Iliac Crest Tissue Transfer

The composite tissues available for free-tissue transfer reconstruction of bone-containing defects of the head and neck are from the fibula, iliac crest, scapula, radius, and metatarsal. This article describes the iliac crest flap, which is based on the deep circumflex iliac artery (DCIA).[1] This flap has many of the desirable qualities of an ideal flap for reconstruction of composite defects of the maxilla and mandible. The flap can be harvested simultaneously with resection or preparation of the recipient bed. The anatomy is predictable, and the bone stock can reliably support dental rehabilitation. The vessels are of appropriate caliber, and the pedicle is usually of sufficient length.[2]

The image below depicts iliac crest tissue transfer.

 

The reconstruction of composite bone-containing defects of the head and neck has always posed a major challenge to head and neck surgeons. Free-tissue transfer has brought valuable additional tools to the armamentarium of the reconstructive surgeon. The mandible often is the focus of head and neck reconstruction because of its proximity to the most common locations for the development of intraoral carcinoma (ie, floor of mouth, tongue, retromolar trigone area). Advanced tumors of the oral cavity require adjuvant radiotherapy and complete surgical resection to achieve appropriate rates of disease control.

Chemotherapy may also be necessary, depending on the extent of the lesion. When these advanced tumors encroach upon or invade the mandible, mandibulectomy is required. Reconstruction of the mandible is often necessary to facilitate airway protection, tracheostomy decannulation, oral nutrition, dental rehabilitation, and the establishment of acceptable facial contour.[3]

From the viewpoints of cost and rehabilitation time, primary reconstruction has proven to be the most appropriate method of therapy. Mandibular reconstruction using free bone grafts has unacceptable rates of infection. Reconstruction using only a bone plate is associated with significant complication rates (eg, plate dehiscence, plate fracture) and fails to meet the requirements of rehabilitation. The surgeon performing mandibular reconstruction secondarily often has the added difficulty of working within an irradiated field.

The free groin flap was one of the first revascularized free-tissue transfers described. Following its description, numerous attempts were made to include the ilium in the flap; however, these efforts proved to be unreliable. No doubt, interest in such a flap for mandibular reconstruction was based on Manchester's description of the anatomic and structural similarities between the anterior ilium and the mandible.

Taylor et al and Sanders and Mayou were the first to recognize the deep circumflex iliac vessels as the dominant blood supply to the anterior ilium. Dye studies demonstrated that the deep circumflex iliac vessels provided perfusion to the ilium through endosteal and periosteal mechanisms.[4, 5] The same year, another study described perforators through the multiple muscular layers of the abdominal wall from the DCIA and the deep circumflex iliac vein (DCIV) to the skin that overlies the anterior ilium. Subsequent work showed that the ascending branch of the deep circumflex vessels was responsible for blood supply to the internal oblique muscle.[6]

The indications, utility, advantages, and disadvantages of the DCIA flap in oromandibular reconstruction were nicely outlined in a couple of articles.[7, 8] One specific indication reported for this flap (as well as a major advantage) is for reconstruction of through-and-through defects of the oral cavity, mandible, and skin. At the same time, one of the most significant problems is the thickness of the soft tissue component and the relative immobility of the skin element in relationship to the bone. Where possible, the internal oblique muscle is used for intraoral lining to circumvent this problem.

Brown contributed to the DCIA flap literature by describing use of the flap for maxillary reconstruction; he demonstrated the adaptability of the flap through various alterations in its orientation to the myriad defects that are encountered in immediate maxillary reconstruction.[9]

The deep circumflex iliac artery (DCIA) flap may be used for mandibular reconstruction, especially in patients with full dentition[10, 11, 12, 13] .

The DCIA flap is indicated for the reconstruction of composite bone-containing defects of the maxilla and mandible. Insufficient bone is contained in the flap to reconstruct an entire mandible. The ability to simultaneously transfer bone, muscle, and skin allows for the reconstruction of complex and large deformities. In current practice, ablative surgeries for neoplastic conditions of the oral cavity, trauma, inflammation, osteoradionecrosis, and congenital deformities are the most common indications for DCIA flaps.[14]

DCIA flaps remain the flap of choice for dentate patients. The fibula free flap, on the other hand, is more useful in edentulous patients or those patients with significant mandibular defects.[15]

Publications describing the use of the iliac crest are limited in number, compared with other options. These other options include the osteocutaneous radial forearm free flap (for small lateral defects) and the fibula and scapular free flaps (larger, through-and-through defects).

