Mode and True Amount of Hypertrophy of Vascularized Fibula Grafts

Vascularized bone grafts have many advantages over free bone autografting, from which bone union cannot be expected for large bone loss. The purpose of this study was to assess the true amount of hypertrophy, to investigate a mode of hypertrophy of a vascularized fibular graft for femoral bone loss and to assess a mode of hypertrophy.

Thirteen cases of vascularized fibular graft for bone loss in the tibia were used for percent of hypertrophy. The thickness of fibular cortical bone at follow-up was divided by the thickness of the same area immediately after surgery. These thickness ratios of four sides of the fibular cortical bone were compared. Eight cases of vascularized fibular graft for bone loss in the tibia were used in regard to cortical bone volume and measurement was obtained using CT scan. The mean length of bone loss was 9.9 cm and that of the fibula grafts was 16.8 cm. In addition, five cases of vascularized double fibular grafting for femoral bone loss were used. The mean length of bone loss was 14.4 cm, and that of the bone grafts was 21.3 cm. Percent hypertrophy of grafted bone was measured radiographically by the method described by Boer and Wood.

In the 13 cases of vascularized fibular graft, the mean percent hypertrophy was 42% from the AP view and 60% from the lateral view. The means of thickness ratio were 207% at the medial side, 209% at the lateral side, 204% at the anterior, and 294% at the posterior sides. The cortical bone volume in the grafted fibula was 2.8 times greater than in the recipient fibula and 86% of the donor side tibia. In the 5 cases of vascularized double fibular grafting the mean percent hypertrophy of intramedullary fibula was 27.1%, and that of extramedullary fibula was 28.1%. The mean cortical bone volume of intramedullary fibula was 61% and extramedullary fibula was 42% of intact femur. Thus, the total cortical bone volume of both intramedullary and extramedullary fibula was the same as that of intact femur.

The diameter of the fibula cannot be hypertrophied the same as that of the tibia. Bone volume of the grafted fibula, however, was almost the same as the healthy tibia on average. Furthermore, fibular cortical bone was hypertrophied in both outer and medullary directions, especially posteriorly. It was thought that hypertrophy does not occur further because there is no biomechanical necessity for it.