Infection Rates: How Do Infection Rates Compare between MIS and Open Spine Techniques?

22 Infection Rates: How Do Infection Rates Compare between MIS and Open Spine Techniques?

MIS: Kurt M. Eichholz
Open: Bryce A. Basques, Daniel D. Bohl, Nicholas S. Golinvaux, and Jonathan N. Grauer

22.1 Introduction

The field of minimally invasive spine (MIS) surgery has seen extensive advances over the past 30 years, and MIS procedures have become increasingly common.1 Following the trends of minimally invasive surgery in other disciplines, MIS aims to provide at least equivalent outcomes while offering benefits, such as decreased soft-tissue disruption, improved cosmesis, reduced blood loss, less postoperative pain, and decreased hospital length of stay following the procedure.¹ The relative rates of complications with open and MIS techniques bear consideration when comparing outcomes with these varying techniques.

Postoperative infection is one complication that is particularly concerning, given that surgical site infection (SSI) of the spine and surrounding structures has significant clinical sequelae. Infection occurs after both open and MIS spine surgery, and there is currently debate over which approach is associated with lower postoperative infection rates.

For the purposes of this chapter, infection was defined according to the Centers for Disease Control and Prevention (CDC)/National Nosocomial Infections Surveillance (NNIS) guidelines.² According to these guidelines, an SSI is defined as an infection that involves skin or subcutaneous tissue (superficial), fascia or muscle layers (deep), or any other anatomic components manipulated during surgery (organ space). While SSI definition varies from study to study, each study’s findings were correlated with the above-noted definitions in order to most accurately represent SSI occurrences and allow comparison among studies.

Understanding the differences in infection rates between MIS and open spine surgery is important for patients, surgeons, and hospitals, as well as the health system in general. Often, a specific disease state may be the driving factor for determining the best surgical approach. However, there are situations where such decisions are surgeons’ or patients’ choice. Especially in those situations, the relative risks may sway clinical decisions. With regard to infection, this may be especially true when treating patients at an elevated risk for infection, such as immunocompromised patients. By critically evaluating the quality and results of existing studies, informed discussions of the relative risks of open and MIS techniques can be facilitated.

22.2 Advantages of Minimally Invasive Surgery

There are several factors that may be considered relative risks or benefits of MIS techniques with regard to infection. First, the potential advantages of MIS procedures will be discussed.

The incisions of MIS techniques are smaller than open techniques. Accordingly, there is less exposure of internal structures. In endoscopic and tubular procedures, generally only the area at the base of the tube or trocar is exposed to the outside environment. The larger incisions of open surgeries could expose increased surface area for bacterial colonization.

Muscle ischemia and damage, which can occur during retraction, is believed to be greater during open procedures than MIS procedures.3 This may lead to compromised tissues at greater risk for infection. Furthermore, there is likely a reduced operative site dead space after the procedure. This may reduce the formation of postoperative seromas or hematomas that could serve as a nidus for an SSI.⁴

Intraoperative blood loss has been consistently reported to be less for MIS versus open transforaminal lumbar interbody fusion (TLIF).^5,6,7,8 As increased intraoperative blood loss has been shown to be a risk factor for postoperative spinal infection,⁹ this may be an advantage of MIS techniques with regard to infection.

Hospital length of stay has been repeatedly shown to be less after MIS procedures compared to open surgeries.^5,6,7,8 As increased length of stay has also been considered a risk factor for spinal SSIs due to nosocomial infection, this may be an additional advantage for MIS techniques.

22.3 Advantages of Open Surgery

There are several advantages of open techniques compared to MIS techniques with regard to infection risk. Compared to MIS techniques, most surgeons have more experience with open procedures, which have an easier learning curve.10 Increased surgeon experience has been shown to lessen risk of complications, including infection.¹¹

In addition, perhaps due to better exposure and an easier learning curve, operative time is generally less for open surgery compared to MIS.^5,12 Increased operative time has been shown to be an independent risk factor for postoperative infection after spine surgery.¹³

Open surgery also has the advantage of requiring less operative equipment, which may decrease risk of infection. Studies of operating microscope and C-arm sterility during spine surgery have shown significant bacterial contamination by the end of the surgical case.^14,15,16 Increased exposure to this contaminated equipment, as is necessary with the increased operative time and radiation exposure associated with MIS surgery, has the potential to increase risk of postoperative infection compared to open cases.^5,12,17,18

22.4 Case Illustration

A 47-year-old man presented with 4 months of pain in the back without radicular pain. He had undergone three prior surgeries—a lumbar microdiscectomy 13 years ago, a lumbar fusion 10 years ago, and then an L4–L5 anterior lumbar interbody fusion (ALIF) with L3–L5 posterior spinal fusion with instrumentation 4 years ago. He was treated conservatively and underwent a series of epidural steroid injections. With this third injection, he had immediate worsening pain that was radiating down the left leg to the lateral aspect of the left foot. He had no right leg radicular pain. On examination, he has weakness in his left hamstrings, anterior tibialis, and extensor hallucis longus at 4/5 with sensory loss in the left S1 distribution. His left Achilles reflex was absent, and his straight leg raise was positive at 30 degrees on the left side. His magnetic resonance imaging (MRI) showed previous instrumentation and interbody graft at L3–L5, and a left paracentral disc herniation causing neural foraminal stenosis at L5–S1 ( Fig. 22.1, Fig. 22.2).

