Introduction
Our basis of primary management of extensor tendon injuries, as with flexor tendon injuries, is early repair and early mobilization, with appropriate primary management being more effective than secondary treatment. However, unlike the flexors, a single system of primary surgery and rehabilitation cannot be applied to extensor tendon injuries because of anatomical and physiological variation along their length. Primary management must be tailored to the particular part of the extensor system that is injured.
It is a common misperception that the skill needed to treat flexor tendon injuries is not necessary for the extensor apparatus. Taken in the wider perspective, dorsal injuries are frequently complex, with extensor injuries having associated skeletal or skin injuries of significance, and the end result of management, particularly of complicated cases, is rarely determined simply by the state of the extensor tendon, but by the many other structures involved.
Anatomical features and zones
Features
Unlike the flexors, the extensor tendons have no synovial tunnels. They rely on the interstitial connective tissue superficial and deep to the tendon to allow tendon gliding. A major problem after any trauma or surgery is the movement of fibrin-laden edema onto the dorsum of the hand and fingers, filling these layers with fibrin, which later turns to scar tissue. In the early stages, the ‘sticky’ fibrin is enough to tether the extensor tendons and stiffen the joint dorsal and lateral ligaments, restricting movement, particularly into flexion. The problem is accentuated by the very small distances these tendons move in the fingers to achieve movement of the joints. This is not only a problem local to extensor tendon injury and surgery but involves the extensor system secondarily in all trauma and surgery to the hand.
Another complicating anatomical feature is that the extensor tendons in the fingers are complex structures, not a single tendon in each finger. The central slip and lateral bands act to extend the proximal interphalangeal (PIP) joint and the distal interphalangeal (DIP) joint, respectively. By the action of the lumbricals, the lateral bands also serve to stabilize the PIP joint and flex the metacarpophalangeal (MCP) joint. The oblique and spiral nature of the lateral bands exerts forces on all three joints and coordinates the motion and stability of the finger during motion and forceful grip. This is a unique feature of the extensor tendon system in the finger and any minor shortening of the central slip and lateral bands will disrupt this balance. Restoration of anatomical length and avoiding shortening of any part of these structures is a requirement in extensor repair in the fingers. Within the finger, a key requirement of direct suture is that extensor shortening be kept to less than 3 to 5 mm to ensure proper function. In contrast, shortening the tendons by 0.5 cm, or even 1 cm, may not affect flexor tendon function.
Tendon structures
The two lateral bands insert into the base of the dorsum of the distal phalanx of each finger. The lateral bands course dorsolaterally over the middle phalanx, laterally around the PIP joint, and then obliquely along the sides of the proximal phalanx to the palmar aspect of the MCP joint where they have their origin in the lumbricals and interosseous muscles ( Fig. 17.1 ). The lateral bands serve to extend the DIP joint and flex the PIP joint. The central slip inserts into the base of the middle phalanx dorsally and courses along the dorsum of the proximal phalanx, serving to extend the PIP joint ( Fig. 17.1 ). The central slip continues proximal to the MCP joint as the extensor digitorum communis (EDC), which serves to extend the MCP joint ( Fig. 17.1 ).
There are dense tendinous connections between the two lateral bands and the central slip where they lie over the dorsum and lateral aspects of the proximal phalanx. At the MCP joint, these tendinous connections, called the sagittal bands , connecting the central slip and the lateral bands are denser and serve to stabilize the MCP joint. Proximal to the MCP joint, the extensor tendon is anatomically simpler, over the metacarpals, with thin fibrous connections (called juncturae tendinum) between adjacent tendons. Because of these connections, the proximal part of any extensor tendon lacerated in the fingers or hand does not retract far, usually less than 1 to 2 cm. However, if lacerated at the wrist or forearm level, the tendon can retract considerably.
The thumb is extended by the extensor pollicis longus (EPL) and brevis (EPB). All of the fingers are extended by the EDC. The index finger has its own separate extensor, extensor indicis proprius (EI or EIP), which enables it to extend independently from the other fingers. Similarly, the little finger has an independent tendon, extensor digiti minimi (EDM). These extensors also serve to extend the wrist, although the wrist extensors are primarily responsible for wrist extension.
