Extensor indicis brevis muscle: report of a rare muscular variant and classification proposal / Músculo extensor corto del índice: reporte de una rara variante muscular y propuesta de clasificación

SUMMARY: The current report presented a rare variant of extensor indicis brevis muscle, replacing extensor indicis, in the left hand of an adult male cadaver. The origin of the muscle was reported, for the first time, to be from the distal margins of radius and ulna. The muscle is inserted into the extensor expansion of the index. A new classification for extensor indicis brevis muscle was proposed based on its origin. Awareness of rare anatomical variations would help clinicians and surgeons in accurately managing suspected cases and planning surgical procedures.

RESUMEN: Este informe presenta una variante rara del músculo extensor corto del índice, que reemplaza al extensor del índice en la mano izquierda de un cadáver masculino adulto. Se informó por primera vez, que el origen del músculo se realiza en la parte distal de los márgenes del radio y la ulna. El músculo se insertaba en la expansión extensora del índice. Se propuso una nueva clasificación para el músculo extensor corto del índice basada en su origen. El conocimiento de las variaciones anatómicas raras es útil para los médicos y cirujanos al abordar los casos sospechosos y planificar los procedimientos quirúrgicos.

Extensor Indicis Brevis: A Case Report / 대한정형외과학회잡지

Anatomical variations of the extensor tendon of the hand are common. However, the majority of anomalous variations are asymptomatic throughout a lifetime and are found incidentally during surgery or after trauma of the hand. The index finger has two independent extensor tendons and lower incidence of anomalous variations than other extensor tendons. We experienced a rare muscular variant of extensor indicis proprius (EIP) during a tendon reconstruction for spontaneous rupture of the 3rd and 4th extensor digitorum communis. Tendon reconstruction using EIP was planned preoperatively. However, EIP was absent and anomalous muscle known as extensor indicis brevis, which originated from the capsular ligament of the wrist and inserted into the ulnar side on the 2nd extensor digitorum communis of the extensor hood, was found. We performed tendon reconstruction using an alternative surgical procedure because extensor indicis brevis was not useful. Attention is required during tendon reconstruction because anatomical variation of EIP may affect a surgical procedure.