Reducing Rod Breakage and Pseudarthrosis in Pedicle Subtraction Osteotomy: The Importance of Rod Number and Configuration in 264 patients with 2-Year Follow-Up

Abstract

Introduction Pedicle subtraction osteotomies (PSO) can provide substantial realignment, but are associated with pseudarthrosis and rod failure. The addition of supplementary rods and interbody fusion (IBF) may decrease the failure rate. Material and Methods Adult spinal deformity patients with ≥1 lumbar PSO and 2-year follow-up were included. Demographic, operative, and outcomes data were collected. Radiographs were assessed for implant failure; IBF; and rod number, material, and diameter. Multiple ( > 2) rod configuration was described as Accessory (connected to primary rods) or Satellite (independently anchored in the pedicles). Potential risk factors were evaluated for PSO site failure (rod breakage or revision for pseudarthrosis). Results From 264 patients included, there were 190 with 2 rods (2R), 36 with 3R, and 38 with 4R. There were no differences in demographics or baseline radiographic parameters across groups. 2R-3R constructs had a trend of higher rates of failure at the PSO site (28%, 29%) than 4R constructs (18%; p = 0.128). The 3–4R patients had significantly fewer revisions for instrumentation failure and/or pseudarthrosis than the 2R group (15% versus 26%; p = 0.035). There were 45 Accessory rods (61%) and 29 Satellite rods (39%). Satellite rods failed significantly less at the PSO site than Accessory rods (10% versus 31%; p = 0.034). Satellite configurations also had significantly fewer revisions for instrumentation/pseudarthrosis (0% versus 23%; p = 0.009) and fewer revisions for all causes (8% versus 50%; p < 0.001) than Accessory rods. 3–4R Accessory constructs were similar to 2R in failures (31% versus 29%; p = 0.452), revisions for implant failure/pseudarthrosis (23% versus 26%; p = 0.388). There were no significant differences in failures across all rod diameters (4.5, 5.5, 6.0, 6.35mm; p = 0.183). Small rods (≤5.5mm) had a trend of higher failure rates than large (≥6mm) rods (30% versus 18%; p = 0.052). In 3–4R constructs, large rods had a significantly lower rate of failure than small rods (5% versus 33%; p = 0.009). Titanium rods had a significantly higher failure rate (39%) than Cobalt Chrome (27%) and Stainless Steel (19%) rods ( p = 0.027). In 2R constructs, Titanium rods failed significantly more (44%) than Cobalt Chrome or Stainless Steel (25%, 24%; p = 0.037). In 3–4R constructs, the trend continued but was not statistically significant ( p = 0.127). IBF (graft or cage) at the PSO level resulted in fewer failures than patients with no IBF (21% versus 33%; p = 0.046). In 4R constructs with fusion above and below the PSO site, there were 0 failures at the PSO site, compared with 22% in 2R with IBF, and 34% in 2R constructs with no IBF at all. There were 0 failures in Satellite rods with IBF, compared with 27% failure in S constructs without interbody fusion ( p = 0.05). Conclusion This study confirms a high rate of pseudarthrosis and rod breakage in the first 2 years following lumbar PSO surgery. The lowest rates of rod failure/pseudarthrosis were found in constructs with Satellite rods, IBF adjacent to the PSO, avoidance of Titanium rods, and larger diameter rods.