Soft-tissue augmentation with calcium hydroxylapatite: histological analysis

To evaluate histologically the extent and character of tissue in-growth after injection of calcium hydroxylapatite for soft-tissue augmentation.

Prospective case series of 8 patients from a private facial plastic surgery practice. Each patient was injected subdermally between the dermis and the subcutaneous fat with 0.1 mL of calcium hydroxylapatite in the superior postauricular sulcus. One month later, 2 patients underwent excision of the injected material, which was submitted for routine histological evaluation by an independent dermatopathologist. The material was stained with hematoxylin-eosin and trichrome to assess new collagen deposition. One of these patients was reinjected in the contralateral postauricular sulcus. Six and 18 months after injection, 3 patients and 1 patient, respectively, underwent excision of the injected material, which was then submitted for histological evaluation of the degree and character of tissue in-growth and tissue reaction.

The calcium hydroxylapatite particles were found to be surrounded by a lymphocytic infiltrate with multiple foreign body giant cells. There was no evidence of new collagen formation, migration, or heterotopic bone growth. Two patients were lost to follow-up.

Calcium hydroxylapatite is a stable soft-tissue filler that stimulates an immune response with lymphocytic infiltration and foreign body giant cell formation. We found no evidence of new collagen formation 1, 6, or 18 months after injection.