- Email: [email protected]
Knee Arthrotomy Closure With Barbed Suture in Flexion Versus Extension: A Porcine Study
The Journal of Arthroplasty 29 (2014) 2211–2213
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Knee Arthrotomy Closure With Barbed Suture in Flexion Versus Extension: A Porcine Study Praveen Kadimcherla, MD a, Andrew J. Lovy, MD, MS b, Chris Sambaziotis, MD, MPH a, c, Yossef Blum, MD a, c, David M. Hirsh, MD a, c, Sun J. Kim, MD a, c a b c
Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Bronx, New York Department of Orthopaedic Surgery, Mount Sinai Hospital, New York, New York Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Bronx, New York
a r t i c l e
i n f o
Article history: Received 20 March 2014 Accepted 19 July 2014 Keywords: knee arthrotomy barbed suture arthrotomy closure suture failure extension
a b s t r a c t The purpose of this biomechanical study was to evaluate knee arthrotomy closure with a barbed suture in flexion versus extension. 48 porcine knees were randomized into three groups: full extension, 30° flexion, and 60° flexion. Each knee was then flexed to 90° and then 120°, with failures recorded. Arthrotomy closure in extension had significantly higher failure rates (6/16) upon flexion to 90° compared to arthrotomy closure in either 30° or 60° flexion (0/32) (P = 0.032). Upon ranging from 0° to 120°, arthrotomy failure occurred in 50% (8/16) of arthrotomies in the extension group, 6.25% (1/16) in the 30° flexion group and 18.75% (3/16) in the 60° flexion group (P = 0.022). Knee arthrotomy closure in extension compared to flexion had significantly higher rates of failure. © 2014 Elsevier Inc. All rights reserved.
Wound healing complications following total knee arthroplasty (TKA) are a known problem that can lead to disastrous outcomes including implant failure [1]. In order to reduce wound healing complications, tight closure of the arthrotomy is crucial, as superficial wound healing problems requiring early surgical intervention following TKA have been shown to significantly increase risk of subsequent major surgery [2]. Hematoma formation can lead to infection. A tight arthrotomy closure can limit the size of the subsequent hematoma and potentially prevent and limit the spread of infection. Furthermore, as early mobilization is encouraged following knee surgery in order to preserve range of motion, arthrotomy repair must maintain its integrity even when facing tensile forces generated during flexion. In 2007, bidirectional barbed suture was introduced in the United States (Quill Self-Retaining System; Angiotech Pharmaceuticals, Inc., Vancouver, British Columbia) allowing tissue to be reapproximated without use of a surgical knot. Use of barbed suture for wound closure has been documented in many surgical disciplines [3], and recent cadaveric studies have demonstrated its efficacy in knee arthrotomy closure [4]. Trials comparing knee arthrotomy closure in flexion versus extension have been done using interrupted sutures, demonstrating the superiority of closure in flexion [5]. However, to our knowledge there are no studies comparing arthrotomy closure in flexion versus
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.07.023. Reprint requests: Sun J. Kim, MD, Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Montefiore Medical Center 1200 Waters Place, Bronx, NY 10461. http://dx.doi.org/10.1016/j.arth.2014.07.023 0883-5403/© 2014 Elsevier Inc. All rights reserved.
extension using barbed suture. The purpose of our study was to compare barbed suture failure rates of knee arthrotomy closure in full extension versus flexion upon ranging the knee from 0° to 120° using porcine specimens. We hypothesized that knee arthrotomy closure conducted in flexion would have lower rates of suture failure compared to knees closed in full extension. Methods Forty eight fresh frozen intact pig knees were obtained. Specimens were stored at −10 °F and thawed at room temperature for 24 hours before use. The specimens were randomly selected into three closure groups of 16 specimens; full extension, 30° flexion, and 60° flexion. Before use, each specimen was examined to ensure at least 120° of motion. For each specimen, a mid-line skin incision of 10 cm was made with a number 10 scalpel blade. Following incision, the skin and subcutaneous tissue was dissected to allow full visualization for closure and testing of the arthrotomy closure. The joint line was identified, and a 7 cm arthrotomy was marked out. Using a ruler, markings were made every 5 mm to represent the distance that should be traversed with each suture throw. The arthrotomy was made to leave a 3 mm cuff of tendon on lateral border of the vastus medialis and also a 3 mm cuff of retinaculum medial to the patella. Upon completion of the arthrotomy the specimen was randomly assigned to closure in full extension, 30° flexion or 60° flexion. Closure angle was determined by a goniometer, and the specimen was secured to the table at the desired degree of flexion using a modified c-clamp.
