Influence of disc prosthesis position on segmental motion in the lumbar spine

Zeitschrift für Orthopädie und Unfallchirurgie
M WeisskopfK Birnbaum

Abstract

Total disc arthroplasty is reported to maintain segmental motion. From finite element studies a rather posterior and central implantation of the prosthesis is recommended. However, there is yet no in vitro study with cadaveric specimens investigating the topic of implant positioning. Ten human lumbar spines were subjected to biomechanical testing. Flexion/extension and side-bending moments were applied from 2.5-7.5 Nm on a spine load simulator. First, the intact specimens were tested in 3 load cycles while motion was monitored with regard to the facet joints under different loads by an ultrasound-based system. An unconstrained total disc prosthesis was then implanted in a central position and the different load cycles were repeated. Finally the implant was positioned in a decentral position with an average offset of 6.2 mm for repetitive data acquisition. Comparison of the facet joint motion in central and eccentric prosthesis positions resulted in the following averaged differences. During flexion of the lumbar spine an average difference of the reference point excursions of 0.38 mm was recorded on the ipsilateral facet joint with reference to the decentral position. For extension, the difference was 0.33 mm on average, for ri...Continue Reading

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