Microsurgical augmentation of the facial skeleton

Key points

• Skin, fat, muscle, fascia, tendon, and bone can all be differentially carried on vascular pedicles from various donor sites in the provision of vascularized tissue to the face.

• Soft tissue, muscle, and bone flaps will all be reviewed with a focus on their use for facial soft tissue or bony augmentation of the face for both aesthetic and reconstructive purposes.

• Each particular flap can be tailored exactly, depending on the defect or lack of tissues that is being addressed, in a “like with like” manner.

• Technical as well as aesthetic considerations to enhance outcomes in these cases will be emphasized.

Introduction

Microsurgical techniques may bring a plethora of vascularized tissue types to the facial skeleton and soft tissue structures when local tissues, grafts, alloplasts, or other materials are insufficient. Thus microsurgery offers the unique ability to truly replace “like with like” tissues. Common etiologies of missing facial tissues include trauma, cancerous or benign tumors, and congenital conditions, among others. In such cases, microsurgery is a key tool in the armamentarium of the plastic surgeon in achieving an equally functional and aesthetic outcome. The tissue provided can be tailored to the exact need of the defect, the deficient tissue, and the patient as a whole. These tissues may include bone, muscle, fascia, tendon, fat, and skin in variable configurations, based on the vascular pedicles on which they are carried. The major disadvantage of microsurgical techniques is donor site morbidity, with each donor site having unique characteristics. However, the majority of donor sites, especially with the increasing use of perforator flaps, tolerate the techniques very well.

As is well-known in the plastic surgery community, the line between aesthetic surgery and reconstructive surgery is always blurred. In many cases, use of microsurgical techniques to obtain distant, vascularized tissue allows for not only a more functional reconstruction but also a more aesthetic reconstruction compared with that of nonmicrosurgical techniques. In certain circumstances, the indication for microsurgical augmentation of the head and neck may be a primarily cosmetic deformity, as in the use of a buried parascapular flap in Parry-Romberg syndrome. In others, microsurgical tools are employed in an effort to aesthetically improve the outcome of a particular procedure and to obtain functional benefits. An example is the implementation of an immediate medial sural artery perforator flap for postparotidectomy defects, not only to provide a layer of vascularized tissue to prevent aberrant nerve regeneration but also to obviate the facial contour abnormalities that are common after parotidectomy alone. Microsurgical flaps play a primarily reconstructive role in the face and facial skeleton in select cases, such as mandibular reconstruction with an osteocutaneous fibula flap after trauma or oncologic resection. However, even in these contexts, the surgeon should have an eye on the ultimate aesthetics of such reconstructions, whether that be achieved primarily or in multiple subsequent stages. Facial composite tissue allotransplantation (CTA) represents the ultimate intersection of aesthetic and reconstructive facial augmentation. Facial CTA has revolutionized the field of facial reconstruction, with the entire facial unit, including bone, muscle, fascia, and skin, provided as a single vascularized flap in the most severe facial deformities. In this manner, an unparalleled aesthetic facial reconstruction is achieved.

Throughout this chapter, we will demonstrate the confluence of aesthetic and reconstructive techniques in discussing flaps for microsurgical augmentation of the facial soft tissues and bony skeleton, including their indications and the important aesthetic considerations in their utilization.

Patient evaluation

History

A complete history must be taken for any patient under consideration for microsurgical augmentation of the face. To begin, the etiology of the expected or actual facial defect should be ascertained. Often, patients are referred to the microsurgeon with an already known diagnosis. However, in the instances when the plastic surgeon will be the first person to evaluate the patient, the surgeon must be able to diagnose a range of etiologies, which will be discussed later. The inciting symptoms, their chronicity, location, and progression, as well as any associated issues should be thoroughly investigated.

Next, full medical and surgical histories are reviewed. Patients with significant multisystem comorbidities that preclude their ability to withstand general anesthesia for a lengthy intraoperative time are not good candidates for microsurgical procedures. Any comorbidity should be medically optimized before proceeding. Special attention should be given to any history suggesting a hypercoagulable state. This includes, but is not limited to, a history of deep vein thrombosis; autoimmune conditions, such as lupus; multiple failed pregnancies in women; and prior microsurgical failures. Any concerning past issues should be further investigated and addressed with laboratory work and/or consultation with a hematologist because hypercoagulability can compromise an otherwise technically sound microsurgical procedure. Patients with a bleeding diastasis should be assessed to ensure that they are able to safely tolerate the postoperative antiplatelet and anticoagulant therapy that may be administered.

