A modular uniplanar pedicle screw assembly for use with a polyaxial bone fastener, the modular uniplanar pedicle screw assembly comprising: a uniplanar tulip assembly adapted to be coupled to a head of the bone fastener and comprising: a detachable tulip element, the uniplanar tulip assembly further comprising a locking clamp assembly, the locking clamp assembly comprising a saddle, having a longitudinal slot and a clamp; and the tulip element and the locking clamp assembly being coupled or assembled together; the uniplanar tulip assembly further comprising an adapter including: (i) a lower portion sized and shaped to be received in a recess of the head of the bone fastener, and (ii) an upper portion extending from the lower portion, the upper portion including a pair of oppositely positioned lateral surfaces, the upper portion being configured to be received in and slide along the longitudinal slot of the saddle to allow movement of the uniplanar tulip assembly in a first plane along a direction that is parallel to a longitudinal axis of the longitudinal slot, each of the lateral surfaces of the adapter abutting against respective oppositely positioned inner walls of the longitudinal slot and thus preventing movement of the uniplanar tulip assembly in a second plane lateral to the first plane relative to the bone fastener. a uniplanar tulip assembly adapted to be coupled to a head of the bone fastener and comprising: a detachable tulip element, the uniplanar tulip assembly further comprising a locking clamp assembly, the locking clamp assembly comprising a saddle, having a longitudinal slot and a clamp; and the tulip element and the locking clamp assembly being coupled or assembled together; the uniplanar tulip assembly further comprising an adapter including: (i) a lower portion sized and shaped to be received in a recess of the head of the bone fastener, and (ii) an upper portion extending from the lower portion, the upper portion including a pair of oppositely positioned lateral surfaces, the upper portion being configured to be received in and slide along the longitudinal slot of the saddle to allow movement of the uniplanar tulip assembly in a first plane along a direction that is parallel to a longitudinal axis of the longitudinal slot, each of the lateral surfaces of the adapter abutting against respective oppositely positioned inner walls of the longitudinal slot and thus preventing movement of the uniplanar tulip assembly in a second plane lateral to the first plane relative to the bone fastener. (i) a lower portion sized and shaped to be received in a recess of the head of the bone fastener, and (ii) an upper portion extending from the lower portion, the upper portion including a pair of oppositely positioned lateral surfaces, the upper portion being configured to be received in and slide along the longitudinal slot of the saddle to allow movement of the uniplanar tulip assembly in a first plane along a direction that is parallel to a longitudinal axis of the longitudinal slot, each of the lateral surfaces of the adapter abutting against respective oppositely positioned inner walls of the longitudinal slot and thus preventing movement of the uniplanar tulip assembly in a second plane lateral to the first plane relative to the bone fastener.