German to English Medical Medical: Instruments Orthopedics, radiology

This is from a German surgery report, patient had been in a car accident and suffered broken thoracic vertebrae.

Optical guidance was used in the surgery, a laminectomy and reduction with osteosynthesis and internal fixator.

The word "Stern" appears as follows:

"Anschließend wird der Stern am BWK7-Dornfortsatz befestigt und die Navigation eingerichtet."

From context it seems that the Stern is a type of attachment or part of the focusing for the optical guidance, but I have never seen this word used in this context and I can't find it by googling either. Can anyone help me figure out what "Stern" means here and what it is in English?

Thanks!

Stephen