Experimental study of the participation of the vertebral endplate in the integration of bone grafts.

The surgical technique of anterior vertebral arthrodesis has been modified by the introduction of cages in spinal surgery. The classical technique recommends removal of the vertebral endplate and exposure of bleeding cancellous bone. However, after the observation of cage subsidence during postoperative follow-up, the vertebral endplate is no longer removed, due to its greater mechanical resistance which can prevent cage subsidence. The mechanical characteristics of the vertebral endplate are well known, in contrast to its osteogenic potential, which was investigated in the present experimental study. The study was conducted on mongrel dogs of both sexes, which were submitted to anterior corpectomy at the cervical spine level. A cortico-cancellous bone graft removed from the tibia was used for the reconstruction of the vertebral segment, which was used with osteosynthesis plates. At the site of contact between the surface of the vertebral body and the bone graft, the vertebral endplate was completely removed and cancellous bone was exposed in the inferior vertebra, whereas in the superior vertebra of the arthrodesed vertebral segment only curettage was performed, and the vertebral endplate was preserved, as recommended for cage implantation. Twenty adult dogs of both sexes were divided into four experimental groups according to time of sacrifice (15, 30, 90, and 180 days). The consolidation of the bone graft with the vertebral body was evaluated by histology using hematoxilin-eosin and Gomori trichrome staining. In the interface between the bone graft and the vertebral body surface in which the vertebral endplate was not removed, graft consolidation was not observed in any of the group I animals (sacrificed after 15 days), and was observed in 1/5 animals of group II (30 days), in 2/5 animals of group III (90 days), and in 4/5 animals of group IV (180 days). In the interface between the graft and the vertebral body in which the vertebral endplate was removed, bone-graft consolidation was observed in all animals of all experimental groups (15, 30, 90, and 180 days). Bone-graft consolidation with the surface of the vertebral body was influenced by the removal or maintenance of the vertebral endplate. Due to the importance of this structure in current surgical procedures, this phenomenon deserves to be studied in more detail in order to understand the basic events involved in this process.