2212
P. Kadimcherla et al. / The Journal of Arthroplasty 29 (2014) 2211–2213
The arthrotomy was closed with a with a running #1 monofilament absorbable knotless suture with bidirectional barbs (Quill; Angiotech, Reading, PA). The closure was initiated in the middle of the arthrotomy and was continued in both directions, reflecting the suture's design with continuous barbs running bidirectional from the center. Care was taken to make sure each throw included 3 mm of tissue and each pass advanced 5 mm. Upon reaching the end of the arthrotomy, the suture was passed back along the arthrotomy for 3 throws. No knots were required, and the excess suture was cut. Each specimen was numbered in order to later determine closure type. All 48 specimens were then examined by a blinded author not present at the time of arthrotomy closure. Initially, each specimen was fixed proximally and allowed to flex to 90° by gravitational force or was flexed manually to 90° and the number of suture breaks was recorded by the blinded subject. The number of suture ruptures was determined visually (range 0–6) and was confirmed by another observer. The knee was then further flexed to 120° of flexion as determined by a goniometer. Once again the number of suture ruptures was determined visually and was confirmed by the blinded author and another observer. In some instances the suture had ruptured in multiple spots and had completely unraveled, leaving the observers unable to determine exactly the number of areas where the suture has ruptured. These instances were recorded as complete failures. For the purposes of statistical analysis complete failures were assigned a value of 6 corresponding to the maximal number of suture ruptures recorded. Arthrotomy failure rates and number of suture throw failures were analyzed using STATA software (version 11, College Station, TX) and a one tailed α of 0.05. Rate of arthrotomy failure, defined as rupture of at least one suture throw, was evaluated using a one sided Fisher's exact test. Following assessment of normality and equal variance, number of suture throw failures (dependent variable) in extension and flexion groups (independent variable) was evaluated using the Wilcoxon rank-sum test. Results Barbed suture failure rates were evaluated upon ranging the knee from 0° to 90° and 120° in 48 porcine specimens grouped into closure at full extension, 30° flexion and 60° flexion. Arthrotomy closure in full extension had significantly higher rates of failure (18.75%, 3/16) upon flexion to 90° compared to arthrotomy closure in either 30° or 60° flexion (0%, 0/32) (P = 0.032). In all three failures, one suture throw ruptured, upon ranging to 90°. Upon ranging from 0° to 120°, arthrotomy failure occurred in 50% (8/16) of arthrotomy closures in the full extension group, 6.25% (1/ 16) in the 30° flexion group and 18.75% (3/16) in the 60° flexion group (P = 0.0022). A significantly greater number of suture throws ruptured among arthrotomy failures in the full extension group compared to the two flexion groups (P = 0.0018). Complete suture failure (Fig. 1) occurred in two of the knees in the full extension group upon ranging to 120° compared to none in the 30° or 60° flexion groups. There was no difference in arthrotomy failure rates between the two arthrotomy groups closed in 30° flexion and 60° flexion upon ranging to 120° (P = 0.60).
Fig. 1. Shows the complete failure of an arthrotomy closure with bi-directional barbed suture. Multiple suture failure sites along the arthrotomy are appreciated along with unwinding of the suture.
Complete failure was noted in two of the knees closed in full extension compared to none in the flexion groups upon ranging from 0° to 120°. This result is particularly concerning given the known consequences of implant failure and even amputation as a result of wound healing problems in TKA [1]. The failure of the barbed suture seemed to occur at the junction of the barb and the core material. This typical site of failure can be noted in the edge of our failed barbed suture in Fig. 2. The proposed method of failure of the closure is thought to be the increased length of the suture as the knee flexes. The bidirectional barbed design of the suture when tightened during the closure embeds the barbs within the tissue at fixed points. As the knee undergoes increasing flexion, tensile forces across the suture construct increase as well. Biomechanical studies have shown that because of the cuts created in the suture material in the creation of the barbed suture, the effective cross sectional area of the suture decreases and the peak tensile load and peak elongation also decrease [6]. This is consistent with our findings that the greatest number of failures occurred as the specimens were flexed to 120.