The DCIA originates on the lateral aspect of the external iliac artery. The diameter of the DCIA at its branching from the iliac artery is 2-3 mm. The DCIA gives off an ascending branch that supplies the internal oblique muscle. This branch typically arises at or about the anterior superior iliac spine (ASIS). The artery provides blood supply to the ilium through periosteal and endosteal branches. Musculocutaneous perforators provide arterial blood supply to the skin overlying the iliac crest. Rarely, the ascending branch and the DCIA have separate origins from the iliac vessel.

The DCIV follows a similar course to the artery. It is slightly longer because the iliac vein is more medial. A small branch always joins the vein just before its origin from the iliac vein. The vein diameter is 3-5 mm.

The vascular pedicle is found in a prominent groove medial to the iliac crest. It is encased within the fascia of the iliacus and transversalis muscles. The vascular pedicle is not seen directly, and a full-thickness muscle cuff must be harvested (approximately 2.5 cm) on the medial aspect of the iliac crest to avoid injury to the pedicle.

The vessel size and length is substantially shorter compared with other microvascular flaps (osteocutaneous radial forearm, fibula, scapula) available for reconstruction to the maxilla and mandible.

The lateral femoral cutaneous nerve has a variable relationship to the vascular pedicle; alternately, it can lie deep or superficial to the vascular pedicle, or it can lie between the vascular pedicles.

Besides prior surgery with injury to the vascular pedicle, chronic cough and steroid use are considered the only contraindications to using the DCIA flap. These situations increase the risk of hernia formation to an unacceptable degree.

In patients who have preexisting impaired mobility due to lower extremity problems, harvesting the flap from the most functional extremity should be discouraged because the recovery process can be protracted.

CT assists in the definition of the extent of the required resection. Evidence of bone resorption is best appreciated by the direct examination of specific bone-enhancing images (bone windows). The printout of life-sized images (1:1 reproductions) and the creation of templates have been described as useful in mandibular reconstruction. These templates can assist the surgeon with molding and recontouring the flap, but these techniques are not widely available and can be costly.

A panoramic radiograph is reportedly effective in predicting bone involvement by overlying squamous cell carcinoma. The additional benefit of demonstrating the presence of dental pathology, which may alter the decision to extract or maintain teeth, also should be considered.

Base flap selection on the careful evaluation of the patient and the defect. Evaluate the defect in terms of the component tissue deficits.

Proper patient selection is paramount. Carefully evaluate patients to exclude the possibility of prior surgical compromise to the donor site. The presence of significant atherosclerosis within the iliac-femoral system is a concern; however, this disease process has not been reported to extend to the deep circumflex vessels. Consider activity level and daily work. The author generally selects other flap donor sites when the patient's occupation or recreational activities place major strain on the abdominal wall. In general, conduct a risk/benefit analysis of potential donor sites for the characteristics of each specific patient.

Patients are kept as near euvolic as possible. Excessive hydration has no value and may prove harmful secondary to interference with normal respiratory function. The author believes that the past practice of overhydration has no role in free-tissue transfer. Recently published evidence supports the abandoning of this practice.

Head and neck procedures, especially those that require free-tissue transfer, often take considerable time to complete. Ensure that appropriate control of the patient's temperature is maintained. The increase in myocardial oxygen demand associated with hypothermia is well documented; temperature regulation is not a specific requirement of the flap. Preservation of appropriate peripheral perfusion is an additional reason to maintain the patient's temperature.

In general, the use of anticoagulation (heparinization) of patients undergoing free-tissue transfer has been discontinued. Aspirin is commonly administered daily beginning the night of surgery. Reports have documented the vulnerability of the flap vessels to compression by hematoma. The incidence of hematoma in patients who are anticoagulated is too high to warrant continuation of this in routine cases.

The harvest of the DCIA flap violates all layers of the abdominal wall except the peritoneum. In some patients, the use of polypropylene mesh seems to strengthen the closure of the wound. The propylene mesh generally is fixated to the residual ilium through drill holes laterally and to the external oblique muscle fascia or linea semilunaris anteriorly.

