Alloplasts in Nasal Surgery




Few concepts in rhinoplasty engender as much discussion and conflict as the use of alloplasts in the nose. Clear divisions within the specialty have developed, with some surgeons using alloplastic implants liberally while others staunchly maintaining that alloplasts should never be used in rhinoplasty. Central to this dichotomy is the risk versus benefit analysis and the thresholds one sets as acceptable. Should an alloplast ever be used in cosmetic or reconstructive rhinoplasty? Does sparing the patient an additional incision and operative site with additional risks (including potential intracranial or thoracic penetration) and donor site morbidity outweigh a small but finite risk of implant material extrusion or infection? Can an alloplast effectively simulate the tissue characteristics (such as bulk, shape, texture, and stability) it is designed to replace? Unfortunately, it is often the patients who most need significant bulk and/or structural support, due to prior surgery, trauma, or inflammatory disease, who may be the worst candidates for alloplastic augmentation. Significant scarring or a thinned, devascularized skin–soft tissue envelope may lead to poor implant integration, skin erosion, and breakdown, as well as implant mobility and/or exposure. This chapter will review the benefits and risks of alloplastic nasal augmentation and will discuss the use of implants in the nose in the context of implant biocompatibility and as related to wound healing.


History


At its most basic level, rhinoplasty is an alteration in the form and function of the nose by removal, modification, or augmentation of existing nasal structures. Historically, nasal mutilation was inflicted with the intention of leaving a visible marker of a degraded social status for thieves, adulterers, and military or political prisoners. The syphilis epidemic in Western Europe in the sixteenth and seventheenth centuries caused a significant number of saddle nose deformities and left victims with conspicuous sequelae of sexual promiscuity. Military wounds also left victims with nasal deformities requiring treatment.


The simplest form of augmentation is the prosthesis. Justinian II (“Rhinotmesis”), a Byzantine emperor whose nose was amputated after he was deposed (nasal and facial deformities precluded individuals from ruling), wore a nasal prosthesis when he reclaimed his throne. Tycho Brahe, the Danish astronomer, wore a silver prosthesis to camouflage a nasal deformity.


Soft tissue reconstruction of the nose with forehead or cheek skin flaps dates from as early as the sixth century bc in India, and forearm pedicled flap repair was well known in Italy prior to Tagiacozzi’s publication in the sixteenth century. These early surgical interventions in the preanesthetic era were intended to replace large amounts of nasal volume and skin coverage. More focused reconstruction of nasal deformities—in particular, the saddle nose deformity—began in earnest in the late nineteenth to early twentieth centuries, as modern anesthetic techniques and antisepsis were introduced. While subtler than the earlier treatment of more dramatic nasal amputations, the repair of these injuries was primarily aimed at restoration of nasal volume and skin coverage. Some of the materials used, including stones from the Black Sea, duck breastbone, pearls, and ivory, may seem inexact and perhaps more than a little odd, but the deformities being treated were severe and even modest improvements were appreciated. At best, the materials may have been well-tolerated foreign bodies with fibrous encapsulation, but it seems obvious they were chosen more for their physical qualities than for their biocompatibility.


The development of synthetic polymers in the mid to late twentieth century led to the greatest increase in the use of nasal implants. In particular, solid silicone implants were introduced and are still in use today. These were designed primarily for dorsal augmentation but some later designs incorporated struts for columellar and tip support. These implants are fairly well tolerated, but implant infections and extrusions have been reported and will be discussed later in this chapter. Other implants have also been developed over the past two decades for isolated columellar support, premaxillary augmentation, and nasal valve support; their use will also be covered in this chapter.




