Surgical treatment of bone tumours often requires a generous resection of bone, leaving defects which are difficult to span. The method of freezing tumours with liquid nitrogen was introduced as an adjunct treatment to intralesional resection, or curettage for extension of the surgical margin of excision. The nitrogen was poured or sprayed directly into the bone cavity [11,13,14,16,24-27]. Due to minimal control of the freezing procedure [12,15] and the risk of vaporization causing gas emboli [23], the widespread use of direct application of nitrogen was limited.
In addition to open application, a closed system has also been described [5,6,9]. For the first time in 1984, Russe and Kerschbaumer used cryoprobes for ablation of bone tumours in humans [21]. The probes were bent, trocar-like, hemispherical or spherical [10], but their cooling ability was poor in relation to the probe's diameter [4,8]. This was mainly due to evaporation of the nitrogen inside the system before it actually reached the freezing zone. Therefore, less nitrogen was available at the tip of the probe, which in turn limited the speed of freezing and the minimum temperature attainable, as well cell destruction [7].
As described by Baust et al. in 1997, the boiling point is lowered by increasing the pressure within the device, thereby preventing premature evaporation [2]. In the Erbokryo CS-6 cryoprobe used here, evaporation is prevented almost completely by an operating pressure of 15 bar at the beginning of the freezing process and by an optimum flow of nitrogen. This ensures quick exposure of the surrounding tissue to the low temperature. Pressure is lowered during freezing, which raises the boiling point of the nitrogen to ensure evaporation of the nitrogen at the tip of the probe, and hence a further drop in temperature in the surrounding tissue. Furthermore, unnecessary tissue injury caused by insertion of the probe was avoided by reducing the probe's diameter to 3.2 mm. While the basic suitability of freezing for the destruction of bone tumours – also when using cryoprobes – has already been documented [21], the use of this high-capacity, fine-calibre miniature cryoprobe for freezing bone tissue has not yet been described. The goal of this in vitro and in vivo experiment was to establish the possible field of therapy for such a miniature cryoprobe in a reference medium and to study whether this miniature cryoprobe is suitable for appropriate tissue cooling in long bones.
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