The extensor retinaculum consists of dense fibrous bands overlying the distal radius and ulna that serve as pulleys for both the finger and wrist extensor tendons. There are 6 compartments under the extensor retinaculum through which pass 12 tendons. These compartments (named the first to the sixth from radial to ulnar) contain the following tendons: the first compartment houses the abductor pollicis longus (APL) and EPB tendons; the second houses extensor carpi radialis longus and extensor carpi radialis brevis; the third (separated from compartment 2 by Lister’s tubercle) houses EPL; the fourth houses EIP and the four EDC tendons; the fifth houses EDM; and the sixth, (running in a groove in the ulnar head, houses) extensor carpi ulnaris (ECU).
Anatomical zones
The zone classification described by Verdan is the basis to any discussion. , Verdan divided the extensors of the fingers into eight zones. Subsequently, Doyle subdivided zone 8 into zone 8, injuries to the tendons in the forearm, and zone 9, injuries within the forearm muscles ( Fig. 17.2 ). It is practical to consider the management of each of these divisions of the extensor system separately as suture technique, the protection afforded to repairs, and appropriate rehabilitation differ according to the part of the system injured.
The 9 zones suggested by Verdan were largely based on anatomical differences of the extensor tendon along the limb and have been used for over 70 years ( Fig 17.2 A). One of the authors (JBT) suggests a reduction to 7 zones as more practical classification ( Fig. 17.2 B). In this system, Zone 1 is distal to the MCP joint and includes the complex extensor apparatus of the fingers, Zone 2 overlies the MCP joints; Zone 3 is the dorsum of the hand and wrist, Zone 4 is the space under the extensor retinaculum, and Zone 5 is the forearm. Zone 1 can be further divided into three subzones: distal to the PIP joint (as Zone 1a), at the PIP joint (Zone 1b), and proximal to the PIP joint (Zone 1c). This zoning may be easier to remember with its resemblance to the current flexor zones and may be a better guide to treatment. However, in this chapter, we continue to use Verdan’s zones while urging readers to consider the new zoning nomenclature.
Zones 1 and 2 (mallet finger)
Zone 1 is that part of the extensor overlying the DIP joint, and Zone 2 that part over the middle phalanx ( Fig. 17.2 ). Injury in both Zone 1 and 2 causes a mallet finger deformity at the DIP joint and is due to either disruption of the extensor tendon near its insertion or an avulsion fracture of the insertion from the base of the distal phalanx. After an open laceration of the proximal part of Zone 2, there may not be an obvious mallet finger as parts of the lateral bands may still be intact.
Causes and types
In most patients, mallet fingers are caused by a closed injury, when the patient’s finger hits a hard object, forcing the DIP to flex, snapping the extensor tendon near its insertion site or avulsing the insertion from the distal phalanx. An open cut on the dorsum of the DIP joint or middle phalanx can also cause a mallet finger. Therefore, mallet fingers divide into two types: those with and those without a bony fragment attached to the proximal tendon.
The displacement of the bony fragment and its size are important consideration when deciding treatment, as these two features determine the stability of the DIP joint and the healing potential of the tendon. If the fracture fragment is considerably displaced or the fragment is more than 30% of the articular surface on the lateral view of the finger, the joint is likely to be unstable and require surgical intervention.
According to the wound conditions and the anatomical structures involved, acute tendon injury in these two zones was classified into four types by Doyle, with the commonest being types 1 and 2 ( Table 17.1 ) ( Fig. 17.3 ).
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Clinical presentation
The patient often gives a clear history of trauma to the fingertip. Flexion of the distal phalanx with inability to actively extend the finger at the DIP joint are the typical findings of a “mallet” finger. There may also be pain on the dorsum of the joint, although pain is often not a feature of this injury. Swelling at the DIP joint may be present in the acute phase, but chronic mallet fingers do not usually have any swelling in the finger. If there is an open cut on the dorsum of the finger, the site of the cut indicates where the extensor is disrupted because gliding of the extensor in this area is very small. With the passage of time without treatment, the mallet finger can develop a secondary swan-neck deformity ( Fig. 17.4 ). If the extension lag is less than 30 degrees, and the joint is not painful, the patient with a closed mallet may not come to clinic for treatment.
