Camptodactyly refers to congenital flexion contracture of the proximal interphalangeal joint of the finger (usually little finger), a condition that is often hereditary and can be bilateral. Although it usually requires no treatment, surgery may be indicated if the flexion contracture is disabling or associated with deformity of the ring finger. Moderate defects are improved by release of the flexor digitorum superficialis tendon and lengthening of the palmar skin, followed by postoperative splinting. More severe cases may require release of the palmar ligament, reconstruction of the extensor tendon, and arthroplasty or arthrodesis.

In the thumb, the absence of one or all of the extrinsic abductor or extensor pollicis tendons produces isolated postural deformities related to the missing structures. Thumb flexion deformities are usually bilateral and symmetric and are frequently hereditary. They must be differentiated from conditions such as trigger thumb, arthrogryposis multiplex congenita, and upper motor neuron disease (spasticity). If a thumb flexion deformity is recognized in infancy, splinting and daily manipulation can prevent soft tissue contractures. Surgery should be postponed until the child has developed more complex grasping movements, which usually occurs by 3 years of age. Surgical correction may require tendon transfers and release of skin contracture, as well as release of contracted adductor or short flexor muscles.

Trigger thumb deformity, which is characterized by flexion of both the metacarpophalangeal and interphalangeal joints, is caused by a nodule on the flexor pollicis longus tendon that interferes with tendon excursion. The condition is rare in the other digits. Surgery is indicated to release the flexor pollicis longus tendon longitudinally.

Occasionally, anomalous anchorage of the deep transverse metacarpal ligament to the first metacarpal or proximal phalanx of the thumb causes adduction contracture of the thumb with narrowing of the first web space. The narrowed web space and deep transverse ligament are released surgically.

Clinodactyly refers to a digit curving medially or laterally in the radioulnar plane. The deformity is due to a failure of skeletal differentiation in a phalanx and is most common in the middle phalanx; the little finger is most often affected. The angulation can begin at the level of the joint or the diaphysis or may result from a delta-shaped phalanx. Relatively severe deformities require surgical treatment.

Arthrogryposis Multiplex Congenita. This deformity is caused by a disseminated failure of differentiation of the soft tissue of the limbs. Isolated muscles or groups of muscles are absent, and the joints they control may become stiff and fuse spontaneously. One or all four limbs may be affected, and usually spinal anomalies are present as well (see Plate 4-24 for a complete discussion).

III. Duplication of Parts

Duplication of parts is believed to be caused by a specific insult that causes the limb bud, or ectodermal cap, to split very early in development. Defects in the hand range from polydactyly to twinning (mirror hands) and can involve the skin and nails, the soft tissues, or both, plus the skeletal structures. A single bone or an entire limb may be duplicated.