Biomechanical comparison of Bunnell, modified Kessler, and Tsuge tendon repair techniques using two suture types

Abstract

Objective

The aim of this study was to compare the biomechanical properties of modified Kessler, Bunnell and Tsuge techniques in sheep Achilles tendon tear repaired using polyester and polydioxanone sutures which are also compared.

Methods

Sixty sheep Achilles tendons were cut transversely as a substitute for rupture and repaired using modified Kessler, Bunnell and Tsuge techniques with No. 2 braided polyester and monofilament polydioxanone sutures. Specimens were loaded to failure. Four biomechanical parameters – ultimate strength (US), strength to 2 mm gap (S2G), strength to 5 mm gap (S5G) and Young’s modulus (YM) – were recorded for statistical analysis.

Results

The Tsuge-Polyester group demonstrated the highest results regarding S2G (21.24±4.75 N) (p=.002) and S5G (38.91±7.45 N) (p=.002). According to YM, the Bunnell-Polyester group was the most superior (1929.9±512.28 kilopascal) (p=.009). In the repairs with the polydioxanone suture, Bunnell technique achieved the best purchase with regard to S2G (18.14±6.86 N) (p=.006) and S5G (35.69±13.49 N) (p=.015). The difference between the three repair techniques with the polydioxanone suture was statistically insignificant regarding US (p=.252) and YM (p=.338). Concerning the repairs with the polyester suture, the repair techniques demonstrated no statistically significant difference in terms of US (p=.195), S2G (p=.667), S5G (p=.689) and YM (p=.195). Regarding the mean S2G and S5G values, the polyester suture was significantly superior to the polydioxanone suture in modified Kessler repairs (S2G: p<.001, S5G: p=.001) and Tsuge repairs (S2G: p<.001, S5G: p=.009). The polyester suture was also significantly superior to the polydioxanone suture in the modified Kessler repairs with respect to YM (p=.003).

Conclusion

This study supports the opinion that Tsuge technique is a promising procedure in Achilles tendon repair (ATR). For Tsuge and modified Kessler repairs, braided polyester suture use appears more advantageous compared to monofilament polydioxanone suture use in biomechanical terms.

The Achilles tendon is the thickest and strongest tendon in the human body, and one of the most commonly ruptured (1, 2). Acute rupture of the Achilles tendon can be managed with conservative or surgical methods, but the optimal treatment approach remains controversial (3–8). Bunnell and modified Kessler techniques are among the preferred procedures for open and percutaneous Achilles tendon repairs (ATRs), and the efficacy of both techniques has been evaluated in numerous biomechanical and clinical studies (3, 5–15). Recently, the Tsuge technique – a flexor tendon repair procedure conventionally used in hand surgery – has gained ground as a favorable option for ATR (16–18). It is also suitable for minimally invasive ATR, which provides accelerated healing and allows early weight bearing (17).

The properties of suture materials are as significant as the repair techniques themselves in achieving favorable clinical outcomes in tendon repairs. Depending on the repair technique, suture of a caliber within the No. 2/0 to No. 5 range is recommended for ATR (19), with braided non-absorbable polyester (PE) and monofilament absorbable polydioxanone (PDS) being two of the most commonly used materials in ATR procedures.

The purpose of this study was to investigate and compare the efficacy of single two-strand Bunnell, modified Kessler, and Tsuge techniques in terms of their biomechanical properties using two different suture materials: No. 2 PE and No. 2 PDS. The comparisons were made using sheep Achilles tendon repair models.

Materials and Methods

Sixty Achilles tendons were harvested from male sheep, butchered by the local slaughterhouse for commercial purposes. The sheep were aged between eight and twelve months and weighed between 40 and 50 kg at time of slaughter. Each specimen contained a muscle-tendon junction proximally, and part of the calcaneus distally; they were freshly frozen to −20°C after harvesting. The specimens were randomly divided into three equal groups for Bunnell, modified Kessler, and Tsuge repairs, respectively. Each group was further divided randomly into two equal subgroups for repair with either USP No. 2 braided PE (Ethibond®, Ethicon, Somerville, NJ) or USP No. 2 PDS (PDS II®, Ethicon, Somerville, NJ) sutures. Hence, a total of six subgroups were formed, with ten specimens per subgroup.

