Etiology

Thumb hypoplasia is rarely familial; rather, it typically appears as a sporadic event unassociated with other congenital differences.

Associated Conditions

Several constellations of anomalies (syndromes) that include hypoplastic or absent thumbs have been recognized, including VACTERL (vertebral anomalies, anal atresia, cardiac anomalies, tracheo-esophageal fistula, renal anomalies, and limb anomalies and Fanconi anemia, a potentially life-threatening condition). Decisions regarding elective reconstructive hand surgery for these children should be made in coordination with pediatricians and hematologists.

Physical Examination and Key Anatomy

A common presentation is the adducted and hypoplastic thumb. The dividing point between augmenting what is present versus pollicization has typically been the stability and potential useful function of the carpometacarpal (CMC) joint of the dysplastic thumb. Blauth refers to this presentation as type 3 and further divides these presentations according to whether the CMC joint is relatively stable (3A) or essentially non-existent (3B). Although there are procedures described that attempt to restore useful function to type 3B hypoplastic thumbs, for many surgeons the preferred treatment is ablation of the hypoplastic part, preserving any useful elements, and index pollicization. Type 3A hypoplastic thumbs have a stable basal joint and, if possible, should be treated by reconstructive procedures unless they are severely hypoplastic.

One should observe how the child uses the thumb in grasping and manipulating objects. If the child bypasses the thumb and uses the index and middle finger for pinch, this indicates that the current thumb has had little practical value and that augmenting the thumb will likely be functionally unsuccessful. Close observation of the first web space will identify the need to deepen this. The thumb will often be adducted at the metacarpophalangeal (MP) joint and lack active abduction. The entire ray may lack ideal extension, especially at the MP joint. Manipulating the child’s thumb frequently will yield some information regarding the stability of the CMC joint of the Blauth type 3 thumb. An x-ray will provide additional evidence in the somewhat older child ( Figs. 5.3.2C and 5.3.3C ).

Pre-Operative Testing Needed

Geographical site-specific pre-operative testing should be performed based on the general health status of the population and the prevalence of specific diseases, parasitical or otherwise. Otherwise, except for the child with total thumb absence and preexisting evidence of Fanconi’s anemia, no special pre-operative testing is needed.

Other Concerns

Pre-operative planning should include showing photographs or videos of children who have undergone these procedures. There may exist cultural differences that will make it difficult for a parent to accept the idea of less than a 5-fingered hand. It is important to respect doubt, hesitation, and rejection of one’s recommendation.

Optimal Timing of Surgery

Buck-Gramcko showed that, in the hands of a skilled and experienced surgeon, index pollicization and the reconstruction of hypoplastic thumbs could be safely performed on infants as young as 6 months of age. However, such delicate reconstructive hand surgery need not be performed during infancy to achieve a very functional outcome and likely is best performed during early childhood, when critical structures such as nerves and vessels are larger. Surgery is best performed after the surgeon has attained some experience operating on children with more common congenital hand differences, for example, syndactyly and polydactyly.

Supplies Needed

The availability of appropriately sized instruments and sutures may make the difference between a frustrating surgical experience and an outcome rewarding to both patient and surgeon. Because the operated hand is likely to be hidden in a cast for several weeks, absorbable skin sutures should be used. A functioning pediatric-size tourniquet is absolutely essential. Sutures likely to be used include:

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  Absorbable 4-0 or 5-0 sutures for skin closure

  
  
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  Non-absorbable 4-0 sutures for tendon approximation

  
  
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  Non-absorbable 2-0 or 3-0 sutures for ligament reconstruction.

Additional useful supplies include:

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  1- or 1.5-mm Kirschner wires (K-wires) for temporary joint stabilization if needed

Anesthesia Concerns

The issue of associated congenital anomalies has been mentioned. Past experience has proved the benefit of a regional block in addition to general anesthesia for these cases. The block lessens the need for deep general anesthesia, and it reduces the likelihood of the child thrashing about while the cast is being applied. In the absence of a regional block, it is important to communicate with the anesthesiologist as the case is nearing completion so that the child does not emerge from anesthesia before the cast has been applied and has hardened.