Chronic low back pain is a significant public health problem in industrialized society. The intact spine carries the upper body and external loads, allows motion in a physiological range and protects the spinal cord. These different demands necessitate a high degree of complexity with various sources for disorders and pain. The Julius Wolff Institute conducts research in order to counter pain causes and to further optimize the pain treatment.
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Severe compression fractures of a vertebral body or a tumour in the region of the spine sometimes require the replacement of a vertebral body by an implant. The loads on such an implant are not well known. In order to measure these loads, the commercially available vertebral body replacement "SYNEX" was modified. It allows the in vivo measurement of three force components and three moments acting on the implant. The 9-channel telemetry transmitter developed in our biomechanics laboratory was placed into the cylinder of the implant together with six load sensors and a coil for the inductive power supply.
Instrumented vertebral body replacements were implanted in five patients since 2006. Implantations in up to 1ten patients are planned. The implant loads, which probably correlate with the spinal load, will be measured for many activities of daily living. The example shows the implant loads for elevation of the right arm with a weight of 50 N in the hand. This causes an increase of the resultant implant force from about 400 N to nearly 900 N. Further results of the load measurements can be found in the data base