Following cold chain transport of the specimens to the biomechanical laboratory, each was thawed at room temperature prior to repair. The narrowest regions of the Achilles tendons were measured with a digital caliper and marked as the tenotomy site with a marker pen; the lengths were measured using a fine ruler, and all measured dimensions were recorded. The suture needle entry and exit points, based on the design of repair to which the sample was allocated, were also located and marked with a marker pen (Figure 1). Each tendon was divided sharply in the transverse plane at the narrowest region using a No. 22 scalpel blade to replicate rupture. Thereafter, repairs were performed using a No. 2 PDS or a PE suture with Bunnell, modified Kessler, or Tsuge techniques, taking entry and exit points of suture needles into consideration (Figure 2). Tension was applied on the sutures until the gaps between the tendon ends were closed. PE and PDS sutures were tied in the same manner with five and six throws, respectively (Figure 3). Epitendinous suture augmentation was not performed in any specimen in order to evaluate the biomechanical features of two-strand core suture techniques. All markings, measurements, and repairs were performed by the same researcher (ND).

Figure 1.

A sample specimen, including the muscle-tendon junction proximally and part of the calcaneus distally (indicated with a solid red arrow), to be repaired with the Bunnell technique using a No. 2 polyester suture. The tenotomy site (indicated with a solid yellow arrow) and the relevant entry and exit points for the suture needle were determined and marked on the specimen

Figure 2.

The repair techniques. Modified Kessler technique: Distances of 1.5 cm and 2 cm from the tenotomy site were chosen as the entry and exit points for the suture needle on both stumps in each specimen. After tension was applied to close the gaps, the knots were tied within the tenotomy site. Bunnell technique: Distances of 1.5 cm and 3 cm from the tenotomy site on the proximal stump and a distance of 2 cm from the tenotomy site on the distal stump were chosen as the entry and exit points for the suture needle in each specimen. After tension was applied to close the gaps, the knots were tied on the distal stump. Tsuge technique: In each specimen, a distance of 2.5 cm from the tenotomy site on the proximal stump was chosen as the first entry and exit points of the needle. The needle was passed under the loop of suture, then inserted into the proximal stump for the second time in the proximal-to-distal direction at a distance of 1.5 cm from the tenotomy site. The needle was removed at a distance of 1.5 cm from the tenotomy site on the distal stump. One strand of the suture was passed from a distance of 1 cm distal to the site, where the needle was removed from the distal stump. After tension was applied to close the gaps, the knots were tied on the distal stump

Figure 3.

Appearance of the specimen repaired with the Bunnell technique using a No. 2 polyester suture

Biomechanical testing was performed using a universal testing device (Z100, Zwick/Roell GmbH; Ulm, Germany) equipped with test Xpert II version 3.2 software. Specimens were mounted on the testing device with two custom-made clamps (Figure 4), preloaded with a force of 2 newtons before the test, and then loaded to failure with a displacement rate of 20 mm per minute (Figure 5). Stress-strain curves indicating the values of ultimate strength (US), strength to 2 mm gap (S2G) and strength to 5 mm gap (S5G) were obtained. Young’s modulus (YM) values were calculated by the testing device software. After completion of the biomechanical tests, location and mode of failure in each specimen were identified macroscopically and recorded.

Figure 4.

Placement of the specimen on the testing device, secured with two clamps, indicated with solid red arrows. The upper clamp grasps the tendinous proximal stump of the specimens, while the lower clamp, which permits 2.5 mm Kirschner wire fixation of the calcanei in the specimens, grasps the bony distal stumps to prevent slippage. Extensometers in the testing device, used to measure displacement in the specimens during loading, are indicated with solid yellow arrows

Figure 5.

