shoulder blade
髆 refers specifically to the shoulder blade bone. It is a narrow anatomical term with no broader conceptual extensions.
髆 combines 骨 (bone) with 尃, which likely provides the sound. The character is a phono-semantic compound specifically coined for the shoulder blade.
The left side 骨 means bone. The right side 尃 looks like a spread-out hand over a field, like a shoulder blade spreading across the back. Together they point to the shoulder blade bone.
For ハク, imagine a doctor tapping your shoulder blade with a small hammer: the sound is a crisp 'haku' (ハク) as the bone is checked.