A. Rohlmann et al., 2000 Volvo Award Winner in Biomechanical Studies - Monitoring in vivo implant loads with a telemeterized internal spinal fixation device, SPINE, 25(23), 2000, pp. 2981-2986
Study Design. Implant loads were measured in 10 patients using telemeterize
d internal spinal fixation devices.
Objective. To determine the postoperative temporal course of implant loads.
Summary of Background Data. Little information exists regarding the tempor
al course of loads on internal spinal fixation devices.
Methods. The telemeterized internal spinal fixator allows the measurement o
f three force components and three moments acting in the fixator. Implant l
oads were determined in up to 20 measuring sessions for different activitie
s, including walking, standing, sitting; lying in the supine position, and
lifting an extended leg while in the supine position.
Results. Implant loads often increased shortly after anterior interbody fus
ion was performed. Several patients retained the same high level even after
fusion had taken place. This explains the reason why screw breakage someti
mes occurs more than half a year after implantation. The time of fusion cou
ld not be pinpointed from the loading curves.
Conclusions. The results show that fixators may be highly loaded even after
fusion has occurred. A flexion bending moment acts on the implant even wit
h the body in a relaxed lying position. This means that already shortly aft
er the anterior procedure, the shape of the spine is not neutral and unload
ed, but slightly deformed, which loads the fixators. Pedicle screw breakage
more than half a year after insertion does not prove that anterior interbo
dy fusion has not occurred.