Discussion Tight closure of arthrotomy in TKA is critical in order to facilitate proper wound healing and prevent infection [1,2]. In our study comparing arthrotomy closure with a barbed suture in full extension versus flexion, arthrotomy closure in full extension was found to have significantly higher rates of failure compared to closure in 30° or 60° of flexion upon ranging to both 90° and 120°. Results of the current study suggest that arthrotomy closure in flexion is preferable to extension as it is associated with significantly lower rates of failure.
Fig. 2. Depicts the failure point of the barbed suture. Closer examination reveals that the barbed suture has failed at the site of the barb, which is also the point of smallest diameter on the suture.
P. Kadimcherla et al. / The Journal of Arthroplasty 29 (2014) 2211–2213
Fig. 3. Demonstrates a closer view of the suture and how the integrity of the suture material is compromised by the creation of the barbs.
The junction of the barb and core material is noted to be the weakest point in the barbed suture construct. Barbed sutures are created by cuts in a monofilament material to create a barb that is oriented to anchor itself into the surrounding tissue (Fig. 3). This modification leads to decreased internal core diameter of the suture and has been shown to be equivalent to a suture that is one size smaller [6]. This should be taken into consideration when choosing the size of suture material. Also, the defect created in the monofilament becomes a location of stress concentration and an ultimate failure point upon excessive loading. The problem of decreased core diameter can only be partially addressed by increasing the size of the suture material used. The calculated peak tensile loads for a given decrease in the diameter of the barbed suture material were much higher than what was observed during testing of the peak tensile loads of the barbed suture [6]. This is explained by the concept of non-uniform “sheath-core” morphology of the monofilament [7]. The outer layers of the suture are more crystalline and more oriented and the inner layers are composed of more amorphous material. The creation of barbs lead to the removal of the crystalline material preferentially and decreased load to failure that is lower than would be expected from the size of center core. The higher proportion of an amourphous region gives the suture an increased ability to elongate initially at lower loads due to the straightening of randomly oriented fibrils in the amorphous region. However, after initial lengthening, the load to ultimate failure is reached quickly without the structural integrity of the crystalline region. This could explain the relatively low number of suture failures observed during the first 90° of motion compared to the last 30° of motion. The efficacy of barbed suture use in knee arthrotomy repair was recently confirmed in a biomechanical study by Vakil et al [4]. In their study, cadaveric knee arthrotomy closure using interrupted biodegradable sutures and running bidirectional barbed sutures was compared in cadaveric specimens, and both groups maintained closure without suture rupture following 2000 flexion cycles [4]. The authors also noted that barbed suture repair was able to withstand a greater number of suture cuts than interrupted suture repair. Another cadaveric study of knee arthrotomy closure compared water tight closure with interrupted absorbable suture and barbed suture. Water-tightness of the arthrotomy closure was compared by simulating a tense hemarthrosis and measuring arthrotomy leakage over 3 minutes. Closure with barbed suture was found to achieve a more water-tight closure as mean total leakage was 356 mL in the barbed group compared to 89 mL in the interrupted group (P = 0.027) [8]. In addition to the biomechanical advantages of barbed suture, these sutures also afford the surgeon the ability to perform a more
2213
efficient closure. Eickmann et al [9] have shown that closure of the retinacular and subcutaneous layers during a total knee arthroplasty using a bidirectional barbed absorbable sutures for running closures resulted in decreased surgical times. The mean times were 85.8 minutes for closure using conventional sutures and 74.3 minutes for barbed sutures. The relatively faster closure technique has also not been associated with any detrimental clinical effects with regards to wound security, cosmesis, or infection risk. Some of the limitations of this study are that we used a pig model and not a cadaveric model. We were also not able to evaluate the arthrotomy closure with cyclical loading. Data from durability of an arthrotomy closure in various degrees of flexion would have given us a better approximation of the in vivo survival of our arthrotomy closure. We have also only evaluated the closure at a static point. However studies have shown that barbed PDO sutures tensile strength varies significantly with time. The barbed PDO suture lost approximately 20% of its initial tensile strength at both weeks 2 and 4 [10]. The loss was 58% at week 6. This change could have varying implications for the knee arthrotomies closed in extension compared to the knee arthrtomies closed in varying degrees of flexion. Also, the stress placed on a closure externally does not approximate the force generated by balanced muscle contractions from varying vectors in vivo. Although prior studies have demonstrated the efficacy of barbed sutures in many surgical disciplines [3] and in cadaveric studies of knee arthrotomy closure [4], no studies have compared knee arthrotomy closure in flexion and extension. Results of our bovine biomechanical study suggest that knee arthrotomy closure in full extension is associated with higher rates of failure compared to closure in flexion. Although the results of the current study were observed in vitro, they raise awareness to the potential wound complications associated with arthrotomy closure in full extension with barbed sutures that should be verified in a clinical study.
