Purpose:

Long-term results of autogenous bone graft for facial augmentation are often disappointing due to unpredictable maintenance of shape and volume. Alloplasts have the potential advantages of unlimited supply and no donor site morbidity. However, selection criteria for the proper alloplasts for specific reconstructive needs have not been established. The present report describes the use and indications for 3 classes of alloplasts in craniofacial reconstruction.

Methods:

A 10-year experience of all cases of alloplastic reconstruction of the craniofacial skeleton, performed by a single surgeon, was reviewed. Alloplastic materials utilized included cement pastes (hydroxyapatite; calcium dahlite), osteoactive powders (bioactive glass; demineralised bone matrix), and prefabricated polymers (porous polyethylene). Inclusion criteria for review were (1) either inlay or onlay reconstruction of the craniofacial skeleton using alloplastic materials, and (2) minimum 6 months post-operative follow-up. Charts and CT scans were reviewed with analysis of (1) patient demographics, (2) site of augmentation, (3) alloplastic material utilized, (4) photographic evidence of bony augmentation, (5) CT scan evidence of bone-density augmentation, and (6) complications.

Results:

22 patients met inclusion criteria and were divided into 3 groups including cement pastes, osteoactive powders, and custom polymers.

Cement paste was used for onlay augmentation to the cranial skeleton in 8 patients. Mean age at implantation was 5.5 years with a mean follow-up of 5.7 years (maximum 10 years). One postoperative infection required partial removal of the implant. There was photographic evidence of bony augmentation in all patients, with no evidence of growth abnormalities or relapse. Postoperative CT scans demonstrated persistent skeletal augmentation with a CT density equivalent to that of the adjacent bone. In one patient, biopsy taken 3 years after onlay implantation with hydroxyapatite cement paste showed a rim of bone which had grown around the periphery of the implant with no evidence of bone ingrowth within the implant.

Osteoactive powders were used for inlay reconstruction of full-thickness cranial defects in 9 patients. Mean age at implantation was 4.3 years with a mean follow-up of 2.1 years (maximum 4 years). Follow-up photography suggested successful skeletal recontouring in all patients. CT scans were taken one year postoperatively were available in 2 patients treated with bioactive glass and in 1 patient treated with demineralized bone. In all of these patients, 75% or more of the reconstructed areas had mineralised to CT bone density by one year.

Porous, prefabricated polymers were used for onlay augmentation in 5 patients. Mean age at implantation was 7.8 years with a mean follow-up of 2.4 years (maximum 6 years). Follow-up photography demonstrated successful augmentation, and all re-operative cases demonstrated fibrovascular ingrowth into the implants. However, the implants never approached CT bone density on follow-up CT scan.

Conclusions:

Long-term follow-up of alloplasts for craniofacial reconstruction has demonstrated that while cement pastes and porous polymers provide excellent volume retention and predictable shape, these implants have little or no bone ingrowth. Significant bone replacement, demonstrated by mineral density on postoperative CT scan, was only seen following inlay reconstruction with osteoactive powders. We therefore recommend the following applications when alloplasts are to be used for craniofacial reconstruction: 1) Cement pastes or prefabricated polymers are best-suited in cases of onlay or inlay reconstruction when further skeletal growth is negligible (after age 3 in the cranial vault; after age 14 in the facial skeleton). 2) Osteoactive powders are best-suited for inlay reconstruction, even when significant skeletal growth remains, as these agents demonstrate conversion to bone. 3) Consider autogenous bone graft, or delaying reconstruction, when onlay reconstruction is required during active skeletal growth.
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