Aberrant Extensor Digitorum Tendon Lies Superficial to Extensor Retinaculum

BACKGROUND: The extensor digitorum muscle (EDM) is located on the posterior aspect of the forearm. The tendons of this muscle typically run deep to the extensor retinaculum (ER), which is a fibrous sheath that stabilizes and aligns the extensor tendons. ER has been used in the past as a graft source to treat Boxer's Knuckle, an injury of the metacarpophalangeal (MP) joint capsule. This indicates the minor role ER plays in physiologic function. EDM is innervated by the posterior interosseous nerve, a branch of the radial nerve, and is used in extending digits 2 through 5. CASE INFORMATION: This case report presents an anatomical variance that was found within a 66-year-old male cadaver's EDM. The most medial tendon of the extensor digitorum lies superficial to the extensor retinaculum. We have theorized that this anatomical variance would present itself in a similar manner as the palmaris longus tendon. CONCLUSION: To our knowledge, this anatomic variation has yet to be documented. The donor's medical history reports no motor dysfunction to the phalanges, thus it has been concluded that this variation contributed to no complications. The lack of previous documentation on this variant, both in scientific literature and the donor's personal medical history, leads us to suspect that the variant is either uncommon or not of mechanical significance.