Safety and Efficacy of Negative Pressure Wound Therapy for Deep Spinal Wound Infections After Dural Exposure, Durotomy, or Intradural Surgery

Journal Pre-proof Safety and efficacy of negative pressure wound therapy (NPWT) for deep spinal wound infections following dural exposure, durotomy or intradural surgery Sami Ridwan, M.D., Alexander Grote, M.D., Matthias Simon, M.D. PII:

S1878-8750(19)32784-6

DOI:

https://doi.org/10.1016/j.wneu.2019.10.146

Reference:

WNEU 13617

To appear in:

World Neurosurgery

Received Date: 30 June 2019 Revised Date:

22 October 2019

Accepted Date: 23 October 2019

Please cite this article as: Ridwan S, Grote A, Simon M, Safety and efficacy of negative pressure wound therapy (NPWT) for deep spinal wound infections following dural exposure, durotomy or intradural surgery, World Neurosurgery (2019), doi: https://doi.org/10.1016/j.wneu.2019.10.146. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Elsevier Inc. All rights reserved.

Safety and efficacy of negative pressure wound therapy (NPWT) for deep spinal wound infections following dural exposure, durotomy or intradural surgery

Sami Ridwan, M.D., Alexander Grote, M.D., Matthias Simon, M.D. Department of Neurosurgery, Bethel Clinic, Bielefeld, Germany

Dr. med. Sami Ridwan, M.D. [email protected] PD Dr. med. Alexander Grote, M.D. [email protected] Prof. Dr. med. Matthias Simon, M.D. [email protected]

Corresponding author: Sami Ridwan, M.D. Department of Neurosurgery Bethel Clinic Kantensiek 11 33617 Bielefeld Germany Tel: 0049-521772778350 [email protected]

Keywords: VAC, NPWT, spinal surgery, spine, revision surgery, spinal infection, dura

INTRODUCTION Exposure of the spinal dura is common in neurosurgical procedures and surgery for intradural pathologies requires some form of dural incision, most often a midline durotomy. Accidental dural tears are a common complication of all kinds of spinal surgeries, and incidence rates ranging from 1% to 17% in patients without and up to 28.6% with previous surgery have been published for decompressive as well as instrumented surgeries1-5. Spinal cerebrospinal fluid (CSF) leaks are a serious complication after spine surgery and can result in severe adverse events. In some cases, deterioration of consciousness and even coma can occur due to intracranial hypotension caused by CSF loss6. This is a major concern when one considers application of negative pressure wound therapy (NPWT) for the treatment of deep wound infections in such patients.

Negative pressure wound therapy was introduced in the early 1990s and was proven to increase skin perfusion7,8. NPWT is widely available and is commonly used in the treatment of soft tissue wound infections. Application of negative pressure as part of the treatment of spinal wound infections has been shown to be an effective surgical option9-13. Deep spinal wound infections (DSWI) or surgical site infections (SSI) are a major complication following spine surgery. Rates for wound infections following spine surgery reported in the literature vary, however, in selected patients the risk may well reach up to 20% 9,14,15. DSWI can occur after instrumented spine surgery as well as surgery for lumbar disc herniations or spinal stenosis. Several risk factors as well as prophylactic measures have been identified16-19. Specifically, a posterior approach and tumor surgery have been associated with an increased risk for DSWI, and prophylactic antibiotics, irrigation and drainage may help to reduce infection rates. In instrumented cases, deep wound infections might compromise the stability

of the instrumentation resulting in repeat surgery with removal of the implanted hardware in some patients10,20.

The literature contains only a few reports of 20 or more patients describing the use of NPWT after spinal surgery10,21. Very limited information is available regarding NPWT in the presence of exposed dura22. In the present paper, we report a fairly large and recent experience with NPWT therapy for deep spinal wound infections in cases with exposed and previously incised dura.

