Extensor Tendon Repair
D. Marshall Jemison, MD
Dr. Jemison or an immediate family member serves as a board member, owner, officer, or committee member of the Tennessee Orthopaedic Society.
PATIENT SELECTION
Indications
Extensor tendon injuries are more common and frequently present to orthopaedic practice. Because of the subcutaneous nature of these tendons just between the thin skin of the dorsal wrist, hand, and fingers and the prominent bony structures, they are particularly vulnerable to injury and are more common than flexor tendon injuries.1 The management of injuries to the extensor mechanism has been written out extensively because of their prevalence. In some cases, simple splint treatment for closed injuries can be effective. Many of the open but less complex injuries can be managed under local anesthesia in the office, emergency department, or operating room using straightforward suture techniques, but simplicity of management does not always equate to an optimal result. In the finger, the dorsal apparatus is thin and suture purchase is therefore tenuous. Furthermore, the extensor mechanism does not tolerate shortening or lengthening and is prone to either adhesions or rupture. Frequently for many of these injuries, a supervised hand therapy program and engagement with a knowledgeable and skilled hand therapist may greatly enhance outcomes following surgical treatment. This chapter will describe the surgical management of the more common injuries to the extensor tendons stratified by anatomical zone, and open or closed status of the injury.
To facilitate appropriate evaluation and treatment, an understanding of the extensor tendon anatomy is necessary. The extrinsic system originates proximally at the elbow or forearm, and the tendinous component crosses the dorsal wrist through six fibro-osseous compartments. These compartments maintain the relative position of the tendons and prevent bowstringing of the tendons. The intrinsic system originates all in the hand and includes the thenar and hypothenar muscles and the dorsal and volar interossei and lumbricals. The intrinsic system’s remarkable complexity produces metacarpophalangeal joint (MCPJ) flexion and interphalangeal extension along with finger abduction and adduction. A breakdown of the component parts of this remarkable mechanism is pertinent for this discussion (Table 1; Figures 1 and 2).
Extensor tendon injuries were classified into eight zones by Kleinert and Verdan in their logical, anatomic description from 1983.2 Doyle expanded the classification for more proximal forearm injuries as a ninth zone. The odd numbers describe injuries at the joint level beginning with Zone I at the distal interphalangeal joint (DIPJ). Thumb extensor injuries are described similarly into five zones (Figure 3). Closed injuries are much more prevalent in the fingers and many of these injuries can be treated nonsurgically with splint techniques. Open injuries result from lacerations or crush and are frequently associated with other soft-tissue or bony injuries. Surgery is essentially always indicated for the open injury in addition to repair of other structures including fractures, nerves, vessels, and wounds.
Contraindications
The primary contraindication to surgery is a type of extensor disruption (usually closed) that is amenable to splint treatment. Delayed treatment may be indicated, particularly in more severe open injuries, if soft-tissue closure of the wounds is complex and requires staged management. Other contraindications to repair might include extensive comorbid conditions or neurologic dysfunction.
DIAGNOSTIC IMAGING
Sophisticated studies (MRI or CT scan) are rarely indicated to diagnose extensor tendon injuries. Plain radiographs, in contrast, are useful to assess for bony avulsion-type disruptions, joint subluxation, or other associated injuries. In the setting of open injuries, plain radiographs of the injured structure(s) in at least two orthogonal planes are needed to rule out retained foreign bodies, fractures, dislocations, and other concerns. Physical examination is the mainstay of diagnosis whether the injury is open or closed, and this will be discussed in each of the following sections.
PROCEDURES
Zone I: Type I Mallet Injuries
Terminal extensor disruption is a common injury that can occur either from an open injury with laceration or as a closed injury from a flexion force to an extended finger.
Doyle described a classification for these injuries, which also is a useful format for describing treatment options3 (Table 2). Type I injuries are the most common and in the more acute setting can be successfully treated with full-time extension splinting for 6 to 8 weeks followed by a weaning period of part-time splinting for 4 to 6 weeks. In healthcare workers and others who would have difficulty with DIP splint compliance, closed pinning with a K-wire crossing the DIPJ is an alternative. In the setting of mallet injuries, one must not only evaluate the DIPJ level, but also the PIP Joint. It is important to assess the injured digit for hyperlaxity and any propensity to PIP hyperextension. In such patients who have a mallet injury, compensatory swanning or hyperextension will be seen at the PIP joint. When this occurs, the tension is not appropriate for the mallet to heal appropriately even with DIPJ splinting. Patients with compensatory PIP joint swanning should be treated with an antiswanning splint or oval-8 splint for the initial 4 to 6 weeks of splinting, to prohibit hyperextension at the PIP joint.
Doyle described a classification for these injuries, which also is a useful format for describing treatment options3 (Table 2). Type I injuries are the most common and in the more acute setting can be successfully treated with full-time extension splinting for 6 to 8 weeks followed by a weaning period of part-time splinting for 4 to 6 weeks. In healthcare workers and others who would have difficulty with DIP splint compliance, closed pinning with a K-wire crossing the DIPJ is an alternative. In the setting of mallet injuries, one must not only evaluate the DIPJ level, but also the PIP Joint. It is important to assess the injured digit for hyperlaxity and any propensity to PIP hyperextension. In such patients who have a mallet injury, compensatory swanning or hyperextension will be seen at the PIP joint. When this occurs, the tension is not appropriate for the mallet to heal appropriately even with DIPJ splinting. Patients with compensatory PIP joint swanning should be treated with an antiswanning splint or oval-8 splint for the initial 4 to 6 weeks of splinting, to prohibit hyperextension at the PIP joint.
