HAND (2009) 4:108–112 cations. K-wire insertion by hammering using a pneumatic hammer could prove to be effective in reaching this goal [11, 23, 25]. It has been shown that hammering of K-wires results in lower heat generation, shorter insertion time, less thermal damage and equal or even better initial fixation compared to drilling without irrigation. All together, this suggests that hammering is a good alternative for drilling. These experiments, however, have one major drawback as they used in vivo or in vitro animal models. Eriksson showed that temperatures measured in animal models are not applicable to the clinical situation [9]. Furthermore, these experiments did not compare drilling with irrigation versus hammering. We therefore designed a study to determine the insertion time, extraction force, and maximum bone temper- ature while inserting K-wires into human cadaver metacar- pals using a pneumatic hammer and comparing these data to conventional drilling with and drilling without irrigation. Materials and Methods Fifteen fresh human cadaver metacarpals were used. They were collected from two male human cadavers who had no reported history of disorders or diseases related to bone which was verified by X-ray examination. Their ages at death were 75 and 77 years. The metacarpals were denuded of all soft tissue and were measured at two places at the diaphysis resulting in an average diameter of 10.3 mm (SD = 2.1 mm). The experiment was conducted at room temperature (21.6°C, SD =1.12°C) with the bones rigidly fixed (Fig. 1). The fixator was placed on the operation device as described before [11, 12]. A weight of 0.5 kg was used for forwards movement of the drill and pneumatic hammer. Three stainless steel trocar-tip K-wires (1.0 mm × Fig. 1 Experimental setup. Drilling Kirschner wire into bone. Two thermocouples are placed at a distance of 0.5 and 1.0 mm from the periphery of the K-wire insertion place. 109 150 mm, Synthes, Zeist, The Netherlands) were inserted, by hammering, drilling without irrigation and drilling with irrigation (10 ml/s, 21.1°C (SD=1.16°C)) in the diaphysis of each metacarpal. Each metacarpal has a proximal, mid, and a distal location for K-wire placement. The three techniques were alternated between these locations, which resulted in five times K-wire insertion for each technique per location. The temperature was measured with two 4.0-millimeter-diameter Type K chromel–alumel thermo- couples placed into the cortex of the metacarpals at a depth of 1.0 mm at a distance of 0.5 and 1.0 mm from the periphery of the insertion site at 180° to each other. The thermocouples were attached to a Pico USB TC-08 8- channel thermocouple data logger with a measuring range of −270 till 1,370°C (accuracy±0.5°C). The temperature was recorded at 1-s intervals. Canals for the thermocouples, 0.5 mm in diameter, were predrilled by a Rosa XY-table (Milan, Italy) with a drill speed of 3,000 rpm. Friction between the thermocouples and the walls of the predrilled canals was sufficient to hold them in place. K-wires were drilled with a speed of 1,200 rpm (Fig. 1) [11]. For hammering K-wires, an adapted Micro-Aire 1500 (Micro-Aire Surgical Instruments Inc., Valencia, California, USA) was used. This is from an origin air-powered osteotome apparatus which we used as pneumatic hammer. The hammering frequency (maximum of 10,000 pulses/min) depends on the air pressure in the hammer and has an inlet pressure varying between 80 and 100 psi (5–7 kg/cm2). Trocar tip K-wires were cut to a length of 60 mm to prevent side bending. The duration of each experiment was counted from the beginning of insertion until the K-wire had penetrated both cortices. After insertion, the K-wires were removed using a 1,000-N (±0.022%) Mecmesin Advanced Force Gauge, (Newton House, West Sussex, United Kingdom). Differences in temperature, insertion time and extraction force were analyzed by Bonferroni Multiple Comparisons. Statistical significance was determined based on p<0.05. The data were analyzed using SPSS 12.0.1 for Microsoft Windows Results In total, 45 K-wires were placed. The cortical temperatures recorded by the thermocouple positioned 0.5 mm from the drilling site were always higher than those recorded by the thermocouple located 1.0 mm from the drilling site. Therefore, temperature data presented below were recorded by the thermocouple located 0.5 mm from the K-wire insertion place. The elevation of the bone temperature during drilling with irrigation was significantly lower compared to hammering and drilling without irrigation. The temperature elevation during hammering however was