To avoid undue straining against the repair during the early postoperative period, perform a presurgical initiation of a bowel regimen the week before surgery. Straining is a concern because these patients typically are in need of narcotic medications in the preoperative and immediate postoperative period. Administer stool softeners when narcotic pain medications are necessary or the week before surgery, whichever comes first. If the patient does not have a bowel movement in the first few days following the reinstitution of enteral nutrition, add motility agents to the regimen. Appropriate hydration also must be provided.

Position patients with a folded sheet under the hip on the donor side. Generously shave the pubic region. Place adherence plastic drapes to exclude the genitals. Ensure that the entire desired field is included in the standard skin preparation and draping by marking the surgical anatomic landmarks before skin preparation. The relevant landmarks are the inferior costal margin, midline of the abdomen, inguinal ligament, iliac crest/spine, femoral vessels, and the skin incision/skin paddle. Visualization of the vascular pedicle is improved with slight rotation of the bed toward the side of the harvest and the avoidance of the reverse Trendelenburg position.

Skin paddle

Minimal difference exists between the harvest of the flap with cutaneous, muscle, and bone elements and the harvest of the flap without the skin. If the skin is to be harvested with the flap, mark out an elliptical skin island to incorporate the zone of the musculocutaneous perforators that exists along the iliac crest from the ASIS approximately 9 cm posteriorly and extends medial to the crest approximately 2.5 cm. The skin paddle generally is centered over this zone. The superior incision must be made first to allow careful dissection between the subcutaneous tissue and the external oblique fascia to identify the musculocutaneous perforators (see the image below).

Identification of the internal oblique and ascending branch

Make an incision at least 2.5 cm away from the iliac crest through the external oblique muscle. Then, dissect within the avascular plane between the external and internal oblique muscles (see the first image below). Extend the dissection and retraction to the costal margin superiorly and the linea semilunaris medially. Incise the internal oblique muscle and isolate it from the underlying transversalis muscle. The change in muscle fiber direction helps delineate this plane. Careful dissection allows identification of the DCIA ascending branch.

The ascending branch is then followed to its junction with the DCIA/DCIV, most often just medial to the ASIS. Proceed with the dissection by isolating the flap vessels to their origin at the external iliac vessels. The position of the lateral femoral cutaneous nerve can vary; it has been identified deep to, superficial to, or between the DCIA/DCIV (see the second image below). A rare anatomic alteration in which the ascending branch has a separate take-off from the external artery has been identified.

Bone harvest

Divide the transversalis muscle and identify the iliacus muscle (see the image below). Divide the iliacus at the site of the planned bone cut. Then, complete the lateral skin incision and dissection. Release the fascia and muscles from the lateral surface of the ilium to the level of the planned bone cut. The author seldom harvests the ASIS because, by not harvesting the ASIS, the insertion of the inguinal ligament is preserved and provides a structure to which the polypropylene mesh is attached. The bone cuts are made with an oscillating saw. The direction and extent depend on the recipient bed defect. Careful retraction and protection of the bowel are required.

Bone contouring

Following ligation of the pedicle and transfer to the head and neck, contour the bone portion of the flap to meet the dimensions of the bone defect (see the image below). Accomplish this by opening osteotomies. These bone cuts traverse the lateral cortex and crest of the ilium without violating the inner cortex. Out-fracturing of the ilium allows it to be bent to shape without compromising the vascular pedicle. The author prefers to adapt the plate to the defect initially and then adapt the bone to the dimensions of the plate.

Secure the bone to the plate and complete the soft tissue inset before the microvascular anastomosis. Pack free cancellous bone into the opening osteotomies. Generally, wrap the internal oblique around the bone if it is not needed elsewhere (see the image below). When exposed to the oral cavity, the muscle undergoes rapid mucosalization. When the resection is limited to the mandible and the soft tissues directly adjacent to it, the muscle forms an excellent mucosalized surface. The muscle atrophy results in a thin but highly vascularized covering of the neomandible. Likewise, when performing maxillary reconstruction, a thin fixed surface is desirable. Design the flap harvest and inset so that the pedicle lies on the lingual surface of the mandible or the medial surface of any opening osteotomies.

