Fig. 3.

Hyaluronic acid injection: longitudinal scan over the flexor tendons of the fourth finger using a high frequency (17 Mhz) linear probe over the metacarpophalangeal joint. The 25 G needle is clearly displayed (empty white arrow) with its tip at the tendon sheath distal to the A1 pulley (full white arrow). Two weeks after corticosteroid injection, low-medium molecular weight hyaluronic acid is injected using the same technique into the synovial space (empty arrowheads) releasing the walls of the tendon sheath. The X and bar on the right are markers of focus in the US display (X is the center, and the bar is the range of focus). FPT = flexor profundus tendon; FST = flexor superficialis tendon; MCH = metacarpal head; PP = proximal phalange.