Cryolesions of bone. An experimental study. part I: Examinations in technique of controlled cryolesion on bone

Fracture risk of vertebral bodies after cryosurgery using a miniature cryoprobe: A biomechanical in-vitro analysis on human bones

INTRODUCTION

Due to spinal instability and compressive neurologic deficits surgical management is sometimes necessary in patients with metastatic spinal lesions. However, in some cases open surgery is not possible and minimally invasive procedures, like cryoablation, are needed. The aim of the current study was to investigate whether a miniature cryoprobe provides adequate tissue cooling in vertebrae and to evaluate the direct impact of cryosurgery on vertebral body stability.

MATERIALS AND METHODS

Twelve thoracic vertebral bodies were harvested from fresh cadavers. After documenting bone density cryoablation was performed in six vertebral bodies according to a standardized procedure. Afterwards temperature inside the vertebral body and maximum breaking force were measured in the control and experimental groups.

RESULTS

Required temperature of -50° was reached in all areas. There was a significant correlation between maximum breaking force and measured bone density (p= 0.001). Mean breaking force within the experimental group was 5047 N (SD = 2955 N) compared to 4458 N (SD = 2554 N) in the control group. There were no observable differences in maximum breaking force between both groups.

CONCLUSION

Miniature cryoprobe can deliver adequate tissue cooling to -50°C in vertebral bodies. The procedure does not seem to influence breaking force of the treated bones in-vitro. Therefore, using miniature probes cryosurgery may provide a valuable alternative to conventional surgical resection of neoplastic diseases as well as of benign locally aggressive bone tumors.

Effect of Storage Temperature on Allograft Bone

BACKGROUND: The recommendations for storage temperature of allogeneic bone are varying between -20 °C and -70 °C and down to -80 °C. The necessary temperature of storage is not exactly defined by scientific data, and the effect of different storage temperatures onto the biomechanical and the biological behavior is discussed controversially. METHODS: The historical development of storage temperature of bone banks is described. A survey on literature concerning the biomechanical and biological properties of allograft bone depending on the procurement and storage temperature is given as well as on national and international regulations on storage conditions of bone banks (European Council, American Association of Tissue Banks (AATB), European Association of Tissue Banks (EATB)). RESULTS: Short-term storage up to 6 months is recommended with -20 °C and -40 °C for a longer period (AATB), and EATB recommends storage at -40 °C and even -80 °C while the regulations of the German German Medical Association (Bundesärztekammer) from 2001 recommend storage at -70 °C. Duration of storage at -20 °C can be maintained at least for 2 years. The potential risk of proteolysis with higher storage temperatures remains, but a definite impairment of bone ingrowth due to a storage at -20 °C was not shown in clinical use, and no adverse biomechanical effects of storage at -20 °C could be proven. CONCLUSION: Biomechanical studies showed no clinically relevant impairment of biomechanical properties of cancellous bone due to different storage temperatures. Sterilization procedures bear the advantage of inactivating enzymatic activity though reducing the risk of proteolysis. In those cases a storage temperature of -20 °C can be recommended for at least a period of 2 years, and the risk of undesired effects seems to be low for native unprocessed bone.

Complications after cryosurgery with new miniature cryoprobes in long hollow bones: an animal trial

BACKGROUND

In vitro studies show that new miniature cryoprobes are suitable for cryoablation of bone tissue. The aim of this animal trial on 24 sheep was to examine the perioperative complications, particularly the danger of embolism, of cryoablation when using miniature cryoprobes.

METHODS

Cryoablations with 2 freeze-thaw cycles each were carried out in the epiphysis of the right tibia and the metaphysis of the left femur. Pulmonary artery pressure (PAP) and central venous pressure (CVP) were measured. Throughout the intra- and perioperative phase, heart rate and oxygen saturation by pulse oxymetry, blood gas and electrolytes were monitored regularly. Postoperative complications were examined up to 24 weeks postoperative.

RESULTS

As result, no significant increase of PAP, CVP or heart rate were observed. Blood gases were unremarkable, with pO2 and pCO2 remaining constant throughout the operation. Regarding pH, standard bicarbonate and base excess, only a non-significant shift towards a slight acidosis was seen. There was a mean hemoglobin decrease of 0.5 g/dl. One animal showed postoperative wound infection and wound edge necrosis. No major peri- and postoperative complications associated with cryosurgery of bone were observed, especially regarding clinically relevant pulmonary embolism.

CONCLUSION

Surgery with new types of miniature cryoprobes appears to be a safe alternative to or a complement to conventional resection of abnormal bone tissue.

Cryosurgery in long bones with new miniature cryoprobe: an experimental in vivo study of the cryosurgical temperature field in sheep

AIM

The aim of this in vivo study was to determine whether new miniature cryoprobes provide adequate tissue cooling in long bones by measuring the field of temperature under various conditions.

