title: Prospective multicenter assessment of risk factors for rod fracture following surgery for adult spinal deformity.
abstract: OBJECTIVE
  Improved understanding of rod fracture (RF) following adult spinal deformity (ASD) surgery could prove valuable for surgical planning, patient counseling, and implant design. The objective of this study was to prospectively assess the rates of and risk factors for RF following surgery for ASD.
  
  
  METHODS
  This was a prospective, multicenter, consecutive series. Inclusion criteria were ASD, age > 18 years, ≥5 levels posterior instrumented fusion, baseline full-length standing spine radiographs, and either development of RF or full-length standing spine radiographs obtained at least 1 year after surgery that demonstrated lack of RF. ASD was defined as presence of at least one of the following: coronal Cobb angle ≥20°, sagittal vertical axis (SVA) ≥5 cm, pelvic tilt (PT) ≥25°, and thoracic kyphosis ≥60°.
  
  
  RESULTS
  Of 287 patients who otherwise met inclusion criteria, 200 (70%) either demonstrated RF or had radiographic imaging obtained at a minimum of 1 year after surgery showing lack of RF. The patients' mean age was 54.8 ± 15.8 years; 81% were women; 10% were smokers; the mean body mass index (BMI) was 27.1 ± 6.5; the mean number of levels fused was 12.0 ± 3.8; and 50 patients (25%) had a pedicle subtraction osteotomy (PSO). The rod material was cobalt chromium (CC) in 53%, stainless steel (SS), in 26%, or titanium alloy (TA) in 21% of cases; the rod diameters were 5.5 mm (in 68% of cases), 6.0 mm (in 13%), or 6.35 mm (in 19%). RF occurred in 18 cases (9.0%) at a mean of 14.7 months (range 3-27 months); patients without RF had a mean follow-up of 19 months (range 12-24 months). Patients with RF were older (62.3 vs 54.1 years, p = 0.036), had greater BMI (30.6 vs 26.7, p = 0.019), had greater baseline sagittal malalignment (SVA 11.8 vs 5.0 cm, p = 0.001; PT 29.1° vs 21.9°, p = 0.016; and pelvic incidence [PI]-lumbar lordosis [LL] mismatch 29.6° vs 12.0°, p = 0.002), and had greater sagittal alignment correction following surgery (SVA reduction by 9.6 vs 2.8 cm, p < 0.001; and PI-LL mismatch reduction by 26.3° vs 10.9°, p = 0.003). RF occurred in 22.0% of patients with PSO (10 of the 11 fractures occurred adjacent to the PSO level), with rates ranging from 10.0% to 31.6% across centers. CC rods were used in 68% of PSO cases, including all with RF. Smoking, levels fused, and rod diameter did not differ significantly between patients with and without RF (p > 0.05). In cases including a PSO, the rate of RF was significantly higher with CC rods than with TA or SS rods (33% vs 0%, p = 0.010). On multivariate analysis, only PSO was associated with RF (p = 0.001, OR 5.76, 95% CI 2.01-15.8).
  
  
  CONCLUSIONS
  Rod fracture occurred in 9.0% of ASD patients and in 22.0% of PSO patients with a minimum of 1-year follow-up. With further follow-up these rates would likely be even higher. There was a substantial range in the rate of RF with PSO across centers, suggesting potential variations in technique that warrant future investigation. Due to higher rates of RF with PSO, alternative instrumentation strategies should be considered for these cases.
authors.affiliation: Department of Neurosurgery, University of Virginia, Charlottesville, Virginia;
authors.forename: Justin S
authors.initials: JS
authors.lastname: Smith
authors.forename: Ellen
authors.initials: E
authors.lastname: Shaffrey
authors.forename: Eric
authors.initials: E
authors.lastname: Klineberg
authors.forename: Christopher I
authors.initials: CI
authors.lastname: Shaffrey
authors.forename: Virginie
authors.initials: V
authors.lastname: Lafage
authors.forename: Frank J
authors.initials: FJ
authors.lastname: Schwab
authors.forename: Themistocles
authors.initials: T
authors.lastname: Protopsaltis
authors.forename: Justin K
authors.initials: JK
authors.lastname: Scheer
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Mundis
authors.forename: Kai-Ming G
authors.initials: KM
authors.lastname: Fu
authors.forename: Munish C
authors.initials: MC
authors.lastname: Gupta
authors.forename: Richard
authors.initials: R
authors.lastname: Hostin
authors.forename: Vedat
authors.initials: V
authors.lastname: Deviren
authors.forename: Khaled
authors.initials: K
authors.lastname: Kebaish
authors.forename: Robert
authors.initials: R
authors.lastname: Hart
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Burton
authors.forename: Breton
authors.initials: B
authors.lastname: Line
authors.forename: Shay
authors.initials: S
authors.lastname: Bess
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Ames
mesh_terms: D000328:Adult; D000368:Aged; D001858:Bone Nails / Q000009:adverse effects*; D002858:Chromium Alloys; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D010027:Osteotomy / Q000009:adverse effects* / Q000295:instrumentation; D011183:Postoperative Complications / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology; D011446:Prospective Studies; D011475:Prosthesis Failure; D011859:Radiography; D012307:Risk Factors; D013122:Spinal Diseases / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000601:surgery*; D013123:Spinal Fusion / Q000009:adverse effects* / Q000295:instrumentation
chemical_list: D002858:Chromium Alloys
keywords: ASD = adult spinal deformity; BMI = body mass index; BMP-2 = recombinant human bone morphogenetic protein–2; CCI = Charlson Comorbidity Index; ISSG = International Spine Study Group; LL = lumbar lordosis; PI = pelvic incidence; PSO = pedicle subtraction osteotomy; PT = pelvic tilt; SVA = sagittal vertical axis; adult; complication; deformity; instrumentation; pedicle subtraction osteotomy; rod fracture; sagittal imbalance; spine; surgery