As with any free flap, postoperative monitoring is essential. Protocols vary; the author's monitoring protocol is described. Nursing documentation of flap color and capillary refill occurs every hour for 48 hours. Physician evaluation is accomplished at least every 6 hours. A 25-gauge needle stick test may be used to clarify the clinical examination as indicated. After the first 24 hours, patients generally are transferred to the regular nursing unit where the physician flap evaluations continue. Patients receive an aspirin per day to inhibit platelet adhesion; this is continued for 60 days.

Patients are kept at bedrest for 3-5 days. Thereafter, a progressive program of ambulation is begun. Nutrition is begun when bowel sounds are present and low-rate tube feeding is tolerated without distension or reported fullness.

Routine follow-up care of patients following DCIA flap reconstruction requires assessment of the operative site for healing without hernia formation, progressive ambulation, and gradual return to unrestricted activity. Physical therapy evaluation and intervention are helpful, if not imperative. A normal gait is expected with appropriate healing and rehabilitation. Compared to the donor site rehabilitation following a fibula harvest, that of the DCIA requires additional time (approximately 1 mo) to achieve pain-free normal mobility.

Flap failure

With careful attention to flap design and harvesting, excellent success rates can be achieved. In general, the healing of the bone portion of the flap is rapid. To avoid extreme angles, kinking, or redundancy, strongly consider the design of the flap and the geometry of the pedicle-recipient vessels. The skin paddle must be designed over the zone of musculocutaneous perforators and is not mobile. In general, the author does not attempt to isolate the entire skin paddle on one perforator to achieve mobility. If mobility of the skin paddle is necessary, then select another flap or an additional flap.

Hernia

Significant weakness of the abdominal wall is produced by the harvest of one of the layers of abdominal muscle. Use direct closure only in the healthiest patients. The author prefers to manage the donor site by supporting the wound closure with polypropylene mesh secured to the residual ilium. The author has not witnessed the formation of a hernia in a patient in whom mesh reconstruction was completed.

Hemorrhage

Particular attention to hemostasis is necessary to prevent the formation of a hematoma. Careful ligation of vessels is mandatory. Hemostasis can be achieved at the bone cuts with bone wax. Drains are indicated in a deep plane and in the subcutaneous tissue.

Skin perforation

A retrospective study by Ritschl et al using free fibula flaps and iliac crest flaps indicated that these microvascular bone flaps lead to less skin perforation than do plates, in mandibular reconstruction.[16]

As with all reconstructive surgery, weigh the potential value of any operation against the donor site deformity. All proposed flaps that meet the criteria required by the defect should be evaluated for their individual merit. The DCIA flap has equal applicability to anterior and lateral defects when the soft tissue requirements of the defect are suitable. In the author's experience, rapid healing and dental rehabilitation have been accomplished with fewer difficulties than in patients reconstructed with a fibula flap (see the image below).

A study by Chen et al reported good results from the use of chimeric DCIA perforator flaps in the reconstruction of oromandibular defects, citing satisfactory alveolar ridge restoration, as well as the benefits of high mobility between the skin paddle and the bone component in composite defect repair. The flap was successfully harvested in five of six patients undergoing the surgery, with all flaps surviving.[17]

The DCIA flap has been used worldwide for 2 decades and has proven utility and reliability. It is a valuable addition to the armamentarium of any surgeon performing head and neck reconstruction. Discussion between reconstructive surgeons regarding their indications for the use of any particular flap in a specific instance will always occur.

The freshly isolated connective tissue progenitor and culture-expanded mesenchymal stem cell populations can be derived from both the anterior and posterior iliac crest for therapeutic application. The yield of colony-founding connective tissue is 1.6 times greater in the posterior compared with the anterior iliac crest.[18]

Immediate placement of osseointegrated implants into the flap remains a topic of considerable debate. Patients requiring a major resection and bone reconstruction obviously have advanced disease; in most instances, the survival rate for such patients is unpredictable. Plenty of evidence exists indicating that the implants heal with acceptable rates of integration when primarily placed at the time of reconstruction and that they can reliably be placed in the primary setting in a position useful for dental rehabilitation. This discussion represents yet another situation in which potential benefit must be carefully evaluated against cost and complications.

A literature review by Khadembaschi et al indicated, using pooled analysis, that the 5-year survival rate for osseointegrated implants in fibula and iliac crest free flaps is 94%, with the same rate seen in both types of flap. Implant survival was reportedly affected by factors such as radiotherapy and malignant disease.[19]