Nylon Skin Sutures Carry a Lower Risk of Post-Operative Infection than Metal Staples in Open Posterior Spine Surgery: A Retrospective Case-Control Study of 270 Patients

Abstract

Background:

Controversy still exists regarding the optimal method for post-operative skin closure in orthopedic surgery. In total knee replacement, closure with metal staples is faster but carries a higher surgical site infection (SSI) risk. Other studies have found differing results in foot and ankle and hip surgery. Very little evidence exists on this subject after spine surgery. The aim of this study was to determine whether closure of the skin incision in open posterior spine surgery carries a different rate of post-operative SSI when using nylon sutures compared with metal staples.

Methods:

Up to 2006, virtually all skin incisions at our spine surgery unit were closed with metal staples and from 2006 onward with nylon sutures. This was a retrospective historical control study comparing the incidence of SSIs in patients operated on before (n = 127; staples) and after (n = 143; sutures) the transition date.

Results:

The staples group had an overall 11.8% combined deep and superficial infection rate whereas the nylon suture group had a 4.2% rate (p = 0.017). The two groups also differed in the type of antibiotic prophylaxis used, likelihood of incisional discharge, and the number of days the vacuum drains remained.

Conclusions:

In our departmental setting, closure of the skin incision with nylon sutures after open posterior spine surgery carried a significantly lower risk of post-operative SSI compared with metal staples. The generalizability of our findings is unclear, but they warrant further investigation.

Two popular alternatives for skin closure after surgery are metal staples and sutures of sorts. Metal staples are faster to apply and thus reduce operative time significantly [1], whereas sutures may produce better skin apposition and cosmesis and reduce superficial surgical site infection (SSI) rates in certain types of operations [2,3]. Good initial skin adaptation is important, as it will allow rapid epithelization of the incision from edge to edge, typically within 24–48 hours post-operatively, and form a bacterial barrier. If the skin edges are not matched, local healing by secondary intention will delay epithelization significantly [4].

Although no convention exists regarding the importance of meticulous skin closure, there appears to be a paucity of published evidence on the subject in orthopedic surgery [5 –11]. Khan et al., in their randomized controlled trial of 187 patients undergoing total hip replacement (THR) and total knee replacement (TKR) surgery, found closure times to be shorter, cosmesis better, and patient satisfaction higher with staples than with subcuticular absorbable suture or octylcyanoacrylate (OCA) adhesive [9]. They did not find a significant difference in late incision complications between closure methods but did note a higher rate of “strike through” staining on the dressing in both the suture and staple group, indicating delayed sealing of the incision. Daniilidis et al., in their retrospective single-surgeon case series, compared nylon skin sutures with staples in 61 foot and ankle operations and found shorter closing times and lower post-operative pain scores in the staples group, with no difference regarding incision outcomes [5].

Slade-Shantz et al., in a randomized trial of 148 patients undergoing non-emergency upper limb, hip, knee, and ankle surgery, found incision closure times to be significantly shorter with staples than with various suture techniques [12]. Perceived incision complications, based on patient self-reporting surveys, were found to be lower for the staples group, but medical-personnel-confirmed infections were identical in both groups. Those investigators concluded that with the 1.48% rate of primary outcome, a sample size of 1,100 patients would be necessary to show a 25% risk reduction in incision complications with 80% power for the combined group of surgical sites in their study.

No study published to date has reached the above-mentioned numbers, but several meta-analyses have been published, attempting to pool available data. Smith et al., in their meta-analysis of six studies including 683 orthopedic incisions closed by either nylon sutures or staples, found a three-fold greater risk of infections with staple closure and a four-fold greater risk after hip surgery [1]. They did not find any studies addressing this issue in spine surgery.

Krishnan et al. published two meta-analyses comparing staples with a variety of suturing methods. The first incorporated 13 studies and concluded that, other than shorter closure times for staples, there was no significant difference in outcomes including SSIs [10]. In the second and more recent analysis, 17 studies were included, pooling 1,575 cases, in which a 2.05 relative risk for SSI was found in the staples group [11]. This study did not stratify the results for different orthopedic operations.

