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Research Papers

CT-Compatible Medical Drilling Stylet

[+] Author and Article Information
Conor J. Walsh

Massachusetts Institute of Technology,
Department of Mechanical Engineering,
Cambridge, MA 02139;
Massachusetts General Hospital,
Department of Radiology,
Boston, MA 02114

Arjan J. H. Meskers

Technical University of Delft,
Department of Biomedical Engineering,
Delft, 2600 AA, The Netherlands

Alexander H. Slocum

Massachusetts Institute of Technology,
Department of Mechanical Engineering,
Cambridge, MA 02139

Rajiv Gupta

Massachusetts General Hospital,
Department of Radiology,
Boston, MA 02114

Manuscript received March 8, 2010; final manuscript received April 10, 2011; published online October 11, 2012. Assoc. Editor: Paul A. Iaizzo.

J. Med. Devices 6(4), 041001 (Oct 11, 2012) (8 pages) doi:10.1115/1.4007280 History: Received March 08, 2010; Revised April 10, 2011

This paper describes the design of a compact, lightweight CT-compatible, drill-press that is designed to be used in either a hand-held or stand-alone mode to assist with percutaneous bone based interventions. Previous medical drilling tools that have been developed have a metal structure and typically have one actuator for advancing the drill (feed) and another for rotating it (speed). After defining the device functional requirements and specifications, a deterministic design process was followed to generate several design concepts that were then evaluated based on their ability to satisfy the functional requirements. A final concept that uses a custom screw-spline to achieve helical motion of a shaft that is attached to a standard orthopedic drill was selected for prototyping. The design uses a single actuator to drive both the screw and spline nuts through two different gear ratios, resulting in a fixed ratio between the feed and speed. Apart from the motor which is placed away from the central drill axis, the device is largely made from plastic materials. A custom experimental setup was developed that enabled drilling into bone inside a CT scanner to be examined. Results showed that the device was successfully able to penetrate thick cortical bone and that its structure did not appreciably distort the medical images.

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References

Figures

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Fig. 1

Illustration of a drill about to penetrate a layer of bone. During the drilling operation there should be a means to protect the soft-tissue from the drilling action. After an access path through the bone has been created, there should be some means to access this from the skin surface.

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Fig. 2

Possible methods for supporting the drilling stylet. In A, the stylet could be attached to a standard cannula that is first placed to the desired bone entry site. In B, the drilling stylet could be mounted on the end of an active or passive positioning arm.

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Fig. 3

Concept 1. A motor is used to drive the drill rotation that moves on a carriage that is driven using a motor and leadscrew. In this concept, independent control of the drilling feed and speed can be controlled.

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Fig. 4

Concept 2. An angled traction drive, where the rollers are not mounted parallel to an inserted shaft (source-file: modified www.zero-max.com solid works file).

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Fig. 5

Concept 3. A screw-spline used to control the drilling feed and speed. It consists of a plastic threaded rod that also has a spline along it. Motors are connected to a threaded and keyed nut that engage the screw and spline, respectively.

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Fig. 6

Final design of the single motor driven screw-spline mechanism with a single motor driving the screw and spline nuts through different gear ratios

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Fig. 7

Final prototype manufactured from largely plastic components. The motor is offset from the central axis of the drill.

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Fig. 8

CT-compatible test rig for supporting the device and a sample of bone

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Fig. 9

CT scan of the device before and after drilling into the bovine bone. There is minimal streaking artifact from the device and the cannula and drill are clearly visible. While, the device was able to successfully drill into bone, some deflection of the bit was observed due to a small shift in the specimen.

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Fig. 10

Conceptual illustration of the CT-compatible drill press mounted on to a stereotactic frame for neurosurgical applications

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