Fig. 22.1 Preoperative T2 sagittal image.

Fig. 22.2 Preoperative T2 axial image.

He underwent a minimally invasive left L5–S1 microdiscectomy. The surgery was performed through a muscle-splitting tubular retractor system, using microscopic techniques. The operative time was 43 minutes, and the patient was discharged 3 hours and 50 minutes after surgery. This resulted in immediate improvement in his left leg radicular pain and sensory loss.

The patient presented for his 6-week follow-up visit and continued to have significant improvement in his left leg radicular pain, but had gradual back, buttocks, and upper thigh pain. He was neurologically intact with the exception of mild sensory loss in the left S1 distribution. His incision was well healed with no evidence of infection.

Over the next 2 weeks, the patient had gradually worsening pain that went down to his left leg and to the lateral aspect of his foot, with difficulty walking. He also had some pain in his right leg. On examination, he had full strength in all muscle groups, with increased sensory loss in the left S1 distribution and an absent left ankle jerk. His incision remained clean, dry, and intact.

A postoperative MRI was performed which showed a ringenhancing epidural mass extending into his hemilaminotomy defect ( Fig. 22.3, Fig. 22.4, Fig. 22.5, Fig. 22.6). He was taken to the operating room, and exploration revealed a significant epidural abscess with purulent material in the central canal. This was evacuated and irrigated, and cultures ultimately were negative. A PICC line was placed, and the patient was prescribed intravenous vancomycin for 6 weeks.

Of note, the patient stated that since postoperative day 3, he had spent at least 30 minutes per day soaking in a hot tub, despite postoperative instructions to the contrary.

22.5 Discussion of Minimally Invasive Spine

MIS surgery has several potential advantages compared to open procedures in terms of risk of infection. These potential advantages may be derived from the smaller incisions, decreased tissue ischemia/damage, reduced operative dead space, decreased intraoperative blood loss, and shorter postoperative length of stay of MIS procedures compared to open procedures.3,4,5,6,7,8 In recent years, there have been a number of studies comparing infection rates between MIS and open spine surgery, with the majority studying fusion cases ( Table 22.1). There are also a number of studies examining the complication rates between MIS and open discectomy as well as other types of MIS procedures from which infection data can be extrapolated ( Table 22.2, Table 22.3).

While other studies have reported infection rates in a single cohort of MIS or open surgery patients, it was felt to be most appropriate to use only those studies that included both cohorts in order to provide accurate comparisons. Most of the following studies looked at complications after various procedures and collected infection data as one of the complication measures. Many of these studies are limited by small patient numbers, making it difficult to accurately compare a rare outcome such as postoperative infection. As such, the quality of studies for each type of procedure varies.

Fig. 22.3 Postoperative T2 sagittal image.

Fig. 22.4 Postoperative T2 axial image.

Fig. 22.5 Postoperative T1 with contrast sagittal image.

Fig. 22.6 Postoperative T1 with contrast axial image.

22.5.1 Level I Evidence in Minimally Invasive Surgery

To our knowledge, only two level I studies have been conducted comparing outcomes between MIS and open surgery.19,20 There have been several other randomized, prospective studies comparing MIS and open spine surgery approaches; however, these other studies did not meet the full criteria for level I evidence, mostly due to inadequate blinding.^{21,22,23,24,25,26}

Both level I studies compared MIS and open approaches for discectomy and found no infections in either treatment group ( Table 22.2). Arts et al included 325 patients in their study, and Ryang et al included 60 patients in their study.^19,20

22.5.2 Level II Evidence in Minimally Invasive Surgery

There have been a number of prospective, level II studies comparing MIS and open techniques in recent years. As mentioned earlier, several of these studies were randomized; however, they are considered level II evidence because of methodological limitations.21,22,23,24,25,26

We identified seven prospective studies that directly compare MIS and open techniques for fusion (six TLIF and one posterior lumbar interbody fusion [PLIF]), which all show no statistically significant difference in infection rates between MIS and open procedures.^{5,18,27,28,29,30,31} Nonetheless, of these studies, three show a greater absolute percentage of infections after open surgery,^27,28 two studies show a greater absolute percentage of infections after MIS procedures,^5,29 and two studies show no infections in either group (no difference).^18,30 It is worth noting that the two infections in the MIS group from the Peng et al⁵ study were from iliac crest donor sites, not from the primary surgical site. Peng et al found the overall complication rate significantly higher in the open group versus the MIS group.

