**Abstract**

Peculiar anatomy of human hand with flexing fingers and opposing thumb give human beings clear edge over other existing living beings. We use hands for carrying out most of our daily activities. But at the same time this makes our hands vulnerable for getting traumatized. Hand injuries which involve underlying tendons make digits dysfunctional, which in turn affects overall precise functioning of hand. In this chapter we will briefly discuss related surgical anatomy of flexor tendons and associated structures, features of flexor tendon injuries at different zonal levels, surgical methods involved and different post-operative protocols used for management of these flexor tendon injuries.

**Keywords:** flexor tendon injuries, flexor digitorum superficialis, hand injuries, flexor digitorum profundus, tenorrhaphy

### **1. Introduction**

Philosophically, physiologically and anatomically, the interaction of the brain and the hand give unique identification to *Homo sapiens*. The progress of mankind has been credited for large extent to evolution of mobile and strong upper limb having independently opposing thumb with cognitive power of using it. The precision, balance and its specialization give human hand a central functional as well as communicative role. The aim of surgical treatment for the injured, diseased or dysfunctional hand is to retain its maximal useful length, stable motion and unimpaired mobility of sensate parts.

All functions of hand are executed with the help of digits, and tendons in turn execute the movement of digits.

Flexion of fingers is done by two tendons viz. flexor digitorum superficialis (FDS) and flexor digitorum profundus (FDP). Flexor digitorum superficial splits into radial and ulnar slips prior to insertion on middle phalanx. Flexor digitorum profundus passes between the two slips of flexor digitorum superficialis, through a space called "Camper's chiasm". Flexor digitorum profundus is inserted on volar aspect, near the base, of distal phalanx of the respective finger.

The Flexor digitorum superficialis and profundus tendons glide together in a fibro-osseous tunnel. This fibro-osseous tunnel is composed of five annular pulleys (A1–A5) and three cruciate pulleys (C1–C3). These pulleys prevent bowstringing and the increase mechanical effectiveness of pull across the joints.

Annular pulleys A2 and A4 pulleys are the most critical to finger function and are located in proximal part of proximal phalanx and middle part of middle phalanx, respectively.

Annular pulleys A1, A3 and A5 pulleys are located at the metacarpo-phalangeal, proximal interphalangeal and distal interphalangeal joints, respectively. Three cruciate pulleys C1, C2 and C3 are located between A2–A3, A3–A4 and A4–A5 pulleys, respectively.

Thumb has three pulleys A1, oblique and A2 pulley located over metacarpo-phalangeal joint, proximal phalanx and inter-phalangeal joint respectively. The oblique pulley is the most mechanically important pulley among them.

Flexor tendons of hand are divided into five zones:

Zone I: Extends from finger top to insertion of flexor digitorum superficialis. Zone II: This extends from insertion of flexor digitorum superficialis up to distal palmar crease.

Zone III: Extends from distal palmar crease up to flexor retinaculum.

Zone IV: This zone lies under flexor retinaculum.

Zone V: Extends from proximal border of flexor retinaculum to musculo-tendinous junction of flexor muscles.

Flexor tendon within fibro-osseous canal (zone II) receives nutrition from two distinct sources i.e. vascular and synovial. Four digital arches are formed by the anastomosis of branches from the two digital arteries. These arches are located at the base and the neck of proximal and middle phalanx. A vinculum arises from each of these arches (V1–V4). Vinculae V1 and V2 supply the flexor digitorum superficialis, whereas V3 and V4 supply flexor digitorum profundus tendon.

The surface of the tendon that is not compressed during flexion is supplied by perfusion with arterial blood, the surface that is compressed i.e. the palmar surface, is supplied by diffusion of synovial fluid. Diffusion is a more significant nutritive pathway than perfusion. The exact proportions of the two have been estimated to be 2:1 in flexor digitorum superficialis, and 5:1 in the flexor digitorum profundus.

Microscopically, tendons are composed of collagen bundles (mainly type I) oriented in regular, spiraling pattern with very few tendon cells (tenocytes), synovial cells and fibroblasts. 'Endotenon' encloses tendon bundles. If the tendon is within a synovial sheath, the outer layer of tendon is called the 'Epitenon' and if the tendon is outside the sheath (extra-synovial), outer loose areolar adventitial layer is called the 'Paratenon', through which blood vessels run longitudinally.

Tendons heal by intrinsic and extrinsic mechanism. Extrinsic mechanism of healing is by fibroblast cells in surrounding tissues and is responsible for adhesion formation, while as intrinsic mechanism of healing is because of tenocytes present within the tendon. Tendon gliding exercises after tendon repair promotes intrinsic mechanism of healing and inhibits the extrinsic mechanism of healing, thus preventing post tendon repair adhesion formation.

