the utility of intraoperative cultures in revision cases for pseudarthrosis, even without preoperative clinical suspicion of SSI.

Silver carboxylate-doped titanium dioxide-polydimethylsiloxane coating decreases Cutibacterium acnes adherence and biofilm formation on polyether ether ketone

BACKGROUND CONTEXT

Cutibacterium acnes (C. acnes) is a gram-positive facultative anaerobe found in the deep sebaceous follicles of the skin on the shoulder and back. C. acnes has been increasingly recognized as a pathogen in spinal surgical site infection (SSI) especially in the presence of instrumentation.

PURPOSE

This study assesses whether a silver carboxylate-doped titanium dioxide-polydimethylsiloxane (TiO₂-PDMS) coating can decrease C. acnes adherence and biofilm formation on PEEK and four other commonly used spinal implant materials, stainless steel, cobalt chromium, titanium, and titanium alloy.

STUDY DESIGN

We compared the adherence of C. acnes over 24 hours between uncoated, 95:5 TiO₂ to PDMS ratio with 10× silver carboxylate coating and a 100% silver carboxylate coating on each implant material, which were uniformly saw cut and sterilized. Implants were then subjected to scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM).

METHODS

Samples were coated using 95:5 TiO₂-PDMS 10× silver carboxylate, 100% silver carboxylate, or left uncoated. C. acnes was applied onto the samples and allowed to adhere for periods of 4, 8, 12, 16, or 20 hours. Nonadherent bacteria were then washed from the samples. These samples were then allowed to continue incubating for a total of 24 hours. SEM and confocal laser scanning microscope were used to visualize all samples for the presence of biofilm and quantification of C. acnes adherence at each time point.

RESULTS

The 95:5 TiO₂-PDMS 10× silver carboxylate coating was able to significantly decrease C. acnes adherence on PEEK after 8, 12, 16, and 20 hours of adherence. No statistical difference was found between the 95:5 TiO₂-PDMS 10× silver carboxylate coating and the 100% silver carboxylate positive control. We previously observed extensive C. acnes biofilm formation on uncoated PEEK, but none on PEEK coated with either the 95:5 TiO₂-PDMS 10× silver carboxylate or 100% Ag coating . Furthermore, no biofilm formation was observed on stainless steel, cobalt chromium, titanium, and titanium alloy coated with 95:5 TiO₂-PDMS 10× silver carboxylate or 100% Ag coating.

CONCLUSION

A 95:5 TiO₂-PDMS 10× silver carboxylate coating decreases C. acnes adhesion and prevents biofilm formation on PEEK and other common orthopedic implant materials.

CLINICAL SIGNIFICANCE

A 95:5 TiO₂-PDMS 10× silver carboxylate coating may help decrease spinal SSI due to C. acnes, especially in procedures with instrumentation.

Indolent Infection After Lumbar Interbody Fusion: An Under-recognized Cause of Pseudarthrosis, Which Can Be Successfully Treated With Anterior Revision Fusion

Introduction:

Methods:

Results:

Discussion:

Bacteria in Surgical Smoke: A Self-controlled Laboratory Study Using Porcine Spinal Tissues

STUDY DESIGN

A laboratory study performed in a self-controlled fashion.

OBJECTIVE

The aim of this study was to examine whether "surgical smoke" generated by using the electrocautery on porcine spinal tissues could contain viable bacteria.

SUMMARY OF BACKGROUND DATA

The year 2020 has seen a surge in legislation regarding surgical smoke evacuation in the operating room across the United States. Surgical smoke contains numerous toxic and carcinogenic substances, which spine surgeons and operating room staff are regularly exposed to. Although the smoke's chemical toxicity has been extensively studied, little is known about its biohazard level.

METHODS

The electrocautery was used to "operate on" 20 segments of porcine spinal tissues on a clean bench. In each operation, the generated smoke was captured with a swab, which was positioned above the surgical site and within the smoke, to obtain bacteria cultures. Two other swabs-a tissue swab (swabbing the porcine tissue itself) and a blank swab (swabbing an empty sterile bowl)-were collected as controls. The culture results were compared among the three groups. An additional experiment was conducted to see whether using a mask can reduce the "infection rate" of the swab.

RESULTS

Although all blank swabs tested negative, 95% (19/20) of the smoke swabs tested positive, with a total of nine bacteria species identified. The most prevalent species observed in the smoke swabs included Serratia liquefaciens, Lactococcus garvieae, and Hafnia alvei, and so on. Among the positive smoke swabs, 84% (16/19) had one or more bacteria species that were consistent with the cultures of their corresponding tissue swabs. Using a surgical or N95 mask reduced the "infection rate" of the swab.

