Changes in the Structure and Mechanical Properties of the Bone after Puncture Cryoablation: Experimental Study

Abstract

Purpose of the study — to evaluate possible impact of cryoablation on a healthy bone and to identify probable causes of postoperative fractures.Materials and Methods. The authors performed cryoablation of the femur in the experiment on 8 mature rabbits of Soviet Chinchilla (SC) breed with a follow up for up to two months. Anitrogenous cryoprobe of 1.5 mm in diameter was introduced into the femur through a perforation hole. The bone was completely frozen up to -180°С in two cycles with continuous thermometry. Pathomorfological examinations were performed after 7 and 55 days along with assessment of bone hardness. Preparation of material stipulated sawing the bone at the fracture site along the bone axis. One half-bone was used for histological examination, and another one — for measuring mechanical properties by local pressing of a diamond indenter onto the bone at certain applied force. The distance between measurement points along the bone was 250 μm. Statistical processing included variance significance analysis using t-test.Results. The authors reported bone fractures at the site of cryodestruction in all animals in one week after the procedure. Statistical analysis of the measurements and histological examination demonstrated that freezing of the entire bone diameter up to -180°С results in its complete destruction. Strength reduction around the fracture site corresponded to the temperature distribution area in the range from -9ºС to -15ºС. However, areas of cooling below -40ºС exhibited some bone segments with normal hardness. Mosaic pattern of strength reduction is explained by microcirculation disorders. Histology confirmed thrombosis of intraosseous blood vessels in the area of cryotherapy. The first focal signs of osteomalacia emerged by the end of the first week after cryoablation. Subsequently, the bone preserved its regenerative properties, but by the end of the second month after the procedure the histogenesis was still not completed and the bone did not regain its strength.Conclusion. The authors believe that a limited number of cases, the specific features of the angioarchitecture of animal bones and their ability to produce a heavy periosteal response do not allow to apply obtained quantitative outcomes of the present study to clinical situations. However, complete freezing of the entire bone diameter inevitably results in fracture formation.