The Acanthostega and Tulerpeton limbs seem to form "elbows" in an axis perpendicular to the flexor and extensor plane of the fin. They seem to "flex" their "elbow" forwards, pre-axially. And, I assume, keep it permanently "flexed", a bit as if their humerus, ulna, and radius has been one single "V-shaped" bone. This adaptation positions the primordial hand forwards. Is this pretty much correct? Why I wonder, I always understood elbows as bending in the flexor/extensor plane, but in the first terrestrial life it seems to be in the pre-axial/post-axial plane. That probably has implications for how limbs continued to evolve, and for the embryogenesis of limbs in mammals like humans. I found that interesting.
The current research doesn't venture many details on the elbows/radius/ulna and locomotion biomechanics.
For the moment they just say the elbow was "slightly flexible" and that the bones were transitioning towards a round shape.
You can research deep into the resources and will perhaps find more.
Here are a resource which give context, found via "locomotor performance in stem tetrapods" https://www.researchgate.net/publication/236460049_Historical_Perspectives_on_the_Evolution_of_Tetrapodomorph_Movement
There's also a 3D study of the legs here: https://www.researchgate.net/publication/227857349_Three-dimensional_limb_joint_mobility_in_the_early_tetrapod_Ichthyostega