Appearance of the specimen after loading. Please note that the gap between the ends of the stumps is excessive for appropriate tendon healing

Ultimate strength (US) refers to the largest load applied before a steep fall due to failure during biomechanical testing (10). The magnitude of displacement was disregarded in this measurement. S2G is the magnitude of load needed to produce a gap size of 2 mm at the repair site. This is considered an essential parameter for achieving tendon recovery close to the original length (20). S5G is the magnitude of load needed to produce a gap size of 5 mm, taken as the upper limit for acceptable tendon elongation in the present study. YM, defined by the slope of the stress-strain curve, is the measure of elastic deformation of the materials under load (21).

Statistical analysis to investigate differences between the groups was performed using IBM SPSS version 21.0 software. The Shapiro-Wilk test showed the data to have a normal distribution; homogeneity was confirmed by analysis with the Levene test. One-way analysis of variance (ANOVA), Tukey’s test, and t test were used for multiple group comparisons, pairwise comparisons, and independent group comparisons, respectively. A p value below 0.05 was considered statistically significant.

Results

The six groups were compared in terms of mean specimen dimensions (length, width, thickness) and biomechanical parameters (ultimate strength, strength to 2 mm gap, strength to 5 mm gap, Young’s modulus) (Table 1). The distribution of the failure modes in the study groups, and the comparisons of the three repair techniques and two suture materials are presented in Table 2, Table 3, and Table 4, respectively.

Table 1.

Mean values and standard deviations of study group specimen dimensions and biomechanical parameters

		Length Mean±SD (mm)	Width Mean±SD (mm)	Thickness Mean±SD (mm)	US Mean±SD (N)	S2G Mean±SD (N)	S5G Mean±SD (N)	YM Mean±SD (Kpascal)
Modified Kessler Technique Group (n=20)	Modified Kessler-PE Group (n=10)	145.4±20.11	9.12±0.58	8.37±0.5	104.13±8.44	20.2±5.48b	36.68±9.23b	1911.8±488.24b
	Modified Kessler-PDS Group (n=10)	158.6±10.93	9.37±0.53	8.57±0.43	106.36±17.79	11.3±2.09a,e	22.06±6.03a,c,d,e	1192.13±433.1a,c
Bunnell Technique Group (n=20)	Bunnell-PE Group (n=10)	152.0±7.26	9.22±0.49	8.83±0.7	127.2±44.27	18.37±10.04	35.29±11.13b	1929.9±512.28b
	Bunnell-PDS Group (n=10)	148.0±13.02	9.46±0.44	8.98±0.4e,f	130.86±45.07	18.14±6.86	35.69±13.49b	1473.3±545.75
Tsuge Technique Group (n=20)	Tsuge-PE Group (n=10)	149.7±9.74	9.04±0.66	8.19±0.59d	120.91±20.55	21.24±4.75b,f	38.91±7.45b	1594.6±336.89
	Tsuge-PDS Group (n=10)	142.0±12.11	9.23±0.5	8.27±0.4d	110.27±35.04	13.11±3.12e	28.8±8.03	1503.5±545.28
	p	0.094	.527	.005*	.293	.002*	.002*	.009*

^*Statistically significant difference between groups. Anova; a:,05

^aStatistically significant difference with modified Kessler-PE group;

^bStatistically significant difference with modified Kessler-PDS group;

^cStatistically significant difference with Bunnell-PE group;

^dStatistically significant difference with Bunnell-PDS group;

^eStatistically significant difference with Tsuge-PE group;

^fStatistically significant difference with Tsuge-PDS group

SD: standard deviation; PE: polyester; PDS: polydioxanone; US: ultimate strength; S2G: strength to 2 mm gap formation; S5G: strength to 5 mm gap formation; YM: Young’s modulus

Table 2.