CONCLUSION

"Surgical smoke" generated by electrocauterization of porcine spinal tissues contains viable bacteria. Further research in actual spine surgery is needed next.Level of Evidence: N/A.

High Failure Rates of a Unilateral Posterior Peri-Apical Distraction Device (ApiFix) for Fusionless Treatment of Adolescent Idiopathic Scoliosis

BACKGROUND

Conventional surgical treatment for adolescent idiopathic scoliosis (AIS) consists of correction of the spinal deformity with rigid spinal instrumentation and fusion. Less-invasive and fusionless surgery could potentially improve patient outcomes. The purpose of the present study was to evaluate the efficacy of a recently U.S. Food and Drug Administration (FDA)-approved posterior peri-apical self-distracting device (ApiFix) that is designed to gradually correct the deformity without spinal fusion.

METHODS

In a prospective cohort study of 20 patients with AIS (Risser stage 1-4; Lenke 1 or 5; major curve Cobb angle, 40° to 55°; and Bunnell scoliometer rotation, <15°) were managed with the ApiFix device. Clinical and radiographic performance was assessed.

RESULTS

Twenty patients with a mean age (and standard deviation) of 14.8 ± 1.4 years were followed for a mean of 3.4 ± 1.0 years. The average major curve was reduced from 45.4° preoperatively to 31.4° at 2 weeks postoperatively and 31.0° at the time of the latest follow-up. The average minor curve measured 31.3° preoperatively, 26.1° at 2 weeks postoperatively, and 24.2° at the time of the latest follow-up. Ten patients had serious complications that required revision surgery, including osteolysis (n = 6), screw and/or rod breakage (n = 2), failure of the ratchet mechanism (n = 1), and pain without explainable cause (n = 1). During revision surgery, metallosis was observed in all patients and cultures showed growth of Cutibacterium acnes in 6 patients. Because of the high failure rate, the study was terminated early.

CONCLUSIONS

The use of the unilateral peri-apical concave self-distracting ratchet rod initially was associated with promising clinical and radiographic results. However, no distraction was observed and the high rate of serious adverse events within 2 years was considered to be unacceptable for further clinical application of this device in our institution, despite recent FDA approval.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

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.

Is Propionibacterium acnes becoming the most common bacteria in delayed infections following adolescent idiopathic scoliosis surgery?

STUDY DESIGN

Retrospective review of hospital charts.

OBJECTIVE

(1) To determine the microbiological profile of patients with surgical site infections following posterior spinal fusion surgery (PSF) for Adolescent Idiopathic scoliosis (AIS). (2) To study the treatment outcome of patients with surgical site infections (SSI) following surgery for AIS. (3) To identify the key differences in presentation and management of acute and delayed SSI following AIS surgery. There has been increasing evidence of the role of P. acnes in deep surgical site infections. Literature related to this is abundant in relation to shoulder arthroplasty; however, it is sparse in relation to spine surgery.

METHODS

We conducted a retrospective review of all patients treated for AIS during a 5-year period (2010-2014) at our institution, with a minimum of 2-year follow-up after the index surgery. Patients with a postoperative infection following their index surgery were included. Charts of AIS patients with post-op infections were reviewed for details of the index surgery, time to presentation of the infection, presenting signs/symptoms, microbiology details, details of surgical and antibiotic treatment, and outcomes.

RESULTS

Nine (2.8%) post-op infections were identified out of 315 cases for AIS during this period. Seven (2.2%) involved P. acnes. Two (0.6%) involved MSSA. The average time for cultures to show growth was 6.1 days (range 5-8 days) in P. acnes group and 2-3 days in MSSA group. Patients with P. acnes infections were treated with implant removal, debridement and antibiotics. All patients achieved solid fusion except two patients from the P. acnes group had pseudoarthrosis and had to undergo revision fusion.

CONCLUSION

Propionibacterium acnes was the single most common bacteria isolated from delayed surgical site infection following PSF in AIS patients. Optimal treatment consists of debridement, implant removal and antibiotics. These patients have high incidence of pseudoarthrosis.

LEVEL OF EVIDENCE

Level IV.

Occult infection in pseudarthrosis revision after spinal fusion

BACKGROUND CONTEXT

Pseudarthrosis after attempted spinal fusion is yet not sufficiently understood and presents a surgical challenge. Occult infections are sometimes observed in patients with pseudarthrosis and no inflammatory signs of infection. The prevalence of such occult infection and its association with patient demographics and inflammatory markers are largely unknown.

