Radiologic analysis of pedicle marker for the cervical spine.

PURPOSE: To elucidate the usefulness of the pedicle marker (PM) for more accurate insertion of cervical pedicle screws (CPSs).

METHODS: Artificial bone study. Fifty pedicles of five artificial bone specimens were examined. PMs were inserted in five different positions (confirmed by computed tomography (CT)); (1) insertion angle correct, insertion point too medial, (2) both insertion angle and insertion point correct, (3) insertion angle correct, insertion point too lateral, (4) insertion point correct, insertion angle too big, and (5) insertion point correct, insertion angle too small. Oblique radiographs were taken to assess the relationships between the pedicle and the PM as IN and OUT. Clinical series. A total of 228 CPSs were inserted in 59 consecutive patients using either CT cutout technique or navigation. During surgery, PMs were inserted, and the locations were confirmed on oblique fluoroscopic views in CT cutout technique and intraoperative CT in navigation. Intraoperative misplaced PM and postoperative misplaced CPS were assessed.

RESULTS: Artificial bone study. Evaluation found 67% of Types 1 and 100% of Type 5 seemed to be IN on the oblique views at 10, 20, and 30° because the pedicle and PM overlapped. All cases of Type 2 were IN at any angles. Almost all Types 3 and 4 were OUT at any angle. Clinical series. The route was modified under the recognition of misplaced PM during surgery in 3.7% (all Type 4) of CT cutout and 4.2% (four Type 4 and one Type 5) of navigation. One CPS was malpositioned (0.9%, Type 1) in CT cutout and none in navigation by postoperative CT.

CONCLUSIONS: By applying PM, lateral displacement is easier to recognize in fluoroscopy. Medial misplacement should be aware because the PM and the rim of the pedicle overlap. Even after launching navigation, PM helped to indicate the wrong route before inserting the CPS during surgery.