Acetabular Roof Reconstruction Using a Free Vascularized Fibular Graft

When hip arthroplasty is performed in patients with acetabular dysplasia and deficient bone stock, finding good bone grafts is still a challenge. Numerous bone grafting techniques have been reported and autografts have been shown to be superior to allografts. However, the amount of bone available for autografts is limited, so allografts are often used, particularly in revision procedures.[1] When large structural allografts are employed for such reconstruction procedures, good early results are obtained, but there is a high mid-term failure rate due to collapse of the graft under loading.[1] [2] [3] Avascular free bone grafts, including structural allografts, are also associated with significant complications such as graft resorption, an increased infection rate, graft fracture, and non-union.[4]

Therefore, we have developed a new method for reconstruction of the superolateral acetabular rim using a free vascularized fibular graft, while the acetabular cavitary defects are filled with cancellous morselized allografts.

The patient was a 49-year-old man who had undergone previous rotational acetabular osteotomy (RAO) once and total hip arthroplasty (THA) four times for his left hip joint since he was 37-years-old. Developmental hip dysplasia should precede the operation. The left hip joint had massive bone defects of the acetabular roof and was completely dislocated in the superior direction before the present operation (Fig. [1]).

Figure 1 Preoperative roentgenogram. There is a massive defect of the left acetabular roof, with superior and lateral migration of the femoral component and the fractured acetabular component. Note the defect of the ipsilateral iliac crest due to previous use for bone grafting.

Our method consisted of two procedures. The first operation started with removal of the acetabular component, followed by the implantation of a vascularized bone graft (VBG) and cancellous morselized allograft (CMA). A 16-cm length of the fibula with a 6-cm vascular pedicle was collected from the right lower limb. Half of it was used as the VBG and the remaining half was applied as an avascular bone graft (ABG).

The inguinal ligament was incised to expose the deep circumflex iliac vessels at the origin from the external iliac artery. These vessels were then dissected and cut inside the iliacus muscle, and reflected as a 7-cm vascular pedicle. The deep circumflex iliac artery (DCIA) was anastomosed to the peroneal artery. Since the deep circumflex iliac vein (DCIV) was too narrow and therefore unsuitable for anastomosis with the peroneal vein, the long saphenous vein was cut in the femoral region and moved upward for anastomosis with the peroneal vein. These vascular anastomoses were performed end-to-end (Fig. [2]). To reconstruct the acetabular roof, a double-barrel graft was prepared by placing the VBG on the ABG and fixing the grafts to the posterior and superior walls of the acetabulum. The VBG was used as the blood supply, with the vascular pedicles being directed upward so that the blood flow in the vessels was not obstructed. The ABG was fixed as a mechanical support that came into contact with the femoral component. Both fibular bone grafts were fixed with three 2-mm Kirschner wires. The remaining defect in the acetabular cavity was filled with CMA (Fig. [3]). The vascular pedicle was confirmed to be patent by angiography at 11 weeks after the first operation (Fig. [4A]).

Figure 2 Intraoperative findings. The vascularized fibular graft (half of the harvested fibula) is connected to the hip by its vascular pedicle, which is indicated by the forceps.

Figure 3 Diagram of our method. The acetabular roof was reconstructed with a double-barrel fibular graft. (EIA = external iliac artery; SV = long saphenous vein; PA = peroneal artery; PV = peroneal vein).

Figure 4 (A) Angiogram of the deep circumflex iliac artery and anastomosed peroneal artery at 11 weeks after bone grafting, demonstrating patency of the anastomosis (white arrow). Contrast medium was injected into the deep circumflex iliac artery by selective catheterization using a microcatheter. At this time, the old acetabular component has been removed, but the femoral component is still displaced. (B) Patency of the anastomosis (white arrow) was also confirmed at 40 weeks after the second operation.