Flexor tendon injuries are common but a difficult problem for the patient, hand surgeon and the therapist. The incidence of flexor tendon injuries in industrialized countries is estimated to be 1 in 7000. The impact to patients may include loss of function, stiffness, vocational impairment and associated social and economical hardships.

### **1.1 Pulley system**

The synovial sheath is reinforced by a fibrous pulley system delimiting the digital canal. This system is composed of five annular pulleys and three cruciform pulleys [1–3]. The first, third and fifth annular pulleys arise respectively from the volar plate of the metacarpophalangeal (MCP) joint, proximal interphalangeal (PIP) joint and distal interphalangeal (DIP) joint. The remaining two annular pulleys second and the fourth one arise respectively from the proximal and middle phalanx; these two pulleys are thicker and broader than the rest. Between the

**125**

*Management of Flexor Tendon Injuries in Hand DOI: http://dx.doi.org/10.5772/intechopen.83483*

**1.2 Healing process of tendons**

immobilization of repaired tendons.

preserved [9–11].

**2.1 General considerations**

second and third annular pulleys is located the first cruciform pulley; between the third and fourth annular pulleys is present the second cruciform pulley; and the third cruciform pulley is located just proximal to the DIP joint. The cruciform pulleys play a role in the production of synovial fluid. The palmar aponeurosis pulley located at distal part of the transverse fibers of the palmar aponeurosis, just close to the beginning of the membranous synovial sheath, should be considered part of the finger pulley system; on each side of the synovial sheath the vertical fibers anchor it to the deep transverse metacarpal ligament. The digital fibrous pulley system keeps the flexor tendons close to the bone thus allowing complete flexion of the finger. The importance of palmar aponeurosis pulley increases significantly in case of absence of any annular pulley. The palmar aponeurosis having breaking strength of 16.5 kg is superior to the A2 pulley with breaking strength of 14 kg [4]. If A2 and A4

The two processes are involved in the healing process of tendons: the extrinsic healing mechanism involving the surrounding tissues, and the intrinsic healing mechanism, that involves the tendon itself and its synovial sheath. Vascular and cellular ingrowths from the surrounding tissues enhance the extrinsic healing. The callus formed allows the cicatrization of the tendon but at the same time restricts its mobility, especially in zone II. To prevent formation of these adhesions, agents like steroids, anti-inflammatory drugs, hyaluronic acid and anti-histaminics have been proposed [5, 6]. However, for decreasing the risk of adhesion formation microsurgical techniques and new suture materials along with an atraumatic approach has been very effective. But many factors, such as associated lesions (skin loss, vascular, nerve injury or fracture) and the nature of the trauma (avulsion, crush injuries, blunt injury) play a significant role in increasing chance of adhesion formation. Gelberman and colleagues [7] reported the benefits of gliding function and protected passive mobilization on the tensile strength as compared to complete

Studies have shown that the tendon cells (tenocytes) themselves have a potential of healing. Lundborg et al. [8] showed that a flexor tendon that is isolated and kept in a synovial fluid environment, without any vascular supply, is able to survive and heal without any formation of adhesions. Therefore, its emphasized that during process of tendon repair, as much as possible synovial sheath should be

Usually flexor tendon repair is performed in an emergency setup. In cases such as dirty trauma or crush injuries, debridement should be done to convert contaminated wound into a cleaner wound. All the injuries (fracture, skin loss, neurovascular bundles) are repaired simultaneously along with flexor tendon repair. However, if the surgeon does not possess enough expertise to treat such lesions, it's advisable to delay the repair till next appropriate time [12]. All injured flexor tendons should be repaired using proper instruments and under magnification in an operating room thus allowing atraumatic repair of such tendons. Cleaning of wound before tenorrhaphy and in certain circumstances administration of intravenous antibiotics just before, during and 6 hours after surgery is indicated. The tendon repair

**2. Surgical techniques for primary flexor tendon repair**

pulleys are absent there is significant loss of finger flexion.

*Management of Flexor Tendon Injuries in Hand DOI: http://dx.doi.org/10.5772/intechopen.83483*

*Tendons*

respectively.

palmar crease.

nous junction of flexor muscles.

Annular pulleys A1, A3 and A5 pulleys are located at the metacarpo-phalangeal, proximal interphalangeal and distal interphalangeal joints, respectively. Three cruciate pulleys C1, C2 and C3 are located between A2–A3, A3–A4 and A4–A5 pulleys,

Thumb has three pulleys A1, oblique and A2 pulley located over metacarpo-phalangeal joint, proximal phalanx and inter-phalangeal joint respectively. The oblique

Zone I: Extends from finger top to insertion of flexor digitorum superficialis. Zone II: This extends from insertion of flexor digitorum superficialis up to distal

Zone V: Extends from proximal border of flexor retinaculum to musculo-tendi-

Flexor tendon within fibro-osseous canal (zone II) receives nutrition from two distinct sources i.e. vascular and synovial. Four digital arches are formed by the anastomosis of branches from the two digital arteries. These arches are located at the base and the neck of proximal and middle phalanx. A vinculum arises from each of these arches (V1–V4). Vinculae V1 and V2 supply the flexor digitorum superficia-

The surface of the tendon that is not compressed during flexion is supplied by perfusion with arterial blood, the surface that is compressed i.e. the palmar surface, is supplied by diffusion of synovial fluid. Diffusion is a more significant nutritive pathway than perfusion. The exact proportions of the two have been estimated to be 2:1 in flexor digitorum superficialis, and 5:1 in the flexor digitorum profundus.

