Construction of a Novel Automated Bone Drilling System

Sangeon Park, Eric Pei, Johann Lee

All graphics, tables, charts, graphs and images in this presentation were created by Sangeon Park, Eric Pei, and Johann Lee, unless otherwise stated under it.

Bone Drilling Accidents

• Bone drilling is a prevalent surgical procedure that relies heavily on the surgeon’s experience and intuition (Lourendo, 2012).

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• Even with experience, drilling often results in unnecessary damage due to over-penetration of the bone (Enokida, 2019)

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• The bone frequently overheats in the drilling process (Pandey, 2013).

Introduction

Figure 1: Thermographic 2D image of temperature spread through cortical bone (Augustin et al., 2009).

Introduction

Bone Structure

Figure 3: Resistance force changes significantly when transitioning from the cortical layer to the trabecular layer, leading to bone drilling accidents (slippage/plunging).

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Source: Lourendo et al., (2012)

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• A typical bone consists of two cortical bones
• There is spongy trabecular layer in between
• The varying density within the bone is why operations often plunge into the soft tissue
• This causes irreversible damage to the blood vessels and nerves around the area, extending the recovery process

Figure 2: Source: Pbroks13 CC BY 3.0

Introduction

Force Control and Automatic Drilling

Automatic Drills using force measurements have been developed to minimize unnecessary damage done to the bone.

• Gilmer et. al presented an automatic drill based on force that prevented penetrating past the cortical wall
• Kastelov et al., constructed an automatic bone drill with a control box to prevent plunge with success rate of 100%.

Temperature Control

Cooling systems effectively control the drilling temperatures (Effat Pawar et al., 2020).

• However, it compromises the safety of the procedure

Thus, optimizing parameters and materials is essential

• Gekkou Drill Bit minimized heat generation (Enokida et al., 2019)

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Introduction

Figure 4: Comparison between the Gekkou Drill bit (b) and a conventional drill-bit (a). Its crescent shape allows lower RPM and reduces heat generation during drilling.

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Source: Enokida et al., 2019

Our Goal

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Develop an automatic bone drilling system that:

1. Prevents advancement past the bone
1. Continuous measurement of resistance force (force required to extend drill)
2. Automatically retract drill once significant changes in density are detected
2. Prevents thermal damage to bone
• Continuous measurement of temperature
• Automatically retract drill once customizable threshold temperature is met

Introduction

Design: Drilling System Mechanism

Methods

Figure 5: Automated Bone Drilling System Design

• 400 RPM Drill was deconstructed to its motor, gear box, and chuck
• The handle was used as the trigger to rotate the drill
• Gekkou Drill Bit was used to optimize drilling parameters
• Linear Actuator provided automated linear movement of the system and the linear guide was used to slide the drill into the bone

Figure 6: The Drilling Mechanism was divided into two sections and connected by a system of pipes

Linear Actuator/Load Cell Module

Drill Head Module

Drill Head Module

Linear Actuator/Load Cell Module

Design: Sensors and Control System

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Methods

Sensors

• Strain Gauge Load Cell detecting changes in resistance force
• Infrared temperature sensor measuring surface temperature of bone

Control System

• The Arduino Uno microcontroller executed the algorithm
• Motor Driver controlled the speed of the linear actuator
• Voltage Amplifier read load cell low voltages.
• Breadboard connected the components together

Arduino

Batteries

Motor Driver

Linear Actuator

Breadboard

Voltage Amplifier

Load Cell

Figure 8: Circuit Configuration

Figure 7: Load Cell with pipes as adapters (left), infrared sensor pointing to drilling area (right)

Automated Bone Drilling System Algorithm

Methods

Figure 9: Architecture of Automated Bone Drilling Algorithm

Data Collection

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Methods

• Data for temperature and force was updated every 94 milliseconds.
• 50 First Cortical Bone Trials and 54 Full Bone Trials were conducted
• Bovine Femur bone was used to test the Automated Drilling System
• Diameter of each bone ranged from 4 cm to 8 cm
• Parameters:
• 400 RPM
• Feed Rate: 4 mm/s
• Drill bit diameter: 3.15 mm

Figure 10: Bovine Bones

Resistance Force Performance (Single Cortical)

• All 50 Single Cortical Wall Trials were conducted were successfully retracting at the end of the first cortical wall.
• Fluctuations of force are observed due to vibrations within the linear actuator

Results/Discussion

Figure 11: Representative Graph of Resistance force during: automatic drilling of a single cortical wall

Enter bone

Retraction

Resistance Force Performance (Full Bone)

Figure 12: Representative Graph of Resistance force during: automatic drilling of full bone at 400 RPM with a feed rate of 4 mm/s and drill bit diameter of 3.15 mm.

Results/Discussion

• All 54 full bone trials went through the first cortical wall and trabecular bone and successfully retracted at the end of the second cortical wall.
• Accuracy of about 0.376 - 1 mm
• calculated using the time between protrusion and retraction and constant feed rate.
• Trabecular bone shown to have negligible force

Enter bone

Retraction

Temperature Performance

Results/Discussion

Figure 13 (a): Representative Graph of Temperature vs. Time for drilling of single cortical layer

• Minimal increase in temperature was observed, due to our effective parameters and materials:
• Gekkou Drill Bit
• Low RPM: 400
• Low feed rate of 4mm/s
• Temperature was artificially increased to test system.
• The Temperature-Based Control System retracted the drill when the temperature reached the threshold value.

Figure 13 (b): Representative Graph of Temperature vs Time during: automatic drilling with artificially elevated temperature and a temperature threshold of 47°C.

Retraction

Heating begins

Conclusions

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• The Automated Drilling System prevented advancements past the bone layer transitions/breakthroughs and thermal damage through an automatic retraction system
• Relied on continuous force and temperature measurement
• 100% success rate with over 100 trials

Future Research

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Limitations in materials and current budget prevented us from creating a surgical system directly applicable for real-life operations

• Improvements in force control can be made with a slower linear actuator
• Realistic Application to surgeries
• Robotic Arm or Stand to mount the automatic system instead of a fixed, linear design