At 14 weeks after the first operation, the second operation was performed to insert new acetabular and femoral components, followed by the additional implantation of CMA in the defects around the acetabular component. The left femoral head was reduced to the same position as on the unaffected side. Partial weight bearing was started from 1 month after the second operation (the final arthroplasty). The VBG was confirmed to be viable by bone scintigraphy at 30 weeks after grafting (Fig. [5]). The patency of the vascular anastomosis was re-confirmed at 40 weeks after the second operation (at 54 weeks after grafting) (see Fig. [4B]). Roentgenograms showed no collapse under load bearing at 17 months after the second operation (Fig. [6]). The patient walks using a stick with full weight bearing, has equal leg lengths, no hip dislocation, and no donor-site morbidity at 17 months after the second operation.

Figure 5 Bone scan showing increased uptake of technetium-methylene diphosphonate at the graft site (arrow), as well as in the ipsilateral hip joint compared with the contralateral hip.

Figure 6 Roentgenogram obtained 17 months after the second operation. The left hip joint has been reduced, there is no loosening of the prosthesis, and the graft has not collapsed. The acetabular roof has been reconstructed with a double-barrel fibular graft.

To our knowledge, only five cases of acetabular reconstruction with VBG have been reported, and all of them received a pedicled iliac bone graft.[3] [5] In 1988, Solonen et al.[5] described the use of pedicled iliac crest grafts for reconstruction of acetabular defects in three patients. Although they reported satisfactory results, this technique has not achieved any popularity.[4] The other patients who underwent acetabular reconstruction with VBG were two patients treated with pedicled iliac bone grafts by Delimar et al.[3]

When revision surgery is done in patients with major bone loss and/or multiple previous operations, as in this case, obtaining a vascularized iliac crest graft may not be feasible because of the limited bone stock at that site.[4] In fact, a pedicled iliac graft could not be raised in the present case because the ipsilateral ilium had already been harvested during previous operations. Therefore, we developed the present method, in which the fibula (with a strong cortex) was used to provide a free vascularized bone graft. The fibula can provide a straight bone graft of up to 25 cm in length, while the anterior 14 cm of the iliac crest is available for grafting.[6] The fibula is 1.5 to 2.0 cm thick, while the iliac crest has a thickness of 0.8 to 1.7 cm. Therefore, the fibula has adequate length and thickness for grafting compared with the iliac crest. Unlike the curved iliac crest, the fibula is a long and straight bone, so it is possible to collect more than one fibular graft by osteotomy and fill a large bone defect completely with a combination of grafts.

The DCIA (which supplies blood to a pedicled iliac graft) was anastomosed to the peroneal artery in this case. The vascular pedicle was 13 cm long, which was comparable with the average pedicle length (12.9 cm) of vascularized iliac grafts reported by Karakurum et al. in a cadaver study,[4] while it was clearly longer than the pedicle length (8 to 10 cm) reported by Huang et al. in clinical cases.[7] Since the long saphenous vein is used as the vein of the pedicle, it is cut as distally as possible and reflected to obtain a sufficient length of vein. Therefore, the pedicle length is actually determined by the total length of the DCIA and the peroneal artery. The pedicle can be lengthened by harvesting the fibula as distally as possible because this will give the surgeon a longer peroneal artery segment. Therefore, unlike the pedicled iliac graft, this method allows enlargement of the rotation arc. Since use of the deep circumflex iliac vessels for anastomosis as recipient vessels has not been reported before, this is the first report showing their potential as recipient vessels during microvascular free transfer around the acetabulum.

Previous studies have reported that CMA are incorporated much more rapidly than large structural allografts when used for acetabular reconstruction.[2] [8] Therefore, the acetabular rim was reconstructed with the fibular grafts and the remaining defects in the acetabular cavity were filled with CMA. Graft union or graft incorporation cannot be predicted accurately by postoperative radiography when allografts are used to reconstruct the acetabulum. Lau et al.[9] reported that the results of angiography and technetium bone scanning at 8 weeks after surgery were useful for determining the viability of VBG. Arai and colleagues[10] showed that VBG formed new bone at the interface with the graft bed by 6 weeks after surgery. In this patient, the vascularized fibular bone graft was confirmed to be viable by angiography at 11 weeks and 54 weeks after grafting, as well as by a technetium bone scan at 30 weeks. Although long-term follow-up is still required to investigate the final outcome of this method, it is considered to be useful for overcoming the drawbacks of avascular free bone grafts and may be a good alternative to the pedicled iliac graft.

REFERENCES

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