Cobalt-chrome and titanium alloy rods provide similar coronal and sagittal correction in adolescent idiopathic scoliosis

Background: Cobalt-chrome (CoCr) and the titanium alloy TA6V (Ti) are the materials most widely used for spinal instrumentations in patients with adolescent idiopathic scoliosis (AIS). The objective of this work was to compare the effectiveness of CoCr and Ti rods in terms of coronal and sagittal correction by pedicle screw constructs in patients with AIS. Hypothesis: Correction is similar with CoCr and Ti rods in patients with AIS. Material and method: A retrospective single surgeon study was conducted in patients with AIS managed using pedicle screw posterior spinal fusion with high implant density and reduction by postero-medial translation. Follow-up was more than 2 years in all patients. Patients were divided into two groups based on whether the rods used were made of CoCr (n = 30) or Ti (n = 33). The groups were identical for age, Risser classification, follow-up duration, type of curve, and implant density. Coronal and sagittal parameters on standing full-spine radiographs were analysed using graphics software before surgery then 1 month after surgery and at last follow-up. Quantitative data were compared by applying Student's t test. Results: The percentage of main curve correction at last follow-up was the same in the two groups (76%/75%) (p = 0.7). Gains in thoracic kyphosis (12°/13°) and lumbar lordosis (8°/10°) were not significantly different between groups. At last follow-up, 3 patients had proximal junctional kyphosis, 1 in the CoCr group and 2 in the Ti group (p = 0.6). Conclusion: For posterior spinal fusion to treat AIS, with a high density of pedicle screws, correction by translation, and 6 mm rods, CoCr rods and Ti rods produce the same amount of coronal and sagittal correction. Level of evidence: IV, comparative retrospective study with no control group