Since their introduction by Taylor et al. and their use in composite reconstruction of the mandible and oral soft tissues by Hidalgo, free fibula osteocutaneous flaps have become the ‘workhorse’ for head and neck reconstruction. Currently, the most common indication for free fibula osteocutaneous flap transfer is mandibular reconstruction after tumour resection, such as segmental mandibulectomy. Good bone union is necessary to allow timely postoperative radiation therapy after cancer resection. Dental rehabilitation with osseointegrated implants in reconstructed mandibles contributes to the restoration of both function and aesthetics. Good bone union is also essential for dental implant placement and prosthesis use in reconstructed mandibles.

Disa et al., in a study with a mean follow-up period of 54 months, reported a bone union rate of 93% in fibulae transferred for mandibular reconstruction, based on panoramic radiographs. Osseous flaps, including fibula, radius, scapula, and ilium, had a bone union rate of 97% in another study with a mean follow-up period of 47 months. A recent study reported radiological non-union in 20% of neomandibles at the time of computed tomography (CT) evaluation (mean follow-up 15 months).

Another study found that panoramic radiographs alone were not sufficient for comprehensive evaluation of the entire bone segment of transferred fibulae in mandibular reconstruction. Therefore, three-dimensional CT scans were used in that study to visualize variations in bone union of fibula free flaps.

The purpose of this study was to sequentially evaluate long-term (≥2 years postoperatively) bone union of transferred fibula flaps in mandibular reconstruction, and to determine adequate methods for evaluating bone union in neomandibles by comparing radiological findings on panoramic X-ray and CT.

Materials and methods

This was a retrospective study of patients who underwent free fibula osteocutaneous flap transfer at Kobe University Hospital between October 2010 and January 2013. All fibulae used in mandibular reconstruction were covered in periosteum, with additional periosteum from the donor site present at both ends. Transferred fibulae were positioned in alignment with the lower border of the residual mandible as a mono-barrel graft. To restore facial contour, fibular osteotomies were performed only at the ‘T’ and ‘A’ positions, described in detail below ( Fig. 1 ). Small gaps between bones at ‘T’ or ‘A’ were filled with free bone chips obtained from the resected fibula ( Fig. 1 ).

Upper panel: The extent of the mandibular defect can be classified simply with points representing the mandibular angle (A) and the mental tubercle (T). Defects that include neither A nor T are defined as defects of the ‘body’ (*). This classification of mandibulectomy defects was originally described by Hashikawa et al. . Middle panel: Panoramic X-ray image scored as 0 (absent callus formation). Lower panel: Panoramic X-ray image scored as 1 (complete callus formation). The arrowheads indicate the gap between bones filled with free bone chips obtained from the resected fibula. Bone union of the filled bone chips in the gap was verified.

Patients who underwent routine follow-up CT and panoramic X-ray imaging during a period of ≥2 years after surgery to monitor for tumour recurrence or to confirm plate fixation, and who did not have early tumour recurrence, were enrolled. CT examinations were performed with an Aquilion 64 CT scanner (Toshiba Medical Systems, Tokyo, Japan) at the Hakubikai Imaging Support Centre or at Kobe University Hospital (tube current 100 mA, scanning time 3 s, slice thickness 2 mm, slice width 2 mm, field of view 25 cm). Evaluations of bone union were performed based on the bone condition on CT images.

All patients provided informed consent for the use of CT and panoramic X-ray images for this study. This study was exempted from the need for ethical approval by the institutional medical ethics committee because of its retrospective nature. The study was performed in accordance with the Declaration of Helsinki.

Medical records were reviewed to determine patient age, sex, underlying disease, the presence of diabetes mellitus, preoperative or postoperative radiation therapy, chemotherapy, fixation hardware, extent of mandibular defects, and time to resumption of oral intake. Mandibulectomy defects were classified according to the four points on the mandible where curvatures are greatest (i.e. the lines along the longitudinal axes of the right and left mental tubercle (T, T′) and the mandibular angles (A, A′)) and the condyle (C, C′). This method has been described previously as the ‘CAT classification’. Defects that included neither the mandibular angle (A) nor the mental tubercle (T) were defined as defects of the ‘body’ ( Fig. 1 ).

Evaluation of bone union

Three independent clinicians evaluated bone union in terms of osseous callus formation. Panoramic X-ray images were assigned a score of 0 or 1, where 0 represents absent callus formation and 1 represents complete callus formation ( Fig. 1 ). In the evaluation of CT images, a scale of 0 to 2 was used as follows: 0, absent callus formation; 1, complete callus formation only on the labial side; and 2, complete callus formation on both the labial and lingual side ( Fig. 2 ).

CT images evaluated on a scale of 0 to 2. Left panel: 0 (absent callus formation); centre panel: 1 (complete callus formation only on the labial side); right panel: 2 (complete callus formation on both the labial and lingual side).