Ergonomics of free fibula flap in mandible reconstruction

INTRODUCTION: Composite defects in the oro-mandibular region commonly resulting from trauma and cancer surgeries pose a great challenge for the reconstructive surgeon. It envisages the surgeon’s planning abilities and abstractive thinking about the defect that has to be reconstructed. Seeing that Mandibular defects occur more commonly secondary to wide local excision for carcinoma in the oro-mandibular region, they produce significant morbidity by affecting both the function and aesthetics of the face. Also most carcinoma patients may already have had a course of radiotherapy or might need radiotherapy post-surgically. This imposes further burden on any of the flaps designed to cover the cancer post-excisional defect. Though various local and loco-regional options, like, pectoralis major myocutaneous flap, lattismus dorsi flap, forehead flap, bilobed forehead flap (Narayanan’s flap) are available for covering the defect, they fail to produce optimal functional and aesthetic results and add to the morbidity of the patient. Hence vascualrized free fibula osteomyocutaneous flaps, with better functional and aesthetic outcome have become the mainstay of treatment for defects in the oro-mandibular region. Reconstruction of the mandible not only brings back the contour of the chin, it also acts as base for fixing prosthetic dentition and thus aids in various functions like chewing, deglutition, breathing and speech. Applying the knowledge gleaned from cadaveric dissection in our clinical scenarios had produced improved results in terms of aesthetics and function. This study of ours tries to streamline the various steps of the harvest, transfer and anastamosis of the vascularised free fibula osteomyocutaneous flaps by studying the various parameters in cadavers and applying that knowledge in clinical scenarios to measure the outcome qualitatively and quantitatively. AIMS/OBJECTIVES: Primary Objectives: To do cadaveric dissections with the objectives of, • To find the location of perforator with good size, diameter and length to serve as the single best perforator for chimeric free fibula osseocutaneous/ osseomyocutaneous flap for reconstruction of mandible • To find the safe site for ostectomy and application of contoured plates and screws Secondary Objective: Application of the cadaveric study findings in reconstructive surgeries of oromandibular defects and assessing the outcome, and • To find the best position of pedicle in the graft without any kinking • To ascertain whether the eccentric location of the perforator with respect to the skin paddle helps in positioning and three dimensional manipulation in reconstruction of composite oro-mandibular defects. MATERIALS AND METHODS: Cadaver Studies: A total of 21 legs were dissected and the peroneal perforator system studied by mercurochrome injection studies. Procedure for Cadaver Dissection: Incision was made on the medial aspect of the popliteal fossa and brought down along the anteromedial border of tibia. The soleus muscle attachement to the soleal line is exposed. The Sartorius, Semimembranosus and gracilis attachements to the upper medial aspect of tibia excised and released. Then soleus muscle was detached from the soleal line exposing the posterior tibial vessels and tibial nerve lateral to the flexor digitorum longus. The posterior tibial artery traced to its site of branching into peroneal artery. A syringe containing mercurochrome was injected pushing it distally into the peroneal artery. Simultaneously, we exposed the distal end of the peroneal artery behind the lateral malleolus, where it branches into ramus perforans and lateral calcaneal artery, lateral to flexor hallucis longus, medial and superior to tibiofibular syndesmosis. The injection continued till the dye is seen entering into the distal parts of the peroneal artery. In fair skinned cadavers, it even caused mild discolouration in perferosomes of the peroneal vessel. OBSERVATIONS AND RESULTS: Injection studies performed in the 20 peroneal artery systems with the following objectives, 1. To find out the location is the single best perforator for the skin paddle 2. To study the configuration of the single best perforator in terms of location, course, size and length. 3. To study the course of the musculoperiosteal vessels of the fibula, to find a safe window for ostectomy without injuring the vessels. In total 20 peroneal arterial systems were studied. We found that, The middle third of the leg had the largest number of perforators with an average of 5.5 perforators; the upper third of the leg had an average of 3.5 perforators while the lower third had an average of 2.5 perforators With the size measured at the origin of the perforator from the main vessel using ordinary calipers, we found that the upper third of the leg has the perforators with average external diameter of 1.3 mm, followed by the middle third of the leg with an average diameter of 1.2 mm, while the lower third had an average diameter of 1 mm. CONCLUSION Vascularized free fibula osteocutaneous flap is an established procedure for reconstruction of the oro-mandibular defects but several questions arises like; what is the location of the single best perforator for the skin paddle? What is the safe skin paddle dimension that can be harvested on a single eccentrically located pedicle? Where are the safe windows for ostectomy located on the harvested free fibula? What is the best position of the skin paddle in the recipient site which does not cause kinking of the vessel? etc., We have done cadaver studies and clinical studies to answer some of these questions. It was found from our studies that the perforators of good length and calibre are best found in the middle third of the leg, and most of the perforators were musculocutaneous travelling through the flexor hallucis longus muscle. Hence if a larger skin paddle is needed, it can reliably be harvested from the middle third of the leg with the pedicle placed eccentrically. But if the defect requires a longer bone stock and a smaller pedicle, it is better to harvest from the lower third of the leg. We also found from our clinical studies that designing the skin paddle with the pedicle eccentrically located allows for better three dimensional manipulation of the skin paddle in the recipient site, allowing it to cover wider area in the facial region like, cheeks, chin, upper neck, upper and lower lips etc., Also from our clinical studies we found that a single eccentrically located perforator of good length and calibre can support a skin paddle of 120 cm2. We also found from our studies that the safe window for ostectomies can be found in the peroneal surface of the fibula as the musculoperiosteal vessles runs in the anteromedial and posteromedial surface of fibula. Hence ostectomies can be performed with the apex of the wedge located at the peroneal surface and base at the interosseus border. We found from our studies that the posteromedial surface of the fibula which contains the peroneal vessel, when positioned inferiorly and posteriorly in mandible reconstruction site, gives better manoeuverability during anastamosis of the flap pedicle to the recipient vessels and also does not cause kinking of the vessel. From of cadaveric and clinical studies we have tried to answer some of the burning questions of the free fibula osteomyocutaneous flap procedure