Extensor Retinaculum
A structure called the "extensor retinacula" consists of a group of
heavy connective fibers in the tissues of the wrist. It connects the
lateral margin of the radius (shorter forearm bone) with the inside border
of the ulna (longer forearm bone) and with certain bones of the wrist. The
retinaculum gives off branches of connective tissue to the underlying
wrist bones, creating a series of sheath-like compartments through which
the tendons of the extensor muscles pass to the wrist and fingers.
As in the case of the wrist, the tissue formations in various regions of
the ankle is thickened to form retinacula. Toward the front, for example,
extensor retinacula connect the tibia and fibula (lower leg bones) as well
as the calcaneus (Achilles tendon) and tissue of the sole of the foot.
These retinacula form sheaths for tendons crossing the front of the ankle.
