Improving Strength and Quality of Epitendinous Repairs

Abstract

Background: Epitendinous sutures not only join the 2 severed tendon edges but also supply strength and support to the repair. Multiple techniques have been described, but none of them include another thread of suture. This could potentially increase the strength of the repair without affecting gliding. Methods: Caprine tendons were harvested, transected, and sutured with 6-0 Prolene. Four groups were created: single thread running (SR), single thread locking (SL), double thread running (DR), and double thread locking (DL). An Instron 5542 was used to pull the repaired tendons apart, and the energy at the break was calculated (gf/mm). For gliding resistance, we harvested a human A2 pulley. A pre- and postrepair value was obtained, and a ratio was elaborated. A single-factor analysis of variance and independent sample t tests were performed. Results: The SR group had a mean energy at break of 9339.71 ± 1630.212 gf/mm; the SL group, 9629.96 ± 1476.45 gf/mm; and the DR group, 9600.221 ± 976.087 gf/mm, with no statistical significance. The DL group was significantly higher at 14 740.664 ± 2596.586 gf/mm (P < .05). When comparing SR with DL for gliding, SR had less than half of the resistance than DL (0.018 ± 0.004 and 0.049 ± 0.015 N/mm, respectively), with statistical significance (P < .05). Conclusion: Using a single suture thread for running epitendinous repair is no different than locking with a single thread or using an extra thread in a running fashion. Performing a double suture thread with a locking technique is significantly stronger than the previously mentioned repairs, with the disadvantage of more resistance at the pulley.

Introduction

Flexor tendon injuries represent 1% of all hand and wrist injuries.¹ Multiple evidence-based practice articles have been published recommending current treatment for this pathology.^1,2 In 1948, Sterling Bunnell defined zone II of the hand as “No man’s land.”^3,4 This zone is located between the insertion of flexor digitorum superficialis and distal palmar crease. The popularity of this region has been attributed to a strong correlation with poor outcomes, reported as high as 20%.⁵ Major advances in the treatment of this infamous zone have been developed. Currently, the common practice is to repair flexor tendon lacerations with core sutures in combination with epitendinous or peripheral sutures.^3,6 There is some controversy regarding who first described the epitendinous suturing. Some authors claim that Verdan was the first to describe in 1960, whereas others claim that Kleinert in 1973 originally reported the technique.^7-9 The original Kleinert technique was described as suturing the epitenon layer in a running fashion, 2 mm from the transected edge.^8,9 Historically, the circumferential epitendinous sutures were thought to only approximate the tendon edges, but this technique has been shown to significantly increase the tensile strength to the overall repair and decrease the need for reoperation.^4,10-13 Unfortunately, strength is not the only feature to achieve in tenorrhaphy at this level, as any intervention to the tendon also needs to maintain a harmonious milieu with their corresponding pulley to avoid adhesions and triggering.⁴ Despite a current trend of only placing M-Tang core suture without peripheral sutures, most of the current literature suggest the use of multiple strand core suture placement with a concomitant epitendinous layer closure to prevent complications.^1,2,14 The most common complications after flexor tendon repair are adhesions (10%) and rupture (4%).¹ Adhesions might be caused by poor tissue handling and rupture due to poor technique, but interestingly enough, epitendinous suture layer has not been proven to be predictive of adhesion formation.¹⁵ Reoperating rates around 6% have been described.¹⁶ The current literature has documented that epitenon suturing can increase the strength of the repair from 10% to 50%.^7,15 Performing epitendinous suture has been described as making the repair 84% less likely to require reoperation.^1,7,15,16 Some authors have recommended even placing this suture before the core stitch. The advantages of this premature maneuver are to decrease bunching of the repair, minimize handling, provide better alignment of the tendons to improve intrinsic healing, and increase strength up to 22%.^17,18 Achieving a correct alignment of both severed epitenon allows them to supply the correct amount of fibroblast to migrate to the center of the tendon and take part in intrinsic healing. Similarly, the tendon heals in 3 phases. The first, also known as “inflammatory,” initiates immediately after repair. It involves red blood cells, white blood cells, platelets, growth factors, and chemo/cytokines.¹⁵ The second, the “proliferative phase,” commences a few days after the first phase, but lasts for approximately 3 weeks. The cellular lineages, mostly involved in this period, are macrophages and tenocytes. At this phase, the repair is the weakest and relies on the suture strength and the knots.¹⁵ After the fourth week, the “remodeling” phase begins and consists mainly of the production of collagen type I and exchange of collagen type III.¹⁵ Performing a durable epitendinous repair can facilitate an extracellular matrix alignment to achieve adequate healing.

