IANAD, but I’m Looking for a lesson in anatomy here.
Suppose I am sitting at a desk, with my palm resting on the desktop. Now I rotate my hand so my palm is facing up. As I watch the motion take place, it doesn’t appear that my wrist is actually performing the rotation; instead, the distal heads of the radius and ulna appear to orbit each other, sort of like binary stars, changing the angle of the line that defines the orientation of my wrist and hand. My wrist rotates in space, but does not appear to deform from its original shape.
The proximal heads of my radius and ulna (near my elbow) do not appear to orbit each other like that. I assume their relative positions are fixed by their participation in the elbow joint. Am I right about that?
Question: do the radius and ulna each rotate about their respective long axes during wrist rotation? That is, if my palm is facing down and I make a mark on the upward surfaces of the distal heads of the radius and ulna, will those marks still be facing upward after I rotate my palm to face up?
The ulna is fairly fixed at its attachment to the humerus by way of the olecranon process. You can feel that the ulna does not rotate by feeling your funny bone and rotating your hand. The radius, on the other hand (ha), does rotate and can be felt as well. There’s a ridge on the lateral side of the radius just under the skin that you can nicely feel rotate to point medially after you rotate your hand. There is a small amount of rotation by the ulna but nothing like the radius.
From this page it looks like in our resting “palms down” position, the radius and ulna (the two long bones connecting your hands to the elbow) are twisted with the radius on top of the ulna in a tall “X” shape. The Pronator Teres Muscle is naturally contracted at about the midway point of the bone, pulling it into that crossed position.
When we have our hands in the “palms up” position, the Pronator Teres relaxes, and the Supinator Muscle (a wide connection taking up the lower fourth of the radius) contracts and pulls the bone into a parallel position (think of the motion as being similar to a pull from over the top, but from the bottom. Like how a rolled up newspaper un-rolls).
You can feel it yourself,touch your forearm anywhere, and feel the bones inside twisting around inside you.
I’ll add, as former X-ray tech, that to get true anatomical-position of’palms-up’ from palms-down’ (technically called AP -v- PA position), the humerus itself generally needs to rotate just a tad on the majority of people. The olecronon process and its articulation with the fossa of humerus are fixed (like a hinge) while radial head is a gliding/rotating type of motion across the humeral capitulum, and its very rare, IME, to be able to turn hand/wrist over completely as described without kinda rolling the elbow 'outwards or leaning torso in direction of thumb to accomplish the full 180 turn.
But, yeah, its the radial head gliding across the humerus that allows for the vast majority of the rotation, for sure.
All I know is that when I tore my bicepital tendon at the elbow last year and had it surgically re-attached, rotating my hand that way was the most difficult and painful part of the ensuing physical therapy. It’s interesting (to me anyway) how much of that action is dependent on a muscle (muscles?) in the upper arm. Previously I had only associated the bicep with an arm curling motion, bringing the hand to the shoulder.
Skammer: it is really common to have seemingly unusual pain like yours from the densely-packed structures (the tendons/ligamenys/fascia, etc) that ‘glide’ across each other during movement(s) of joints with multiple ranges of motion such as elbow/ankle/knee - if I make sense. Joints like elbow/ankle with articulated bones held together by tendons/ligaments can be very painful when one smallish area is afflicted as there is lots of ‘cabling’ and soft-tissue ‘padding’ going on around them. I always considered the upper-arm down to fingertips to be a marvel of evolutionary engineering with how intertwined everything is for all the motions possible.
Machine Elf: I came across this site which has a lot of images (73 pics as a slideshow) that break down the elbow nicely. I stopped looking around image 35 or so, but starting around img 15-ish or so (with 17 being a good show bone position of both supination -v- pronation), and it shows/labels things re: thread rather nicely. I will go ahead and mention that a ‘tuberosity’ is generally an area of raised bony structure where tendons/ligaments attach if you view that site. Plus, a fossa is a ‘depression’ where structures fit into (like the coronoid fossa of humerus provides space for the coronoid process of the ulna). Worthy site/cite if you feel like learning more ‘technical anatomy’ and movement(s), IMHO. HTH
