A comprehensive study of the extensor tendons to the medial four digits of the hand.

Background: Awareness of the anatomy and variations of the extensor tendons on the dorsum of the hand is necessary when assessing the traumatized or diseased hand and when considering tendons for repair or transfer. A complete quantitative documentation of the extensor tendons is lacking.

Method: The arrangements of extensor tendons to the medical four fingers namely, the extensor digitorum communis (EDC), extensor indicis proprius (EIP) and extensor digiti minimi (EDM) on the dorsum of the hand and the intertendinous connections between them were studied in 100 upper limb specimens. The findings were photographed, tabulated and analyzed statistically.

Results: In 98% of the specimens, the EIP was a single tendon with a single insertion, whereas in two right upper limbs there were two EIP tendons with two insertions. In 77% of the specimens the EDC distally had tendons to the middle three fingers (EDC index, EDC longus and EDC ring). The EDC small was present in only 34% of samples and the EDM showed normal anatomy in only 20%. The most common types of juncturae tendinum in the 2nd, 3rd and 4th intermetacarpal spaces were Type 1, 2 and 3r, respectively. Two accessory muscles were seen. One was the extenson medii proprius in 5% of samples and the other, the extensor digitorum brevis manus, was seen in 3%.

Conclusion: Variations of the extensor tendons were common in this study, especially for the middle and ring fingers which showed multiple tendons of the EDC.