29/09/2026
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✨ FLEXOR POLLICIS LONGUS
The flexor pollicis longus is a long flexor of the thumb whose belly is located in the deep compartment of the anterior forearm.
It is the only muscle in the body that crosses the interphalangeal joint of the thumb, so it is the only muscle that flexes the distal phalanx of the thumb (at the interphalangeal joint).
It also crosses the wrist joint (anteriorly), so it flexes the hand at the wrist joint.
As seen in the illustration, it also crosses the elbow joint (anteriorly), so it also flexes the elbow joint… but… sometimes the humeral head is not present, so when it isn’t, this muscle doesn’t cross the elbow, therefore it cannot flex the elbow joint.
PALPATION
Even though it is in the deep anterior forearm, the flexor pollicis longus is easy to palpate.
Place your palpating finger pads (I recommend using your index and middle finger pads), on the distal anteroradial forearm, just proximal to the wrist joint. Now ask the client to flex the thumb only at the interphalangeal joint, and anything that engages should be our target muscle.
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🚨Please note that the use of this artwork requires proper credit to be given (Permission: Dr. Joe Muscolino. www.learnmuscles.com – art work Giovanni Rimasti)
