A bone plate assembly including at least one bone plate, polyaxially adjustable fixation elements and a polyaxially adjustable locking mechanism. A first plate includes at least one polyaxial element for lockable connection with a fixation pad, and a connection feature which allows the plate to translate and polyaxially rotate relative to the locking mechanism. A second plate includes at least one polyaxial element for connection with a fixation pad and a connection feature for non-rotatable connection with the locking mechanism. The locking mechanism allows translation and polyaxial adjustment of the first plate relative to the second plate and locks the first and second plates via a taper lock. The fixation pad includes a deflectable spacer configured to prevent premature locking of the pad. Methods for implantation of the bone plate assembly between two bone structures are disclosed. Instrumentation for implantation, compression and locking of the bone plate assembly is disclosed.