Procedure 38 Reconstruction for Congenital Thumb Hypoplasia

Jennifer Waljee, Sandeep J. Sebastin, Kevin C. Chung

Congenital thumb hypoplasia can vary from mild size discrepancy to complete absence. The Blauth classification is useful for categorizing the degree of development (Table 38-1). It is critical to assess the stability of the thumb carpometacarpal (CMC) joint to determine the appropriate surgical treatment for thumb hypoplasia. The goal of surgical intervention for children with a stable CMC joint (Blauth types I, II, and IIIA) is preservation of the existing thumb and augmentation of the deficient soft tissue elements. Conversely, if the CMC joint is unstable or absent (Blauth types IIIB, IV, and V), any remnants of the existing thumb should be ablated, and reconstruction should proceed by pollicizing the index finger. This chapter focuses on the reconstruction of Blauth types I, II, and IIIA hypoplasia.

Table 38-1 Blauth Classification of Thumb Hypoplasia and Treatment Options

Type	Features	Treatment Options
I	Mild hypoplasia with all elements present	No treatment
II	Narrow first web, ulnar collateral ligament insufficiency, and absence of thenar intrinsic muscles	No treatment Z-plasty of first web, UCL strengthening/reconstruction, and opponensplasty
III	Type II plus extrinsic tendon deficiencies and/or skeletal deficiency
IIIA	Stable CMC joint	Same as type II
IIIB	Unstable CMC joint	Pollicization
IV	Absent metacarpal and rudimentary phalanges “Pouce flottant”	Pollicization
V	Total absence	Pollicization

Indications

Congenital thumb hypoplasia is seen with a stable CMC joint with varying degrees of soft tissue deficiency (Blauth types I, II, and IIIA). The important soft tissue deficiencies are the following:

• Narrow first web space (<50 degrees of radial thumb abduction)

• Atrophic or absent thenar muscles leading to the inability to oppose the thumb to small finger

• Attenuated or absent ulnar collateral ligament (UCL) of the metacarpophalangeal (MCP) joint with an unstable MCP joint (>20-degree difference in UCL laxity compared with the normal side)

Reconstructive procedures for thumb hypoplasia (Blauth types I, II, and IIIA) can be performed at a later age (2 to 4 years) because the child can use the thumb for activities without developing maladaptive compensation patterns. However, it is preferable to correct these deformities before the child enters school to avoid any stigma from an uncorrected deformity.

Examination/Imaging

Clinical Examination

The child should be examined to assess the degree of first web narrowing, opposition function of the thumb, and stability of the thumb MCP joint (Fig. 38-1). Serial examination of a child is required to differentiate between Blauth types IIIA and IIIB. A newborn child uses digital grasp and begins to use the thumb in grasp at about 1 year of age. If the child uses the thumb in manipulating objects, this suggests that a type IIIA deficiency is present. If the child prefers to grasp objects between the index and long finger web space, this web space appears wider because the index finger is pronated toward the thumb. This suggests type IIIB hypoplasia because the child is incapable of using the unstable thumb for effective pinch.