Malar and Submalar Alloplastic Implants Treatment & Management

Alloplastic Implants

Alloplastic implants offer many advantages over reconstruction using autogenous tissue, including availability of materials, simplification of operative procedure, and no donor site morbidity. Alloplastic implants can reduce the time under general anesthesia, thereby minimizing the risks that accompany such anesthesia.

The wide variety of compositions of synthetic materials allows the surgeon to choose a specific combination of strength, elasticity, and durability for a given procedure. Varied surface characteristics are available to suit different clinical situations; for example, texturing is useful if tissue adhesion and ingrowth are desired, while smooth capsule formation can facilitate easy implant removal. The ideal implant should be nonimmunogenic, nontoxic, cost-effective, easily tailored and sculpted, and resistant to infection.^{[3, 1]} No implant fulfills all of these characteristics.

The success of synthetic implants depends upon the interaction between implant material and host reaction. Biocompatibility, defined by Williams in his review of implantable prostheses, is "a state of affairs when a biomaterial exists within a physiologic environment without either the material adversely and significantly affecting the body, or the environment of the body adversely and significantly affecting the material."^[4] This biocompatibility depends upon the characteristics of the synthetic material, the proposed location and function of the implant, and the surgical technique of the operator.

Non–carbon-based polymers

Silicone (silastic) was first reported for use in facial implants in 1953. Silicone is highly resistant to degradation and has a high degree of chemical inertness because of its silicon-oxygen bonds and cross-linked nature.^[1] No significant clinical toxicity or allergic reactions have been proven to exist. It can be vulcanized into solid rubber, the most common form for facial implants, and can be carved intraoperatively with a scalpel.^[5] It also comes in the form of room temperature vulcanized (RTV) silicone, which hardens when mixed and can be molded or implanted before it hardens.

Silicone implants retain their strength and flexibility though a wide range of temperatures and can be sterilized easily. When silicone implants are fixed against a bony surface in their solid form, long-term stability is very high. Bony erosion has been reported with silicone implants when load is applied to them.^[6] However, when subjected to repeated movement with mechanical loading (eg, joint arthroplasties), silicone has a tendency to fragment and deteriorate.

Because of its inert nature, the body reacts to silicone implants by forming a capsule, and no tissue ingrowth occurs.^[1] With solid silicone implants, this capsule usually remains stable throughout the life of the implant. Since tissue ingrowth does not occur, silicone implants are easy to remove by incising the capsule and simply removing the implant. Some authors believe that encapsulation and movement cause most of silicone late complications.^[7] Should the implant ever need to be removed, the capsule allows for easier removal of smooth silicone than of porous or textured implants. However, in the liquid or gel form, the silicone is not as inert and can incite a chronic inflammatory reaction.^[1] Debate exists within the literature whether silicone should be injected into the face for rejuvenation.^[8]

Carbon-based polymers

Commonly used carbon-based polymers include polytetrafluoroethylene (PTFE), polyethylene (PE), aliphatic polyesters, and methylmethacrylate.

Although the Food and Drug Administration (FDA) issued a public health advisory in 1991 about the temporomandibular joint implant Proplast, PTFE has reentered the market as Gore-Tex.^[1] PTFE (Gore-Tex) consists of a fibrillated polymer of polytetrafluoroethylene, with pores between the fibrils averaging only 22 μm in diameter; this limits tissue ingrowth and eases removal, like silicone.^[9] Silicone arrives as block and can be sculpted to the needs of the surgeon. Schoenrock and Reppucci reported only a 0.2% rate of infection necessitating removal in facial implantation.^[10]

Solid porous polyethylene implants (Medpor) have become popular implants in the facial skeleton. The pore size (125-250 um) allows tissue in growth and relative incorporation.^{[11, 7]} Medpor implants have been designed in multiple shapes, sizes and dimensions for use in facial alloplastic reconstruction. These implants come off the shelf ready for implantation and can require minimal contouring. In addition, custom-made polyethylene implants have been used for cases of congenital anomalies by this author. Yaremchuk presents a large case series with lengthy follow-up attesting to the durability of these implants with infection rates of 3%. He stresses subperiosteal placement and screw fixation.^[7]

Aliphatic polyesters are resorbable materials and do not have durability and permanency like other carbon-based polymers, thereby limiting their usefulness for permanent facial implantation. Methylmethacrylate (MMC), frequently known as bone cement, is formed by mixing a liquid monomer with a powered polymer.^[1] This process is extremely exothermic and must be performed outside of the recipient field. MMC becomes encapsulated, is not biodegradable, and is very durable. MMC has a very high bacterial adhesion property, making it susceptible to infection.^[1] MMC is frequently used in cranioplasties but has only a limited role in facial implantation because of the abovementioned reasons.

