Post-Operative Infection after Minimally Invasive versus Open Transforaminal Lumbar Interbody Fusion (TLIF): Literature Review and Cost Analysis

Inhaltsübersicht

Abstract

Introduction: Surgical site infection (SSI) in the setting of lumbar fusion is associated with significant morbidity and medical resource utilization. To date, there have been no studies conducted with sufficient power to directly compare the incidence of SSI following minimally invasive (MIS) vs. open TLIF procedures. Furthermore, studies are lacking that quantify the direct medical cost of SSI following fusion procedures. We set out to determine the incidence of SSI in patients undergoing MIS vs. open TLIF reported in the literature and to determine the direct hospital cost associated with the treatment of SSI following TLIF at our institution.

Methods: A systematic Medline search was performed to identify all published studies assessing SSI after MIS or open TLIF. The cumulative incidence of SSI was calculated from all reported cohorts and compared between MIS vs. open TLIF. In order to determine the direct hospital costs associated with the treatment of SSI following TLIF, we retrospectively reviewed 120 consecutive TLIFs performed at our institution, assessed the incidence of SSI, and calculated the SSI-related hospital costs from accounting and billing records.

Results: To date, there have been 10 MIS-TLIF cohorts (362 patients) and 20 open-TLIF cohorts (1 133 patients) reporting incidences of SSI. The cumulative incidence of reported SSI was significantly lower for MIS vs. open-TLIF (0.6% vs. 4.0%, p=0.0005). In our experience with 120 open TLIF procedures, SSI occurred in 6 (5.0%) patients. The mean hospital cost associated with the treatment of SSI following TLIF was $ 29 110 in these 6 cases. The 3.4% decrease in reported incidence of SSI for MIS vs. open-TLIF corresponds to a direct cost savings of $ 98 974 per 100 MIS-TLIF procedures performed.

Conclusions: Post-operative wound infections following TLIF are costly complications. MIS vs. open TLIF is associated with a decreased reported incidence of SSI in the literature and may be a valuable tool in reducing hospital costs associated with spine care.

Key words

minimally invasive procedures - transforaminal lumbar interbody fusion - TLIF - post-operative infection

Introduction

Surgical site infection (SSI) in the setting of lumbar fusion is associated with significant morbidity and medical resource utilization [1] [2]. Reported rates of spinal SSIs in the literature range from 0.7 to 16% [1] [3] [4] [5]. Spinal SSIs can be challenging to manage and often require prolonged hospitalizations, extended antibiotic therapy, repeated surgery for wound debridement, instrumentation removal, or delayed complications of deep infection. These factors serve to increase health care resource utilization and cost, and may worsen overall clinical outcomes [6] [7] [8].

Transforaminal lumbar interbody fusion (TLIF) allows for a circumferential fusion via a single posterolateral approach and is being performed with increasing regularity due to its well documented efficacy [9] [10] [11]. Minimally invasive techniques for TLIF (MIS-TLIF) have recently been introduced with the aim of smaller wounds, less tissue trauma, and faster recovery [11] [12]. MIS techniques in general have been applied to various spinal surgical cases for more than a decade now, and reported series have suggested a very low rate of SSI after MIS spine surgery [13] [14]. Based on decreased tissue destruction, reduced blood loss, and shortened length of hospitalization reported for MIS- vs. open-TLIF, many authors have suggested that MIS approaches to TLIF may be associated with a decreased risk of SSI [11] [12].

To date, there have been no studies conducted with sufficient power to directly compare the incidence of SSI following minimally invasive (MIS) vs. open TLIF procedures. Furthermore, the direct medical cost of treating SSI following TLIF procedures is poorly understood and has not been assessed to date. We set out to determine the incidence of SSI in patients undergoing MIS vs. open TLIF as reported in the literature and to determine the direct hospital cost associated with the treatment of SSI following TLIF at our institution.