There have been four prospective studies comparing MIS and open discectomy. Microscopically assisted percutaneous nucleotomy (MAPN) and microsurgical discotomy were compared by Franke et al 22 and video-assisted arthroscopic lumbar microdiscectomy was compared with open laminotomy and discectomy by Hermantin et al.²⁴ Both Franke et al²² and Hermantin et al²⁴ found no infections in both MIS and open cohorts. Ruetten et al²³ compared full-endoscopic interlaminar and transforaminal lumbar discectomy to the conventional microsurgical technique and found zero infections in the MIS cohort and one infection in the microsurgical cohort (1.1%), with the overall complication rate being significantly higher with the microsurgical “open” approach (p < 0.05). Teli et al compared outcomes after microendoscopic lumbar discectomy, micro lumbar discectomy, and open lumbar microdiscectomy and found no statistically significant difference in infection rates between groups.²¹

Prospective studies comparing other MIS and open procedures have also found no significant difference in infection rates between the two approaches. Ruetten et al²⁶ compared full-endoscopic posterior cervical foraminotomy with conventional microsurgical anterior decompression and fusion and found no infections in either cohort. In a different study, Ruetten et al²⁵ compared full-endoscopic transforaminal or interlaminar decompression to the traditional microsurgical approach and found no infections in the MIS cohort, while there were 2 out of 81 infections in the open cohort (2.5%). This difference, however, was not statistically significant. Regan et al found no significant difference in incidence of infection between a laparoscopic transperitoneal (1.4%) and open retroperitoneal approach (2.0%) for lumbar interbody fusion.³²

22.5.3 Level III Evidence in Minimally Invasive Surgery

There have been many retrospective studies comparing MIS and open techniques; however, most studies available are limited by a relatively small sample size.

We identified 13 retrospective, level III studies that compared MIS and open techniques for fusion (nine TLIF only, two TLIF plus PLIF, one posterior fusion, and one ALIF) and found no statistically significant difference in infection rates between the two procedures for any study. One study was a database review,33 while the other 12 studied single-institution patient cohorts. Seven of the 13 studies showed similar or superior infection rates in the MIS cohort versus the open cohort.^{6,8,34,35,36,37,38}

Three studies have looked at the difference in infection rates between MIS and open discectomy procedures. Lee et al³⁹ compared techniques for single-level lumbar discectomy and found no infections in the MIS group and one infection out of 45 patients (2.2%) in the open group, a finding that was not significant. Harrington and French⁴⁰ compared open and MIS lumbar microdiscectomy and found no infections in either group. Wu et al⁴¹ compared microendoscopic discectomy with the open procedure and also found similar infection rates (1.0 and 1.4%, respectively).

MIS and open techniques for decompressive surgery have been compared by two retrospective studies. Shih et al¹² compared microendoscopic decompression of stenosis versus open lumbar decompression and found no infections in the MIS group and one infection out of 26 patients in the open group (3.8%), a difference that was not significant. Rahman et al⁴² looked at MIS versus open lumbar laminectomy in 71 patients and found an insignificant difference in infection rates (2.6 and 6.1%, respectively).

There have been several retrospective studies that compared infection rates between MIS and open techniques for multiple procedures simultaneously. Ee et al⁴³ identified a cohort of TLIF, laminectomy, and discectomy patients with postoperative infections and performed a nested case–control analysis. This study used multivariate analysis to determine that open surgery is associated with a five times greater risk of postoperative infection compared to the MIS approach. Siddaraju et al¹³ looked at TLIF, laminectomy, laminotomy, and discectomy procedures and also found the open approach to be significantly associated with increased risk of postoperative SSI. Finally, Smith et al⁴⁴ used the Scoliosis Research Society database, which collects morbidity and mortality data from its members, to assess rates of postoperative wound infection after all types of spine surgery (indications include scoliosis, degenerative disease, spondylolisthesis, fracture, kyphosis, and tumor). This study included the most cases out of all studies identified (108,419). They found that a minimally invasive approach was associated with a lower rate of infection for lumbar discectomy (0.4 vs. 1.1%; p = 0.001), TLIF (1.3 vs. 2.9%; p = 0.005), and all procedures combined (0.5 vs. 2.4%; p < 0.001).

22.6 Conclusion of Minimally Invasive Surgery

MIS techniques have been increasingly utilized in spine surgery for several reasons. Across many different spine procedures, MIS surgery has been shown to offer reduced blood loss, decreased postoperative pain, and decreased hospital length of stay when compared to open spine surgery.3,5,6,7,8,9

It is important to remember that SSIs are a multifactorial phenomenon, and that an open or minimally invasive approach is only one aspect that may or may not contribute to an SSI in any particular patient. Risk factors for SSIs can be either patient related, surgical, or physiologic. Patient-related risk factors include preexisting infection, low serum albumin concentration, advanced age, history of smoking, diabetes mellitus, vascular disease, and irradiation of the area of surgery. Physiologic factors include trauma, shock, blood transfusion, hypoxia, hyperglycemia, and hypothermia. In addition, surgical risk factors including prolonged length of operating time, inadequate surgical scrub, inadequate skin preparation, and contamination of surgical instruments may increase the risk of SSIs, which are independent of using an open versus minimally invasive approach.⁴⁵