A common linking error that happens all the time in games is that the clavicle is attached to the humerus and over 99% of all artists SKIP the SCAPULA.  

Or as gamers put it – link the shoulder bone to the upper arm bone.

This has been a problem plaguing gamers forever. And they usually just wind up guessing a point for the joint. 

And as a result this gives a weird look to the way the shoulders perform.

This error is repeated in all books and even in IK software like biped.  This is incorrect linking.  So that is why most  game characters have a weird look in the shoulders. 

And one can make superficial fixes all year long …… and one can puzzle on it forever….and it will still not look right….until you fix the root of the problem.

The shoulder is more complex than just one joint.  The shoulder should have 3 axis. Not 2 axis. 

The scapula rotates and allows the arm to extend the clavicle forward and upward.   Skipping the scapula makes it look like the character cant bend all the way forward.  With 2 Axis its like having limited mobility.

If we take a look at a realistic skeleton overlaid with a typical LINK setup – then the error becomes completely obvious……….the collarbone is at an opposite angle of where it should be to compensate for the missing axis of the scapula.

And we all know from anatomy that if your bodies bones are a fraction of an inch off that causes major alignment issues.  And when one  applies mocap data that is why things can look stiff.

Now it may seem like it makes sense to cut out the scapula, since there is so little distance between the scapula that it can be simplified and cut out….and that is what most game artists conclude.   And this belief is even perpetuated through books and manuals.  Even in IK systems tutorials they all go by this simplified skeleton.

Skipping the scapula is like skipping the knee joint between hip and ankle. If one does that then the leg will move stiff and no fix in the world will be able to make it look right until you return the knee joint.   Then it makes sense.

Scapula pivot is shorter distance but same theory applies. Skipping Scapula is like skipping the knee.

Now in order to SOLVE THIS  there is …….only one logical solution – just put an extra bone into the Arm hierarchy.

Now the SCAPULA becomes like HELPER BONE to the Clavicle and it helps to extend the mobility of the arm on extreme extensions. Looks like a more natural setup already. 

When shooting for 100% realism you have to apply the natural laws of nature.

An Artist just can not make up their own anatomy that goes contrary to nature and then wonder why it looks all unnatural…..then instead of fixing the core problem they spend all their time on superficial fixes that never seem to quite work.

And that is the core problem many artists only concentrate on what they see outside and forget to look inside.