METHODS Patient population The hospital’s electronic database was searched for all spinal surgery cases treated at the Department of Neurosurgery, Bethel Clinic, Bielefeld, Germany from January 2014 until June 2018. Twenty-seven patients receiving NPWT treatment for spinal wound infections were identified. The diagnosis of a deep spinal wound infection was made based on a combination of a clinical examination suggestive of infection (i.e. purulent secretion, fever, erythema), laboratory results with elevated inflammation markers and imaging findings consistent with an infection. In two cases a deep wound infection was diagnosed solely because of increased WBC and CRP values (WBC = 12 and 15 /nl, CRP = 124 and 499 mg/l). Intraoperative cultures were positive in one case (S. aureus). The decision to proceed with NPWT therapy rather than to attempt a direct wound closure was made by the operating neurosurgeon and was based on the preoperative and intraoperative clinical as well as laboratory and imaging findings. Twenty-five patients with various indications for spinal surgery (Figure 1) and documented exposure of the dura during the initial surgery were included in this analysis. During the study period, another 13 patients (6 females and 7 males; aged 4 – 88 yrs.; 61.5% instrumented cases) with superficial/epifascial spinal wound infections (N=7; 54%) and infections involving the subfascial compartment at least to some degree were (all successfully) managed with conventional revision surgery or NPWT (2 cases with no exposure of the dura) as deemed appropriate by the treating neurosurgeon. We defined application of NPWT during the first revision surgery for DSWI as “early”, and NPWT following one or more conventional revision surgeries is defined as “delayed”.

Clinical and treatment data This was a retrospective study. Pertinent data were collected retrospectively from the patients’ clinical records and the hospital’s database and were analyzed. The study was approved by the responsible institutional review board for human research (Ethikkommission der Ärztekammer Westfalen-Lippe und

der Westfälischen

Wilhelms-Universität Münster, Az 2019-003-f-S).

In addition to demographic and epidemiologic data, initial spine pathology and surgery, number of segments involved, instrumentation, intraoperative dura incision and type of closure, antibiotic treatment, duration of NPWT therapy, number of dressing changes and the patients’ clinical course were recorded. Comorbidities were also reviewed and the Charlson Comorbidity Index (CCI) was calculated as described in the literature and then tested for possible correlations with the treatment data19,23-25. Microbiology findings were also extracted from the hospital’s electronic database.

Revision surgery and NPWT treatment During revision surgery debridement was performed followed by irrigation and inspection of the wound. When present, CSF leakage was treated as required to achieve a watertight closure. Microbiology samples were acquired during revision surgery after sterilization of the skin and proper draping of the surgical site. Antibiotic treatment was initiated after revision surgery on an empirical basis and modified according to the microbiological findings as soon as they became available.

Renasys (Smith and Nephew) grey foam NPWT dressings were applied, followed by a transparent self-adhesive plastic sheet generously exceeding the wound margins to achieve optimal sealing. Next, a self-adhesive connecting tube was attached to the center of the dressing after performing a small incision of the plastic sheet. NPWT treatment was performed with a continuous negative pressure of 60 mmHg in all cases.

Most patients received NPWT treatment as in-patients, only one patient was treated as an out-patient between dressing changes. Per routine, dressing changes were performed every 3 to 4 days. All NPWT dressing surgeries were conducted in the operating theatre under sterile conditions. General anesthesia was applied when patients could not tolerate dressing changes under local analgesia, and for first revision and final wound closure. All patients were followed through the outpatient clinic at least until wound closure and suture removal.

Statistical analysis Statistical analysis was performed using standard methods (Fisher exact test, chisquare test, trend tests, Student t-test, ANOVA) for univariate analyses (IBM Corp. Released 2015. IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp).

RESULTS Clinical characteristics From January 2014 until June 2018, we treated twenty-five patients (12 males and 13 females) with dural exposure during primary spinal surgery for deep spinal wound infections in our department. The mean age was 69 years (range 42 - 88 yrs.). Indications for primary spinal surgery included degenerative spine disease in 8 (32.0%) cases, spinal infection in 8 (32.0%), tumor in 7 (28.0%) and trauma in 2 cases (8.0%; Figure 1). The primary surgery was performed in the cervical spine in one case (4.0%), for thoracic spine disease in 8 (32.0%) and in the lumbar spine in 16 patients (64.0%). 18 patients (72.0%) received instrumentation in addition to decompression surgery. The median number of segments addressed was 2 (range 1-9). All patients had a posterior surgical approach. Clinical characteristics of the patients and details of the primary surgical treatment can be found in table 1.