PURPOSE

To determine the prevalence of unexpected low-grade infection in spinal pseudarthrosis revision surgery, and to evaluate whether such infection is associated with patient demographics and inflammatory markers.

STUDY DESIGN

Retrospective observational study.

PATIENT SAMPLE

One-hundred-and-twenty-eight patients who underwent thoracolumbar revision surgery due to presumed aseptic pseudarthrosis after spinal instrumentation.

OUTCOME MEASURES

Culture-positive infections or noninfectious pseudarthrosis.

METHODS

Samples were routinely taken for microbiological examination from all adults (n=152) who underwent revision surgery for presumed aseptic thoracolumbar pseudarthrosis between 2014 and 2019. A full intraoperative microbiological workup (at least three intraoperative tissue samples) was done for 128 (84%) patients, and these patients were included in further analyses. Patient characteristics, medical history, inflammatory markers, and perioperative data were compared between those with and without microbiologically-confirmed infection based on samples obtained during pseudarthrosis revision.

RESULTS

The microbiological workup confirmed infection in 13 of 128 cases (10.2%). The predominant pathogen was Cutibacterium acnes (46.2%), followed by coagulase-negative staphylococci (38.5%). The presence of infection was associated with the body mass index (30.9±4.7 kg/m² [infected] vs. 28.2±5.6 kg/m² [controls], p=.049), surgery in the thoracolumbar region (46% vs. 18%, p=.019), and a slightly higher serum C-reactive protein level on admission (9.4±8.0 mg/L vs. 5.7±7.1 mg/L, p=.031). Occult infection was not associated with age, sex, prior lumbar surgeries, number of fused lumbar levels, American Society of Anesthesiologist score, Charlson Comorbidity Index, presence of diabetes mellitus, and smoking status.

CONCLUSIONS

Occult infections were found in 10% of patients undergoing pseudarthrosis revision after spinal fusion, even without preoperative clinical suspicion. Occult infection was associated with higher body mass index, fusions including the thoracolumbar junction, and slightly higher C-reactive protein levels. Intraoperative microbiological samples should be routinely obtained to exclude or identify occult infection in all revision surgeries for symptomatic pseudarthrosis of the spine, as this information can be used to guide postoperative antibiotic treatment.

Low-Grade Infection and Implant Failure Following Spinal Instrumentation: A Prospective Comparative Study

BACKGROUND

Spinal instrumentation can be associated with complications, including implant loosening. Hitherto, implant loosening has mainly been attributed to mechanical overload.

OBJECTIVE

To examine the role of low-grade infections as the cause of implant failure in suspected aseptic implant loosening following spinal instrumentation.

METHODS

A prospective single center observational study was performed. All patients who had revision surgery following spinal instrumentation between August 2015 and February 2018 were screened. Patients with revision surgery due to screw loosening on the computed tomograhy scan constituted the study group. Patients in which the screws where not loosened but removal was performed for other reasons formed the comparison group. Intraoperative swabs were taken and sonication was performed with the explanted material. Results of microbiological cultivation were analyzed.

RESULTS

A total of 59 patients were included in the study group and 34 in the comparison group. In the study group in 42.4% of the cultures a bacterium was detected, while in the comparison group only in 17.6%. 84%, and 83.3% of these germs were detected by sonication in the study and comparison group, respectively. The rate of positive cultures was significantly higher in the study group compared to the comparison group (P = .001). The most frequent bacterium cultivated in both groups was Propionibacterium acnes, followed by Staphylococcus species.

CONCLUSION

For patients with screw loosening a high level of suspicion for a low-grade infection should be raised. Cultures should be performed from the sonication fluid of the explanted devices in all patients with symptomatic screw loosening.

Prevalence of Occult Infections in Posterior Instrumented Spinal Fusion

STUDY DESIGN

This is a prospective observational study.

OBJECTIVE

The aim of this study is to determine the rate of occult infection after instrumented spine surgery in presumed aseptic patients.

SUMMARY OF BACKGROUND DATA

The reported incidence rate of delayed/occult infection determined by positive culture swabs after instrumented spine surgery in prospective studies is 0.2%-6.9%. However, this rate may be higher as delayed infections are challenging to diagnose. Fever can be absent and inflammatory markers are often normal. If indolent organisms exist in low concentrations surrounding the instrumentation, these organisms can possibly avoid detection and disrupt bone formation leading to instrumentation loosening, pain generation, and/or failure of a solid fusion.

