Thermal effect of percutaneous radiofrequency ablation with a clustered electrode for vertebral tumors: In vitro and vivo experiments and clinical application

Safety assessment of microwave ablation in sheep vertebral bodies

BACKGROUND

Spine is the most common location for bone metastases. Microwave ablation (MWA) is a technique for minimally invasive tumor treatment. The aim of the current study was to determine whether MWA is a safe option for treatment in vertebral bodies and to gain data on the amount of cortical insulation in the spine.

METHOD

MWA was applied with different settings for power and time in both in- and ex-vivo sheep vertebral bodies. Safety was evaluated by temperature measurements at critical surrounding structures (e.g. spinal cord, nerve root). Furthermore, the distribution of heat through the bone at 5 mm from the ablation needle was measured and compared to the temperature at the posterior wall.

RESULTS

An effect of cortical insulation in the spine was found, for ablations with 20-30 and 50 W (p < 0.01). Ablations with wattage levels of 40-50 W almost instantly led to temperatures over 60 °C at the posterior wall. The temperature remained below 60 °C for 4 min in ex-vivo ablations with 20 and 30 W. However, in the in-vivo experiment paralysis was frequently seen (10/12 sheep) in lower wattages (20-30 W) as well and the experiment was therefore terminated.

CONCLUSION

MWA is an effective approach for local bone destruction in the spine. However, given the high risk of complications, caution is advised for treatment in vertebral bodies without better local distribution accuracy. Since cortical insulation appears insufficient to protect the spinal canal from excess heat, MWA involves a risk of paralysis.

Progression of Femoral Osteolytic Metastases after Intramedullary Nailing and Subsequent Salvage Techniques

Intramedullary nailing insertion from the proximal-to-distal femur is frequently performed for impending and complete pathological femur fractures due to osteolytic metastases. After nailing through cancer-laden bone, residual chemotherapy- and/or radiation-resistant tumor may progress. Progression of osteolysis risks future nail failure or pathological fractures. This study assesses the incidence of cancer progression following intramedullary nailing in a femur-only cohort and describes a percutaneous rod-retaining salvage technique. A single-institution, retrospective study was conducted to identify adult patients who underwent intramedullary nailing for femoral osteolytic lesions for complete or impending nail failure from 2016 to 2023. Progression was defined as enlargement of the pre-existing lesion and/or appearance of new lesions on radiographs. Surgical outcomes were assessed with a combined pain and functional score. A total of 113 patients (median age 66.8 years (IQR = 16.4); median follow-up 6.0 months (IQR = 14.5)) underwent intramedullary nailing. Sixteen patients (14.2%) exhibited post-nailing cancer progression. Pre- and postoperative radiation and chemotherapy did not decrease the odds of cancer progression. Three patients underwent initial open surgical salvage consisting of proximal femur replacement arthroplasty, and six patients did not receive salvage due to poor surgical candidacy or patient choice. Seven patients (median follow-up 10.7 months (IQR = 12.9)) received percutaneous salvage. In this group, pain and functional scores improved by 4.0 points (p = 0.0078) at two-week postoperative follow-up and 2.0 points (p = 0.0312) at the most recent follow-up (mean follow-up 13.0 ± 9.4 months). All three nonambulatory patients became ambulatory, and six patients were able to ambulate independently without walking aids. No major complications were reported 30 days postoperatively. Progression of femoral osteolytic metastases may occur following intramedullary nailing. Continued monitoring of the entire femur is needed to maintain improved functional status and to prevent catastrophic progression of pre-existing lesions or appearance of new lesions. In patients with more proximal metastases only, the customary practice of bringing a long nail from the proximal femur to distal metaphysis should be reconsidered. Furthermore, there is concern of mechanical transport of cancer cells during guide wire insertion, reaming, and rod insertion through cancer laden bone to cancer free distal bone.

