Bony Hypertrophy in Vascularized Fibular Grafts

Abstract

Background: Vascularized fibula graft (VFG) transfer is an established method of repairing large skeletal defects resulting from trauma, tumor resection, or infection. It obviates the process of creeping substitution that conventional bone grafts undergo and therefore exhibits better healing and improved strength. The aim of this study is to evaluate hypertrophy in VFG. Methods: We retrospectively reviewed patients undergoing VFG and studied immediate and late postoperative radiographs. Orthogonal views were measured for width of graft cortex and intramedullary canal, as well as adjacent recipient bone. Changes were measured for total cross sectional area, cortical area, intramedullary area, and graft width. Results: Thirty patients were included in the analysis, with recipient sites including 3 forearm, 4 humerus, 12 tibia, and 11 femur. Mean follow-up was 7.6 years (0.5-24.9 years). Patients' mean age was 31 (16-59 years). Average hypertrophy was 254% in early postoperative period and 340% in the late postoperative period. There was rapid graft hypertrophy in early postoperative period that plateaued with time. The width of the graft increased over time but didn't exceed the width of the adjacent recipient bone. In the later postoperative period, the size of graft intramedullary canal increased. Upper and lower extremity grafts showed similar hypertrophy. Conclusions: Using VFG to treat large skeletal defects is an attractive option in part due to the graft's ability to hypertrophy. We describe an early period of periosteal hypertrophy, followed by endosteal hypertrophy. These processes have relevance to function, mechanical strength, and surgical decision-making.

Keywords: fibular graft; hypertrophy; vascularized bone grafting.

Figure 1.

Radiographs of VFG tibial reconstruction from a study subject with adequate radiographs. External stabilization of the graft is present immediately post operation (a and b), but absent in later postoperative radiographs (c and d). AP (a and c) and lateral (b and d) radiographs were obtained for early postoperative follow-up and after graft union. VFG = vascularized fibula graft.

Figure 2.

Example measurements of total bone width and intramedullary width for recipient and VFW are shown on AP (right) and lateral (left) radiographs. Dashed lines indicate total bone width and solid lines indicate intramedullary width; cortical width was taken as their difference. Total, cortical, and intramedullary surface areas were calculated using the average of bone diameters measured from AP and lateral radiographs. VFG = vascularized fibula graft.

Figure 3.

Each data point on the graph represents an individual patient’s VFG hypertrophy value at the final follow up with % hypertrophy represented on the Y axis and follow-up in days on X axis. VFG = vascularized fibula graft.

Figure 4.

Hypertrophy data divided into (a) upper extremity and (b) lower extremity.

Figure 5.

The index of total graft width, increases to but doesn’t exceed 1.

Figure 6.

Changes in VFG (a) cortical area and (b) IM area. Each data point on the graph represents an individual patient’s hypertrophy value. VFG = vascularized fibula graft; IM = intramedullary.

Figure 7.

Proposed model for VFG hypertrophy: On the basis of hypertrophy data, our model shows continuous hypertrophy of the periosteum beginning in the immediate postoperative period, but delayed hypertrophy of the endosteum and growth of the intramedullary canal. Periosteal hypertrophy occurs to a lesser degree in the late postoperative period. VFG = vascularized fibula graft.