A bone plate for use in anterior lumbar spinal fixation has interlocking components to prevent dislodgement of the plate due to anatomical forces. The exposed surface of the plate is smooth to prevent trauma to internal body tissue. The plate spans the intervertebral space with each end attached to an adjacent vertebrae by locking screws threadably engaged with tubular bone anchors. The bone anchors include helical members are threaded through the bone plate and inserted into holes within the bone. The plate has a countersunk cavity including portions overlapping the locking screws. A locking cap fits in the cavity to secure the other end of the locking screws from backing-out of the plate. The locking cap includes at least two chamfered portions that cooperate with mating recesses in the countersunk cavity of the bone plate.