An Evaluation of Spatial Anchoring to position AR Guidance in Arthroscopic Surgery

Research Background and Problem

• What issues or challenges did the authors identify?

  • In arthroscopic knee surgery, precisely drilling bone tunnels to replace damaged ligaments is a challenging task that requires avoiding damage to surrounding anatomical structures. However, limited visibility, non-intuitive hand-eye coordination, and restricted tool mobility make the operation complex.
  • Existing studies have found significant discrepancies between preoperative tunnel planning and postoperative outcomes, with a mean target deviation of 13 mm.
  • Although augmented reality (AR) has been applied in surgical navigation, there is a research gap regarding how different spatial anchoring strategies affect performance and user satisfaction, especially in tool-centric tasks such as cutting or drilling.

• Why is this problem important?

  • Arthroscopic knee surgery is one of the most common minimally invasive surgeries, and addressing this issue can significantly improve surgical precision and safety.
  • Accurate bone tunnels contribute to better postoperative joint function recovery and significantly reduce complications.
  • Research on spatial anchoring strategies can optimize AR applications in tool-centric tasks and extend to other domains requiring precise tool usage.

• Research Motivation and Related Work

  • This study aims to fill the gap in research on spatial anchoring strategies (techniques for positioning visual information) in AR-guided systems.
  • Investigations revealed that surgeons recommend displaying AR information on the patient’s knee, the tool, or directly in front of their field of view, which served as the basis for designing spatial anchoring strategies.
  • Additionally, there is a lack of exploration into combining visual representation methods (2D vs. 3D) with different anchoring strategies in AR guidance.

Solution

• What methods or solutions did the authors propose?

  • The authors proposed and compared three spatial anchoring strategies: 1) patient-anchored (information displayed on the patient’s knee), 2) tool-anchored (information attached to the surgical tool), and 3) surgeon-anchored (information fixed in front of the surgeon’s field of view). These were applied to two common AR guidance techniques: 3D trajectory and 2D crosshair.
  • They explored the impact of combining different anchoring strategies with AR guidance techniques on surgical task accuracy, efficiency, and user preferences.

• What is innovative about this solution?

  • This is the first systematic comparison of different spatial anchoring strategies in tool-centric tasks.
  • The proposed optimized designs combine anchoring strategies with visual representation techniques, based on real-world needs collected through pre-study interviews with surgeons.
  • Two experiments were conducted to test the solution’s generalizability, involving both non-professional participants and experienced surgeons.

• What are the implementation steps and key technologies used?

  1. Preliminary Study: Conducted semi-structured interviews with surgeons to understand their requirements for AR guidance systems.
  2. Experiment 1 (Non-professional Participants): Recruited 24 non-professional participants to test six anchoring strategies (3 anchoring strategies × 2 AR techniques) using 3D-printed objects for drilling tasks.
  3. Experiment 2 (Professional Surgeons): Recruited six experienced surgeons to perform tasks on simulated bones that closely resemble real surgical scenarios.
  4. Data Analysis: Statistical analysis focused on target error (accuracy), completion time (efficiency), usability ratings, and user preferences to evaluate the performance of each method.

Research Findings

• What specific findings were achieved?

  • For the 3D trajectory technique:
    • Tool-anchored strategy was the most accurate, but users preferred the patient-anchored strategy.
    • Patient-anchored strategy was slightly faster than tool-anchored, though the difference was not significant.
    • Surgeon-anchored strategy performed the worst due to unstable information and lack of directional cues.
  • For the 2D crosshair technique:
    • Anchoring strategies had no significant impact on accuracy, but participants preferred patient-anchored and surgeon-anchored strategies.
    • Tool-anchored strategy had poor user experience due to display instability.
  • Comparing the two techniques, 58% of non-professional participants and all surgeons preferred the 2D crosshair technique.

• What advantages does it have over existing solutions?

  • Clear recommendations for spatial anchoring design were provided: use tool-anchored with 3D trajectory or patient/surgeon-anchored with 2D crosshair.
  • The study systematically examined the interaction between task performance and subjective preferences, addressing a research gap.
  • Comprehensive experimental results offer insights applicable to both non-professional users and professional surgeons.

• What were the experimental or evaluation results?

  • In terms of target error:
    • Tool-anchored + 3D trajectory was the most accurate, with the smallest error.
    • Surgeon-anchored strategy significantly increased target error.
  • In terms of user preferences:
    • Patient-anchored strategy received the most positive feedback for its stability.
    • Tool-anchored strategy, despite its accuracy, was rated lower due to perceived instability.
    • Surgeon-anchored strategy was recognized for comfort but increased cognitive load.

• Limitations and Future Directions

  • Limitations:
    • The sample size of professional surgeons was small, with only six participants in Experiment 2, limiting statistical power.
    • Simulated bones used in Experiment 2 enhanced realism but could not fully replicate real patients.
    • Slight tool and visual display jitter may have influenced subjective preferences.
  • Future Directions:
    • Recruit more surgeons for larger-scale experiments to ensure statistical significance.
    • Use improved sensors and algorithms to reduce tool-anchored jitter and tracking errors.
    • Explore anchoring optimization in other tool-centric tasks, such as engineering construction or assembly tasks.

This study provides critical design guidelines for tool navigation in surgery by comprehensively comparing different spatial anchoring strategies and AR techniques. It also offers strategic design references for similar tasks across various fields.