Temperature Monitoring in Hyperthermia Treatments of Bone Tumors: State-of-the-Art and Future Challenges

Bone metastases and osteoid osteoma (OO) have a high incidence in patients facing primary lesions in many organs. Radiotherapy has long been the standard choice for these patients, performed as stand-alone or in conjunction with surgery. However, the needs of these patients have never been fully met, especially in the ones with low life expectancy, where treatments devoted to pain reduction are pivotal. New techniques as hyperthermia treatments (HTs) are emerging to reduce the associated pain of bone metastases and OO. Temperature monitoring during HTs may significantly improve the clinical outcomes since the amount of thermal injury depends on the tissue temperature and the exposure time. This is particularly relevant in bone tumors due to the adjacent vulnerable structures (e.g., spinal cord and nerve roots). In this Review, we focus on the potential of temperature monitoring on HT of bone cancer. Preclinical and clinical studies have been proposed and are underway to investigate the use of different thermometric techniques in this scenario. We review these studies, the principle of work of the thermometric techniques used in HTs, their strengths, weaknesses, and pitfalls, as well as the strategies and the potential of improving the HTs outcomes.

Radiofrequency ablation may improve the beneficial results of vertebroplasty for vertebral hemangiomas: analysis of 46 patients

OBJECTIVES

To evaluate the effect of vertebroplasty (VP) alone or combined therapy of radiofrequency ablation (RFA) with vertebroplasty on pain relief with visual analog scale (VAS) and Oswestry Disability Index (ODI) scores in vertebral hemangiomas.

METHODS

Forty-six patients with hemangiomas were evaluated retrospectively: 20 males and 26 females were included. In group 1 (n = 25) only VP was performed, while RFA+VP were performed in the same treatment session in group 2 (n = 21). Radiological diagnosis was performed with X-ray, CT-scan and MRI images in all patients. The intensity of pain was assessed with the VAS together with the assesment of life quality with the ODI. The assesments were performed before, at first day, at first month and 6 months after treatment.

RESULTS

There was no significant difference between mean preprocedural VAS and ODI scores, but a significant decrease was seen in postprocedural VAS and ODI scores between group 1 and 2, when compared with the preprocedural values. Although lack of a statistically significant difference in long term results, mean VAS score was 3.7 for group 1, while it was 1.8 for group 2, and the mean ODI score was 38 for group 1, and 22.48 for group 2 at 6th month assesment.

DISCUSSION

Although minimally invasive percutaneous techniques are indicated as other modalities are ineffective or contraindicated, combining RFA with vertebral augmentation provide prevention of mechanical loading pain, and prevention of somatic pain in patients with spinal hemangiomas.

Contactless treatment for scoliosis by electromagnetically controlled shape-memory alloy rods: a preliminary study in rabbits

PURPOSE

To evaluate the safety and efficacy of a system aiming to correct scoliosis called "electromagnetically controlled shape-memory alloy rods" (EC-SMAR) used in a rabbit model.

METHODS

We heat-treated shape-memory alloy (SMA) rods to achieve a transition temperature between 34 and 47 °C and a C-shape austenite phase. We then developed a water-cooled generator capable of generating an alternating magnetic field (100 kHz) for induction heating. We next studied the efficacy of this system in vitro and determined some parameters prior to proceeding with animal experiments. We then employed a rabbit model, in which we fixed a straight rod along the spinous processes intraoperatively, and conducted induction heating postoperatively every 4 days for 1 month, while performing periodic X-ray assessments.

RESULTS

Significant kyphotic deformations with Cobb angles of about 45° (p < 0.01) were created in five rabbits, and no complications occurred throughout the experiment. The rabbits are still very much alive and do not show any signs of discomfort.

CONCLUSIONS

This is the first system that can modulate spinal deformation in a gradual, contactless, noninvasive manner through electromagnetic induction heating applied to SMA alloy rods. Although this study dealt with healthy spines, it provides promising evidence that this device also has the capacity to correct human kyphosis and even scoliosis in the future. These slides can be retrieved under Electronic Supplementary Material.