Anatomy


Five main areas can typically be considered for alloplastic nasal augmentation: the dorsum, premaxilla, nasal valve, ala, and columella. Additionally, some implants will include aspects designed to augment the nasal tip. Congenitally shallow nasal dorsal profiles often seen in Asian and African American patients are amenable to dorsal onlay implants. In patients with limited or weak tip projection and support, a single-piece implant can be used to both augment dorsal height and to provide tip support. A retruse premaxilla can be augmented with an implant to restore proper balance to the lower third of the nose. Recently, new implants have been introduced to modify/support the internal nasal valve without adding excessive bulk. Implants can be added to the nasal ala to correct alar contour, while implants placed in the columella can aid in augmenting tip projection, altering tip rotation or reshaping the columella itself. In general, space-occupying implants are better tolerated than those that provide structural support; there are exceptions to this rule, and factors such as the health and vascularity of the local soft tissues, implant stabilization, and the physical and chemical characteristics of the implant itself will also have a significant impact on implant success.




Alternatives


Traditional teaching of rhinoplasty techniques dictates the use of autologous materials whenever possible. Autologous septal, conchal, and costal cartilage are the most commonly used material for nasal grafting. They are readily harvestable, have minimal donor site morbidity, can generally provide sufficient volume of cartilage, are relatively easy to carve, and provide fairly predictable results. Alternatively, outer table calvarial or iliac crest bone grafts can be used, but due to their rigidity, they are only practical for dorsal onlay (and columellar support) grafts. Temporalis fascia can be used to soften graft edges but provides neither volume augmentation nor support. Erol and colleagues described the use of the “Turkish Delight” graft: minced cartilage is mixed with autologous blood and wrapped in oxidized cellulose. The subsequent fibrotic response provides bulk augmentation for the nasal dorsum but cannot be used in structural settings.


Homografts, such as irradiated rib cartilage (IRC), can be considered as an alternative if autologous tissue is unavailable or insufficient or the patient refuses a second surgical incision. IRC is harvested from human cadavers and processed to reduce the potential for infection transmission or immunologic host rejection. It has been in use for over 20 years and the literature is mixed as to the ultimate fate of irradiated cartilage. Schuller et al. initially described good results using IRC. However, subsequent long-term follow-up in these cases is mixed with preservation of volumization but loss of tip support reported when IRC is used. Considerable warping can also occur over time.


Another homograft, acellular dermal matrix (ADC; LifeCell Corp., Branchburg, NJ), has been used as a dorsal onlay implant, either alone or in combination with autologous cartilage. ADC provides a three-dimensional collagen scaffold for host tissue ingrowth and fibrosis and can be used to provide subtle volume augmentation (especially in the radix). It can also be used to camouflage irregularities of the dorsum or from other cartilage grafts. At best, only a portion of the volume of ADC will persist long term.


Finally, temporary injectable fillers such as hyaluronic acids and calcium hydroxylapatite have been described for nasal contouring. These are generally simple and effective but temporary solutions, and the long-term safety of permanent filler material in this area is unclear.




Implant Biocompatibility


The body’s biologic response to an alloplast is dependent on factors related to both host and implant. The chemical composition, surface electrical charge, surface texture, and porosity all contribute to the specific response that occurs around an alloplastic implant. Simply put, a nasal implant is a rather large subcutaneous or submuscular foreign body. Following implantation, the implant is coated with host proteins such as fibrin, fibronectin, and other proteins that become partially denatured on contact with the implant. These proteins are essential for the subsequent host inflammatory response. The severity, cellular activity, and longevity of this response are determined in large part by the qualities of the implant. Neutrophils and monocytes migrate to the implant surface. When the initial inflammatory response subsides, the neutrophilic content decreases, giving way to macrophage increase and accumulation of giant cells, fibroblasts, and some lymphocytes around the material. A fibrotic response ultimately results, with a capsule of fibrosis around the implant; any fragments, left behind in the manufacturing of the implant, related to surgical technique, or formed as a result of implant degradation in situ, will promote additional inflammatory reactions around each particle of material. Some early implants no longer in use today were found to undergo degradation and released new fragments into the surrounding tissues; a vibrant secondary foreign body response developed and persisted around the implant causing significant collateral damage. By contrast, the three most commonly used solid nasal alloplasts today (expanded polytetrafluoroetheylene [e-PTFE], porous high density polyethylene [PHDPE], and silicone) are associated with quite different early responses, which represent different points on a common spectrum. These implants have been designed to avoid particulate degradation.


