Internal Oblique-Iliac Crest Osteomyocutaneous Free Flap in Oromandibular Reconstruction

M. L. URKEN

The iliac crest osteocutaneous flap, based on the deep circumflex iliac artery and vein (DCIA and DCIV), was a major innovation in oromandibular reconstruction and helped to revolutionize the approach to the management of oral cancers (1). The problem with this composite flap was related to the soft-tissue component, which was often too bulky and unreliable, especially when positioning the skin paddle in ways that threatened its normal anatomic relationship to the bone. Such demands on the skin paddle are frequent when reconstructing the three-dimensional geometry of the oral cavity and oropharynx. The internal oblique muscle, supplied by the ascending branch of the DCIA and DCIV, provides a broad sheet of thin, pliable, and well-vascularized soft tissue that enhances the versatility of the iliac donor site.

INDICATIONS

The advantage of the iliac donor site is that it provides the best source of vascularized bone for stable and retentive implant placement among the three donor sites (i.e., ilium, scapula, and fibula) that are most commonly used for oromandibular reconstruction (2). The choice of the best donor site is based on a variety of factors unique to the patient and the disease process. Choice of the correct flap depends on the dimensions, location, components of the defect and, most important, soft-tissue requirements; the patient’s body habitus; location and quality of teeth in both jaws; irradiation status of the patient; prognosis for survival of the disease process that led to the segmental mandibulectomy defect; whether the reconstruction is done in a primary or secondary setting; and patient motivation. There is no single flap that solves all the reconstructive needs of all patients. The iliac, scapular, and fibular donor sites must be considered and a choice made for all patients undergoing this type of reconstruction. The ilium continues to have definite indications, despite the increasing popularity of the fibula in these reconstructions, especially for patients in whom preoperative angiography demonstrates that the fibular blood supply is not favorable.

Current indications for iliac-crest osteocutaneous or osteomyocutaneous flaps include (a) primary reconstruction of a lateral oromandibular defect with a minimal to moderate defect of the tongue; (b) reconstruction of the symphyseal region in a patient with a dentate residual mandible to achieve parity of bone height of the native tooth-bearing mandibular segment and the neomandible; (c) reconstruction of the symphysis in conjunction with a total or near-total glossectomy (3); (d) reconstruction of the symphysis in a patient who is not a candidate for dental rehabilitation so that the height of the neomandible that can be achieved with the ilium is sufficient to maintain the position of the lower lip and help insure oral competence; (e) reconstruction of the lateral mandible in conjunction with a portion of the infrastructure of the maxilla, where the internal oblique muscle is used to resurface both the oral and sinus aspects of the defect; and (f) reconstruction of composite defects of the oral cavity involving mucosa, bone, and skin.

ANATOMY

The DCIA and DCIV arise from the external iliac artery and vein within 1 to 2 cm above the inguinal ligament. Although the DCIV may run either deep or superficial to the external iliac artery, it always takes a cephalad turn, to enter the external iliac vein up to 3 cm above the junction of the DCIA and the external iliac artery. The DCIA and DCIV travel in a linear course toward the anterior superior iliac spine (ASIS), where they then assume a more curvilinear course along the inner table of the ilium. The pedicle is easily identified at the junction of the transversus abdominis and iliacus muscles, lying from 0.5 to 2.5 cm beneath the lip of the iliac crest (4). During its course, the deep circumflex pedicle gives rise to the ascending
branch, perforators to the ilium and the inner periosteum, and an array of cutaneous perforators that traverse the three muscles of the abdominal wall. These latter perforators exit the external oblique muscle in a zone that extends from the ASIS to a point about 9 cm lateral, where the DCIA terminates as a large cutaneous perforator. The key to ensuring the blood supply to the skin is to be certain to design the skin paddle over this zone of perforators and to harvest a cuff of the three muscle layers to maintain the integrity of these delicate vessels.

The ascending branch(es) of the DCIA and DCIV, which supply the internal oblique muscle, arise at any point from the external iliac vessels to the ASIS. Through cadaver dissections, it has been shown that the ascending branch arises within 1 cm medial to the ASIS in 65% of cases but has a more medial takeoff, from 2 to 4 cm medial to the ASIS, in 15% of cases. In the remaining cases, there is no single dominant ascending branch but rather an array of branches that supply the internal oblique muscle. Therefore, in roughly 80% of cases, the internal oblique muscle has an axial-pattern blood supply with a single dominant ascending branch (1, 5, 6, 7). Because of this axial pattern, the muscle can be maneuvered safely in virtually any direction relative to the bone to restore the anatomy of this region (6, 7).

FLAP DESIGN AND DIMENSIONS

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