Two in one: Double free flap from a single free fibula osteocutaneous unit

Abstract

In the past two decades, the advancement in the microsurgical techniques has revolutionised the reconstruction of post-oncological head and neck defects. Free fibula osteocutaneous flap (FFOCF) has been considered as the treatment of choice by many for mandible reconstruction. The improvement in the surgical resection and adjuvant treatment has improved the survival rates even in patients with advanced cancer. Simultaneously the reconstruction is addressed towards more functional and aesthetic aspects to improve the quality of life in these patients. In this respect, a double free flap is advocated in certain cases of extensive composite oromandibular defects (COMDs). But in our institute, we have managed two such cases of extensive COMD with a single FFOCF unit – fibula bone with a skin paddle for inner lining and a perforator-based skin paddle from the proximal part of the FFOCF unit, anastomosed separately for outer cover. Compared to two separate free flaps, this method has the advantage of single donor site and reduction in reconstruction time. Though the technique of divided paddle, deepithelisation and supercharging has been mentioned for FFOCF, no such clinical cases of two free flaps from a single FFOCF unit have been mentioned in the literature.

INTRODUCTION

Reconstruction of composite oromandibular defects (COMD) is a challenging task as it involves different tissues, needs large size flap for both lining and cover, and requires tridimensional inset of flap to maintain contour and function. The extensive composite or “en bloc” defects as described by Daniel et al.[1] comprise skin, bone, mucosal lining and an additional soft tissue component. There is an increasing trend towards double free flap reconstruction for these defects.[2,3] The bone and the mucosal lining are reconstructed with free fibula osteocutaneous flap (FFOCF) in all these patients and the second free flap is used for the external lining. We present two cases in which the external skin defect was managed with a free flap based on a perforator from the proximal part of the FFOCF.

CASE REPORT

Both the patients were cases of cancer lower alveolus with T₄ stage and involvement of skin. The intraoperative details regarding the bone defect, external skin requirement and their locations are shown in Table 1.

Table 1.

Details of patient, bone defect and skin defect dimensions

Operation details

The resection was done by the head and neck oncosurgery team. Both cases were planned for middle one-third segmental mandibulectomy and bilateral Modified Neck Dissection. The skin excision was done based on clinical examination, intra-op findings and frozen section reports.

The FFOCF is harvested under tourniquet control by the anterolateral approach. We always harvest on the left side unless contraindicated.[4] We do preoperative hand-held Doppler examination for locating the perforators. For composite defects, we design FFOCF with a larger skin paddle with more width on the proximal aspect as this skin flap usually will come for the external cover. We start harvest simultaneously with the resection team, and do the anterior part of the dissection. Once the final excision markings are done by the resection team, we modify the skin paddle and make the posterior incision accordingly. If the tentative excision plan shows that the combined internal and external defect is larger than the fibula skin paddle, then we plan for a second free/pedicled flap. Osteotomy and contouring are done on back table. The neomandible fixation, intraoral inset and the anastomosis are done in sequence. The anastomosis details are shown in Table 2.

Table 2.

Time and details of anastomosis

Case 1

This patient was a case of cancer lower alveolus crossing midline. The patient received 3 cycles of neo-adjuvant chemotherapy. Sutures are taken prior to chemotherapy to identify the extent of the skin involvement. The patient had a contour deformity on the right side face post chemotherapy [Figure 1a and b]. The resection included the mandible excision from right ramus to left body, B/L Type III MND and the involved skin [Figure 2]. During flap harvest, the FFOCF skin paddle had only one perforator distally. It had an additional perforator in the proximal part (upper one-third of leg), 10 cm from the head of fibula, which was dissected separately for about 6 cm in length. The perforator was harvested with a cuff of soleus muscle and the additional time required was 20 min. This pedicle could not be dissected up to the origin since it was deep in the region of the popliteal/tibio-peroneal trunk. After the bone fixation [Figure 3] and intraoral inset, we attempted dedeepithelisation for the external cover. But the skin paddle did not have adequate perfusion distally [Figure 4a]. The lie of the pedicle was not appropriate for supercharging. Hence, the paddle was divided, insetted in appropriate position [Figure 4b] and a separate set of anastomosis done based on the perforator [Figure 5].

Figure 1.

Pre-op – (a) Frontal view, (b) worm's eye view

Figure 2.

Intra-op – Defect

Figure 3.

Contoured fibula

Figure 4.

Intra-op: (a) Attempted deepithelisation, intra-op; (b) external skin paddle with the pedicle

Figure 5.

