An OT practitioner is testing thumb interphalangeal (IP) flexion strength. The therapist definitely observes flexion of the IP joint but cannot palpate a contraction of the flexor pollicis longus (FPL). What is the most likely reason?

Question

A. The FPL may be too weak to palpate.
B. The client is giving less than maximal effort.
C. The flexor pollicis brevis may be substituting.
D. The extensor pollicis longus may be substituting.

Answer 1

ANS: D
It is common for other muscles to compensate for the function of a weaker muscle to accomplish a movement. The therapist should be familiar with possible substitutions and be vigilant in de-tecting them. For thumb IP flexion a quick contraction and release of the extensor pollicis longus may cause apparent flexion of the IP. If the FPL is contracting enough to cause visible IP joint flexion, the contraction should be palpable. Client effort is an important factor in manual muscle testing, but lack of effort is not a likely cause in this instance because there is visible IP joint flexion. It is not possible for the flexor pollicis brevis to flex the thumb IP joint because it inserts proximal to the distal phalanx.