Traumatic Extensor Carpi Ulnaris Disruption: Subluxation, Dislocation, Rupture

Traumatic disruption of the extensor carpi ulnaris (ECU) tendon mechanism manifesting as subluxation, overt dislocation, or occasionally rupture is a relatively common sports injury, especially among racquet or stick-handling athletes. Characteristically, the injured person experiences localized pain, tenderness, and swelling at the ulnar aspect of the wrist and a palpable or visible snap over the distal ulna as the forearm rotates from pronation to supination. Painful symptoms and signs are readily reproduced by passive forearm supination combined with wrist ulnar deviation and flexion. This same combination of motions generated by a pathologic force is also the mechanism of ECU injury.

Typically, the condition recurs; with chronicity, ECU disruption is increasingly problematic as tendon subluxation or dislocation becomes a frequent and often disabling occurrence. Surgical treatment is recommended for active persons with symptomatic ECU disruption participating in athletics or other strenuous activities.

ANATOMY, PATHOMECHANICS, AND PATHOANATOMY

The muscle fibers of the ECU typically end as a large-diameter tendon in the distal forearm. At the wrist, beneath and independent from the cover of the dorsal retinaculum ( Fig. 14-1 A), the ECU tendon enters the sixth compartment, which is a distinct fibro-osseous tunnel that overlies and is attached to the distal 2.0 to 3.0 cm of the nonarticular aspect of the ulna. Well constrained within its osseous groove at the distal ulna by a fibrous sheath, the ECU tendon enhances stability of the distal radioulnar joint (DRUJ) as it courses distally across the ulnar carpus to insert at the base of the fifth metacarpal ( Fig. 14-1 B).

The soft tissue component or lining of this separate sixth-compartment fibro-osseous tunnel constitutes a duplication of the deep antebrachial fascia, which inserts on the borders of the osseous groove, enclosing the ECU tendon, at the distal ulna, and has been termed the ECU subsheath. The subsheath is further reinforced at its ulnar attachment or medial wall by longitudinal fibers, termed the linea jugata. These fibers originate distally from the base of the ulnar styloid and spread proximally and dorsally over the ECU tendon, merging with the retinaculum and the antebrachial fascia. The linea jugata creates a dynamic septum or restraint permitting physiologic ulnar translation of the ECU tendon during forearm rotation but preventing pathologic subluxation of the tendon at the extremes of supination. The dorsal retinaculum courses over this subsheath but does not attach to the distal ulna; rather, it inserts on the pisiform and triquetrum, thereby allowing unrestricted forearm pronation and supination. The unique anatomic features of the sixth compartment with its distinctive fibro-osseous tunnel play a critical role in maintaining ECU stability, ensuring that the tendon is in close proximity to the distal ulna throughout the extremes of wrist motion.

The ECU tendon within its intact subsheath is also an important stabilizer of the DRUJ. Spinner and Kaplan, in their clinical and anatomic evaluation of the ECU, emphasized the major contribution of the sixth compartment to ulnar wrist stability. Their study explicitly demonstrated that a separate fibro-osseous tunnel attached to the dorsum of the distal ulna—and not the extensor retinaculum—stabilizes the ECU tendon. Furthermore, this study affirmed that an intact ECU tendon, maintained within its fibro-osseous tunnel, also is a key stabilizer of the DRUJ. Moreover, the ECU sheath itself, through its attachments to the dorsal groove of the ulnar head, the dorsal radioulnar ligaments, and the ulnar carpus, augments the ulnar aspect of the dorsal wrist capsule, thus providing an additional stabilizing influence. Clearly, integrity of the sixth compartment is essential for optimal stability of both the ECU tendon and the DRUJ.