The distribution of failure modes in the study groups

	Suture pullout from distal stump	Suture pullout from proximal stump	Suture rupture at the knot	Knot loosening
Modified Kessler-PE group (n=10)	3	1	6	0
Modified Kessler-PDS group (n=10)	3	7	0	0
Bunnell-PE group (n=10)	4	1	4	1
Bunnell-PDS group (n=10)	4	0	4	2
Tsuge-PE group (n=10)	6	1	3	0
Tsuge-PDS group (n=10)	4	2	3	1
PE group (n=30)	13	3	13	1
PDS group (n=30)	11	9	7	3

PE: polyester; PDS: polydioxanone

Table 3.

Comparison of repair techniques in relation to biomechanical parameters

	US Mean±SD (N)	S2G Mean±SD (N)	S5G Mean±SD (N)	YM Mean±SD (Kpascal)
Modified Kessler-PE Group (n=10)	104.13±8.44	20.2±5.48	36.68±9.23	1911.8±488.24
Bunnel-PE Group (n=10)	127.2±44.27	18.37±10.04	35.29±11.13	1929.9±512.28
Tsuge-PE Group (n=10)	120.91±20.55	21.24±4.75	38.91±7.45	1594.6±336.89
p	.195	.667	.689	.195
Modified Kessler-PDS Group (n=10)	106.36±17.79	11.3±2.09b	22.06±6.03b	1192.13±433.1
Bunnel-PDS Group (n=10)	130.86±45.07	18.14±6.86a,c	35.69±13.49a	1473.73±545.75
Tsuge-PDS Group (n=10)	110.27±35.04	13.11±3.12b	28.8±8.03	1503.5±545.28
p	.252	.006*	.015*	.338

^*Statistically significant difference between groups. Anova; a:,05

^aStatistically significant difference with modified Kessler-PDS group;

^bStatistically significant difference with Bunnell-PDS group;

^cStatistically significant difference with Tsuge-PDS group

SD: standard deviation; PE: polyester, PDS: polydioxanone; US: ultimate strength; S2G: strength to 2 mm gap formation; S5G: strength to 5 mm gap formation; YM: Young’s modulus

Table 4.

Comparison of suture materials in relation to biomechanical parameters

	US Mean±SD (N)	S2G Mean±SD (N)	S5G Mean±SD (N)	YM Mean±SD (Kpascal)
Modified Kessler-PE Group (n: 10)	104.13±8.44	20.2±5.48	36.68±9.23	1911.8±488.24
Modified Kessler-PDS Group (n: 10)	106.36±17.79	11.3±2.09	22.06±6.03	1192.13±433.1
p	.724	<.001*	.001*	.003*
Bunnell-PE Group (n: 10)	127.2±44.27	18.37±10.04	35.29±11.13	1929.9±512.28
Bunnell-PDS Group (n: 10)	130.86±45.07	18.14±6.86	35.69±13.49	1473.73±545.75
p	.857	.953	.944	.07
Tsuge-PE Group (n:10)	120.91±20.55	21.24±4.75	38.91±7.45	1594.6±336.89
Tsuge-PDS Group (n: 10)	110.27±35.04	13.11±3.12	28.8±8.03	1503.5±545.28
p	.419	<.001*	.009*	.658

^*Statistically significant difference between groups. Independent samples t test; a:,05

SD: standard deviation; PE: polyester; PDS: polydioxanone; US: ultimate strength; S2G: strength to 2 mm gap formation; S5G: strength to 5 mm gap formation; YM: Young’s modulus

Ultimate strength

In terms of US, the Bunnell-PDS group had the highest mean value, without statistical significance (p=.293) (Figure 6a). The repair groups were arranged as Bunnell, Tsuge, and modified Kessler in descending order of US mean values. The differences between the repair groups were insignificant for both the PDS suture (p=.252) and the PE suture (p=.195) (Figure 6b). The PDS suture was insignificantly superior to the PE suture in modified Kessler repairs (p=.724) and Bunnell repairs (p=.857), while the PE suture was superior to the PDS suture without statistical significance in Tsuge repairs (p=.419) (Figure 6c).

