Introduction: Review of literature or current anatomy textbooks provides scanty description of the extensor apparatus of thumb. Existing studies on extensor tendons of hand revolve around their application in surgical repairs of ruptured tendons or in reconstructive surgeries involving re-routing of flexor tendons to extensor tendons in radial n palsy. The knowledge about the prevalence of variations in the structure and formation of the extensor expansion of thumb would help surgeons in planning new reconstructive techniques for better functional output. Aim: To study the variations in the formation and structure of dorsal digital expansion of thumb in cadavers and statistically analyze the prevalence of its variations in males and females. Method: By cadaveric dissection of 11 right and 11 left thumbs, the formative tendons of extensor expansion of thumb (EET) were observed; namely extensor pollicis longus(EPL) and extensor pollicis brevis(EPB), and presence of contributing tendons of extensor expansion of thumb (EET) namely Abductor pollicis brevis(ABP), adductor pollicis(ADP)and palmar interossei (PI) were noted. Results: In all the 22 thumbs a triangular shaped extensor expansion existed over the dorsal aspect of base of proximal phalanx.9 out of 22 thumbs had tendinous extension of EPB extending with EPL upto the distal phalanx. ABP, ADP and PI were contributing to EET in 2, 1, and 9 thumbs respectively. Conclusion: Extensor expansion of thumb, hitherto not mentioned in standard textbooks of Anatomy was dissected and its formation, design and variations displayed.
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