A plain radiograph should be taken to evaluate whether there is an avulsion fracture at the insertion of the extensor tendon onto the distal phalanx. If there is a fracture, the displacement and size of the fragment should be assessed.
Nonsurgical treatment
Just proximal to its insertion, the extensor tendon is thin and flat, making tendon repair problematic as the tendon is too weak to allow strong suturing, then early movement and healing is slow. As a consequence, conservative treatment is considered for most patients with a closed injury.
For any patient with a closed mallet finger without avulsion fracture or a small, minimally displaced avulsion fracture, the common treatment is a distal finger splint. The splinting can be done using an aluminum (Zimmer) splint strapped onto the dorsal or palmar (the preference of all of the authors) surface of the finger from just distal to the PIP joint to the fingertip, allowing full movement of the PIP but preventing all movement at the distal joint ( Fig. 17.5 ) ( Box 17.1 ), or that described by Stack. The length of the splinting is 6 to 8 weeks. Closed mallet fingers in pediatric patients, which are rare, are almost always treated conservatively with finger splinting, usually for 6 weeks.
- 1.
Splinting the finger or thumb in extension for 6 to 8 weeks with the proximal interphalangeal joint free.
- 2.
For an open wound, surgical repair with a running suture or tendon–skin suture.
- 3.
For bony mallet finger, use of a finger splint or dorsal blocking K-wire fixation.
- 4.
Chronic painful mallet finger may need distal interphalangeal arthrodesis.
- 5.
Chronic tendinous mallet finger may be treated by tendon grafting.
The long period (6–8 weeks) of external splinting necessary to achieve healing is inconvenient for the patient. Despite the explanation that the slightest movement into flexion will separate the tendon ends, some patients take the splint off every time it gets wet. If possible, the splint is replaced every 2 weeks in the clinic. Bringing the patient back, repeating the warnings, and replacing the splint may improve compliance. After 6 to 8 weeks, all of the authors recommend for the patient to use the splint at night for 2 to 3 weeks.
Having a minor mallet deformity at the end of the splinting is common. Even with surgery, slight extension lag is an almost inevitable end point of treatment. The tendon heals with scar tissue between the ends, and every increase of tendon length by 0.6 to 0.7 mm will drop the DIP joint by 10 degrees from full flexion. That complete correction is impossible should be explained to the patient early in treatment. If the mallet deformity after splinting is more than 30 degrees, some surgeons repeat the 6 to 8 week splinting regime, whereas others move to open repair, which is also often the preference of some patients. Some patients accept the failure without repeating the splinting or proceeding to surgery.
Operative treatment
Direct repair of the extensor tendon.
Operative treatment is indicated for the patients with (1) extensor tendon laceration in an open wound, (2) failure of splinting for at least 8 to 10 weeks as a closed injury, (3) a bony mallet finger, in which the bony fracture is large and not reducible when the DIP joint is held in full extension. If the fracture fragment is large but reducible, the patient may not need surgery.
In patients with an open wound, the extensor tendon is exposed by extension of the wound. After thorough washing and debridement, there are various alternative techniques used for this tendon repair. The lead author usually repairs the tendon in both zones with small transverse mattress sutures of 5-0 nylon, followed by a simple running suture of the same material over the superficial surface of the tendon. The coauthors prefer combined tendon and skin suturing in Zone 1 and separate extensor tendon repair with a running suture (with 4–0 nylon) in Zone 2. Suturing the disrupted tendon with the skin, a so-called ‘tenodermodesis,’ is intended to strengthen the repair ( Fig. 17.6 ). A 4-0 or 3-0 nylon is used, then the fingertip splinted with a palmar finger splint or a temporary Kirschner (K) wire fixation through the DIP joint to allow healing of the tendon ( Fig. 17.6 ). The suture is removed 4 to 6 weeks later, but the splinting is continued for 2 to 3 weeks longer. If a K-wire is used, the K-wire is removed 4 weeks after surgery. If the distal tendon is too short, the tendon can be sutured to a horizontal bone hole in the distal phalanx or attached using a bone anchor ( Fig. 17.7 ) ( Box 17.1 ). Although the bone cortex is compromised, the joint will be immobilized by a K-wire postoperatively for 4 weeks supplemented by splinting for a few weeks after K-wire removal, so allowing bone healing. Some surgeons prefer to use a finger splint to protect the finger for about 6 weeks after surgery without inserting a K-wire across the DIP joint.
