Summary: Multicenter, retrospective analysis of rod fracture (RF) following multi‐level fusion for adult spinal deformity demonstrated a 5.4% incidence over 6 years. Most RFs occurred within one year and occurred with all rod compositions and diameters and all fusion lengths. Early failure was most common following PSO and occurred at the PSO site. Residual postoperative sagittal malalignment may increase the risk for RF.
Introduction: Instrumentation failures continue to be problematic and are poorly understood. Objective: evaluate the etiology and time course of symptomatic rod fracture (RF) following multi‐level posterior instrumented fusion for adult spinal deformity (ASD).
Methods: Multicenter, retrospective review of RF in ASD during a 6‐yr period (2004‐2010) at 10 study sites. Inclusion criteria: ASD, age>18 yrs, and >5 levels posterior instrumented spinal fusion. Exclusion criteria: post‐traumatic or neuromuscular deformity, tumor, and infection. RF were divided into early (≤12 mos) and late (>12 mos) failures.
Results: Of 558 patients that met criteria, 5.4% had symptomatic RF. Patient demographics: mean age=61 yrs (range: 29‐79); 13 men and 17 women. Diagnosis included: scoliosis (n=21; 70%) and sagittal malalignment (n=26, 87%). The upper instrumented vertebra was cephalad to T6 in 20 patients (67%), 26 patients (87%) had iliac fixation. Seventeen (57%) RF patients received pedicle subtraction osteotomy (PSO). The incidence of RF following PSO was 14.9%. Rod composition in RF cases included: titanium alloy (n=18), stainless steel (n=9), and cobalt chromium (n=3), and rod diameters were 5.5 mm (n=6), 6.0 mm (n=2), and 6.35 mm (n=6). Mean duration to early RF (63%) was 6.4 mos (range: 2‐12). Mean duration to late RF (37%) was 31.8 mos (range: 14‐73). The majority of RFs following PSO (n=12; 71%) were early (mean 10 mos; range 2.0‐29.3). Rod fracture occurred at the PSO site in 15 cases (88%). Among RF cases, SVA improved from preoperative (mean=163mm, range: 0‐300mm) to postoperative (mean=76.9mm; range: ‐25‐233mm) measures (p<0.001), however, 16 had postoperative malalignment (SVA>50mm; mean=109mm; range: 50‐233mm).
Conclusion: Symptomatic RF occurred in 5.4% of ASD cases and in 14.9% of PSO cases. The majority of RFs occurred within one year and occurred with all rod compositions and diameters. Early failure was most common following PSO and occurred at the PSO site, suggesting that RF may be due to stress at the PSO site or excessive rod contouring. Postoperative sagittal malalignment may increase the risk for RF.