Wassel VI Thumb Duplication With Triphalangeal Radial and Ulnar Thumbs: Anatomy and Surgical Reconstruction

Abstract

A 6-year-old otherwise healthy girl presented with a Wassel VI duplication of the left thumb metacarpal and triphalangeal radial and ulnar thumbs. The patient underwent successful thumb reconstruction by transposition of the distal ulnar thumb onto the radial thumb metacarpal. To the best of our knowledge, this case report represents the first published anatomical dissection and surgical reconstruction of a Wassel VI duplication with triphalangeal radial and ulnar thumbs.

Introduction

Preaxial polydactyly is a common congenital hand difference, although with significant variability in the degree of duplication. The Wassel-Flatt classification delineates 7 distinct categories based on the osseous anatomy from distal to proximal, with odd numbers referring to bifid duplications at the distal phalangeal (I), proximal phalangeal (III), and metacarpal (V) levels; even numbers referring to complete duplications of the distal phalanges (II), the proximal phalanges (IV), and the metacarpals (VI); and the seventh being triphalangealism. ¹ This has since been expanded to include unique presentations, which affects the use of Wassel-Flatt–based treatment algorithms.

We present a case report of a 6-year-old girl with duplication of the left thumb metacarpal with triphalangeal radial and ulnar thumbs, which we deemed a Wassel VI duplication with triphalangeal radial and ulnar thumbs, which has not been previously described in the literature.

Case Report

A 6-year-old otherwise healthy girl presented with duplication of both her thumbs and both great toes. Family history was notable for congenital hand anomalies in the mother and maternal grandmother. The right thumb presented with a Wassel II polydactyly, whereas the left had a complete duplication of the first metacarpal with triphalangeal radial and ulnar thumbs, which we deemed Wassel VI with triphalangeism (Figure 1). No other abnormalities were noted.

Figure 1.

Preoperative presentation of the bilateral duplicated thumbs, along with left hand imaging.

On physical examination, the left radial first metacarpal was able to oppose to all 4 fingers, although the radial thumb angulated ulnarly distal to the metacarpophalangeal (MCP) joint and flexion was weak. The ulnar thumb was well formed distally with good range of motion at the MCP and proximal interphalangeal (PIP) joints. However, the first Web space was narrow and there was no flexion at the distal interphalangeal (DIP) joint. Therefore, we opted to proceed with left thumb reconstruction with transposition of the ulnar phalanges to the radial metacarpal.

Surgical Technique

A modified racquet incision was designed around the MCP joint of the ulnar thumb with the longitudinal axis continued along the radial aspect of the thenar eminence. Volar and dorsal rectangular skin flaps were designed over the metacarpal of the radial thumb (Figure 2).

Figure 2.

Preoperative marking showing the planned resection and skin flaps.

Each thumb had 2 rudimentary extensor tendons, corresponding to an extensor pollicis longus (EPL) and extensor pollicis brevis (EPB) (Figure 3).

Figure 3.

Dorsal dissection of duplicated thumbs delineating extensor anatomy.

Volarly, the radial thumb had an abductor pollicis brevis (APB) muscle inserting at the radial base of the proximal phalanx as well as an adductor pollicis (AdP) muscle (Figure 4). The radial thumb was supplied by a single radial digital artery and nerve. A single flexor tendon was encountered within the flexor tendon sheath, representing the flexor pollicis longus (FPL).

Figure 4.

Volar dissection demonstrating flexor anatomy.

The ulnar thumb also had an AdP muscle with appropriate insertion onto the ulnar aspect of the base of the proximal phalanx (Figure 4). The flexor sheath again contained a single flexor tendon without motion at the DIP joint. Unlike the radial thumb, the ulnar thumb was supplied by both a radial and ulnar digital nerve and artery.

After dissection, the radial APB and AdP muscles were disinserted and the radial FPL transected distally to allow for amputation at the MCP joint. Approximately one-third down the radial metacarpal shaft, an osteotomy was made. A corresponding osteotomy midway on the ulnar metacarpal was also made. The residual proximal base of the ulnar thumb metacarpal was completely excised down to the level of the carpometacarpal joint.

To allow for transposition, the ulnar thumb’s ulnar neurovascular bundle was dissected proximally to the common digital bundle and the radial digital artery branch to the index finger was ligated.

