Simplifying four-strand flexor tendon repair using double-stranded suture: a comparative ex vivo study on tensile strength and bulking

Biomechanical evaluation of the ST-knot: A new suture for flexor tendon repair

PURPOSE

Although tendon lacerations are common, there is currently no consensus on choice of suture. Easy and fast sutures that impart enough strength to allow mobilization are needed. This study compared the ex vivo biomechanical strength (force required to create a 2 mm tendon gap) of a novel suture (ST-knot) with that of a conventional suture (double Kessler).

MATERIALS AND METHODS

Forty fresh deep flexor tendons from porcine forelimbs were used. Both repaired tendon ends were mounted on standard traction jaws of an axial traction machine at an initial distance of 40 mm for all tendons. A high-definition camera was used to determine the force forming a 2 mm gap. Ten tendons in group 1 (ST-knot) and 10 in group 2 (double Kessler) were prepared with PDS 4.0 (single thread for Kessler, double thread for ST-knot). Tendons in groups 3 (ST-knot) and 4 (double Kessler) were repaired with PDS 1.0 using the same principle.

RESULTS

There was no significant difference in the force required to form a 2 mm tendon gap between groups 1 and 2, and this trend was identical when using a stronger thread in groups 3 and 4. The maximum force before rupture, mode of repair failure, stress and stiffness were also comparable, with no significant differences between groups 1 and 2, or between groups 3 and 4.

CONCLUSIONS

The ST-knot showed comparable results to the double-Kessler knot, whichever the thread used. Because it involves fewer steps than conventional techniques and is easy to perform, the ST-knot may offer a therapeutic solution, particularly in complex trauma with multiple tendon injury.

Gap Resistance and Tensile Strength of a Q Suture Technique During Curved Loading: An Ex Vivo Porcine Flexor Tendon Study

PURPOSE

This study aimed to determine the mechanical properties of the double Q suture technique in angular motion and to compare the gap formation associated with tendon repairs during curved and linear loading.

METHODS

Eighty porcine flexor tendons were repaired with one of two 4-strand sutures: double Q suture or double modified Kessler plus peripheral running sutures. The repaired tendons were cyclically loaded sequentially against a pulley with a radius of 2.0, 1.5, and 1.0 cm or linearly without any pulleys. The number of tendons that formed an initial or 2-mm gap at the repair site during cyclic loading, the gap size between tendon ends when cyclic loading ended, and the ultimate strength were recorded.

RESULTS

The gap at the repair site formed gradually from the dorsal to volar aspect during curved loading. No double Q repairs, but half of the double Kessler plus running suture repairs, formed an initial or 2-mm gap on the volar aspect during curved loading. The double Q group had a significantly smaller gap size on the dorsal aspect than the double Kessler plus running suture group at all three radii of curvature. The ultimate strength was similar between the two groups. There were no significant differences in linear motion between these two repairs.

CONCLUSIONS

The double Q suture is superior to the conventional 4-strand tendon core suture plus running peripheral sutures in gap resistance in angular motion. This study provides insight into the formation of an unbalanced gap on the dorsal and volar aspects of tendon repair during curved loading.

CLINICAL RELEVANCE

The double Q suture provides a simple and efficient option for flexor tendon repair considering the high risk of gap formation on the dorsal aspects of the tendon repair in angular motion.

The Effects of the TSOL Knot on the Repair Strength and Gliding Resistance Following Flexor Tendon Repair

BACKGROUND

The stability of a suture knot construct has been realized as an important parameter that affects the strength of flexor tendon repairs. A novel 2-strand-overhand-locking (TSOL) knot, which is not commonly used in the clinical setting, recently was reported to increase repair strength and to decrease tendon gliding resistance in a 2-strand repair technique. The purpose of the present study was to investigate the effect of the TSOL knot on tendon repair strength and gliding resistance compared with a typical surgical knot in both 2-strand and 4-strand repair techniques using an in vitro turkey flexor tendon model.

METHODS

Sixty flexor digitorum profundus tendons from the long digit of the turkey foot were divided evenly into 4 groups and repaired with the following techniques: (1) a 2-strand modified Pennington repair with a square knot, (2) a 2-strand modified Pennington repair with a TSOL knot, (3) a 4-strand grasping cruciate repair with a square knot, and (4) a 4-strand grasping cruciate repair with a TSOL knot. Repaired tendons were tested for failure mode, gliding resistance, and repair strength at failure.

RESULTS

The repair strength and stiffness of the 4-strand repairs were significantly higher than those of the 2-strand repairs, regardless of knot type (p < 0.05). The repair strength at failure of the TSOL knot was significantly greater than that of the square knot in 2-strand repairs (p < 0.05) but not in 4-strand repairs. The gliding resistance of the TSOL knot was significantly decreased compared with that of the square knot in both 2-strand and 4-stand repairs (p < 0.05). With regard to failure mode, the TSOL knot was less likely to fail due to knot unravelling.

CONCLUSIONS

In this in vitro biomechanical study involving the use of turkey flexor tendons to compare gliding resistance and repair strength characteristics for knot-inside 2 and 4-strand repairs, the TSOL knot was associated with decreased repaired tendon gliding resistance, regardless of the number of strands used. Although the TSOL knot also increased the repair strength, the difference was only significant when 2-strand repairs were used. The results of our study support the use of the TSOL knot in the clinical setting of flexor tendon repair using 2 or 4-strand, knot-inside methods.

CLINICAL RELEVANCE

In surgical repair of flexor tendons, there is substantial interest in maximizing strength while minimizing friction. This study shows the potential utility of the TSOL knot to increase repair strength while decreasing gliding resistance, particularly in 2-strand repairs.

Recent developments in flexor tendon repair techniques and factors influencing strength of the tendon repair

Over the last decade, both basic researchers and surgeons have sought to identify the most appropriate techniques to be applied in flexor tendon repairs. Recent developments in experimental tendon repairs and clinical outcomes of newer repair techniques have been reviewed in an attempt to comprehensively summarize the most critical mechanical factors affecting the performance of tendon repairs and the surgical factors influencing clinical outcomes. Among them, attention to annular pulleys, the purchase and tension of the core suture, and the direction and curvature of the path of tendon motion have been found to be determining factors in the results of tendon repair.