Eur J Trauma Emerg Surg (2011) 37:79–84 DOI 10.1007/s00068-010-0019-8
ORIGINAL ARTICLE
Flexor tendon repair using a new suture technique: a comparative in vitro biomechanical study M. Scha¨del-Ho¨pfner • J. Windolf • T. T. Lo¨gters M. Hakimi • I. Celik
•
Received: 25 July 2009 / Accepted: 30 January 2010 / Published online: 20 April 2010 Ó Urban & Vogel 2010
Abstract Introduction The purpose of this experimental study was to evaluate the biomechanical characteristics of two new four-strand core suture techniques for flexor tendon repair. Materials and methods The two new suture techniques (Marburg 1, Marburg 2) are characterized by four longitudinal stitches which are anchored by a circular or semicircular suture. They were compared with three commonly used core suture techniques (modified Kessler, Tsuge, Bunnell). Fifty porcine flexor tendons were randomly assigned to one of the five core suture techniques. Outcome measures included ultimate tensile strength, maximum of lengthening, mode of failure and 1 mm gap formation force. Results The highest ultimate tensile strength was found for the modified Kessler technique (115 N). Both new techniques showed an ultimate load exceeding 50 N (57 N for Marburg 1, 54 N for Marburg 2). The Marburg 1 technique showed the highest gap resistance of all tested suture techniques. The Bunnell and Tsuge core suture techniques produced the poorest mechanical performance. Conclusion From these experimental results, the new Marburg 1 core suture technique can be considered for flexor tendon repair in a clinical setting with the use of active motion protocols.
Keywords Flexor tendon repair Biomechanical testing Ultimate tensile strength Gap resistance Marburg core suture technique
Introduction In the recent past, numerous in vitro and in vivo studies have been published on methods of flexor tendon surgery. Early active mobilization after flexor tendon repair is of high interest since it was found to decrease peritendinous adhesions, to improve tendon excursion and to increase tensile strength by a biological stress response at a cellular level. Although the running epitenon suture contributes significantly to stability, the core suture of the severed tendon is crucial since it must be adequate to guarantee both high tensile strength and gap resistance during the early stages of healing [1–7]. In this study, we present the results of a biomechanical evaluation of two new four-strand flexor tendon core suture techniques which are designed for early active motion.
Materials and methods Selection and preparation of tendons
M. Scha¨del-Ho¨pfner (&) J. Windolf T. T. Lo¨gters M. Hakimi Department of Trauma and Hand Surgery, University Hospital, Moorenstraße 5, 40225 Du¨sseldorf, Germany e-mail:
[email protected] I. Celik Institute of Theoretical Surgery, University Hospital, Marburg, Germany
For this biomechanical study, flexor tendons from the forelimb of 6 month old domestic pigs were used. From each trotter two long flexor tendons were harvested. These tendons had no muscular connections over a length of about 8 cm and with a diameter of 5 mm, their cross-sectional dimensions were similar to human flexor tendons. The tendons were kept fresh-frozen in sealed plastic bags at -20°C. For the testing, the tendons were defrosted to room
M. Scha¨del-Ho¨pfner et al.
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temperature by immersing the plastic bags in a water bath at 37°C. Tendons were lacerated sharply in the middle. During the experiment, the tendons were kept moist by regular spraying with normal saline solution. To maintain consistency, one surgeon performed all the repairs under loupe magnification. First, ten of these tendons were tested for ultimate tensile strength to ensure that their stability was comparable to that of human flexor tendons. Testing of suture techniques Fifty tendons were randomly assigned to one of five core suture techniques (Figs. 1, 2, 3): two new four-strand methods (Marburg 1 and Marburg 2), modified two-strand Kessler technique, single-loop two-strand Tsuge, and twostrand Bunnell. Additional epitendinous sutures were not performed because only the core sutures should be tested for tensile strength and gap formation. With the exception of the Tsuge technique, each suture technique was performed with Maxon 4-0. The Tsuge suture was only performed with the original Tendo-loop. Ten tendons were tested for each suture technique. For the Marburg 1 core suture technique (Fig. 1) two double armed sutures are used. A circular suture is placed in the epitenon of every tendon stump one centimetre from the cut. This suture is knotted twice and both ends are placed longitudinally through the tendon entering the opposite stump in the same direction. Here both ends are knotted three times over the contralateral circular suture. With the Marburg 2 technique (Fig. 2) the circular sutures are replaced by semicircular sutures that are positioned palmar (i.e. opposite to the identifiable remnants of the vincula). This modification was done to avoid damage to the vincula which are dorsally situated.
