Anatomisches Institut der Georg-August-Universität Göttingen, Germany Biomedical Research Centre, Dept. of Orthopaedic Surgery, Academic Hospital, Pretoria, South Africa To date, no animal model for disc degeneration has gained much acceptance, mostly due to the fact that most animals are quadrupeds and thus lack basic biomechanical characteristics of human spines. An adequate model would be of invaluable interest for degeneration related research. In a standardized series of animal experiments in 18 adult Minipigs and 20 adult Cercopithecus aethiops monkeys all animals obtained nucleotomy in one lumbar FSU from a ret-roperitoneal approach and were sacrificed at last 24 weeks afterwards. The Minipigs were x-rayed at time of sacrifice, the monkeys prior to operation and at termination of the experiment. Vice versa, the Minipigs obtained intradiscal pressure recordings at these occasions. The Minipig spines were formol fixed whereas the monkey spines were harvested after perfusion with PBS, fresh frozen, and obtained CT and MRI scans prior to thawing, fixation and comprehensive histological evaluation. The lumbar FSU of Minipig and Cercopithecus mainly consists of the same elements as in man. There are certain differences concerning the porcine endplates which ossify as an epiphyseal-like formation with ossification starting in its center, different from the so-called “Randleiste”. Whereas the operative procedure in the Minipigs came in handy, in the Cercopithecus monkey it proved to be demanding, though feasible, due to relatively wide transverse processes and thick psoas muscle structures. The psoas could not be easily detached and needed to be split instead, thus directly exposing the segment nerves. The histological, standard radiological, CT, MRI, and mechanical observations were very similar to those which can be made during the natural aging process of the disc in man. Both animal models are recommendable for further research: Cercopithecus FSUs are more difficult to expose. Logistic reasons may favour Minipigs in Europe. In case of fusion related experiments the use of primates yet seems inevitable.