Intra-op picture showing anastomosis: A1 V1, bone and intraoral paddle; A2 V2, external paddle

Case 2

This patient had the disease predominant on the left side but crossing the midline [Figure 6a and b]. This patient had an external skin defect in the anterior and submental region and the bone defect from left ramus to right body [Figure 7a and b]. Since the defect was in different planes, we expected a difficult inset with the same flap, and hence dissected the perforator of the proximal skin paddle. In this case, there was no peroneal perforator proximally. But a soleal perforator was identified 8 cm from the head of fibula and dissected up to its origin from the posterior tibial artery. The perforator dissection took 25 min. After the bone fixation and the intraoral inset, the remaining skin paddle along with this perforator was divided [Figures 8 and 9]. This was later anastomosed on the same side of the primary anastomosis [Figure 10].

Figure 6.

Pre-op: (a) AP view, pre-op; (b) mouth open view showing the lesion

Figure 7.

Intra-op: (a) External skin defect, (b) bone defect

Figure 8.

Intra-op – Neomandible fixed and intraoral inset

Figure 9.

Divided proximal skin paddle with the pedicle

Figure 10.

Intra-op – Anastomosis: A1 V1a V1b, bone and intraoral paddle; A2 V2, external paddle

Post-op course

All the four free flaps survived completely. Patient 1 had neck wound infection which settled after a course of antibiotics. The contour deformity in patient 1 had also been corrected by the skin paddle used for external cover [Figure 11a]. Donor site graft take was 100% and the patients were mobilised on POD-5 with support. The flaps settled well [Figures 11b–d, 12a and b] and both patients were discharged on day 10. Patient 1 received adjuvant post-op radiotherapy (RT) as per the schedule and there was minimal reduction in flap volume [Figure 11e]. The absence of facial muscles which maintain the skin turgor, the effect of post-op RT and reconstruction of the various aesthetic subunits of face with a single paddle are the reasons for the contour deformity in the late post-op. But as far such large defects are concerned, these results are definitely considered to be acceptable.

Figure 11.

Post-op: (a) Immediate, post-op; (b) AP view, post-op; (c) mouth open showing intraoral and external paddle, post-op; (d) worm's eye view; (e) post RT

Figure 12.

Post-op: (a) AP view showing intraoral paddle; (b) post-op showing outer paddle

DISCUSSION

Reconstruction of the oromandibular defects by free flaps has superior results both functionally and aesthetically compared to pedicle flaps.[5,6] Though most of the defects can be covered with a single free flap, multiple free flaps in head and neck reconstruction have been described for indications such as increased soft tissue requirement, need for inset in different planes and requirement of tissues of different texture and thickness to optimally replace missing tissues.[6–8] In these cases of multiple free flaps, the FFOCF is used for the bone defect and the inner lining. For the external cover, the flaps that are described are ALT, free radial forearm, rectus abdominus flap and lateral arm flap.[3] Wei et al.[9] advocate ALT compared to others because of the ease of simultaneous harvest, low donor site morbidity, possibility of primary closure and the advantage of primary thinning. But all these cases have an additional donor site.

There are many reports regarding the reliability of the skin paddle of the fibula free flap. But now it has been established anatomically and clinically that the skin paddle of the free fibula osteocutaneous is reliable.[10] The skin component of the flap is supplied predominantly by septocutaneous perforators[11] in the lower two-thirds of leg. According to Wei et al.[12,13] most of these perforators are concentrated between the mid one-third and lower one-third junction. The study by Yu et al.[14] has also shown that these distal perforators are mostly septocutaneous and are consistently present in the third quarter of the fibula. In the proximal one-third of the leg, the skin is usually supplied by musculocutaneous perforators.[10,14] They pass through soleus, gastrocnemius or flexor hallucis longus before reaching the skin. The incidence of these musculocutaneous perforators is variable. In the anatomical study by Jones et al.[10] the incidence of the musculocutaneous perforators was 67%, and the clinical analysis of the perforators by Yu et al.[14] has shown the incidence of these musculocutaneous perforators to be as high as 84%. But none of these studies has mentioned the exact location or reference points for these perforators as these are not commonly used in free fibula flap.The origin of the musculocutaneous perforators can be from peroneal artery, popliteal artery or posterior tibial artery.[15] Separate anastomosis of these perforators to salvage the flap has been reported in the literature.[16,17] But in these cases, the perforator anastomosis is used as superchargers. But complete harvest of the skin paddle as a free flap and using for COMD has not been mentioned.

