CASE                               30                               

An 11-month-old patient is brought to you by his parents for “two thumbs on one hand.” Examination of the hand is significant for diverging, converging thumb duplication on the right. He has a duplication of the proximal and distal phalanges. On palpation, there is a singular thumb metacarpal.

What is the most appropriate next step in the patient’s management?

1. Cardiac ultrasound and renal ultrasound

2. CBC, peripheral blood smear, and chromosome breakage analysis

3. Barium swallow and spine MRI

4. LFTs and chromosome analysis

5. Hand x-ray

Discussion

The correct answer is (E). Thumb duplication is most often sporadic but occasionally autosomal dominant. It is not associated with other conditions, with the exception of triphalyngeal duplicated thumbs (Wassel type VII, see below). The following conditions are associated with thumb hypoplasia, not thumb duplication.

Holt–Oram: cardiac ultrasound

Thrombocytopenia Absent Radius (TAR) CBC, peripheral blood smear Fanconi anemia: chromosome breakage analysis

VATER/VACTERRL: barium swallow, spine imaging

A cardiac ultrasound and renal ultrasound are indicated with thumb or radial-sided hypoplasia, not duplication.

The patient undergoes x-ray of the thumb shown in Figure 4–17.

Figure 4–17

What is the Wassel classification of the thumb?

1. Type II

2. Type III

3. Type IV

4. Type V

5. Type VI

Discussion

The correct answer is (C).

The Wassel classification is as follows:

I: Bifid distal phalanx

II: Duplicated distal phalanx

III: Duplication of the distal phalanx bifid proximal phalanx IV: Duplication of the distal phalanx and proximal phalanx

V: Duplication of the distal phalanx, proximal phalanx, and bifid metacarpal

VI: Duplication of the distal phalanx, middle phalanx, and metacarpal of the thumb VII: Thumb duplication with a triphalyngeal thumb.

The classification number corresponds with the number of abnormal bones in the duplication.

Which of the following is likely involved in the etiology of thumb duplication?

1. AER—apical ectodermal ridge

2. ZPA—zone of polarizing activity

3. Vascular insult of the radial artery

4. Separation of chorion from amnion

5. Notochord development

Discussion

The correct answer is (A). The apical ectodermal ridge (AER) is critical in limb development, particularly in the proximal to distal direction. It is thought to be implicated in duplicated thumbs. The zone of polarizing activity on the limb bud has pattern organizing activity for antero/posterior formation (ZPA = AP formation). Vascular insult to the radial artery is one theory in the development of radial club hand. Separation of the chorion from the amnion can result in amniotic band syndrome. Abnormal notochord development can result in spina bifida and other spinal anomalies.

What is the most common and second most common type of thumb duplication?

1. Most common = Type 1; Second most common = Type 2

2. Most common = Type 2; Second most common = Type 1

3. Most common = Type 2; Second most common = Type 4

4. Most common = Type 4; Second most common = Type 2

5. Most common = Type 4; Second most common = Type 6

Discussion

The correct answer is (D). Type 4 is the most common (43%). Type 2 is the second most common (15%).

What is an appropriate step in the initial surgical management of this patient?

1. Removal of the central portion of each thumb and combining the radial half of one thumb with the ulnar half of the other (the Bilhaut–Cloquet procedure)

2. Excision of the divergent/convergent thumbs and pollicization of the index finger

3. Stabilization of the carpometacarpal joint of the thumb

4. Combining the proximal component of the radial thumb with the distal component of the ulnar thumb

5. Excision of the radial thumb and transferring the extrinsic tendons of the radial thumb to the ulnar thumb

Discussion

The correct answer is (E). Combining the two digits into one by removing central tissue is indicated for type 1, 2, and 3 thumbs. This is not performed with type 4 thumbs where four bones would need to be combined to two. The Bilhaut–Cloquet procedure can result in stiffness. Removal of the thumbs and pollicization is indicated in hypoplastic thumbs without a stable CMC joint, not in thumb duplication. The CMC joint is not affected in type four thumbs and does not need to be stabilized. An on-top plasty (combining the proximal component of one thumb with the distal component of the other) is indicated when one digit has a superior proximal component and the other digit has a superior distal component. When the two thumbs are equal in size, such as in this case, the radial thumb is usually excised. Excision of the radial thumb with transfer of the flexor tendons to counteract the Z deforming forces is indicated in this Wassel IV thumb.

Objectives: Did you learn...?

Classify thumb duplication?

Describe the appropriate workup of duplicated thumb versus thumb aplasia? Identify the embryologic contribution to thumb duplication?

Pinpoint the most common types of thumb duplication? Surgically manage thumb duplication?