Microscopically, tendons are composed of collagen bundles (mainly type I) oriented in regular, spiraling pattern with very few tendon cells (tenocytes), synovial cells and fibroblasts. 'Endotenon' encloses tendon bundles. If the tendon is within a synovial sheath, the outer layer of tendon is called the 'Epitenon' and if the tendon is outside the sheath (extra-synovial), outer loose areolar adventitial layer is called

Tendons heal by intrinsic and extrinsic mechanism. Extrinsic mechanism of healing is by fibroblast cells in surrounding tissues and is responsible for adhesion formation, while as intrinsic mechanism of healing is because of tenocytes present within the tendon. Tendon gliding exercises after tendon repair promotes intrinsic mechanism of healing and inhibits the extrinsic mechanism of healing, thus

Flexor tendon injuries are common but a difficult problem for the patient, hand surgeon and the therapist. The incidence of flexor tendon injuries in industrialized countries is estimated to be 1 in 7000. The impact to patients may include loss of function, stiffness, vocational impairment and associated social and economical

The synovial sheath is reinforced by a fibrous pulley system delimiting the digital canal. This system is composed of five annular pulleys and three cruciform pulleys [1–3]. The first, third and fifth annular pulleys arise respectively from the volar plate of the metacarpophalangeal (MCP) joint, proximal interphalangeal (PIP) joint and distal interphalangeal (DIP) joint. The remaining two annular pulleys second and the fourth one arise respectively from the proximal and middle phalanx; these two pulleys are thicker and broader than the rest. Between the

Zone III: Extends from distal palmar crease up to flexor retinaculum.

pulley is the most mechanically important pulley among them. Flexor tendons of hand are divided into five zones:

lis, whereas V3 and V4 supply flexor digitorum profundus tendon.

the 'Paratenon', through which blood vessels run longitudinally.

preventing post tendon repair adhesion formation.

Zone IV: This zone lies under flexor retinaculum.

**124**

hardships.

**1.1 Pulley system**

second and third annular pulleys is located the first cruciform pulley; between the third and fourth annular pulleys is present the second cruciform pulley; and the third cruciform pulley is located just proximal to the DIP joint. The cruciform pulleys play a role in the production of synovial fluid. The palmar aponeurosis pulley located at distal part of the transverse fibers of the palmar aponeurosis, just close to the beginning of the membranous synovial sheath, should be considered part of the finger pulley system; on each side of the synovial sheath the vertical fibers anchor it to the deep transverse metacarpal ligament. The digital fibrous pulley system keeps the flexor tendons close to the bone thus allowing complete flexion of the finger. The importance of palmar aponeurosis pulley increases significantly in case of absence of any annular pulley. The palmar aponeurosis having breaking strength of 16.5 kg is superior to the A2 pulley with breaking strength of 14 kg [4]. If A2 and A4 pulleys are absent there is significant loss of finger flexion.

### **1.2 Healing process of tendons**

The two processes are involved in the healing process of tendons: the extrinsic healing mechanism involving the surrounding tissues, and the intrinsic healing mechanism, that involves the tendon itself and its synovial sheath. Vascular and cellular ingrowths from the surrounding tissues enhance the extrinsic healing. The callus formed allows the cicatrization of the tendon but at the same time restricts its mobility, especially in zone II. To prevent formation of these adhesions, agents like steroids, anti-inflammatory drugs, hyaluronic acid and anti-histaminics have been proposed [5, 6]. However, for decreasing the risk of adhesion formation microsurgical techniques and new suture materials along with an atraumatic approach has been very effective. But many factors, such as associated lesions (skin loss, vascular, nerve injury or fracture) and the nature of the trauma (avulsion, crush injuries, blunt injury) play a significant role in increasing chance of adhesion formation. Gelberman and colleagues [7] reported the benefits of gliding function and protected passive mobilization on the tensile strength as compared to complete immobilization of repaired tendons.

Studies have shown that the tendon cells (tenocytes) themselves have a potential of healing. Lundborg et al. [8] showed that a flexor tendon that is isolated and kept in a synovial fluid environment, without any vascular supply, is able to survive and heal without any formation of adhesions. Therefore, its emphasized that during process of tendon repair, as much as possible synovial sheath should be preserved [9–11].
