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Table 4 Sensitivity analysis—association of patient characteristics with AIS conversion from multiple binary logistic regression models using natural cubic splines for age and time between SCI and surgery

From: Association of age with the timing of acute spine surgery–effects on neurological outcome after traumatic spinal cord injury

Total sample (n = 191) (splines for age and time from SCI to surgery)
Covariates Odds ratio (95% CI) p-value
Age (years)
Spline coefficient for Age (df = 2) 1 0.02 (0.00–0.36) 0.009
Spline coefficient for Age (df = 2) 2 0.73 (0.13–4.24) 0.728
Gender (male, ref: female) 1.47 (0.59–3.67) 0.406
CCI (per one point increase) 0.87 (0.65–1.15) 0.325
AIS admission –  
AIS D (ref) 1 –
AIS C 5.66 (1.68–19.06) 0.005
AIS B 6.27 (1.18–33.21) 0.031
AIS A 0.67 (0.28–1.62) 0.377
NLI admission (cervical, ref: thoracolumbar) 2.29 (0.97–5.43) 0.059
TBI (yes, ref: no) 0.59 (0.22–1.56) 0.289
Time from SCI to surgery (hours, log-transformed)
Spline coefficient for logarithmised time (df = 2) 1 0.09 (0.01–1.46) 0.091
Spline coefficient for logarithmised time (df = 2) 2 0.002 (0.00–0.26) 0.012
Enrollment period (retrospective, ref: prospective) 0.38 (0.17–0.84) 0.017
  Cragg & Uhler’s pseudo R2 = 0.41
AIS A (n = 81) (without splines)
Covariates Odds ratio (95% CI) p-value
Age (years) 1.03 (0.99–1.08) 0.165
Gender (male, ref: female) 1.77 (0.31–10.08) 0.519
CCI (per one point increase) 0.55 (0.27–1.13) 0.102
NLI admission (cervical, ref: thoracolumbar) 12.72 (2.19–73.94) 0.005
TBI (yes, ref: no) 0.30 (0.05–1.98) 0.210
Time from SCI to surgery (hours, log-transformed) 0.44 (0.20–1.00) 0.049
Enrollment period (retrospective, ref: prospective) 1.14 (0.28–4.63) 0.858
  Cragg & Uhler’s pseudo R2 = 0.42
AIS B–D (n = 110) (spline for age)
Covariates Odds ratio (95% CI) p-value
Age (years)
Spline coefficient for Age (df = 2) 1 0.0002 (0.00–0.03) 0.001
Spline coefficient for Age (df = 2) 2 0.31 (0.03–3.12) 0.322
Gender (male, ref: female) 3.10 (0.88–10.87) 0.077
CCI (per one point increase) 0.98 (0.68–1.42) 0.921
AIS admission
AIS D (ref) 1  
AIS C 12.12 (2.83–51.94) 0.001
AIS B 5.84 (1.10–30.87) 0.038
NLI admission (cervical, ref: thoracolumbar) 2.03 (0.57–7.26) 0.278
TBI (yes, ref: no) 0.71 (0.18–2.82) 0.627
Time from SCI to surgery (hours, log-transformed) 0.70 (0.44–1.10) 0.122
Enrollment period (retrospective, ref: prospective) 0.14 (0.04–0.49) 0.002
  Cragg & Uhler’s pseudo R2 = 0.54
  1. Multiple binary logistic regression models with AIS conversion until discharge as dependent variable in the total sample (top) and stratified for severity of SCI into complete SCI patients AIS A (middle) and incomplete SCI patients AIS B–D (bottom). Coding of the dependent variable AIS conversion (no = 0, yes = 1). Natural cubic splines were used for age and time from SCI to surgery where appropriate (decision based on AIC comparison between models). For the adjusted cubic spline curves see Fig. 5. Abbreviations: AIC = Akaike information criterion, AIS = ASIA Impairment Scale, CCI = Charlson comorbidity index, df = degrees of freedom, NLI = neurological level of injury, SCI = spinal cord injury, TBI = traumatic brain injury
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