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Technical Note Loop security as a determinant of tissue fixation security
Technical Note
Loop Security as a Determinant of Tissue Fixation Security Stephen S. Burkhart, M.D., Michael A. Wirth, M.D., Matthew Simonick, M.D., Daniel Salem, M.D., Dan Lanctot, B.S., and Kyriacos Athanasiou, Ph.D., P.E.
Summary: Secure arthroscopic repair of rotator cuff tears and Bankart lesions requires tight knots (knot security). Equally important, but usually overlooked, is the tightness of the suture loop (loop security). This study compared loop security in knots tied with No. 1 PDS suture using three different methods: (1) hand-tied, (2) single-hole standard knot pusher, and (3) cannulated double-diameter knot pusher. The results of this study show that the double-diameter knot pusher maintained tight suture loops that were equivalent in circumference to hand-tied loops and were significantly tighter than suture loops tied with a standard single-hole knot pusher. This study highlights the fact that loop security is equally important to knot security in tissue fixation. Key Words: Suture—Knots—Rotator cuff repair—Arthroscopic knots.
T
ight loops have long been a major concern of seamstresses, fishermen, and executioners. Despite the obvious importance of maintaining tight suture loops (loop security) in surgery, the surgical literature has focused on knot security1-12 and has totally ignored loop security. This oversight is unfortunate because it is obvious that a suture loop that is initially loose will cause loss of tissue fixation no matter how tightly the knot is tied (Fig 1). Because loop security is so important to soft tissue fixation, we sought to determine the optimum means of obtaining loop security arthroscopically. MATERIALS AND METHODS Knots were tied around a 5-cm circumference dowel to create closed loops using No. 1 PDS suture using From the University of Texas Health Science Center at San Antonio and the San Antonio Orthopaedic Group, P.A., San Antonio, Texas, U.S.A. Address correspondence and reprint requests to Stephen S. Burkhart, M.D., 540 Madison Oak Dr, Suite 620, San Antonio, TX 78258-3913, U.S.A. r 1998 by the Arthroscopy Association of North America 0749-8063/98/1707-1909$3.00/0
three different methods: (1) hand-tied, (2) single-hole standard knot pusher (Linvatec, Largo, FL), and (3) cannulated double-diameter knot pusher (Surgeon’s Sixth Finger; Arthrex, Naples, FL). Furthermore, four knot types were tied using each of the three methods. Knot tying was randomly assigned among the various groups to the two senior surgeons (S.S.B., M.A.W.) and the two surgeons in training (M.S., D.S.) so that experience level would not be a factor in any of the groups of knots. The knots were all repeating sliding knots with four throws each and included the following: (1) same post–same loop direction, (2) same post–reverse loop direction, (3) reverse post–same loop direction, and (4) reverse post–reverse loop direction. Seven knots were tied for each combination of knot type and method, for a total of 12 groups and 84 knots. A servo-hydraulic materials testing system (MTS) (model 858 Bionix MTS; Bionix, Eden Prairie, MN), was used to measure the circumference of the closed loops created by the knots. Two parallel rods were mounted onto the actuators of the MTS and set at a known distance apart, which would allow a 5-cm circumference loop to be placed around the rods without any tension in the suture. The rods were pulled apart at 1.0 mm/second while the force and displace-
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 14, No 7 (October), 1998: pp 773–776
773
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S. S. BURKHART ET AL.
FIGURE 1. (A) A tight suture loop holds the soft tissue tightly apposed to the prepared bone bed. (B) A loose loop allows the soft tissue to pull away from the prepared bone bed, regardless of how securely the knot may be tied.
ment were measured and recorded at 10 points/second. The loop circumference was determined by measuring the distance between the rods when the tension force had reached 5 N, assuring that all the slack had been taken out of the loop. Circumference was calculated using the formula: circumference ⫽ 2 ⫻ D (distance between centerline of rods) ⫹ 19.95 mm (rod circumference). This measurement indicated the initial loop tightness (loop security). For example, a loop that is maximally tight and secure should have a circumference of 5 cm, which is the circumference of the dowel. It should be noted that PDS suture will stretch under load and that it has memory (recoil) so that theoretically a very tight loop could recoil when it was unloaded from the dowel, giving a circumference of less than 5 cm. Figure 2 shows the four types of knots that were tied using each method. For experimental analysis, the mean and standard deviation for each group were calculated and graphed. Also, statistical
FIGURE 2.
comparison of loop circumference was examined using analysis of variance (ANOVA). The Fisher’s Least Significant Difference (FLSD) comparisons test of the means was applied when the F-test in ANOVA was significant. The statistical significance level was set at P ⬍ .05 for all comparisons.