References 1. Vince KG, Abdeen A. Wound problems in total knee arthroplasty. Clin Orthop Relat Res 2006;452:88. 2. Galat DD, McGovern SC, Larson DR, et al. Surgical treatment of early wound complications following primary total knee arthroplasty. J Bone Joint Surg Am 2009;91:48. 3. Murtha AP, Kaplan AL, Paglia MJ, et al. Evaluation of a novel technique for wound closure using a barbed suture. Plast Reconstr Surg 2006;117:1769. 4. Vakil JJ, O'Reilly MP, Sutter EG, et al. Knee arthrotomy repair with a continuous barbed suture a biomechanical study. J Arthroplasty 2011;26:710. 5. Emerson Jr RH, Ayers C, Head WC, et al. Surgical closing in primary total knee arthroplasties: flexion versus extension. Clin Orthop Relat Res 1996;331:74. 6. Ingle NP, King MW. Optimizing the tissue anchoring performance of barbed sutures in skin and tendon tissues. J Biomech 2010;43:302. 7. Chu CC, Greisler HP, von Fraunhofer JA. Wound closure biomaterials and devices. New York: CRC-Press; 1997 78. 8. Nett M, Avelar R, Sheehan M, et al. Water-tight knee arthrotomy closure: comparison of a novel single bidirectional barbed self-retaining running suture versus conventional interrupted sutures. J Knee Surg 2011;24:55. 9. Eickmann T, Quane E. Total knee arthroplasty closure with barbed sutures. J Knee Surg 2010;23:163. 10. Leung JC, Ruff GL, Megaro MA. Barbed, bi-directional medical sutures: biomechanical properties and wound closure efficacy study. Society for Biomaterials 28th Annual Meeting Transactions, #724; 2002.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Knee Arthrotomy Closure With Barbed Suture in Flexion Versus Extension: A Porcine Study Praveen Kadimcherla, MD a, Andrew J. Lovy, MD, MS b, Chris Sambaziotis, MD, MPH a, c, Yossef Blum, MD a, c, David M. Hirsh, MD a, c, Sun J. Kim, MD a, c a b c
Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Bronx, New York Department of Orthopaedic Surgery, Mount Sinai Hospital, New York, New York Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Bronx, New York
a r t i c l e
i n f o
Article history: Received 20 March 2014 Accepted 19 July 2014 Keywords: knee arthrotomy barbed suture arthrotomy closure suture failure extension
a b s t r a c t The purpose of this biomechanical study was to evaluate knee arthrotomy closure with a barbed suture in flexion versus extension. 48 porcine knees were randomized into three groups: full extension, 30° flexion, and 60° flexion. Each knee was then flexed to 90° and then 120°, with failures recorded. Arthrotomy closure in extension had significantly higher failure rates (6/16) upon flexion to 90° compared to arthrotomy closure in either 30° or 60° flexion (0/32) (P = 0.032). Upon ranging from 0° to 120°, arthrotomy failure occurred in 50% (8/16) of arthrotomies in the extension group, 6.25% (1/16) in the 30° flexion group and 18.75% (3/16) in the 60° flexion group (P = 0.022). Knee arthrotomy closure in extension compared to flexion had significantly higher rates of failure. © 2014 Elsevier Inc. All rights reserved.