To increase bony stability, the distal ulnar thumb metacarpal was telescoped into the medullary canal of the proximal radial thumb metacarpal (Figure 5). The reconstructed thumb reached no further than the PIP joint of the index finger, had good opposition to all 4 fingers, and had appropriate abduction and pronation. The osteosynthesis was secured with interosseous wiring and covered with a layer of periosteum and soft tissue. The APB of the radial thumb was inserted into the radial lateral band of the transposed ulnar thumb. The radial thumb AdP was passed underneath the ulnar thumb FPL and sutured to the ulnar lateral band of the transposed ulnar thumb.

Figure 5.

Telescoping of ulnar thumb into radial metacarpal.

The extensor tendons were tensioned by reattachment to the extensor hood of the transposed ulnar thumb. The native AdP of the translocated ulnar thumb was left in its original anatomical position.

The skin was draped around the reconstructed thumb; the volar and dorsal rectangular skin flaps were found to be redundant and excised. The skin was closed with absorbable sutures and the thumb immobilized in a sugar-tong splint. The child was admitted for frequent capillary refill checks before discharge home without complication on postoperative day 3.

Postoperative Course

Three months postoperatively, she had already incorporated her reconstructed thumb into her daily activities without any difficulty. She had excellent opposition to all 4 fingers with full flexion and extension at the MCP and PIP joints but slightly decreased radial abduction. Sensation was completely normal throughout the thumb and index finger. At 18 months postoperatively, she continued to have excellent function (Figure 6), with return to near-normal function and a Japanese Society for Surgery of the Hand score of 20/20. Radiographs demonstrated bony consolidation of the proximal radial thumb proximal metacarpal to the ulnar thumb distal metacarpal without any hardware complication (Figure 7).

Figure 6.

18-month postoperative outcome.

Figure 7.

18-month postoperative imaging.

Discussion

The Wassel-Flatt classification system provided pediatric hand surgeons with a common nomenclature for the discussion and management of preaxial polydactyly. ¹ However, many cases of preaxial polydactyly are poorly described by the Wassel-Flatt classification, prompting new systems to emerge. Both Wood ² and Miura ³ introduced subcategories for Wassel IV thumbs, while Wood ² subdivided Wassel VII thumbs into 4 patterns. In 2008, Zuidam et al ⁴ published the Rotterdam classification for complex triphalangeal thumbs and triplications. Other classification schemes include those by Buck-Gramcko and Behrens, ⁵ Blauth and Olason, ⁶ and Chung et al, ⁷ but the Wassel classification remains the most commonly used.

Using the original Wassel ¹ classification system, our patient would be classified as a Wassel VI with triphalangeal radial and ulnar thumbs. Under Wood’s ² modification, the patient would be classified as Wassel VII type B duplication. By the Rotterdam classification, the patient would be classified as a type VI triphalangeal ulnar/radial (VI Tph u/r) duplication. ⁴

Wassel VI polydactyly with triphalangeal radial and ulnar thumbs is incredibly rare. A thorough review of the literature reveals very few published cases, mainly associated with mutations on chromosome 7q. ⁸ Discussions of these cases focus on inheritance patterns of genetic mutations rather than on anatomy and reconstructive options.^{9 -12}

Within the hand surgery literature, discussion of this pattern is nonexistent. Wood ² described 1 type B with 2 equal radial and ulnar triphalangeal thumbs; although he presented imaging, he provided no details of surgery. Zuidam et al ⁴ presented 5 similar cases to all but again there was no mention of the reconstruction performed and no radiographs were provided.

Iba described 2 children with Wassel VI thumb duplications with a hypoplastic metacarpal of the ulnar thumb treated by excision of the radial thumb and transposition of the head of the ulnar thumb metacarpal onto the radial metacarpal. The APB was reattached to the proximal phalanx of the ulnar thumb. ¹³ Al-Qattan et al ¹⁴ reported 1 case of a Wassel VI thumb duplication with a metacarpal and 2 phalanges in each thumb.