RESULTS Figure 2 shows the types of knots that were tied in each group. Table 1 lists the mean and standard deviation values of loop circumference for the three methods of tying and the four knot types. Figure 3 illustrates the results in a bar graph that shows descending order of values and statistical comparisons. The horizontal line spanning the bars on the graph indicate that the groups under the same line are not significantly different (P ⬎ .05). As seen in Fig 3,
(A) Knot configurations tied with a single post suture. (B) Knot configurations tied with alternating post sutures.
LOOP AND TISSUE FIXATION SECURITY
775
TABLE 1. The Loop Circumference (Mean and Standard Deviation) Using Four Types of Knots Created With Three Different Methods (Surgeon’s Sixth Finger, Hand Tie, and Standard Knot Pusher)
Knot Type
Method
Loop Circumference (mm) Mean ⫾ SD
1 (same post-same loop) 1 (same post-same loop) 1 (same post-same loop) 2 (same post-reverse loop) 2 (same post-reverse loop) 2 (same post-reverse loop) 3 (reverse post-same loop) 3 (reverse post-same loop) 3 (reverse post-same loop) 4 (reverse post-reverse loop) 4 (reverse post-reverse loop) 4 (reverse post-reverse loop)
Sixth Finger Hand tied Standard knot pusher Sixth Finger Hand tied Standard knot pusher Sixth Finger Hand tied Standard knot pusher Sixth Finger Hand tied Standard knot pusher
50.51 ⫾ 2.25 52.89 ⫾ 2.33 51.78 ⫾ 0.63 49.93 ⫾ 1.01 50.70 ⫾ 0.37 51.61 ⫾ 0.31 50.03 ⫾ 0.88 50.48 ⫾ 0.41 51.45 ⫾ 1.13 50.19 ⫾ 0.98 49.78 ⫾ 0.38 50.94 ⫾ 0.41
all four knots tied with the Surgeon’s Sixth Finger were significantly tighter than knots 1 and 2 when they were tied with the standard knot pusher. The tightest loop created with the standard knot pusher, knot type 4, is only significantly larger than knot type 2 tied with the Surgeon’s Sixth Finger and knot type 4 tied by hand. For the entire experiment, the loosest loop was the hand-tied knot type 1 and the tightest was the hand-tied knot type 4. Because of the recoil of the PDS suture, the two groups with the smallest loop circumference were actually less than 5 cm on average. Figure 4 is a bar graph that shows the combined values
FIGURE 3. Bar graph comparing loop circumference for the various knot types tied by hand, standard knot pusher, and double-diameter knot pusher. Groups under same line are not significantly different (P ⬎ .05). Knot types: 1: S⫽S⫽S 2: SxSxS 3: S//S//S 4: S//xS//xS
FIGURE 4. Bar graph shows that the Surgeon’s Sixth Finger knot pusher forms a loop that is significantly smaller than those formed by hand or by a standard single-hole knot pusher. Groups under the same line are not significantly different (P ⬎ .05).
from all four knot types for each of the three methods. As seen in this graph, the loops whose knots were tied with the Surgeon’s Sixth Finger were significantly tighter than the ones created with the single-hole standard knot pusher and the loops tied by hand. DISCUSSION A suture loop will never be tighter than at the moment it is tied. A loose suture loop will not adequately appose tissues, no matter how securely the
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S. S. BURKHART ET AL.