Wound healing complications following total knee arthroplasty (TKA) are a known problem that can lead to disastrous outcomes including implant failure [1]. In order to reduce wound healing complications, tight closure of the arthrotomy is crucial, as superficial wound healing problems requiring early surgical intervention following TKA have been shown to significantly increase risk of subsequent major surgery [2]. Hematoma formation can lead to infection. A tight arthrotomy closure can limit the size of the subsequent hematoma and potentially prevent and limit the spread of infection. Furthermore, as early mobilization is encouraged following knee surgery in order to preserve range of motion, arthrotomy repair must maintain its integrity even when facing tensile forces generated during flexion. In 2007, bidirectional barbed suture was introduced in the United States (Quill Self-Retaining System; Angiotech Pharmaceuticals, Inc., Vancouver, British Columbia) allowing tissue to be reapproximated without use of a surgical knot. Use of barbed suture for wound closure has been documented in many surgical disciplines [3], and recent cadaveric studies have demonstrated its efficacy in knee arthrotomy closure [4]. Trials comparing knee arthrotomy closure in flexion versus extension have been done using interrupted sutures, demonstrating the superiority of closure in flexion [5]. However, to our knowledge there are no studies comparing arthrotomy closure in flexion versus
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.07.023. Reprint requests: Sun J. Kim, MD, Department of Orthopaedic Surgery, Albert Einstein College of Medicine, Montefiore Medical Center 1200 Waters Place, Bronx, NY 10461. http://dx.doi.org/10.1016/j.arth.2014.07.023 0883-5403/© 2014 Elsevier Inc. All rights reserved.
extension using barbed suture. The purpose of our study was to compare barbed suture failure rates of knee arthrotomy closure in full extension versus flexion upon ranging the knee from 0° to 120° using porcine specimens. We hypothesized that knee arthrotomy closure conducted in flexion would have lower rates of suture failure compared to knees closed in full extension. Methods Forty eight fresh frozen intact pig knees were obtained. Specimens were stored at −10 °F and thawed at room temperature for 24 hours before use. The specimens were randomly selected into three closure groups of 16 specimens; full extension, 30° flexion, and 60° flexion. Before use, each specimen was examined to ensure at least 120° of motion. For each specimen, a mid-line skin incision of 10 cm was made with a number 10 scalpel blade. Following incision, the skin and subcutaneous tissue was dissected to allow full visualization for closure and testing of the arthrotomy closure. The joint line was identified, and a 7 cm arthrotomy was marked out. Using a ruler, markings were made every 5 mm to represent the distance that should be traversed with each suture throw. The arthrotomy was made to leave a 3 mm cuff of tendon on lateral border of the vastus medialis and also a 3 mm cuff of retinaculum medial to the patella. Upon completion of the arthrotomy the specimen was randomly assigned to closure in full extension, 30° flexion or 60° flexion. Closure angle was determined by a goniometer, and the specimen was secured to the table at the desired degree of flexion using a modified c-clamp.
2212
P. Kadimcherla et al. / The Journal of Arthroplasty 29 (2014) 2211–2213
The arthrotomy was closed with a with a running #1 monofilament absorbable knotless suture with bidirectional barbs (Quill; Angiotech, Reading, PA). The closure was initiated in the middle of the arthrotomy and was continued in both directions, reflecting the suture's design with continuous barbs running bidirectional from the center. Care was taken to make sure each throw included 3 mm of tissue and each pass advanced 5 mm. Upon reaching the end of the arthrotomy, the suture was passed back along the arthrotomy for 3 throws. No knots were required, and the excess suture was cut. Each specimen was numbered in order to later determine closure type. All 48 specimens were then examined by a blinded author not present at the time of arthrotomy closure. Initially, each specimen was fixed proximally and allowed to flex to 90° by gravitational force or was flexed manually to 90° and the number of suture breaks was recorded by the blinded subject. The number of suture ruptures was determined visually (range 0–6) and was confirmed by another observer. The knee was then further flexed to 120° of flexion as determined by a goniometer. Once again the number of suture ruptures was determined visually and was confirmed by the blinded author and another observer. In some instances the suture had ruptured in multiple spots and had completely unraveled, leaving the observers unable to determine exactly the number of areas where the suture has ruptured. These instances were recorded as complete failures. For the purposes of statistical analysis complete failures were assigned a value of 6 corresponding to the maximal number of suture ruptures recorded. Arthrotomy failure rates and number of suture throw failures were analyzed using STATA software (version 11, College Station, TX) and a one tailed α of 0.05. Rate of arthrotomy failure, defined as rupture of at least one suture throw, was evaluated using a one sided Fisher's exact test. Following assessment of normality and equal variance, number of suture throw failures (dependent variable) in extension and flexion groups (independent variable) was evaluated using the Wilcoxon rank-sum test. Results Barbed suture failure rates were evaluated upon ranging the knee from 0° to 90° and 120° in 48 porcine specimens grouped into closure at full extension, 30° flexion and 60° flexion. Arthrotomy closure in full extension had significantly higher rates of failure (18.75%, 3/16) upon flexion to 90° compared to arthrotomy closure in either 30° or 60° flexion (0%, 0/32) (P = 0.032). In all three failures, one suture throw ruptured, upon ranging to 90°. Upon ranging from 0° to 120°, arthrotomy failure occurred in 50% (8/16) of arthrotomy closures in the full extension group, 6.25% (1/ 16) in the 30° flexion group and 18.75% (3/16) in the 60° flexion group (P = 0.0022). A significantly greater number of suture throws ruptured among arthrotomy failures in the full extension group compared to the two flexion groups (P = 0.0018). Complete suture failure (Fig. 1) occurred in two of the knees in the full extension group upon ranging to 120° compared to none in the 30° or 60° flexion groups. There was no difference in arthrotomy failure rates between the two arthrotomy groups closed in 30° flexion and 60° flexion upon ranging to 120° (P = 0.60).
