Knotless, barbed, sutures are widely available as an option for wound closure during TKA [6, 9, 12, 19, 21]. Several studies have highlighted the time and cost savings associated with their use [8, 10, 20, 21], with randomized control trials (RCT) showing savings of nearly 5 minutes and from USD 95 to USD 175 per TKA [7, 15]. Three RCTs using barbed sutures to close the arthrotomy and subcutaneous layer [7, 20], or all wound layers , did not find differences in postoperative complications between patients receiving the two suture types. Similarly, retrospective studies evaluating barbed sutures for closing the arthrotomy and subcutaneous layer found no differences in closure-related perioperative complications to conventional sutures [8, 10, 19].
However, concerns related to extensor-mechanism failures when using barbed sutures for arthrotomy closure  and higher risks of infection with barbed closure of subcuticular  or all layers  also have been reported. These concerns were validated by a study showing substantially higher proportions of deep infection (4.7% barbed versus 0.8% standard, p = 0.018), superficial infection (11.8% versus 3.2%, p = 0.001), and overall wound complications (19.5% versus 7.3%, p < 0.001) when barbed sutures are used for subcutaneous and subcuticular closure in a group of patients undergoing partial TKAs and TKAs . One large retrospective study of unicompartmental knee arthroplasties (UKA) found an increased risk of wound-related complications in patients whose UKAs were closed with barbed suture for the subcuticular layer or for the subcuticular and arthrotomy layers, but use of a barbed suture for arthrotomy closure was not independently associated with risk of infection . Our synthesis is that previous studies have raised greater wound-healing concerns with the use of barbed sutures for subcutaneous or subcuticular closure [4, 5] than for their use for the arthrotomy repair [7, 15, 20]. Postoperative complications are rare occurrences requiring large sample sizes to determine whether differences truly exist, and this has been a limitation of most studies to date. Recent meta-analyses have pooled data and reported no differences in minor complications, major complications, deep infection, or wound dehiscence [2, 11, 24], but remain limited by sample size, using overall pooled observations of fewer than 1800 patients. Additional studies including more patients and prospective data are needed to definitively compare wound-related complications between barbed and traditional sutures in TKAs.
Among the surgeons performing TKAs at our institution, many have adopted using barbed sutures for arthrotomy closure while others use more-traditional methods, but all use more-traditional closure methods in the more-superficial layers. This variation in technique between surgeons and with time provided an opportunity to compare the suture material through our longitudinally maintained orthopaedic data repository.
We therefore asked: (1) Do 90-day TKA reoperation rates differ between patients undergoing a barbed suture arthrotomy closure compared with a traditional interrupted closure? (2) Do the 90-day reoperation rates of wound-related, deep infection, and arthrotomy failure complications differ between barbed suture and traditional closures?
After our institutional review board conducted an approved expedited review and waived consent approval, we retrospectively reviewed a longitudinally maintained database of all TKAs completed at our academic tertiary institution in rural northeastern USA from April 2011 through September 2015 (Fig. 1). TKAs were performed by 11 surgeons; nine surgeons used both suture types during the study period. The database included at least 90 days of followup for each patient to ascertain reoperations.
The database review produced 1887 eligible patients who underwent 2002 primary TKAs, 480 of whom underwent simultaneous bilateral procedures with two attending surgeons, resulting in 2482 knees. Twelve patients, constituting 22 TKAs, were excluded from the initial patient cohort owing to unknown suture type (n = 10), necessity for flap closure (n = 1), or miscoding (n = 1). There were no other exclusions. This allowed 884 knees with a barbed suture arthrotomy closure to be compared with 1598 knees closed with traditional sutures. We confirmed in-person followups and available data past 90 days for 97.4% (1556 of 1598) of the knees of patients with standard sutures and 94.8% (838 of 884) of the knees of patients with barbed sutures. Suture-purchasing data and operative notes were used to group patients.
There were no differences in terms of age, sex, BMI, or tobacco use between the cohorts, although there were preoperative differences in race/ethnicity and patient-reported physical function (Table 1).
