38: Reconstruction for Congenital Thumb Hypoplasia

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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

image 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)

image 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

image 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.

image The entire upper extremity should be examined for other elements of radial deficiency, and patients should be examined for systemic manifestations of associated hematologic and cardiac syndromes such as Holt-Oram, thrombocytopenia-absent-radius (TAR) syndrome, VACTERL (i.e., vertebral abnormalities, anal atresia, cardiac abnormalities, tracheoesophageal fistula and/or esophageal atresia, renal agenesis and dysplasia, and limb defects), and Fanconi anemia.

image

FIGURE 38-1

Imaging

image Radiographs of the hands, wrists, and forearms are useful in determining the degree of metacarpal and phalangeal hypoplasia of the thumb and index finger and can identify the presence of other associated upper extremity anomalies (Fig. 38-2).

image

FIGURE 38-2

Surgical Anatomy

image The anatomic deficiencies associated with thumb hypoplasia are detailed in Figure 38-3. The ulnar collateral ligament spans the MCP joint of the thumb and is lax in type II and type III thumbs.

image The intrinsic muscles of the thumb (abductor pollicis brevis [APB], opponens pollicis [OP], flexor pollicis brevis [FPB], and adductor pollicis [AP]) are deficient in types II and III and absent in types IV and V.

image The flexor pollicis longus (FPL) and extensor pollicis longus (EPL) are hypoplastic in type III thumbs. Often, there may be an anomalous connection between the FPL and the EPL at the level of the MCP joint, known as pollex abductus. This connection can attenuate the UCL over time and prevent active interphalangeal joint motion.

image

FIGURE 38-3

Positioning

image The procedure is conducted under general anesthesia with the patient placed supine on the operating room table. The entire upper extremity is prepared and draped after a tourniquet is applied.

Exposures

image The authors use a four-flap Z-plasty to widen the first web space and perform a transfer of the abductor digiti minimi (Huber transfer) for opponensplasty (Fig. 38-4), and a reefing combined with an adductor advancement for strengthening the UCL and stabilizing the MCP joint. All patients may not need all three procedures, and incisions should be planned appropriately.

image The four-flap Z-plasty is designed by drawing a line along the first web space from the base of the thumb to the base of the index finger (Fig. 38-5). A dorsal limb is added along the dorsum of the thumb MCP joint at 120 degrees to the previous line. Similarly, a palmar limb is added along the palmar aspect of the index finger MCP joint at 120 degrees to the line (see Fig. 38-5). The dorsal limb of the Z-plasty is usually sufficient for exposure of the UCL. However, if a Z-plasty is not required, a 2-cm curvilinear incision can be made over the ulnar aspect of the base of the thumb MCP joint (Fig. 38-6).

image A 2-cm chevron incision is marked over the radial aspect of the thumb MCP joint to expose the APB tendon (Fig. 38-7).

image A curvilinear incision is marked from 1 cm proximal and ulnar to the pisiform, along the radial aspect of the hypothenar eminence, to the ulnar aspect of the base of the small finger to expose the hypothenar muscles for thumb abductorplasty (see Fig. 38-7).

image

FIGURE 38-4

image

FIGURE 38-5

image

FIGURE 38-6

image

FIGURE 38-7

Pearls

The radial limb of the four-flap Z-plasty should be designed dorsally, and the ulnar limb should be designed in a palmar direction. This will allow exposure of the thumb MCP joint and UCL through the radial limb incision.

The incision for exposure of the abductor digiti minimi (ADM) should not be along the ulnar border of the hand but slightly palmar, so that the scar is not compressed when the hand is resting.

Procedure

Step 1: Elevation of Four-Flap Z-Plasty Flaps

image The skin is incised as previously marked, and thick skin flaps are elevated in the loose areolar plane superficial to the muscles.

image Any tight fascial bands overlying the first dorsal interosseous are divided.

Step 1 Pitfalls

Care must be taken to prevent injury to the radial digital nerve to the index finger during elevation of the radial limb and the dorsal sensory branches of the radial nerve during elevation of the ulnar limb of the four-flap Z-plasty.

Step 2: Exposure of the Ulnar Collateral Ligament

image The ulnar limb of the four-flap Z-plasty is mobilized to expose the tendon of the adductor pollicis and the extensor expansion.

image The adductor pollicis tendon is divided at its insertion into the extensor expansion and reflected ulnarly to expose the thumb UCL.

Step 3: Pinning of Thumb MCP Joint

image A single 0.045-inch K-wire is passed obliquely from radial to ulnar through the MCP joint to maintain the MCP joint in neutral position (Fig. 38-8).

image

FIGURE 38-8

Step 3 Pitfalls

The K-wire should not exit through the radial aspect of the metacarpal head, where it may impinge on the insertion of the ADM tendon following opponensplasty.

A tip protector should be placed over the end of the K-wire to prevent inadvertent injury during the subsequent portion of the surgery.

Step 4: Strengthening of the UCL

image Multiple 4-0 Ethibond sutures are placed in a horizontal mattress configuration to reef the lax UCL.

image The tendon of the adductor pollicis is mobilized, advanced, and sutured to the reefed UCL and extensor expansion to further strengthen the UCL.

Step 5: Transposition of Four-Flap Z-Plasty Flaps

image The Z-plasty flaps are transposed and sutured using 4-0 chromic catgut.

image Figure 38-5 shows the arrangement of the flaps before and after transposition.

