Pull Through, Visor Flap, and Transmandibular Surgery
General Considerations
When oral cavity or oropharyngeal tumors cannot be satisfactorily approached through the open mouth, due to size, location, local extension, or proximity to the mandible or maxilla, an access procedure becomes necessary. This chapter will focus on the prevention and management of complications arising from access procedures, including mandibulotomy, mandibular lingual release or “pull-through”, and lower cheek flap and visor flap approaches.
Selecting the Correct Approach: Patient and Tumor Factors
In cases of tumors requiring enhanced access with one of these procedures, the first step in avoiding complications is to ensure that the chosen approach is appropriate given oncologic, functional, and aesthetic considerations. For example, intraoperative recognition of a need for segmental mandibulectomy, or substantial marginal mandibulectomy, after performing an access mandibulotomy, will place the patient at risk of unplanned extension of the operative procedure, without adequate reconstructive support, leading to poor wound healing and suboptimal functional outcome. Therefore, detailed and accurate pre-operative evaluation is necessary for surgical planning. This includes a thorough head and neck examination and appropriate imaging, commonly computed tomography scan and panoramic dental X-rays, to evaluate the relationship of the tumor to the bone, and the status of the teeth.1–4 Preoperative dental evaluation is essential, and some authors have underscored the importance of optimizing oral hygiene preoperatively to reduce the risk of bacterial translocation.5
Risk Factors for Complications
The risk factors for wound infection after surgery for oral cavity and oropharyngeal tumors are readily identifiable. Diabetes, impaired nutritional status, and blood transfusion are all significant independent predictors of postoperative wound infection on multivariate analysis.6 The first two conditions underscore the importance of medically and nutritionally optimizing patients in the preoperative and perioperative periods. Risks associated with blood transfusion are likely to be attributable to the escalated extent of surgery signified by the need for transfusion; however, blood transfusion does have immunosuppressive sequelae and it is prudent to optimize hemostasis during surgery.7 In addition, poor dental hygiene, with grossly infected teeth, and previous exposure to radiation, also contribute to the risk of infection. Risks specifically associated with mandibular plating can be inferred from the mandibular trauma literature, which has established tobacco and alcohol use as a strong independent predictor of infectious complications or bony nonunion.8–12
Because oral cavity or oropharyngeal surgery requiring enhanced access is clean-contaminated surgery, prophylactic antibiotics (a first-generation cephalosporin and metronidazole, or clindamycin) should be given before skin incision and continued for 24 to 48 hours.1 Contemporary research has not confirmed any effectiveness for extended antibiotic use beyond the perioperative period in decreasing rates of infection.13 Therefore extended antibiotic use is usually limited to high-risk patients.
Mandibulotomy
The lip-splitting mandibulotomy was first described by Roux in 1839,14 and was subsequently described by others, including Sedillot15 and Trotter.16 Although the mandibulotomy fell out of favor during the era of composite mandibular resection, it was later understood that mandibular resection is not universally required in all patients in whom a tumor is encroaching on the mandible.4,17 Subsequently, interest in the mandibulotomy was rekindled by Spiro and colleagues at Memorial Hospital in New York in the 1980s.18–21 Compared with the pull-through or visor flap approaches, the lip-splitting mandibulotomy affords unparalleled exposure to the posterior oral cavity and oropharynx, although it was initially viewed by many as a disfiguring operation, subject to frequent complications. Technical refinements supported by contemporary outcomes data confirm that this technique can be performed with favorable aesthetic and functional outcomes, and with a low risk of morbidity.
Complications after Mandibulotomy: Historical Data
The safety of mandibulotomy in radiated patients was once controversial. However, the consensus of contemporary evidence is now that there is no escalated risk of complications after mandibulotomy, either in patients with a history of radiation therapy or in patients who go on to receive postoperative radiation therapy.22–24 There is extensive literature describing the incidence and nature of complications after mandibulotomy. The largest series of mandibulotomies for oral or oropharyngeal cancers consists of 313 patients from Memorial Hospital, reviewed by Dubner and Spiro18 in 1991. A total of 44% of patients experienced minor or major complications: 19% developed hardware exposure, 14% developed soft tissue wound infections, and 11% developed cardiac or pulmonary complications. The majority of local complications were minor and resolved with conservative measures such as drainage or wound packing. Other series have confirmed comparable rates of wound infection, ranging from 5 to 42%, and rates of fixation failure ranging from 0 to 26%.22 Recent data drawn from 220 patients at the University of Alberta revealed a 7.7% rate of wound infection, and 2.7% rate of fixation failure.22,25 These historical data can be challenging to interpret, as they reflect a variety of different surgical techniques, in addition to significant advances in plating and radiation therapy techniques over the past 30 years. This section will focus on technical refinements focused on preventing complications related to the incision, osteotomy, and bone fixation.
Incision Design
Skin Incision
The mandibulotomy typically necessitates a lip-splitting incision. Several authors have described the technique for paramedian mandibulotomy using only a cervical incision and no lip-splitting incision, mainly to enhance transcervical access to the parapharyngeal space, without swinging the mandible laterally.26,27 Although this approach offers the potential benefits of avoiding a facial incision and tracheotomy, it provides very limited exposure, because of the minimal mobility of the divided segment of the mandible, and does not enhance access to the oral cavity or oropharynx. For access to these areas, a lip-splitting incision and mandibular swing are necessary parts of the mandibulotomy approach. However, the lip-splitting incision need not be aesthetically disfiguring, if carefully planned and meticulously closed.
