Biologic Behavior of Hydroxyapatite Used in Facial Augmentation.

INTRODUCTION: The recent finding that shrinkage of key areas of the facial skeleton contributes to the aging appearance of the face has prompted a search for the most appropriate bone-like implant material. Evidence that hydroxyapatite, in granular form, maintains volume in the long term supports its use in the correction of aging, in addition to its use in the correction of inherently deficient areas of the facial skeleton. The biologic response of hydroxyapatite needs to be fully understood for its use to be confidently recommended. MATERIALS AND METHODS: Samples of 'living' hydroxyapatite from the anterior maxilla, zygoma, and mandible of 17 patients were analyzed. These were obtained during revision procedures performed between 6 months and 15 years following original placement on the facial skeleton. RESULTS: Histology showed that in every case, the individual granules were embedded within a mass of collagen that made up about half of the total implant volume. The collagen mass also contained fine elastin, fibroblasts, lymphocytes, occasional granulomas, and vessels. By 2 years, a new compact bone containing osteoblasts and osteocytes was present in all specimens in the deep (osseous) aspect. Bone progressively replaced the original collagen between the granules with a sharply defined transition at the interface. CONCLUSIONS: This study confirmed a two-stage biologic change following onlay placement of hydroxyapatite granules on the facial skeleton, i.e., initial collagen formation with subsequent conversion to bone. This integrates the implant with the host bone which stabilizes the implant position and shape initially and in long term. NO LEVEL ASSIGNED: This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors. www.springer.com/00266 .

The fate of porous hydroxyapatite granules used in facial skeletal augmentation.

Facial appearance is largely determined by the morphology of the underlying skeleton. Hydroxyapatite is one of several materials available to enhance projection of the facial skeleton. This study evaluated the long-term maintenance of augmented bony projection when porous hydroxyapatite granules are used on the facial skeleton. Ten female patients aged 28-58 years were studied following aesthetic augmentation of the facial skeleton at 24 sites using porous hydroxyapatite granules. Postoperative CT scans at 3 months served as the baseline measurement and compared with scans taken at 1 and 2 years, with the thickness of the hydroxyapatite measured in axial and coronal planes. Thickness of original bone plus overlay of hydroxyapatite, thickness of the overlying soft tissue, and the overall projection (bone plus soft tissue) were recorded. It was found that 99.7% of the hydroxyapatite was maintained at 2 years, with no statistical difference (t test) from the baseline measurement. The overall projection (bony and soft tissue) was maintained as there was no evidence of native bone resorption or soft tissue atrophy. Radiographic results confirmed that the use of porous hydroxyapatite granules for enhancement of the facial skeleton is not only a predictable procedure, but maintains full bony projection at 2 years.

Surgical anatomy of the lower face: the premasseter space, the jowl, and the labiomandibular fold.

The anatomic basis for the jowl has not been fully described. A formal analysis was performed of the sub-superficial musculoaponeurotic system (SMAS) areolar tissue layer, which overlies the lower part of the masseter. For this research, facial dissections were performed on 16 fresh cadavers ages 12 to 89 years, and detailed anatomic observations were made during the course of several hundred rhytidectomy procedures. Tissue samples from varying age groups were examined histologically. The areolar cleavage plane overlying the lower masseter has specific boundaries and is a true space named the "premasseter space." This space is rhomboidal in shape, lined by membrane, and reinforced by retaining ligaments. The masseter fascia lines the floor, and branches of the facial nerve pass under its deep surface. Histologically, the floor is formed by a thin layer of dense connective tissue, which undergoes minor deterioration in architectural arrangement with age. The roof, lined by a thin transparent and adherent membrane on the underside of the platysma, has a less dense collagen network and contains more elastin. With age, there is a significant reduction in the collagen density of the roof. Expansion of the space with aging, secondary to weakness of the anterior and inferior boundaries, results in formation of the jowl. Medial to the premasseter space is the buccal fat in the masticator space, which descends with aging and contributes to the labiomandibular fold and jowl. Application of the premasseter space in surgery provides significant benefits. The SMAS incision should be forward of the traditional preauricular location to be over the space, not behind. Because the space is a naturally occurring cleavage plane, dissection is bloodless and safe, as all facial nerve branches are outside. The premasseter space should be considered as the preferred dissection plane for lower (cervicofacial) facelifts.

Histologic and ultrastructural evaluation of sutures used for surgical fixation of the SMAS.

In extensive SMAS face-lift surgery, retaining ligaments are released, and the SMAS is resutured to the deep fascia to maintain the advanced position. The suture used to reattach the SMAS should replicate the quality of support provided by the original ligaments. Nonabsorbable sutures (monofilament and braided) retrieved intraoperatively from 22 patients undergoing secondary face-lift procedures were examined by light microscopy and transmission electronmicroscopy. A distinctive enclosure of dense collagen and elastin formed around both types of suture. Based on the presence of inflammatory cells, fibroblasts, collagen, and elastin, the tissue reaction to monofilament suture was less than with the braided suture. The collagen and elastin were thicker around the braided suture, and, additionally the collagen matrix infiltrated between the individual filaments. Ultrastructural analysis of the braided suture showed significant collagen binding around each individual filament. The greater quantity of connective tissue around the thread which continued into the interstices of the braided suture has the characteristics of a ligament. This suggests a stronger and more lasting tissue fixation.