Fig. 1. Shows the complete failure of an arthrotomy closure with bi-directional barbed suture. Multiple suture failure sites along the arthrotomy are appreciated along with unwinding of the suture.
Complete failure was noted in two of the knees closed in full extension compared to none in the flexion groups upon ranging from 0° to 120°. This result is particularly concerning given the known consequences of implant failure and even amputation as a result of wound healing problems in TKA [1]. The failure of the barbed suture seemed to occur at the junction of the barb and the core material. This typical site of failure can be noted in the edge of our failed barbed suture in Fig. 2. The proposed method of failure of the closure is thought to be the increased length of the suture as the knee flexes. The bidirectional barbed design of the suture when tightened during the closure embeds the barbs within the tissue at fixed points. As the knee undergoes increasing flexion, tensile forces across the suture construct increase as well. Biomechanical studies have shown that because of the cuts created in the suture material in the creation of the barbed suture, the effective cross sectional area of the suture decreases and the peak tensile load and peak elongation also decrease [6]. This is consistent with our findings that the greatest number of failures occurred as the specimens were flexed to 120.
Discussion Tight closure of arthrotomy in TKA is critical in order to facilitate proper wound healing and prevent infection [1,2]. In our study comparing arthrotomy closure with a barbed suture in full extension versus flexion, arthrotomy closure in full extension was found to have significantly higher rates of failure compared to closure in 30° or 60° of flexion upon ranging to both 90° and 120°. Results of the current study suggest that arthrotomy closure in flexion is preferable to extension as it is associated with significantly lower rates of failure.
Fig. 2. Depicts the failure point of the barbed suture. Closer examination reveals that the barbed suture has failed at the site of the barb, which is also the point of smallest diameter on the suture.
P. Kadimcherla et al. / The Journal of Arthroplasty 29 (2014) 2211–2213
Fig. 3. Demonstrates a closer view of the suture and how the integrity of the suture material is compromised by the creation of the barbs.
The junction of the barb and core material is noted to be the weakest point in the barbed suture construct. Barbed sutures are created by cuts in a monofilament material to create a barb that is oriented to anchor itself into the surrounding tissue (Fig. 3). This modification leads to decreased internal core diameter of the suture and has been shown to be equivalent to a suture that is one size smaller [6]. This should be taken into consideration when choosing the size of suture material. Also, the defect created in the monofilament becomes a location of stress concentration and an ultimate failure point upon excessive loading. The problem of decreased core diameter can only be partially addressed by increasing the size of the suture material used. The calculated peak tensile loads for a given decrease in the diameter of the barbed suture material were much higher than what was observed during testing of the peak tensile loads of the barbed suture [6]. This is explained by the concept of non-uniform “sheath-core” morphology of the monofilament [7]. The outer layers of the suture are more crystalline and more oriented and the inner layers are composed of more amorphous material. The creation of barbs lead to the removal of the crystalline material preferentially and decreased load to failure that is lower than would be expected from the size of center core. The higher proportion of an amourphous region gives the suture an increased ability to elongate initially at lower loads due to the straightening of randomly oriented fibrils in the amorphous region. However, after initial lengthening, the load to ultimate failure is reached quickly without the structural integrity of the crystalline region. This could explain the relatively low number of suture failures observed during the first 90° of motion compared to the last 30° of motion. The efficacy of barbed suture use in knee arthrotomy repair was recently confirmed in a biomechanical study by Vakil et al [4]. In their study, cadaveric knee arthrotomy closure using interrupted biodegradable sutures and running bidirectional barbed