Distal to, Proximal to ,Cranial to: What is the meaning of "to"?

"In all patients, the injection was administered proximal to the knee."

"The ankle is distal to the knee."

What is the meaning of "to" in these sentences ?

--- Comparing or a connection, relation between things ?

"to", in "proximal to the knee" (and "distal to") means "in relation to".
TFD - definition 8. in a particular relationship with.

In the illustration below, A is "nearer the center of the body when compared to the knee."

• proximal - "situated next to or near the point of attachment or origin or a central point."

• distal - "situated away from the point of attachment or origin or a central point especially of the body."

"proximal" and "distal" are anatomical terms that describe location in relation to an origin or to the center of the body. When we say there is a proximal obstruction in a coronary artery, it means the obstruction is close to its origin. If, on the other hand, we say the obstruction is distal, it means it's located far away from the origin, at its final portion.

This illustration shows that "proximal" and "distal" can also be used in relation to a specific point.

As you can see, A is proximal to the knee and B is distal to it. ("A" is closer to the origin of the limb than the knee)

Likewise, "cranial" and "caudal", describe how close or far something is to the skull or to the tail of an animal.