Influence of load carrying on loads in internal spinal fixators.

After spinal stabilization with an implant, patients want to know whether carrying loads will endanger their spine and their implant. Therefore, the effect of carrying a weight on the loading of internal spinal fixation devices was determined in 10 patients using instrumented, telemeterized internal fixators. Patients carried a 5kg dumbbell in one hand as well as up to 20kg in both hands. Compared to normal standing carrying a weight caused only a slight increase of the fixator loads in all patients. The maximum flexion bending moment in the fixators was then lower than during walking. Carrying a weight even decreased the axial compression force in the fixators of the patients with the T11 or T12 vertebra bridged. Patients also raised their arms in anteversion while holding weights of up to 5kg with both hands. This increased the flexion bending moment in the fixators. Only a small part of a carried weight is taken over by internal fixators. Carrying a shopping bag only slightly increases the risk of pedicle screw breakage, however, since the spine has to support most of the additional weight, it represents a risk with regard to correction loss and bone sintering.