Radiesse™ Calcium Hydroxylapatite Injectable Filler

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Radiesse™ Calcium Hydroxylapatite Injectable Filler

Nikita Gupta¹, Onir L. Spiegel², and Jeffrey H. Spiegel^2,3

¹ Department of Otolaryngology – Head and Neck Surgery, University of Kentucky Medical Center, Lexington, KY, USA

² The Spiegel Center, Advanced Facial Aesthetics, Newton, MA, USA

³ Division of Facial Plastic and Reconstructive Surgery, Boston University School of Medicine, Boston, MA, USA

In December 2006 the FDA approved calcium hydroxylapatite (CaHA) as an injectable dermal filler for the correction of moderate to severe facial wrinkles and treatment for HIV lipoatrophy. Previously, it had been used safely for vocal fold augmentation, as a radiographic marker, to fill in oral/maxillofacial defects, as well as for stress urinary incontinence though in a somewhat different formulation. In 2016, it was approved for hand rejuvenation via injection into the dorsum of the hands. The material (trade name Radiesse, Merz Aesthetics) is composed of microspheres of CaHA with 25–45 μm particle sizes suspended in a carrier gel made of water, glycerin, and sodium carboxymethylcellulose.

This formulation, made of 70% carrier gel and 30% CaHA (chemical formula Ca₁₀(PO₄)₆(OH)₂), has an effect lasting between 10 and 14 months, with an average of 12 months [1]. Unlike the microporous formulations used as ceramics for bone reconstruction, the microsphere formulation does not support vascular ingrowth or have osteoconductive properties. The carrier gel dissipates within weeks and the microspheres remain at the site of injection until they are degraded after several months into calcium and phosphate ions excreted normally by the body. While present, they induce a fibroblastic reaction and are replaced by fibrovascular stroma [2]. The result after injection is immediate and then later sustained by neocollagen formation. As a result, Radiesse has often been considered to be a “somewhat permanent” filler, in that it induces tissue growth.

Marmur et al. initially demonstrated neocollagen formation around CaHA microspheres at six months in human skin biopsies taken after postauricular injection [3]. A canine model was used to show that CaHA injection led to endogenous collagen production with a qualitative increase in collagen formation in intradermal versus subdermal injections [4].

Berlin et al. further characterized this collagen formation with biopsies of postauricular CaHA injection in humans at six months. Hemotxylin and eosin (H&E) staining showed deposition of collagen around and infiltration into filler microspheres with a fibroblastic and a mild histiocytic tissue response. Immunohistochemical (IHC) staining confirmed Type I collagen formation and picrosirius red (PSR) staining demonstrated both Type I and Type III collagen fibers [5].

In a radiographic study, Carruthers et al. demonstrated that while filler material was visible on CT scans its appearance is distinct from underlying structures, it is unlikely to be confused with a pathologic finding, and it does not obscure underlying structures. The material was distinctly separate from bone and showed no osteogenesis. At the 12 month touch‐up visit, preinjection CT scans showed significant decrease in the calcium deposition but a continued clinical improvement consistent with an induced neocollagen reaction in the area. This study was performed on patients obtaining injection for HIV lipoatrophy and despite the large amounts of material injected (up to 34.1 ml total), the material did not obscure underlying structures nor create new bone [6].

Multiple studies have compared the clinical results of CaHA to other dermal fillers. A pivotal trial comparing CaHA and collagen in the nasolabial folds (NLF) used a multicenter, randomized split face comparison to show superior improvement by blinded observers, similar adverse events related to injection, and decreased amount of material was needed to achieve the desired results. In the 117 patient trial, 79% of subjects had a superior result at six months (p < 0.0001) [7]. In a similar comparison between CaHA and hyaluronic acid (Restylane), CaHA was noted to be more effective at all time points up to 12 months and required 30% less material injected [8]. In a later comparison between CaHA and two hyaluronic acid products (Juvéderm Ultra and Perlane) for NLF augmentation, CaHA resulted in better patient satisfaction, longer durability, but had similar volume of material injected [9].

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