Although the unique fibro-osseous anatomy of the sixth compartment is critical to ECU tendon and DRUJ stability, it also creates, of necessity, a restraint to free excursion of the ECU tendon, a biomechanical feature that increases tension on the tendon and its sheath during forearm rotation. During pronation, the ECU tendon is located centrally within its osseous groove at the ulnar aspect of the ulnar head, distancing itself from the extensor digiti mimimi (EDM) in the fifth extensor compartment and typically creating a gap between the two tendons. In this position, the ECU tendon adopts an obtusely angled, essentially direct, pathway to its attachment at the base of the fifth metacarpal, which exerts minimal stress on the adjacent subsheath tissues ( Fig. 14-2 A). In supination, however, the ECU tendon translates radially, approximating the EDM and eliminating the intertendinous gap. This radial translation results in a more acutely angled, ulnarly directed change in course of the ECU tendon as it traverses the distal ulna to the fifth metacarpal base ( Fig. 14-2 B). With hypersupination, especially when combined with wrist ulnar deviation and flexion, this ulnar-directed angle abruptly increases. As the ECU muscle contracts, a substantial force is generated ulnarly against the adjacent fibro-osseous tunnel that is prone to cause subsheath injury and tendon subluxation ( Fig. 14-2 C and D). Repetitive stress on the subsheath also may result in stenosing tenosynovitis, especially with chronic overuse as the sheath becomes scarred and contracted.

Because of the recognition of these physiologic, potentially detrimental, stress-provoking positional changes of the ECU tendon during forearm rotation, forceful supination combined with wrist ulnar deviation and flexion is expressly acknowledged as the mechanism of either complete rupture or detachment of the ECU sheath from the distal ulna osseous groove. In both instances, the ECU tendon is destabilized and subluxates ulnarly and volarly over the distal ulna beneath an intact dorsal retinaculum. With increasingly severe injuries, and in more chronic cases, the ECU tendon is prone to complete dislocation from its groove in the distal ulna. With repeated injury, longitudinal or transverse tears may develop in the ECU tendon ( Fig. 14-3 ). Moreover, without treatment, a complete rupture of the tendon may occur.

Inoue and Tamura, in their experience with surgical treatment of recurrent ECU dislocation, described three types of fibro-osseous sheath disruption ( Fig. 14-4 ). In type A lesions, the sheath ruptures at the ulnar border or medial ridge of the osseous groove. Such ruptures are characterized by sheath retraction and scarring, usually precluding direct repair and necessitating sheath reconstruction ( Fig. 14-5 A). Type B lesions occur at the radial border of the osseous groove and may result in interposition of the disrupted sheath between the groove and the dorsally displaced ECU tendon. This soft tissue interposition eliminates the possibility of spontaneous healing or successful treatment with cast immobilization. Surgical intervention is necessary for restoration of ECU stability, and, in contrast to type A injuries, type B sheath lesions may be suitable for a secondary, direct repair ( Fig. 14-5 B). In type C lesions, an essentially intact but redundant subsheath with the adjacent periosteum is detached from the ulnar groove and displaces ulnarly, creating a false pouch into which the ECU tendon repeatedly displaces ( Fig. 14-5 C). The tendon readily dislocates out of the osseous groove but remains within an expanded sheath. With these lesions, the sheath requires reattachment to the medial border of the ulnar groove either through drill holes or by bone anchors.

Subsequently, Allende and Le Viet published a similar classification of subsheath lesions as well as a description of ECU tendon disruption. Among their series of 28 ECU injuries requiring surgical treatment, ulnar border type A ruptures occurred most frequently and all required reconstruction. Moreover, 23 of the cases revealed tendon disruptions, 19 of which were partial longitudinal tears and 4 were complete transverse ruptures. This frequency of tendon disruption has been corroborated by Montalvan and associates in their series of ECU injuries among professional tennis players. They reported MRI documentation of longitudinal tears in 14 (50%) of the 28 cases and complete ECU rupture in two, both of which necessitated tendon graft reconstruction.

Various authors also have noted that a shallow osseous groove in the distal ulna is either an anatomic variant contributing to ECU instability or the result of bony abrasion caused by repeated subluxation of the ECU tendon. In one series of operative cases, 4 of the 28 lesions were associated with a shallow groove; in another clinical study of 21 patients with chronic ECU subluxation, flattening of the groove was observed in all patients. In the latter series, the incompetent osseous groove was considered an integral part of the operative pathology. In all cases, surgical reconstruction consisted of deepening the groove, relocating the subluxated sheath with the enclosed ECU tendon, and reattaching the sheath to the medial border of the revised osseous groove.

