Penetrating hand trauma is common, and in this kind of trauma the tendons of the hand or wrist are frequently injured. The flexor tendon repair was the standard procedure that it is very common for general orthopedic or hand surgeon but the outcomes are optimal due to suture technique and surgeon experience. Recently, many studies have tried new techniques in order to improve the tensile strength. In this study, we focused specifically on the technique used in the 4-strand suture method, and our findings can be combined with other studies on other techniques to determine the most effective surgical technique for tendon repair.
The initial strength of a repaired tendon depends on the number of suture strands crossing the repair site, core suture purchase length, anchoring technique, lock diameter and core suture material [5, 9]. The suturing method is also important in terms of post-operative outcomes such as restriction in motion. The purpose of this study was to assess a novel surgical suturing technique for flexor tendon repair compared with the 4-strand double-modified Kessler technique that is commonly used in orthopedics. We applied a single continuous suture to repair the tendon, adding surgical knots in the same place as the surgical knot at the repair sites(Fig. 2) theorizing that this technique would improve both max failure load and cyclic testing to failure. The testing protocol we chose was based on the 4 strands that comprise the core components of the tendon repair because the 4-core strand suture is the standard. The repair site gap formation is a very important issue in end-to-end flexor tendon repairs, as studies have shown that it can be associated with poor clinical outcomes [9]. A previous study found that increasing the number of core sutures used in the standard technique improved the ultimate strength of the core strand sutures [6, 8, 11]. The reason we chose to examine biomechanical tendon repair was that we believe this technique has not achieved its full potential in terms of technique development. Therefore, we applied a continuous suture to repair the tendon, adding surgical knots in the same place as the surgical knot at the repair sites in order to increase the strength in the repair site to improve tension resistance in the early motion using a simple suture technique. The biomechanical properties examination showed that tendon repair in the continuous double knots technique group had a higher tensile strength than in the 4-strand double-modified Kessler technique group. There were significant differences between the groups in terms of ultimate failure load and cyclic testing to failure for the flexor tendon sutures. The most common failure mode of tendon repair was suture breakage. Interestingly, the knot failure was less likely occur in the continuous double knots technique group compared with the double-modified Kessler technique group. This implies that the continuous double knots technique results in more secure knots. In this study, we found that knotting together of the continuous double knots suture technique can improve strength more than tie knots separately. The first possible reason for this is that, the two sutures could help share the load and balance the tension. The rate of double suture breakage when using the continuous double knots suture technique in our study is lower than in the double modified Kessler technique. Usually, two separate sutures will have different tensions, so the higher tension suture tends to rupture first. When knotted together, the higher tension suture can pass tension to the second suture and reduce the tension on itself.
The continuous double knots technique is an addition to the modified Kessler technique. This technique improved the strength of the procedure. Hence, the improved strength resulting from the knotting together of two separate sutures could be helpful for other techniques where two separate stitches could also be strengthened by tying the knots together. Other tendon repair techniques such as the Strickland technique or Becker technique might also benefit from this type of double knotting technique.
For the second reason, we observed that the broken sutures were not always completely separated from the tendon. One side of the broken suture might still be attached to the knot while the other side remained attached, but with reduced tension, as shown in Table 2. This indicates that the ruptured suture still carries a partial load but cause the other side to accept increased tension. In this situation, even though the tension is only slightly reduced, it can still slow the failure of the remaining suture. However, it may be reduced tension only partially but it is useful and may slows down the failure of last remained suture. Finally, we noted that the when the knots remained intact, they were difficult to pull out. Failure mode of knot failure in the continuous double knots technique was lower than double modified Kessler technique. In our technique found that tying the knots together would save time and reduce steps. Therefore, this technique may be more useful for other suture materials and other repair methods knotting that are slippery and tend to be easily pulled out. As same as the 4-strand cross-locked cruciate flexor tendon repair technique (Adelaide technique) has been shown to have comparably high resistance to gap formation and ultimate tensile strength [12, 13].
However, Adelaide repair technique had the single knot in two loops and cross-locking in proximal only [13]. This continuous double knots technique tie each knot of the two loops together and lock the proximal and distal part of the tendons. The cross-locking of the distal part of both tendon ends can be a practical technique to control and optimize the length of the tendon to reduce the gap formation.
Primary flexor tendon repair is an important surgical skill in orthopedic surgery [14]. The technique for end-to-end repair of flexor tendons should achieve a strong enough repair for early mobilization and healing in order to prevent adhesions. The evidence from other studies indicated that the strength of a repair is almost directly proportional to the number of knots and core sutures [15,16,17]. A previous in vivo study found that the effect of suture knot location on tensile strength after flexor tendon repair had no deleterious effects on tensile strength and may even have stimulated tendon healing [18]. However, the formation of a gap at the tendon repair site represents a dehiscence of the repair. Other studies have suggested that the formation of such a gap could lead to flexor tendon adhesions, decreased tendon glide, and consequent digital stiffness [19,20,21,22,23]. Gelberman et al. [24] found that repaired flexor tendons with a gap of less than 3 mm had increased strength compared to those with a gap of greater than 3 mm. Current evidence shows good to excellent outcomes in 75% of primary flexor tendon repairs [21, 25]. The rupture rate is 4–10% of primary flexor repairs [21, 25]. Active rehabilitation protocols give a better range of movement, smaller flexion contractures, and greater patient satisfaction when compared to the passive rehabilitation protocols [20, 21, 26].
The limitation of this study was that it was only a biomechanical study of core sutures. After tendon repair, the conditions of the paratenon and excursion are as important as the gap. This technique needs to be validated in a clinical trial in the future study.