Outline

Recent reports concerning management of zone 5 flexor tendon injuries have identified this injury as more significant in terms of digital motor dysfunction than previously thought. Recent research has shown that, despite a small risk of losing differential tendon gliding when the superficialis tendons are repaired, repair of both sets of tendons is beneficial and to be recommended.

Arguably, flexor tendons are more commonly injured in the flexor aspect of the distal forearm (zone 5) than in any other zone, yet less is written about the management after tendon divisions in this zone than in any other. This may relate directly to a comment by Kleinert and his colleagues over 30 years ago that “tendon gliding in this area should not be a problem.”¹

Clinical Features

These cases are an everyday feature of upper limb trauma units. The mechanisms of injury include laceration by broken glass (alcohol-related in many instances), sharp machinery at work, knives, and self-inflicted injuries. The flexor aspect of the distal forearm transmits eighteen longitudinal structures superficial to the wrist and carpal joints, with the pronator quadratus lying transversely across the wrist area between the skeleton and these longitudinal structures. Any, or all, of these structures can be injured. Most emergency surgery is concerned with the (longitudinal) running flexor tendons, radial and ulnar arteries, and the median and ulnar nerves. A “spaghetti” wrist is defined as one with a flexor laceration in which at least 10 of the 15 longitudinal structures (11 tendons, 2 arteries, and 2 nerves, excluding the palmaris longus) have been transected.² Often forgotten are the palmar branches of the median and the ulnar nerves, division of which is almost inevitable if the main longitudinal structures are divided. These can, occasionally, cause significant problems of end-neuroma pain if ignored at primary surgery.³^–⁵

The wounds are generally transverse, or nearly so, across the wrist. Access is easiest by converting the wound to an “H” or “Z.” Whatever is done with the skin, it is unusual to have healing problems with the skin as whatever extension incisions of the primary laceration are made surgically to aid access, the flaps so designed (without thought) will be broad-based, short fasciocutaneous flaps with the radial and ulnar arteries feeding directly into their bases. It is rare to be unable to achieve safe primary wound closure for this reason.

The tendon repairs are carried out largely using the techniques used in zone 2, so this will not be discussed further, except to say that the anatomy mostly allows for larger core and circumferential sutures than in zones 1 and 2. The tendon repairs are, theoretically, easier than in the fingers because the tendons are not confined within a tendon sheath. However, the multitude of structures and the associated nerve and, sometimes, arterial injuries make flexor wrist injuries daunting and long operations for junior training surgeons and these injuries should not be dismissed by seniors as “good training cases,” to be left without help to junior surgeons. The many structures to be repaired can turn these operations into marathons in inexperienced hands! It is, also, often the case that the individual tendons are not cut transversely but obliquely, with different tendons cut at different levels relative to the carpal canal or, even, within the carpal tunnel by shards of glass. The tendons may be “shredded” longitudinally, making textbook repairs difficult. Where multiple structures are divided or surgery is lengthy and, particularly, when the tendon repairs approximate to the proximal edge of the carpal ligament on full digital extension, the carpal tunnel should be decompressed to avoid both the development of secondary carpal tunnel syndrome ⁶ and loss of extension as a result of the tendon repairs impinging on the carpal ligament on full extension of the wrist and digital joints.

Following surgery, these injuries are mobilized using the same regimes as zone 2 injuries and these are not discussed further. When the carpal ligament has been divided, the fingers are mobilized with the wrist splinted in the neutral position or slight extension. In other circumstances, a straight wrist or only slightly flexed wrist position may be preferred, but it should be remembered that the 30° flexed wrist position originally advocated for rehabilitation is little different from the Phalen test we use to irritate the median nerve when diagnosing carpal tunnel syndrome and may precipitate this problem postoperatively if the carpal ligament remains intact.

One point about rehabilitation of zone 5 flexor tendon repairs that is unique to this zone is that there will be no intrinsic proximal interphalangeal (PIP) joint extensors of the ulnar fingers if the ulnar nerve has also been divided. This requires that the metacarpophalangeal (MCP) joints of these fingers be held in flexion during the 4-week postoperative splinting period to activate PIP extension by the long extensor tendons, if PIP joint contractures are to be avoided.⁷

It is also frequently forgotten by surgeons what may be being asked of a patient with a spaghetti, or near-spaghetti, wrist. At 1 to 3 days after surgery, the patient is being expected to move a large number of swollen tendons, possibly bristling with unabsorbable suture ends and tightly bound down by swollen fasciocutaneous flaps across repaired median and/or ulnar nerves. This is painful! Mobilization may be hindered by lack of adequate analgesia, making the therapist’s job impossible and the ultimate result less than perfect.

The Flexor Digitorum Superficialis Tendons: To Repair or Not

Until the introduction of early mobilization of flexor tendon repairs in the latter half of the twentieth century, it was believed that repair of divided flexor digitorum superficialis (FDS) tendons following wrist lacerations in which both the superficial and deep digital flexor tendons had been divided caused adhesions with limitation of excursion of the associated fingers.^8,⁹ However, the superficial digital flexors increase the grip of the hand and make pinch and flexion of the PIP joint more stable, in addition to providing superior individual finger flexion.¹⁰ For these reasons and, possibly, reassured by the comment that “tendon gliding in this area should not be a problem,”¹ repair of the superficial digital flexors became routine with the advent of early mobilization.^1,¹⁰^–¹² The possibility of PIP hyperextension following failure to repair the FDS tendon in zone 5, although of less significance, is suggested by a single case report.¹³ The possibility of adhesions causing limitation of finger excursion and/or loss of independent FDS action, despite early mobilization, was not researched at that time.

