Each attaches proximally at the head of the metacarpal bone, and distally at the base of the phalynx.

[3] The collateral ligaments originate on depressions on each side of the metacarpal heads dorsal to axis of rotation.

From there, they extend obliquely and distally to their insertions onto tubercles at the base of the proximal phalanx.

[1] Due to the relation between their insertions on the sides of the metacarpal head and the axis of rotation in the joint, the collateral ligaments are taut in flexion but lax in extension, while the accessory collateral ligaments are lax in flexion but taut in extension.

[3] As a result, the joint is stable during full flexion while the relaxed collateral ligaments allows lateral and rotation movements during extension.