Figure 6. a–c.

Comparison of study groups in terms of ultimate strength (US). Comparison of all six groups, representing all combinations of suture technique and suture material (a). Comparison of suture techniques (b). Comparison of suture materials (c)

PE: polyester suture, PDS: polydioxanone suture

Strength to 2 mm gap

The highest mean S2G value was observed in the Tsuge-PE group (p=.002) (Figure 7a). In PDS suture repairs, the repair groups were arranged as Bunnell, Tsuge, and modified Kessler in descending order of mean S2G values, and the difference between the repair groups was statistically significant (p=.006). In PE repairs, the difference between groups was statistically insignificant (p=.667) and the ranking of groups based on descending mean values (Tsuge, modified Kessler, and Bunnell) was different to that obtained with PDS suture (Figure 7b). Regarding mean S2G values, the PE suture was significantly superior to the PDS suture in modified Kessler repairs (p<.001) and Tsuge repairs (p<.001). The PE suture was also superior to the PDS suture in Bunnell repairs, but the difference was statistically insignificant (p=.953) (Figure 7c).

Figure 7. a–c.

Comparison of study groups in terms of strength to 2 mm gap (S2G). Comparison of all six groups, representing all combinations of suture technique and suture material (a). Comparison of suture techniques (b). Comparison of suture materials (c)

^aStatistically significant difference with the modified Kessler-PE group; ^bStatistically significant difference with the modified Kessler-PDS group; ^cStatistically significant difference with the Bunnell-PE group; ^dStatistically significant difference with the Bunnell-PDS group; ^eStatistically significant difference with the Tsuge-PE group; ^fStatistically significant difference with the Tsuge-PDS group

PE: polyester suture, PDS: polydioxanone suture

Strength to 5 mm gap

The Tsuge-PE group had the greatest mean S5G value (p=.002) (Figure 8a). In PDS repairs, the groups displayed a statistically significant difference (p=.015) and were sorted in descending order of mean S5G values as Bunnell, Tsuge, and modified Kessler. In PE repairs, the difference between groups was statistically insignificant (p=.689), and the groups were ordered in descending order of mean S5G value as Tsuge, modified Kessler, and Bunnell (Figure 8b). The PE suture was significantly superior to the PDS suture in modified Kessler repairs (p=.001) and Tsuge repairs (p=.009), while the PDS suture had better results without a statistically significant difference in Bunnell repairs (p=.944) (Figure 8c).

Figure 8. a–c.

Comparison of study groups in terms of strength to 5 mm gap (S5G). Comparison of all six groups, representing all combinations of suture technique and suture material (a). Comparison of suture techniques (b). Comparison of suture materials (c)

^aStatistically significant difference with the modified Kessler-PE group; ^bStatistically significant difference with the modified Kessler-PDS group; ^cStatistically significant difference with the Bunnell-PE group; ^dStatistically significant difference with the Bunnell-PDS group; ^eStatistically significant difference with the Tsuge-PE group; ^fStatistically significant difference with the Tsuge-PDS group

PE: polyester suture, PDS: polydioxanone suture

Young’s Modulus

The Bunnell-PE group had the highest mean YM value (p=.009) (Figure 9a). In PDS repairs, the groups were arranged in descending order of YM mean value as Tsuge, Bunnell, and modified Kessler, and a statistically insignificant difference (p=.338) was observed. In PE repairs, the difference between groups was also statistically insignificant (p=.195), with groups ordered in descending order of mean YM value as Bunnell, modified Kessler, and Tsuge (Figure 9b). The PE suture showed statistically significant superiority to the PDS suture in modified Kessler repairs (p=.003). Although statistically insignificant, the PE suture was superior to the PDS suture in Bunnell repairs (p=.07) and Tsuge repairs (p=.658) (Figure 9c).

Figure 9. a–c.

