Randomized Controlled Trial: Comparison of Ultrasonic Osteotome and Conventional Drill Osteotome
Phase: NA
Conditions: Arthrodesis
Sponsor: Seoul National University Hospital

 
 
 

 
 
 

Study protocol  
 
Patient population and randomization  
The present study included patients for whom COL was planned with 1) cervical myelopathy 
at 3 or more levels due to spondylosis, congenital stenosis, or OPLL; 2) aged more than 20 
years; and 3) with American Society of Anesthesiology physical status class 1 or 2.27 The 
exclusion criteria were as follows: 1) concomitant neurological disease such as cerebral palsy 
or amyotrophic lateral sclerosis; 2) concurrent cancer or infection; 3) previous cervical spinal 
surgery; 4) a trauma-associated lesion; 5) inability to be followed up; and 6) refusal to 
participate in the study. The proportions of fusion failure were assumed to 30% and 10% in 
laminoplasty with a conventional drill and with a UBS.12 To provide a power of 80% with a 
two-tailed significance level of 0.05, 72 patients for each surgical method were required.12 
Considering a drop-out rate of 25%, 95 patients in each group were enrolled. A computer-
generated variable randomized block design was used for randomization and a research nurse 
independent of this trial provided randomization with concealed assignment. A total of 190 
patients were equally allocated to one of two treatments (Fig. 1). The attending surgeons, 
patients, and staff members in the operating room were blinded to the surgical method until 
the day of surgery. Recruitment of patients started in July 2015 and ended in February 2018.  
 
Statistical analysis  
Continuous data were summarized as mean or median (min, max) values depending on 
normality. Categorical variables are summarized as frequency (%). The analysis for the 
primary outcome was performed on data from the intention-to-treat population, which 
included all subjects who were randomized. Since about 14% of subjects missed the CT to 
assess bone union at 6 months, multiple imputation was applied. Five multiply-imputed data 
sets were created using a monotone logistic regression model. The variables in Table 1 were 
included in the imputation model. A sensitivity analysis was performed with the subjects who 
received a CT scan at 6 months, who were defined as the per-protocol population. The union 
rate was compared between the drill group and the UBS group using logistic regression. 
Because each subject had several laminae, logistic regression with the robust sandwich 
covariance estimate was used to account for the correlation among laminae within a subject. 

Secondary outcomes were compared using the chi-square test for non-continuous values and 
the t-test or Wilcoxon rank-sum test for continuous values.21 A linear mixed model was used 
for clinical outcomes to evaluate between-group differences and changes during each 
postoperative period compared to the preoperative point, and adjusted p-values were 
evaluated using the Bonferroni method. The fixed effects were group, time, and the 
interaction between group and time. All statistical analyses were performed using SAS 
version 9.4 (SAS Institute, Cary, NC, USA), and statistical significance was defined as p < 
0.05 (two-sided).