Orthopedic Surgery for Flexor Tendon Lacerations Treatment & Management

The general principles of a tendon repair include the administration of intravenous (IV) antibiotics when indicated and the evaluation of the patient's tetanus immunization status.

Optimal surgical treatment of flexor tendon lacerations remains a matter for discussion. In 2014, the Flexor Tendon Committee of the International Federation of Societies for Surgery of the Hand (IFSSH) published a report summarizing the current views, practices, and suggestions of six senior hand surgeons from six countries. ^[11] There was significant common ground but also significant variance in approach.

There is some controversy regarding the proper management of partial flexor tendon lacerations. ^[12] A literature review by Lineberry et al suggested that partial lacerations involving 90% of the cross-sectional area could be safely treated without surgical repair in many cases. ^[13]  If there are concerns about complete injury, triggering of the involved digit, or entrapment of the tendon, exploration and treatment would be indicated. For tendon triggering or entrapment with less than 75% cross-sectional injury, surgical treatment would include beveling of the tendon edges; injuries involving more than 75% would be repaired with a noncircumferential simple epitendinous suture. 

As a rule, all flexor tendon repairs should be done in the main operating room because this arena, unlike many emergency departments, is a controlled, sterile environment. Surgical exposure can be obtained through Brunner (volar zigzag) or lateral incisions. Hemostasis, irrigation, and debridement are of vital importance. Debris and nonviable tissue left within the wound are niduses for infection, which can severely compromise the final range of motion (ROM) of the finger.

The surgeon should handle only the lacerated edges of the tendon to avoid tendon bunching and trauma to the uninjured area of the tendon. Exposed knots and sutured ends may promote adhesion formation. One or two core sutures and a running epitendinous suture should be used. Early initiation of rehabilitation is important for an optimal result.

The ideal repair is reliable, simple, and strong and does not impair healing. The optimal time for repair of the flexor tendons is within 24 hours of the injury. The longer the severed tendons have to develop adhesions and scar tissue, the smaller the possibility of restoring full function. Most repairs should be performed within the first 2 weeks following injury, since the tendon ends and tendon sheaths become scarred, and the musculotendinous units retract. Subsequent repairs after this time decrease the ultimate mobility of the fingers.

Repairs of the flexor tendon are performed under tourniquet control. Brunner or lateral (midaxial) incisions are used so that adequate exposure of the flexor fibro-osseous canal can be obtained. Care is taken not to breach the integrity of the neurovascular bundles, which can be quite superficial in the finger.

The location of the severed flexor tendon ends depends on the position of the finger at the time of injury. In a flexed finger, the flexor tendon is pulled proximally. The distal end of the flexor tendon is drawn distally as the finger assumes an extended position. The opposite is true for an extended finger, in which the distal flexor tendon end can usually be found at the site of the laceration.

The proximal tendon end retracts to a variable degree into the palm because of the muscle tension of the profundus and lumbrical muscles. The vincula to the tendons may prevent the proximal tendon from retracting during retrieval. The tendon can be retrieved with Jacob forceps or fine clamps, aided by milking the tendon proximally to distally.

Alternatively, a pediatric feeding tube can be used to pull the tendon back into the wound. A counterincision in the palm must be made to find the proximal end of the severed tendons. Once identified, the feeding tube is introduced at the distal wound site through the fibro-osseous canal, to emerge through the palmar counterincision site. The feeding tube is sutured to the end of the tendon and pulled out distally, carrying with it the proximal end of the flexor tendon. The tendon is held in this position with a 25-gauge needle in the palm.

Disruption of the pulleys, especially A2 and A4, should be avoided. If the laceration is at these pulleys or if the repair is hindered because of the pulleys, then Z-plasties in the pulleys or partial releases may be required. The pulleys are repaired after the tendon is repaired. Shredded or mutilated pulleys may be reconstructed with a slip of the flexor digitorum superficialis (FDS) tendon, tendon grafts, or extensor retinaculum grafts.

The initial intraoperative steps in repair of flexor tendon injuries should follow the principles of all open wound management and consist of irrigation and debridement. All devitalized tissue is excised, the wound is thoroughly irrigated, and the vital structures are identified and isolated for repair.

An atraumatic technique for tendon manipulation prevents further injury to the tendons and decreases the amount of adhesion formation. Every traumatic site along the tendon is another potential spot for adhesion formation. Delicate forceps, such as the Bishop-Harmon or Iris forceps, should be used to pick up the tendon at its severed end, though not along the sides of the tendon.

