Isolated flexor digitorum superficialis tendon function is determined by assessing:

B. Flexion of the proximal interphalangeal joint with the adjacent digits held in extension.

DISCUSSION: Metacarpophalangeal joint flexion is effected by intrinsic flexor digitorum profundus or flexor digitorum superficialis contraction and therefore cannot be utilized to assess isolated flexor digitorum superficialis integrity. The flexor digitorum superficialis tendon, by inserting on the middle phalanx, acts to flex the proximal interphalangeal joint. Since the flexor digitorum profundus tendon inserts distal to this level, it may also flex this joint. To negate this influence of the flexor digitorum profundus, the adjacent digits should be passively maintained in full extension to isolate flexor digitorum superficialis function in the digit. Distal interphalangeal flexion is the isolated function of the flexor digitorum profundus. The proximal interphalangeal joint may be flexed by the flexor digitorum profundus or flexor digitorum superficialis.