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Mandibular  reconstruction
 

Mandibular reconstruction

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    Mandibular  reconstruction Mandibular reconstruction Document Transcript

    •  MANDIBULAR RECONSTRUCTION Dr.Anil Haripriya  Despite so many advances in reconstructive surgery and microvascular free tissue transfer, the reconstruction of composite mandibular defects, even today, remains a formidable challenge to many of us. It is one of the few areas of the reconstructive surgery, where precision in preoperative planning and technical execution is vastly important. Before discussing the various modalities for mandibular reconstruction, it is essential to briefly review the relevant salient anatomical features of the mandible.   It is the largest and strongest bone of the face. It is the tubular long bone with corticocancellous component. It has two anatomically similar right and left halves united anteriorly giving K the 'horse-shoe' shape. Each half comprises of a horizontal 'body' and a vertical 'ramus' joined posteriorly at the 'angle' of the mandible. The 'body' has upper, tooth bearing ‘alveolar segment’ and the lower 'basilar segment'. Each half has independent endosteal and periosteal blood supply. The endosteal (nutrient artery) blood supply is by the inferior alveolar artery (a branch of maxillary artery) which enters at the mandibular foramen, runs in the mandibular canal supplying both the bone and the teeth, emerges at the mental foramen and ends by supplying branches to the lower lip and chin. The periosteal blood supply is through the various muscles and soft tissues attached to the mandible. MANDIBULAR RECONSTRUCTION: GOALS Discontinuity of the mandibular arch causes impairment in speaking, chewing, swallowing and salivary control. Besides these functional problems, the facial aesthetics also gets disturbed. Therefore, the goals in mandibular reconstruction are to achieve form, function and the aesthetics. For truly successful functional and cosmetic end result, one should strive for the following1:  a) Restore the continuity of missing bone segment. b) Provide foundation for dental restoration. c) Provide soft tissues for internal lining and the external cover. d) Restore sensate and functioning lower lip with adequate buccal sulcus.  HISTORICAL ASPECTS  Wide variety of techniques and materials have been used for over a century to repair both the functional and cosmetic deficits resulting from mandible resection. In 1889, Martin2 used a prosthetic appliance for immediate reconstruction of mandible . Bardenheuer3 used a pedicied forehead flap with periosteum and bone in 1892. In 1900, Sykoff4 first described the use of free bone grafting for repair of a mandibular defect. Subsequent reconstructive efforts included the use of ivory, K-wires5,6, fenestrated tantalum trays7, chromium cobalt alloy cribs8, titanium trays with cancellous bone9,10, dacron trays with bone chips11,12, various metallic prostheses13, autoclaved resected mandibles14, frozen autogenous mandible grafts15, irradiated autogenous resected mandible grafts16, freeze-dried, decalcified allograft mandible17 carved as trough with bone chips of cancellous bone packed in it. All these techniques had some success but none were reliable enough to be routinely used. In 1970, Snyder et al18 described 'live osteocutaneous flaps' for mandibular reconstruction Subsequently, various pedicled bone flaps were described involving clavicle, scapula, sternum, rib and skull. With advances in microvascular techniques in 1980's, free vascularized bone flaps became popular and are now being routinely used successfully for mandibular reconstruction. These include the rib, second metatarsal, iliac crest, radius and the fibula.   CARDINAL PREREQUISITES OF SUCCESSFUL BONE GRAFTING  1. Bone transplantation into healthy tissues. 2. Wide contact between adjacent bone and the graft. 3. Recipient area with adequate blood supply 4. Positive fixation. IMMEDIATE vs DELAYED RECONSTRUCTION OF MANDIBLE  Today, with advancement in techniques, instrumentation and the optics, the free tissue transfer is being successfully used for single-stage reconstruction of even three-dimensional complex defects. In our opinion, probably, the only indication for delayed mandibular reconstruction is poor general condition of the patient, which doesn't allow him to tolerate prolonged general anaesthesia and lengthy surgical procedures. Before performing immediate mandibular reconstruction, it is important to ensure that the margins of surgical resection are free of tumour.  Advantages of Immediate Reconstruction  The requirement of size, contour and bone orientation to the opposing maxilla can be evaluated and achieved more precisely. Bone grafts can be placed in a fresh and scarless bed. The distortion produced by forces of wound contraction on the remaining soft tissues and the mandibular fragments after resection and radiotherapy is lessened. Early patient rehabilitation is possible. Number of operations is reduced minimizing the hospital stay and the morbidity. TECHNIQUES FOR AUTOGENOUS BONE REPLACEMENT  I. Non-vascularized bone grafts II. Vascularized bone flaps  Out of the two, the technique to be used is determined by the following factors:   1)    Quality of the soft tissues environment (the history of radiation, previous graft failure and infection produces lot of scarring compromising the soft tissue bed). 