The facial incision can be designed in one of four ways: midline,14,16 lateral,28 midline with a circummental extension,29,30 or midline with a chevron in the mentolabial sulcus31 ( Fig. 15.1 ). These approaches were compared in 60 patients by Rapidis et al32 from Athens. The lateral incision was associated with the poorest outcomes, both cosmetic and functional, notably a high rate of oral incompetence with food and saliva because of facial nerve and mental nerve transection. Midline incisions avoided these sequelae and achieved favorable cosmetic outcomes as rated by both patients and physicians. Similar results were reported by Dziegielewski et al25 from Alberta, who administered validated scar and functional quality-of-life instruments to patients undergoing either midline lip-splitting mandibulotomy or peroral resection. Levels of scar satisfaction and functional outcome after lip-splitting mandibulotomy were equivalent to those in patients undergoing peroral resection, confirming that meticulous closure of the midline lip incision results in good aesthetic outcome. To reduce the possibility of linear scar contracture, several authors have advocated placement of a chevron, either in the labiomental sulcus or the submental region.22,31,33 Rapidis, Hayter and McGregor′s groups have advocated the circummental extension, to avoid scar contracture and loss of chin pad contour, and to respect the chin aesthetic subunit.29–32 Although Rapidis et al32 did not observe a significant advantage of any modifications to the straight midline incision, these incision designs may have utility in patients at risk of hypertrophic scarring. To facilitate precise closure of the vermilion border of the lip, a stair-step or chevron incision can sometimes be helpful, although this is not strictly necessary. We prefer a straight midline lip-splitting skin incision. Precise repair aligning the vermilion border, sublabial, mental, and submental skin creases, gives an excellent aesthetic result.
Mucosal Incision
Before making the paralingual mucosal incisions, care should be taken to preserve at least a 1-cm cuff of gingival mucosa for closure, to minimize salivary leakage, hardware exposure, infection, and possible fistula formation. Meticulous closure of the trifurcation in the vestibule at the junction of the midline lip and marginal mucosal incisions is necessary, as this overlies the osteotomy and is a frequent location for wound breakdown.34
Incision Closure
At closure, the stumps of the divided mylohyoid muscle should be reapproximated: although this closure is imprecise, it helps to obliterate the dead space.1 Before skin closure, the orbicularis oris muscle should be carefully reapproximated to best preserve oral competence. A mentalis-tacking stitch, to anchor the mental soft tissues over the midline chin, may help to maintain chin contour and protect the inferior aspect of the osteotomy site.21 Before closing the skin, a single interrupted nylon stitch is first used to precisely align the vermilion border of the lip, as a disparity as small as 1 mm will be evident to the eye.1,35 The skin should be closed meticulously with fine permanent suture.
Osteotomy
Location
There is a significant range of surgeon preference with respect to design of the mandibular osteotomy. Osteotomy sites can be either midline,5,14,36 paramedian,1,4,5 or lateral (through the body or angle of the mandible). The lateral osteotomy is not recommended because of a high rate of complications, attributable to transection of the inferior alveolar nerve, disruption of blood supply to a large segment of distal mandible, unequal muscle pull on the lateral and medial bone segments, and placement of the osteotomy site within radiation fields. The midline mandibulotomy avoids these problems, but it places the roots of both central incisors at risk, unless one is extracted. In general, dental extraction at the time of mandibulotomy should be avoided because the empty socket becomes an additional possible focus of infection. Furthermore, midline mandibulotomy requires division of the geniohyoid and genioglossus from the genial tubercle, delaying rehabilitation of swallowing and chewing function. The genioglossus muscle draws the tongue inferiorly, reducing its convexity, and channeling fluids posteriorly. The geniohyoid muscle pulls the hyoid bone and tongue anteriorly, facilitating swallowing. For these reasons, a paramedian osteotomy, located between the lateral incisor and canine, or between the canine and first premolar, is the preferred site. This location permits preservation of muscle insertion at the genial tubercle (except for the mylohyoid, which is divided with minimal functional consequence), and remains anterior to the mental nerve, permitting its preservation. There is a greater angle of divergence, and wider horizontal distance, between the roots of the canine and lateral incisor than between the roots of the two central incisors, meaning that osteotomy is less likely to injure teeth if placed in the paramedian location.5
After incising the periosteum by the midline, care must be taken to minimize elevation of periosteum off the surface of the mandible, as this compromises periosteal blood supply to the anterior mandible. The mental nerve must be identified and preserved in its foramen to minimize the likelihood of postoperative oral incompetence. Depending on the size of plate chosen, the contralateral periosteum may not need to be elevated to the contralateral mental nerve.
Note
It is helpful to adapt plates to the mandible contour, drill holes, and measure depth for screw lengths before the osteotomy, to facilitate restoration of the mandible to its native orientation after tumor resection. This minimizes the probability of postoperative malocclusion.
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