MATERIALS AND METHODS

This study included 50 consecutive presumed aseptic patients undergoing a posterior revision requiring removal of instrumentation at least 6 months following their index procedure. Common markers of infection were examined preoperatively. Multiple culture swabs were taken directly from the removed instrumentation and cultured for 14 days.

RESULTS

Of the 50 patients, 19 (38%) were culture-positive (CP) for bacteria upon removal of their instrumentation, with 14 patients (28%) having ≥2 positive specimens of the same organism. The average length of time between the index procedure and the revision surgery was 4.55 years (range: 0.53-21 y). Polymicrobial infections were found in 26% (5/19) of CP patients. The most prevalent microorganism found was Propionibacterium acnes, in 63% (12/19) of CP patients. There was no significant difference between CP and culture-negative patients regarding preoperative markers for infection, age, or length between index and revision procedures.

CONCLUSIONS

The results of this study indicate a positive culture rate of 38% in presumed aseptic patients who had previously undergone instrumented spine surgery. These results are consistent with other retrospective studies and are >6 times greater than any previous prospective study utilizing culture swabs.

LEVEL OF EVIDENCE

Level-III.

The Prevalence of Bacterial Infection in Patients Undergoing Elective ACDF for Degenerative Cervical Spine Conditions: A Prospective Cohort Study With Contaminant Control

STUDY DESIGN

Prospective cohort study.

OBJECTIVES

To determine the prevalence of bacterial infection, with the use of a contaminant control, in patients undergoing anterior cervical discectomy and fusion (ACDF).

METHODS

After institutional review board approval, patients undergoing elective ACDF were prospectively enrolled. Samples of the longus colli muscle and disc tissue were obtained. The tissue was then homogenized, gram stained, and cultured in both aerobic and anaerobic medium. Patients were classified into 4 groups depending on culture results. Demographic, preoperative, and postoperative factors were evaluated.

RESULTS

Ninety-six patients were enrolled, 41.7% were males with an average age of 54 ± 11 years and a body mass index of 29.7 ± 5.9 kg/m². Seventeen patients (17.7%) were considered true positives, having a negative control and positive disc culture. Otherwise, no significant differences in culture positivity was found between groups of patients. However, our results show that patients were more likely to have both control and disc negative than being a true positive (odds ratio = 6.2, 95% confidence interval = 2.5-14.6). Propionibacterium acnes was the most commonly identified bacteria. Two patients with disc positive cultures returned to the operating room secondary to pseudarthrosis; however, age, body mass index, prior spine surgery or injection, postoperative infection, and reoperations were not associated with culture results.

CONCLUSION

In our cohort, the prevalence of subclinical bacterial infection in patients undergoing ACDF was 17.7%. While our rates exclude patients with positive contaminant control, the possibility of contamination of disc cultures could not be entirely rejected. Overall, culture results did not have any influence on postoperative outcomes.

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.

Comprehensive treatment algorithm of postoperative spinal implant infection

Postoperative spinal implant infection (PSII) is a commonly found and serious complication after instrumented spinal surgery. Whereas early-onset PSII usually can be diagnosed by clinical symptoms, the diagnosis of late-onset PSII can be often made only by examination of intraoperatively collected samples. The treatment of PSII consists of surgical and antibiotic therapy schemes. In case of early PSII, the retention of spinal implants is a feasible option, whereas late PSII is usually treated by one-staged exchange of the spinal implants. Radical debridement of surrounding tissue should be performed in any case of PSII. The antibiotic treatment depends on either the implants can be removed or need to be retained or exchanged, respectively. If the causative pathogens are sensitive for biofilm-active antibiotic agents, the duration of antibiotic treatment amounts to 12 weeks with retention of spinal implants. In case of problematic pathogens, the application of antibiotics needs to be prolonged for an individual duration. Antibiotic treatment should always be initiated with an intravenous application for at least 2 weeks.

Low sensitivity of histopathological examination of peri-implant tissue samples in diagnosing postoperative spinal implant infection

AIMS

To evaluate the histopathological examination of peri-implant tissue samples as a technique in the diagnosis of postoperative spinal implant infection (PSII).

METHODS

This was a retrospective analysis. Patients who underwent revision spinal surgery at our institution were recruited for this study. PSII was diagnosed by clinical signs, histopathology, and microbiological examination of intraoperatively collected samples. Histopathology was defined as the gold standard. The sensitivity for histopathology was calculated. A total of 47 patients with PSII and at least one microbiological and histopathological sample were included in the study.

RESULTS

PSII occurred in approximately 28% of the study population. Histopathology showed a sensitivity of 51.1% in the diagnosis of PSII. The most commonly found pathogens were Cutibacterium acnes and gram-positive staphylococci.

