Date Published: April 18, 2019
Publisher: Public Library of Science
Author(s): Anne Carolus, Wolfgang Richter, Claus-Peter Fritzen, Kirsten Schmieder, Christopher Brenke, Benjamin Elder.
Manual skull drilling is an old but in modern neurosurgery still established procedure which can be applied quickly and universally in emergency situations. Electrical drilling requires more complex equipment and is usually reserved to the Operating Room (OR). It also seems desirable to apply an electrical drill for bedside usage but a suitable product does not exist so far.
Our experimental study using a manually and an electrically driven skull drill included a total of 40 holes drilled into synthetic biomechanical sheets. Half of the holes were produced with a prototype electrical drilling machine of the company Kaiser Technology and half of them with a traditional manual drill. Different drilling parameters such as the geometry of the borehole, the drilling forces and the drilling vibrations were captured during all experiments.
The electrical drilling needed higher vertical force by the operators and a longer time to penetrate the sheet. A reason was the relatively lower rotational speed provided by this particular drill. When drilling electrically the vibrations were substantially less which in turn led to a more precise shape of the holes (revealed by observation via a microscope).
The electrification of bedside drilling can in principle enable emergency craniostomies to be performed with greater ease and accuracy. The power of the electric drive, however, must be at least equivalent to the power of the traditional manual drill. Otherwise, the vertical forces exerted on the scull by the operator become inhibitive. The challenge is to combine cost-efficiency and re-sterilizability of an electrically driven drilling machine which at the same time is small and simple enough to qualify for emergency applications.
Skull drilling is a surgical procedure that has been practiced since prehistoric times [1, 2, 3, 4]. In neurosurgery, the manual drilling technique survived to date [5, 6, 7]. Electrically driven drills are suitable for the Operating Room (OR) since they either depend on a drilling shaft or are large battery drills . The manual twist drill prevailed in emergency situations, first and foremost for external ventricular drainage (EVD) application, because of several advantages: It is cheap, re-sterilizable, rugged (concerning mechanical loads and environmental conditions), totally independent from the OR with its electrical power supply  and has a compact size. On the contrary, the main problem of manual drilling is that the skull may be penetrated in an uncontrolled and abrupted way [9, 10, 11]. This may result in brain injury and intracerebral or acute epidural hematoma [10, 12, 13]. Some technical modifications to reduce these risks have been developed, for instance a pre-adjustable distance holder  or a percutaneous needle which replaces the turning drilling bit [14, 15]. But none of those devices has become widely accepted. Prediction and control of thrust forces and torques as well as possibly an optimized drill design are typical tasks related to mechanical engineering; see e.g. the publications [16, 17, 18]. This contribution tries to bridge the gap between engineering work and every day´s neurosurgical practice. Our hypothesis is that electrical drilling leads to significant advantages compared to manual drilling and that a well designed electrical drilling machine should be able to replace the twist drill in modern neurosurgery even in a bedside setting. The results of this study are thought to contribute to an improved list of specifications for an advanced electric drill, based on sound experimental results utilizing a battery-driven prototype drilling machine which was developed for bedside usage by Kaiser Technology, and a traditional manual drill. The study was carried out in cooperation of the Department of Neurosurgery, Knappschaftskrankenhaus Bochum and the Chair for Applied Mechanics, Department Mechanical Engineering at the University of Siegen.
With regard to the emergency situation at the patient´s bedside, we can make the following statements: An electrically driven drilling machine contributes to a more controlled drilling in the sense that it generates less irregular movements in the xy direction and has a higher direct penetration rate. The round drilling holes nearly come up with the diameter of the drilling bit. This can help to achieve a precise trajectory for a ventricular catheter. In the manual drilling, the action for the operator is more complex: Turning the crank with the right and conducting the drilling machine with the left hand causes more lateral deviation of the drilling bit.