Robotic-Assisted Pedicle Screw Placement in Spine Surgery

Proportion of patients in which at least one pedicle screw is not accurately placed (substudy 1)

Accurate screw placement is defined as a pedicle screw that remains entirely within the cortical boundary of the pedicle, or with up to 2 mm breach of the pedicle wall (corresponds to Gertzbein-Robbins Grade A and B), assessed on a computed tomography. To evaluate screw placement accuracy, we will define a binary per-patient outcome: whether at least one screw is not accurately placed. The planned sample size for this substudy is 75 patients in the robotic-assisted surgery group, and 426 patients in the non-robotic-assisted group, for a total of 501 patients. For this outcome, previously treated cases may be included as specified in the approved protocol.

Time frame: Periprocedural

Learning curve (substudy 2)

To evaluate the learning curve associated with robotic-assisted surgery, we will model operative time as a function of case number. Operative time is expected to decrease with experience, then plateau. We will use mixed-effects piece-wise linear regression with the surgeon as a random effect to estimate the case number at which operative time levels off. The sample size in this substudy is 100 robotic-assisted spine surgeries in each of the 3 centers currently using robotic-assisted spine surgery (Umeå, Örebro, Uppsala), in total 300 surgeries. For this outcome, previously treated cases may be included as specified in the approved protocol.

Time frame: Periprocedural

Reoperation rate at 2 years (substudy 3)

The primary outcome is the occurrence of reoperations of any cause within 2 years from the index surgery. The expected reoperation rate in the non-robotic group is likely to be higher than 3-5% over a 2-year period, and may in the robotic-assisted group be 1% or less. A difference of 2 percentage points or greater is considered clinically meaningful. Power analyses (80% power, alpha 0.05) have been made in two scenarios, with reoperation rates of 3% vs 1%, or 5% vs 3%. We estimate a ratio of 1:6 for robotic-assisted surgery vs navigation-assisted or free hand surgeries. Comparing 3% and 1% reoperation rates, 420 robotic-assisted surgery patients and 2,520 non-robotic surgery patients are needed (yielding a total sample size of 2,940 patients). In case reoperation rates are 5% and 3%, 866 robotic-assisted surgery patients and 5,196 non-robotic surgery patients are needed (yielding a total sample size of 6,062 patients).