Kim et al. conducted a meta-analysis of eight studies comparing sutures with staples after 828 total knee arthroplasties [13]. They found a higher risk of superficial and deep infection, abscess formation, and incision dehiscence in the sutures group, but the difference in all of these outcomes did not reach statistical significance.

Yilmaz et al., reviewing the limited available literature specific to spine surgery, concluded that there is a lack of evidence regarding the optimal closure technique after open posterior spine surgery [14]. Searching the PubMed database, we were unable to find any relevant study of skin closure methods in spine surgery since their study was published.

The purpose of our study was to determine whether skin closure with metal staples carries a higher rate of SSIs than closure with nylon sutures.

Patients and Methods

Up to 2006, virtually all skin incisions at our spine surgery unit were closed with metal stapes (Coviden Appose 35W stainless steel [Medtronic, Minneapolis, MN] and other brands). As a departmental policy change, all incisions since 2006 are closed with continuous nylon 3-0 sutures (Ethilon; Ethicon, a division of Johnson and Johnson, Bridgewater, NJ). Using our hospital's electronic health record database, we conducted a retrospective historical control study comparing post-operative SSI rates in two groups of patients: those operated on before (“staples group”) and after (“suture group”) this transition.

For statistical analysis, a sample size of at least 120 patients in each group was needed. Included were all patients aged 16 years and over who underwent an open posterior spine operation before and after the transition to sutures until the target patient number was reached. Excluded were anterior approaches, micro-discectomies, minimally invasive surgery, percutaneous surgery, biopsies, and operations performed for an existing infection. In total, three pre-transition and four post-transition years were reviewed.

The patients in each group were compared for age, gender, diabetes mellitus history, smoking history, type of surgery, anatomic site of the operation (cervical/thoracic/thoraco-lumbo-sacral/lumbar/lumbo-sacral), operation type (decompression, non-instrumented fusion/ instrumented fusion), number of levels operated on (one or two/three or more), post-operative incisional discharge, infection rate, antibiotic prophylaxis received (yes/no and identity of the antibiotic agent), number of vacuum drains left post-operatively, number of days vacuum drains remained, occurrence of SSI, leukocytes >10,000 on any post-operative day, re-operation (yes/no), re-operation rate within 90 days, need for post-operative invasive procedure (deep incision debridement/irrigation, computed tomography (CT)-guided drain insertion, peripherally inserted central catheter insertion, etc.), dural tear, and any other surgical complication.

Incisions were dressed with layered gauze pads without any lotions or ointments and replaced at least once every 24 hours. Incisional discharge was recorded daily on the basis of the extent of staining of the dressing and appearance of the site. Post-operative superficial incisional, deep, and organ/space SSI diagnosis was made according to the U.S. Centers for Disease Control (CDC) January 2013 guidelines revision April 2015 [8].

The difference between the groups was evaluated using the χ² test/Fisher exact test/independent t-test as applicable. Statistical analysis was done using SPSS V. 19 software (IBM, Armonk, NY USA).

This study was approved by our Institutional Review Board for all included patient age groups. As treatment did not differ from the usual, informed consent was not required.

Results

A total of 270 consecutive patients were reviewed, 127 in the staples group and 143 in the sutures group. The minimal follow-up period for all of the patients was 90 days. The groups were similar regarding age, gender, diabetes mellitus history, and smoking history. There was no statistical difference regarding the anatomic location, the number of vertebral levels operated on, or the re-operation rate. The number of decompressions and the number of instrumentations was similar in the two groups, but the sutures group had six non-instrumented fusion cases whereas the staples group had none, thus producing an overall dissimilarity that was on the verge of significance.

Three distinct dissimilarities between the two study groups emerged. Although both groups had a similar percentage of peri-operative antibiotic prophylaxis (95.2% and 97.2%; p = 0.523), 70.7% of the staples group versus 92.1% of the sutures group received vancomycin as the prophylactic drug, the remainder receiving cefazolin.

