Effect of an orthosis on the loads acting on a vertebral body replacement

BackgroundThe spinal load reduction by an orthosis is still a matter of debate. Some studies predicted a load reduction while others found no effect. The aim of this study was to measure the in vivo effect of the Lumbo TriStep brace and the hyperextension orthosis medi 3C on the spinal implant loads.MethodsTelemeterized vertebral body replacements were implanted in 5 patients suffering from a severe fracture of the L1 or L3 vertebral body. The implant allows the measurement of 6 load components acting on it. For several activities during standing, sitting and walking, implant loads were measured in patients with and without an orthosis.FindingsThe average resultant force on the vertebral body for 26 activities was reduced by 9% with the Lumbo TriStep brace, and by 19% with the hyperextension orthosis. The force reduction is usually more pronounced for activities performed during sitting than it is for those performed while standing. However, considerable inter- and intra-individual variation was observed. In several cases, the measured implant forces were even higher when the patients were wearing an orthosis.InterpretationIn some patients, for certain activities, an orthosis may reduce the force on a vertebral body replacement and thus on the anterior column of the spine. However, in other patients for the same activities, an orthosis may increase the force. The measurements do not allow a clear recommendation to wear an orthosis since the clinically relevant reduction of implant forces is unknown.