sutures was compared in cadaveric specimens, and both groups maintained closure without suture rupture following 2000 flexion cycles [4]. The authors also noted that barbed suture repair was able to withstand a greater number of suture cuts than interrupted suture repair. Another cadaveric study of knee arthrotomy closure compared water tight closure with interrupted absorbable suture and barbed suture. Water-tightness of the arthrotomy closure was compared by simulating a tense hemarthrosis and measuring arthrotomy leakage over 3 minutes. Closure with barbed suture was found to achieve a more water-tight closure as mean total leakage was 356 mL in the barbed group compared to 89 mL in the interrupted group (P = 0.027) [8]. In addition to the biomechanical advantages of barbed suture, these sutures also afford the surgeon the ability to perform a more
2213
efficient closure. Eickmann et al [9] have shown that closure of the retinacular and subcutaneous layers during a total knee arthroplasty using a bidirectional barbed absorbable sutures for running closures resulted in decreased surgical times. The mean times were 85.8 minutes for closure using conventional sutures and 74.3 minutes for barbed sutures. The relatively faster closure technique has also not been associated with any detrimental clinical effects with regards to wound security, cosmesis, or infection risk. Some of the limitations of this study are that we used a pig model and not a cadaveric model. We were also not able to evaluate the arthrotomy closure with cyclical loading. Data from durability of an arthrotomy closure in various degrees of flexion would have given us a better approximation of the in vivo survival of our arthrotomy closure. We have also only evaluated the closure at a static point. However studies have shown that barbed PDO sutures tensile strength varies significantly with time. The barbed PDO suture lost approximately 20% of its initial tensile strength at both weeks 2 and 4 [10]. The loss was 58% at week 6. This change could have varying implications for the knee arthrotomies closed in extension compared to the knee arthrtomies closed in varying degrees of flexion. Also, the stress placed on a closure externally does not approximate the force generated by balanced muscle contractions from varying vectors in vivo. Although prior studies have demonstrated the efficacy of barbed sutures in many surgical disciplines [3] and in cadaveric studies of knee arthrotomy closure [4], no studies have compared knee arthrotomy closure in flexion and extension. Results of our bovine biomechanical study suggest that knee arthrotomy closure in full extension is associated with higher rates of failure compared to closure in flexion. Although the results of the current study were observed in vitro, they raise awareness to the potential wound complications associated with arthrotomy closure in full extension with barbed sutures that should be verified in a clinical study.
References 1. Vince KG, Abdeen A. Wound problems in total knee arthroplasty. Clin Orthop Relat Res 2006;452:88. 2. Galat DD, McGovern SC, Larson DR, et al. Surgical treatment of early wound complications following primary total knee arthroplasty. J Bone Joint Surg Am 2009;91:48. 3. Murtha AP, Kaplan AL, Paglia MJ, et al. Evaluation of a novel technique for wound closure using a barbed suture. Plast Reconstr Surg 2006;117:1769. 4. Vakil JJ, O'Reilly MP, Sutter EG, et al. Knee arthrotomy repair with a continuous barbed suture a biomechanical study. J Arthroplasty 2011;26:710. 5. Emerson Jr RH, Ayers C, Head WC, et al. Surgical closing in primary total knee arthroplasties: flexion versus extension. Clin Orthop Relat Res 1996;331:74. 6. Ingle NP, King MW. Optimizing the tissue anchoring performance of barbed sutures in skin and tendon tissues. J Biomech 2010;43:302. 7. Chu CC, Greisler HP, von Fraunhofer JA. Wound closure biomaterials and devices. New York: CRC-Press; 1997 78. 8. Nett M, Avelar R, Sheehan M, et al. Water-tight knee arthrotomy closure: comparison of a novel single bidirectional barbed self-retaining running suture versus conventional interrupted sutures. J Knee Surg 2011;24:55. 9. Eickmann T, Quane E. Total knee arthroplasty closure with barbed sutures. J Knee Surg 2010;23:163. 10. Leung JC, Ruff GL, Megaro MA. Barbed, bi-directional medical sutures: biomechanical properties and wound closure efficacy study. Society for Biomaterials 28th Annual Meeting Transactions, #724; 2002.