FIGURE 5. Double-diameter knot pusher (Surgeon’s Sixth Finger) maintains a tight loop by holding pressure against the first suture throw with the metallic cannulated tube while simultaneously stacking subsequent throws on top of the first by means of a sliding plastic cylinder (outer diameter tube)
knots are tied. Therefore, it seems strange that so much effort has been devoted to knot security and so little to loop security. Prior studies1,6,10,11 have assumed that 3 mm of knot slippage would cause loss of soft tissue apposition, since one must assume that a loop that slips 3 mm as the knot is being tied would also lose soft tissue apposition. In open surgical procedures, the surgeon frequently secures the first throw of his knot by having his assistant place a hemostat or clamp on the first throw until the second throw is securely in place. This maneuver also can be performed arthroscopically. However, this maneuver is difficult, requires the use of a second portal for the grasping instrument, and potentially weakens the suture where it is held by the grasping instrument. When one ties knots arthroscopically with a standard knot pusher, the first throw invariably slips when the knot pusher is withdrawn to place the second throw. Often, but not always, the first throw will tighten as the second throw advances under the knot pusher. However, the second throw sometimes locks the first throw before all the slack is taken out of the suture loop, leaving a loose loop. If the loop is loose, tissue fixation may be lost (Fig 1). With the cannulated double-diameter knot pusher, loop security is maintained by the cannulated inner diameter tube, which pushes against the first throw of the knot while subsequent throws are advanced with the sliding outer diameter cylinder (Fig 5). In this way, the throws of the knot are sequentially stacked without allowing the suture loop to become lax. This method is
analogous to holding one’s finger on the first throw of a shoelace to prevent slippage while tying the overlying slip knot. This study compared hand-tied knots with those tied with a standard single-hole knot pusher and those tied with a cannulated double-diameter knot pusher. The hand-tied knots served as the standard for comparison. The results of this study show that the doublediameter knot pusher maintained tight suture loops that were equivalent in circumference to the hand-tied loops and significantly tighter than the suture loops tied with a standard single-hole knot pusher. This study was not intended to compare brands of knot pushers, since most companies make a standard single-hole knot pusher that functions identically to the one used in this study. The issue was loop security, and the goal was to find the best means to hold a tight suture loop. We conclude that arthroscopic knot-tying with a cannulated double-diameter knot pusher ensures consistently tight suture loops for greater tissue fixation security and greater loop security than standard arthroscopic knot-tying. REFERENCES 1. Brouwers JE, Oosting H, deHaas D, Klopper PJ. Dynamic loading of surgical knots. Surg Gynecol Obstet 1991;173:443448. 2. Gerber C, Schneeberger AG, Beck M, Schlegel U. Mechanical strength of repairs of the rotator cuff. J Bone Joint Surg Br 1994;76:371-380. 3. Gunderson PE. The half-hitch knot: A rational alternative to the square knot. Am J Surg 1987;154:538-540. 4. Herrmann JB. Tensile strength and knot security of surgical suture materials. Am Surg 1971;37:209-217. 5. Holmlund DE. Knot properties of surgical suture materials. Acta Chir Scand 1974;140:355-362. 6. Loutzenheiser TD, Harryman DT II, Yung SW, et al. Optimizing arthroscopic knots. Arthroscopy 1995;11:199-206. 7. Rodeheaver GT, Thacker JG, Edlich RF. Mechanical performance of polyglycolic acid and polyglactin 910 synthetic absorbable sutures. Surg Gynecol Obstet 1981;153:835-841. 8. Taylor FW. Surgical knots. Ann Surg 1938;107:458-468. 9. Tera H, Aberg C. Tensile strength of twelve types of knots employed in surgery, using different suture materials. Acta Chir Scand 1976;142:1-7. 10. Trimbos JB, Booster M, Peters AAW. Mechanical knot performance of a new generation polydiaxanon suture (PDS-2). Acta Obstet Gynecol Scand 1991;70:157-159. 11. Trimbos JB, Van Rijssel EJC, Klopper PJ. Performance of sliding knots in monofilament and multifilament suture material. Obstet Gynecol 1986;68:425-430. 12. Van Rijssel EJ, Trimbos JB, Booster MH. Mechanical performance of square knots and sliding knots in surgery: A comparative Study. Am J Obstet Gynecol 1990;162:93-97.