The goal of the tendon repair is to coapt the severed ends without bunching or leaving a gap. Bunching of the repair may inhibit tendon excursion under the pulley system. A gap left at the repair site can either weaken the repair, which will subsequently be prone to rupture, or foster an overabundance of adhesions, limiting excursion of the tendon.

The suture material that is used to repair the severed tendon varies. The usual caliber of suture is either 3-0 or 4-0. Braided or monofilament sutures also have been used.

Strickland concluded that six-strand repairs are stronger than four-strand repairs, which, in turn, are stronger than two-strand repairs. ^{[14, 15, 16, 17, 18, 19]} The tendon repair strength is thus proportional to the number of sutures that are placed across the repair site. A peripheral epitendinous suture permits an approximation of tendon ends and increases the repair strength.

Types of repairs

The various types of repair are listed below. This list illustrates the importance of a core suture followed by an epitendinous suture to complete the tendon repair.

Commonly used techniques for end-to-end flexor tendon repair are as follows:

• Kessler grasping suture
• Tajima suture
• Kessler-Tajima suture
• Bunnell suture
• Tsuge suture
• Becker suture (bevel technique)
• Double loop suture (Lee)
• Interlock suture (Robertson)
• Single-cross grasp six-strand suture (Sandow)
• Double-grasping single suture ^[20]
• Double-grasping two sutures ^[20]
• Six-strand suture using three suture pairs (Lim and Tsai)
• Strickland suture
• MGH suture
• Indianapolis four-strand suture

An eight-strand cross-locked cruciate repair using 4-0 caliber double-stranded suture has also been described. ^[21]

Peripheral tendon (epitendinous) suture techniques are as follows:

• Simple running suture ^[5]
• Running lock loop suture (Lin)
• Cross-stitch epitendinous repair technique (Silfverskiold)
• Halsted continuous horizontal mattress suture (Wade)
• Horizontal mattress intrafiber suture (Mashadi and Amis)

A dorsal splint is recommended to keep the wrist in 30° of flexion and metacarpophalangeal (MCP) joints in 50-70° of flexion. The proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints should be able to extend fully. In zone IV lacerations, the wrist is splinted in neutral position and MCP joints in 75-90° of flexion. When the flexor pollicis longus (FPL) is injured, the wrist is flexed at 50° and the MCP and DIP joints are flexed at 15-20°.

The most common complication of flexor tendon laceration is the development of adhesions, which causes stiff joints. Factors that promote adhesion formation are trauma to the tendon and sheath, bleeding in the tendon sheath, foreign material in the tendon and sheath, tendon ischemia, digital immobilization, the loss of the tendon sheath or pulleys, gap formation following tendon repair, and prolonged edema.

Factors that suppress adhesion formation are tendon mobilization, tendon stress, and minimal tendon or sheath trauma. Flexor contractures of IP joints after the initiation of an early hand therapy rehabilitation program require prompt protocol modification. Greater joint extension and dynamic splints are recommended.

Akbari et al, in a study evaluating the efficacy of heparin in reducing or preventing postoperative tendon adhesions in 100 patients with surgically repaired zone II flexor tendon lacerations, found that mean flexion gaps were significantly better in the patients treated with heparin than in the control subjects, who did not receive heparin. ^[22] However, there was a significantly higher rate of tendon rupture in the heparin-treated patients.

Rupture of the tendon repair is most common between postoperative days 7 and 10. If the clinical diagnosis of a digital flexor tendon rupture is uncertain, magnetic resonance imaging (MRI) can be used for this evaluation. This noninvasive tool can be very helpful in the early postoperative period, when active flexion is not possible to aid in the clinical diagnosis of tendon rupture. Also, MRI can be used to differentiate adhesions from tendon rupture as the cause of immobility.

Other possible complications of flexor tendon laceration are skin-flap compromise, injury to neurovascular structures and the development of reflex sympathetic dystrophy (RSD), bowstringing of the tendon, infection, and permanent contractures.

The key to success of flexor tendon repair is close adherence to a regimented hand therapy rehabilitation program. Complete immobilization is recommended for children younger than 10 years and for patients who are unable or unwilling to follow a controlled-motion protocol. Various protocols for care after flexor tendon repair are available. Each protocol must take into consideration the stress placed on flexor tendons before and after the repair.

