CHAPTER 78 EXTENSOR TENDON SURGERY
MARK E. PUHAINDRAN
The extensor system is complex and intricate. A fine balance exists between the long extensors, innervated by the radial nerve, and the intrinsic muscles of the hand, innervated by the median and ulnar nerves. The superficial location on the dorsum of the hand makes the extensor system vulnerable to injury. Because small variations in tendon length and tension result in significant functional deficits, outcomes of treatment may be suboptimal.
The purpose of this chapter is to review the anatomy of the extensor system and the surgical management and rehabilitation of commonly encountered injuries and conditions that affect the extensor system.
There are 12 extensor muscles, all of which are innervated by the radial nerve directly or its terminal motor branch, the posterior interosseous nerve (PIN). The brachioradialis, anconeus, and extensor carpi radialis longus (ECRL) are innervated by the radial nerve. The extensor carpi radialis brevis (ECRB) innervation may arise from the radial nerve or the PIN. All other extensor muscles are innervated by the PIN. The most distally innervated muscle is the extensor indicis proprius (EIP).1 The brachioradialis, ECRL, and ECRB muscles originate from the lateral supracondylar ridge and epicondyle of the distal humerus, and from the mobile wad of muscles in the proximal forearm. The extensor digitorum communis (EDC), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), and anconeus originate from the common extensor origin at the lateral epicondyle of the humerus, and the other muscles originate more distally in the forearm. The extensor muscles are arranged in two layers, superficial and deep, within the forearm—the anconeus, ECRL, ECRB, EDC, EDM, and ECU form the superficial layer. The deep layer consists of the supinator, abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and EIP.2
At the wrist, the tendons of the extensor muscles run under the extensor retinaculum and are separated into six compartments (five fibro-osseous and one fibrous). The first compartment contains the APL and EPB tendons and the second contains the ECRL and ECRB tendons. The EPL winds around Lister tubercle and occupies the third extensor compartment. The EDC and EIP tendons run in the fourth compartment, the EDM runs in the fifth compartment—the only fibrous compartment—and the ECU runs in the sixth compartment (Figure 78.1).3
Over the dorsum of the hand, there are bands, the juncturae tendinae, that connect the ring EDC tendon to the EDC of the middle and small fingers, as well as from the middle to the index finger.4 The EIP and EDM tendons lie ulnar to their respective EDC tendons and insert at the level of the metacarpophalangeal joint (MCPJ).
At the MCPJ, the extensor tendon is held in position by the sagittal bands, a sling that arises from the volar plate of the MCPJ and intermetacarpal ligaments.5 These bands facilitate extension of the MCPJ through a lasso effect around the base of the proximal phalanx. The extensor tendon becomes broad and thin over the dorsum of the proximal phalanx where the EDC tendon trifurcates, with the central portion becoming the central slip that inserts into the base of the middle phalanx, and the lateral portions joining the tendons of the interosseous muscles and lumbricals to form the lateral bands (Figure 78.2). These lateral bands come together over the middle phalanx and form the most distal part of the extensor tendon that inserts into the base of the distal phalanx.6 The lateral bands translate in a palmar–dorsal direction relative to the axis of rotation during proximal interphalangeal joint (PIPJ) flexion and extension and are prevented from subluxation in a dorsal direction by the transverse retinacular ligament (TRL), or in a volar direction by the triangular ligament, found over the dorsum of the middle phalanx. The oblique retinacular ligaments, originally described by Landsmeer,7originate from the distal aspect of the second annular pulley and travel obliquely and insert into the extensor tendon over the middle of the distal phalanx. They are not easily identified in all digits and help coordinate extension in between the PIPJ and DIPJ (distal interphalangeal joint).
Many variations to the classic anatomy of the extensor system are found.8 Examples include the presence of accessory muscles like the extensor carpi radialis intermedius and extensor medii proprius, which are present in 10% of hands.9 Variations exist in the number of EDC slips to the digits and anatomy of the juncturae tendinae over the dorsum of the hand.8 There is also variation within the EDC muscle, which has been described to have a common muscle belly. Intramuscular branching of the nerve in the muscle may occur,10 and this allows independent index finger extension following EIP harvest for tendon transfer.
FIGURE 78.1. Dorsal wrist compartments. APL, abductor pollicis longus; EPB, extensor pollicis brevis; ECRL, extensor carpi radialis longus; ECRB, extensor carpi radialis brevis; EPL, extensor pollicis longus; EIP, extensor indicis proprius; EDC, extensor digitorum communis; EDM, extensor digiti minimi; ECU, extensor carpi ulnaris.