Methods

Systematic literature review

We performed a systematic review of the literature to identify all reported incidences of surgical site infection after MIS- vs. open-TLIF for the treatment of grade I−II spondylolithesis or degenerative disc disease. To answer these questions, search terms were identified and combined with appropriate Boolean connectors, and a search was carried out on English language publications on Medline (PubMed). The search sequence submitted was the following: (“interbody fusion”[MeSH] OR “transforaminal fusion”[MeSH] OR “minimally invasive”[MeSH] OR “interbody fusion”[title] OR “transforaminal fusion”[title]) AND (English [lang]) AND (“Treatment Outcome”[MeSH] OR “Outcome”[MeSH] OR (“infection”[All Fields] OR “surgical outcomes”[All Fields]); limits: English, publication date from 1975–2009.

All titles obtained from these search criteria were reviewed. Case reports, technical notes, and animal or laboratory studies were discarded. All remaining abstracts were then reviewed. Studies reporting outcomes of open or MIS transforaminal interbody fusion for indications other than grade I−II lumbar spondy­lolithesis or lumbar degenerative disc disease were discarded. Papers describing either open or MIS posterior lumbar interbody fusion (PLIF) were also discarded. The remaining manuscripts were then read in their entirety and included only if the incidence of post-operative infection was assessed. During the review, the incidence of SSI was classified as 0% only if the study reported 0% incidence. Studies not mentioning an incidence of SSI were excluded. In all studies, SSI was defined as an erythematous or purulent wound that was culture-positive requiring long-term intravenous antibiotics or surgical debridement. 2 authors independently reviewed each study. Any discrepancies in the assigned incidence of SSI were discussed between reviewers at the conclusion of review. If needed, a blind assessment was made by a third author to finalize the assessment of SSI incidence. For purposes of this review, transforaminal lumbar interbody fusions that were performed through a tubular retractor (rigid or expandable) and supplemented with percutaneous pedicle screws were considered as MIS-TLIF. Transforaminal lumbar interbody fusions that were performed via a midline incision with paraspinal muscle retraction and open pedicle screw placement was considered as open-TLIF.

Cost assessment

After institutional IRB approval, we retrospectively reviewed our most recent 120 consecutive open-TLIF procedures in order to identify our incidence and hospital cost of post-TLIF SSI. Operative notes, hospital discharge summaries, and clinic notes were reviewed to confirm the performance of open-TLIF for degenerative disc disease or grade I spondylolithesis and to identify all patients developing SSI following surgery. For patients developing post-operative SSI, institutional billing and accounting records were reviewed to assess all SSI-related hospital charges. Medical resources utilized for the comprehensive treatment of post-TLIF SSI were also recorded. Direct medical cost was defined as 70% of billing values [15].

Statistical analysis

The cumulative reported incidence of SSI was calculated from all reported MIS and open-TLIF cohorts in the literature and compared between MIS- and open-TLIF via the Fisher exact test. The mean direct hospital billing costs associated with the treatment of SSI at our institution were determined and the cost savings per 1% reduction in SSI incidence calculated. The cost savings per 1% reduction in SSI at our institution were used to estimate the cost savings associated with the cumulative reduction in SSI reported in the literature.

Results

Literature review

To date, there have been 10 MIS-TLIF cohorts, comprising 362 patients, and 20 open-TLIF cohorts, comprising 1 133 patients, reporting incidences of surgical site infection (SSI) following TLIF procedures. Mean age at the time of surgery was similar for patients reported in the MIS- vs. open-TLIF cohorts (53.6 vs. 47.8 years, p=0.17). Gender was also similar between reported MIS- and open-TLIF cohorts (male: 42.4% vs. 46.4%, p=0.10). All reviewed cohorts were first-time TLIF, and did not include revision surgery. Indication for surgery was degenerative disc disease or grade I−II spondylolisthesis for all reported MIS- and open-TLIF cohorts. The cumulative incidence of reported SSI was significantly lower in the MIS-TLIF cohorts at 0.6% vs. 4.0% in the open-TLIF cohorts, p=0.0005 ([Table 1] ).