CONCLUSION

Histopathology has low sensitivity for detecting PSII. In particular, infections caused by low-virulence microorganisms are insufficiently detected by histopathology. Cite this article: Bone Joint J 2020;102-B(7):899-903.

Delayed periprosthetic collection after cervical disc arthroplasty

Cervical disc arthroplasty is a treatment option for symptomatic cervical disc disease. There is a paucity of literature on long-term safety outcomes, durability, and device-related failure rates. The M6-C artificial cervical disc is a device with titanium alloy endplates and a complex polymeric centerpiece. To date, trials have exhibited acceptable safety profiles.This case series describes the presentation, management, and pathological findings of a delayed prevertebral periprosthetic mass anterior to the M6-C disc. Four patients at 3 different institutions underwent cervical disc replacement with the M6-C disc. Two to seven years postoperatively, they presented with dysphagia secondary to a compressive mass anterior to the disc. Case notes were reviewed to collect data on symptoms, management, and outcomes. The patients were systemically well and presented with progressive dysphagia. They had imaging findings of a mass anterior to the disc. They underwent a decompressive procedure, with 2 patients undergoing device removal and fusion. In 2 cases, a soft-tissue mass was seen intraoperatively, with frank pus. In 3 cases, Propionibacterium acnes was identified and antibiotic treatment given. Histopathology demonstrated mixed inflammatory infiltrates with foreign body-type granulomas. Postoperatively, the dysphagia resolved.The development of delayed dysphagia in a patient with an M6-C disc should prompt investigation to identify a mass lesion. To the authors' knowledge, this is the first report of delayed infection, or suspected delayed-type hypersensitivity reaction, following M6-C disc implantation. It is important for this to be added to the device safety concerns. Further prospective studies are needed to establish the incidence and the long-term safety and failure rates of the M6-C disc.

Surgical Site Infection Prevention Following Spine Surgery

STUDY DESIGN

Literature review.

OBJECTIVES

Surgical site infection (SSI) following spine surgery leads to significant patient morbidity, mortality, and increased health care costs. The purpose of this article is to identify risk factors and strategies to prevent SSIs following spine surgery, with particular focus on avoiding infections in posterior cervical surgery.

METHODS

We performed a literature review and synthesis to identify methods that can be used to prevent the development of SSI following spine surgery. Specific pearls for preventing infection in posterior cervical spine surgery are also presented.

RESULTS

SSI prevention can be divided into patient and surgeon factors. Preoperative patient factors include smoking cessation, tight glycemic control, weight loss, and nutrition optimization. Surgeon factors include screening and treatment for pathologic microorganisms, skin preparation using chlorhexidine and alcohol, antimicrobial prophylaxis, hand hygiene, meticulous surgical technique, frequent irrigation, intrawound vancomycin powder, meticulous multilayered closure, and use of closed suction drains.

CONCLUSION

Prevention of SSI following spine surgery is multifactorial and begins with careful patient selection, preoperative optimization, and meticulous attention to numerous surgical factors. With careful attention to various patient and surgeon factors, it is possible to significantly reduce SSI rates following spine surgery.

A review of microscopy-based evidence for the association of Propionibacterium acnes biofilms in degenerative disc disease and other diseased human tissue

PURPOSE

Recent research shows an increasing recognition that organisms not traditionally considered infectious in nature contribute to disease processes. Propionibacterium acnes (P. acnes) is a gram-positive, aerotolerant anaerobe prevalent in the sebaceous gland-rich areas of the human skin. A ubiquitous slow-growing organism with the capacity to form biofilm, P. acnes, recognized for its role in acne vulgaris and medical device-related infections, is now also linked to a number of other human diseases. While bacterial culture and molecular techniques are used to investigate the involvement of P. acnes in such diseases, definitive demonstration of P. acnes infection requires a technique (or techniques) sensitive to the presence of biofilms and insensitive to the presence of potential contamination. Fortunately, there are imaging techniques meeting these criteria, in particular, fluorescence in situ hybridization and immunofluorescence coupled with confocal laser scanning microscopy, as well as immunohistochemistry.

METHODS

Our literature review considers a range of microscopy-based studies that provides definitive evidence of P. acnes colonization within tissue from a number of human diseases (acne vulgaris, degenerative disc and prostate disease and atherosclerosis), some of which are currently not considered to have an infectious etiology.

RESULTS/CONCLUSION

We conclude that P. acnes is an opportunistic pathogen with a likely underestimated role in the development of various human diseases associated with significant morbidity and, in some cases, mortality. As such, these findings offer the potential for new studies aimed at understanding the pathological mechanisms driving the observed disease associations, as well as novel diagnostic strategies and treatment strategies, particularly for degenerative disc disease. These slides can be retrieved under Electronic Supplementary Material.

