The Learning Curve for Pedicle Screw Selection in Robotic-assisted and Intra-operative Navigation guided Minimally Invasive Transforaminal Lumbar Interbody Fusion (MI-TLIF) — The International Society for the Study of the Lumbar Spine
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  3. The Learning Curve for Pedicle Screw Selection in Robotic-assisted and Intra-operative Navigation guided Minimally Invasive Transforaminal Lumbar Interbody Fusion (MI-TLIF)

The Learning Curve for Pedicle Screw Selection in Robotic-assisted and Intra-operative Navigation guided Minimally Invasive Transforaminal Lumbar Interbody Fusion (MI-TLIF) (#1129)

Avani Vaishnav 1 , Pratyush Shahi 1 , Hikari Urakawa 1 , Catherine Himo Gang 1 , Sidhant Dalal 1 , Dimitra Melissaridou 1 , Junho Song 1 , Daniel Shinn 1 , Kasra Araghi 1 , Sheeraz Qureshi 1 2
  1. Hospital for Special Surgery, New York, NY, United States
  2. Weill Cornell Medical College, New York

Introduction:

Minimally invasive transforaminal lumbar interbody fusion(MI-TLIF) has been performed using 2D fluoroscopy1, intra-operative navigation (ION)2,3 and more recently, robotic navigation. While there are reports on the learning curve of MI-TLIF using fluoroscopy1 and ION4 in terms of operative time and radiation exposure, there is little data on the learning curve of implant selection with intra-operative image-guidance modalities. Pedicle screw size is linked to construct stability, and consequently fusion rates and outcomes. Thus, the goal is typically to place the largest possible screw that can be safely accommodated within the patient’s anatomy. The purpose of this study was to assess pedicle screw size selection for ION and robotic navigation, and to assess the learning curve for the same.

Methods:

  • Study design: Retrospective review of prospectively collected data
  • Population: Consecutive patients who underwent elective single-level MI-TLIF by a single surgeon using ION or robotic navigation were selected (ION 2017-19, robotic navigation 2019-21, resulting in prospective cohorts of consecutive patients for each modality).
  • Outcomes: Pedicle screw size (diameter and length). For each patient, the mean length and mean diameter of all the screws placed was calculated. E.g. if a patient received two 7.5x45mm screws and two 8.5x50mm screws, the mean length and mean diameter would 8 and 47.5mm respectively. This “mean screw size” calculated for each patient was used for analysis.
  • Statistical Analysis: Chronologic case number was plotted against each outcome for each modality. Derivative of a nonlinear curve fit to the dataset was solved for the point at which the slope of the curve equalled the linear slope, suggesting a plateau in learning had occurred.

Results:

154 patients (77 ION, 77 robotic navigation) were included. There were no significant differences in age (p=0.104), gender (p=1.00), BMI (p=0.826), race (p=0.910), insurance type (p=0.068), Charlson Comorbidity Index (p=0.108), ASA class (p=0.378), diabetes (p=0.100) or hypertension (p=0.735).

Robotic navigation resulted in the placement of larger pedicle screws (median diameter of 7.42 [IQR 6.5-7.88] mm vs 6.5 [IQR 6.5-6.5] for ION, p<0.0001; median length 47.5 [IQR 45-50] mm vs 45 [IQR 43.75-47.5] for ION, p<0.0001). There were no intraoperative complications in either group.

For ION, screw size selection was not associated with chronology (p=0.079 for screw length, p=0.752) i.e. there was no learning curve.

For robotic navigation, proficiency in screw diameter selection was achieved at 20 cases, with median diameter of 6.5mm before proficiency vs 7.5mm afterwards (p<0.0001) and proficiency for screw length was achieved at 15 cases, with median length of 45mm before proficiency vs 48.75mm afterwards (p=0.139)

Conclusion:

Robotic navigation resulted in the placement of larger screws compared to ION, likely attributable to the intraoperative screw size and trajectory planning capabilities of newer generation robotic systems. Furthermore, robotic navigation, but not ION demonstrated a learning curve in pedicle screw sizing, with proficiency achieved at 15 and 20 cases for screw length and diameter respectively. These findings suggest that robotic navigation likely allows for the safe placement of larger pedicle screws, but this benefit may only be apparent after an initial learning curve.  

  1. 1. Kumar A, Merrill RK, Overley SC, et al. Radiation Exposure in Minimally Invasive Transforaminal Lumbar Interbody Fusion: The Effect of the Learning Curve. Int J spine Surg. 2019;13(1):39-45. doi:10.14444/6006
  2. 2. Vaishnav AS, Merrill RK, Sandhu H, et al. A Review of Techniques, Time Demand, Radiation Exposure, and Outcomes of Skin-anchored Intraoperative 3D Navigation in Minimally Invasive Lumbar Spinal Surgery. Spine (Phila Pa 1976). 2020;45(8):E465-E476. doi:10.1097/brs.0000000000003310
  3. 3. Vaishnav AS, Saville P, McAnany S, et al. Retrospective Review of Immediate Restoration of Lordosis in Single-Level Minimally Invasive Transforaminal Lumbar Interbody Fusion: A Comparison of Static and Expandable Interbody Cages. Oper Neurosurg. 2020;18(5):518-523. doi:10.1093/ons/opz240
  4. 4. Vaishnav AS, Gang CH, Qureshi SA. Time-demand , Radiation Exposure and Outcomes of Minimally Invasive Spine Surgery With the Use of Skin-Anchored Intraoperative Navigation The Effect of the Learning Curve. 2021;00(00):1-10.
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