Loop Security as a Determinant of Tissue Fixation Security Stephen S. Burkhart, M.D., Michael A. Wirth, M.D., Matthew Simonick, M.D., Daniel Salem, M.D., Dan Lanctot, B.S., and Kyriacos Athanasiou, Ph.D., P.E.
Summary: Secure arthroscopic repair of rotator cuff tears and Bankart lesions requires tight knots (knot security). Equally important, but usually overlooked, is the tightness of the suture loop (loop security). This study compared loop security in knots tied with No. 1 PDS suture using three different methods: (1) hand-tied, (2) single-hole standard knot pusher, and (3) cannulated double-diameter knot pusher. The results of this study show that the double-diameter knot pusher maintained tight suture loops that were equivalent in circumference to hand-tied loops and were significantly tighter than suture loops tied with a standard single-hole knot pusher. This study highlights the fact that loop security is equally important to knot security in tissue fixation. Key Words: Suture—Knots—Rotator cuff repair—Arthroscopic knots.
T
ight loops have long been a major concern of seamstresses, fishermen, and executioners. Despite the obvious importance of maintaining tight suture loops (loop security) in surgery, the surgical literature has focused on knot security1-12 and has totally ignored loop security. This oversight is unfortunate because it is obvious that a suture loop that is initially loose will cause loss of tissue fixation no matter how tightly the knot is tied (Fig 1). Because loop security is so important to soft tissue fixation, we sought to determine the optimum means of obtaining loop security arthroscopically. MATERIALS AND METHODS Knots were tied around a 5-cm circumference dowel to create closed loops using No. 1 PDS suture using From the University of Texas Health Science Center at San Antonio and the San Antonio Orthopaedic Group, P.A., San Antonio, Texas, U.S.A. Address correspondence and reprint requests to Stephen S. Burkhart, M.D., 540 Madison Oak Dr, Suite 620, San Antonio, TX 78258-3913, U.S.A. r 1998 by the Arthroscopy Association of North America 0749-8063/98/1707-1909$3.00/0
three different methods: (1) hand-tied, (2) single-hole standard knot pusher (Linvatec, Largo, FL), and (3) cannulated double-diameter knot pusher (Surgeon’s Sixth Finger; Arthrex, Naples, FL). Furthermore, four knot types were tied using each of the three methods. Knot tying was randomly assigned among the various groups to the two senior surgeons (S.S.B., M.A.W.) and the two surgeons in training (M.S., D.S.) so that experience level would not be a factor in any of the groups of knots. The knots were all repeating sliding knots with four throws each and included the following: (1) same post–same loop direction, (2) same post–reverse loop direction, (3) reverse post–same loop direction, and (4) reverse post–reverse loop direction. Seven knots were tied for each combination of knot type and method, for a total of 12 groups and 84 knots. A servo-hydraulic materials testing system (MTS) (model 858 Bionix MTS; Bionix, Eden Prairie, MN), was used to measure the circumference of the closed loops created by the knots. Two parallel rods were mounted onto the actuators of the MTS and set at a known distance apart, which would allow a 5-cm circumference loop to be placed around the rods without any tension in the suture. The rods were pulled apart at 1.0 mm/second while the force and displace-
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 14, No 7 (October), 1998: pp 773–776
773
774
S. S. BURKHART ET AL.
FIGURE 1. (A) A tight suture loop holds the soft tissue tightly apposed to the prepared bone bed. (B) A loose loop allows the soft tissue to pull away from the prepared bone bed, regardless of how securely the knot may be tied.
ment were measured and recorded at 10 points/second. The loop circumference was determined by measuring the distance between the rods when the tension force had reached 5 N, assuring that all the slack had been taken out of the loop. Circumference was calculated using the formula: circumference ⫽ 2 ⫻ D (distance between centerline of rods) ⫹ 19.95 mm (rod circumference). This measurement indicated the initial loop tightness (loop security). For example, a loop that is maximally tight and secure should have a circumference of 5 cm, which is the circumference of the dowel. It should be noted that PDS suture will stretch under load and that it has memory (recoil) so that theoretically a very tight loop could recoil when it was unloaded from the dowel, giving a circumference of less than 5 cm. Figure 2 shows the four types of knots that were tied using each method. For experimental analysis, the mean and standard deviation for each group were calculated and graphed. Also, statistical
FIGURE 2.
comparison of loop circumference was examined using analysis of variance (ANOVA). The Fisher’s Least Significant Difference (FLSD) comparisons test of the means was applied when the F-test in ANOVA was significant. The statistical significance level was set at P ⬍ .05 for all comparisons.
