Difficult thoracic pedicle screw placement in adolescent idiopathic scoliosis

Study Design: Retrospective radiographic and clinical consecutive case series. Objective: The objective of this study was to identify patients treated with posterior spinal fusion and pedicle screw instrumentation for adolescent idiopathic scoliosis (AIS) in whom it was not possible to place a planned pedicle screw, and describe the possible difficulties in screw placement. Summary of Background Data: Despite the knowledge of anatomic characteristics of upper thoracic spine pedicles and considerable experience in thoracic pedicle screw placement, inserting pedicle screws in some patients with AIS may be difficult. Methods: We reviewed 96 patients with AIS in whom the intent was to use an all-screw construct in 2004. Placement of the pedicle screws was usually by the freehand method, with intraoperative fluoroscopy used as needed. If a screw could not be safely placed after multiple attempts, a down-going supralaminar or transverse process book was placed. Medical records were reviewed and radiographs were measured by one of the authors. Results: We identified 17 cases (18%) in which a hook had been placed. All cases had a major thoracic curve (Lenke 1, 2, and 3) and the single hook had always been placed at the most cephalad level of the construct on the patient's right side. The most common levels for hook placement were T3 and T4; these pedicles were noted to be sclerotic, narrow, and have a moderate amount of rotation on the preoperative posterior-anterior and side bending radiographs. Conclusions: Care should be exercised during pedicle screw instrumentation in the apical region of the proximal thoracic curve, whether structural or nonstructural, especially in the concavity. The preoperative radiographs may give helpful clues to intraoperative challenges of pedicle screw insertion at the uppermost level of instrumentation. Hook fixation was satisfactory in this scenario.