Another statistically significant difference was the number and duration of drains left in the site post-operatively. In the staples group, 20.5% of the patients had no drain left versus only 3.5% in the sutures group (p < 0.001). The mean duration of vacuum drainage in the staples group was 2 days (standard deviation [SD] 0.51) versus 3.8 days (SD 1.42) for the sutures group.

A total of 46 of the patients in the staples group (36.5%) and 17 patients in the sutures group (11.9%) had a post-operative incisional discharge (p < 0.001). The total infection rate was 11.8% (15/127) in the staples group and 4.2% (6/143) in the sutures group (p = 0.017). Some 12 (80%) of the 15 infected patients in the staples group and 3 (50%) of the 6 infected patients in the sutures group had a post-operative incisional discharge that was diagnosed as reflecting superficial SSI according to the CDC criteria. The remainder, 3/127 (2.3%) in the staples group and 3/147 (2.04%) in the sutures group, had a deep or organ/space infection. This difference did not reach statistical significance.

For a summary of all the results see table.

Table 1.

Results of Closure Method

	Characteristic	Staples (%)	Sutures (%)	p	Statistical test
Demographics	N	127	143
	Male/female	69/58	76/65	0.903	Fisher exact
	Mean age (range 16–87)	54.23 (SD 16.8)	55.03 (SD 17.2)	0.643	Independent t
	Diabetes mellitus (%)	19 (15)	27 (18.9)	0.392	χ²
	Smoking (%)	33 (37.1)	43 (30.5)	0.301	χ²
Anatomic site (%)	Cervical	5 (3.9)	15 (10.5)	0.194	χ²
	Thoracic	6 (4.7)	8 (5.6)
	Thoracolumbo-sacral	10 (7.9)	13 (9.1)
	Lumbosacral	106 (83.5)	107 (74.8)
Operation type (%)	Decompression (47.8)	64 (49.6)	65 (50.4)	0.051	Fisher exact
	Non-instrumented fusion (2.2)	0	6 (4.2)
	Instrumented fusion (50)	63 (46.7)	72 (53.3)
Levels operated on	One or two	93 (73.2)	90 (62.9)	0.09	χ²
Levels operated on	Three or more	34 (26.8)	53 (37.1)	0.09	χ²
Antibiotic prophylaxis	Peri-operative antibiotics	121 (95.3)	139 (97.2)	0.523	Fisher exact
	Cefazolin	36 (29.3)	11 (7.9)	<0.001	χ²
	Vancomycin	87 (70.2)	128 (92.1)	<0.001	χ²
Main outcome	Surgical site infection	15 (11.8)	6 (4.2)	0.017 (1 sided)	χ²
Discharge	Discharge from incision	46 (36.5)	17 (11.9)	<0.001	χ²
Drains	0	26 (20.5)	5 (3.5)	<0.001	χ²
	1	32 (25.2)	15 (10.5)
	2	57 (44.9)	107 (74.8)
	3⁺	12 (9.5)	16 (11.2)
	Drain removal day	2 ± 0.5 (SD 0.51)	3.8 ± 1.4 (SD 1.42)	<0.001	Independent t
Post-operative complications	Leukocytes >10,000	79 (63.7)	61(43)	0.001	χ²
	Re-operation	1 (0.8)	2 (1.4)	1	Fisher exact
	Invasive procedure	3 (2.3)	6 (4.2)	0.507	Fisher exact
	Dural tear	14 (11)	13 (9.1)	0.612	χ²
	Other	3 (2.3)	7 (4.9)	0.342	Fisher exact

Discussion

We have found that after open posterior spine surgery, closure with metal staples carried a higher combined superficial and deep infection rate than nylon sutures, but when only deep and space/organ infection rates were compared, the difference between the groups did not reach statistical significance.

