I. Failure of Formation of Parts: Transverse Arrest

Category I, which is subdivided into transverse arrest and longitudinal arrest, comprises congenital deficits characterized by either partial or complete failure of limb formation.

Transverse arrest deficits include all congenital amputation-type malformations and are classified by the level at which the existing portion of the limb terminates; all elements distal to that level are absent. Deficits in this group range from aphalangia (absence of a digit) to amelia (complete absence of a limb) (see Plate 4-38) and are sometimes referred to as congenital amputations, which should not be confused with intrauterine amputations. The transverse stump represents an arrest of formation in the limb anlage. It is usually well padded with soft tissue, and rudimentary digits or dimpling may be present.

Phalangeal Deficiency. One or more digits may be involved, and this defect may occur at any level of the digit. The mildest forms require no treatment. In patients with severe deficits and functional impairment, a cosmetic prosthesis or surgical reconstruction (e.g., bone lengthening, digital transposition, or transplantation) may be indicated. Phalangeal deficiencies in the foot usually require shoe correction only.

Transmetacarpal Amputation Type. This defect is relatively rare, usually unilateral, and often accompanied by a transtarsal amputation-type defect in the foot. The hand is short and wide, and skin nubbins may be present (see Plate 4-39). Bone mass insufficiency rules out phalangization (surgical formation of a finger or thumb from a metacarpal). Children with these defects are fitted with an opposition palmar pad prosthesis secured to the distal forearm with a Velcro strap. Wrist flexion opposes the hand remnant to the prosthesis and provides a crude type of palmar prehension with sensation.

Transcarpal Amputation Type. In this rare defect, the phalanges and metacarpals are totally absent. In some patients, five skin nubbins are present. The wrist joint is normal, and the epiphyses of the distal radius and ulna appear normal on radiographs. The carpal bones are often fused to some degree. Because the limb is usually too long for a wrist disarticulation prosthesis, an opposition palmar pad prosthesis is used to provide prehension with sensation.