In cases with larger bone fragment pull-offs, the bone fragments should be wired. A commonly used method is the Ishiguro procedure, which holds the bone fragment in position using a dorsal percutaneous K-wire as a lever while a second K-wire is passed across the fully extended DIP joint ( Fig. 17.8 ). It is unknown whether compression of the reduced fragment is necessary. Whether a finger splint holding the DIP in hyperextension or K-wire fixation of a fully extended DIP joint work any less well than the Ishiguro technique is also unknown. A variety of other methods are reported to fix large bony fragments in the DIP joint ( Fig. 17.9 ).
K-wire fixation of the DIP is used mostly for failures of conservative treatment of type 1 mallet fingers and when repairing open injuries. Stiffness after wire removal is common. If the K-wire is not buried, pin track infection may infect the joint. A buried K-wire avoids this and is more convenient for the patient but requires a second operation. Such is the power of the profundus flexor tendon, K-wires can bend across the DIP and, occasionally, may even snap, with removal through a middle phalangeal approach being necessary.
Dip joint fusion.
DIP fusion is an alternative solution to this problem and, performed as a primary procedure, may be acceptable to patients, especially the elderly, as this will relieve extension lag and pain. It also becomes our salvation when other treatments fail repeatedly. Although this sounds drastic to the patient, it should be mentioned at the first visit as part of the explanation that the problem may be small but is far from simple. If the patient has considerable pain at first consultation, then mention of fusion is a must. If x-rays show the DIP joint to be already osteoarthritic, some will not lose the joint pain without fusion, even if the arthritis was previously asymptomatic.
Complications
Loss of flexion.
Although this joint contributes only 15% of the range of active digital flexion and power gripping, we need to be able to move it back and forth quite rapidly through 30 to 40 degrees for fine pinching and span gripping activities. Tendon adherence to the skeleton after the long period of splinting is common, particularly if absolute immobility of the DIP joint has been maintained with a K-wire. This may require lengthy therapy to achieve any flexion: 4 weeks of K-wiring, then 2 to 4 weeks of external splinting, is a possible compromise, but the patient may be reluctant to have this switch to external splinting.
Chronic mallet deformity.
Chronic mallet deformity is often seen. In treating this deformity, the scarred tendon part can be resected and tightened. There is a possibility after resecting scar that the tendon ends cannot be rejoined. Therefore, it is safer to simply divide the tendon (without excision) on the dorsum of the middle phalanx and then resuture the tendon with a horizontal mattress suture, so tightening the tendon by the very small amount necessary. The coauthors found resuturing to be useful, but the resutured extensor tendon remains weak for a long time and can loosen again after forceful DIP flexion. In such cases, a tendon graft is used to replace the thin and weakened tendon ( Fig. 17.10 ). An alternative in these patients, particularly with powerful fingers, is to reconstruct the spiral oblique retinacular ligament (SORL) with a thin strip of tendon graft, the so-called ‘SORL procedure’. , The tendon graft is sutured to the terminal part of the extensor tendon in Zone 1 and passed laterally around the middle phalanx to the volar aspect of the PIP joint where it is sutured to the periosteum of the distal part of the proximal phalanx and the proximal part of the PIP volar plate. The coauthors prefer using a tendon graft to connect the terminal tendon to the lateral bands (as in Fig. 17.10 ) rather than the SORL procedure.
Secondary swan-necking.