Fig. 2 Marburg 2 core suture technique
Fig. 3 Modified Kessler a, Tsuge b and Bunnell c core suture techniques
Design for evaluation of gap formation and load-to-failure testing
Fig. 1 Marburg 1 core suture technique
All native tendons and sutured tendons were tested using a universal testing machine (Shimadzu Autograph AG2000A). The tendons were fixed with custom-made clamps with transverse ridges. The preload was set at 1.0 N in all tendons to normalize data from all specimens. Traction force was applied with a speed of 30 mm/min. Lengthening of the tendon was measured by a linear displacement transducer and load by a force transducer. Both values were constantly recorded by an attached computer. A single pull to failure was performed until sutures ruptured or pulled out. Ultimate tensile strength was defined as the highest recorded load value before tendon or suture failed. At this time the maximum of lengthening was
Flexor tendon repair using a new suture technique
measured. In addition, for all suture techniques the tensile force was recorded when a gap width of 1 mm was reached. This force was defined as maximum gap resistance. Measurements of gap distance were quantified with a reference scale affixed parallel to the tendon. For each testing procedure a high-resolution video camera simultaneously recorded the changes of the tendon and the biomechanical values displayed on the attached computer monitor. A frame analysis was performed later for gap formation, tensile strength and type of failure. Statistical analysis Descriptive statistics were performed using the median and range system. Explorative analysis was performed for ordinal data using a nonparametric two-sided test for unpaired samples (Kruskal–Wallis-Test for k-samples). Only when this global testing showed significant differences, was it followed by a post hoc test (Dunn’s Multiple Comparisons Test). Data management and analysis were performed using the software package SPSS 10. A P value \0.05 was considered significant.
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Tensile loading and lengthening at failure (Tables 1, 2) The modified Kessler repair had the highest ultimate tensile strength at failure (median 115.2 N, range 40.3–148.0) which differed significantly from the Bunnell and Tsuge techniques, but not from the Marburg 1 and Marburg 2 techniques (Dunn’s Multiple Comparisons Test). The Marburg 1 (median 57.1 N, range 39.5–72.2) and Marburg 2 (median 53.7 N, range 43.2–61.0) suture techniques were stronger than the Bunnell and Tsuge techniques, but this difference was significant only for comparison with the Tsuge technique (Dunn’s Multiple Comparisons Test). The Tsuge technique showed the lowest ultimate tensile strength at failure (median 34.6 N, range 30.7–39.8). In most of the cases (Bunnell, Tsuge, Marburg 1 and Marburg 2) the repair failed by suture rupture (Table 1). Only for modified Kessler repair failure was caused half by slip out of the suture and half by suture rupture. In four cases, the tendon slipped out of the clamps. Maximal lengthening at the time of failure (Table 1) was similar for modified Kessler, Tsuge, Marburg 1 and Marburg 2 techniques. However, for Bunnell repair lengthening was significantly increased compared to the four other techniques (Dunn’s Multiple Comparisons Test).
Results
Tensile loading at 1 mm gap width (Tables 3, 4)
Native tendons
For all suture techniques tensile load at 1 mm gap width (Table 3) varied considerably. The Marburg 1 technique showed the highest tensile load (median 31.8 N, range 15.4–41.8) which differed significantly from all other techniques except the modified Kessler repair (Dunn’s Multiple Comparisons Test). On the other hand, tensile load at 1 mm gap width after Tsuge repair (median 1.3 N, range 0.4–3.6) was significantly lower than after all other techniques (Dunn’s Multiple Comparisons Test).
All native porcine tendons resisted a traction force up to 200 N without sign of tear. Over 200 N the tendons tended to slip out of the clamps. For these tendons with a diameter of 5 mm, the mean area of the cross-section was 20 mm2. Thus, the tensile strength of the porcine tendons was found to be at least 10 N/mm2 which is equal to or even higher than those of human flexor tendons [8].
Table 1 Pull to failure of different suture techniques (ten tendons per group) Suture technique
Ultimate tensile strength (N) median (range)
Maximal lengthening (mm) median (range)
Kessler
115.2 (40.3–148.0)
11.7 (5.1–18.8)
Mode of failurea 5 Suture rupture 5 Pull out
Bunnell
47.4 (33.8–60.2)
17.9 (13.9–22.9)
8 Suture rupture 2 Slip out of clamps
Tsuge
34.6 (30.7–39.8)
10.5 (9.6–13.1)
Marburg 1
57.1 (39.5–74.2)
10.8 (8.9–12.3)
10 Suture rupture 8 Suture rupture 2 Slip out of clamps
Marburg 2
53.7 (43.2–61.0)
11.5 (9.4–15.4)
8 Suture rupture 2 Pull out
Median (range) for ultimate tensile strength and maximal lengthening, mode of failure a
Data is expressed as number of tendons with a given mode of failure
M. Scha¨del-Ho¨pfner et al.
82 Table 2 Statistical analysis (P value) of different 4-0 suture techniques
Kessler Kessler
Bunnell
Tsuge
Marburg 1
Marburg 2
p < 0.05
p < 0.001
ns
ns
ns
ns
ns
p < 0.01
p < 0.05
Bunnell
p < 0.05
Tsuge
ns
p < 0.001
Marburg 1
ns
p < 0.01
ns
Marburg 2
ns
p < 0.05
ns
Ultimate tensile strength ( ns - not significant
above right) and maximal lengthening (
Table 3 Pull to 1 mm gap width of different 4-0 suture techniques (ten tendons per group) Suture technique
Tensile strength (N) median (range)
Kessler
19.9 (3.8–31.8)
Bunnell
3.4 (2.4–7.2)
Tsuge
1.3 (0.4–3.6)
Marburg 1
31.8 (15.4–41.8)
Marburg 2
11.4 (8.4–19.4)
Median (range) for tensile strength
Table 4 Statistical analysis (P value) of different 4-0 suture techniques
Kessler
Bunnell
Tsuge
Marburg 1
Marburg 2
P \ 0.05
P \ 0.001
n.s.
n.s.
n.s.