FIGURE 78.2. Extensor tendon complex over the dorsum of a digit. EDC, extensor digitorum communis.
EXTENSOR TENDON INJURIES
Finger extension is achieved through a balance of two separate systems—the radial nerve innervated extrinsic extensors and the intrinsic muscles, innervated predominantly by the ulnar nerve, with some contribution from the median nerve. Distal to the MCPJ, the extensor tendon is thin, making core repairs difficult. Furthermore, there is a precise balance between the various components of the tendon during movement, which is difficult to restore following injury.6 Although there is more excursion of the tendon at the level of the wrist, there is minimal excursion at the level of the PIPJ and DIPJ, with 0.6 mm of excursion for every 10° of movement at the DIPJ; hence, tendon shortening at this level from tendon repair will result in significant loss of movement.11
Extensor tendon injuries are classified based on eight anatomical zones described by Kleinert and Verdan.12 Odd numbered zones are located over the joints, whereas even numbered zones are found in between (i.e., zone 1 lies over the DIPJ, zone 3 over the PIPJ, zone 5 over the MCPJ, etc.) (Figure 78.3). In the thumb, the interphalangeal joint (IPJ) is zone 1 and MCPJ is zone 3.
Several difficulties and pitfalls in the clinical assessment of patients with acute extensor tendon injuries are highlighted:
I. Juncturae tendinae—Digit extension at the MCPJ may still be possible after complete EDC laceration because of the variable interconnections between the EDC tendons over zone 6.8 This has to be taken into account when assessing patients with dorsal hand lacerations. Surgical exploration is frequently the best way to determine if the EDC tendon has been cut.
FIGURE 78.3. Zones of injury for the extensor system. DIP, distal interphalangeal; PIP, proximal interphalangeal; MP, metacarpophalangeal.
II. Testing for the EPL—The EPL tendon functions mainly to extend the IPJ of the thumb. It also extends the MCPJ (together with the EPB) and the carpometacarpal joint (together with the APL), and it adducts the thumb toward the palm when the thumb is in full extension. However, the EPB, APB, and FPB can also cause IPJ extension due to their insertion on the extensor apparatus. Hence, the best way to assess for EPL function to ask the patient to lift the thumb up while the palm placed flat on a table (Figure 78.4).
III. Testing for a closed central slip rupture—This test was first described by Elson.13 The PIPJ of the patient is maximally flexed by the examiner and the patient asked to extend the PIPJ while the examiner resists (Figure 78.5). Should the central slip be ruptured, minimal extension power is felt at the PIPJ while more power is felt at the DIPJ because of the force generated through the intact lateral bands.
FIGURE 78.4. Testing of EPL function by asking the patient to place the palm flat on the table and lift the thumb.
MANAGEMENT OF ACUTE EXTENSOR TENDON INJURIES
Zone 1 Injuries
Injuries over the DIPJ (zone 1 injuries) have been classified into four types by Doyle (Table 78.1).14 Type I or closed injuries are the most common and can be treated by splinting the DIPJ in extension for 6 to 8 weeks, followed by night splinting for another 6 weeks. Patients presenting a few months after injury can still be treated using this technique.15 Alternatively, the joint can be splinted internally using a Kirschner wire for patients who cannot tolerate an external splint or for patients who must continue working, such as a surgeon. Patients are advised to continue moving the PIPJ while the DIPJ is splinted. Long-term, slight extensor lag of 10° is to be expected following conservative treatment, and patients are counseled about this limitation at the start of treatment.16 A similar splinting protocol can also be used for patients with closed thumb mallet injuries.17
FIGURE 78.5. Elson’s test for central slip integrity.
Type II injuries are lacerations that involve the tendon and can be treated with wound debridement and repair of the skin and tendon. The sutures can be used to catch and oppose both the skin and the tendon at the same time, or they can be repaired separately. This is followed by splinting just as in type I injuries.
Type III injuries are those with loss of skin and tendon and may require skin coverage and/or tendon grafts. Postoperative splinting of the DIPJ is required for 6 weeks and is more easily accomplished using a Kirschner wire to avoid the need for splint removal during dressing changes, and with it the risk of jeopardizing the tendon repair.
