The present invention is generally directed to orthopedic fixation devices that comprise a coupling element and a bone fastener, whereby the bone fastener can be loaded into the coupling element through the bottom of a bore in the coupling element. The orthopedic fixation devices described herein can include modular locking clamp assemblies that can be fixed onto fasteners that are already implanted in bone. The modular locking clamp assemblies can include polyaxial locking clamp assemblies, as well as monoaxial locking clamp assemblies.