Silicone


Silicone nasal implants are nonporous and smooth surfaced. The inert nature of the polymer generally is associated with a thin fibrous capsule with quiescent fibroblasts and rare giant cells. There is no tissue ingrowth making removal simple but predisposing the implant to infection (from early contamination or late bacteremia) and instability within the implant pocket. As there is no rigid fixation of the implant, the micromotion of the implant can cause a synovial reaction within the implant.


e-PTFE


e-PTFE is a soft and pliable microporous material. The most commonly used e-PTFE was produced by W.L. Gore & Associates but the manufacturer has ceased production. Currently, a preformed composite e-PTFE/silicone implant is available (Implantech Associates, Inc., Ventura, CA). These implants have a solid silicone core with a bonded e-PTFE coating. The e-PTFE acts as a cushion between the firm silicone core and the soft tissue envelope, and the porous surface of the e-PTFE allows limited tissue ingrowth into the periphery of the implant. This ingrowth effectively binds the implant to the surrounding tissue and seals it from the outside environment, eliminating dead space and potential micromotion, while the silicone core can provide structural support. The surrounding capsule is composed of a few thin layers of collagen and relatively quiescent fibroblasts.


Phdpe


PHDPE (MEDPOR; Stryker Corp., Kalamazoo, MI) is a rigid implant with pores averaging 150 microns in size. These larger pores promote a more vibrant fibrovascular soft tissue ingrowth than e-PTFE, and ultimately the implant, which is 50% porous, is completely ingrown by host tissue. This provides a dense attachment to the surrounding soft tissue and assists with implant fixation. Porous implants have been shown to be more susceptible to early infections (prior to soft tissue invasion of the implant) but more resistant to late infections (because of the protective effect of host tissue invasion and integration of the implant) compared to solid implants.




Special Considerations


A careful assessment of surgical needs for which the implants will be used to address is critical in choosing the correct implant. Each area is examined to assess the patient’s surgical requirements. Is dorsal augmentation necessary, and if so, to what degree? If the dorsum is to be augmented, is tip projection required as well? Does the alar base or the columella need additional volume? The answers to these questions will help select the most appropriate implant.


In assessing patients preoperatively, standard functional and aesthetic rhinologic evaluation should be performed. Specific aesthetic and structural needs should be identified. The intended volume augmentation should be assessed, as should the anticipated amount and quality of autogenous cartilage available. In general, autogenous cartilage is better tolerated and more forgiving in the nose (especially in revision and posttraumatic cases), and should be considered as a “first-line” choice. If septal and/or conchal cartilage is insufficient for the patient’s needs, costal cartilage and calvarial bone grafts are considered. Patient preference and the potential associated morbidity of these autografts make consideration of alloplasts reasonable. Both short- and long-term risks and benefits should be fully discussed with the patient. The decision to use an alloplastic implant is made jointly.


A major factor affecting the success of nasal alloplasts is the integrity of the skin–soft tissue envelope beneath which the implant is placed. The overlying tissues must be sufficiently thick and healthy to withstand contact with and pressure from a solid implant. Patients with exceptionally thin skin may be more prone to skin compromise when an alloplast is used; likewise, the multi-revised rhinoplasty patient or patients with known vascular compromise will have an increased risk of implant/soft tissue complications due to diminished vascularity. Patients with septal perforation are also at an increased risk of complications because of diminished local tissue vascularity secondary to prior surgery or trauma. Additionally, chronic nasal crusting of the perforation edges may allow transient bacterial seeding of the local tissues. When an alloplast is present, this can lead to chronic inflammation or infection around the implant. When present, septal perforation should be closed if an alloplast is used, and if there is any uncertainty as to the anticipated success of the perforation repair, placement of the alloplast should be deferred. Tobacco use, while always a hindrance to wound healing, is especially problematic in the postoperative period after placement of a nasal implant; success of the alloplast is dependent on proper healing of the soft tissue pocket surrounding the implant, especially in the early postoperative period.


