Distribution of coolant during drilling with open type internally cooled medical steel drill

INTRODUCTION

Internally cooled bone drills with an open system, conduct coolant directly to the point of contact of cutting surface of the drill and the bone and lower the temperature at the drilling site. During bone drilling with internally cooled drills of open type, there is a possibility that coolant enters the intramedullary canal and has an adverse effect on intramedullary pressure. In this research, the intramedullary distribution of the coolant during and after drilling was analyzed.

MATERIALS AND METHODS

Specially constructed open type internally cooled medical steel drills were used. Experimental studies were conducted on the porcine femoral bone diaphysis. Coolant (saline) was mixed with water-soluble contrast agent and x-ray images of the distribution of coolant during and after drilling were taken with different regimes of drilling (drill rotational speed from 1300 rpm to 5000 rpm, and coolant flow rate from 0,6 l/min to 1,35 l/min).

RESULTS

An x-ray images showed that coolant did not spread from the borehole and has not spread intramedullary with any combination of coolant flow and drill rotation regimes.

CONCLUSION

Coolant does not disperse into the intramedullary canal outside of the borehole in given flow ranges (0,6-1,35 l/min) and drill rotational speed regimes (1300-5000 rpm). Open type internally cooled can safely be used for bone drilling.

Experimental and finite element analysis of surgical drill bits with and without irrigation channel - A case study approach

The aim of this study was to perform a finite element and experimental comparative analysis of the mechanical characteristics of surgical drill bits used in bone and joint surgery applications with and without an irrigation channel. Internally cooled drills are very efficient in maintaining the drilling temperature below the critical level. However, a cooling channel could potentially have a negative influence on the drill structure, particularly in the flutes zone. A commercially available type of surgical drill bit without irrigation channel and a modified variant with the built-in channel were simultaneously loaded with torque, axial and bending forces with magnitudes similar to and higher than those utilized in clinical practice. When loaded under the same conditions, both types of drills showed very similar mechanical properties in the sense of the average von Mises stress in chosen sections and the deflections after plastic deformation. The highest stress was observed in the bending zone which was located at the beginning of the flutes section of the drill. All analysed drills suffered only from plastic deformation without any breakage despite the fact that they were loaded with forces higher than those expected in normal operational conditions.

Cortical bone drilling and thermal osteonecrosis

BACKGROUND

Bone drilling is a common step in operative fracture treatment and reconstructive surgery. During drilling elevated bone temperature is generated. Temperatures above 47°C cause thermal osteonecrosis which contributes to screw loosening and subsequently implant failures and refractures.

METHODS

The current literature on bone drilling and thermal osteonecrosis is reviewed. The methodologies involved in the experimental and clinical studies are described and compared.

FINDINGS

Areas which require further investigation are highlighted and the potential use of more precise experimental setup and future technologies are addressed.

INTERPRETATION

Important drill and drilling parameters that could cause increase in bone temperature and hence thermal osteonecrosis are reviewed and discussed: drilling speed, drill feed rate, cooling, drill diameter, drill point angle, drill material and wearing, drilling depth, pre-drilling, drill geometry and bone cortical thickness. Experimental methods of temperature measurement during bone drilling are defined and thermal osteonecrosis is discussed with its pathophysiology, significance in bone surgery and methods for its minimization.