The lengthening of the distal tendon in a mallet deformity, whether presenting early or late throws a greater force onto the central slip at the PIP joint and may cause swan-necking ( Fig. 17.11 ). Correction of the mallet at the DIP joint may correct the PIP problem but sometimes does not. The SORL procedure, described above, may be used to correct both the DIP and PIP deformities. Alternatively, elongation of the central slip by central slip tenotomy alone or carried out at the same time as distal tendon repair or shortening may be used. After this tenotomy, slight lengthening only of the central slip, avoiding creating a Boutonnière deformity, is achieved by splinting the PIP joint to prevent full flexion for 4 weeks.
Mild swan-necking, as seen in congenital swan-necking, is in itself, not a functional problem and does not require treatment. However, should fingers with congenital swan-necking rupture the distal extensor, the forces setting the finger into the swan-neck position after release from splinting or repair of the mallet deformity are so strong that they are likely to stretch the repair, returning the DIP joint to the mallet position and accentuating the swan-necking. Although the lead author’s experience of these patient groups is limited, they have been treated successfully by the SORL procedure.
Pain.
Pain may be caused by stretching, or division, of the subcutaneous nerves innervating the skin of the proximal nail fold as they cross the dorsum of the DIP joint. Straightening the joint may relieve the pain, presumably by taking tension off the small nerves. The problem may settle over several months of intermittent use of a Stack splint. If not, DIP fusion will relieve the pain. In rare cases, relocation of the terminal nerve branches into the middle phalanx is indicated if the pain persists.
Outcomes
Trickett et al reported 218 bony mallet fractures (211 adult patients) treated using a custom-made thermoplastic splint. The joints were congruent in 168 and subluxed in 50. They did not find any differences in range of movement, extensor lag, or patient subjective outcomes associated with articular subluxation or the size of the articular fragment. Lin and Somara reviewed 99 mallet fingers (94 pediatric patients), among which 98 were treated conservatively by extension splinting. The majority of injuries were bony mallets (80%). The outcomes resulted in a residual extension lag in 12% of the cases with acute injury, with an overall small extension lag. The study showed that the majority of pediatric mallet finger injuries can achieve good outcomes with conservative treatment.
With respect to the various techniques of immobilization, Pike et al reported no difference in the incidence of extension lag of the DIP joint between custom thermoplastic, dorsal padded aluminum or volar padded aluminum splints for Type I acute mallet fingers. Algar et al reported 70 individuals with a mallet injury randomized to 6 weeks of full immobilization with either a 3-point prefabricated orthosis and elastic tape or a cast holding the DIP joint in extension. The overall findings for both treatment groups included means of <15 degrees of extensor lag and minimal pain at the 6-month outcome assessment and concluded that both are appropriate options for management of the mallet finger.
The clinical outcomes do not significantly differ between extension block pinning and nonsurgical management for mallet fractures involving more than one-third of the articular surface but without a significant degree of DIP subluxation. For bony mallet fingers with involvement of more than one-third of the joint surface but without primary joint subluxation, in a randomized clinical trial comparing conservative splinting and extension-block K-wiring, Thillemann et al , in Denmark, found splinting to be safe and efficient in restoring DIP joint motion. However, splinting does not prevent secondary subluxation of the joint adequately, so repeated radiographic follow-up during splinting is necessary. Akgun et al reported no difference in functional recovery, radiological values, or complications between use of one and two dorsal K-wires for extension blocking of mallet fractures.
Treatment of acute complex injury
Tendon loss.
Surgical repair is indicated in patients with tendon loss. The conventional method is to turn over a tendon flap from the central part of the extensor immediately proximally. However, this tendon slip is very thin and difficult to suture. Because only one lateral band is needed to extend the DIP, an alternative method is to remove one lateral band proximally and use this as a graft distally. Because all these treatments involve a long period of immobile tendon protection, most tendon reconstructions lead to tethering and tenodesis of the DIP in extension. Short tendon grafting can be used for primary tendon defects or after failed direct suture repair for acute or chronic mallet fingers.
The coauthors use palmaris longus tendon grafting to reconstruct primary tendon defects and defects after resection of scar. More recently, in complex injuries at this level, including distal replantation, the lead author has ignored the extensor tendon and moved the finger immediately without tendon reconstruction or splinting. The result is a finger that flexes fully and then recoils on relaxation of the profundus flexor to about 20 to 30 degrees of extension deficit, which is more useful functionally than a DIP tenodesis in extension.
