Character Deforms Badly at Joints
Pinching, collapsing or spiking at elbows, shoulders and knees
Also known as: Candy wrapper skin · Elbow collapse · Shoulder deformation bad · Mesh spikes when animated · Bad skinning joints · Character mesh breaks in pose
Quick answer
A character pinches, collapses or spikes at the joints when the topology or the skin weights cannot support the movement. Add two or three edge loops around elbows, knees and shoulders so the mesh has geometry to bend, clean up the weights so each vertex follows the right bones and sums to one, and add corrective shapes or helper joints for extreme poses. Always test with extreme poses, not just the bind pose.
How to fix it
Check the bind pose first, since a stiff or crossed pose makes weights harder, and a relaxed A-pose works well for shoulders. Mirror weights, then fix the center. Limit the influences per vertex to what the engine allows, usually four, and check that the result still looks right. Twist joints help forearms and upper arms, and corrective blend shapes fix the shapes weights cannot give.