Type IV injuries include fractures of the distal phalanx. Type IVA injuries, also known as Seymour’s fractures, are fractures through the physis in children.18 Open fractures must be sought under the eponychial fold where they can be hidden by the overlying nail plate. Open wounds are debrided, irrigated, and the fracture treated with an axial Kirschner wire that spans the DIPJ. Type IVB fractures involve between 20% and 50% of the joint surface and type IVC fractures involve more than 50% of the joint surface and have volar subluxation of the distal phalanx. Both operative treatment with extension block pinning and nonoperative treatment with splints are acceptable, with no technique of intervention clearly superior to the other.19 Surgical fixation is generally preferred, especially for patients with type IVC injuries, because surgical intervention allows accurate restoration of the articular surface and possibly reduces the risk of osteoarthritis developing in the future.
Zone 2 Injuries
Repair of a laceration involving less than 50% of the extensor tendon in zone 2 is not required, and active mobilization can be commenced once the wound has healed. A laceration involving more than 50% of the tendon is repaired with a running suture using a 5-0 nonabsorbable suture. It is not possible to place core sutures in the tendon in zone 2 because the tendon is too thin. After repair, the DIPJ should be splinted or pinned in extension for 6 weeks while the PIPJ is actively mobilized. Zone 2 injuries of the thumb are treated in a similar way.
Zone 3 Injuries
The treatment for injuries in zone 3 depends on which component (central slip or lateral band) is injured, as well as the extent of injury. Closed central slip injuries can be treated by pinning or splinting the PIPJ in extension for 6 weeks while the DIPJ is actively mobilized. If the central slip is avulsed with a large bone fragment, then fixation with a Kirschner wire or screw is required.
Open zone 3 injuries frequently breach the joint capsule and involve the PIPJ, so a proper debridement is performed prior to tendon repair. Lacerations involving just one lateral band do not require repair, though lacerations that involve more than 50% of the central slip should be repaired with core sutures, if possible, or attached to the bone using bone tunnels or a suture anchor if there is insufficient tendon substance distally. The PIPJ is pinned or splinted in extension. Chronic central slip injuries can result in boutonniere deformities, and the management is discussed later in this chapter and in Chapter 91.
Zone 4 Injuries
The extensor tendon is draped over much of the dorsal and lateral surfaces of the proximal phalanx; hence, lacerations over the dorsum or open fractures often result in injuries to the extensor tendon. Lacerations involving more than 50% of the tendon can be repaired using core sutures through the thicker central slip and lateral bands using 4-0 prolene, supplemented with a continuous running repair using 5-0 prolene.20 Postoperatively, early motion can be started with dynamic extension splint in order to minimize adhesions. Alternatively, static splinting is instituted for 4 weeks before mobilization is commenced.
Thumb zone 4 injuries occur over the metacarpal, where the tendons are thick enough to perform standard repairs with core sutures using 3-0 or 4-0 sutures supplemented by epitendinous repairs using 5-0 prolene. This is followed by protected early motion postoperatively.
Zone 5 Injuries
Lacerations over the MCPJ are approached with caution because they are often human bites, resulting from a “punch” to the mouth, with the teeth causing a penetrating injury. Patients often omit the history of a fight, and the external wound may appear small and innocuous. Most bite wounds involve the MCPJ, and a careful wound exploration is performed to look for breach in the dorsal capsule of the joint (Figure 78.6). A thorough debridement and washout of the joint should be done, and tendon repair deferred till the wound is considered clean. Failure to recognize and treat these human bite injuries can result in septic arthritis and destruction of the MCPJ and tendon.21 Tendon lacerations in zone 5 can be repaired with strong core 3-0 or 4-0 sutures supplemented with an epitendinous suture using 5-0 prolene.
FIGURE 78.6. Human bite injury after a fight with breach of the joint capsule (arrow). A. Pre-op appearance. B. Intraoperative appearance.
