Cleaning problems associated with diamond trephine drills in bone surgery.

Dear Sir,

We would like to draw your attention regarding cleaning problems associated with diamond trephine drills in bone surgery. Trephine drills are widely used in bone surgeries such as biopsies, bone transplantation, and dental implants removal.[12] Classic trephines are metal cylinders with a saw-like cutting end.[3]

There is a certain demand for less micro fractures and more precise grinding of bone cylinders to achieve a better sample quality for analysis or more reproducible dimensions of the bone material for press fit transplantation.[14] Diamond drills proved to fulfill these demands with precise grinding rather than rough cutting.[5] Several products are in market including Meisinger Diamond Trephine Control (Hager and Meisinger Inc., Neuss, Germany) and the Diamond TwInS System (Karl Storz Inc., Tuttlingen, Germany). We used these drills in various experimental settings.[567] We randomly observed the cleaning outcomes of instruments used in those studies and present them in this publication.

We used the Meisinger Diamond Trephine Control System (Meisinger, Neuss, Germany) to grind fresh porcine cancellous bone cylinders from the proximal tibia.[7] In another study, rabbit bone was similarly harvested from the distal femur.[6] Human bone cylinders were obtained from the pelvic rim in the related study using the forerunner model of Diamond TwInS System.[5] Bone cylinders were generated with all drill sizes mentioned in the studies.[567] Continuous water rinsing was applied at a speed of 800 RPM (rounds per minute). Then, drills treatment was performed following the standard cleaning protocol for used surgical instruments. Treatments were sequentially carried out as following: Initial disinfection bath in 10% hydrogen peroxide (30 min), ultrasound cleaning in detergent bath (20 min), mechanical brush cleaning and professional instrument washing machine.[8] The cleaning cycle was repeated for three times.

These results are from randomly observed and microscopically examined drills used in three studies conducted by our group.[567] The drills were cleaned as mentioned above. Figure 1a shows an example of a pre-cleaned drill, in Figure 1b the same drill after a single cleaning cycle is seen. Even after three cleaning procedures, bone residues within the diamond surface structure were observed [Figures 2a and b]. All examined drills showed similar residues.

Figure 1

(a) Example for a diamond trephine after bone surgery prior cleaning (Diamond Trephine Control, Hager and Meisinger Inc., Neuss, Germany) (microscope: Keyence VHX-2000), (b) The same trephine bur after a single standardized cleaning cycle (microscope: Zeiss Stemi-2000)

Figure 2

(a) Example for a diamond trephine after three cleaning cycles (Diamond Trephine Control, Hager and Meisinger Inc., Neuss, Germany) (microscope: Keyence VHX-2000), (b) Same trephine; red stars are marking the white bone matrix residues after cleaning (microscope: Zeiss Stemi-2000)

The observation presented here is reproducible and occurs with most common cleaning protocols in settings following federal hygiene guidelines as applied in our studies.[567]

There are risks of infection associated with the bone remains contamination of the diamond drills. This includes several communicable germs that cannot be simply ruled out by sterilization. It is known that infectivity of prions in bone material remains after sterilization resulting in the possible risk of several associated neurodegenerative diseases including scrapie and bovine spongiform encephalopathy (BSE).[9] Autoclaving does not guarantee a safe sterilization of bone grafts even though one would not expect that small bone residues are comparable to full size grafts examined elsewhere.[10]

Bone residues were identified on Diamond coating with particle-size of approximately 100 μm after cleaning process as shown in this report. Therefore, smaller particle-size coatings, as applied in dental diamond drills, may contribute to better outcomes.[8]

Some manufacturers recommend specific cleaning instructions combining potassium hydroxide with ultrasound bath to remove the gluey bone residues on the diamond drills, as done by Karl Storz Inc. for their Diamond TwInS System. However, potassium hydroxide is a dangerous chemical with extreme risk of harm for skin and eyes that cannot be easily applied in a central hospital instrument sterilization facility. This special cleaning process requires a dedicated working place with all necessary safety measures. A validation of the Diamond TwInS System cleaning protocol by experts or the Federal office for disease control is recommended to prove the success of this method. Alternatively, diamond instruments for bone surgery could be used as disposables to ensure appropriate infection control conduct. We do follow this safe practice in clinical application.