Shen additionally described several children with Wassel VI thumbs with a triphalangeal thumb on the radial side. Those with functional radial and ulnar thumbs underwent transposition of the ulnar thumb on to the radial thumb metacarpal with reattachment of the thenar muscles to the base of the proximal phalanx of the transposed ulnar thumb, with good results, though anatomical details were not provided. ¹⁵

The basic tenet of reconstruction of radial polydactyly is creation of a functional and aesthetically pleasing thumb. For patients with Wassel VI and VII thumbs, the exact surgical technique is dictated by the relative quality of the 2 native thumbs. In most patients, 1 thumb is better developed than the other; in such situations, the lesser thumb is resected or ablated. ¹⁶ In rare instances, 1 thumb will be more fully developed distally, whereas the other thumb is more developed proximally. In such situations, an “on-top plasty” can be considered, in which the better developed distal thumb is transposed onto the better developed proximal thumb. ¹⁶ The literature contains several reports of successful “on-top plasty” for Wassel VI thumbs in which both thumbs are biphalangeal.^13,14,17 As previously mentioned, Shen et al ¹⁵ described 5 patients with Wassel VI thumbs in which the radial thumb was triphalangeal who underwent “on-top plasty” by transposition of the distal ulnar biphalangeal thumb onto the radial thumb metacarpal, so eliminating the triphalangeal component and establishing normal thumb skeletal anatomy. Bessho reported 12 Wassel VI thumb duplications; 1 child had hypoplasia of the distal portion of the radial thumb and hypoplasia of the ulnar thumb metacarpal, so underwent an “on-top plasty” of the proximal and distal phalanges of the ulnar thumb on top of the radial thumb metacarpal. The other 11 children underwent excision of the radial thumb and reattachment of the thenar muscles onto the ulnar thumb metacarpal. ¹⁷

Our patient’s triphalangeal radial and ulnar thumbs posed a unique reconstructive challenge. While the basic principle of transposing the most functional distal thumb onto the base of the most functional proximal thumb remained, the ideal location for the osteotomy of the ulnar thumb was not immediately obvious. There were 2 reconstructive options: osteotomy and transposition at the level of the metacarpal versus at the level of the proximal phalanx. Intraoperative examination confirmed that while the ulnar thumb had functional MCP and PIP joints, the DIP joint was nonfunctional. Therefore, it was elected to perform the osteotomies and transposition at the level of the metacarpals. Although the reconstructed thumb remained triphalangeal by bony anatomy, nevertheless, it functioned as a biphalangeal thumb because the PIP joint functioned as the thumb interphalangeal joint.

Detailed anatomical descriptions of the Wassel VI thumb have been previously published.^{18 -20} Munabi described 2 children with Wassel VI thumb duplications who just underwent excision of the radial duplicated thumb. No mention was made of the FPL, EPL tendons, or digital nerves, but the opponens was reflected off the radial thumb metacarpal and reinserted onto the ulnar thumb metacarpal. ¹⁹ Kareh described 1 child with a Wassel VI thumb duplication. Magnetic resonance imaging scan at 16 months showed a widened distal trapezium with 2 facets and splitting of the thenar muscles. Flexor pollicis brevis and opponens pollicis were attached to the ulnar thumb and APB was attached to the radial thumb. The radial thumb was excised together with the distal radial facet of the trapezium. Abductor pollicis brevis was transferred to the radial base of the proximal phalanx of the ulnar thumb. ²⁰ Saito et al ¹⁸ published a series of 4 children who underwent resection of the radial thumb and transposition of soft tissue structures and noted aberrant insertions of the APB and superficial head of the flexor pollicis brevis tendon.

In comparison with these previous case reports, our patient had both radial and ulnar triphalangeal thumbs and underwent reconstruction with “on-top plasty” at the level of the metacarpals. The radial thumb contained an APB, AdP, FPL, EPB, and EPL. The ulnar thumb contained an AdP, FPL, EPB, and EPL. Dissection was not performed proximally enough to assess the abductor pollicis longus muscle. Our anatomical dissection highlights that in patients with relatively well-developed duplicated thumbs, relatively normal anatomy can be appreciated intraoperatively.

Conclusion

A 6-year-old otherwise healthy girl with a strong family history of thumb duplication was born with a Wassel type II duplication of the right thumb and a Wassel type VI duplication of the left thumb with triphalangeal radial and ulnar thumbs. To the best of our knowledge, this is the first published description of the anatomical dissection and surgical reconstruction of a Wassel VI duplication with triphalangeal radial and ulnar thumbs by transposition of the distal ulnar thumb onto the radial thumb metacarpal.