Metals

Gold and titanium are frequently used in facial implantation. Although not typically used for augmentation, both have unique properties that make them useful for facial implantation. Gold, a noble element, does not oxidize after implantation.^[1] Gold weights are used frequently in acquired facial nerve palsies for ptosis correction and corneal protection. They are well tolerated, with a low extrusion rate from the upper lid. Titanium is extremely durable for its weight and can achieve osseointegration. Hearing aids and facial prosthetics are attached to titanium screws that have incorporated into the bone.

Ceramics

Hydroxyapatite (HA) is calcium phosphate salt, the principal inorganic compound in bone matrix. HA must cure once placed into the recipient site but is porous enough to allow fibrous ingrowth. Unfortunately, HA is extremely brittle and does not tolerate load well without cracking. Occasionally used for cranioplasties, its role in facial implantation is limited.

Implant Placement

During placement, all opportunities for contamination must be minimized and eliminated. Minimal handling, no-touch technique, and changing gloves prior to implantation have all been advocated. Pocket irrigation with antibiotic solution is frequently employed, as well.

Prior to the start of the procedure, appropriate antibiotics should be administered (depending upon surgical approach) to minimize bacterial loads. Without foreign material present, 100,000 bacteria per gram of tissue are required for infection. In the presence of foreign material, only 100 bacteria per gram of tissue are required. Ideally, antibiotics should be given 30 minutes prior to the start of the procedure in order to reduce the bacterial count. Postoperative antibiotics are also advocated; however, the ideal duration of antibiotics has not been established.

Proper preoperative planning also minimizes the risk of implant infection or extrusion. Placing the implant in a well vascularized area with adequate tissue coverage and pocket laxity is paramount in preventing infection and extrusion. Previous scarring, infection, or radiation increases the risk of negative sequelae from surgical implantation. Although the vascularity of the face is exceptional, scarring and radiation can limit the tissue ingrowth into the implant, which can be desirable.

Appropriate antibiotics should be administered prior to the start of the procedure. Assessing the proposed area of implantation for tissue laxity and integrity is paramount.

A myriad of approaches can be used for the placement of malar implants. Most authors recommend subperiosteal placement of the implant.^[7] The intraoral approach is popular, as it leaves no visible scar on the face. An upper gingival buccal incision is made, followed by a cranial subperiosteal dissection until the desired pocket is formed. de la Pe ñ a-Salcedo et al advocate an intranasal approach.^[12]

An intraoral approach carries a theoretically higher risk of infection due to the bacterial load of the oral cavity. Closing the intraoral incision in layers should be strongly considered. When performing synchronous eye surgery, the implant can be placed via a transconjunctival approach that may require a canthotomy. A subciliary incision can be associated with the risk of ectropion. Coronal and face-lift incisions have also been implemented for placement of these implants.

Proper pocket dissection is essential, followed by securing the implant. In his series, Yarmechuk strongly advocates securing the implant to the bone and credits this with his excellent results.^[7] Proper placement, symmetry, location, and desired effects should be judged from multiple views of the patient.

The patient should be instructed to elevate the head of bed for the first 24 hours after surgery to minimize postoperative edema. Strenuous physical activity, especially contact sports, must be minimized until healing is complete.

Careful and frequent follow-up is required to monitor for seromas, hematomas, or infections. Malposition of the implant causing facial asymmetry should be watched for as well.

• Hematomas and seromas are rare complications and can be minimized by careful surgical technique.
• Infection and extrusion of alloplastic implants are dreaded complications. Using antibiotics, proper dissection, and implant fixation, Yarmechuk has reduced his acute and late infection rates to a total of 3%.^[7]
• Facial asymmetry following implantation can be prevented by proper intra-operative sculpturing. When asymmetry or malposition occurs, removal of the implant, replacement of the implant, and subperiosteal mid-face resuspension is advocated.^[13]
• The incidences of hypoesthesia (transient), hematoma, infection, and extrusion range from 1-3% depending upon the length of patient follow-up.^{[11, 7, 14]}

Most patients are satisfied with the results of malar implantation, with satisfaction rates above 80%.^{[7, 15]}

The search for the ideal biocompatible implantable material continues. Researchers are trying to synthesize materials that meet more of the goals outlined above (eg, malleability, strength, resistance to infection).