Cutibacterium acnes in Spine Pathology: Pathophysiology, Diagnosis, and Management

Cutibacterium acnes, long thought to be skin flora of pathological insignificance, has seen a surge in interest for its role in spine pathology. C acnes has been identified as a pathogen in native spine infection and osteomyelitis, which has implications in the management compared with more commonly recognized pathogens. In addition, It has also been recognized as a pathogen in postoperative and implant-associated infections. Some evidence exists pointing to C acnes as an unrecognized source of otherwise aseptic pseudarthrosis. Recently, it is hypothesized that low virulent organisms, in particular C acnes, may play a role in degenerative disk disease and the development of Modic end plate changes found in MRI. To this end, controversial implications exist in terms of the use of antibiotics to treat certain patients in the setting of degenerative disk disease. C acnes continues to remain an expanding area of interest in spine pathology, with important implications for the treating spine surgeon.

Is pseudarthrosis after spinal instrumentation caused by a chronic infection?

HYPOTHESIS

To assess whether a chronic bacterial infection is present in a subset of patients with pseudarthrosis after instrumented spinal fusion.

METHODS

This was a prospective diagnostic study including adult patients with previous instrumented spinal fusion. Patients underwent revision surgery for either pseudarthrosis or other causes (e.g. implant removal, curve progression or junctional kyphosis) (control group). Five separate biopsies were randomly collected, intraoperatively, from the pseudarthrosis site and cultivated under both aerobic (5 days) and anaerobic (14 days) conditions. If cultivation was positive in at least 2/5 tissue samples, the biopsy was sectioned and stained using peptide nucleic acid fluorescence in situ hybridization (PNA-FISH). Confocal laser scanning microscopy was used to examine the sections and visualize bacterial aggregates.

RESULTS

The study included 32 pseudarthrosis and 32 control patients. Cultivation yielded bacteria in at least 1/5 biopsies in 52% of patients with no difference between the groups (p = 1.0). Bacteria of the same species was found in at least 2/5 samples in seven pseudarthrosis patients and four controls (p = 0.509). Propionibacterium acnes was found in 8 of these 11 samples. Microscopy demonstrated tissue-embedded bacterial aggregates in two of these patients but with no inflammatory cells indicating an active infection. The presence of bacteria was not associated with the number of previous spinal procedures or the pre-revision fusion length (p ≥ 0.503).

CONCLUSIONS

Pseudarthrosis after instrumented spinal surgery was not significantly associated with the presence of bacteria at the pseudarthrosis site. Positive cultivation results are common after spinal instrumentation, but our results indicate that they rarely represent an organized infection. These slides can be retrieved under Electronic Supplementary Material.

Unexpected positive cultures in presumed aseptic revision spine surgery using sonication

AIMS

During revision procedures for aseptic reasons, there remains a suspicion that failure may have been the result of an undetected subclinical infection. However, there is little evidence available in the literature about unexpected positive results in presumed aseptic revision spine surgery. The aims of our study were to estimate the prevalence of unexpected positive culture using sonication and to evaluate clinical characteristics of these patients.

PATIENTS AND METHODS

All patients who underwent a revision surgery after instrumented spinal surgery at our institution between July 2014 and August 2016 with spinal implants submitted for sonication were retrospectively analyzed. Only revisions presumed as aseptic are included in the study. During the study period, 204 spinal revisions were performed for diagnoses other than infection. In 38 cases, sonication cultures were not obtained, leaving a study cohort of 166 cases. The mean age of the cohort was 61.5 years (sd 20.4) and there were 104 female patients.

RESULTS

Sonication cultures were positive in 75 cases (45.2%). Hardware failure was the most common indication for revision surgery and revealed a positive sonication culture in 26/75 cases (35%) followed by adjacent segment disease (ASD) in 23/75 cases (30%). Cutibacterium acnes and Staphylococcus epidermidis were the most commonly isolated microorganisms, observed in 45% and 31% of cases, respectively. C. acnes was isolated in 65.2% of cases when the indication for revision surgery was ASD.

CONCLUSION

Infection must always be considered as a possibility in the setting of spinal revision surgery, especially in the case of hardware failure, regardless of the lack of clinical signs. Sonication should be routinely used to isolate microorganisms adherent to implants. Cite this article: Bone Joint J 2019;101-B:621-624.

