Biomechanische Untersuchung zur Primärstabilität ventraler Plattenosteosynthesen bei osteoligamentären Luxationsfrakturen der unteren Halswirbelsäule in Abhängigkeit des Ausmaßes begleitender Facettengelenksverletzungen – Methodenentwicklung und erste Ergebnisse

The choice of the surgical approach and the appropriate instrumentation for unstable injuries of the subaxial cervical spine involving the facet joints are matters of ongoing debate. The mechanical significance of the articular processes of the facet joints after surgical treatment has not yet been examined sufficiently. This biomechanical study is based on the assumption that the articular processes have a significant influence on the stability of the operated spinal segment after a complete disruption of the discoligamentous complex and the facet capsules. Our primary aim was to examine the significance of uni- and bilateral facet fractures for the primary stability of single level anterior cervical discectomy with fusion and plating during abnormal anterior translation. We used human cervical spine specimens in which we generated facet dislocations without, with unilateral or with bilateral facet fractures of the C4/C5 segment. All the spines were stabilized thereafter by means of anterior plating. We performed a pilot study by testing the experimental set-up on 12 formalin fixed spinal specimens. For the main experiment we used 15 fresh-frozen human lower cervical spines. In contrast to the pilot study, we simulated the in situ load on the spine by constant compressive preload. All specimens were tested until there was a mechanical failure of the fusion and we registered the required maximum load. We then compared the group without facet fractures with those with unilateral and those with bilateral facet fractures. Absence of a facet fracture had a statistically significant influence on the spinal stability compared with bilateral facet fractures in the main experiment and showed a non-significant trend in the pilot study. Based on these results, a posterior approach should be considered for patients with facet fractures in addition to a single anterior approach. However, the generalizability of our results is limited, because the specimens used in our experiment were taken from elderly donors and largely showed an osteoporotic bone structure. Furthermore, results from biomechanical cadaveric studies may not necessarily be applicable to the in-vivo environment. Further experimental and clinical studies are needed to examine the stabilizing influence of the facet joints in injuries of the subaxial cervical spine.