Stability changes after cryosurgery in long tubular bones in correlation to histological results: an animal trial.

STUDY QUESTION: Pathologic bone fractures in cryosurgery of bone tumors have been described in literature. This study utilizing a sheep model should prove the possible reduction of potential fracture while using a new miniature cryoprobe minimizing tissue damage and providing accurate control of the ablation process. Furthermore, postoperative histological changes should be investigated and the results correlated with the stability trials. METHODS: In 24 sheep, ablation of the femur and the tibial bone on one side was carried out. Ablation of the right femur was limited to an area of 2 cm(2) with single cortical bone, whereas at the left tibia the whole proximal tibial plateau was included. The other side served as a control entity without cryoablation. After a period of 2, 4, and 6 months postoperative investigation of bending resistance of the femoral bone and of compression resistance of the tibial bone as well as histological findings were done in eight animals each. RESULTS: After 2 months there was a significant difference (P < 0.05) regarding compression resistance between the treated and the contralateral tibia, whereas the bending resistance in the treated femur was slightly lower than on the contralateral side. After 4 and 6 months the cryo-treated part showed a tendency towards weakness. Histological findings showed bone necrosis with slight beginning repair after 2 months. Four and six months later, bone necrosis still existed with increasing development of woven bone and conversion into lamellar bone. DISCUSSION: A thorough control of the freezing process and the low iatrogenous weakening of the bone due to placing the probe when modern miniature cryoprobes are used can minimize the risk of pathological postoperative fractures. However, at least 2 months after operation there is histological proof of bone healing with appropriate reduction of bone stability, which should be considered for the clinical application of this new technique.

[Changes in stability after cryosurgical treatment of long tubular bones. An animal experiment study]. / Stabilitätsveränderungen nach kryochirurgischer Behandlung an langen Röhrenknochen. Eine tierexperimentelle Studie.

The incidence of spontaneous fractures after cryosurgical treatment is described in the literature. The purpose of this study in the sheep model was to analyze the possibility of minimizing the potential risk of bone failure using a new miniature cryoprobe with minimal tissue traumatism and exact control of the ablation. In each of 24 sheep ablations at the right femur and left tibia were performed by drilling. The ablation at the femur was restricted to an area of 2 cm(2) of only one cortical bone, whereas at the proximal tibia the whole tibial plateau was included. The opposite side, which was treated with analog drillings without cryoablation, served as control. The ultimate bending strength of the femur and the ultimate compression strength of the tibia were examined 2, 4, and 6 months after the operation. After 2 months there was a significant difference ( p<0.05) in the ultimate compression strength between the treated and untreated tibiae, whereas the ultimate bending strength of the treated femora tended to be lower. After 4 and 6 months the side treated with cryosurgery was only marginally weaker than the untreated side. Spontaneous fractures were not observed during the whole experimental period. The good controllability of the freezing procedure and the low iatrogenic weakening of the bone using a modern miniature cryoprobe minimizes the risk of pathological postoperative fractures. After ablation of larger bone sections, the treated extremity should be partially unloaded or managed by osteosynthesis for at least 3 months.