27. Implants and Alloplasts (Nonbreast)
Biomaterials are naturally occurring and synthetic materials used to replace, reconstruct, or augment tissues in the human body.
Biomaterials are frequently used in aesthetic surgery for volume or contour augmentation.
Factors to consider when choosing a biomaterial are shown in Box 27-1.
Chemically inert | Sterilizable |
Biocompatible | Easy to handle |
Nonallergenic | Radiopaque |
Noncarcinogenic | Ability to stabilize |
Cost-effective |
The most important clinical aspect of an implanted material is its permanence.
The long-term biocompatibility of a material is a function of the dynamic relationship between the host and implant.
Permanence is therefore achieved with harmony between host and chemical and mechanical factors.
Frequently, the interaction between host and implant is not ideal, and various biologic reactions may be observed (Box 27-2).
Immediate inflammation with early rejection | Incomplete encapsulation with ongoing cellular reaction |
Delayed rejection | Slow resorption |
Fibrous encapsulation | Incorporation |
Definitions
Autografts: Living tissue derived from the host
Allografts: Nonliving tissue derived from same species donor (i.e., cadaver)
Xenografts: Nonliving tissue derived from different species donor (i.e., bovine)
Alloplasts: Synthetic material
Autografts
Advantage
Benchmark because of their tolerance and biologic integration into the host
Disadvantages
Requires a second operative site, increasing patient morbidity
Requires increased operative time to harvest
Limited in quantity
Plagued by variable amounts of resorption over time
Bone
General Characteristics
All free bone grafts undergo some degree of resorption and remodeling.
The degree to which each type of graft is affected is unclear.
Cortical grafts maintain their volume significantly better than cancellous grafts regardless of embryologic origin. 1
Fixation reduces graft resorption when they are placed under mobile tissues. 2
Sources include calvarium, iliac crest, rib, tibia, radius, and mandible.
Advantages
Relative resistance to infection
Incorporation by the host into new bone
Lack of host response against the graft
Disadvantages
Donor site morbidity
Variable graft resorption
Limited ability to contour some types of bone
Cartilage
General Characteristics
Infection and resorption are rare. 3
Histologic studies have shown the survival of chondrocytes within normal matrix and a general absence of fibrous ingrowth and resorption of the graft. 2 , 4 – 7
Postulated that cartilage grafts will calcify with time 8
Main sources: Cartilaginous nasal septum, conchal cartilage, rib
Frequently used for soft tissue augmentation, nasal and ear reconstruction
Advantages
Ease of harvest
Flexibility
Limited donor site morbidity
Allogeneic Materials
General Characteristics
Allogeneic materials (allografts, homografts) and xenografts contain no living cells.
May possess osteoinductive and/or osteoconductive properties
Become incorporated into host tissues by providing a structural framework or scaffolding for ingrowth of host tissues
Do not require a second operative site
Require less operative time
Abundant in supply
Both xenograft and allogeneic materials are processed by various methods to reduce antigenicity.
Xenografts have more antigenic potential than homografts.
Used less frequently
Before placement of xenografts, surgeons should inquire about previous use of xenografts in the patient, because delayed hypersensitivity reactions have been reported. 12
Despite meticulous and careful sterilization techniques, the risk of transmission of infectious disease is the most worrisome disadvantage of allogeneic materials.
Variable resorption is common.
Lyophilized Fascia
Homologous Bone
Provides a scaffold for new bone formation and has the same working properties of autogenous bone
Slower to become incorporated and revascularized than autogenous bone 15
Associated with few complications when used for reconstructing the maxillofacial skeleton 16
Supplied in many forms, including whole bone cribs
Homologous Cartilage
Undergoes ossification and calcification with time 4 , 17
Greater tendency for homologous cartilage to undergo resorption and replacement with fibrous tissue than with autogenous cartilage 3 – 6
Preserved cartilage has significantly greater amounts of resorption and increased rates of infection. 3
Senior Author Tip:
Despite the report of Vuyk and Adamson, 3 in my more than 20 years of experience using irradiated homologous nasal cartilage in more than 500 rhinoplasties, little significant absorption and no infections have occurred. This work, however, was never published.
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