Treatment of thoracic scoliosis: are monoaxial thoracic pedicle screws the best form of fixation for correction?

STUDY DESIGN: Multicenter retrospective cohort study of 100 consecutive patients.

OBJECTIVE: Compare the coronal and sagittal plane radiographic outcomes and clinical rib hump deformity correction in patients who underwent posterior spinal fusion for adolescent idiopathic scoliosis using hybrid instrumentation, polyaxial (POLY) segmental pedicle screw fixation, or monoaxial (MONO) segmental pedicle screw fixation.

SUMMARY OF BACKGROUND DATA: Instrumentation for the treatment of scoliosis has evolved. Current techniques include use of a combination of hooks, sublaminar wires, and pedicle screws (HYBRID), as well as segmental pedicle screw fixation with either monoaxial or polyaxial screw anchors.

METHODS: Data were obtained from a multicenter prospective database registry. Radiographic assessment was performed from radiographs taken before surgery and 2 years after surgery. Intraoperative parameters assessed included operative time, estimated blood loss, and whether or not a thoracoplasty was performed. Clinical evaluation of the angle of trunk rotation was done with an inclinometer.

RESULTS: Preoperative thoracic curvature and curve flexibility, age, Lenke curve type, and number of levels fused was similar for each group. Significantly more anchors per level were used in the MONO group (1.69) and in the HYBRID group (1.24) compared to the POLY group (1.06). There were no statistical differences among the groups with respect to major thoracic curve correction (MONO: 69%; POLY: 68%; HYBRID: 62%, P = 0.22). POLY constructs maintained thoracic kyphosis, whereas MONO and HYBRID had a tendency toward loss of thoracic kyphosis and there was a trend toward a greater percent thoracic angle of trunk rotation correction in the MONO group (55%) compared with the POLY group (32%, P = 0.10), but no differences compared with Hybrid (55%, P > 0.05).

CONCLUSION: Similar coronal and sagittal plane correction was achieved in thoracic adolescent idiopathic scoliosis with 3 different constructs. There was a trend toward improved correction of clinical rib hump deformity with MONO screw constructs compared with POLY screw constructs.