Ultrasonographic Evaluation of Flexor Pollicis Longus Tendon Location in Various Functional Hand Positions

<b>Background:</b> Flexor pollicis longus (FPL) tendon injury is a significant complication following distal radius fractures treated with volar locking plate fixation. We were unable to find any studies investigating the FPL tendon in relation to the distal radius in various functional hand positions. The aim of this study is to comprehensively evaluate FPL tendon location in essential functional hand positions commonly encountered in daily life, including pulp pinch, key pinch, chuck grip, power grip, cylindrical grasp and spherical grasp. <b>Methods:</b> We assess the position of the FPL tendon and finger flexor tendons concerning the radius in various functional hand positions. Sixty-two wrists in 31 healthy volunteers were examined using transverse ultrasonography at the watershed area of the radius in six different functional hand positions, including pulp pinch, key pinch, chuck grip, power grip, cylindrical grasp and spherical grasp. <b>Results:</b> The shortest distance between the FPL tendon and radius was observed in the key pinch position with a mean of 3.37 mm, while the cylindrical grasp position showed the farthest distance with a mean of 4.21 mm. <b>Conclusions:</b> The location of the FPL tendon and finger flexor tendons varies across different functional hand positions. Our study shows that these tendons are closest to the radius when the hand is in the key pinch position. <b>Level of Evidence:</b> Level IV (Diagnostic).