Tensile stress on normally repaired flexor tendons is as follows:

• Passive motion - 500-750 g
• Light grip - 1500-2250 g
• Strong grip - 5000-7500 g
• Tip pinch, index flexor digitorum profundus (FDP) tendon - 9000-13,500 g

Edema and scar tissue increase the drag on a tendon, thereby increasing the force needed to carry out a given task. At the same time, the strength of the repair is variable over the course of the healing process. Initially rather strong, the repair strength decreases significantly between days 5 and 21.

The tendon is weakest during this period because of minimal tensile strength. Strength increases rapidly when tendon is stressed. Controlled stress is applied in proportion to increasing tensile strength. Stressed tendons heal faster, gain strength faster, and have fewer adhesions and better excursion. Tensile strength begins to gradually grow stronger at 3 weeks. Generally, blocking exercises are initiated 1 week after active ROM excursion (5 weeks postoperatively).

Passive ROM in extension exercises start 2 weeks after active ROM excursion (6 weeks postoperatively). Graded excursion strengthening starts 8 weeks postoperatively. If the digital nerve was repaired simultaneously, the PIP joint should be splinted at 30° of flexion in a dorsal blocking splint. Extension may increase by 10° weekly, starting from week 4.

No protocol allows forceful use of the hand until the end of postoperative week 8. The greatest achievement with ROM is seen between 12 and 14 weeks after surgery. Unrestricted motion and normal hand use are allowed 12 weeks after the repair. A plateau may be seen after 6-8 weeks.

The use of a dorsal-blocking splint places repaired tendons in a protected, shortened position to alleviate stress to anastomosis and prevents full  active extension. Rubber-band traction maintains digits in a flexed position. Also, it extends splint restraint because flexors do not contract. Rubber bands pull digits back into flexion, alleviating any active flexor contraction. Rubber-band traction provides tendon excursion to repaired tendons while minimizing stress.

Tendon glide during the healing phase minimizes scar adhesions while promoting intrinsic tendon healing. The patient should be observed for fixed flexion contracture of the PIP joint. Three main protocol groups exist: active extension associated with rubber-band flexion, controlled active motion, and controlled passive motion.

Injuries to zones I, II, and III

An early mobilization protocol is recommended. A well-motivated and reliable patient can initiate a Duran or Indianapolis protocol. Otherwise, the Kleinert protocol is applied, using rubber bands attached to hooks that have been glued to the patient's fingernails.

Modified Kleinert protocol

In the modified Kleinert protocol, pulleys are added at the level of the distal palm to obtain maximal DIP flexion. Rubber bands are removed at night. All patients are instructed to passively extend the PIP joint completely inside the splint to avoid flexion contractures.

At surgery, a half (dorsal-blocking) cast is applied with the wrist at 20-30° of flexion, MCP joints at 70-80° of flexion, and interphalangeal (IP) joints straight.

After 1 week, the cast is removed and a thermoplastic splint is applied with the joints at the same angles. All digits stay in splint. The index finger may be left free if only the ring or small finger tendon is involved. Dynamic traction is applied with the distal palmar pulley on the involved finger. The patient begins active extension from the dorsal-blocking splint against rubber band traction. He or she performs passive PIP and DIP motion within the restraints of the dorsal-blocking splint four times daily.

After 2 weeks, sutures are removed. On intermittent days, the IP joints are positioned straight, with a dorsal-blocking splint used only if fixed flexion contractures are developing.

After 4 weeks, the patient begins active composite flexion and active extension out of splint. Dorsal blocking continues between exercises.

After 5 weeks, the dorsal-blocking splint is discontinued. The patient may initiate blocking exercises and functional electrical stimulation (FES) as necessary.

After 6 weeks, the patient begins gentle passive extension. If necessary, a static extension splint is used for extrinsic flexor tightness.

After 8 weeks, light strengthening exercises with a firm but squeezable foam ball (eg, Nerf ball), putty, or a hand helper are begun.

After 12 weeks, the patient resumes normal activities.

Duran protocol

The Duran protocol is most frequently used and modified by hand therapists. If a flexion contracture develops, two options exist: initiation of the Kleinert technique or controlled passive extension of IP joints (with the more proximal joints in the protected position of full flexion).

At surgery, a half (dorsal-blocking) cast is applied with the wrist at 20-30° of flexion, the MCP joints at 70-80° of flexion, and the IP joints straight.

At 1 week, the cast is removed and a dorsal splint is placed. The wrist is held in 20° of flexion, and the MCP joints are held in relaxed flexion. With the MCP and PIP joints flexed, the DIP joint is passively extended. Then, with the DIP and MCP joints flexed, the PIP joint is extended. Thus, FDP and FDS tendon repairs diverge.