Skeletal and skin damage.
Complex injuries may include skeletal disruption or loss, and/or loss of any of the soft tissues from skin to skeleton. Missing skin is less of a problem given the plentiful availability of local homodigital flaps or the easy availability of skin substitutes. The coauthors now use skin substitutes in almost all skin defects in the dorsal finger, instead of a flap transfer. Middle phalangeal fractures require internal fixation. Previously, if the DIP joint could not be repaired, it was fused. Now, providing there is no significant bone loss, the lead author prefers to replace the joint with a Swanson prosthesis.
Secondary surgery
Secondary surgery is necessary for delayed presentations of both simple and complex injuries and failures of primary treatment, including tendon tethering with loss of DIP flexion.
Tendon adherence.
Tenolysis at this level is liable to fail. The movement range of the freed tendon is small, with the surgery creating further fibrin-edema in the small interstitial spaces above and below the tendon.
Fowler’s extensor tenotomy over the middle third of the middle phalanx ( Fig. 17.11 ), and then release of the dorsal and lateral ligaments of the DIP joint, may regain flexion. Because of the secondary ligament changes of the DIP joint, a mallet rarely occurs after this tenotomy. Rather, the problem is trying to get the DIP joint to flex even after extensive releases. Even if K-wired in flexion for 4 to 6 weeks, the DIP often settles back into the straight, or even hyperextended, position on removing the K-wire. This is also nearly always the end result when this component of a Boutonnière deformity is treated in this way. Division of the extensor at this level is close enough to the DIP joint to allow ligament releases while ensuring that there is tendon cover of the joint when flexing, should the skin stitches give way during postoperative mobilization. The Dolphin tenotomy more proximally on the middle phalanx ( Fig. 17.11 ), intended to preserve the oblique retinacular ligaments to maintain passive DIP extension on extension of the PIP joint, is too far from the distal joint to allow release of the ligaments of the joint.
Tendon, bone, or skin reconstruction.
Secondary surgery may require tendon, bone, or skin reconstruction: the techniques are those used at primary surgery for complex cases.
Zones 3 and 4
Zone 3 is that part of the extensor overlying the PIP joint and Zone 4 that part over the proximal phalanx.
Clinical presentation
In Zone 3, laceration or closed disruption of the central slip at its insertion will cause a failure of active extension of the PIP joint. Sometimes, a closed injury causes attenuation of the central slip at the insertion site without complete disruption, causing weakness of active PIP joint extension or only a partial loss of PIP extension. With intact lateral bands, in the first a few days or weeks, the deformity may not be remarkable, but later the characteristic ‘ Boutonniere ’ or ‘ Buttonhole ’ deformity develops, with flexion of the PIP and hyperextension of the DIP due to volar subluxation of the lateral bands ( Figs. 17.12 and 17.13 ) ( Box 17.2 ). This deformity may become severe and increasingly obvious over months if untreated.
- 1.
Closed disruption/attenuation of the central slip insertion (acute, <4 weeks) can be treated with a splint maintaining the proximal interphalangeal (PIP) joint in full extension with the distal interphalangeal joint free to flex, such as in lead author’s patient, with a volar Zimmer splint for 3 weeks, and then mobilized in a PIP spring splint for 5 weeks, or a relative flexion splint for 6 weeks in coauthors’ patients. Additional part-time splinting may be needed.
- 2.
Open laceration of the central slip can be treated by direct repair or a bone anchor.
- 3.
Chronic boutonniere deformity develops if the treatment is delayed, and is treated by reconstruction of the central slip, by lateral band relocation, secondary tendon reconstruction with a tendon graft, or triangular ligament reconstruction and distal Fowler’s or Dolphin tenotomy.
Injury in Zone 4 is often an open injury, causing laceration of the central slip over the proximal phalanx together with partial laceration of the lateral bands, leading to loss of active PIP extension. As it often involves an open wound, Zone 4 injury is easier to diagnose.
