5. Flexor tendon repair principles

This section will focus on repair principles. The reader is encouraged to seek alternative resources regarding specific repair techniques.

## Physiology of Flexor Tendon Healing and Rationale for Treatment Protocols DOI: http://dx.doi.org/10.5772/intechopen.86064

All suture tendon repair methods have been shown to significantly increase the gliding resistance compared to the intact tendon [45]. Gliding resistance is affected by [18, 46, 47]:


interface. This continuously stimulates cellular apoptosis, in turn reducing the density and strength of the adhesion fibres, resulting in an increasingly greater

Recent research has examined methods to augment intrinsic biological healing of

• Transforming growth factor β (TGF-β): Small amounts of TGF-β are found in the uninjured tendon [31]. The isoform TGF-β1 increases significantly after tendon injury [32, 33]. TGF-β1 has the highest association with adhesion formation and is therefore a major treatment target [31]. A neutralising antibody to TGF-β was shown to control scarring in rat dermal wounds [34, 35]. Furthermore, the same antibodies increased the total range of motion after flexor tendon repair in a rabbit model [36]. Additionally, the TGF-β1 receptor inhibitor SD208 can prevent progression and can improve tendon mechanical strength and decrease rupture rates [31]. However, suppression of TGF-β has been shown to decrease strength of tendon repair [37, 38]. This seems to be supported by gene therapy studies. Decreased TGF-β was

examined by deleting the TGF-β inducible early gene (Tieg1)—this resulted in decreased collagen I deposition in an in vitro model of tendon healing [39].

• Vascular endothelial growth factor (VEGF): It is known that tenocytes secrete VEGF and are present in synovial fibroblasts [8]. The VEGF family consists of several isoforms (VEGF-A, VEGF-B, VEGF-C, VEGF-D and VEGF-E and placenta growth factor), and these isoforms exert their effects through 3 tyrosine kinase receptors [31]. VEGF has been implicated in wound healing through epithelialization, collagen deposition and angiogenesis [40]. During flexor tendon repair, Boyer et al. showed that VEGF mRNA is increased during flexor tendon repair. It is postulated that the increased VEGF expression is associated with neovascularization [31]. VEGF genes delivered by adenoassociated virus (AAV) vectors in a chicken model demonstrated that healing

strength was improved without increased adhesion formation [41].

strength with reduced adhesions [42].

5. Flexor tendon repair principles

108

alternative resources regarding specific repair techniques.

• Basic fibroblast growth factor (bFGF): bFGF, found within the tendon and tendon sheath, has been shown to influence wound healing due to its role in fibroblast chemotaxis, proliferation and angiogenesis [42]. However, its role in tendon healing remains unclear. Delivery of bFGF to injured tendons via adenoviral vector demonstrated improved tendon healing and increased

• Tissue engineering: In their study, using a devitalised acellular allograft tendon containing recombinant AAV expressing growth and differentiation factor-5, Basile et al. [43] were able to repopulate the graft, decrease scar tissue and enhance the gliding property relative to the control graft. Tissue-engineered synovial membranes [44] have also been shown to decrease peritendinous adhesions.

This section will focus on repair principles. The reader is encouraged to seek

elasticity and breakup of the adhesion fibres in the late healing stage.

the flexor tendon whilst minimising adhesions.

4.7 Research trends

Tendons


Therefore, the ideal method of flexor tendon repair should allow a healing response precisely at the tendon ends but not between the tendon and its surroundings, create a repair site with minimal bulk and low friction and place enough force across the repair to promote motion and remodelling [22].

Strickland described the characteristics of an ideal tendon repair [48], and these were supported by further studies [22]. These are:


### 5.1 Repair strength

Initially, the strength of tendon repair depends solely on the repair technique [45]. It is postulated that postoperative tenomalacia may develop at the suture

tendon junction, therefore decreasing initial repair strength [49]. The initial strength of the repair depends on the material properties and knot security of the sutures as well as on the holding capacity of the suture grips of the tendon [45]. Immobilisation significantly decreases the strength of repair within the first 3 weeks of healing [50], whereas early passive and early active motion have been shown to prevent the initial weakening, leading to progressively increased repair strength, starting from the time of repair [50–52]. The initial strength of the repair depends on the material of the suture itself, knot security of the suture and the holding capacity of the suture grips on the tendon [45]. Therefore, the biomechanical properties of the suture can be improved by:

leading to failure by suture rupture before the true biomechanical properties of the locking loops are obtained [45]. Additionally, the size of the locking loop influences the biomechanical properties of the repair technique [59–61]. In the modified Pennington technique, increasing the cross-sectional area of each loop from 5 to 15% improved the ultimate force, whilst further increase did not improve strength, and the tendency for gap formation increased [60]. In the four-strand cruciate repair, the locking loops of 25% reached the highest gap force, ultimate force and

Variations in the construction of the link component—arc, loop or knot—result

• A sliding suture allows the suture to slide within the tendon substance when tension is applied to one of the longitudinal components. An arc link

• An anchored suture does not allow the suture to move independent of the tendon. A knot link component results in an anchored suture. When anchored sutures are used, the longitudinal strands are fixed. However, any slack in the suture will result in uneven distribution of tension and gapping at the tendon

The length of the core suture purchase in the tendon logically determines how much of the segment of the tendon is incorporated into the repair. The optimal range of core suture purchase has been determined as 1.0 cm with increased gap force, ultimate force and stiffness [62, 63]. The purchase of 0.4 cm results in very weak repairs, whilst any increase over 1 cm does not improve the biomechanical properties [63]. Increasing the suture calibre has been shown to increase the ultimate force in static testing and fatigue strength in dynamic testing; however, it has not been shown to improve the yield force or gap resistance of the repairs [45]. The strength of the 4–0 suture has been reported to be less than the holding capacity of several locking and grasping repair techniques with failure occurring mostly by suture rupture [54, 64]. A 3–0 suture failure due to suture rupture and pullout has been reported [54, 64]. Therefore, the use of 3–0 suture is generally recommended to offer safety over the

The ideal suture material for flexor tendon repair should be strong enough; prevent gapping; be easy to use and knot; be absorbable but maintain its tensile properties until tendon repair has achieved adequate strength; and have minimal tissue response [65]. Non-absorbable, synthetic sutures, (especially coated braided polyester), monofilament nylon and monofilament polypropylene are used in flexor tendon repair [45]. Coated braided polyester suture is the most common core suture material, though nylon is also used, especially in repairs performed with looped suture. Monofilament polypropylene is mainly used in the peripheral sutures. Coated braided polyester suture demonstrates significantly higher tensile strength and stiffness than monofilament nylon and polypropylene sutures and maintains its tensile properties in the body temperature, whilst the stiffness of both polypropylene and nylon suture has been shown to decrease significantly [66, 67]. A braided polyblend polyethylene suture (Fiberwire®) has been introduced for flexor tendon repair. It has significantly higher ultimate force and stiffness than coated braided polyester, monofilament nylon and polypropylene sutures and a similar ultimate force but higher stiffness than braided stainless steel [66]. Bioabsorbable suture

component results in sliding suture. When sliding sutures are used, tension is

in a sliding or an anchored suture on each half of the divided tendon [55].

Physiology of Flexor Tendon Healing and Rationale for Treatment Protocols

DOI: http://dx.doi.org/10.5772/intechopen.86064

equally distributed among the different longitudinal strands.

4–0 suture by increasing the material strength [45, 54, 64].

stiffness [59].

ends.

111

5.3 Suture principles