Step 6: Exposure of the APB Tendon on the Radial Aspect of the Thumb MCP Joint

image The chevron-shaped incision is used to expose the APB tendon.

Step 6 Pearls

Anomalous bands may exist from the FPL on the palmar aspect of the hand to the EPL on the dorsal aspect of the hand (pollex abductus), which should be identified and divided (Fig. 38-9).

image

FIGURE 38-9

Step 7: Exposure of the ADM

image The skin is incised in line with the previously marked incision. The ADM is identified in the midportion of the hypothenar eminence and is the most ulnar and superficial of the hypothenar muscles in this location. More proximally, the palmaris brevis overlies the ADM, but it can be differentiated by the transverse orientation of its fibers.

image The ADM is separated from the other hypothenar muscles, including the opponens digiti minimi and the flexor digiti minimi, which are deeper and more radial (Fig. 38-10).

image

FIGURE 38-10

Step 7 Pitfalls

Care must be taken to identify and protect the digital nerve to the ulnar side of the small finger. This nerve will pass obliquely superficial to the ADM in the distal half of the incision.

The palmaris brevis should be divided to mobilize the proximal portion of the ADM. Care must be taken to protect motor branches of the ulnar nerve during proximal mobilization of the ADM.

Step 8: Division of the Insertion of the ADM

image The ADM has two insertions, one to the ulnar aspect of the base of the proximal phalanx and the other to the extensor expansion. Both of these must be divided to allow the muscle to be elevated (Fig. 38-11).

image

FIGURE 38-11

Step 8 Pearls

The ADM barely reaches the APB insertion. Harvesting a slightly longer tendon will make insertion of the transfer easier (Fig. 38-12).

image

FIGURE 38-12

Step 9: Elevation of the ADM

image The ADM is elevated to its origin from the pisiform. The neurovascular bundle to the ADM enters the muscle on the dorsoradial aspect, and care must be taken during proximal elevation of the muscle to prevent injury to the pedicle (Fig. 38-13). The pedicle does not need to be visualized during the harvest. The muscle is dissected to its insertion at the pisiform.

image

FIGURE 38-13

Step 9 Pearls

Although the ADM can be elevated off the pisiform to improve the length of the transfer, this maneuver can weaken this delicate muscle. Alternatively, placing the wrist in flexion or using a tendon graft (rarely necessary) can improve the length of the transfer.

Step 10: Creation of a Subcutaneous Tunnel

image A wide subcutaneous tunnel is made from the pisiform to the radial aspect of the thumb MCP joint using a large curved hemostat.

Step 10 Pearls

The tunnel must be wide enough to accommodate the ADM without compromising the viability of the muscle or increasing the risk for adhesions. An additional incision can be made at the base of the thenar eminence to ensure a wide tunnel.

Step 11: Transfer of the ADM

image The elevated ADM is turned 180 degrees like the page of a book, rather than rotating it 90 degrees, to prevent twisting of the pedicle (Fig. 38-14).

image A hemostat passed from the incision at the radial aspect of the thumb through the subcutaneous tunnel is used to bring the ADM to the radial aspect of the thumb MCP joint.

image The ADM tendon reaches the APB insertion with sufficient tension, and overcorrection is unnecessary.

image The ADM tendon is passed under the APB insertion and anchored with 4-0 Ethibond mattress sutures (Fig. 38-15).

image

FIGURE 38-14

image

FIGURE 38-15

Step 12: Wound Closure

image The tourniquet is released, and meticulous hemostasis is secured.

image All skin incisions are closed with 4-0 chromic catgut (Fig. 38-16).

image A thumb spica splint to maintain the wrist in slight flexion and to keep the thumb in maximal palmar abduction is provided.

image

FIGURE 38-16

Postoperative Care and Expected Outcomes

image The child is maintained in a thumb spica splint for 4 weeks. The K-wire is removed at 4 weeks and a thermoplastic splint fashioned to maintain the position of the thumb.

image At 4 weeks, children are started on range-of-motion and strengthening exercises and are weaned off the splint gradually over a period of 2 to 4 weeks.

image The results of surgery for thumb hypoplasia are good, and almost all patients have improvements in thumb function.

Evidence

Abdel-Ghani H, Amro S. Characteristics of patients with hypoplastic thumb: a prospective study of 51 patients with the results of surgical treatment. J Pediatr Orthop. 2004;13:127-138.

The authors describe the outcomes of 51 patients and 82 hypoplastic thumbs, of whom 18 patients underwent surgical reconstruction with 3-year follow-up. In this series, type V thumb hypoplasia was most common, and the majority (86%) suffered from associated anomalies. Among patients who underwent opponensplasty and UCL reconstruction, the majority achieved stability (70%) at the MCP joint as well as the ability to oppose the finger to the small finger (89%). (Level IV evidence)

Fraulin FO, Thomson HG. First webspace deepening: comparing the four-flap and five-flap Z-plasty. Which gives the most gain? Plast Reconstr Surg. 1999;104:120-128.

The authors use simulated models to determine the anticipated gain between four- and five-flap Z-plasty for web space deepening. The authors conclude that the percentage of deepening achieved by a five-flap Z-plasty is similar to that of a single 60-degree Z-plasty, approximately 75%, and a four-flap Z-plasty using 90-degree angles yields greater deepening (114%). (Level III evidence)

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