Injuries involving the sagittal band of the extensor tendon can result in subluxation of the tendon to the side opposite to the injury. Closed ruptures are seen more frequently than open lacerations, and subluxation takes place after more than two-thirds of the proximal band is cut. Open injuries are treated by simple mattress sutures followed by buddy splinting to the adjacent finger while allowing gentle mobilization. Closed sagittal band injuries can occur following blunt trauma or resisted extension of the digit and often involve the radial side of the middle and ring fingers. The patient may complain of a snapping sensation on flexion due to the tendon subluxing, and the finger may be adducted ulnarly. In addition, the patient may have difficulty initiating extension when the MCPJ is in full flexion even though the tendon is in a central position during full extension.22 When assessing these injuries, the opposite hand should be examined as patients with hyperlaxity have nonpathologic tendon subluxation. Patients with closed sagittal band injuries seen within 3 weeks of injury can be treated with flexion block splints that limit flexion of the MCPJ and allow the tendon to heal in the reduced position. Active MCPJ and PIPJ movement is allowed within the splint, which should be worn continuously for up to 8 weeks.23 Patients seen after 3 weeks, and those who have failed conservative treatment with splinting, are treated surgically. Several techniques of surgical repair have been described for reconstruction of sagittal band injuries, and these include direct repair or the use of slips of the EDC or juncturae tendinae as slings to centralize the tendon.
Zone 5 of the thumb lies over the wrist. Injuries to the extensor tendon here can be treated with core suture repairs supplemented with epitendinous sutures, followed by splinting and protected active mobilization.
Zone 6 Injuries
Complete laceration of an EDC tendon in zone 6 may not result in an extensor lag at the MCPJ because of the juncturae tendinae that interconnect the EDC tendons. It is advisable, therefore, to surgically explore lacerations on the dorsum of the hand. Because the extensor tendons are thick in zone 6, core suture repair followed by an epitendinous suture are performed. Good outcomes can be expected for zone 6 tendon repairs because strong repairs can be performed, allowing aggressive rehabilitation, and there is also adequate soft tissue coverage.
Zone 7 Injuries
To perform tendon repairs in zone 7, the extensor retinaculum is opened to gain access to the extensor tendons. A “Z” or oblique incision is used to facilitate repair of the extensor retinaculum following repair. Tendon repair can be performed using similar techniques as in zone 6, though the surgeon must be prepared to extend the wound to the forearm in order to retrieve retracted tendons. The EPL tendon should be transposed subcutaneously following repair of the ECRL/ECRB to protect it from the suture knots of the tendon repair as this can result in tendon rupture.
Zone 8 Injuries
Injuries at the level of the musculotendinous junction or in the muscle are difficult due to the poor suture holding in muscles.24 Repair of the intramuscular tendon can be performed and augmented by a repair of the muscle belly, followed by static splints postoperatively. In addition, the PIN should be explored and the intra- and extra-muscular portions repaired, especially for proximal injuries, because this will help preserve function of the distal muscles (EPL, EIP, APL, and EPB).25
REHABILITATION FOLLOWING TENDON REPAIR
Unlike flexor tendons, the extensor tendon in zones 1 and 2 is thin, making strong tendon repairs with core sutures difficult. Furthermore, core sutures will also cause tendon shortening and excessive bulk of the repair. Hence, static splinting for 6 to 8 weeks is normally required following tendon repair in zones 1 and 2.25 The tendon in zones 4 to 8 is thicker and amenable to strong tendon repairs; hence, early protected mobilization with dynamic splinting or controlled active movement is possible.26 Complications encountered following extensor tendon repair include extensor lag, which can be due to failure of the tendon repair, stretching of the tendon, or tendon adhesions. Conversely, there can be loss of flexion, which can be due to adhesions or excessive tensioning of the tendon repair. Tenolysis can be considered 6 months after surgery if there is no further improvement with therapy.
CHRONIC EXTENSOR TENDON PROBLEMS
Four chronic conditions that affect the extensor tendon system are addressed in this section:
1. Swan neck deformity (SND)
2. Boutonniere deformity
3. Tendon loss and tendon grafts
4. Attritional tendon rupture and tendon transfers
Swan Neck Deformities (Chapter 91)
SNDs are characterized by PIPJ hyperextension, with reciprocal flexion at the DIPJ and MCPJ, and it can be caused by a variety of conditions, from rheumatoid arthritis to cerebral palsy. A patient with SND has impaired function due to an inability to make a full fist due to loss of PIPJ flexion.
SNDs can develop due to pathology at the PIPJ, DIPJ, MCPJ, or the wrist. Hence, it is important to understand how pathology at each of these joints can contribute to the deformity.27
PIPJ. Synovitis at the PIPJ can cause attenuation of the volar plate and TRL, which allows dorsal translation of the lateral band, as well as destruction of the flexor digitorum superficialis insertion. This allows hyperextension of the PIPJ, which in turn results in increased tension in the flexor digitorum profundus tendon, as well as loss of tension in the lateral bands, resulting in DIPJ flexion. Over time, adhesions develop and convert this into a fixed deformity.
