Extensor tendons and variations of the medial four digits of hand: a cadaveric study.

A total of 100 cadaveric limbs were dissected to study the anatomy of the forearm and hand extensor musculature. Four types of contributions to the index finger were found for the extensor indicis proprius (EIP), including one new type where the double tendons of the EIP inserts volar and radial to the extensor digitorum communis of the index finger (EDC-I). Four variant muscles were identified including the extensor medii proprius (EMP) (in five cadavers), extensor digitorum brevis manus (EDBM) (in one cadaver), extensor indicis et medii communis (EIMC) (in four cadavers) and extensor pollicis et indicis (EPI) (in four cadavers). The absence of the EIP in four cases was substituted by either the EIMC or the EPI. Two unpreviously published cases were found. In one hand, the variant EIMC was present along with the EPI. In another hand, both the EMP and the EDBM were present, and the EMP tendon inserted to the tendon of the EDBM. Awareness of the variations on the dorsum of the hand is essential for diagnosis, surgical planning and treatment of diseased hands.