After 4.5 weeks, the splint is removed, and a wristband with rubber band traction is applied. While awake, the patient passively flexes all joints of the affected finger toward the palm and then actively extends the finger to the splint hood 15-25 times per hour.

After 5.5 weeks, the patient begins active flexion with wristband removal.

After 7.5 weeks, the patient begins resisted flexion.

Indianapolis protocol

The Indianapolis protocol is indicated for patients with four-strand Tajima and horizontal mattress repair with an additional peripheral epitendinous suture. Patients should be motivated and understanding. Digits should have minimal or moderate edema and minimal wound complications.

Two splints are used, the traditional dorsal-blocking splint—with the wrist at 20-30° of flexion, MCP joints in 50° of flexion, and IP joints in neutral—and the Strickland tenodesis splint. The latter allows full wrist flexion and 30° of dorsiflexion, while digits have full ROM, and MCP joints are restricted to a 60° extension.

For the first 1-3 weeks, the modified Duran protocol is used. The patient performs repetitions of flexion and extension to the PIP and DIP joints, as well as to the whole finger, 15 times per hour. Exercise is restrained by the dorsal splint. Then, the Strickland hinged wrist splint is applied. The patient passively flexes the digits while extending the wrist. The patient then gently contracts the digits in the palm and holds for 5 seconds.

At 4 weeks, the patient exercises 25 times every 2 hours without any splint. A dorsal blocking splint is worn between exercises until week 6. The digits are passively flexed while the wrist extends. Light muscle contraction is held for 5 seconds, and the wrist drops into flexion, causing digit extension through tenodesis. The patient begins active flexion and extension of the digits and wrist. Simultaneous digit and wrist extension is not allowed.

After 5-14 weeks, the IP joints are flexed while the MCP joints are extended, and then the IP is extended.

After 6 weeks, blocking exercises commence if digital flexion is more than 3 cm from the distal palmar flexion crease. No blocking is applied to the small-finger FDP tendon.

At 7 weeks, passive extension exercises are begun.

After 8 weeks, progressive gradual strengthening is begun.

After 14 weeks, activity is unrestricted.

Delayed mobilization in zone I-V injuries

Delayed mobilization in zone I-V injuries is indicated for patients who are unreliable, patients with a poor-quality flexor tendon (as a result, for example, of a crush injury or a revascularization problem), children aged 10 years or younger, and patients with multiple anatomic structures involved other than flexor tendons. ^[19]

A dorsal-blocking splint is applied. The wrist is held at 30° of flexion, the MCP joints are held at 50° of flexion, and the IP joints are extended.

At 3 weeks, active and passive motion exercises are performed within the restraints of the splint.

After 4.5 weeks, active and passive motion exercises are performed outside of the splint. Protective splinting is continuous.

After 6 weeks, the splint is discontinued, and passive motion exercises are begun in extension.

Injury in zones IV-V

At surgery, a half (dorsal-blocking) cast is applied with the wrist at 30° of flexion, the MCP joints at 50° of flexion, and the IP joints at full extension.

After 3-5 days, the cast is removed, and a dorsal-blocking splint is applied at the same angles. The splint may vary, depending on which tendon is injured (wrist vs digital tendon). Passive ROM is begun within splint restrains.

At 3 weeks, active ROM is begun within splint restraints. FES is initiated a few days after the initiation of active ROM.

After 4 weeks, active ROM outside of the splint is begun.

After 6 weeks, splint use is discontinued, and passive extension is begun.

Flexor pollicis longus injury

At surgery, a dorsal blocking cast is applied with the wrist in 20° of flexion, the MCP and IP joints in 15° of flexion, and the carpometacarpal (CMC) joint in palmar abduction. The dynamic or static protocol used in injuries to zones I-V is used.

Excursion/differential gliding

Hook and fist positions produce more gliding of the FDP tendon than of the FDS tendon. In the rooftop (angle) and straight fist positions, FDS tendon excursion exceeds that of the FDP tendon. The greatest excursion for the FDS tendon is in the straight fist position, and the greatest excursion for the FDP tendon is in the full fist position. Maximum gliding between the FDP and FDS tendons is in the hook position.

The straight, fist, and hook positions provide maximum differential gliding for both flexors. When the hand is held in the fist position for a sustained period, the two flexors require the greatest amount of muscle contraction.