Spinal fixation system connectors comprising spring cage elements. In some embodiments, an engagement member, such as a bone screw, may be configured to be coupled with and received within a connector body. A spring cage structure may also be configured to be coupled with the connector body. The spring cage structure may comprise a spring configured to be positioned in a relaxed configuration and a flexed configuration, such that the spring defines an opening having a first size in the relaxed configuration and a second, larger size in the flexed configuration to allow the opening to receive and engage a head of the engagement member within the connector body.
