Advances in postoperative defect repair for head and neck tumors: free tissue flap grafting The primary goal of surgical treatment of head and neck tumors is to completely remove the tumor to achieve a radical cure; therefore, sufficient safety boundaries should be resected in all directions during tumor resection. In the past, due to the lack of ideal repair means, the surgeon should first ensure that the wound can be closed, which may lead to insufficient tumor resection boundaries and tumor recurrence. Therefore, the surgeon should only perform lesion resection as needed for radical treatment if it is clear that the surgical defect can be properly repaired. The technique of free tissue flap grafting, developed in the last 20 years or so, provides the head and neck surgeon with the assurance that adequate and appropriate resection of the tumor can be achieved. I. Why are free tissue flaps preferred for repair of head and neck defects? Since the 1990s, various free tissue flaps have played an increasingly important role in the repair of postoperative head and neck tumor defects due to their advantages and advances in microsurgery. For example, at the Sloan-Kettering Hospital in New York and the Tokyo Cancer Center in Japan, the proportion of free tissue flap repair to all repair methods has increased from 30% in the 1980s to more than 95%, with a success rate of about 95%. The advantages of free tissue flaps over conventional adjacent or tipped tissue flaps are clear (Table 1). It is particularly advantageous in the resection of recurrent or uncontrolled tumors after previous surgery or radiation therapy. Free tissue flap repair has become an important indicator of the level of head and neck cancer surgery. Various free tissue flap repair methods should be routinely carried out in the clinic to keep up with the world trend for the benefit of patients. II. How to choose a suitable flap for head and neck defect repair? The selection of a suitable flap for the repair of head and neck defects among many free tissue flaps has always been a problem for head and neck prosthetic surgeons. Although head and neck defects are a complex category that encompasses various subregions, practical work has shown that there is no need for a large number of free tissue flaps, and that the use of 4-5 free flaps is sufficient to handle most reconstruction problems [1]. Defects in the head and neck can be broadly classified as oral cavity, mandible, hypopharynx, midface, skull base, skin, and scalp, and according to the principle of similar tissue replacement, appropriate free tissue flaps can be used for different sites and tissue defects [2]. 1. Oral cavity: for partial defects of the oral tongue, a forearm flap or anterolateral femoral flap is recommended to provide thin and soft skin, which can facilitate residual tongue movement and thus restore the quality of articulation; for total or near-total defects, a larger volume of tissue flap is required, and a rectus abdominis muscle flap or a perforator flap of the inferior abdominal wall artery should be selected; for oral mucosal defects other than the tongue, such as the floor of the mouth and buccal mucosa, a thin anterolateral femoral 2. mandibular defects: the bone tissue flaps that can be applied are fibula, iliac and scapular tissue flaps. The peroneal flap is preferred [5] because this free flap provides long enough cortical bone for osteotomy shaping and because the lateral peroneal skin island is more reliable for blood flow and can simultaneously repair concomitant oral mucosal defects. However, the height of the alveolar bone for fibula repair is not high enough, and free iliac bone graft can be chosen. However, the complications in the free iliac bone donor area and the short vascular tip affect its wide application; the scaphoid tissue flap requires the patient to change position to lateral recumbency during excision, and another constraint of the scaphoid tissue flap clinical application is its short vascular tip. 3. hypopharyngeal mucosal defects: most hypopharyngeal mucosal circumferential defects are accompanied by cervical segmental esophageal defects, which are generally repaired with free jejunum, which is more in line with the physiological structure of the tissue compared with skin flaps [6]; of course, anterolateral femoral flap or forearm flap rolled into a tube can be used for repair, and the latter may have better postoperative esophageal articulation quality [7]. Depending on the size of the defect, partial hypopharyngeal defects can be repaired with dissected free jejunal pieces (e.g., posterior hypopharyngeal wall) or anterolateral femoral flaps (e.g., with a larger oropharyngeal defect), and some patients may have preserved laryngeal function at the same time. 4. mid-facial defects: repair of mid-facial defects is the most difficult, because of the three-dimensional defects involving a variety of tissues, the design of the free flap is difficult, and generally speaking, a free flap with a large amount of tissue is required for three-dimensional reconstruction. According to Brown’s typing [8], for maxillary defects type II-IV, free peroneal muscle flaps are generally used to repair the dental arch and hard