Fibula Osteocutaneous Free Flap for Tertiary Reconstruction of a Segmental Diaphyseal Femoral Defect

Dear Sir,

Reconstruction of skeletal defects with autologous bone grafts has successfully been utilized for more than half of the century.[1] However, long diaphyseal defects resulting from high-energy trauma, and tumor resections, as well as segmental non-unions due to infection or poor vascularization, still remain a challenge to the surgeon. With the development of free-tissue transfer, various free vascularized bone grafts have been used for these indications.[2]

The femur is the longest and largest bone in the body that bears a great amount of body weight and is subject to high biomechanical loading due to the effect of overlying muscles. While conventional bone grafting may generally be successfull for bridging bone gaps up to 6 cm in length, this is frequently not the case in diaphyseal femoral reconstruction due to an inadequate surrounding vascular bed and loss of soft tissue resulting from trauma or tumor resection. These are the most common indications for free bone or osteocutaneous flap transfer in this area. Since its first description by Taylor and colleagues,[3] free fibula has been used for bridging various bone defects in the lower extremities up to 30 cm in length. While conventional fibula-to-tibia transfer has been extensively reported in the literature, only a small number of articles and case reports[2] [4] describe reconstruction of the femoral shaft with fibula free flap after high-energy trauma. We present an illustrative case of successfull femoral diaphyseal reconstruction with free vascularized osteocutaneous fibular flap, and discuss previous experience found in the literature, as well as possible technical pitfalls in microvascular reconstruction of complex femoral shaft injuries.

A 34-year-old male patient sustained a complex open multi-fragmentary fracture of the distal third of the femoral diaphysis and proximal third of the tibial diaphysis on the left in a motor vehicle collision. Both fractures were initially treated by external fixation (Fig. [1]), together with intramedullary screw fixation for tibial fracture and primary wound closure. External fixation was removed 8 months after the operation and x-rays showed a completely healed femoral fracture but the patient was still instructed to use crutches due to inadequate callus formation. One month after external fixation was removed, the patient fell during physical therapy and sustained a re-fracture of the femoral diaphysis, which was again managed by means of external fixation. Delayed union was noted during the regular postoperative follow-up and the patient underwent necrectomy of the non-vascularized bone in the re-fracture area, together with spongioplasty from the illiac crest. Even though follow-up x-rays showed solid bone union at the fracture site at this time, the bone was too thin to bear the patient's body weight, and normal biomechanical loading would undoubtfully lead to femoral re-fracture.

Figure 1 Multi-fragmentary diaphyseal femoral fracture with external fixation.

For this reason, we decided to enforce the previous fracture site with an osteocutaneous fibula free flap. After the recepient site was prepared by the trauma surgeon who removed non-viable bone and fibrosis, an osteocutaneous fibula free flap was fixed to the remaining femoral bone at the previous fracture site with one cortical screw proximally and two cortical screws distally (Fig. [2]). Additionally, spongioplasty between the free fibula flap and the remaining femur was performed with spongiosus bone from the illiac crest. At the same time, another team elongated the fibula free-flap vascular pedicle with an interpositional saphena magna vein graft. The recepient vessels were prepared on the medial side of femur in the region of Hunter's canal. Upon vessel preparation, a passage through a musculus rectus femoris was dissected laterally and end-to-side microvascular anastomosis to the superficial femoral artery was carried out, followed by end-to-end anastomosis to one of the superficial femoral veins.The vascular pedicle was pulled medially through a pre-formed muscular passage before the anastomoses were done. Upon blood flow, a check up was made by intra-operative Doppler ultrasound, and external fixation was carried out to additionally immobilize the femur.

Figure 2 Osteosynthesis with free fibula.

Postoperative recovery was uneventful and the patient was mobilized on the 5th day after surgery. Follow-up x-rays showed complete bone healing 4 months after operation(Fig. [3]). The patient was able to walk without cruthches approximatelly 6 months after surgery. Normal length and rotation were accomplished in the left lower extremity (Fig. [4]).

Figure 3 Complete bone healing 4 months postoperative.

Figure 4 Almost normal length and rotation in the left leg 6 months postoperative.

While conventional avascular cancellous bone grafting could be sufficient for shorter diaphyseal defects without significant surrounding soft-tissue damage, free-tissue transfer has proven successful in non-unions and longer segmental gap bridging, especially if active infection or avascular sclerosis coexist.[5] The viability of free vascularized bone graft based on its intrinsic blood supply, as opposed to conventional bone graft, is the main reason for biologic and, therefore, much more sucessful and faster bone healing. This was validated in both animal and clinical studies.[6] It is known that intrinsic weakness at the site of non-vascularized bone graft can last for more than 2 years.[7]

Although several different free bone flaps could be utilized for the reconstruction of the femoral diaphysis,[2] the free fibula has been the flap of choice for several reasons. It has a linear configuration with an available length of up to 30 cm, and a cortical structure which makes it suitable for internal fixation by screws or plate.[2] Furthermore, due to its anatomic qualities, it can be osteotomized and transferred as a two-strut free fibular graft for shorter defects where a skin island is not necessary.[8] While there are a number of series regarding free-fibula reconstruction of post-traumatic diaphyseal defects in the tibia,[9] [10] there are only several smaller series and isolated case reports describing post-traumatic femoral shaft non-union management with this method.[2] [4] [8]

The free fibula has more commonly been used for femoral reconstruction after tumor resection in orthopedic oncology[11] with a high success rate. However, in late post-traumatic long-bone reconstructions, the recipient site consists of avascular fibrotic tissue which usually requires several surgical procedures before microvascular reconstruction.[12] This, as well as frequent need for elongation of the vascular pedicle, as with our patient, make the reconstruction technically a challenging and lengthy procedure. We think that a combination of free fibula flap and bone allograft,[13] together with cancellous bone grafting, can achieve more rapid healing and graft incorporation than free fibula alone. The literature reports a relatively high stress fracture rate when fibula is used as a sole bony replacement in lower extremity reconstruction.[14] Hou and Liu[8] proposed a double-strut fibula free flap for post-traumatic femoral defect reconstruction which can expand the flap cortical cross-section area and double the biomechanical support, thus theoretically hastening bone healing. In our opinion, the osteotomy necessary to perform such a procedure will shorten the length of bone in a situation where the extremity has already been shortened by a non-united comminuted fracture, thus making normal limb restoration even more difficult. We believe that a combination of a single non-osteotomized fibula free flap and cancellous bone allografting can be an adequate management option for the reconstruction of long diaphyseal femoral defects after non-united comminuted fractures due to high energy trauma.

REFERENCES

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