Risk Factors for Positive Cultures in Presumed Aseptic Revision Spine Surgery

STUDY DESIGN

Retrospective case-control study.

OBJECTIVE

To report culturing patterns and results in the setting of presumed aseptic revision spinal surgery.

SUMMARY OF BACKGROUND DATA

The indications for obtaining cultures in revision spinal surgery remain unclear in the absence of a definitive diagnosis of infection. Culture results and risk factors for having positive cultures in this setting have not been previously studied.

METHODS

We retrospectively reviewed 595 consecutive revision spine surgeries performed by four senior spine surgeons between 2008 and 2013. Preoperative workup revealed the diagnosis of infection in 17 cases which were excluded from review. The remaining 578 presumed aseptic cases were included. Univariate and multivariate analyses were performed to identify variables associated with obtaining cultures and risk factors for positive cultures.

RESULTS

Cultures were obtained in 112 (19.4%) cases and were positive in 40.2%. Pseudarthrosis was the most common revision diagnosis when cultures were obtained (49.1%) and Propionibacterium acnes was the most common organism isolated from positive cultures (48.8%). Regarding culture results, multivariate analysis demonstrated that male sex (odds ratio [OR] = 3.4) and pseudarthrosis (OR = 4.1) were significantly associated with having positive cultures while fusion procedures (OR = 0.3) were negatively correlated, with area under the curve (AUC) 0.71.

CONCLUSION

Unexpected positive cultures occurred commonly and P. acnes was the predominant isolated organism. Male sex, pseudarthrosis, and non-fusion cases predicted positive cultures. Considering these results, we recommend cultures be obtained in revision cases for pseudarthrosis, even in the setting of negative infectious work-up preoperatively.

LEVEL OF EVIDENCE

4.

Surgical Site Infections in Spine Surgery: Preoperative Prevention Strategies to Minimize Risk

STUDY DESIGN

Literature review.

OBJECTIVES

A review of the literature identifying preoperative risk factors for developing surgical site infections after spine surgery and discussion of the preventive strategies to minimize risks.

METHODS

A review of the literature and synthesis of the data to provide an updated review on the preoperative management of surgical site infection.

RESULTS

Preoperative prevention strategies of reducing surgical site infections in spine surgery remains a challenging problem. Careful mitigation of modifiable patient comorbidities, blood glucose control, smoking, obesity, and screening for pathologic microorganisms is paramount to reduce this risk. Individualized antibiotic regimens, skin preparation, and hand hygiene also play a critical role in surgical site infection prevention.

CONCLUSIONS

This review of the literature discusses the preoperative preventive strategies and risk management techniques of surgical site infections in spine surgery. Significant decreases in surgical site infections after spine surgery have been noted over the past decade due to increased awareness and implementation of the prevention strategies described in this article. However, it is important to recognize that prevention of surgical site infection requires a system-wide approach that includes the hospital system, the surgeon, and the patient. Continued efforts should focus on system-wide implementation programs including careful patient selection, individualized antibiotic treatment algorithms, identification of pathologic organisms, and preoperative decolonization programs to further prevent surgical site infections and optimize patient outcomes.

Growth of Cutibacterium acnes is common on osteosynthesis material of the shoulder in patients without signs of infection

Background and purpose - Cutibacterium acnes, formerly known as Propionibacterium acnes, is often isolated from deep tissues of the shoulder. It is recognized as an important causative agent of foreign-material associated infections. However, the incidence and significance of its detection in tissues from patients without clinical evidence for infection is unclear. We assessed the incidence of C. acnes colonization of osteosynthesis material in asymptomatic patients, and evaluated the short-term outcome in relation to the microbiological findings. Patients and methods - We microbiologically analyzed osteosynthesis material of 34 asymptomatic patients after surgery on the clavicle. Material obtained from 19 asymptomatic patients after osteosynthesis of the fibula served as a control group. Patients were clinically followed up for 3-24 months after removal of the osteosynthesis material. Results - Bacteria were recovered from devices in 29 of 34 patients from the clavicle group. 27 of 29 positive samples grew C. acnes. Isolation of C. acnes was more common in male than in female patients. No bacterial growth was observed on foreign material from patients in the fibula group. All patients remained asymptomatic at follow-up. Interpretation - Growth of C. acnes is common on osteosynthesis material of the shoulder, especially in males. Samples were positive irrespective of clinical signs of infection. Therefore, detection of C. acnes in this clinical setting is of questionable clinical significance. The high positivity rate in asymptomatic patients discourages routine sampling of material in cases without clinical evidence for infection.

