THE EFFECT OF BOUNDARY-CONDITIONS ON EXPERIMENTALLY MEASURED TRABECULAR STRAIN IN THE THORACIC SPINE

Vertebral bodies are the primary structural entities of the spine, and trabecular bone is the dominant material from which vertebral bodies are composed. Understanding the mechanical characteristics of vertebra l trabecular bone, therefore, is of critical importance in the many cl inical conditions that affect the spine. Numerous studies have loaded vertebral bodies to investigate the influence of trabecular bone chara cteristics on deformation and failure patterns, but the methods of loa d application have been inconsistent. These differences in the method of load application are a potential confounding factor in the interpre tation of the experimental results. We investigated this problem by me asuring the distribution of minimum principal strain and maximum shear strain magnitude within 6.35 mm thick samples cut from thoracic spine segments (T8-T10) and loaded to simulate three common experimental co nfigurations. Measurements were made using the texture correlation tec hnique, which extracts deformation patterns from digitized contact rad iographs of samples under load. The three loading configurations exami ned were a three-body construct, a single vertebral body loaded throug h sectioned intervertebral discs, and polymethylmethacrylate molded di rectly to the endplates. Results indicate that from both probability a nd spatial distribution standpoints the best simulation of ill vivo lo ading generates the least uniform strains. Loading through disc remnan ts or through plastic molded to the endplates causes increasing degree s of strain homogenization. This result has implications not only for the design of experiments involving spinal loading, but also for theor ies concerning the adaptation of trabecular bone to functional loads. (C) 1998 Elsevier Science Ltd. All rights reserved.