RESULTS Figure 2 shows the types of knots that were tied in each group. Table 1 lists the mean and standard deviation values of loop circumference for the three methods of tying and the four knot types. Figure 3 illustrates the results in a bar graph that shows descending order of values and statistical comparisons. The horizontal line spanning the bars on the graph indicate that the groups under the same line are not significantly different (P ⬎ .05). As seen in Fig 3,
(A) Knot configurations tied with a single post suture. (B) Knot configurations tied with alternating post sutures.
LOOP AND TISSUE FIXATION SECURITY
775
TABLE 1. The Loop Circumference (Mean and Standard Deviation) Using Four Types of Knots Created With Three Different Methods (Surgeon’s Sixth Finger, Hand Tie, and Standard Knot Pusher)
Knot Type
Method
Loop Circumference (mm) Mean ⫾ SD
1 (same post-same loop) 1 (same post-same loop) 1 (same post-same loop) 2 (same post-reverse loop) 2 (same post-reverse loop) 2 (same post-reverse loop) 3 (reverse post-same loop) 3 (reverse post-same loop) 3 (reverse post-same loop) 4 (reverse post-reverse loop) 4 (reverse post-reverse loop) 4 (reverse post-reverse loop)
Sixth Finger Hand tied Standard knot pusher Sixth Finger Hand tied Standard knot pusher Sixth Finger Hand tied Standard knot pusher Sixth Finger Hand tied Standard knot pusher
50.51 ⫾ 2.25 52.89 ⫾ 2.33 51.78 ⫾ 0.63 49.93 ⫾ 1.01 50.70 ⫾ 0.37 51.61 ⫾ 0.31 50.03 ⫾ 0.88 50.48 ⫾ 0.41 51.45 ⫾ 1.13 50.19 ⫾ 0.98 49.78 ⫾ 0.38 50.94 ⫾ 0.41
all four knots tied with the Surgeon’s Sixth Finger were significantly tighter than knots 1 and 2 when they were tied with the standard knot pusher. The tightest loop created with the standard knot pusher, knot type 4, is only significantly larger than knot type 2 tied with the Surgeon’s Sixth Finger and knot type 4 tied by hand. For the entire experiment, the loosest loop was the hand-tied knot type 1 and the tightest was the hand-tied knot type 4. Because of the recoil of the PDS suture, the two groups with the smallest loop circumference were actually less than 5 cm on average. Figure 4 is a bar graph that shows the combined values
FIGURE 3. Bar graph comparing loop circumference for the various knot types tied by hand, standard knot pusher, and double-diameter knot pusher. Groups under same line are not significantly different (P ⬎ .05). Knot types: 1: S⫽S⫽S 2: SxSxS 3: S//S//S 4: S//xS//xS
FIGURE 4. Bar graph shows that the Surgeon’s Sixth Finger knot pusher forms a loop that is significantly smaller than those formed by hand or by a standard single-hole knot pusher. Groups under the same line are not significantly different (P ⬎ .05).