Nonsurgical treatment
An acute closed central slip injury can be treated by splinting the injured finger, with the PIP in extension, with the DIP, MCP, and wrist joints free to move, for 3 to 5 weeks. This is then followed by a few weeks of night splinting if necessary. In the lead author’s practice, closed central slip disruption occurring after acute forceful PIP flexion or volar PIP dislocation, when the tendon has not pulled off with a bone fragment, are immobilized in a volar Zimmer splint for 3 weeks, and then mobilized in a PIP spring splint for 5 weeks. The coauthors use a relative flexion splint for 6 weeks. This is a narrow strip splint applied at the proximal phalanges of three fingers, which bridges the injured finger with the neighboring fingers to keep the injured finger in flexion relative to the neighboring fingers. Relative flexion splinting, by putting the injured finger into flexion relative to the other fingers at the MCP joint, eases tension on the attenuated central slip and is now often used in treating this closed injury ( Box 17.2 ).
Surgical treatment
Surgical treatment is indicated for (1) open injuries in Zone 3 and 4, (2) severe flexion deformity with a bony avulsion fracture of the central slip at the base of the dorsal middle phalanx, and (3) extensor tendon injuries with a concomitant PIP joint fracture-dislocation.
If there is an open wound with laceration of the central slip, surgical repair is indicated. Central slip injury in Zone 4 is mostly treated by surgical repair as this is usually an open injury. In Zone 3, the avulsed central slip can be sutured back to the insertion directly ( Fig. 17.14 ), or using a suture anchor or a screw (or K-wire) fixation of the avulsed bone ( Box 17.2 ). Where a K-wire is used, it is not passed across the PIP joint, so does not interfere with early mobilization. The finger is conventionally protected in full extension of the PIP joint after surgery with a finger splint for 3 to 4 weeks. In the lead author’s practice, the bone fragment is reattached by suture to a horizontal bone hole in the dorsum of the base of the middle phalanx or a bone anchor. The finger is then splinted for only 2 weeks and then mobilized in a PIP spring splint for 4 weeks. If a K-wire is used to fix the avulsed bone, the K-wire can be removed 4 to 5 weeks after surgery.
In Zone 3, the three parts of the extensor are only loosely bound together and do not function as a single tendon. Consequently, exactly what has been divided in open injuries is uncertain on preoperative examination, except when all three parts have been cut and the PIP sits in full flexion. When only one lateral band is divided, the finger can be moved immediately after tendon repair without splinting as the DIP joint will extend with only one lateral band functioning. Having the repair adhere is more of a problem than loss of function of one lateral band should the repair rupture. Where the central slip has been divided, with or without one, or both, lateral bands also divided, everything must be repaired. In the experience of the lead author, temporary oblique K-wire fixation of the PIP joint for 2 to 3 weeks is often convenient as it takes this time for the overlying soft tissues and skin to heal to a degree that will tolerate the direct pressure of a splint on the dorsum of the joint. During this period, the lateral bands are mobilized from the first postoperative day by active DIP movement, except when both lateral bands have been repaired, when DIP mobilization is delayed until the third week. After removing the K-wire, the finger is mobilized in an armchair spring splint or a dynamic outrigger for a further 5 weeks. Both splints can be modified to restrict flexion of only the PIP or both interphalangeal (IP) joints.
Injury in Zone 4 is mostly treated by surgical repair as this is usually an open injury. In this zone, the three constituent tendons are so interwoven that this is, essentially, a single and substantial tendon, which will survive suturing and early movement in splints. Given the curved shape of the underlying skeleton, a lacerating injury is often partial, and, if less than 50% of the total tendon width, the repair can be mobilized immediately without protection. To avoid tethering, all other repairs are also mobilized immediately but in a dynamic splinting system, either a dorsal outrigger or volar “armchair” splint, which holds both the PIP and the DIP in extension at rest and allows flexion against resistance.
In exceptional circumstances, simple lacerations at these levels can be treated successfully without surgery, by completely immobilizing the PIP in extension for 4 weeks and then mobilizing the finger in a dynamic splint for another 4 weeks.