Nineteen patients had spinal imaging prior to their revision surgery. In 13/18 cases undergoing MR scanning, imaging findings suggested the presence of a DSWI. One patient had a CT investigation compatible with an infection. 13 patients presented with markedly elevated inflammation markers (WBC > 12 /nl and/or CRP > 100 mg/l). Wound secretion was observed in 22 cases.

Complications and comorbidities The majority of patients (N=21; 84.0%) had at least one documented comorbidity (median 4; range 0-12) including diabetes in 7 (28.0%) patients. The distribution of comorbidities among the patient cohort (in terms of the CCI) is shown in table 2. Three patients suffered medical complications during in-hospital treatment. Kidney failure was diagnosed in one case and another patient had to be treated for a urinary

tract infection. Pulmonary edema was seen in the third case. One patient died of cardiovascular complications while still receiving NPWT therapy.

Interestingly, the CCI score (i.e. the presence of comorbidities) did not correlate with duration of NPWT treatment, the number of dressing changes or the occurrence of medical complications. This was also the case for diabetes alone and when using the median CCI score (< vs. ≥ 5 points; range 0-10) as a cut-off value.

Dural exposure and durotomy cases The dura was exposed in all cases during the primary spinal surgery and incised/opened either accidentally or on purpose in 10 cases (40.0%). On closer analysis, the dura was incised on purpose in 3 and accidentally in 7 patients. The dura was sutured in 6 cases with a self-adhesive patch (Tachosil® sealant matrix, Takeda Austria GmbH) additionally applied in 5 of these patients. A self-adhesive patch without suture was used in the remaining 4 patients.

During revision surgery, the muscle fascia was reopened, and the dura re-exposed in all cases without preceding durotomy. In patients with injury of the dura during the primary surgery the muscle facia was reopened in 7/10 cases. During revision, a dural laceration was observed in 3 patients. All three had delayed NPWT treatment 2, 3 and 4 days after their first revision surgery. The dural tear was addressed using a muscle patch with additional adhesive in one case and only an adhesive patch in the other two cases. Actual CSF leakage during revision surgery was documented in one of these patients.

Patients with a durotomy during primary surgery received NPWT therapy significantly less often as part of their first revision surgery “early” when compared to those with intact dura (durotomy: 4/10; 40.0% vs. no durotomy: 13/15; 86.7%; p=0.01). However, a previous durotomy did not affect time to revision or NPWT therapy, duration of NPWT treatment or number of dressing changes.

NPWT treatment results The average time period between primary surgery and revision surgery was 25.0 ± 53.8 (median: 12) days, and between primary surgery and NPWT therapy 27.6 ± 53.2 (median: 14) days. One case needed revision surgery 280 days after the initial operation. Excluding this patient, average time to revision and NPWT therapy was 14.4 ± 9.3 (median: 11.5; range 5-38) and 17.1 ± 8.7 (median: 13.5; range 6-38) days. NPWT therapy was initiated as part of the first revision surgery “early” in 17 patients (68.0%), while 1-2 revisions were performed prior to NPWT treatment “delayed” in the other 8 (32.0%) cases (table 1). The number of surgical foam/dressing changes required for eventual wound closure ranged from 2-14 (median: 4; mean: 4.8 ± 3.2), and the duration of NPWT therapy from 10 to 70 (median: 19; mean: 26.8 ± 17.7) days.

Early versus delayed NPWT treatment Applying NPWT treatment after the first revision operation (i.e. “early”) did not have a significant impact on the overall duration of treatment or NPWT treatment until wound closure when compared to delayed NPWT therapy. Overall treatment durations were 41.5 ± 17.0 days for early vs. 40.2 ± 21.3 days for delayed NPWT treatment. Average NPWT treatment duration was 24.8 ± 15.3 days for early and 31.7 ± 23.0 days for delayed NPWT. The number of dressing changes required until wound closure was

lower for early NPWT (mean: 3.9 ± 2.2 for early vs. 6.6 ± 4.5 for delayed NPWT, p=0.05). Patients with primary surgery for degenerative disease received early NPWT treatment in only 3/8 (37.5%) cases, whereas patients with primary surgery for spine infections were mostly treated with NPWT during first revision (7/8 cases = 87.5%; p=0.09). There were no further correlations between the diagnoses leading to primary surgery (tumor, trauma, degenerative, infection), location of the DSWI (cervical, thoracic, lumbar) and instrumentation with the duration and number of NPWT surgeries or microbiological findings.