Table 1 Summary of all MIS and open-TLIF cohorts in the literature to date assessing incidence of post-TLIF infection.

MIS TLIF Series	Cohort Size	Post-op Wound Infections	Infection Incidence (%)	Open TLIF Series	Cohort Size	Post-op Wound Infections	Infection Incidence (%)
Peng 2009 [11]	29	0	0.0	Peng 2009 [11]	29	1	3.4
Dhall 2008 [12]	21	0	0.0	Dhall 2008 [12]	21	0	0.0
Villavicencio 2005 [23]	73	2	2.7	Villavicencio 2005 [23]	51	0	0.0
Kim 2009 [24]	46	0	0.0	Lowe 2002 [25]	40	1	2.5
Starkweather 2008 [26]	17	0	0.0	Grob 2009 [27]	63	1	1.6
Deutsch 2006 [28]	34	0	0.0	Lauber 2006 [29]	39	1	2.6
Schwender 2005 [30]	49	0	0.0	Hsieh 2007 [31]	25	2	8.0
Selznick 2009 [32]	43	0	0.0	Faundez 2009 [33]	65	6	9.2
Lee 2008 [34]	27	0	0.0	Rodriguez 2008 [35]	20	3	15.0
Jang 2005 [36]	23	0	0.0	Humphreys 2001 [37]	40	0	0.0
				Hee 2001 [38]	111	5	4.5
				Hackenberg 2005 [10]	52	1	1.9
				Potter 2005 [39]	100	2	2.0
				Houten 2006 [40]	33	1	3.0
				Taneichi 2006 [41]	92	1	1.1
				Rosenberg 2001 [42]	22	2	9.1
				Chastain 2007 [43]	40	5	12.5
				Crandall 2009 [44]	20	1	5.0
				Carter 2009 [45]	20	1	5.0
				Rihn 2009 [46]	130	5	3.8
				Parker 2010	120	6	5.0
all series	n=362	n=2	0.6%	all series	n=1 133	n=45	4.0%

Cost analysis

120 patients underwent open-TLIF procedures at our institution over the reviewed period. Similar to the mean age reported in the literature for open-TLIF, mean age of patients undergoing open-TLIF was 48.4±13.2 years. Similar to the literature, the minority of patients were male [50 (41.7%)] and all surgeries were performed for degenerative disc disease or grade I–II spondylolisthesis. All cases were first-time lumbar fusion procedures. There were 3 (2.5%) instances of CSF leak. The mean±SD length of hospitalization was 5.1±3.4 days.

6 (5.0%) patients developed surgical site infection following open-TLIF. Management of SSI resulted in a mean±SD length of hospitalization of 12±10 days, 3.5±3.4 CT scans, 0.5±0.8 MRI scans, and 2.2±1.9 radiographs. A total of 15 subspecialty consults was obtained. 1 (16.7%) patient developed a deep venous thrombosis (DVT) during admission for SSI. 2 (33.3%) patients required rehabilitation during and after admission for SSI. 1 (16.7%) patient experienced an abnormal reaction (dermatological) to antibiotic treatment, which resolved following alteration of the antibiotic regiment. All patients required PICC lines for a mean length of intravenous antibiotics of 40±10 days.

The mean cost associated with the treatment of the 6 patients experiencing a SSI following open-TLIF was $ 29 110. At this mean cost of SSI, the 3.4% decrease in reported incidence of SSI for MIS vs. open-TLIF observed in the literature review corresponds to a cost savings of $ 98 974 per 100 MIS-TLIF procedures performed ($ 989 per MIS-TLIF).

Discussion

In our systematic review of the literature, the reported incidence of post-TLIF surgical site infection was significantly lower for MIS- vs. open-TLIF. 9 of the 10 published cohorts of MIS-TLIF reported a zero incidence of SSI. Of the 20 published cohorts of open-TLIF, all but 4 reported post-operative SSIs, ranging from 1.1–15%. To date, the cumulative reported incidence of SSI after MIS-TLIF is nearly 7-fold less than after open-TLIF.

