Biomechanical testing of different ventral fixation devices on the bovine lumbar spine

Aim: The primary stability of ventral fixation systems has been improved over the past years and special implants supporting minimally invasive procedures have been developed. The aim of this study was to analyze the primary stability of several of these implants, Methods: Thirty (30) lumbar segments from 5 to 7-month old calves were harvested and tested on a pure moment apparatus (PMA) as well as a modified materials testing machine (MTS) according to the European standard recommendations of Wilke et al. Three different implant systems (MACS, Centaur and Z-plate) were included. ROM, neutral zone and stiffness were tested on the PMA up to 10 Nm, stiffness at an eccentric axial load of up to 1500 N was tested on the MTS. Bone density-was investigated for all specimens. Statistical analysis was performed by ANOVA and LSD tests. Results: Primary stability was improved by all fixation devices compared to the physiological-specimen. The MACS implant was more stable than the Centaur and Z-plate with the exception of in lateral bending [where the Z-plate was stiffer]. Bone density was comparable in the three different experimental groups. Conclusion: Minimal invasive ventral fixation devices are becoming popular. The primary stability of the minimal invasive MACS was comparable to those of other well-known ventral fixation devices of the lumbar spine.