Complications and Revision Rates in Minimally Invasive Robotic-Guided Versus Fluoroscopic-Guided Spinal Fusions

The MIS ReFRESH Prospective Comparative Study

Christopher R. Good, MD; Lindsay Orosz, MS, PA-C; Samuel R. Schroerlucke, MD; Andrew Cannestra, MD; Jae Y. Lim, MD; Victor W. Hsu, MD; Faissal Zahrawi, MD; Hunaldo J. Villalobos, MD; Pedro M. Ramirez, MD; Thomas Sweeney, MD; Michael Y. Wang, MD


Spine. 2021;46(23):1661-1668. 

In This Article

Abstract and Introduction


Study Design: Prospective, multicenter, partially randomized.

Objective: Assess rates of complications, revision surgery, and radiation between Mazor robotic-guidance (RG) and fluoro-guidance (FG).

Summary of Background Data: Minimally invasive surgery MIS ReFRESH is the first study designed to compare RG and FG techniques in adult minimally invasive surgery (MIS) lumbar fusions.

Methods: Primary endpoints were analyzed at 1 year follow-up. Analysis of variables through Cox logistic regression and a Kaplan–Meier Survival Curve of surgical complications.

Results: Nine sites enrolled 485 patients: 374 (RG arm) and 111 (FG arm). 93.2% of patients had more than 1 year f/u. There were no differences for sex, Charlson Comorbidity Index, diabetes, or tumor. Mean age of RG patients was 59.0 versus 62.5 for FG (P = 0.009) and body mass index (BMI) was 31.2 versus 28.1 (P< 0.001). Percentage of smokers was almost double in the RG (15.2% vs. 7.2%, P = 0.029). Surgical time was similar (skin-to-skin time/no. of screws) at 24.9 minutes RG and 22.9 FG (P = 0.550). Fluoroscopy during surgery/no. of screws was 15.5 seconds RG versus 35.4 seconds FG, (15 seconds average reduction). Fluoroscopy time during instrumentation/no. of screws was 3.6 seconds RG versus 17.8 seconds FG showing an 80% average reduction of fluoro time/screw in RG (P < 0.001). Within 1 year follow-up, there were 39 (10.4%) surgical complications RG versus 39 (35.1%) FG, and 8 (2.1%) revisions RG versus 7 (6.3%) FG. Cox regression analysis including age, sex, BMI, CCI, and no. of screws, demonstrated that the hazard ratio (HR) for complication was 5.8 times higher FG versus RG (95% CI: 3.5–9.6, P < 0.001). HR for revision surgery was 11.0 times higher FG versus RG cases (95% CI 2.9–41.2, P < 0.001).

Conclusion: Mazor robotic-guidance was found to have a 5.8 times lower risk of a surgical complication and 11.0 times lower risk for revision surgery. Surgical time was similar between groups and robotic-guidance reduced fluoro time per screw by 80% (approximately 1 min/case).

Level of Evidence: 2


Precise implant placement during spinal surgery is crucial to avoid neurologic and vascular damage, while providing proper fixation and stability to support the formation of bone fusion. This procedure is particularly challenging in minimally invasive surgery (MIS) because surgeons must rely on indirect visualization of the anatomy by imaging systems. In recent years, guidance has been shown to be both reliable and accurate when instrumenting pedicles;[1,2] however, accuracy alone may not predict clinical outcome.[3–6]

Advances in technology have provided spine surgeons with several options of enhanced guidance abilities in the operating room. Currently available guidance systems can be generally divided into different categories: optical navigation-based systems that track reference markers (NAV), NAV systems with robotic arms (RNAV), and automated anatomy recognition-based robotic guidance (Mazor). RNAV systems typically utilize a floor-mounted mechanical arm and rely on tracking reference markers attached to the patient, with registration to the patient usually performed by intraoperative 3-dimensional (3D) imaging. Mazor systems are patient- or bed-mounted systems that connect directly to the patient's bony anatomy and rely on preoperative planning using high-resolution 3D imaging. The automated anatomy recognition software recognizes individual vertebrae and uses two fluoroscopy images to merge the segmented spine to the 3D images with the patient's location relative to the robotic system, with each vertebra registered individually.

While some recent reports in the literature on robotguidance have related to RNAV,[7] most reports have focused on Mazor, with accuracy rates ranging from 83.4% to 100%.[8–23] Prospectively collected data on complications and revisions following robot-guided spinal instrumentation are more limited.

The purpose of the MIS ReFRESH study was to prospectively evaluate surgical outcomes by comparing the complication and revision rates between Mazor and fluoroscopy- guided (FG) surgery in MIS instrumentation of degenerative lumbar or lumbosacral spine disease. In addition, the exposure to intraoperative radiation was analyzed.