The other methods for using the same FFOCF for lining and cover are deepithelisation[18,19] and division of skin paddle based on perforators.[20,21] The disadvantages of deepithelisation are part of the flap is wasted while turning out the skin paddle, extra time and altered contour at the suture line. Moreover, the survival of the distal part is dependent on the quality of the proximal perforator, the depth of deepithelisation and the thickness of the dermis. In cases where the flap has two or more perforators, the skin paddle can be divided based on separate perforators for lining and cover. In such cases, preserving this proximal perforator may limit the actual pedicle length and there is a possibility of traction on the pedicle. In our experience of more than 200 free fibula flaps for composite defects, we have found in few cases that location of these perforators may not be suitable for a divided paddle providing inner lining and outer cover.

Hence, in cases where a large COMD is expected, during harvest of the fibula, the perforator in the proximal part of the FFOCF is dissected till its origin or the maximum possible length. We harvest with a cuff of muscle to safeguard the perforator. After bone fixation and intraoral inset, the options for the external cover using the same fibula osteocutaneous flap are: (i) deepithelisation, (ii) dividing the skin paddle based on different perforators for lining and cover and (iii) complete division and thus converting into a free flap. Deepithelisation is done when there is (i) A single good perforator, (ii) Adequate length of flap for deepithelisation and external cover, and (iii) Pliable skin quality for turning the flap without compression of the perfortor. The criteria for division of the skin paddle based on the perforators are the presence of two or more perforators and the location of the perforator should be appropriate for division. If the lie of the perforators is not appropriate and the flap not suitable for deepithelisation, then the remaining flap could be divided and converted into a free flap based on the perforator. The flap based on the perforator should be divided once the intraoral inset is completed or the lining defect is appropriately calculated. This allows for maximum utilisation of the flap tissue for the large external defect. This skin paddle is insetted for the outer cover and a separate set of anastomosis is performed. The technique of converting the attached skin paddle into a perforator-based free flap gives more leverage for placing the pedicle, allows better lie of the flap and a smooth contour at the flap native skin junction.

In both our cases, the bone defect was extending from one side ramus to the opposite side body. Hence, the inner lining required is also more. At the same time, the external defect was in a different plane, hence becomes difficult to turn the flap and cover. Moreover, there was no possibility of dividing based on perforators as there was only one distal perforator from the peroneal artery. In patient 1, the proximal perforator was dissected, assuming it was from the peroneal artery. Then finally, an intraoperative decision was made to convert it into a free flap. The experience from the first case made us to cautiously dissect the proximal musculocutaneous perforator in patient 2. Then, the plan was executed in the case. Both the perforator's pedicles had one artery and two veins of size 1.5 mm and 2 mm, respectively, and were suitable for anastomosis.

The vascular status of the lower limb is assessed by clinical examination, and the status of the dorsalis pedis and posterior tibial artery pulsations in both limbs are documented. The perforators over the lateral aspect of the leg should be marked with Doppler preoperatively. But until the time of the flap elevation, it will not be possible to differentiate whether these are musculocutaneous or septocutaneous perforators. But Doppler examination gives an idea and confidence to the surgeon so that extra care can be taken during the dissection of the corresponding regions. Angiography or 3D CT for assessing vascularity localisation of perforators is not done routinely. However, in future, these modalities could be used for planning such cases preoperatively.

This method of reconstruction using two free flaps from the fibula osteocutaneous unit has the advantage of having the same donor site and reduction in overall operative time, compared to a double free flap from two different sites. Basically it is two free flaps: o0ne from the peroneal artery and the other based on the perforator, but are harvested together and can be utilised as needed [Figure 13]. The contour and the tissue utilisation are better when compared to the technique of deepithelisation. The reported incidence of these proximal musculocutaneous perforators can be as high as 84% and furthers favours the plan of identification and dissection of these perforators. The perforators are also of adequate size suitable for anastomosis. These types of cases with such large defects are infrequently met with. In such instances, dissection of the proximal perforator and the idea of double free flap from a single free fibula osteocutaneous unit will provide an additional tool in the reconstructive armamentarium of the surgeon.

Figure 13.

Diagrammatic representation of the two free flaps from single FFOCF

The disadvantage of this technique is that it cannot be applied to all cases where a double free flap is required because we might not have a proximal perforator in all patients. Moreover, the size, length and the exact location of these perforators have not been reported in the literature.

In cases where a large COMD is anticipated, the surgeon should harvest a larger proximal skin paddle and take care to dissect the proximal perforator, whenever present, up to an adequate length to be used if needed. If the expected intraoral mucosal defect and the external skin defect are larger than the designed fibula skin paddle, then a second free/pedicled flap should be planned. This novel method of doing a double free flap from a single free FFOCF unit should be considered in patients where double free flaps from different sites are planned. This reduces the overall operating time and saves another donor site, in case that may be required in the future.