2)    Adequacy of the soft tissue (associated lining and cover requirement). 3)    Size and contour of the defect. 4)    Experience of the surgeon.   I. NON VASCULARIZED BONE GRAFTINGThis is done usually for small defects of mandible with little or no loss of soft tissue. The bone graft is placed in a well-vascularized bed. The adjacent bone-fragments are stripped of periosteum so that adequate bone to bone contact is established. Chips of cancellous bone are packed in any interstices between the ends of the fragments and also over the junction line. These chips promote bone consolidation as they get rapidly revascularized. If adequate fixation is provided, the graft is usually uneventful. Adequate haemostasis should be achieved to avoid haematoma formation. The contico-cancellous grafts are always preferred with as much cancellous bone as possible to provide rapid revascularization. The cortical component provides strength to the graft. One should try to preserve the periosteum aver the cortex since K assists in revascularizabon of the graft through the cortical layer.The common donor sites for non-vascularized bone grafts are the rib and the iliac crest. The rib can be used as the 'whole rib graft' or 'split rib graft'. The ‘whole rib graft' is less successful because it gets revascularized very slowly owing to the absence of exposed cancellous bone. On the contrary, 'split rib grafts' provide large areas of exposed cancelious bone for its rapid revascularization. Two split rib grafts (joined to each other anteriorlly and inserted into the rami posteriorly on each side - 'Fry’s technique’) can be used to reconstruct entire body of the mandible (Figure-1). The iliac crest is another favoured site for non-vascularized bone grafts as it provides good amount of cortical as well as cancellous bone and is easily accessible. It can be used to reconstruct the medium size mandibular defects (Figure 2) as left0           well as for reconstruction of entire ramus, and posterior portion of the mandibular body (Fig.3). Because of its natural curvature the iliac crest can even be sculpted to reconstruct the hemimandible (Figure-4). Careful preoperative planning, designing of the template and the selection of the side (right or left iliac crest) should precede the operation. Immobilization just be maintained for 6-8 weeks to ensure consolidation. The problems with iliac crest harvest include pain, bleeding, haematoma, ileus, contour deformity, limping post operatively and injury to lateral cutaneous nerve of thigh. II. VASCULARIZED BONE TRANSFERS Indications: 1) Compromised soft tissue bed. 2) Composite tissue reconstruction (bone and soft tissue lose)3)  When large segments of mandible require reconstruction. Advantages: Vascularized bone flaps heal more rapidly, require shorter period of immobilization and have less chances of non-union. There is less risk of bone resorption and a greater resistance to infecton. The quality of the recipient bed does not influence the survival permitting the placement even in heavily irradiated and scarred sites. There is no creeping substitution. The union between the graft and the bone is similar to fracture healing with transferred bone and the recipient bone, both contributing to callus formation.   TypesVascularized bone transfer can be broadly divided into two types:-A. Pedicled Bone flaps. B. Microvascular bone flaps (free tissue transfer). A. PEDICLED BONE TRANSFER  Various musculocutaneous flaps incorporating a segment of bone with its periosteal blood supply have been used for mandibular reconstruction :                       i.            Rib-pectoralis major osseomyo-cutaneous flap                   ii.            Sternum pectoralis major osseo-myacutaneous flap                 iii.            Clavicle -sternocleidomastoid osseomyocutaneous flap                iv.            Scapula-trapezius osseomyo-cutaneous flap                  v.            Rib-lattisimus dorsi osseomyo-cutaneous flap   Commonly used option is the rib-pectoralis major osseomyo-cutaneous flap, but it has many problems in clinical practice. The thin cortex and small caliber make the rib less than ideal as a replacement for the mandible. Besides, proper contouring and positioning are severely 6ited by the vascular pedicle. Complex three-dimensional reconstruction requiring precise orientation of skin and bone are often impossible to achieve.The pedicled osseomyo-cutaneous flaps should be reserved for small segment bone replacement when orientation of the skin and bone is not a problem. When large segments of bone needing osteotomies for contour and soft tissue replacement for both lining and cover are required, microvascular free tissue transfer is preferred.   