Outcomes
Kayalar et al reported 16 patients who underwent surgical repair for isolated simple central slip injuries in Zone 3. The central slip was repaired directly. The patient was instructed to actively flex the finger over a short range without remarkable flexion. Functional results were assessed using the Strickland criteria. After mean follow-up of 58 months (range 8 to 120 months), an excellent result was noted in 15 patients and a good result in one patient. Pratt et al reviewed 31 fingers in 27 patients with open central slip (Zone 3) injuries. After surgical repair, a combination of immobilization and controlled active mobilization was performed. All fingers achieved an excellent or good recovery with a mean PIP flexion of 94 degrees and a mean DIP flexion of 57 degrees.
Treatment of delayed presentation
Some closed central slip injuries do not present immediately as the lateral bands remain on the extensor surface of the joint and continue to extend the finger. With ongoing movement, the tear is presumed to extend proximally between the central slip and the lateral bands, and the latter descends laterally off the extensor surface and can no longer extend the joint, which is held in slight flexion.
The differential diagnosis of this slightly swollen joint is a volar plate contracture. A careful history of the nature of the injury and pressure with the tip of a biro on the base of the middle phalanx, on each surface, will usually identify the primary pathology. The Elson test may also be used ( Fig. 17.15 ): the PIP joint is flexed to 90 degrees over the edge of a table and the middle phalanx extended against resistance. Without a functional central slip, PIP extension is weak and the DIP goes tight in extension as the lateral bands tighten. If the central slip is intact, the PIP extends and the DIP remains slack. Having established the pathology, most will respond to conservative splinting, as above, however long after the injury the patient presents, provided the PIP can be passively extended fully.
Treatment of complex dorsal injuries
The primary surgical management of complex dorsal injuries at this level with any combination of skin, joint, and/or bone and tendon problems is oriented toward creating a stable skeleton with good skin cover and an intact extensor tendon to allow movement of the tendon as early as possible, either free if the tendon is longitudinally intact or in a dynamic splint if it has been repaired, to avoid tendon tethering while allowing skin healing.
Tendon loss.
In an acute situation, small segments of missing tendon can be replaced using the same techniques used to reconstruct the central slip in the Boutonniere deformity. With larger tendon losses, long lengths of tendon graft are needed. We usually reconstruct the tendon in two stages. The risk of tendon tethering is very high in these injuries, so primary grafts are likely to adhere. A secondary consideration is the need for the flexor tendons and the joints to be mobilized quickly after this degree of injury, which is less easy if an extensor tendon graft has to be protected. A third, mechanical consideration is that it is difficult to keep a tendon on the curved dorsal surface of a MCP or PIP joint while mobilizing these joints into flexion. Using two-stage reconstruction, the rod creates a tunnel for the tendon, and the scar formation lateral to the tunnel prevents lateral slippage of the graft. The disadvantages of the two-stage procedure is the need for outrigger extension of the PIP and preventing secondary volar plate contracture of the PIP joint.
Tendon shredding.
With severe bone and skin injuries, shredding of the tendon is common. Where the tendon is intact, or partially intact, longitudinally, it is often possible to suture the “shreds” into something of a tendon and mobilize the finger very quickly postoperatively. The alternative of excision and tendon graft replacement, whether in one or two stages, is more time-consuming. Both risk tendon tethering.
Skeletal damage.
Associated proximal phalangeal fractures are the most common factor to lead to complications ( Fig. 17.16 ). Simple fractures of these phalanges are common and, even when the extensor tendon is undamaged, frequently cause tendon tethering. Severe injuries are often complicated by skin loss and tendon shredding, making tethering even more likely. With the exception of the elderly with dorsal angulated fractures, in whom a loss of full flexion is accepted in exchange for simplicity of management by resting the hand on a plaster for 2 to 3 weeks, then mobilization, these fractures are internally fixed in most patients to allow earlier movement of the finger(s) ( Fig. 17.16 ). Nevertheless, extensor tethering remains a regular source of secondary surgery. The methodology of bone fixation is debated. It is most useful to augment any surface wire or mini-plate fixation of unstable comminuted fractures of the proximal phalanx with a dowel of either cortical bone or metal in the medulla of the bone. This greatly strengthens the bone fixation , allowing early movement without the risk of a surface fixation slipping when power flexing begins, usually at about 4 to 6 weeks.
