HAND (2009) 4:108–112 different tip shapes, similar differences were obtained. The short insertion time, seen in all experiments with different insertion forces, is an important characteristic of the hammering technique. Thermal-related osteonecrosis is a product of insertion time and the temperature reached. We further know that osteonecrosis will occur when bone is heated to a temperature of 50°C for 1 min [5]. Therefore, when using the hammering technique, the bone is exposed to lower temperatures during a shorter insertion time with the same insertion weight or with optimized weights for each method. Theoretically, this should result in less thermal damage resulting in better-fixated K-wires. Our results suggest such a relation since the highest extraction forces were needed to remove the faster inserted hammered K-wires. These results confirm the experiments of Wassenaar et al. in which K-wires were hammered and drilled into ribs of pigs. Those K-wires needed 129.0 N and 57.4 N, respectively, to remove them [23]. Notwithstanding the fact that significant more extraction force was needed to remove the hammered K-wires in both, our and Wassenaar et al. [23] experiments, there is an absolute difference between the extraction forces needed in both experiments. This is probably due to the fact that Wassenaar et al. [23] drilled with 600 rpm, used a variable insertion force, pig ribs, and a different diameter K-wire. On the other hand, in one of our earlier in vivo experiments we showed no significant difference in the extraction forces [11]. We suggested that there was no significant difference due to the rabbit model we used. Based on these results, we conclude that hammering K-wires is a good alternative for drilling with irrigation and is superior when irrigation can not be properly applied using the drilling technique. Despite our promising results concerning hammering K-wires, we have to keep in mind that we used a human cadaver model. Our experimental conditions differ from the clinical setting in several aspects. The metacarpals were stripped of soft tissue, were at room temperature instead of body temperature and there was no cortical blood flow. The function of this cortical blood flow, however, is debatable. It is possible that it may absorb heat generated in vital bone, but on the other hand, the cortical blood flow rate is normally very low and coagulation of small vessels occurs very rapidly when heated [10]. The relative differences, however, may still be significant and need further investigation. In two cases, it was not possible to insert the K-wire through the opposite cortex using the pneumatic hammer. This is probably due to the maximum “hammer” power produced by the Micro-Aire 1500 we used. The apparatus which was originally designed for performing osteotomies was not powerful enough to penetrate the two K-wires which were stuck in the first cortex, through the opposite cortex. It is likely that this can be prevented in the near future by using a more powerful pneumatic hammer. 111 This experiment suggests that hammering can be superior to drilling without irrigation because it results in lower temperatures, higher extraction forces, and short insertion times. The latter was managed in this experiment by using similar insertion forces for both insertion techniques. This of course is not comparable with drilling in the clinical setting because K-wires are normally inserted much faster with unknown raise in bone temperature around the wire. The only advantage of drilling with irrigation compared to hammering is the lower mean maximum temperature, which is, however, difficult to realize in daily practice. We therefore conclude that hammering is a good alternative for drilling K-wires and is the preferable method when proper external irrigation is not possible. Acknowledgments The authors wish to thank Mr. W.J.A. van Wolferen and Mr. S Plomp from the department of Pharmacology and Anatomy, University Medical Center (UMC) Utrecht, the Netherlands, Mr. R. Mansvelt Beck from the Heart Lung Institute, Department of Cardiothoracic Surgery, UMC Utrecht, the Netherlands and Mr. C.J.S. Magielse from the Department of Biomedical Engineering, UMC Utrecht, The Netherlands for their technical assistance. Further we like to thank Mr. M.S. Cune DDS, PhD and Mr. A. van Rhijn from the Head and Neck Division, Department of Oral & Maxillofacial Surgery, Prosthodontics and Special Dental Care, UMC Utrecht, the Netherlands, Mr. J.H.G.M. Klaessens dep. Medical Technology and Clinical Physics, UMC Utrecht, the Netherlands and Oudshoorn Chirurgische Techniek b.v., Oss, The Netherlands for the use of their equipment. We also would like to thank Synthes, Zeist, The Netherlands for the K-wires they kindly sponsored. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which per- mits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References 1. Abouzgia MB, James DF. Temperature rise during drilling through bone. Int J Oral Maxillofac Implants 1997;12:342–53. 2. Berman AT, Reid JS, Yanicko DR, et al. Thermally induced bone necrosis in rabbits. Relation to implant failure in humans. Clin Orthop Relat Res 1984;186:284–92. 3. Botte MJ, Davis JL, Rose BA, et al. Complications of smooth pin fixation of fractures and dislocations in the hand and wrist. Clin Orthop Relat Res 1992;276:194–201. 4. Brisman DL. The effect of speed, pressure, and time on bone temperature during the drilling of implant sites. Int J Oral Maxillofac Implants 1996;11:35–7. 5. Eriksson AR, Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury: a vital-microscopic study in the rabbit. J Prosthet Dent 1983;50:101–7. doi:10.1016/0022-3913 (83)90174-9. 6. Eriksson RA, Albrektsson T. The effect of heat on bone regeneration: an experimental study in the rabbit using the bone growth chamber. J Oral Maxillofac Surg 1984;42:705–11. doi:10.1016/0278-2391(84)90417-8.