According to the literature, ankle fusions and reconstruction with bone graft is the primary methods for salvaging the distal tibia. The fibular graft is the widly used bone graft that is easy to obtain and results in minimal donor-site morbidity. It can be inserted into the medullary canal of the tibia perfectly. Then, fibular graft has the bability to become hypertrophy under the stimulation of weight-bearing after bony union[18, 19]. When this bone construction is created, initial stability is a guarantee of host-graft healing. However, it is difficult to investigate the biomechanical effect in vivo. Beside, it is tough to enroll enough cases to detect the clinical outcomes of different surgical methods due to the rare incidence of this disease. As FEA has been widely used for mechanical analyses, it has the potential to predict the preoperative mechanical environment, help the surgeon to decide the optimal recontruction. Therefore, we aim to evaluated the initial stability of double-strut fibula ankle arthrodesis.
This work has several limitations. Firstly, the FEA model was based on the anatomy of a single patient. Secondly, the role of muscles or ligaments was not simulated because of the difficulty in assessing the soft tissue changes after excision and reconstruction of the distal tibia. Therefore, the stability offered by the surrounding soft tissues was ignored. But, this technical limitation affected all the groups equally and it didn’t question the validity of our findings. Thirdly, it is a static simulated study and further studies are needed to explore the dynamic loading process. Finally, anatomical variations in the distal tibia and the extent of excision may affect the results.
According to the vertical pressure analysis, cracks usually occurred at the area of the concentrated stress and with obvious displacement. In our study, the maximum stress of fibular graft in Model B and Model C were similar (22.73 MPa vs. 23.69 MPa) when loading the vertical force of 600 N, which were both acceptable. In Model B and Model C, we noted that concentration of stress was at the implant. This can be easily explained by the fact that the plate can resisted the upward displacement effectively and protect the fibular graft in early time. The outcome exhibited that fibula in Model B has a higher value of stress (12.07 MPa) than that in normal bone model (0.67 MPa), indicating the ipsilateral fibula acts as an ancillary structure for weight-bearing. It uphold the current recommendations that the double-strut reconstruction can provide satisfactory initial stability[10, 11].
The Model C simulated the reconstruction method of ankle fusion with centralisation of the fibula which was reported by Kundu et al.. In these authors’ study, 9 patients with distal tibia tumor underwent this surgical option, resulting in a mean MSTS score of 76%. There was no stress fracture of the fibula after surgery, however, a angulation at the proximal fibula graft was observed in one case. In this study, we found that this technique of centralization of fibular graft was not stable enough compared with double-strut fibula reconstruction, and has a high rate of fracture of fibular graft in early period after surgery. Therefore, Kundu et al. recommended that weight-bearing was not allowed in the first 8 weeks. Guarded weight-bearing was carried out 8–10 weeks onward when radiological bone union began, and the full-leg cast was replaced by a below-leg cast after 16–20 weeks, when radiographs showed sign of bone union. Therefore, this procedure requires quite a long time to get rid of cast and to start full weight-bearing.
Prosthesis can provide initial stability, resulting good early function, however, it is still associated with a significant set of complications such as high risk of infection, loosening, talus collapse, and ankle instability. Due to lack of muscle coverage in this distal tibia, it will complicate the reconstruction of prosthetic replacement, and burdened the prosthesis with long-term complications. A mid-term study and a long-term stduy exhibited that the aseptic loosening and infection were main reason of prosthetic reconstruction failure[20, 21]. Zhao et al.  performed a literature review comparing prosthetic replacement with biological reconstruction (allograft or autograft), and revealed that autograft or allograft reconstruction performed better than prostheses. Therefore, in this study, we did not investigate the biomechanical effect of prosthetic replacement. However, in recent years, the introduction of 3D printed prosthesis with surface of bone-growth may reduce the complications, further long-term study is needed.
The non-vascular autogenous fibular graft has some important advantages over other donor sites due to its length, geometry and mechanical strength. The fibula being a long, straight tubular bone, with perfect shape allows tibial intramedullary insertion. And it is an easy, inexpensive biological procedure that does not require micro-vascular skills. The current FEA study suggest that reconstruction with fibular graft after tumor resection of distal tibia is an accept solution, but the additional plating is required to sustain initial stability.