• Research + Development   Combination treatment of vertebral metastases

Combination treatment of vertebral metastases

For the first time ever, clinical trials are currently investigating a combination procedure for the low-impact treatment of vertebral bodies affected by metastases. In the first treatment stage, tumorous tissue is eliminated with the aid of radiofrequency ablation. This is followed by restabilisation of the compromised sections of the spinal column by kyphoplasty using a special bone cement.
In Germany alone, about 1.5 million people suffer from cancer. Of the various types of tumour, some such as breast carcinoma show a great tendency to form metastases. These make their appearance mainly in the liver, lungs and skeletal system. Metastases of the spinal column cause special complications because they penetrate into the vertebral bodies and undermine them. As a result, the vertebrae lose their stability, creating the risk of compression fractures. As a whole, the spinal column becomes unstable and the patients affected suffer extreme pain.
Amongst current types of treatment for vertebral body metastases is the use of radiotherapy accompanied by painkillers. The disadvantage of this procedure is the extreme cost and the fact that it takes some time for pain reduction to take effect.
The surgical approach to osteolytic vertebral body metastases is highly intricate because this is a difficult environment for the operator to work in. The hard bone tissue and its plentiful supply of blood are directly adjacent to important neural pathways.
On the other hand, there is a constant rise in the incidence of such tumorous disorders, which explains the need to find treatment methods with prospects of success. Because today’s practice is to favour effective yet low-impact interventions, minimally invasive solutions are sought in preference to others. This explains the current specialist medical research focus on localised nuclear medicine and thermal ablative procedures and the application of stabilising bone cements as a complementary measure. The American medtech manufacturer DFine is pursuing a promising approach in this direction. Collaborating with the Orthopaedic Clinic of the Mainz University Medical Department, this manufacturer is developing a treatment strategy which combines two minimally invasive procedures in one.

The first arm is the STAR system, a bipolar navigation tool which enables the doctor to perform precise ablation of spinal tumour necroses. This is followed by kyphoplasty treatment based on DFine’s StabiliT Vertebral Augmentation System. This system is a low-impact method of introducing high-viscosity cement into bone tissue.
Ablation is the surgical term for the removal of diseased or undesirable tissue. Radiofrequency ablation (RFA), which uses thermal energy, has been successfully applied for some time to remove tumorous tissue from organs such as the liver and lungs. However, owing to the complex anatomy of the spinal column, the conduit for sensitive bone marrow, it has only recently become possible to establish this procedure for this organ.
The STAR radiofrequency ablation system developed by DFine renders these interventions safe by delivering a small, manoeuvrable tool into the hands of operators, thus enabling very precise navigation. The controlled dosage of radiofrequency energy destroys the tumorous tissue without endangering the adjacent sensitive neuronal structures.
The radiofrequency probe is introduced into the vertebral body through a cannula and inserted into the tumour. A tip, about two centimetres long, is located at the end of the probe. Because this tip is flexible, the doctor can move it in metastatic tissue wherever required and destroy it thermally with pinpoint precision. Computer tomography imaging enables the operator to observe his actions with sufficient accuracy.

Reconstruction follows destruction
A high-frequency current at the fine tip of the ablation probe generates the heat which ‘cooks’ the tumorous tissue into oblivion. The current is alternating between 450 and 750 kHz, which is enough to generate the required temperatures in the target area. To maintain control over the tissue destruction, the system is impedance-controlled, i.e. the power input is automatically reduced when tissue resistance has reached the pre-set limit value. This happens at a temperature of approximately 50° C. One treatment cycle, in which the tumorous tissue and a sufficient safety margin are destroyed, lasts about 25 minutes. Following elimination of the vertebral metastases with the aid of radiofrequency energy, the second stage of the treatment involves filling up the resultant lacunae in the vertebral bodies with a special bone cement.

As a consequence of invasive tumorous growth, the bone structures of the vertebral bodies are infiltrated with metastatic tissue. When treatment is initiated, this process is generally so far advanced that the affected vertebrae are at risk of fracturing, threatening the whole spinal column with instability. To maintain as far as possible the functionality of the vertebral bodies in their role of supportive tissue, it seems obvious that the defect should be eliminated by using a suitable application system to introduce bone replacement material to fill the cavities.

