vinculum

The vincula are fine connective-tissue mesenteric folds that traverse the synovial portion of the flexor tendon sheath, carrying small branches from the digital arteries to the flexor tendons. The classical textbook description of "one short and one long vinculum per tendon" is a useful approximation that understates the documented variability of vincular anatomy; in practice the number, position, and calibre of vincula vary between digits and between individuals. Vincular flow is one of two routes of tendon nutrition within the synovial zone; the other is diffusion of synovial fluid through the sheath, which experimental work in the 1980s established as at least equally important. The clinical relevance is that complete proximal retraction of an avulsed FDP tendon (Leddy and Packer Type I jersey finger) disrupts both vincula, leaving the tendon stump avascular and the operative window for repair restricted to about seven days.