Clinical and histological comparative outcomes after injections of poly‐L‐lactic acid and calcium hydroxyapatite in arms: A split side study

BACKGROUND: Although much has been published on the use of poly-L-lactic acid (PLLA) and calcium hydroxyapatite (CaHA) for off-face indications, questions remain regarding their exact mechanisms of action in subcutaneous tissue and their comparative efficacy. OBJECTIVE: To present the clinical and histological results of the PLLA and CaHA injections into the opposing arms of the same patients. METHODS: Five women received superficial subcutaneous injections of PLLA into the left arm and CaHA into the right arm. After three sessions, the clinical and histological outcomes were analyzed. RESULTS: After the first session, three patients showed improvement in the right arm (CaHA), but at the end of study, two patients showed better results in the left arm (PLLA). Histologically, moderate to intense lymphocytic and giant cell infiltrate, as well as collagen and elastic fiber neoformation, were observed equally near the particles of both products. Dermis had no inflammatory or fiber alterations. CONCLUSION: In this study, there were no clinical differences between these two fillers. Despite current thinking and previous histological studies, we found both products produced moderate to intense inflammatory reaction, as well as collagenic/elastogenic fiber neoformation, only in the subcutaneous tissue of the immediate vicinity and surrounding the individual filler particles.