The literature on injuries to the flexor aspect of the distal forearm immediately prior to 2000 is scant.^11,¹³^–¹⁶ Two of these reports were small and concentrated their reviews mainly on the injuries to the median and ulnar nerves and not on the outcome of the finger flexor tendon injuries.^11,¹⁶ In 1985, Puckett and Meyer reviewed 37 patients who suffered a minimum of three and an average of eight completely transected longitudinal structures at the wrist.¹⁵ One-third of their patients had “spaghetti” wrists. The hands were mobilized postoperatively using a Kleinert regimen. Tendon function was considered to be excellent when digital range of motion was 85% to 100% of normal or finger flexion brought the fingertip within 1.0 cm of the distal palmar crease; good with 70% to 84% of normal digital range of motion or the fingertip within 2.0 cm of the distal palmar crease; fair with 50% to 60% of normal digital range of motion; or poor with fixed contractures or adhesions. Thirty-three (97%) of 34 wrists available for assessment were reported to have good or excellent ranges of digital motion and one patient to have a fair range of motion. The method by which the overall results were derived from the assessment of the individual fingers was not given. No tendon ruptures occurred in their series.

In 1992, Stefanich et al ¹³ reported independent FDS action in only 30% of a retrospective series of 23 patients who underwent zone 5 flexor tendon repairs that were mobilized using Kleinert’s early mobilization (active extension-passive flexion) regimen. In this series, five patients had transection of a single digital (finger or thumb) flexor tendon and 18 patients had transections of multiple digital flexor tendons. The total active motion (TAM) of the associated digits as well as for the corresponding unaffected digits was calculated, as suggested by the American Society for Surgery of the Hand, but, unfortunately, the associated scoring system of excellent/good/fair/poor was not recorded. Instead the average TAM (as a percentage of the uninjured contralateral digit) was given for the whole group of 23 patients for each of the five digits. Sixteen of the 23 patients regained full digital flexion of all digits but the number of digits in these patients that had not suffered flexor tendon injury was not stated. There was an average PIP extension deficit of 8° and distal interphalangeal extension deficit of 4°. Two patients (9%) had extremely limited motion. Rupture of one flexor pollicis longus in one patient and rupture of one ring finger flexor digitorum profundus (FDP) in an additional patient occurred in their series. This report reintroduced the question of adhesion of the flexor tendons after repair of both tendon groups in zone 5 and the possibility that loss of digital excursion and/or independent FDS action is more common than had been assumed.

Subsequent to this small study,¹³ we carried out a larger prospective study¹⁷ over a 2-year period to examine the results of routine repair of both finger flexor tendons in zone 5 followed by early postoperative mobilization using the variant of the controlled active mobilization (active extension-active flexion) regimen described previously and used routinely in our unit.¹⁴ In this study, after mobilizing the injured hands using an early active motion regimen, good or excellent results were achieved in 90% of fingers that had repair of completely divided flexor tendons in zone 5 and independent FDS action was achieved in 66% of the fingers. No tendon ruptures occurred in this series. The group of patients with “FDS injuries only” fared better than those with ‘“FDS and FDP” injuries in terms of independent FDS action, the difference being statistically significant. This most probably reflects the difference in magnitude of the total injury to the wrist between those with more superficial injuries and deeper injuries, rather than simply a difference between division of one or two tendon groups. Multivariate analysis showed that the presence of a “spaghetti” wrist injury had a significant adverse effect on the overall hand recovery in terms of independent FDS action but had no significant adverse effect on the overall hand recovery in terms of digital range of motion. While the extensive scar tissue likely to follow a “spaghetti” wrist injury might be expected to eliminate differential gliding of the tendons, the resultant tendon mass appeared to be capable of moving the fingers through a full, or near full, range of motion in most cases. Age was not a significant factor in determining recovery of either independent FDS action or range of digital motion. A statistically significant association between recovery of independent FDS action and recovery of the digital range of motion appears to confirm that wrists that do well with respect to one modality will do well with respect to the other. Those fingers with FDS tendons lying close to the FDP tendons at the wrist—namely, the index and little—are more likely to lose independent FDS action after division and repair of their tendons at the wrist. The little finger had the lowest incidence of independent FDS action in this study. However, those little fingers without independent FDS action after repair of the FDS at the wrist in this study may include fewer failures of mobilization than is suggested by our figures as it has been shown that the superficialis tendon of the little finger, although present at the wrist, cannot achieve flexion of this finger in one-third of normal individuals.^18,¹⁹

For the first time, an analysis was presented to mathematically to analyze these injuries in terms of the effect on overall hand function rather than by consideration of the individual fingers that had sustained division of flexor tendons at the wrist. This showed that there was a statistically significant interdependence of the flexor systems of the different fingers in those wrists with injuries to the flexors of all four fingers. This indicates that the consequences of this injury in respect of hand function are more complex than the mere sum of its constituent tendon injuries and future attempts to assess the zone 5 injury need to change to reflect this complexity.

Since our study, few reports on zone 5 have been written.²⁰^–²⁴ Two of these studies lend support to the benefit of active, as opposed to passive, mobilization of zone 5 flexor repairs.^22,²³ In 2005, Wilhelmi et al reviewed 168 zone 5 tendon flexor divisions²⁴

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