Multiple epitendinous or peripheral suture techniques have been described to date.^8,19 Despite some studies demonstrating how peripheral sutures can decrease gliding coefficient of the repair or decrease strength when used in conjunction with barbed core sutures, this modality is used frequently across the United States.^3,5,20 Gibson et al demonstrated with a cross-country survey, in which they obtained a total of 410 replies from hand surgeons of different background (Plastic, Orthopedics, and General), that 96.7 % of them affirmed that they routinely performed epitendinous suturing when repairing zone II flexor tendons.³ Some authors also use the term “finishing suture” to refer to epitendinous suture. This might sound like an accessory step, but this portion takes at least 64% to 77% of the load of the repair, being more vulnerable to rupture before the core sutures.^10,21,22 Improving “load sharing” will improve the quality of the repair and avoid gap formation between the 2 severed ends, which could jeopardize tendon healing.²³

There have been important findings in how to improve this portion of the repair, such as the purchase distance from the edge of tendon laceration and depth of suture placement.^{4,10,13,23-25} Deeper purchase in the epitendinous repair can improve stiffness to 91% and have 80% higher failure loads compared with superficial placed sutures.⁴ Many studies have been performed to assess the biomechanical properties of various types of epitendinous repair techniques, in which all have employed the use of a single circumferential suture thread.^8,10,26 To this date, no studies have been performed with the addition of a second suture thread. We use the term “thread,” not to be confused with strand, as that has been overused in the literature to refer to the amount of times the suture crosses the repair.^3,5,27 The aim of this study was to compare the maximal tensile strength and gliding resistance of 2 types of suture repair: running and locking. This will be achieved using a single suture thread to complete the full repair and a double suture thread technique when each separate suture thread will be used to fix 180° of the circumference of the tendon.

Methods

Samples

All institutional and national guidelines for the care and use of laboratory animals were followed. Caprine extensor carpi ulnaris tendons from goats, which were used for other studies, were harvested and trimmed to segments of 4 cm each. These were transected into half and classified into groups depending on the configuration of the repair and the amount of suture thread used. Prolene suture 6-0 (Ethicon, Somerville, New Jersey) was used to repair all the tendons. Repairs were performed by the same surgeon (A.F.). The samples were divided into 4 groups: single thread running (SR), single thread locking (SL), double thread running (DR), and double thread locking (DL). Figure 1 is a graphical illustration of the placement of the suture on the severed ends of the tendons in each of the groups. The SR group consisted in using a single suture and performing a simple running suture 2 mm from the edge and with 0.5 mm distance between each throw, resulting in approximately 3 to 5 throws from each side (dorsal and ventral) (Figure 2). The SL group consisted in using a single suture similar to the SR group, but locking each throw.²⁰ The DR and the DL were exactly as their previous counterparts described, but instead we used 2 separated suture threads that were tied to each other, with the knots situated in opposite directions. All the knots were located on the outer and lateral surface of the tendons, with 1 for SR and SL and 2 at each side for DS and DL. As elasticity properties of tendons are affected by formalin, these tendons were tested freshly after harvesting (approximately 20 hours).²⁸ The proximal and distal ends of the tendons were placed into the loading cell of an Instron 5542 machine (Norwood, Massachusetts) (Figure 3). Energy at the break (gf/mm) was calculated, and a mean of each group was considered. Tendons that slipped from the loading cell before breaking were discarded.

Figure 1.

Schematic illustration of different epitendinous groups.

Figure 2.

Photos of different epitendinous groups.

Figure 3.

Tendon repaired on Instron 5542 about to be tested.

To test our repairs for gliding, a human fifth proximal phalanx bone with its correspondent A2 pulley was chosen to be harvested due to its smaller size. This was obtained under the cadaveric anatomical gift program, in compliance with institutional policies and under the supervision of support personnel. Using an electric drill, 2 small holes were placed at each end of the bone, and a wire was threaded and tied to itself to prevent slippage from the machine (Figure 4). This bone/pulley complex was fixed in formalin. The remaining tendons, which were not used in the first phase of the project, were also fixed in formalin and tested for gliding through the pulley. The size of the tendons ranged between 3 and 5 mm wide. One end of the tendon was placed on the superior loading cell, and the bone/pulley mount was held by the inferior loading cell. The specimens were tested before and after the repair to normalize each tendon. A ratio from pre- and postintervention was used to quantify the amount of resistance that was enforced after the repair. These tendons were classified the same way as in the first phase.

Figure 4.

Instron 5542 with fixed metacarpal and corresponding A2 pulley. On the superior loading cell, the repaired tendon was held to test gliding.

Statistics

A single-factor analysis of variance (ANOVA) of all 4 groups was performed, with Bonferroni correction. Independent sample t tests were performed to compare individual groups with each other. Values of P < .05 were considered significant.

Results

We obtained a total of 8 samples (N = 8) for the SR group, 9 (N = 9) for the SL group, 8 (N = 8) for the DR group, and 9 (N = 9) for the DL group. In the first phase of our project, we noticed that the mean energy at the break of the SR group was 9339.71 ± 1630.212 gf/mm. For the SL group, the mean resulted in 9629.96 ± 1476.45 gf/mm and for the DR group, 9600.221 ± 976.087 gf/mm (Figure 5). A statistical difference between groups was determined by single-factor ANOVA (P = .0068) even with a Bonferroni correction (α = 0.0083) applied. The DL group was significantly stronger, resulting in a mean energy at the break of 14 740.664 ± 2596.586 gf/mm with statistical significance when compared with the other 3 groups (P < .05). No other significance was determined between groups. Noticing the preliminary result of the first phase, we decided only to compare SR with DL group for gliding under the pulley. We constructed 16 tendons (N = 16) for the SR group and 17 tendons (N = 17) for the DL group. The SL group had less than half of the resistance than the DL group (0.018 ± 0.004 N/mm and 0.049 ± 0.015 N/mm, respectively) and reached statistical difference (P < .05).