Comparison of study groups in terms of Young’s Modulus (YM). Comparison of all six groups, representing all combinations of suture technique and suture material (a). Comparison of suture techniques (b). Comparison of suture materials (c)

^aStatistically significant difference with the modified Kessler-PE group; ^bStatistically significant difference with the modified Kessler-PDS group; ^cStatistically significant difference with the Bunnell-PE group; ^dStatistically significant difference with the Bunnell-PDS group; ^eStatistically significant difference with the Tsuge-PE group; ^fStatistically significant difference with the Tsuge-PDS group

PE: polyester suture, PDS: polydioxanone suture

Discussion

The Achilles tendon is the conjoint tendon of the gastrocnemius and soleus muscles, and one of the most frequently ruptured tendons in the human body, with incidence of rupture on the increase, particularly in middle aged and elderly populations (1, 2, 22). Despite ongoing controversy regarding the optimal treatment method (operative vs. conservative), surgical treatment is usually chosen for young, physically active patients (3, 5–8).

While the literature contains numerous reports on commonly used open and/or percutaneous ATR techniques (3, 5–8, 15), very few clinical studies have investigated the efficacy of the Tsuge technique in ATR. Fu et al. reported a series including 36 Achilles tendon injuries, which were treated using the double Tsuge suture technique (18). The authors described the technique, which achieved 97.2% good or excellent outcomes in the series, as being practical and offering minimal interference with tendon blood circulation (18). Fu and Qu compared the double-Tsuge loop repair with the mini-incision approach to the open modified Kessler repair in a study of 60 patients, operated on due to acute closed Achilles tendon rupture (17). The authors recommended the miniopen Tsuge repair technique, based on their findings of shorter operating times and rehabilitation periods, smaller skin incisions, and fewer complications (17). Despite reports of favorable clinical outcomes, no biomechanical study of the Tsuge repair technique could be found in the current literature.

Some notable biomechanical studies of common ATR procedures, performed on animal or human cadaver Achilles tendons, are available in the literature: Watson et al. studied the biomechanical features of the Kessler, Bunnell, and locking loop techniques on 18 Achilles tendons in human cadavers (10). The authors reported the locking loop technique to provide superior results to the Bunnell and Kessler techniques, both of which demonstrated equivalent results in terms of US (10). Yildirim and Esemenli investigated initial tendon pull-out strength on 48 sheep Achilles tendons for the Kessler, Bunnell, and Krackow repair techniques using No. 5 polyester suture (12). While the authors did not mention any statistically significant difference between the Krackow and Bunnell techniques, they did report the Kessler technique to have inferior strength in terms of US (12). Herbort et al. worked on 24 Achilles tendons from human cadavers in their study comparing Kessler and Bunnell repairs biomechanically under cyclic loads (9). No statistically significant difference was mentioned in terms of biomechanical parameters (stiffness, yield load) except for maximum load, in which regard the Bunnell repair was found to be superior to the Kessler repair (9).

Consistent with the study by Watson et al., in which No. 1 Ethibond non-absorbable suture material was used for repairs, the present study revealed no statistically significant difference in mean US values between the modified Kessler, Bunnell, and Tsuge techniques in PE repairs (10). However, this finding differs from results reported by Yildirim and Esemenli (12). The present study has also demonstrated no statistically significant difference in mean US values between the three suture techniques in PDS repairs. This differs from the findings of Herbort et al. regarding repairs with PDS suture (9). These differences can be attributed to dissimilarities in the study designs (i.e. cyclic loading of human cadaver tendons, and investigation of initial tendon pull-out strength without using tenotomy in the studies of Herbort et al. and Yildirim and Esemenli, respectively (9, 12).

Many biomechanical studies have evaluated ATR techniques in terms of US, which indicates the maximum load applied in the stress-strain curve (9, 10, 12–14). The fine measurements made in the present study demonstrated that gap formation greatly exceeding 5 mm, associated with unfavorable outcomes such as tendon elongation and impaired healing, occurred as US levels were reached during loading. Therefore, we suggest use of S2G and/or S5G rather than US for biomechanical evaluation of repair technique strength.

