Robotic Cutting Bur Control for Cortical Bone Skiving Mitigation

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Solution Overview

Problem

Robotic systems face challenges in achieving accurate placement of pedicle screws due to skiving at the entry point of the pedicle, inaccuracies in registration/mapping of the spine CT scanned model with the robot's coordinate system, and movement of vertebral bodies during surgery, leading to potential nerve injury from breaching the pedicle wall.

Innovation Solution

A surgical system with a robotic manipulator and sensors that control a cutting bur to align and penetrate cortical bone, adjust rotational speed and feed rate based on sensed forces, and navigate through cancellous bone regions to create a precise entry point for pedicle screw insertion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a rotary cutting tool is used to penetrate cortical bone, then the cutting tool can effectively create an entry point, but skiving occurs at the entry point causing inaccuracy and potential nerve injury

Engineering Contradiction:

Improveentry point accuracyVSAvoidskiving effect

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the traditional rotary cutting mechanism with an ultrasonic cutting mechanism. The ultrasonic burr vibrates at high frequency (20-100 kHz) with small amplitude (1-10 micrometers), creating a micro-chipping action that eliminates skiving. This substitution of mechanical rotation with ultrasonic vibration resolves the contradiction by maintaining cutting effectiveness while eliminating the harmful skiving effect at the cortical bone entry point.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent applies mechanical vibration through ultrasonic frequencies to the cutting burr. The burr oscillates longitudinally at ultrasonic frequencies with controlled amplitude, creating a non-contact-like cutting action that prevents skiving. This vibration-based cutting mechanism allows precise penetration of cortical bone without the lateral displacement and tearing associated with rotary tools, thereby improving entry point accuracy while eliminating skiving.

Inventive Principle:

Principle #18Mechanical vibration

2Manufacturing precision

If force is applied to advance the cutting bur through cancellous bone, then the cutting bur can penetrate the bone structure, but excessive force can displace the bone structure causing inaccuracies

Engineering Contradiction:

Improvecannulation accuracyVSAvoidforce applied to bone

Core Design Contradiction:

Manufacturing precisionVSForce

Solution Approach 1:

The patent incorporates force sensors that continuously monitor the axial force applied to the cutting bur during cannulation. When the force approaches a predetermined threshold that could cause bone displacement, the system automatically adjusts cutting parameters (reducing feed rate or ultrasonic power) to maintain force below the threshold. This closed-loop feedback control ensures accurate cannulation while preventing excessive force that would displace the cancellous bone structure.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent implements dynamic adjustment of cutting parameters based on real-time force measurements. The system continuously adapts the feed rate and ultrasonic power during the cannulation process, transitioning from higher rates in less resistant bone to lower rates when encountering denser cancellous bone. This dynamic control allows effective penetration while maintaining force within safe limits to prevent bone displacement and ensure accuracy.

Inventive Principle:

Principle #15Dynamics

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The system enhances accuracy by preventing cortical bone breach and maintaining control over the cutting bur, reducing the risk of nerve injury and improving the precision of pedicle screw placement.

Implementation Method 1

a cutting bur rotatable about a cutting axis... rotate the cutting bur about the cutting axis to penetrate the first cortical region

Methodology Applied

Scientific EffectAbrasion: Abrasion

Implementation Method 2

penetrate the first cortical region of the bone structure to create an entry point; and advance the cutting bur through the entry point and into the cancellous bone region to displace and cannulate the cancellous bone region

Methodology Applied

Scientific EffectFracture Mechanics: Fracture Mechanics

Data Source

PatentUS12465442B2Robotic surgical systems and methods for mitigating skiving between rotary cutting tool and cortical bone

Publication Date: 2025.11.11 MAKO SURGICAL CORP

AI summary

Surgical systems and methods involve manipulation of a bone. A robotic manipulator supports and moves a surgical tool that has a cutting bur rotatable about a cutting axis. Controller(s) control the manipulator to align the cutting axis to a target axis associated with the bone and advance the cutting bur along the target axis towards a cortical region of the bone. The controller(s) control the surgical tool to rotate the cutting bur about the cutting axis and contact the cortical region. The controller(s) detect, from sensor(s), forces applied to the cutting bur by the cortical region and compare the sensed forces to a threshold indicative of skiving of the cutting bur relative the cortical region. In response to the sensed forces exceeding the threshold, the controller(s) adjust control of the manipulator and/or surgical tool to reduce forces applied to the cutting bur by the cortical region.