from all four knot types for each of the three methods. As seen in this graph, the loops whose knots were tied with the Surgeon’s Sixth Finger were significantly tighter than the ones created with the single-hole standard knot pusher and the loops tied by hand. DISCUSSION A suture loop will never be tighter than at the moment it is tied. A loose suture loop will not adequately appose tissues, no matter how securely the
776
S. S. BURKHART ET AL.
FIGURE 5. Double-diameter knot pusher (Surgeon’s Sixth Finger) maintains a tight loop by holding pressure against the first suture throw with the metallic cannulated tube while simultaneously stacking subsequent throws on top of the first by means of a sliding plastic cylinder (outer diameter tube)
knots are tied. Therefore, it seems strange that so much effort has been devoted to knot security and so little to loop security. Prior studies1,6,10,11 have assumed that 3 mm of knot slippage would cause loss of soft tissue apposition, since one must assume that a loop that slips 3 mm as the knot is being tied would also lose soft tissue apposition. In open surgical procedures, the surgeon frequently secures the first throw of his knot by having his assistant place a hemostat or clamp on the first throw until the second throw is securely in place. This maneuver also can be performed arthroscopically. However, this maneuver is difficult, requires the use of a second portal for the grasping instrument, and potentially weakens the suture where it is held by the grasping instrument. When one ties knots arthroscopically with a standard knot pusher, the first throw invariably slips when the knot pusher is withdrawn to place the second throw. Often, but not always, the first throw will tighten as the second throw advances under the knot pusher. However, the second throw sometimes locks the first throw before all the slack is taken out of the suture loop, leaving a loose loop. If the loop is loose, tissue fixation may be lost (Fig 1). With the cannulated double-diameter knot pusher, loop security is maintained by the cannulated inner diameter tube, which pushes against the first throw of the knot while subsequent throws are advanced with the sliding outer diameter cylinder (Fig 5). In this way, the throws of the knot are sequentially stacked without allowing the suture loop to become lax. This method is
analogous to holding one’s finger on the first throw of a shoelace to prevent slippage while tying the overlying slip knot. This study compared hand-tied knots with those tied with a standard single-hole knot pusher and those tied with a cannulated double-diameter knot pusher. The hand-tied knots served as the standard for comparison. The results of this study show that the doublediameter knot pusher maintained tight suture loops that were equivalent in circumference to the hand-tied loops and significantly tighter than the suture loops tied with a standard single-hole knot pusher. This study was not intended to compare brands of knot pushers, since most companies make a standard single-hole knot pusher that functions identically to the one used in this study. The issue was loop security, and the goal was to find the best means to hold a tight suture loop. We conclude that arthroscopic knot-tying with a cannulated double-diameter knot pusher ensures consistently tight suture loops for greater tissue fixation security and greater loop security than standard arthroscopic knot-tying. REFERENCES 1. Brouwers JE, Oosting H, deHaas D, Klopper PJ. Dynamic loading of surgical knots. Surg Gynecol Obstet 1991;173:443448. 2. Gerber C, Schneeberger AG, Beck M, Schlegel U. Mechanical strength of repairs of the rotator cuff. J Bone Joint Surg Br 1994;76:371-380. 3. Gunderson PE. The half-hitch knot: A rational alternative to the square knot. Am J Surg 1987;154:538-540. 4. Herrmann JB. Tensile strength and knot security of surgical suture materials. Am Surg 1971;37:209-217. 5. Holmlund DE. Knot properties of surgical suture materials. Acta Chir Scand 1974;140:355-362. 6. Loutzenheiser TD, Harryman DT II, Yung SW, et al. Optimizing arthroscopic knots. Arthroscopy 1995;11:199-206. 7. Rodeheaver GT, Thacker JG, Edlich RF. Mechanical performance of polyglycolic acid and polyglactin 910 synthetic absorbable sutures. Surg Gynecol Obstet 1981;153:835-841. 8. Taylor FW. Surgical knots. Ann Surg 1938;107:458-468. 9. Tera H, Aberg C. Tensile strength of twelve types of knots employed in surgery, using different suture materials. Acta Chir Scand 1976;142:1-7. 10. Trimbos JB, Booster M, Peters AAW. Mechanical knot performance of a new generation polydiaxanon suture (PDS-2). Acta Obstet Gynecol Scand 1991;70:157-159. 11. Trimbos JB, Van Rijssel EJC, Klopper PJ. Performance of sliding knots in monofilament and multifilament suture material. Obstet Gynecol 1986;68:425-430. 12. Van Rijssel EJ, Trimbos JB, Booster MH. Mechanical performance of square knots and sliding knots in surgery: A comparative Study. Am J Obstet Gynecol 1990;162:93-97.