Comparison of 4 Different 4-Strand Core Suturing Techniques for Flexor Tendon Laceration: An Ex Vivo Biomechanical Study

Biomechanical analysis of cadaver rabbit Achilles tendons after full transection and suture: Comparison of U-Tang 4-strand with the cross-locked version of U-Tang 4-strand suture technique

Introduction

Tendon injures rank as the second most common hand injuries, and unsatisfactory repair can significantly impact a patient's everyday life. Over the years, various suture techniques have been studied in the pursuit of finding the optimal repair method. The ideal tendon repair should achieve maximum strength, while being easy to perform and minimizing tissue trauma. This study aims to compare the mechanical properties of the cross-locked U-Tang 4-strand suture to its unmodified version, the U-Tang 4-strand suture, to assess which technique offers greater repair strength.

Methods

Sixteen Achilles tendons from New Zealand White rabbits were randomly assigned to one of two suture technique groups; an original U-Tang 4-strand suture or a cross-locked U-Tang 4-strand suture, both performed using a 4-0 Supramid thread. The specimens were tested in uniaxial tension after a preconditioning phase. Cross-sectional area, load until failure, gap formation, stiffness, elastic modulus, and failure stress were determined.

Results

The standard U-Tang 4-strand suture withstood a maximum force of 25.48 ± 6.06 N, while the cross-locked version endured 33.90 ± 6.09 N. This indicates that the modified version demonstrated significantly greater strength (p = 0.021). The elastic modulus of the cross-locked U-Tang 4-strand suture (0.02 ± 0.003 MPa) was significantly higher than that of the original version (0.01 ± 0.006 MPa) (p = 0.028). No significant differences were observed regarding the cross-sectional area, load at 2 mm gap formation, stiffness and failure stress.

Conclusion

Employing the cross-locked U-Tang 4-strand suture results in a significantly greater maximum force and elastic modulus compared to the original U-Tang 4-strand suture, utilizing the same thread and number of strands and knots. Therefore, the cross-locking version provides an alternative for achieving more stable initial repair strength.

Flexor Tendon Zone II Repair

Background

Flexor-tendon injury is a historically challenging problem for orthopaedic surgeons. Much research has been dedicated to finding solutions that offer balance in terms of the strength and ease of the repair versus the rate of complications such as adhesions. The number of core sutures, distance from the tendon edge, and use of an epitendinous stitch have been shown to affect repair strength1-4. A number of configurations have been described for the placement of the suture; however, none has been identified as a clear gold standard5. This article will highlight the preferred tendon repair technique of the senior author (R.J.S.), the Strickland repair with a simple running epitendinous stitch. Relevant anatomy, indications, operative technique, and postoperative management will be discussed.

Description

The flexor tendon is typically accessed via extension of the laceration that caused the initial injury. After the neurovascular structures and pulleys are assessed, the tendon is cleaned and prepared for repair. A 3-0 braided nylon suture is utilized for the 4-core strand repair and placed in the Strickland fashion. A 5-0 polypropylene suture is then utilized for the simple running epitendinous stitch.

Alternatives

Multiple alternative techniques have been described. These vary in the number of core strands, the repair configuration, the suture caliber, and the use of an epitendinous or other suture. Nonoperative treatment is typically reserved for partial flexor-tendon laceration, as complete tendon discontinuity will not heal and requires surgical intervention.

Rationale

The 4-core strand configuration has been well established to increase the strength of the repair as compared with 2-core strand configurations, while also being easier to accomplish and with less suture burden than other techniques1. The presently described technique has excellent repair strength and can allow for early active range of motion, which is critical to reduce the risk of postoperative adhesions and stiffness.

Expected Outcomes

Excellent outcomes have been demonstrated for primary flexor-tendon repair if performed soon after the injury1,2,6,7. Delayed repair may lead to adhesions and poor tendon healing8. Early postoperative rehabilitation is vital for success9. There are advocates for either active or passive protocols10-12. The protocol at our institution is to begin early active place-and-hold therapy at 3 to 5 days postoperatively, which has been shown in the literature to provide improved finger motion as compared with passive-motion therapy13-16.Important Tips:: The proximal end of the tendon may need to be retrieved via a separate incision if it is not accessible through the flexor-tendon sheath.The proximal end of the tendon may be held in place with a 25-gauge needle in order to best place sutures into both ends of the tendon.The epitendinous suture is run around the back wall before the core sutures are tied down, in order to prevent the tendon and repair from bunching up and becoming overly bulky.The entire A4 pulley and the distal A2 pulley can be divided for exposure if necessary.Up to 2 cm of the flexor-tendon sheath can be divided.If there are concomitant digital nerve injuries, repair these after the tendon, in order to avoid damaging the more delicate nerve repair while manipulating the tendon for repair.The most common major complications following tendon repair are formation of adhesions and rerupture. Acronyms and Abbreviations:: FDS = flexor digitorum superficialisFDP = flexor digitorum profundusMCP = metacarpophalangealPIP = proximal interphalangealDIP = distal interphalangeal.