Fig. 3

Patterns of extensor tendons and their connecting fibrous bands on the dorsum of the hand based on anatomical literature, showing the most common pattern (A) and one of the many anatomical variations (B). Figures are based on data presented in Supplementary Tables S1 and S2. A The most common pattern, where the index finger has a single extensor digitorum communis tendon (in dark grey) and a single extensor indices tendon (in lighter grey) that inserts at the MCP-joint ulnar to the extensor digitorum communis. The middle finger has a single extensor digitorum communis. The ring finger originates as a single extensor digitorum communis tendon that diverges into two tendons midsubstance that again merge into one right before insertion at the MCP-joint. The little finger has a single extensor digitorum communis and a double extensor digiti minimi with double insertion at the MCP-joint. The fibrous bands are present in the 2nd, 3rd and 4th intermetacarpal spaces. B In this variation, the index finger has a single extensor digitorum communis tendon and a double extensor indices tendon (in lighter grey) that inserts at the MCP-joint ulnar to the extensor digitorum communis. The middle finger has a double extensor digitorum communis and the ring finger a single extensor digitorum communis tendon. The little finger has a single extensor digiti minimi and an absent extensor digitorum communis. The fibrous band in the second intermetacarpal space is absent and has a Y-shape in the third and fourth intermetacarpal space (y-subtype)