Article

The aims of motion preserving implants are to ensure sufficient
stability to the spine, to release facet joints by also allowing a physiological
loading to the intervertebral disc. The aim of this study was to assess disc load
contribution by means of annular fiber strains and disc bulging of intact and
stiffened segments. This was compared to the segments treated with various motion
preserving implants. METHODS: A laser scanning device was used to obtain
three-dimensional disc bulging and annular fiber strains of six lumbar
intervertebral discs (L2-3). Specimens were loaded with 500N or 7.5Nm moments in
a spine tester. Each specimen was treated with four different implants; DSS,
internal fixator, Coflex, and TOPS. FINDINGS: In axial compression, all implants
performed in a similar way. In flexion, the Coflex decreased range of motion by
13%, whereas bulging and fiber strains were similar to intact. The DSS stabilized
segments by 54% compared to intact. TOPS showed a slight decrease in fiber
strains (5%) with a range of motion similar to intact. The rigid fixator allowed
strains up to 2%. In lateral bending, TOPS yielded range of motion values similar
to intact, but maximum fiber strains doubled from 6.5% (intact) to 13.8%. Coflex
showed range of motion, bulging and strain values similar to intact. The DSS and
the rigid fixator reduced these values. The implants produced only minor changes
in axial rotation. INTERPRETATION: This study introduces an in vitro method,
which was employed to evaluate spinal implants other than standard biomechanical
methods. We could demonstrate that dynamic stabilization methods are able to keep
fiber strains and disc bulging in a physiological range.
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Langue : ANGLAIS