Specific Alloplasts


Silicone


Silicone refers to a family of polymers of the compound dimethysiloxane ([(CH 3 ) 2 SiO 2 ] x ). Silicone implants have been used extensively for dorsal augmentation and enhancement of tip projection, while single L-shaped silicone implants can be used for both purposes. As silicone is nonporous and is surrounded by a fibrous capsule, stability of the implant depends primarily on creation of a precisely positioned and sized pocket, one that allows neither implant movement nor excessive pressure against the overlying soft tissue. The implant should be placed directly over the nasal bone periosteum from the nasal root to just above the anterior septal angle. If an L-shaped implant is chosen, the vertical strut portion is placed in between the medial crura of the lower lateral cartilages and rests anterior to the anterior nasal spine. These implants can be placed via an external approach, but creation of a discrete implant pocket may be more effective via an endonasal approach. All incisions should be closed meticulously so as to establish a distinct and separate cavity from the external environment.


Phdpe


PHDPE implants are made of a highly porous material that facilitates fibrous ingrowth. The standard nasal dorsal implant should rest directly over the nasal bones from the nasal root to rest over the cartilaginous dorsum. In patients with reasonable tip support and form, the implant can be used without the nasal tip portion; however, in patients with thick nasal tip skin or those with limited nasal tip architecture, the nasal dorsum/nasal tip implant can be used. In general, the soft tissue fibrosis that occurs postoperatively coapts the nasal tip skin to the nasal tip portion of the implant yielding an acceptable form. A thin PHDPE sheet (0.85 or 1.5 mm thick) can be cut into an ovoid or rectangle shape, for use as an alar batten or a columellar strut, respectively.


Because of the rough surface of the PHDPE, these implants do not slide easily into position and will catch on the surrounding soft tissue. A wider dissection pocket than required for a silicone implant must be created; this is especially true for columellar and dorsal placement. A useful trick is to wrap the implant in its sterile plastic liner prior to placement; this will allow the implant to slide into position more easily. Once properly positioned, the wrapper can be advanced out, leaving the implant in the desired location. Stabilization of dorsal PHDPE implants is not mandatory, although this can be performed with a monocortical titanium screw placed through the implant into the nasal bone. This is recommended when premaxillary implants are placed. Implants at other sites can be secured much in the same was as cartilage grafts, although effective soft tissue apposition to the implant is essential for long-term success.


e-PTFE


e-PTFE implants are porous materials that also promote soft tissue ingrowth. The pore size in e-PTFE is notably smaller than in PHDPE, which limits the fibrous ingrowth of the implant to the outer few tenths of a millimeter. e-PTFE does not result in a well-developed capsule. This degree of ingrowth stabilizes the implant and isolates its interior from bacteria, while allowing for relatively simple implant removal when necessary. e-PTFE alone, however, is soft and flexible and cannot be used to provide structural support. Numerous studies have been published documenting the safety and efficacy of e-PTFE implants.


Recently, preformed e-PTFE nasal implants have become unavailable, and e-PTFE–coated dorsal as well as dorsal/columellar silicone implants have been introduced. (Implantech Associates, Inc, Ventura, CA). These implants are covered by a thin layer of e-PTFE bonded to a silicone core. The e-PTFE integrates the implant with surrounding soft tissues and serves as a cushion between the overlying skin and soft tissues and the firmer silicone, while the central silicone portion of the implant maintains a consistent shape and structure. In theory, these implants should perform as well as standard e-PTFE implants; however, e-PTFE implants were never used to provide structural support, and in this setting these implants may behave similarly to all-silicone implants. Care should be taken to avoid applying excessive pressure of the implant against the skin.


Again, the implant is placed into the dissected pocket, sliding easily into position. e-PTFE/silicone implants require a relatively precise pocket; alternatively, the edge can be sutured to the surrounding soft tissue to maintain implant position.

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Mar 23, 2019 | Posted by in OTOLARYNGOLOGY | Comments Off on Alloplasts in Nasal Surgery

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