Prior history of radiation to the face should be ascertained because resultant tissue fibrosis and impaired wound healing will impact dissection in the area. The surgeon must also assess for prior surgical interventions undertaken in the head and/or neck as well as any potential donor sites. Scarring of recipient sites in the head and neck region can influence dissection as well as availability of recipient vessels for anastomosis. Donor site scarring from prior surgery may lead the surgeon to select another area offering similar tissues for transfer.

Medications and allergies are also assessed—specifically, any medications with a hypercoagulability profile, including oral contraceptives and selective estrogen receptor modulators, among others. These should be held for at least a week before the surgical procedure. Patients who are active smokers should stop smoking for at least 4 to 6 weeks preoperatively and for at least 2 weeks postoperatively. Although smoking has not been shown to increase the risk of microsurgical failure, it may increase risk of wound healing complications, especially those involving the donor site, through the mechanisms of platelet aggregation and microvascular vasoconstriction. Finally, the patient’s occupations and hobbies should be reviewed. This information will assist in selecting a donor site that will tolerate the procedure well, with the least possible adverse impact on the patient’s daily life.

Differential diagnosis

The differential diagnosis of the various conditions that necessitate microsurgical facial augmentation can be categorized by the affected facial tissues. This differentiation becomes apparent upon gathering a complete history, as described previously, and through a meticulous physical examination, as discussed later. Missing or deficient facial tissue layers may occur in isolation, such as in a full-thickness skin resection of a basal cell tumor, or in combination, such as in a trauma-related composite mandibular defect that includes skin, muscle, and bone.

The soft tissue of the face begins superficially as the skin and superficial fat, below which are the superficial musculoaponeurotic system (SMAS) fascia and deeper fat compartments. Skin and soft tissue loss requiring microsurgical augmentation may occur as a result of surgical resection, trauma, congenital, or idiopathic causes. Advanced locally aggressive benign or malignant tumors in the face may result in large defects that are insufficiently reconstructed with local tissues or other methods, mandating distant tissue be brought in for reconstruction. Alternatively, specialized areas of the face, such as the eyelids, nose, and mouth, may require distant tissue for reconstruction even with smaller defects due to their specialized function and paucity of local tissues available for reconstruction. In the setting of prior or future radiation, local tissues will be poorly suited for reconstruction, and microsurgical tissue transfer may be required for defects that otherwise may be amenable to local tissue rearrangement.

Similarly, trauma can result in complex and substantial soft tissue defects of the face, which, due to size and/or location, are best reconstructed with microsurgical techniques. Importantly, with traumatic injuries, there exists a zone of injury surrounding the area of maximum trauma that impacts vascular inflow. The surgeon should ensure that the recipient vessel of choice for any free tissue transfer is outside of this zone of injury, and this may necessitate vein grafting.

Congenital causes of facial soft tissue deficiency include various forms of hemifacial microsomia and the associated syndromes, in which the facial soft tissue as well as bone can be hypoplastic. The most common idiopathic causes of facial soft tissue loss or deficiency are linear scleroderma and Parry-Romberg syndrome, which are slowly progressive and usually unilateral conditions of unknown cause. The severity of such deficiencies with these causes is variable. In significant cases, microsurgical augmentation with soft tissue flaps offers the advantage of greater volume with improved stability and longevity compared with augmentation with alloplastic or autologous grafting techniques.

The facial muscles are invested by the SMAS layer, lying superficial to the facial skeleton. Microsurgical augmentation of the facial musculature is generally undertaken to restore lost facial nerve function in the setting of native facial muscle fibrosis after a prolonged period of denervation. Etiologies of facial nerve dysfunction include idiopathic causes, such as Bell’s palsy, nerve tumors or involvement of adjacent tumors, most commonly of the parotid gland, as well as trauma and congenital cases as in Möbius syndrome.

