Mechanical principles of compressive interbody fusion.
METHODS
A biomechanical study on cadaveric lumbar spines was performed measuring interfragmentary forces and contact areas between intercorporal bone blocks and vertebral endplates.


OBJECTIVE
To show the correct application of internal fixators to achieve interfragmentary compression between bone blocks and adjacent endplates.


BACKGROUND
Several researchers have previously tried to compress interbody bone blocks by internal fixator systems. Knowledge of the correct way to use the internal fixator systems for this purpose has been lacking.


METHODS
Ten cadaveric lumbar spines were analyzed by instrumenting each motion unit with an intercorporal bone block and a dorsal transpedicular arbeitsgemeinschaft osteosynthesefragen internal fixator. Interfragmentary load and compression surface and their distribution were measured with a capacitive measuring mat. The internal fixator was loaded in compression in two different ways to determine the optimum mode of application.


RESULTS
Simple compression of an internal fixator did not achieve sufficient interfragmentary forces and compression surfaces. Usually lordotic contouring of the instrumented spinal motion unit with a decrease in interfragmentary forces and width of compression surfaces developed. Preloading the fixator in slight kyphosis and compressing it in a second step achieved significantly improved interfragmentary forces and sufficient compression surfaces.


CONCLUSIONS
Preloading an internal fixator in kyphosis and secondary compression is mandatory to get sufficient interfragmentary forces and compression surfaces between interbody bone blocks and adjacent vertebral endplates. The technique described provides a compressive interbody fusion and can be performed preserving the physiological shape of the spine.
Krödel
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Orthopaedic Department of Ludwig-Maximilians-University Munich, Klinikum Grosshadern, München, Germany.
D001696:Biomechanical Phenomena; D006801:Humans; D016268:Internal Fixators; D007738:Kyphosis / Q000601:surgery; D008159:Lumbar Vertebrae / Q000502:physiology* / Q000601:surgery; D013123:Spinal Fusion; D016474:Weight-Bearing / Q000502:physiology