INFLAMMATORY CELLS IN FULL-THICKNESS ANULUS INJURY IN PIGS - AN EXPERIMENTAL DISC HERNIATION ANIMAL-MODEL

Study Design. Inflammatory cells were studied by indirect immunocytoch emistry in experimental full-thickness anulus fibrosus lesions in pigs . Objectives. First, to determine the occurrence, by immunocytochemist ry, of T lymphocytes and macrophages. in experimentally produced, ante rolateral full-thickness disc lesions in pigs, and second, to compare the presence of inflammatory cells in 1) the injury area, 2) the adjac ent noninjured part of the disc, and 3) control discs. Summary of Back ground Data. Previous studies on disc herniation material obtained fro m human disc surgeries have demonstrated inflammatory cells in a subgr oup of herniations. Macrophages were most prevalent, being more numero us than lymphocytes. Macrophages have furthermore been suggested to be important in the resorption process of extruded disc tissue. No simil ar studies on an animal model of disc herniation, however, have so far been presented. Methods. A full-thickness anular incision, 10 mm long , was made with a scalpel in the L3-L4 or L4-L5 intervertebral discs o f 12 adult pigs. The incision was made in the anterolateral part of th e disc. Nucleus material was observed outside the injury site when tis sue samples were taken, suggesting a disc herniation. Tissue then was analyzed from the area of injury, from the area adjacent to the injury , and from separate control discs from three additional pigs of the sa me age. Thin frozen sections were studied by indirect immunocytochemis try (alkaline phosphatase anti-alkaline phosphatase method) using mono clonal anti-human antibodies applicable to porcine tissues, T lymphocy tes (CD3), and macrophages (CD68). Cells were graded as: -, absent; (), only a few scattered cells; and +, abundant cells. Disc tissue samp les were taken 1 month (three discs), 2 months (four discs), and 3 mon ths (five discs) after the operation. Results. Macrophages were presen t more commonly than T cells, and were abundant in seven of 12 discs ( 58%), with T cells abundant in four of 12 discs (33%). Only a few macr ophages were present in the injured tissue from one additional disc, a nd scattered T cells were seen in four additional discs. Abundant macr ophages were also observed in one of two discs in the adjacent noninju red area, whereas only a few T lymphocytes at the most were present in such noninjured disc tissue. In four (33%) and three (25%) injured di scs, respectively, no macrophages or T lymphocytes could be found. No inflammatory cells were observed in three of 12 discs (25%). The three control discs showed no inflammatory cells. Conclusions. inflammatory cells, predominantly macrophages, were present in a subsample of expe rimental discs with full-thickness anulus defects, as has previously b een observed for human disc herniations. In this animal model, macroph ages may have spread to adjacent noninjured parts of the disc. The ind uced herniation in this animal model is, however, anterolateral and ma y not fully correspond to clinical disc herniations, most of which are posterolateral. However, the results from this model support a role f or inflammation in disc herniation.