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 . <EOS>