Höhenrekonstruktion und -erhalt osteoporotischer Wirbelkörperkompressionsfrakturen – Eine biomechanische Vergleichsstudie der Standard Ballon-Kyphoplastie zur Radiofrequenz-Kyphoplastie an einem Kadaver-Modell

Osteoporosis and osteoporotic vertebral body fractures represent a significant health and socioeconomic problem with increasing potential in the context of demographic change and the increasingly aging population. The underlying osteoporosis is characterized by a pathological decrease in bone density and an associated reduction in bone stability. The etiology is multifactorial. Identified risk factors are age and female gender. According to estimates, every fourth woman over the age of 50 in Germany is affected by osteoporosis. The lifetime risk of suffering an osteoporotic fracture is about 40-50% for women, depending on gender. The probability of suffering another fracture after a previous fracture is estimated to be 4-5 times higher in those affected than in the general population. Vertebral body fractures account for about 15% of all osteoporotic fractures and are mostly compression fractures of various degrees because of low-energy trauma, which would not lead to a fracture in a healthy bone. The literature assumes an increase in the incidence of osteoporotic fractures of about 40% by 2030. Over the last decades, multimodal therapy concepts have been developed which are regularly updated. These include standardized diagnostics as well as conservative and surgical therapy options, which ultimately aim at an individual and interdisciplinary therapy concept. In this context, minimally invasive vertebral cement augmentations represent the most important surgical therapy options. The Vertebroplasty and the Balloon-Kyphoplasty have become widely established over the decades due to their extensive availability, good area-wide expertise, and good therapeutic results with a relatively low complication rate. Nevertheless, there is the possibility of further improving the minimally invasive procedures, especially with regard to minimizing the serious complications, such as cement extravasation, with comparable therapeutic results and preserving intact tissue. As a result, radiofrequency kyphoplasty was developed by the DFine company, which was intended to represent an alternative to the established procedures using smaller amounts of highly viscous bone cement via a unipedicular access and targeted, economical cavity shaping. The aim of our work was the quantitative comparison of the Radiofrequency-Kyphoplasty to the established Balloon-Kyphoplasty with regard to their results in height Restoration and height preservation of stable osteoporotic vertebral compression fractures (wedge fractures) of the classification Genant II-III in an in vitro cadaver model. In addition, we wanted to implement a procedure for generating standardized vertebral compression fractures with a 30% reduction in height. For this purpose, we had two fresh-frozen donor spines from two Caucasian women, 75 and 73 years old respectively, with no known malignancy, previous vertebral body fractures and known high-grade osteoporosis. An initial DXA of both Specimens showed a T-score of -7 and -7.4 and thus the presence of severe osteoporosis. A CT performed prior to the experiment confirmed the suitability of the Specimens for our experimental setup. In each case, the vertebral bodies T6 to L5 and a single L6 were selected, individually dissected and prepared down to the bony structures and individually enclosed in a plastic polymer on the cover and base plates. This was followed by randomization into two groups according to a matched-pair design. The fractures were generated on each individual vertebral body Specimen via continuous axial loading under 100 N minimum applied load in the loading machine until the desired wedge fracture was achieved with a 30% reduction in height. This was achieved satisfactorily for all preparations with no statistical difference between the two groups. The operation was carried out as planned with a base load of 100 N and in compliance with the manufacturer's specifications on 12 vertebral bodies in the BKP group and 13 vertebral bodies in the RFK group. A good height reconstruction could be achieved in both groups with no statistical difference between the two groups. Subsequently, all Specimens were loaded in a loading machine to emulate a physiological post-operative period of 3 months according to a fixed, standardized test protocol (100-600, 1 Hz, 100,000 cycles). The results were comparable to those of clinical studies and showed no statistical difference between the test groups. What was striking was the statistically significant lower amount of bone cement used in the RFK group, which corresponds to the surveys of clinical studies. With our fracture model, we have succeeded in generating standardized compression fractures on an osteoporotic vertebral body in an in vitro cadaver model. Our study was able to show in vitro that the Radiofrequency-Kyphoplasty is at least an equivalent alternative to the Balloon-Kyphoplasty in regard to height reconstruction and height preservation of osteoporotic vertebral compression fractures, while at the same time requiring significantly less cement volume. The latter could represent an advantage of RFK over BKP with regard to the complication profile in cement extravasation, interdigitation, fracture healing and the occurrence of subsequent fractures. Due to the use of a cadaver model and only an approximate simulation of physiological conditions, our results can only be transferred to an in vivo situation to a limited extent, despite good quantitative comparability. Nevertheless, our study provides valid evidence of a possible superiority of RFK, which should be further determined in large clinical studies.