MCPJ. Synovitis at the MCPJ can lead to weakening of the insertion of the long extensors into the base of the proximal phalanx, causing the force to be transmitted to the base of the middle phalanx, resulting in PIPJ hyperextension. The synovitis can also cause weakening of the volar plate, resulting in subluxation of the MCPJ, allowing adhesion and later shortening of the intrinsic muscles, further contributing to the PIPJ hyperextension and SND.
DIPJ. Rupture of the terminal extensor tendon, which can occur following trauma or due to synovitis, allows proximal migration and relaxation of the lateral bands. Extensor power is then concentrated on the central slip, resulting in PIPJ hyperextension and SND as the volar restraints weaken over time.
Wrist. Synovitis at the wrist can result in carpal collapse, carpal supination, and ulnar translation. Carpal collapse causes relative lengthening of both long flexors and extensors, allowing the intrinsic muscles to overpower their action and cause MCPJ flexion and PIPJ extension, which in time can lead to an SND.
SNDs have been classified by Feldon et al. into four types, depending on PIPJ mobility and the condition of the joint surfaces, that determine surgical treatment28 (Table 78.2). The main objective is to restore active flexion at the PIPJ if possible, or to fuse the joint in a functional position should this not be possible.
Boutonniere deformities are characterized by a flexion deformity of the PIPJ, with reciprocal extension at the MCPJ and DIPJ. It is more an aesthetic than a functional problem, because patients can still make fists and grasp objects. Boutonniere deformities develop due to pathology at the PIPJ alone, unlike SND. Initially, the central slip becomes dysfunctional, due to either an injury or attenuation secondary to synovitis from inflammatory disorders like rheumatoid arthritis. Second, the triangular ligament stretches and allows the lateral bands to sublux in a volar direction, maintaining persistent PIPJ flexion. The ruptured central slip also allows the force from the lumbricals and interosseous muscles to be transmitted directly to the distal phalanx, resulting in DIPJ extension. Over time, a chronic boutonniere deformity with fixed joint contractures develops.
Boutonniere deformities can be classified into four stages29 (Table 78.3). Stages I and II can be treated with splinting,30 to achieve full PIPJ extension while DIPJ passive flexion exercises are done. Splinting should be continued for at least 2 to 3 months to gain the maximum possible correction, and surgical release of the joint considered only if splinting fails, especially for stage III disease. Any tendon surgery should be delayed until good passive motion of the joint is restored. Options include central slip reconstruction, distal extensor tenotomy, and lateral band mobilization. Care must be taken not to jeopardize flexor function in an effort to restore PIPJ extension, since this will result in a greater functional deficit than the Boutonniere deformity.
Extensor Tendon Loss and Tendon Grafts
Tendon grafts are indicated in cases where there is loss of tendon substance but there remains a functional neuromuscular unit. The most commonly used tendon graft is the palmaris longus, due to its ease of harvest and minimal donor-site morbidity. Tendon grafting should be performed in a well-vascularized and noninfected bed, with good passive range of movement of the joints that the tendon crosses. Frequently, tendon loss in dorsal hand injuries is accompanied by soft tissue loss and soft tissue reconstruction is required before tendon grafting.
Attritional Tendon Rupture and Tendon Transfers
The most common tendon transfers for extensor function include those done to restore thumb, digit, and wrist extension following radial nerve injuries or following attrition ruptures due to rheumatoid arthritis or following distal radius fractures. Attrition ruptures following distal radius fractures can occur whether the fractures are treated with a cast or with internal fixation, whether with volar or dorsal plates.31 Often, direct repair of the ruptured tendons cannot be performed due to the excessive fraying of the tendon, and tendon transfers are required. Donor musculotendinous units for tendon transfer should have a low donor morbidity, synergistic functions, and similar excursion and force generation as the recipient. The EIP tendon is an ideal donor to the EPL to restore thumb extension, because it has a synergistic action, is easily harvested, and has minimal donor morbidity. Independent index finger extension is still possible after this transfer.32
In chronic zone 6 tendon injuries, tendon transfers may not be required, with side-to-side repairs of the EDC sufficient to restore function. At times, surgical repair may not even be necessary if the function has been adequately substituted by adjacent tendons via the juncturae.
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