When the six groups were compared, the Bunnell-PDS group demonstrated the best US result without a statistically significant difference in mean US values. The Bunnell-PE group had the highest mean YM value, with statistical significance. The Tsuge-PE group achieved the best purchase with a statistically significant difference in mean S2G and S5G values, respectively. Based on these findings, the combination of PE suture with the Tsuge repair technique seems favorable for ATR.

Properties of the suture materials used for ATR influence the outcome. Yildirim et al. evaluated the suture purchase of No. 2 PDS, No. 1 PDS, No. 2 Vicryl, No. 1 Vicryl, No. 2 PE, and No. 1 Prolene on 60 sheep Achilles tendons using the Kessler technique without tenotomy (13). The authors reported failure for all specimens due to suture pullout, with No. 2 PDS and No. 2 PE having the best and worst suture purchase, respectively, showing a significant difference in US (13). This differs from the present study in which the modified Kessler-PDS group was insignificantly superior to the modified Kessler-PE group based on mean US values. The inconsistency between the results of these two studies can be explained by the different study designs (i.e. the specimens were tested without performing tendon repair in the study of Yildirim et al.) (13).

In the present study, the PE suture was significantly superior to the PDS in the modified Kessler repairs (in relation to S2G, S5G, and YM) and Tsuge repairs (in relation to S2G and S5G). The PE suture also achieved greater mean US and YM values than the PDS. However, the difference was statistically insignificant. Biomechanical test results for the two suture materials in the Bunnell repairs were equivocal, with both sutures (the PE suture in relation to S2G and YM, and the PDS suture in relation to US and S5G) demonstrating superior mean values without statistical significance.

In terms of knot consistency, the braided PE suture (one knot loosening in 30 specimens) was superior to the PDS suture (three knots loosening in 30 specimens), despite the fact that one more throw was applied to the repairs performed with monofilament PDS suture, which is associated with poor knot consistency (23). Conversely, seven suture ruptures occurred in PDS repairs, versus 13 suture ruptures in repairs using PE suture. The latter finding can be explained by the higher elasticity of the PDS suture, as indicated by the lower mean YM values in specimens repaired with PDS.

The strengths of the present study are homogeneity of study groups, the inclusion of two distinct suture materials (absorbable monofilament PDS and non-absorbable braided PE), and the use of fine parameters (S2G, S5G) to evaluate repair strengths.

The present study also has some limitations: Biomechanical testing was performed in an ex vivo animal model, so the influence of repair technique and suture material on tendon biology could not be analyzed. Additionally, clear cut tenotomy does not represent acute Achilles tendon rupture, which includes fringing of the tendon stumps, and linear loading is less representative of loads on human Achilles tendons than cyclic loading.

In conclusion, this study, which was designed to analyze and compare the biomechanical features of single two-strand core suture techniques, demonstrates the Tsuge suture technique to be as effective as the modified Kessler and Bunnell suture techniques in biomechanical terms. However, based on the low mean values for the biomechanical parameters we measured, these two-strand suture techniques appear to lack sufficient strength to allow early rehabilitation and weight bearing. Therefore, the authors suggest double (four-strand), triple (six-strand) or more repairs using Tsuge technique, particularly with a minimally invasive approach, to be a promising procedure for ATR.

For Tsuge and modified Kessler repairs, use of braided polyester suture appears more advantageous in terms of biomechanical parameters compared to monofilament polydioxanone suture.

MAIN POINTS.

• Single two-strand Tsuge suture technique is found to be as effective as single two-strand modified Kessler and Bunnell suture techniques in biomechanical terms.

• The low mean values of biomechanical parameters measured in this study suggest that these two strand core suture techniques lack sufficient strength to allow early rehabilitation and weight bearing in clinical settings.

• Braided polyester suture use appears more advantageous compared to monofilament polydioxanone suture use with regard to biomechanical parameters in Tsuge and modified Kessler repairs.