Osseous defects or deficiencies of the facial skeleton can arise from a variety of etiologies. The most common include trauma; malignant or locally invasive tumors, the most common of which are squamous cell carcinoma and ameloblastoma, respectively; osteoradionecrosis; and osteomyelitis. Given the deep location and close investing relationship of bone to other facial tissues, isolated bony defects are less common. Often, resection of tumors, infection, or osteoradionecrosis will also involve resection of the skin, mucosa, or musculature, creating composite defects that are best treated with free tissue transfer.

Aging will also result in facial soft tissue loss, specifically loss of the deeper fat compartments, as well as bony resorption of the facial skeleton. However, microsurgical augmentation of involutional fat deflation or osseous changes associated with aging are more appropriately treated with fat grafting or other means, rather than microsurgical techniques.

Physical examination

The physical examination should first focus on the actual or potential defect to be addressed microsurgically. To begin, if a defect or deficiency already exists, it is examined to determine its extent and the layers of the face, from the skin to bone, that are involved. This includes an intraoral examination. The quality and laxity of facial tissues surrounding the real or future defect are assessed to determine whether they are sufficient for reconstruction. The presence or absence of stigmata of prior radiation or facial scars are determined. A full cranial nerve examination should always be performed, with a focus on the ability of the patient to close the eyes fully, smile symmetrically, and achieve oral competence. This is especially important when assessing patients as candidates for microsurgical facial reanimation with free muscle transfer. The neck should also be examined, with special attention given to any prior scars that may influence recipient vessel selection.

Once the recipient site has been addressed, potential donor sites must be examined. These will vary, depending on the needs of the defect/deficiency; however, the most common are the upper and lower extremities as well as the back. The donor sites should be examined for prior scarring, tissue quality, pliability, laxity, and color for the best match for the needs of the recipient site. In the extremities, it is imperative to assess the distal vasculature to ensure that harvesting of the donor vessel pedicle will not compromise perfusion to the remaining extremity. In the upper extremity, the Allen test should be performed to assess a radial- or ulnar-dominant extremity, which would preclude the use of a radial or ulnar forearm flap, respectively. In the lower extremity, the dorsalis pedis and the posterior tibial arteries should be palpated to ensure good perfusion of the extremity. Lack of palpable pulses requires further investigation with Doppler ultrasonography or more invasive imaging.

Imaging or other preoperative diagnostic evaluations

Various imaging modalities can assist the surgeon in the evaluation of patients for microsurgical augmentation of the face. While assessment of the facial soft tissues is best achieved through clinical examination, imaging of the recipient site(s) in the head and neck region may help define the defect or deficiencies to be addressed and establish the vascular status of potential recipient vessels. Three-dimensional (3D) imaging has proven to be a useful adjunct to predict volume deficiencies or differences in unilateral cases. This can help plan the amount or configuration of donor tissue required, in turn, will assist in donor site selection, dissection, and inset into the recipient site. Magnetic resonance imaging (MRI) also has utility in assessing the location and volume of facial soft tissue deficiency. In cases of planned microsurgical free muscle transfer, electromyography and nerve conduction studies may be useful in assessing the status of the facial nerve and musculature to determine patient candidacy. Osseous defects are best appraised with Panorex plain films or computed tomography (CT). CT or magnetic resonance angiography (MRA) can assist in assessing the availability of recipient vessels for anastomosis.

Importantly, imaging of the donor site gives the surgeon valuable information by delineating flap perforator and pedicle orientation, location, and course, and helps determine adequate distal perfusion with extremity flaps—for example, ensuring lack of a dominant peronea magna, which would result in a dysvascular leg with fibula flap harvest. Formal angiography is the gold standard; however, this is rarely necessary, given its invasive nature, except in cases where noninvasive imaging cannot be performed or is inconclusive. CT or MRA are noninvasive modalities to assess the perforator and pedicle vascular anatomy of flap donor sites. Computed tomography angiography (CTA) is quicker and less expensive but may be precluded in patients with renal disease or other contraindications, in which case MRA is a second-line choice. Routine preoperative imaging, in the form of CT or MRA, is generally employed for bony or fasciocutaneous flaps and less commonly for muscle flaps, to precisely ascertain the spatial relationships between the pedicle and the perforators. Regardless of the flap type, imaging is prudent if surgical intervention had been previously undertaken in the region to ensure that damage to the perforators or the pedicle of the planned flap has not be compromised.

