A variant of extensor medii proprius: A case report

Introduction Variations of human hand extensor muscles have been previously described [1]. The extensor medii proprius (EMP) is one such variation reported with an incidence ranging from 0.8% (2 out of 263 specimens) [2], to 10.3% (6 out of 58 dissected hands) [3]. The EMP often co-exists with the extensor indicis muscle or its variant, the extensor indicis proprius on one hand or both hands [1, 4, 5]. Based on these reports, the EMP originates from the distal 1/3 of the ulna and inserts on the dorsal aponeurosis (extensor expansion) of the 3rd manual digit [1, 3–5]. We present a case where the EMP originates from the lunate, an origination not previously described. We propose that this variant be termed extensor medii proprius brevis (EMPB). We also present the innervation of this variant of EMP as observed in this case.