Polylactide Interbody Cages: The Effect Of In Vivo Loading

摘要

Spinal interbody cages are currently made of non-resorbable materials. Commonly used metals like titanium, however, have considerable disadvantages: they are radio-opaque, exceed cortical bone stiffness and permanently remain as a foreign body. PEEK or carbon cages address the first two, but they are still non-resorbable. Polylac-tic acid (PLA) is radiolucent and has low stiffness, but also resorbs over time. In previous studies on bioresorbable cages, we saw a discrepancy between their strength in vitro as compared to their strength in vivo in a stand-alone configuration in a goat model. Unloaded in vitro degradation showed that cage strength remained larger than vertebral yield strength for at least six months. In vivo, however, the cages failed within three months, resulting in a fusion rate of only 50% at six months (n=6). Many factors influence the resorption rate of polylactic acids. Faster resorption in vivo could be explained by enzymatic activity, but also by the larger mechanical loads in vivo (body weight) as compared to in vitro (none). In this study, we decreased the mechanical loading in vivo in order to determine its effect on cage degradation. The results were compared to our previous studies.