However, the various augmentation techniques relying on conventional bone cement also have their critical aspects, i.e. since the cement is injected by hand into the vertebral bodies, its viscosity needs to be such to allow it to be introduced through the thin cannulas. The downside is that fluid, non-viscous cement can easily escape through cracks and endanger sensitive areas, such as bone marrow and the fibrous bundles of the bone marrow nerves. It can also escape through vessels into the lungs and cause embolisms there. The technique known as balloon kyphoplasty is an attempt to prevent this. In this technique, a balloon is used to straighten the compressed vertebral body again before it is filled with an injection of cement into the cavity. Yet even this method entails a risk, that of destroying intact bone substance through insufficient control of the expansive forces of the balloon.

The StabiliT Vertebral Augmentation System from DFine provides a minimally invasive procedure allowing operators kyphoplasty with minimal impact on bone. This has a hydraulic delivery system capable of feeding ultra high-viscosity cement into the vertebral body. Both the application technique and cement properties reduce to a minimum the risk of cement leaks. In detail, the procedure works as follows. With the aid of CT visual control, a small access point is first created through which the fine cannula of the StabiliT appliance is inserted into the vertebral body requiring treatment. Then the operator accesses small bone channels by means of navigable MidLine Osteotome. Precise cement injection is assured by a start-stop function, operated by remote control. Immediately before the cement is injected, radiofrequency energy is used to alter the state of the bone cement aggregate, which gives the substance a viscous, resin-like consistency.

The hydraulic action cement applicator ensures that the bone cement is injected into the prepared cavity at a constant injection speed of 1.2 millilitres per minute, which is very slow. This in turn ensures that the highly viscous substance enters the porous vertebral body under very controlled conditions. Of special significance in this technique is the slow processing time made possible by the very slow curing properties of this special cement. This largely preserves the bone interior and minimises the risk of cement escaping into sensitive areas.
Once the cement has penetrated into the fine bone structures and has hardened, it exerts an even pressure on the deck plates of the fractured vertebral body. This ensures that the vertebral bodies regain their former stability and prevents changes to the kyphotic angle of the spine. Since this repair method can compensate for height losses in the vertebral bodies, there is generally no need for additional action to support the spinal column. Radiofrequency kyphoplasty is performed with the patient under total or local anaesthetic. This intervention takes about. 20 to 25 minutes per vertebra. That is just under half the time needed for conventional procedures. In the USA, the FDA, the American licensing authority, has already given the DFine STAR system the green light as a medical product for the targeted treatment of spinal tumours using heat ablation.

In July this year, the Orthopaedic Clinic of the Mainz University Medical Department began a study with ten subjects, the results of which are to be used to obtain the European marketing authorisation. The controlled study will test the safety and efficacy of combining RF ablation with RF kyphoplasty in patients with painful vertebral metastases and examine the degree of relapse probability. “Already, initial treatment of a 50-year-old woman has proved successful,” confirms Prof. Andreas Kurth, Director of the Orthopaedic Clinic of the Mainz University Medical Department and director of the study.

Two keys to success
Previous treatment strategies have generally included external ionising radiation in addition to painkilling medication, but this procedure is costly and pain reduction does not take effect immediately. Also, during the treatment period, chemotherapy to combat the primary tumour must be discontinued to keep side effects to a bearable scale.
Instead, the targeted, direct destruction of vertebral metastases and subsequent spinal column stabilisation enabled by RF combination therapy brings immediate pain reduction for the patient and a concomitant and considerably improved quality of life.
Dr. Helmut Bruckner

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German Summary
Weltweit erstmals klinisch erprobt wird gegenwärtig ein Kombinations-Verfahren zur schonenden Behandlung von Metastasen-befallenen Wirbelkörpern. Im ersten Behandlungsschritt wird das Tumorgewebe mithilfe der Radiofrequenz-Ablation eliminiert. Anschließend werden die geschädigten Teile der Wirbelsäule durch Kyphoplastie mit einem besonderen Knochenzement wieder stabilisiert. Der deutschsprachige Beitrag ist nachzulesen auf: www.meditec-international.com/medi0611kyp