Duplication of the Extensor Pollicis Longus and Index Extensor Digitorum Communis: Report of a Novel Anomaly and Review of Literature

Abstract

Accessory extensor tendons in the hand are not rare, usually asymptomatic, and recognized incidentally during elective surgery or cadaveric dissection. This report describes a novel case of symptomatic duplication of accessory extensor tendons to both the thumb and the index finger causing a painful dorsal wrist tenosynovitis. Excision of the accessory tendons with decompression and tenosynovectomy of the fourth extensor compartment alleviated the patient’s symptoms without compromising motion or function.

Introduction

Numerous anatomists and surgeons have described accessory tendons to the thumb usually with interconnections to the index finger. ^1-3 Wood was the first to label the connection between the extensor pollicis longus (EPL) and the extensor indicis proprius (EIP) as the extensor pollicis et indicis in the 1860’s. ¹ In contrast to the numerous descriptions of the extensor tendon anomalies of the fingers, reports of tendon variations of the thumb are infrequent. Although variations have been reported, the most common anomaly of the EPL is duplication that passes through the fourth compartment. ^4,5 Türker et al. formulated a classification system in 2010 based on a meta-analysis of an extensive review of anomalies of the EPL. ⁴ This system emphasizes that duplication, albeit uncommon, may assume varied configurations, and that, if present, require physician awareness to avoid confusion and ensure an uncomplicated plan of treatment. The type of thumb anomaly is classified by the presence of either a separate tendon variation or an interconnection with another extensor tendon, and by the location and pathway of the accessory tendon. ⁵

Although the classification is a valid attempt to organize a diverse anomaly, its efficacy is limited by the low number of reported cases of EPL duplication. The supernumerary extensor variant is usually asymptomatic and is typically noted incidentally during elective surgery or cadaveric study. Although EPL duplication supposedly is not prone to tenosynovitis, our literature review has revealed several cases of duplicated EPL with the third or fourth extensor compartment causing a painful tenosynovitis and requiring surgery. An example of this is a reported case of a patient who complained of painful clicking at the dorsoradial aspect of the wrist, reproduced by extension of the wrist and the thumb, and associated with tenderness and swelling adjacent to Lister’s tubercle. There was no joint or tendon damage and X-rays and MRI of the wrist were normal. The pain ultimately led to operative treatment and resolved following tenosynovectomy and decompression of the third extensor compartment with excision of a duplicated EPL. ⁵

Unlike the thumb, reports of variation of the extensor anatomy to the index finger have been relatively frequent and have described duplication of the EIP, anomalies of the extensor digitorum communis (EDC), and accessory dorsal hand muscles inserting on the index finger. ^{6 -8} Concurrent accessory extensors to both the index finger and the thumb are unusual and only have been noted in cadaveric studies. These concurrent extensors have demonstrated origins from the third and fourth dorsal compartment and distal tendinous insertions. ⁹ An additional clinical case illustrates an anomalous extensor tendon to the thumb connected to an accessory tendon to the index extensor. ¹⁰ However, to date there has been no report of a symptomatic clinical case with concurrent and separate EPL and EDC tendon duplication. In contrast, this article describes a case of duplicated tendons to both the thumb and the index finger that resulted in painful stenosing tenosynovitis of the fourth extensor compartment. Surgical tenosynovectomy and excision of the accessory tendons successfully treated the patient’s symptoms without compromising function.

Case Report

The patient, a 61-year-old woman, presented with a 3-month history of dorsal wrist pain and swelling, and with no history of preceding trauma or systemic disease. The pain was localized to the dorsoradial wrist and worsened with extension of both the thumb and the index finger. Her exam was remarkable for swelling and tenderness over the extensor tendons in the fourth compartment, adjacent to Lister’s tubercle (Figure 1). Although painful, she demonstrated full extension of her fingers and thumb and a full fist. The preoperative radiographs were unremarkable for bone or joint pathology, but were notable for dorsal wrist soft tissue swelling.

Figure 1.

Preoperatively, the patient had intermittent episodes of dorsal swelling and pain of her wrist due to stenosing extensor tenosynovitis resulting from the excessive bulk of the duplicated tendons.