Figure 5.

Energy at the break of different groups. Single running, single locking, and double running showed no statistical significance (P > .05). Double locking was stronger than the rest of the groups with statistical significance (P < .05).

Discussion

Initially, our hypothesis consisted of performing an epitendinous or finishing repair with an extra thread to improve strength and that using a locking configuration will potentiate the resistance to break. Our ex vivo study has shown efficiently how performing different types of epitendinous repair and adding a new thread have the same effect on holding both severed stumps together. Using a locking or running configuration with only one thread, it does not seem to affect the strength of the repair. Also, adding extra suture in a simple running fashion does not affect it either. Transpose this to the clinical setting, we can conclude that regardless of which type or repair you use, it is irrelevant to the maximal strength of the peripheral or epitendinous suture only, when performing a routine tendinoplasty in vivo. Choosing the simplest technique will save operating room time and costs. This can be the future clinical aims of our investigation.

The main exception of our findings was when adding a separate suture thread and placing it in a locking fashion produced a significantly stouter result compared with the other interventions. It has been demonstrated since the Lin et al paramount paper in 1988 that a locking repair was 3.77 and 1.26 times better than running and Lambert sutures, respectively.⁹ Despite that our repair was not performed exactly as their original design, our results correlate with them when using this configuration with 2 threads of suture. We believe that the grasping power that the suture applies when placed in this type of arrangement is the key factor that makes the difference with this technique. The strength of the locking suturing is independent of the suture’s resistance to break—reason why there was no significant difference when we compared the single running group with the double running configuration.

Peripheral sutures tend to fail by pulling through or by breaking.^22,29 In the previous literature, it has been reported that knots added tensile weakness to flexor repairs, but we noted that all of our repairs pulled through the tissues instead of suture breaking or unraveling at the knot.³⁰ We hypothesize that adding a new thread of suture could share the load circumferentially equally and increase the strength of the repair. Silfverskiöld and Andersson by placing a palmar-only epitendinous suture increased the strength of a repair to 41%. By placing 2 independent sutures (one dorsal and one ventral), they can act independently increasing the failure load of the repair, and not relying mainly on the resistance to break of a single suture material.²⁹ Applying this to the clinical arena, we believe that this repair can be used on failed repairs or patients with high risks of rupture. This would allow them to start early active or passive range of motion and avoid contractures and fibrosis.³

Previously, it has been demonstrated how epitendinous suture has improved gliding.¹³ To assess whether our repairs affected performance under the pulley, we decided to carry out a second phase in our study. When testing for gliding resistance, we adjusted the second phase of the study to compare 2 groups only: SR due to the similarities with other groups and DL. Having twice as high the resistance for DL can be explained by the increment in the bulk of the repair, mainly due to its external component. The presence of the 2 knots at each side increased the surface area in contact with the pulley. Previous studies showed how certain types of repairs (eg, Becker’s) produced higher friction and more adhesions, due to the amount of suture exposed to the pulley. This is especially true when these types of repairs were compared with a modified Kessler type, which has minimal amount of suture exposure and hence better gliding.³¹ Wu and Tang also corroborate in their work how suture exposure can affect gliding.¹³ We also believe that in the DL group, the location of the knots might have influenced resistance to gliding.³² Perhaps increasing the amount of knots can also negatively influence the excursion of the tendon by displacing the contralateral knot to more unfavorable position. If this repair could ever be used in vivo, we probably will recommend to vent the pulley to avoid triggering.^14,13,33

Certainly, our work is not immune to limitations. First and foremost is the size of the samples. The samples examined were tendons of different sizes with a single A2 pulley. Logistically, it was laborious to harvest the tendon with its corresponding pulley. We believe that by comparing a pre- and postintervention tendon, we were able to normalize the samples and determine how the repair directly affected gliding. In the future, a cadaveric tendon study with its own pulley can be designed. Second, most of the tendon literature has been done with double pulleys and cyclic loading. We were interested on linear loading and decipher how much maximal strength the epitendinous repairs could withstand without core suture support. Finally, by being an ex vivo study, we could not assess the effect inflammation or fibrosis had over our tendon repairs.

Conclusion

When reapproximating the epitendinous layer, choosing from an SR or SL configuration, and even a DR fashion, is irrelevant when comparing strength. Placing a locking epitendinous repair with 2 separate suture threads (DL) is a stronger option that comes with the downside of decreased gliding and increased resistance. Further in vivo studies need to be performed to validate our results.