Anterior cruciate ligament reconstruction complicated by Propionibacterium acnes infection: case series

Anterior cruciate ligament (ACL) reconstruction is one of the most commonly performed orthopaedic procedures. While generally successful, failure resulting in revision surgery is reported to be between 1.9 - 4.9%. However, when not related to traumatic re-injury, failure mechanism is poorly understood. One potential but understudied mechanism of ACL reconstruction failure is infection. We describe three patients with previous ACL reconstructions who later developed infection with Propionibacterium acnes. Two cases presented with knee pain and swelling, and one presented with instability. While only two of the three cases received antibiotic treatment, all three cases were free of knee and infectious symptomatology at most recent follow-up. P. acnes infection may represent one potential mechanism for biologic failure of ACL reconstruction and anaerobic operative cultures may be used to identify its presence.

Revision spine surgery in patients without clinical signs of infection: How often are there occult infections in removed hardware?

PURPOSE

To examine the incidence of occult infection in revision spine surgeries and its correlation with preoperative inflammatory markers.

METHODS

We retrospectively reviewed all patients who underwent revision spine surgery and hardware removal between 2010 and 2016. Patients who had preoperative clinical signs of infection were excluded. The hardware and surrounding tissue culture results were obtained. The patients' diagnosis and preoperative inflammatory marker (ESR, CRP, and procalcitonin) levels were recorded.

RESULTS

A total of 162 consecutive patients were included in this study. The patients' mean age was 61 years (range 14-88). One hundred and three patients (63.6%) were female. Seventy-two patients (44.4%) had loose hardware and 88 patients (54.3%) had pseudarthrosis. Postoperatively, the hardware and/or surrounding tissue culture was positive in 15 patients (9.3%). The most commonly identified organisms were Propionibacterium acnes (7/15, 46.7%) and Staphylococcus (6/15, 40.0%). The other identified organisms were Pseudomonas aeruginosa (1/15, 6.7%) and Serratia marcescens (1/15, 6.7%). Only four patients with positive cultures had elevated preoperative ESR and CRP levels. Only two patients with positive cultures had elevated preoperative procalcitonin levels. There is no correlation between the patients' preoperative ESR, CRP, procalcitonin levels, and positive culture results (p > 0.05).

CONCLUSIONS

Our study shows that occult infections are present in 9.3% of patients who underwent revision spine surgery and hardware removal although they did not have clinical signs of infection. Those commonly used preoperative inflammatory markers such as ESR, CRP, and procalcitonin may not be sensitive enough to detect occult infections in these patients. These slides can be retrieved under Electronic Supplementary Material.

Propionibacterium acnes biofilm is present in intervertebral discs of patients undergoing microdiscectomy

Background

In previous studies, Propionibacterium acnes was cultured from intervertebral disc tissue of ~25% of patients undergoing microdiscectomy, suggesting a possible link between chronic bacterial infection and disc degeneration. However, given the prominence of P. acnes as a skin commensal, such analyses often struggled to exclude the alternate possibility that these organisms represent perioperative microbiologic contamination. This investigation seeks to validate P. acnes prevalence in resected disc cultures, while providing microscopic evidence of P. acnes biofilm in the intervertebral discs.

Methods

Specimens from 368 patients undergoing microdiscectomy for disc herniation were divided into several fragments, one being homogenized, subjected to quantitative anaerobic culture, and assessed for bacterial growth, and a second fragment frozen for additional analyses. Colonies were identified by MALDI-TOF mass spectrometry and P. acnes phylotyping was conducted by multiplex PCR. For a sub-set of specimens, bacteria localization within the disc was assessed by microscopy using confocal laser scanning and FISH.

Results

Bacteria were cultured from 162 discs (44%), including 119 cases (32.3%) with P. acnes. In 89 cases, P. acnes was cultured exclusively; in 30 cases, it was isolated in combination with other bacteria (primarily coagulase-negative Staphylococcus spp.) Among positive specimens, the median P. acnes bacterial burden was 350 CFU/g (12 - ~20,000 CFU/g). Thirty-eight P. acnes isolates were subjected to molecular sub-typing, identifying 4 of 6 defined phylogroups: IA₁, IB, IC, and II. Eight culture-positive specimens were evaluated by fluorescence microscopy and revealed P. acnes in situ. Notably, these bacteria demonstrated a biofilm distribution within the disc matrix. P. acnes bacteria were more prevalent in males than females (39% vs. 23%, p = 0.0013).

Conclusions

This study confirms that P. acnes is prevalent in herniated disc tissue. Moreover, it provides the first visual evidence of P. acnes biofilms within such specimens, consistent with infection rather than microbiologic contamination.