Systematic review and meta-analysis for the impact of rod materials and sizes in the surgical treatment of adult spine deformity

PURPOSE: To assess clinical and safety outcomes associated with different rod materials and diameters in adult spinal deformity (ASD) surgery. METHODS: A systematic literature review and meta-analysis evaluated ASD surgery using pedicle screw fixation systems with rods of different materials and sizes. Postoperative outcomes (i.e., Cobb, sagittal vertical axis, and pelvic tilt angle) and complications (i.e., pseudarthrosis and rod breakage) were assessed. Random effects models (REMs) pooled data for outcomes reported in ≥ 2 studies. RESULTS: Among 50 studies evaluating ASD surgery using pedicle screw fixation systems, 17 described rod material/diameter. Postoperative outcomes did not statistically differ between cobalt–chromium (CoCr) vs. titanium (Ti) rods (n = 2 studies; mean [95% confidence interval (CI)] sagittal vertical axis angle: CoCr 37.00° [18.58°–55.42°] and Ti 32.58° [24.62°–40.54°]; mean [95% CI] pelvic tilt angle: CoCr 26.20° [22.87°–29.53°] and Ti 20.15° [18.0°–22.31°]). The pooled proportion (95% CI) of pseudarthrosis was 15% (7–22%) for CoCr and 12% (− 8–32%) for stainless steel (SS) (n = 2 studies each; Chi(2) = 0.07, p = 0.79). The pooled proportion (95% CI) of broken rods was 12% (1–22%) for Ti (n = 3 studies) and 10% (2–19) for CoCr (n = 1 study). Among 6.0–6.35 mm rods, the pooled (95% CI) postoperative Cobb angle (n = 2) was 12.01° (9.75°–14.28°), sagittal vertical axis angle (n = 4) was 35.32° (30.02°–40.62°), and pelvic tilt angle was 21.11° (18.35°–23.86°). CONCLUSIONS: For ASD patients undergoing posterior fixation and fusion, there are no statistically significant differences in postoperative outcomes or complications among rods of varying materials and diameters. Benchmark postsurgical outcomes and complication rates by rod material and diameter are provided. LEVEL OF EVIDENCE: III