Although the exact reason for this difference cannot be determined from this study, the staples group discharged through the incision in the post-operative period in greater numbers than the suture group, presumably leading to delayed epithelization of the skin edges, theoretically allowing pathogens a longer time to colonize and infect the site. A possible reason might be that a continuous suture provides a tighter seal than interrupted staples, reducing post-operative discharge. Another possible explanation is better apposition of the skin edges, which is achieved more easily with sutures.

There is very little published evidence on the correlation between post-operative incisional discharge and the SSI rate. Khan et al. compared metal staples with subcuticular suture and octylcyanoacrylate (OCA) glue in total joint arthroplasty [9]. They, too, found the suture group to have less post-operative incisional discharge than patients having staples (2/28 compared with 4/27 for TKR and 1/33 compared with 2/36 for THR). In contrast to our findings, they did not find a correlation between incisional discharge and post-operative SSI. Daniilidis et al. found similar rates of post-operative day 5 incisional discharge in both the staples and sutures group, with no difference in the SSI rate [5].

Yuenyongviwat et al., in a randomized controlled trial of 70 patients undergoing total knee replacement, with half of the incisions closed with staples and half with nylon sutures, found 4/70 of the patients in the staples group to have a post-operative day-5 discharge compared with 2/70 in the suture group, and 1/70 in the staples side to have a post-operative day 14 discharge compared with 0/70 for the sutures side [15]. Despite these differences, there was no significant difference in the SSI rate.

In addition to the paucity of studies comparing staple with suture closure, the definition of an SSI is not standardized, making the results even less conclusive. We have used the CDC criteria [16] and hope this will enable more accurate pooling with other studies in the future.

We have not found many studies in the current literature addressing the question of optimal skin closure in open spine surgery directly. Ando et al. compared staples with OCA skin adhesive in 609 patients, using a “switch date” for a historical control, similar to our study design, and assessing SSI rates using the 1992 CDC criteria [17]. They found 2/294 superficial SSIs and 6/294 deep SSIs in the staples group compared with 0/315 in the OCA group. Galetta et al. published the results of the 2018 Second International Consensus Meeting (ICM) on Musculoskeletal Infection, discussing risk factors, prevention, and incision care of SSI in spine surgery [18,19]. No discussions of closure means were reported, and the group did not reach an agreement on the optimal closure method once an infection has been treated.

Our study has several limitations. Because of its retrospective nature, it is impossible to control all variables, and other changes during the study period might have affected the results. One change was the gradual transition to minimally invasive procedures in degenerative cases and percutaneous instrumentation in trauma, which were excluded from this study theoretically shifting the case-mix during this time. Another change was the prophylactic antibiotic choice. Because of an increasing incidence of methicillin-resistant Staphylococcus aureus (MRSA) at our hospital during the time, we temporarily changed the prophylactic drug of choice from cefazolin to vancomycin. This change did not coincide chronologically with the switch from staples to sutures, leading to a significantly greater percentage of patients in the suture group receiving vancomycin prophylaxis. Similarly, the number and duration of vacuum drain usage was changed to a minimum of one drain, with removal only if the total daily drain production was <50 mL. Inotsume-Kojima et al. found this intervention to reduce the infection and complication rates significantly in obese obstetric and gynecologic patients [20]. Although never demonstrated in spine surgery, the same effect might have influenced our results. There is no way to isolate this variable in our results and determine its contribution to SSI reduction.

Another possible explanation for our results is a greater awareness by the surgeons of the importance of meticulous skin apposition after the transition to nylon sutures and the discussions that led to it. Perhaps the same results could have been achieved with staples had other interventions focusing on skin closure technique been implemented.

To the best of our knowledge, this is the first therapeutic Level 3 study to demonstrate that nylon skin sutures might carry a reduced risk for post-operative SSIs in open posterior spine surgery compared with metal staples. A prospective randomized study with fewer confounders is needed to confirm this conclusion.

Footnotes

Author Disclosure Statement

This study was performed at the Department of Orthopedics B and Spine Surgery of the Galilee Medical Center, Nahariya, Israel.

All authors report no conflict of interests.

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