Comparative Analysis of Autonomous Robotic and Manual Techniques for Ultrasonic Sacral Osteotomy: A Preliminary Study

TL;DR

This work tackles the challenge of sacral osteotomy precision in proximity to critical nerve roots, where manual approaches guided by navigation are limited by operator variability. It introduces a robotic USO platform that fuses a seven-DoF manipulator with an ultrasonic osteotome and an optical tracker, enabling autonomous, multi-directional control of both surface trajectory and cutting depth. In Sawbones phantoms, the robotic system achieves sub-millimeter trajectory accuracy ($e_{RMSE} = 0.11$ mm) and precise depth control (mean depths near 4.2 mm for a 4 mm target and 8.1 mm for an 8 mm target), while manual procedures exhibit larger trajectory errors ($e_{RMSE} \approx 1.10$ mm) and unsafe over-penetration (up to 16 mm depth). The results demonstrate that robotic automation can markedly improve precision, safety, and efficiency in sacral resections and lay groundwork for more complex, anatomy-aware osteotomies.

Abstract

In this paper, we introduce an autonomous Ultrasonic Sacral Osteotomy (USO) robotic system that integrates an ultrasonic osteotome with a seven-degree-of-freedom (DoF) robotic manipulator guided by an optical tracking system. To assess multi-directional control along both the surface trajectory and cutting depth of this system, we conducted quantitative comparisons between manual USO (MUSO) and robotic USO (RUSO) in Sawbones phantoms under identical osteotomy conditions. The RUSO system achieved sub-millimeter trajectory accuracy (0.11 mm RMSE), an order of magnitude improvement over MUSO (1.10 mm RMSE). Moreover, MUSO trials showed substantial over-penetration (16.0 mm achieved vs. 8.0 mm target), whereas the RUSO system maintained precise depth control (8.1 mm). These results demonstrate that robotic procedures can effectively overcome the critical limitations of manual osteotomy, establishing a foundation for safer and more precise sacral resections.

Figures (6)

• Figure 1: A) Anterior view of the sacrum illustrating the clinically-derived osteotomy task. The dashed line represents a 100 mm transverse cut path. B) Sagittal view of the sacrum.
• Figure 2: Experimental setup for the comparative experiments. A) The MUSO setup consisting of Misonix BoneScalpel and NDI Optical Tracker. B) The RUSO setup, featuring the KUKA LBR Med 14 Robot actuating the same osteotome.
• Figure 3: Coordinate frames and transformations for calibration and control. Frames assigned to key components of the system: robot base $\{S\}$, end-effector $\{EE\}$, osteotome tip $\{\text{Tip}\}$, optical tracker $\{OT\}$, and the rigid body tool $\{\text{Tool}\}$. Key transformations, such as the hand-eye calibration ($^{S}T_{OT}$), are also shown.
• Figure 4: Pivot calibration process for localizing the osteotome tip. The optical tracker measures the transformation to the tool's rigid body ($^{OT}T_{\text{Tool}_i}$) across multiple poses as the tip is pivoted in a 'Fixed divot'.
• Figure 5: Qualitative comparison of the completed osteotomy cuts on the bone phantoms: A) MUSO trials and B) RUSO trials for the 4 mm target depth. C) MUSO trials and D) RUSO trials for the 8 mm target depth. The super-scripted numbers are the trial numbers.