Follow up outcomes No local surgery-related complications were observed. Specifically, there were no CSF leaks and no CSF infections, and no patient required removal of her or his instrumentation. Patients were followed in the outpatient clinic or through consultation as needed. Mean follow-up after the last NPWT surgery was 92.9 ± 127.8 days (median 29; range 5 – 474 days). Wounds were eventually surgically closed in 20 cases (80.0%). Two of these patients required further and ultimately successful conservative wound treatment due to prolonged healing after surgical closure. One patient required a second NPWT treatment after undergoing NPWT followed by closure surgery with a delay of 96 days until the wound was finally healed (from first to final wound closure surgery). One patient required reconstructive surgery using a musculocutaneous flap to achieve final wound closure, which was performed by a plastic surgeon. Five patients were not eligible for surgical closure and received further conservative wound management. Two of these patients were transferred to other departments with ongoing NPWT treatment and were eventually lost to follow up before documentation of final wound healing (both malignant tumor cases). One

patient died after 6 dressing changes (see above). In the remaining two cases wound healing was eventually documented.

Microbiological findings Microbiological studies of all patients were available and were positive in 21 cases (84.0%). Staphylococcus aureus accounted for the majority of infections (N=12; 48.0%). A mixed infection was detected in four cases (16.0%). Gram-negative infections were detected only in a few cases with mixed infections. There was no case with a gram-negative monobacterial infection. A detailed list of the microorganisms cultured is provided in table 3. Mixed wound infections (4 cases) required more dressing changes as compared to monobacterial infections (7.3 ± 5.4 vs. 3.9 ± 2.8; p=0.08). Otherwise, overall and duration of NPWT therapy as well as number of dressing changes did not vary with the microbiological findings.

DISCUSSION The management of deep spinal wound infections (DSWI) poses very significant challenges. Removal of the implants is a major concern in instrumented patients

20

.

The development of discitis or spondylodiscitis is another dreaded complication26,27. A deep wound infection in patients with exposed dura or even a durotomy during primary surgery also carries a very significant risk of meningitis or other CNS infection. Negative pressure wound therapy (NPWT) has been more recently added to the surgical armamentarium and has been reported to be safe and efficacious in DSWI cases

12,22

. Moreover, some studies demonstrated that NPWT treatment might

prevent implant removal in instrumented patients 22,28,29.

The present study reports reasonable wound outcomes and no complications related to CSF-leakage in a sizable cohort of N=25 patients who had previous spinal neurosurgery including dural exposure in all and an accidental or intended durotomy in 40.0% of the cases (N=10). We feel that this is an important piece of information. Conceptually, the risk for the development of a CSF leak and CNS infections should be a major concern if one considers NPWT treatment in the presence of exposed dura and in particular following a previous durotomy. Indeed, serious complications such as intracranial hemorrhages and rapid deterioration of consciousness have been reported following spine surgery with reported or suspected CSF leakage.30-33 Duration of NPWT treatment and number of dressing changes were higher in our cohort when compared to the series reported by Lee et al. and Mehbod and coworkers which might reflect the relatively high percentage of patients (12/25 = 48.0%) with primary surgery for malignant spine disease or spinal infections in this study.

Our findings confirm a recent analysis of 42 instrumented spine cases including 30 patients with exposed dura, which also addressed the safety of NPWT treatment in patients with exposed dura22. Lee et al. prospectively collected cases from two major orthopedic hospitals. Our study was retrospective and smaller but included a similar number of cases with dural exposure, and its case mix reflects a neurosurgical rather than orthopedic practice in a single institution over a somewhat shorter time period (4.5 vs. 7.75 yrs.).

