An animal model of early-stage femoral head osteonecrosis induced by cryo-insult in small tailed Han sheep.

PURPOSE

This study investigated the ability of liquid nitrogen cryo-insults to induce early-stage osteonecrosis of the femoral head (ONFH) in small tail Han sheep.

METHODS

16 animals were subjected to unilateral cryo-insult using cryogen equipment with a cryo-insult probe, followed 1, 3, and 6 months later by X-ray, CT scanning, micro-CT scanning, and histological evaluation.

RESULTS

X-ray evaluation of operative femoral heads (Op-FHs) at each time point showed low density areas under the cartilage surface that paralleled sclerosis belts, and CT scans showed sclerosis and cyst areas in Op-FHs. Micro-CT analysis showed that the ratio of bone to total volume and mean trabecular thickness of regions of interest (ROIs) were lower in Op-FHs than in normal femoral heads (No-FHs) at each time point (n = 4, < 0.05). Histological evaluation at 1 month showed that necrotic changes were dominant as evidenced by moderate empty lacunae, decreases in the number of hematopoietic cells, and moderate increases in the number of fibroblasts. At 3 and 6 months, fractured trabeculae, fibroblasts, and new blood capillaries were increased, indicating an absorption and repair process. Bone volume fraction of ROIs of Op-FHs was lower than in No-FHs at each time point (n = 4, < 0.05) in histological evaluation. At 6 months, the maximum load of No-FHs was higher than Op-FHs (n = 4, < 0.05).

CONCLUSION

These findings indicate that early-stage ONFH can be induced in small tail Han sheep using cryogenic equipment.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

This animal model may be helpful in developing new treatment modalities for human ONFH.