Melone and Nathan, in an operative evaluation of triangular fibrocartilage complex (TFCC) pathoanatomy, reported that because of the complex anatomy of the TFCC ( Fig. 14-6 A) with its multiple and discrete, but merging, components, disruption of the triangular fibrocartilage (TFC) proper, also termed the articular disk, seldom occurred as an isolated injury. Destabilizing injuries of the DRUJ characteristically disrupted not only the TFC but also the adjacent ECU subsheath as well as other critical soft tissues to a variable extent. In this series, 28 (67%) of their 42 cases had associated injury to the ECU subsheath with subluxation of the ECU tendon. Other key components of the TFCC prone to concurrent injury were the distal radioulnar capsular ligaments, the suspensory ulnocarpal ligaments attaching to the ulnar carpus, and the adjoining lunotriquetral intercarpal ligament. After a thorough assessment of the operative pathology, the authors concluded that traumatic TFCC disruption constituted a spectrum of injury that was categorized into five stages of increasing severity ( Fig. 14-6 B). Awareness and repair or reconstruction of all damaged components were essential to successful surgery ( Fig. 14-6 C and D).

This concept of multicomponent injury of the TFCC has also been acknowledged by Allende and Le Viet. In their series of 28 patients with ECU disruption, 15 (54%) demonstrated substantive concomitant injury, usually involving the TFC. This clinical study also emphasized that restoration of ulnar wrist stability requires repair of all pathologic components. Recognition of this variable, often extensive, spectrum of injury at the ulnar wrist is essential to optimal management of ECU sheath disruption resulting in ECU tendon and DRUJ instability. A successful recovery is often contingent on a comprehensive repair of multiple components of the TFCC.

Anatomic variations of the ECU, usually tendon duplication or accessory tendon slips, have been described with relative frequency. In an anatomic study, Nakashima noted duplication or accessory tendons in 82 (34%) of the 240 wrists evaluated. Allende and Le Viet, in their clinical study, reported accessory tendons in 8 (29%) of the 28 operative cases. These accessory tendon slips originated from the ECU tendon, either proximal to or within the subsheath, and invariably perforated the wall between the sixth and fifth compartments to join the EDM tendon.

Although personal experience with more than 100 operative cases of ECU injury has not corroborated this relatively high incidence of tendon duplication, awareness of the possibility and identification of these anomalous tendons within the sixth compartment nonetheless are an important component of the management of ECU injury. The accessory tendons may be a contributing factor to the pathology by creating relative stenosis within the fibro-osseous tunnel or by adversely altering ECU tendon structure, course, and excursion. These tendons also may prove a source of residual tenosynovitis with persistent pain after surgery if not recognized and excised at the time of operative repair.

PRINCIPLES OF MANAGEMENT

ECU injury is prone to occur among active persons whose wrists are subjected to excessive torsional forces while engaged in vigorous ventures. In the past, the majority of patients were male, ranging in age from 18 to 40 years; in recent times, however, because of the increasing emphasis on healthy exercise for all sectors of the population, the gender gap has undoubtedly narrowed and the age range has expanded. ECU disruption is acknowledged as a common occurrence in sports, especially among racquet or stick-handling athletes. The wrist adjacent to the handle of the stick is usually injured; thus, in baseball, golf, lacrosse, and usually hockey, the nondominant wrist is the predictable side of injury, whereas in tennis and other racquet sports the dominant wrist is usually injured.

Diagnosis

Optimal management begins with an accurate diagnosis. Examination usually demonstrates the classic features of tenderness and swelling at the ulnar border of the wrist directly over the course of an excessively prominent ECU tendon ( Fig. 14-7 A). Passive supination exacerbates the pain, and with tendon instability active supination in conjunction with wrist flexion and ulnar deviation provokes visible, palpable, and at times audible snapping of the ECU tendon over the ulnar styloid ( Fig. 14-7 B). Planar radiographs, always bilateral for comparison, are obtained to detect previously incurred and predisposing skeletal injuries such as distal radius or Galeazzi fractures with residual DRUJ subluxation or ulnar styloid nonunion, as well as congenital disparities such as ulnar variance—conditions that may require simultaneous treatment for restoration of ECU stability. Radiographs also demonstrate an arthritic process resulting in TFC and ECU disruption. In such cases, the primary focus of management is diagnosis and treatment of the arthropathy, requiring rheumatologic evaluation and assistance.