In contrast to the present paper the study by Lee et al. provides no details with respect to dural injuries and CSF leaks during the primary or revision surgeries, and their respective management. We report three cases of successful NPWT treatment following surgery for intradural pathologies. Of note, three of our cases with delayed NPWT therapy application after a prior revision required closure of the dura during the preceding revision surgery and received NPWT treatment only a few days afterwards (2 – 4 days) without suffering any CSF leak-related complication. One of these cases presented with an active leak during NPWT surgery which was sealed before NPWT application. Data regarding NPWT application in cases with active CSF leaks do not exist in the literature. Together, these data suggest that NPWT therapy for DSWI is very safe in the presence of exposed dura even following (a very recent) accidental or intended durotomy. Of note, we have always paid close attention to a watertight dural closure, and all our patients had an adequate closure of the dura before NPWT therapy was initiated. We would also like to point out, that we and others have used a substantially lower vacuum pressure setting (i.e. 50-60 mmHg) in the presence of exposed dura than what is commonly recommended for the treatment of other deep wound infections at 125 mmHg12,14,22,34-37.

Our series also included 18 (72.0%) patients with (posterior) instrumentation of up to 9 segments (median: 2). No patient required hardware removal for final wound closure. Loss of metalwork might constitute a serious problem at least in some patients. Depending on the specific pathology, number of spinal segments addressed and if and to what extent bony fusion has already occurred, instrumentation removal will result in a variable degree of loss of correction

10,21,22,38-40

. Of note, the relation

between fusion, implant loosening and infection might be far from trivial with some low-grade infections actually promoting or even causing instrumentation failure41.

The question of whether or when NPWT treatment is advantageous over a more conventional strategy including multiple aggressive debridement and continuous irrigation/suction is not easy to answer. Our data as well as several other studies suggest an important role for NPWT therapy in the treatment of at least difficult spinal wound infections. Mehbod et al. reported that NPWT reduced frequency of surgical debridement10. Ploumis et al. highlighted the role of NPWT therapy as an option even after repeat procedures in a large retrospective cohort21. Labler et al. described NPWT treatment as a valuable alternative for spinal wound management9. Somewhat in contrast, Yuan et al. have recently compared NPWT treatment with a policy of continuous irrigation and suction and found that both treatment methods were comparable regarding wound healing. NPWT treatment was even shown to be more expensive and resulted in longer hospital stays42. Finally, Jones et al. pointed out serious complications associated with NPWT therapy in patients with spinal injuries14.

For the present study, coexisting medical conditions were assessed using a wellestablished comorbidity index (CCI). A higher CCI has been shown to correlate with higher readmission rates following orthopedic surgery in general43. We found no evidence that comorbidities had an impact on our treatment outcomes. This almost certainly reflects the limited number of patients included in our study, however, we still feel that these data exclude a very major role of coexisting diseases on the time course and outcome of NPWT treatment, and that NPWT treatment for DSWI is safe and efficacious even in severely ill and multimorbid patients (when compared to more conventional alternatives).

Microbiological findings in our cohort differed from previously published studies as our data revealed S. aureus as the major causative organism followed by CoNS

13,22

.

This might reflect regional, hospital or specialty-related characteristics. Not unexpectedly, infections with multiple bacteria proved more difficult to cure. Similar observations were also published by Ploumis et al., who reported that patients with mixed bacterial infections were more likely to require repeated revision surgery and NPWT treatment21. Of note, NPWT treatment was still successful in our hands despite a difficult infectiological setting.

Finally, we would like to acknowledge several limitations of the present study. Most notably, the overall number of patients is small, even though no really substantially larger case cohort has been published so far. The study was retrospective, and it lacks controls. On the other hand, our major finding, that NPWT treatment for DSWI even in the presence of a dural tear or recent durotomy is safe and efficacious is well supported by our data, and we feel that it is important to share this information.

Conclusion: Application of NPWT treatment in deep spinal wound infections (DSWI) is safe and efficacious in cases with exposure of the dura or durotomy during the (preceding) surgery. After proper dural closure the risk of a CSF leak (and associated complications) should not be a major concern when NPWT therapy is considered in revision spine surgery.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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Table 1: Patient and treatment data No.