P \ 0.001
n.s.
P \ 0.001
P \ 0.01
Bunnell Tsuge Marburg 1
n.s.
Tensile strength at pull to 1 mm gap width n.s. not significant
Discussion For this biomechanical study porcine flexor tendons were chosen because they are easily available and show biomechanical properties comparable to human tendons. Pig flexor tendons are recommended by anatomical studies [9] and commonly used for biomechanical testing of flexor tendon suture techniques [10–13]. Other authors used canine flexor tendons [14–16] or sheep tendons [17] but did not report on the native strength of such tendons. Most authors agree on a breaking strength of human flexor tendons of the order of 9 N/mm2 [8]. In our series, tensile strength of porcine tendons was measured higher than 10 N/mm2. For that reason,
ns ns down left)
the employment of porcine flexor tendons was considered adequate for the applied biomechanical testing model. Although being tested before, the clamping technique used has been found not reliable in 4/50 cases with the tendons slipping out. Another weakness of the study design is that only a single pull to failure was performed and no cyclic testing. Stronger flexor tendon repair techniques have been recently favoured for use within active motion protocols. To increase tensile strength several multistranded and augmented repairs have been developed. On the one hand, the strength of flexor tendon repair is roughly proportional to the number of sutures strands [13, 18, 19]. On the other hand multistranded core sutures are in discussion because of problems with tendon gliding, bulking at the repair site and increased tissue handling which can lead to increased adhesions [20]. Four-strand repairs are considered most advantageous since they provide adequate tensile strength while minimizing interference with tendon gliding [18, 21]. We wished to compare our own four-strand suture techniques with three clinically proven techniques (Kessler, Tsuge, Bunnell) which are all two-strand. This reduced comparability of the results. The Marburg suture techniques meet several of the main demands [19, 22] for strong core sutures: (1) There are no locking loops, which could collapse and lead to gapping. (2) Suture knots are located outside the tendon repair site. (3) Equal tension is easy to apply to all suture strands. The presented data show that the Marburg core suture techniques indeed had a high ultimate tensile strength. This was exceeded only by the modified Kessler repair, but this difference was not significant. On the other hand, tensile loading at a gap width of 1 mm showed better values for the Marburg 1 technique compared to the modified Kessler technique, although this difference did not reach significance. Since gapping at the repair site is considered the weakest part of a sutured tendon [19], the high tensile load
Flexor tendon repair using a new suture technique
required to produce a 1 mm gap is a point in favour of the Marburg techniques. The Marburg 2 technique was developed to protect the vincula by a palmar placement of the suture. Biomechanical testing revealed a slightly lower ultimate tensile strength but a much lower resistance to gap formation compared to the Marburg 1 technique. This supports the results of other biomechanical studies which have found a dorsal suture placement to be more advantageous than a palmar placement [23–25]. After four-strand repair, Angeles et al. [21] found slightly higher values for ultimate tensile strength for the Becker suture (mean, 69 ± 8 N), the locked cruciate suture (mean, 64 ± 16 N) and the modified double Tsuge suture (mean, 60 ± 15 N). Barrie et al. [18] recorded in an in situ testing model even higher values for ultimate tensile strength after four-strand repairs with the Kessler suture (mean, 66 N), the cruciate (mean, 70 N) and the locked cruciate suture (mean, 79 N). These higher values may be also the result of additional circumferential epitendinous sutures which are said to increase tensile strength between 10 and 50 percent [19, 26, 27]. In our study, we have omitted additional epitendinous repair because this would have worked as bias by introducing other variables such as the epitendinous suture technique and suture material. For several common two-strand repairs (Bunnell, Kessler, Strickland, Tsuge), other authors [13, 15, 28–33] have found a mean ultimate tensile strength below 35 N, even with epitendinous repair. With an ultimate tensile strength of more than 50 N both Marburg core suture techniques are able to withstand forces of 35 N which are generated during active unresisted finger motion [19, 34]. This study introduces two new four-strand techniques of flexor tendon repair which have been tested biomechanically. The presented experimental results can not be transferred without reservation into clinical practice. But the data support the clinical application of the Marburg 1 technique which has already shown encouraging results with the use of active motion protocols. Further in vivo testing within different testing models is desirable to compare the Marburg repair technique with other commonly used four-strand repair techniques. Acknowledgments The authors would like to thank Professor Madeleine Ennis (Queen’s University of Belfast) for linguistic review and Mr. Axel-Reiner Dupke for the drawings. Conflict of interest statement
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