METHODS

Freezings were performed in femoral and tibial bones of 10 sheep under general anaesthesia. Applying one cryoprobe, temperatures of -75 degrees C resp. -51 degrees C could be reached within 0.75 cm resp. 1.00 cm of the probe.

RESULTS

Histological examinations revealed compact bone and marrow necroses along the isotherm in all 10 sheep. Using two cryoprobes simultaneously, a mean temperature decrease to -71 degrees C between the two cryoprobes was achieved thanks to the synergistic freezing effect. Looking at consecutive freezes, it was apparent that with similar cryoprobe end temperatures, the temperature dropped faster if the number of freezing cycles was increased.

CONCLUSION

In conclusion, it was seen that despite its small diameter, the new miniature cryoprobe delivers adequate in vivo tissue cooling in long tubular bones. Employing the synergistic freezing effect by using two or more cryoprobes simultaneously, efficient in vivo freezing of larger bone segments is also possible. Thus, cryosurgery with the new miniature probes can provide a valuable complement to conventional resection of long tubular bones, and offers a viable alternative to surgical treatment of neoplastic diseases of the skeletal system.

The use of a new miniature cryoprobe for ablation of bone tissue: in vivo assessment of the probe and application of the method to bone in a sheep model

BACKGROUND

So far, modern miniature cryoprobes were used for local destruction of soft tissue tumours without damaging the adjacent healthy tissue. In this study, cryoablation methodology was applied to bone and the cooling capacity of the probe was examined in vitro and in vivo.

METHOD

Freezing was performed by cooling one or two probes (diameter 3.2 mm) to -180 degrees C with liquid nitrogen. The cooling capacity of the probes was determined optically and thermally against a homogeneous reference gel, followed by in vivo measurements on femoral and tibial sheep bone followed by histological examination.

RESULTS

Thanks to the synergistic effect, the simultaneous use of 2 probes produced an almost spherical expansion of cold in the homogenous gelatin. During the in vivo freezes, the temperature curves showed a more moderate trend. Nevertheless, due to the synergistic effect, temperatures below -50 degrees C could be reached at a distance of 1 cm from the probe. No local or systemic intraoperative complications were observed. Histological examination revealed cell necrosis up into the -10 degrees C isotherm.

CONCLUSIONS

Adequate tissue cooling of the bone matrix can be achieved with in vivo freezes by means of one or more miniature cryoprobes. Therefore, this probe could provide an alternative to or supplement surgical resection of pathological bone processes.

Two freezing cycles ensure interface sterilization by cryosurgery during bone tumor resection

Cryosurgery utilizing an argon-based system allows bone-tumor interface sterilization, while avoiding the risks of conventional cryosurgery. This study was conducted in order to evaluate the number of freezing cycles required for interface sterilization in cases of aggressive human bone tumors. Sixteen tumors were included (six chondrosarcomas, eight metastatic carcinomas, and two giant cell tumors). All occurred within long bones. In all cases a standardized marginal resection was performed. Following thorough curettage, we sampled five different locations within the tumor interface by a cylindrical hollow trephine. The interface viability was assessed using the XTT method. Quantitative histological evaluation was based on the percentage of live cells divided by total lacunae number in five random medium-power fields. One freezing cycle (5 min, -40 degrees C) reduced tumor viability to approximately 5% of prefreezing. However, there were still live specimens. Two or three freezing cycles led to complete interface sterilization. The difference between a single freezing cycle and two freezing cycles was significant (ANOVA, F = 130, P < 0.01). The difference between two freezing cycles and three freezing cycles was not significant (ANOVA, F = 0.14, P < 0.6). The results of the XTT method for the assessment of interface viability correlated well with histological evaluation of the percentage of viable cells (r = 0.89), as well as with cell culture results of frozen vs. prefreezing tumor samples. In conclusion, two freezing cycles are adequate to achieve tumor-bone interface sterilization in aggressive human bone tumors.

MR appearance of skeletal neoplasms following cryotherapy

Cryotherapy is an increasingly popular mode of therapy adjunctive to surgical curettage in the treatment of certain skeletal neoplasms, such as giant cell tumors or chondrosarcomas. The magnetic resonance (MR) findings following cryotherapy have not been previously reported. We reviewed the MR findings in seven patients with skeletal neoplasms following curettage and cryotherapy. In six cases we found a zone of varying thickness extending beyond the surgical margins, corresponding to an area of cryoinjury to medullary bone. This zone displayed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images, consistent with the presence of marrow edema. This zone of edema almost certainly reflects underlying thermal osteonecrosis. This zone may vary in size and intensity over time as the area of cryoinjury evolves or resolves. MR is currently the imaging procedure of choice for follow-up of most musculoskeletal neoplasms. Knowledge of the MR findings following cryotherapy should help prevent confusion during the interpretation of follow-up MR examinations.