In some cases, posterior (from the backside) fixation is needed in the cervical spine. One way to achieve this end is to use screws on the back side of the spine called Lateral Mass Screws. These screws go into a part of the bone called the "lateral mass" where there is more bone for a screw to potentially secure the bone.
So as to not stress the screws, a stress that might cause the screws to lose purchase/bite in the bone, the rods are contoured to fit the alignment of the screw heads.
After a drill hole is carefully made using anatomic landmarks, screws are placed into the lateral masses.
The bones are effectively connected/stabilized by applying the end caps or locking screws to secure the rod to the screws.