B. MICROVASCULAR FREE BONE TRANSFERComplex mandibular reconstruction requiring large bone replacement and multiple osteotomies in a compromised soft tissue environment, especially when both soft tissue and bone require replacement are the prime indications for microsurgical reconstruction.   Types:                i. Nutrient supplied Bone Flaps : Examples include, rib, second metatarsal and the iliac crest. The posterior segment rib flap (nutrient artery from posterior intercostal vessels) requires formal thoracatomy. The skin island is too bulky and unreliable with high donor site morbidity. Because of availability of better options, its no longer used now.  The second metatarsal, based on the dorsalis pedis artery and first dorsal metatarsal branch provides up to seven cms of vascularized bone along with thin, pliable and hairless skin paddle suitable for providing lining. The main disadvantages being variable course of first dorsal metatarsal artery and high donor site morbidity.   The iliac crest based on deep circumflex iiiac vessels yields about 16-18 cms of bone sufficient for hemi-mandibular and interangular reconstructions. The versatility of the flap allows either ileum to be used facilitating pedicle orientation on either side of the neck. It permits multiple contouring osteotomies on the outer table while still maintaining the bone perfusion. Further more, the excellent quality of the bone transferred facilitates the use of osseo-integrated implant for denture reconstruction. The major disadvantages are its tedious dissection, technical difficulty in flap harvest, abdominal weakness and chances of inguinal hernia post operatively.            ii.     Periosteally supplied Bone Flaps : Examples include the rib, scapula, radius and fibula.               The periosteally supplied rib, based on the intercostal vessels, has the same problems as those described previously. Besides, osteotomies and contouring is too difficult to achieve. its clinical applications are very limited. The Scapular flap19 is based on the circumflex scapular artery, which divides into two cutaneous and multiple bone branches supplying the lateral border of the scapula. This vascular pattern allows for two skin paddles and a bone paddle, all on separate vascular stalks, which makes flap inset and manipulation easier. Complex soft tissue and bone reconstructions can be accomplished. Its long and large vascular pedicle also facilitates proper flap orientaflon independent of the recipient vessel availability. Its major disadvantages are the quality of the bone and difficulty in maintaining bone perfusion when multiple osteotomies are required. It requires repositioning the patient during the procedure. More over, the skin paddies may be very thick. The radial forearm osseocutaneous flap20 (Figure 5), based on radial vessels is the workhorse of the reconstructive surgeon. It is very reliable, provides large thin, pliable skin paddle and has a long, large vascular pedicle. It provides only up to 10 cm of bone, making it best suited for small defects. The major disadvantages are the requirement for skin graft closure of the donor site and the necessity for immobilization of the forearm and hand in a cast for 6-8 weeks to prevent fracture of the native radius.   The free fibula flaps21,22, based on the peroneal vessels has gained maximum popularity. Fibula is the largest expendable bone providing up to 25 cms of tubular, corticocancellous bone of excellent quality. It has large and long vascular pedicle. Its segmental periosteal bood supply permits multiple osteotomies to match the contour of the resected mandible. Being remotely located, its simultaneous harvest along with mandibular resection is possible without changing the position of the patient. The blood supply to the skin paddle comes from the myocutaneous perforators, through the soleus and flexor hallucis longus muscles. Therefore, it is advisable to include a cuff of these muscles when harvesting an osteocutaneous fibular flaps (Fig.6).   However, recently it has been proved both anatomically (dye injection studies) and clinically that the skin paddle is very reliable even only on septocutaneous perforators. It is thus not mandatory to harvest the cuff of soleus and/or FHL muscles.   The decision of which leg to harvest the flap from depends on the need for a skin paddle. If no skin paddle is needed, ipsilateral leg can be used. However, if a skin paddle is needed for lining, then the contraiateral leg should be used (Figure-7). The complications with free fibular osseocutangous flap could be total flap less, infection, haemorrhage and haematorna, plate exposure etc. Donor site complications involve partial graft loss, wound dehiscence, joint instability etc.   SUMMARY  The method of choice in treating skeletal defects of the mandible remains the replacement by autogenous bone. Free-flap reconstruction permits immediate, one stage reconstruction providing healing by first intention and facilitating early dental rehabilitation. Although various donor sites have been described the most commonly used flaps are deep circumflex iliac artery based iliac bone and peroneal artery based tibular flap.    <br />