Description of Experiment, Treatment, or Surgery
Two thousand four hundred eighty-two knees were completed though a medial parapatellar approach and included, depending on surgeon preference and patient anatomy, quadriceps tendon splitting, mid-vastus, and subvastus arthrotomies. In general, most surgeons in the study gradually adopted the use of the barbed suture after it was introduced at our institution in 2012, and ultimately used it near exclusively for their unilateral cases. There were a smaller number of surgeons who either never used the barbed suture or used them for a short period in 2012 or 2013 before returning to standard methods. In the traditional closure group Number 1 Vicryl® (Ethicon Inc; Cincinnati, OH, USA) was used in an interrupted fashion to close the arthrotomy. In the barbed suture group a Number 1 StratafixTM Spiral PDO (Ethicon Inc), 36 cm in length was used in a running fashion to close only the arthrotomy. In all knees, the subcutaneous layer was closed with Number 2-0 Vicryl® (Ethicon Inc), while the skin was closed according to surgeon preference.
Variables, Outcome Measures, Data Sources, and Bias
The rate of reoperation within 90 days of the index TKA included open or arthroscopic procedures of any type on the same knee. Wound-related reoperations were procedures completed to address any type of wound issue including septic or aseptic complications, similar to groupings in previous studies [4, 5, 10]. We defined deep infections according to the Musculoskeletal Infection Society guidelines . The presence of an arthrotomy failure was determined intraoperatively as an opening or dehiscence through the previous arthrotomy closure. If a patient sustained a periprosthetic fracture at the time of the arthrotomy violation, this was not classified as a failure. All of this information was obtained through review of operative and clinical notes. All preoperative variables, including provider-recorded BMI and Veterans RAND-12 (VR-12) patient-reported physical and mental function, were obtained through standard clinic visits. Peri- and postoperative findings were obtained through our standing orthopaedic data repository, with additional chart or purchasing review as needed.
Statistical Analysis, Study Size
Few variables were missing values and we had no concerns with missing data (Table 1). As reoperation and infection percentages varied widely in earlier studies [2, 4, 5, 7, 11, 15, 20, 24], we were unsure what percentage of reoperations we would find by suture a priori. With our captured reoperations, post hoc power analyses of the primary and secondary outcomes showed power of 0.29 for 90-day reoperations, 0.41 for wound-related reoperations, and 0.70 for arthrotomy failures. We used chi-squared analyses and Student's t tests for qualitative and quantitative comparisons, respectively (Table 1). There were five arthrotomy failures, all of which occurred after TKAs with barbed sutures (Table 2). Unadjusted bivariate logistic regressions were performed for 90-day and suture-related reoperations (Table 3). All arthrotomy failures occurred in the barbed cohort, making regression analyses between groups impossible. Deep infections were too rare to be compared meaningfully. All analyses were performed used Stata 12MP™ (StataCorp, College Station, TX, USA).
There was no association between suture type and 90-day reoperation (odds ratio [OR], 1.70; 95% CI, 0.82-3.53; p = 0.156) (Table 3). No variables were associated with 90-day reoperations.
We found no difference between barbed and conventional sutures for 90-day wound-related reoperations (OR, 2.73; 95% CI, 0.97-7.69; p = 0.058) (Table 3). No other variables were associated with 90-day wound-related reoperations (Table 3). There was a 0.6% (five of 884) rate of arthrotomy failure in the barbed cohort and no failures (0 of 1598) in the traditional cohort (p = 0.003) (Table 1). Two deep infections were observed in the barbed suture group, and none in the traditional closure group; these numbers were too small to compare statistically.
Although barbed sutures generally have been considered to be an accepted alternative to a traditional interrupted closure [6, 7, 10, 15, 19, 20], recent studies have shown concerns regarding increased risk of infection in arthroplasty wounds closed with barbed sutures in the deep and superficial layers  or superficial layers alone , indicating that further study is warranted. We present the results of a large-scale, single-center, retrospective cohort study of prospectively collected data comparing barbed suture arthrotomy closure with traditional closure in TKA. To our knowledge, our study is the largest on this topic, including pooled meta-analyses [2, 11, 24], by hundreds of knees. Using our data, we estimate that approximately 4235 knees would be needed of each suture type to achieve power of 0.80 for 90-day reoperations, assuming the point estimates for event rates are as we observed them, an amount that does not seem achievable at a single institution for many years. With the numbers available, our findings indicate no difference in the 90-day reoperation or 90-day wound-related reoperation rates between the suture types when used for arthrotomy closure.
