231. The use of fusion mass screws in revision spinal deformity surgery: preliminary results and analysis

Abstract

BACKGROUND CONTEXT Revision spinal deformity surgery in a previously fused spine often presents a number of challenges. Conventional landmarks for pedicle screw placement may be obscured or nonexistent, increasing the potential for inadequate fixation and spinal cord or nerve root injury. In these situations, screws through an existing fusion mass in patients with prior spinal fusion represent an alternative to pedicle screw fixation. This may provide stable fixation while reducing the risk of complications related to pedicle screw placement. PURPOSE To further elucidate the safety and efficacy of fusion mass screws (FMS) in revision spinal deformity surgery as an alternative and/or adjunct to pedicle screw fixation. STUDY DESIGN/SETTING Case series. PATIENT SAMPLE Adult patients undergoing revision spinal deformity surgery. OUTCOME MEASURES BMD of fusion mass, AP thickness of fusion mass, presence and degree of canal breach, screw loosening, screw failure, pseudarthrosis. METHODS Fourteen freehand FMSs were placed in six cases of revision adult spinal deformity surgery between 2016 and 2018. All screws were 5 mm in diameter. FMSs were used to save distal levels from fusion, assist in closing a three-column osteotomy, stabilize a Charcot spine with severe degeneration, and achieve fixation in the setting of pedicular dysplasia associated with NF-1. The bone mineral density (BMD) and thickness of the posterolateral fusion mass was assessed on preoperative CT scans at the level of each planned FMS when available. The accuracy of FMS placement and presence of pseudarthrosis were evaluated on postoperative CT scans. RESULTS Fourteen freehand FMSs were placed in six cases of adult spinal deformity. In all cases, FMSs were combined with pedicle screws, at times at the same levels. There were no neurophysiologic alerts observed during FMS placement and no neurologic deficits or complications postoperatively. On postoperative CT, 1/14 screws had a low-grade breach into the canal ( CONCLUSIONS A mature fusion mass consists of a dense, vacant surface for screw fixation. FMSs may be used to achieve stable fixation in revision spinal deformity cases when pedicles are dysplastic and/or normal anatomical landmarks are obscured by an extensive fusion mass. Additionally, FMSs may provide an additional anchor at a level where two pedicle screws are already placed to increase the strength and rigidity of the construct, assist in osteotomy closure, and potentially shorten the construct. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.