palate mucosa respectively; if facial skin defects are also present, the need for bone tissue repair takes a back seat to the need to close the operative cavity and restore the feeding function, and we suggest choosing flaps with larger tissue volume, such as the rectus abdominis muscle flap, the inferior abdominal wall artery perforator flap and latissimus dorsi muscle flap. The purpose of skull base repair is to avoid intracranial infection from the oral and nasal cavities and to eliminate dead space, so the rectus abdominis flap or the latissimus dorsi myocutaneous flap are ideal, and the anterolateral femoral flap with broad fascia can also be chosen to repair the composite meningeal-skull defect. For large skin defects of the face and neck that cannot be repaired with local flaps, forearm flaps can be chosen. Large scalp defects can be repaired using a latissimus dorsi flap with skin graft, which has a better shape [9]. III. New advances in flap repair: application of perforator flaps Kroll and Koshima et al [10,11 ] invented a new myocutaneous perforator flap with only skin and subcutaneous tissue based on the myocutaneous flap. They found that as long as the nutrient vessels through the muscle were retained, the flap was still viable even if the muscle as a carrier was removed. Complications in the donor area were also reduced. The advantages of the perforator flap are: (1) preservation of the donor muscle, fascia and nerves; (2) minimization of donor complications; (3) greater flexibility in flap design and better compliance; (4) compliance with the principle of “similar tissue replacement” for a more perfect repair; and (5) reduced postoperative pain, faster recovery and shorter hospital stay. The TRAM flap, deep inferior epigastric artery perforator (DIEAP) and normal human abdominal wall strength were compared, and it was found that the abdominal extensor and lumbar muscles in the TRAM group were significantly weaker than those in the DIEAP and normal human groups; however, the abdominal muscles in the DIEAP group were still weaker than those in the normal human group, suggesting that DIEP making process also leads to weakening of abdominal wall muscle strength. It has also been confirmed that DIEP patients have a reduced postoperative morphine dosage and a correspondingly shorter hospital stay kroll [13]. The anatomical basis of the perforator flap may be based on the concept of “vascular donor area” proposed by Taylor [14]. The study of fresh specimens injected with lead oxide revealed that the human surface can be divided into 40 vascular supply zones based on well-known supply arteries. There are approximately 374 skin penetrations with a vessel diameter of ≥0.5 mm, all of which could be potential penetrating flaps. Clinically applicable penetrating flaps must have the following characteristics: (1) predictable and constant blood supply; (2) at least one or more large penetrating vessels (≥0.5 mm); (3) adequate vessel tip length; and (4) direct suture closure of the donor area. The choice of the type of penetrating flap depends on a variety of factors, such as the desired area and thickness, the size of the cosmetic impact, the patient’s preference, and the experience of the operator. However, some penetrating flaps have their own unique indications, such as DIEAP which is most suitable for breast reconstruction in women. The main contraindication to the application of a thru-branch flap is the lack of larger thru-branch vessels, and in addition, scarring of the donor area and a history of heavy smoking are relative contraindications. From the current bulk reports, the success rate of perforator flaps is high, at 95-97% [15,16]. It is numerically not lower than the conventional myocutaneous flap. III. How to perform free tissue flap grafting? As a surgeon who performs free tissue flap transplantation in the head and neck, the most important qualities are self-sacrifice and dedication, a passionate commitment to the cause, and a collaborative attitude. In order to be competent in free tissue flap transplantation, one can first start with training in the microsurgery laboratory, where one is fully trained in microvascular anastomosis, first doing basic suture tying, then doing apparent microvascular suturing in the rat body, and finally can do animal flap transplantation. It is recommended to attend a short microsurgery course with a special instructor for strict formal instruction, which is generally less costly than training on your own. The second step is to learn the acquisition of free tissue flaps, which should be practiced repeatedly on fresh cadavers when available, or can be learned gradually on the operating table under expert guidance. When the technique is mature, clinical practice can be started from relatively simple microvascular free tissue flaps such as forearm flap, and further more difficult free tissue flap transplantation can be carried out based on continuous accumulation and summary of experience and lessons learned. Large head and neck cancer centers should train their own microsurgical prosthetists, and general hospitals can gradually develop free tissue flap grafting techniques with the help of plastic surgeons or hand surgeons.