Conservative management was unsuccessful and subsequent surgery revealed a chronic extensor tenosynovitis involving the fourth dorsal compartment. Two sizable accessory tendons (Figure 2) created excessive bulk, narrowing the extensor compartment and constricting and inflaming the extensor tendons to the index, long, ring, and small fingers. The accessory tendons were duplications of the EPL and the EDC to the index finger and had excellent excursion. These tendons arose from the distal forearm and passed through the fourth compartment. No separate compartment was present for either tendon. The accessory EPL passed through the fourth compartment and inserted on the EPL just proximal to the metacarpophalangeal (MP) joint. Prior inserting on the EPL, the accessory tendon bifurcated and an additional tendon slip traversed dorsally and ulnarly and attached to the accessory index EDC tendon proximal to the MP joint. The accessory EDC to the index finger also passed through the fourth compartment and arose from the common extensor tendon juncture proximally and inserted at the radial aspect of the EDC proper of the index finger just proximal to the MP joint.

Figure 2.

A, Operative exposure of anomalous duplication of the extensor digitorum communis of the index finger and to the extensor pollicis longus of the thumb. B, Schematic drawing of the wrist extensor anatomy showing anomalous double tendon duplication of both the thumb and index finger.

Prior to resection, a thorough assessment of the normal and anomalous tendon excursion was conducted to ensure that the resection of the accessory tendons would not compromise any function. After a thorough tenosynovectomy of the 4th compartment, the EPL tendon was completely mobilized and transected proximally after placing tension on the tendon. This tendon demonstrated a proximal muscle belly adjacent to, but separate from, the native EPL origin. Distally, the insertion of the tendon was carefully identified and sectioned, with accessory slip to the EDC of the index finger. The anomalous tendon was then completely removed. The duplicated tendon to the index finger EDC similarly was first transected proximally, mobilized, and then transected distally. Thus, the 4th compartment was decompressed thoroughly by a tenosynovectomy and excision of the anomalous tendons. The stenosis was eliminated and all tendons glided freely through the 4th compartment.

At her last follow up, 6 months postoperatively, the patient was pain free and demonstrated normal digital and wrist motion as well as grip strength of 40 kgs and pinch strength of 10 kgs, measures equivalent to the contralateral hand (Figure 3).

Figure 3.

Postoperative the patient demonstrates (A) full extension of her thumb with a full fist, (B) full extension of the index finger, and (C) full extension of index and adjacent digits with an inconspicuous surgical scar.

Discussion

The EPL tendon is typically a constant anatomical structure with only occasional reports of anomalies. The foremost but infrequent anomaly is tendon duplication with a wide array of configurations. The classification of Turker et al. ⁴ is comprehensive and depicts the various patterns of the EPL anomalies. However, it does not include the more common EPL variation of additional connections to other digits adjacent to the thumb. Toward to this end, the extensor pollicis et indicis (EPI) is usually described as an anomalous common motor unit that divides into separate tendons extending the thumb and index finger. ³ As such the EPI is both an EPL and an EIP anomaly.

The present case study describes a novel EPL anomaly associated with an accessory EDC tendon of the adjacent index finger. This previously unreported anomaly comprises 2 co-existent, completely separate, and functional accessory tendons originating from the distal forearm, passing through the fourth dorsal compartment, inserting separately into the thumb and index finger, and ultimately causing a painful tenosynovitis. The unique type of anomaly, it’s clinical presentation with a painful dorsal tenosynovitis, and surgical treatment by tenotomy and tenosynovectomy considerably differentiate this case from reports of other recognized extensor anomalies.

In this case the anomalous tendons clearly proved pathological. However, since they are often sizeable and expendable, the accessory tendons may also prove beneficial for surgical procedures requiring additional tendon substance, such as grafts and transfers. Cadaveric studies have shown that accessory tendons of the EIP could potentially be used for tendon transfer in cases of functional loss of the EPL providing thumb extension without compromising index finger extension. Somewhat surprisingly, the cadaveric studies have shown a relatively frequent incidence of these anomalies in up to 16% of extremities. ²

Recognition of extensor anatomic variations is vital to ensure optimal surgical orientation and uncomplicated treatment. In this case the anatomical location and insertion of the accessory tendons rendered them suitable for resection with no resultant compromise of function. However, due to the variable location of extensor anomalies and a multitude of tendon interconnections, prior to resecting the anomaly a thorough assessment of the anatomy is essential for preservation of functional integrity.

In summary, based on this experience, and in the absence of trauma or systemic disease, accessory extensor tendons should be considered a possible etiology for dorsal wrist tenosynovitis. In such cases, selective MR imaging may identify the accessory tendons and confirm the diagnosis. ¹¹ Furthermore, this case demonstrates that EPL tendon duplication is not only an anatomical curiosity but also, potentially, an anomaly of clinical significance.