[Symbrachydactyly--a roentgenographic and clinical study of 126 cases].

One hundred and twenty-six cases of symbrachydactyly were analyzed roentgenographically and clinically. This curious anomaly of the hand is sporadic and of unknown etiology. It is predominantly one-sided, either isolated or combined with ipsilateral pectoral muscle defect (fifty-one cases). On X-ray pictures, the skeletal abnormalities of the hands ranged from mild involvement featured with hypoplastic or aplastic middle phalanges to the most severe involvement in which all the phalanges were missing, providing a continuous spectrum. Even in the mildly affected hands hypoplasia involves all the phalanges and metacarpals, most severely in the middle phanges followed by distal, proximal phalanges and metacarpals in turn. The forearms and arms are less affected than the hands. The tendency is observed in the severely affected hands. In the most severely affected hand all the digits are missing, but there exist several finger-buds which carry often nail rudiments. Synostosis is seen in the remaining hypoplastic metacarpals often and in carpals infrequently. Although remarkable shortening and curving forearm bones are observed often, the humeral involvement remains mild. Abnormalities of muscles and tendons are frequently observed in the hand and forearm. The anomaly is classified roentgenographically into three types: Type I (brachydactyly type) which is featured with fingers having three or two phalanges (fifty-four hands), Type II (partial ectrodactyly type) in which one to four digits have only one phalanx or none(thirty-nine hands), and Type III(total ectrodactyly type) in which all the digits have only one phalanx or none (thirty-five hands). The symbrachydactyly seems to be caused by a extensive defect in an undifferentiated mesenchyme of the arm bud at about developmental stage 16, which may later cause a failure of separation of skeletal and muscular tissues of the hand and forearm or an arrest in their development.