The flexor carpi ulnar is a mighty important muscle of the forearm and the hand as well …
those are the important words that should come to our mind when u remember this muscle
substantial excursion, fleshy to the bone, a grasp muscle not a release one, not an expendable source for muscle transfer except in CP patients, and finally a polyarticular one
here are the TEN functions of the FCU muscle:
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This muscle is a poly-articular muscle capable of moving the wrist in two planes, flexing the elbow, and moving the CMCJs at its distal insertion points, it is no surprise the length of its fleshy part and its great excursion ability
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Wrist flexion with ulnar deviation is a more natural path of describing wrist flexion given the wrist oblique mediolateral axis of rotation. The throwing phase of throwing a dart is a very commonly used example of the action of this muscle.
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It can produce pure ulnar deviatory forces if it acted with the Extensor carpi ulnaris as a co-agonist. As it inserts on the most ulnar side of the wrist, it has to angularly shorten more to produce the available substantial ulnar deviation range of the wrist. It has a great moment for producing the famous ulnar torque of the hand, especially useful for manual workers who need to generate strong ulnar deviatory torques in forcible power grasp, which is very useful in farmers, shovel and blacksmith workers. The risk of potential active insufficiency is minimized by the massive excursion capacity of this important muscle.
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Its wrist flexion moment is maximized by the presence of its sesamoid, the pisiform, that pushes the muscle’s line of pull farther anterior from the wrist center of rotation. Given its great wrist flexion moments, wouldn’t it have been great if it was a grasping muscle as grasping is the power-derived hand function??? yes it would , but how can a wrist flexor be a grasping muscle??? .
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This muscle is more favored for the grasping function, which might seem a bit odd given its wrist flexing ability. Actually, it is selected for grasp given its ulnar deviatory ability rather than its wrist flexing one. Ulnar deviation brings the thumb more in line with the forces that act on it, provides the much-needed adjustment of the long flexor tension-force optimization by angulating the path of those tendons across the wrist, thus maintaining their degree of tension. It does so by acting co-agonistically with the extensor carpi ulnaris, the latter offsets its flexion moments and augments its ulnar deviatory capacity. Those two ulnaris muscles are a complex example of muscles that can act co-agonistically “coronal plane”, antagonistically “sagittally”, and synergistically to one another. Recruitment of the flexor carpi ulnaris as a power grasp muscle happens when we need much more power; in the early phases of power grasp the wrist rather extends, but if we tried increasing the power of our grip, we would notice the wrist coming to neutral sagittally and drifting in ulnar deviation more.
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Do you remember when we said that the ample ulnar deviation range can put the ulnar ligamentous side of the wrist in a great degree of slack?? Especially because it is mainly stabilized and fortified by ligamentous structures. The peculiar attachment of both the ulnar wrist deviators to the ulnar-sided wrist ligaments and capsule prevents this slack as they pull them tight during ulnar deviation, augmented and aided by the never shortening ulnar carpal column.
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Finally, this muscle produces CMCJ flexion of the 4th, 5th rays, necessary for the cupping function “accentuation of the distal transverse arch”, enabling these two relatively short rays to oppose against the thumb in precession handling and to flex forcibly in the palm to hold small objects.
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The ulnar deviation during grasp increases the ulnar deviation of the medial four MCP joints, enabling them to oppose against the thumb without too many stresses on the little fingers CMC joints.
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Can be a strong elbow flexor if the distal joints are held in full extension “refer back to biarticular muscles and how they work in the biology muscle section”, a tricky nice contact fighting tip
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it acts synergistically with all and every first ray action especially that of the thumb abductors to neutralize their radial deviatory forces. try abducting your thumb while feeling your FCU tendon
you will feel it tighten with every thumb abduction. Remember, the best mechanical advantage for a muscle to produce radial deviation is for the thumb abductors, not the radial wrist deviators