This study is limited by some baseline differences between the two cohorts (Table 1). Owing to rare outcomes, we were unable to adjust for these differences in analyses. Although differences are noted, there are no discrepancies that can clearly account for an increased complication rate in the barbed suture cohort, nor were any variables associated with reoperations (Table 3). More patients in the traditional suture cohort underwent simultaneous bilateral TKAs, although this is likely owing to the higher proportions of institutional bilateral TKAs during the years before barbed sutures (data not shown). In addition, preoperative patient-reported VR-12 values were higher in the barbed suture group, but the clinical importance of this is debatable [1, 18]. Some complications may not have been captured if patients presented to another institution; however, we have in-person followups and available data past 90 days for 97.4% (1556 of 1598) of the knees in patients with standard sutures and 94.8% (838 of 884) of the knees in patients with barbed sutures (data not shown). There may be differences in surgical techniques by surgeon, such as in skin closure techniques. However, there were no differences in 90-day reoperation rates by surgeon, and most surgeons used both sutures (Table 1). In addition, recent randomized control trials suggest no differences in wound complications when comparing staples with nylon sutures in TKAs  and staples with intradermal sutures in THAs . There may be concerns that more “difficult” TKAs were treated with barbed sutures, leading to higher wound complications; however, there were no differences in sutures by preoperative BMI and physical function scores (Table 1), and with only minimal exclusions. There may be a learning curve with barbed sutures, which we have not captured, that may be associated with higher failure rates; however, most study surgeons have extensive experience with both suture types; surgery year and surgeon were not associated with any outcomes and no arthrotomy failures were observed during the first year of barbed suture use. A final limitation of our study is the limited power, as described previously, although this is a frequent issue with rare surgical outcomes. It would be difficult for any individual institution to achieve a power of 0.80 for all-cause reoperations, which we determined to be approximately 4235 knees for each suture group, and this level of surgical detail is generally unavailable in large multisite repositories. We therefore consider our study to be pilot data for larger multicenter trials to conduct further research on the topic.
We found no difference in the rates of 90-day reoperation between the groups, with the numbers available. This metric captures the myriad of complications that necessitate return to the operating room for primary TKA, and suggests that overall there is no difference in the performance of the two closure methods. It is difficult to directly compare our primary and secondary outcomes with previous studies as 90-day overall reoperation rates have not been reported, to the best of our knowledge, in prior barbed suture studies. Our observation of no between-group differences in 90-day reoperation rates between the cohorts is in agreement with previous smaller studies that reported no differences in overall complications when using barbed sutures to close the arthrotomy and superficial layers [6-8, 19, 20].
When comparing wound-related complications including infections and wound dehiscence, we found no differences. Our observation of differences in wound-related reoperations between the cohorts is in agreement with several studies that specifically noted no differences in wound complications [6-8, 10, 20]. Although Gilliland et al. , in their RCT, found no increased complications with use of barbed sutures for arthrotomy and subcutaneous closure in TKA, their 6-week followup would miss potential delayed complications. In our data, three of the 29 reoperations occurred after this period. Studies have highlighted increased risks of infection, particularly when using barbed suture closures for the superficial wound layers [4, 5, 14]. In the study by Chawla et al. , highlighting increased risks of wound infection when using barbed sutures in UKA, barbed suture was used for arthrotomy closure in some knees; however, subgroup analysis showed no independent association between infection and barbed suture arthrotomy closure. Some authors have suggested that tightening of the tissue closure resulting in ischemia , increased tissue inflammation, or bacterial colonization of the deep barbs may cause wound complications . In our study there were five arthrotomy failures in the barbed suture cohort whereas none was observed in the traditional suture cohort. These findings lend support to a previous case series highlighting arthrotomy failures with barbed sutures  in TKAs. Although some studies [4, 8] have not reported arthrotomy failures as a separate outcome, others have noted rates of 0 of 50 for barbed sutures , two of 89 for barbed sutures and 0 of 750 in standard sutures , and one of 17 for barbed sutures and 0 of 18 with standard sutures . These additional studies highlight that arthrotomy failure following a barbed suture arthrotomy closure warrant further study. Deep infection counts were too low to be compared in our study, and future large-scale studies will be necessary to determine if risks of infection are affected by barbed suture closures.
Our results showed no difference in overall 90-day reoperation rates or wound-related reoperation rates in the barbed suture cohort. However, there were no arthrotomy failures in the conventional suture cohort (0 of 1598) and five (of 884) arthrotomy failures in the barbed suture cohort. Although these differences are not necessarily large enough to change clinical practice in our pilot data, they do warrant further investigation. Future multicenter, high-quality studies with larger sample sizes are needed to definitively determine the safety and efficacy of barbed sutures in TKAs.
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