Age

Sex

(yrs.)

Primary

Instrumented

Diagnosis

Surgery

Durotomy

Dressing

Rev.

changes

pre

Microbiology

Year

NPWT

Cervical 1

74

F

C6 fracture

Thoracic & thoracolumbar Meningioma 2 79 F T1/2 Meningioma 3 51 F T2/3 Ependymoma 4 42 F T3-5

Yes

Yes

2

0

CoNS

2014

No

Yes**

2

0

S. aureus

2016

No

Yes**

2

1

S. aureus

2016

No

Yes**

2

0

S. aureus

2015

5

58

M

T1-5 deformity

Yes

No

4

1

S. epidermidis

2017

6

82

M

Discitis T12/L1

Yes

No

3

0

CoNS

2015

7

63

M

Yes

No

6

0

Negative

2017

8

47

M

Yes

Yes

12

1

S. aureus

2016

9

61

M

Yes

No

5

0

S. aureus

2014

10

78

F

Stenosis L3/4

No

No

2

0

11

77

M

Stenosis L3-5

No

Yes

4

1

12

58

M

Stenosis L4/5

No

Yes

3

1

S. aureus

2017

13

49

M

Empyema L3-5

No

No

7

0

Negative

2017

14

70

F

Sarcoma L1/2

No

No

5

0

Negative

2016

15

54

F

L1 fracture

Yes

No

3

0

S. aureus

2015

16

67

F

Yes

Yes

3

0

Enterococcus

2018

17

73

F

Yes

No

2

0

S. aureus

2015

18

77

F

Yes

No

5

1

S. aureus

2014

19

69

F

Yes

Yes

14

2

S. aureus E. Coli

2016

20

89

M

Discitis L2/3

Yes

No

2

0

S. haemolytic.

2017

21

81

F

Discitis L2-5

Yes

No

7

0

S. aureus

2017 2016

Thoracic metastasis T1 Thoracic metastases T1-5 Thoracic metastasis T2

Lumbar

Stenosis and mobility L3/4 Stenosis and mobility L3/4 Stenosis and mobility L4/5 Stenosis and mobility L4/5

CoNS Corynebact. E. Coli Enterococcus

2016 2016

22

64

F

Discitis L3-5

Yes

Yes

9

2

S. epidermidis Klebsiella Citrobacter

23

72

M

Discitis L3-5

Yes

No

2

0

S. epidermidis

2018

24

54

M

Discitis L4/5

Yes

No

8

0

S. aureus

2016

25

79*

M

Discitis L4/5

Yes

No

6

0

Negative

2018

C: Cervical, CoNS: Coagulase Negative Staphylococci, L: Lumbar, No.: Number, NPWT: Negative Pressure Wound Therapy, Rev.: Revision, T: Thoracic, Yrs.: Years, * patient deceased ** intended durotomy

Table 2: Distribution of comorbidities Charlson Comorbidity Index CCI

Patients

0 Points

1

1 Points

3

2 Points

1

3 Points

2

4 Points

3

5 Points

5

6 Points

3

8 Points

6

10 Points

1

Table 3: Microbiological findings Infection

Gram

N

S. aureus

+

11

CoNS (incl. S. epidermidis)

+

4

Enterococcus species

+

1

S. haemolyticus

+

1

E. coli and Enterococcus

-/+

1

CoNS and Corynebacterium

+/+

1

+/-/-

1

+/-

1

S. epidermidis, Klebsiella and Citrobacter S. aureus and E. coli

Abbreviation list CCI

Charlson comorbidity index

CoNS

Coagulase negative staphylococcus

CSF

Cerebrospinal fluid

CT

Computed tomography

DSWI

Deep spinal wound infection

E. coli

Escherichia coli

MRI

Magnetic resonance imaging

NPWT

Negative pressure wound treatment

S. aureus

Staphylococcus aureus

S. epidermidis

Staphylococcus epidermidis

S. haemolyticus

Streptococcus haemolyticus

SSI

Surgical site infection

VAC

Vacuum-assisted closure