There are several mechanisms by which the risk of SSI may be reduced with minimally invasive approaches to TLIF. Increased blood loss is an accepted risk factor for post-operative spinal infection [16]. Operative blood loss has been consistently reported to be less for MIS- vs. open-TLIF [11] [12] [17] [18]. Furthermore, many pathogens underlying spinal SSIs arise from nosocomial contamination of the wound. Length of hospital stay has also been consistently reported to be less for MIS- vs. open-TLIF [11] [12] [17] [18]. Decreased duration in the hospital after MIS-TLIF may directly reduce exposure to these hospital-acquired pathogens. Lastly, significant tissue ischemia and injury occurs with muscle retraction during open TLIF procedures [19] [20] [21]. This tissue injury which may delay wound healing and predispose to infection, may be minimized by MIS tubular approaches.

The incidence of SSI after open-TLIF was 5% in our experience. This is consistent with our calculated cumulative SSI incidence reported in the literature (4%). The mean direct cost for the 6 cases of post-TLIF SSI at our institution was $ 29 110. While all 6 of our patients with post-TLIF SSI were admitted to the hospital for comprehensive evaluation, 3 were successfully managed with 6-weeks of intravenous antibiotics and local wound care without further surgery. However, 3 patients required surgical debridment and drainage of deep purulent collections. Spinal instrumentation was not removed in these cases. One patient required further surgical repair and wound care by plastic surgery. In each of these cases, infection resolved and successful fusion occurred by 1-year post-operatively. The high costs associated with SSI observed here are likely applicable to other institutions since our SSI treatment protocol falls well within the standard of care. The medical resources consumed and costs associated with open-TLIF infection here are likely applicable to the treatment of MIS-TLIF since treatment would be similar. In all cases of post-TLIF SSI, patients underwent MRI evaluation to assess extent of infection as well as serological laboratory evaluation. Patients not requiring surgery were discharged as soon as infectious disease consultation was completed, long-term intravenous access was implanted (PICC line), and home antibiotics were secured. Patients with deep purulence underwent surgical washout. Hospitals with more aggressive SSI treatment protocols involving hardware removal or lower thresholds for surgical debridement may experience even greater hospital costs associated with post-TLIF SSI. Furthermore, the indirect costs of SSI were not assessed in this study. When accounting for indirect occupational and societal loss, the economic burden of SSI and the SSI-associated cost-savings of MIS may be greater than reported here.

While this literature review and retrospective cohort analysis is valuable in that it provides a comprehensive look at post-TLIF SSI as well as provides the first cost assessment of TLIF-specific SSI, it provides only a summation of level IV evidence (single cohorts) [22]. Furthermore, this analysis does not take into account variations in minimally invasive tubular approaches. Approaches which utilize wide areas of periosteal dissection with rigid tubes, widely expanded tubes, or unilateral open placement of pedicle screws through expandable tubes may be associated with higher infection rates. While all reviewed cohorts included a fairly homogenous patient population (first-time, single-level, DDD or spondylolithesis, L4-5 or L5-S1) and included pre- and peri-operative prophylactic antibiotic use with TLIF surgery, variance in surgeon sterility and techniques cannot be accounted for in this literature review. Since prospective cohort studies have been unable to enroll the several hundreds of patients required to properly compare SSI, this cumulative review of the literature is the first analysis to analyze SSI after MIS- vs. open-TLIF. Our findings suggest the growing need for a randomized controlled trial or a large-scale prospective comparison study with sufficient power to assess differences in low SSI rates.

Conclusions

Post-operative wound infections following TLIF were costly complications at our institution. MIS vs. open TLIF is associated with a decreased reported incidence of SSI in the literature and may be a valuable tool in reducing hospital costs associated with spine care. Prospective randomized trails powered to compare surgical site infection are warranted.

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