A Case of Bilateral Interconnected Abductor Pollicis Longus Accessory Tendon and Abductor Pollicis Brevis Accessory Head, With Absent Extensor Pollicis Brevis

Anatomical variations in the abductor pollicis longus and extensor pollicis brevis muscles are frequently reported in the literature and can raise implications for functionality, inflammatory conditions, and surgical considerations. This case study presents a unique combination of morphological features affecting the abductor pollicis longus (APL), abductor pollicis brevis (APB), and extensor pollicis brevis (EPB) muscles. It also discusses the potential etiology and functional and clinical implications of this variation. Phase 1 medical students dissected the forearm and hand of a male donor during their formal anatomy curriculum, revealing a bilateral interconnection between an accessory tendon of APL and an accessory head of APB, as well as the absence of EPB. This variation likely resulted from the aberrant separation of muscle precursors and the failure of regression of a muscle slip in the hand during embryonic development. Probable functional implications include weakened thumb extension and opposition and an altered range of motion at the affected joints. Understanding the diversity of anatomical variations in the forearm and hand is important for effective treatment of related inflammatory conditions.