Indications and contraindications

The indication for a microsurgical approach to facial reconstruction is lack of facial soft tissue and/or bone that cannot be adequately or safely replaced with local tissues, grafts, alloplasts, or other materials. Microsurgery has the advantage of offering distant, diverse, and vascularized tissues on a vascular pedicle in these cases. Often, these are primary cases of tissue loss due to trauma, locally aggressive benign or malignant tumors, or congenital conditions (e.g., Parry-Romberg syndrome). However, secondary microsurgical facial augmentation may also be indicated in certain scenarios. These commonly include primary reconstruction with other methods that proved insufficient over time, especially when the primary extirpation was combined with radiation therapy. In general, bony defects greater than 6 cm in length will benefit from microsurgical tissue transfer compared with traditional bone grafting. Furthermore, central bony defects of the mandible that are even a few centimeters in length are better served with vascularized bone. With missing muscle function due to muscle fibrosis from prolonged facial nerve palsy lasting greater than 18 to 24 months, the best approach is with microsurgical muscle transfer because muscle grafts will not survive without direct vascularization. Missing facial soft tissues of moderate to significant dimension are often better reconstructed with microvascular tissue transfer because they are not limited by variable resorption, as with fat grafting. Importantly, in the face of radiation, vascularized tissue offers distinct advantages compared with grafts and alloplasts, which have complications, such as poor take, extrusion, and infection.

Contraindications to microsurgical approaches in facial augmentation are similar to those for all microsurgical procedures. To begin, the overall condition of the patient must be considered. Although advances in microsurgical principles have increased the efficiency of these procedures, patients must be physiologically able to tolerate prolonged general anesthesia to be candidates. Furthermore, the risk of systemic thrombosis should be assessed. Patients with a history of real or possible thrombotic events, such as deep vein thrombosis, those with multiple failed pregnancies, and those prone to thrombotic events, such as those with factor V Leiden deficiency, lupus, or sickle cell anemia, are at higher risk of vessel thrombosis and microsurgical flap failure. Consultation with a hematologist, specific testing, and consideration of different techniques for facial augmentation in these patients are advised.

Next, recipient and donor site assessments must be made in determining patient candidacy. The recipient site is assessed in terms of potential vascular inflow for the microsurgical flap. A recipient vessel of adequate location, inflow, size match, and expendability must be present. If such a vessel is not present, microsurgical techniques are not necessarily precluded; however, adjunctive measures, such as vein grafting or arteriovenous loop creation, may be necessary. Similarly, availability of donor sites must be ensured in determining a patient’s candidacy for microsurgical facial augmentation. A donor site offering a match in terms of quality and amount of tissues available, vessel caliber and length, and minimal and acceptable associated morbidity must be present to proceed.

Preoperative planning

Preoperative planning begins with a thorough history and physical examination, as discussed previously. The types and dimensions of missing tissues and the areas of the face to be augmented are first assessed. Functional and aesthetic goals are set with the patient. Once these aspects are determined, an appropriate donor site must be selected. As discussed, the ideal donor site is one that provides the exact amount and types of tissues desired, with a vascular pedicle that is of sufficient caliber and length for tension-free anastomosis to the recipient inflow vessels. Moreover, the donor site should be tolerant of the procedure and with the least possible morbidity with regard to form and function. Although no donor site may be ideal in any given clinical scenario, the one closest to meeting these criteria should be selected.

Preoperative imaging plays a significant role in planning microsurgical augmentation of the face, as discussed previously. Furthermore, the intersection of imaging and microsurgery is virtual surgical planning (VSP), which has helped optimize outcomes in complex head and neck microsurgical reconstructions. Primarily employed in cases of bony reconstruction, VSP permits surgeons to conceptualize and modulate any imaged recipient and donor site. As such, the facial skeleton can be adjusted on the basis of the operative plan to better visualize the expected or real defect. Similarly, donor site tissues can be manipulated to determine the dimensions required to adequately address the needs of the recipient site. Moreover, operative models and even cutting guides for bone cuts based on this planning can be printed in 3D for utilization in the operating room. Incorporation of VSP offers the opportunity to maximize efficiency and optimize surgical results in cases of complex, microsurgical facial augmentation. However, a relatively steep learning curve is involved.

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