Extensor Medii Proprius: A Cadaveric Case Report

During routine dissection of 11 cadavers that originated with the Body Donor Program at Philadelphia College of Osteopathic Medicine (PCOM) Georgia, a 69-year-old African American male with bilateral extensor anomalies in the dorsal forearm compartment was encountered. The distinct muscle belly, identified as the extensor medii proprius (EMP), originated from the distal ulna and was inserted near the dorsal aponeurosis of the third digit. Manual traction of the right EMP tendon resulted in the extension of the third digit, suggesting the functional significance of the anomalous muscle. This case study analyzes the EMP found during dissection, as well as the anomalous muscle’s prevalence, embryologic origin, and clinical relevance. The presence of the EMP muscle and tendon can be considered when assessing pain in the dorsum of the hand and when preparing for surgical repair or tendon transfer.