80

On radiographs, there appears to be mild ulnar positive variance (Fig. 80–1). The thumb ray is made of a metacarpal and two phalanges, albeit hypoplastic. The carpal ossification is normal for age, with the hamate and capitate ossified.

PEARLS

• Careful assessment of the patient and his or her hand is critical to a good outcome.
  
• When possible, surgery should be performed before the age of 18 months and ideally at 9 to 12 months of age.

PITFALLS

• Surgeon must be aware of the anatomic variability that can exist, and be flexible in his or her preoperative planning, and intraoperative decision making.

Figure 80–1  Anteroposterior (AP) radiograph of the patient’s hand. There is mild ulnar positive variance, which is suggestive of type I radial dysplasia. The ossified capitate and hamate are consistent with the child’s age; it is too early for ossification of the scaphoid or trapezium. The thumb ray is short.

Differential Diagnosis

Our case illustrates the principles involved in reconstructing most type II and IIIA hypoplastic thumbs. It is important to realize that the spectrum of deficiencies can range from simple shortening of the thumb ray to its complete absence. The choices for treatment include no treatment, surgical reconstruction, amputation, index pollicization, free tissue transfer, and any combination of the former. In 1981, Buck-Gramco expanded upon Blauth’s previous classification system that is helpful in understanding this spectrum and in choosing operative treatment. In 1995, Manske further divided type III hypoplastic thumbs into two variants based on the integrity of the CMC joint. Type IIIA thumbs have an intact and stable CMC joint, whereas type IIIB thumbs do not. The main difference for treatment is that some believe that the lack of a CMC joint precludes any successful attempt at reconstruction, and these thumbs therefore should be amputated. This classification system is illustrated in Table 80–1. Type I hypoplasia is often treated with observation only. Types II and IIIA hypoplastic thumbs are two common variants amenable to surgical reconstruction. Types IIIB and IV are usually treated by amputation and index pollicization. Type V is treated by index pollicization, provided there is a sufficient index finger present. Although our case illustration is that of a patient with type II hypoplasia, the principles involved in assessment and treatment apply to all hypoplastic thumbs.

When examining an infant or child, it is important to take account of the child’s health, as well as to examine the entire extremity. Associated syndromes include VATER (vertebral defects, imperforate anus, tracheoesophageal fistula, and radial and renal dysplasia), Holt-Oram, and Fanconi’s anemia. In 1996, James et al surveyed a large group of patients with hypoplastic thumbs. They found radial dysplasia in 59%, and associated syndromes in 43% of the patients.

There are several key points to keep in mind when examining the hand. First, the examiner should check the appearance of the thumb, particularly its size and length. The examiner should also test for the stability of the thumb ray at all joints including the interphalangeal (IP), MP, and CMC joints. Interphalangeal joint stiffness may be present, and parents focus on the lack of motion; however, these patients often have no functional problems, and the parents should be steered away from considering surgical intervention in these cases. Next, the examiner should assess the motors of the thumb ray. Careful observation with the child at play allows for assessment of the extrinsic and intrinsic flexors, extensors, adductors, and abductors. Depending on the severity of the hypoplasia, any of several muscles or muscle groups may be absent or deficient, including the median innervated thenar intrinsic muscles, the ulnar innervated thenar intrinsic muscles, and the thumb extrinsic muscles. The examiner should assess the thenar web space. Often, as in our case illustration, there is evidence of adduction contracture secondary to a lack of median innervated intrinsics with consequent thenar space narrowing. Finally, radiographs of the hand and forearm allow for assessment of the integrity of the bony architecture. In fact, the appearance of the bones can aid in the diagnoses of associated syndromes, including radial dysplasia, Fanconi’s anemia, and Holt-Oram syndrome, in addition to others. A discussion of such radiographic features is beyond the scope of this chapter and is available elsewhere.

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