TABLE 1 Component Parts of the Extensor (Dorsal) Apparatus | |||||||||||||||||||||||||||||||||
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 FIGURE 1 Illustration of the lateral view of the anatomy of the extensor mechanism at the metacarpophalangeal joint. The sagittal band arises from the volar plate and intermetacarpal ligament and stabilizes the extensor tendon. DIP = distal interphalangeal, MP = metacarpophalangeal, PIP = proximal interphalangeal. (Reproduced with permission from Kleinhenz BP, Adams BD: Closed sagittal band injury of the metacarpophalangeal joint. J Am Acad Orthop Surg 2015;23:415-423.) |
Surgical Technique
Closed Pin Fixation of the Distal Interphalangeal Joint
The procedure can be performed under local anesthesia with mini or regular C-arm fluoroscopy. A K-wire with a
diameter of 0.045″ (preferable) or 0.035″ is used and can be directed axially or obliquely across the joint with the joint in full extension. This author prefers an axial wire direction beginning at the distal tuft and just under the nail plate, and that the wire should be in the intramedullary canal. It is very important to stop the pin at the subchondral bone of the base of the middle phalanx and to avoid proximal interphalangeal joint (PIPJ) penetration. To avoid PIPJ penetration, the surgeon can dull the leading sharp point of the fixation pin with a wire cutter. If the wire is to be left buried under the skin, it can then be withdrawn a few millimeters and cut at the skin level. The wire is then grasped with a small hemostat and tapped into position just below the skin.
diameter of 0.045″ (preferable) or 0.035″ is used and can be directed axially or obliquely across the joint with the joint in full extension. This author prefers an axial wire direction beginning at the distal tuft and just under the nail plate, and that the wire should be in the intramedullary canal. It is very important to stop the pin at the subchondral bone of the base of the middle phalanx and to avoid proximal interphalangeal joint (PIPJ) penetration. To avoid PIPJ penetration, the surgeon can dull the leading sharp point of the fixation pin with a wire cutter. If the wire is to be left buried under the skin, it can then be withdrawn a few millimeters and cut at the skin level. The wire is then grasped with a small hemostat and tapped into position just below the skin.
 FIGURE 2 Illustration of the dorsal view of the anatomy of the extensor mechanism at the metacarpophalangeal joint. DIP = distal interphalangeal, MP = metacarpophalangeal, PIP = proximal interphalangeal. (With permission from Kleinhenz BP, Adams BD: Closed sagittal band injury of the metacarpophalangeal joint. J Am Acad Orthop Surg 2015;23:415-423.) |
Others prefer an obliquely oriented wire across the DIPJ, entering the middle phalanx and then engaging and just exiting the far cortex, so that if the pin breaks, it may be more easily retrieved. In all cases, postoperative care should include a splint supporting the DIPJ in place as much as feasible to avoid potential pin breakage.
 FIGURE 3 Illustration of the eight extensor tendon zones. T = thumb. (Reproduced with permission from Hunt TR, Wiesel SW: Operative Techniques in Hand, Wrist, and Forearm Surgery, ed 1. Philadelphia, PA, Wolters Kluwer Health, 2010.) |
Zone I Injuries: Type II Open Mallet Injury
Sharp or crushing lacerations to the dorsal distal joint frequently injure the terminal extensor tendon. The joint will generally be open, necessitating débridement and arthrotomy. The extensor tendon can then be repaired with either direct suturing or with a dermatotenodesis technique suturing skin and tendon as one layer.4 The suture material should be smaller diameter (4-0 or 5-0) and the best needle is a small taper type that will not cut through the very thin tendon. This author prefers a pliable braided nylon suture like Supramid that is not dyed. A fixation pin across the joint is optimal and can either be buried as described above or cut outside of the distal finger and a pin protector placed. A mallet-type splint should be used and the pin removed by 6 weeks (Figure 4, A and B).
Suture Techniques
The extensor mechanism in the finger is very thin measuring approximately 0.65 mm in the finger past the PIPJ. The complex mechanism does not tolerate shortening or lengthening particularly in the finger. Numerous studies have evaluated the biomechanics of multiple extensor suture techniques. Various core suture techniques like the
modified Kessler and modified Bunnell are appropriate for the more tubular and substantial extensor anatomy in Zone V-VII and in some cases a simple buried figure of 8 is satisfactory3 (Figure 5). Recent evidence is supportive of the efficacy and strength of a dorsal epitendinous suture called the running-interlocking horizontal mattress suture technique (RIHM) (Figure 6, A and B). This configuration is both strong and avoids tendon shortening and is useful for extensor tendon injuries in Zone I through VI.5,6
modified Kessler and modified Bunnell are appropriate for the more tubular and substantial extensor anatomy in Zone V-VII and in some cases a simple buried figure of 8 is satisfactory3 (Figure 5). Recent evidence is supportive of the efficacy and strength of a dorsal epitendinous suture called the running-interlocking horizontal mattress suture technique (RIHM) (Figure 6, A and B). This configuration is both strong and avoids tendon shortening and is useful for extensor tendon injuries in Zone I through VI.5,6
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