Femur Flap for Tibial Reconstruction: Circumference Required to Convey a Mechanical Advantage over the Fibula

A free vascularized fibula flap is commonly used to reconstruct the tibia following segmental loss of bone. The fibula flap is associated with a significant risk of postoperative fracture in the reconstructed limb. A vascularized bone flap with greater load-bearing strength would be desirable to reduce post-reconstructive fractures and also to decrease the length of time to full weight-bearing status. A flap using a non-circumferential piece of the distal femur was proposed. It would receive vascular supply from the overlying vastus intermedius muscle via the descending branch of the lateral femoral circumflex artery. The purpose of the study was to evaluate the load-bearing and fracture characteristics of a partial circumferential femur segment required to produce greater structural strength than a corresponding fibula flap and to assess the potential donor-site morbidity to the femur related to the harvest of such a flap.

Femurs and fibulas were harvested from eight preserved cadavers from 77 to 95 years old. The structural strength of 10 cm fibula and femur segments was assessed using a three-point bending device. Pilot studies, comparing 15–30% circumference femur segments to fibulas, were performed. Based on the results, five 35% circumference flaps and four 40% flaps were cut for definitive analysis. Uniaxial compression testing was performed on the osteotomized and whole femurs to assess the potential donor-site morbidity of taking these flaps.

The 35% femur flap segment (mean maximum force at fracture 869 N) was not significantly stronger than the fibula flap (626 N, p > 0.05). The 40% femur flap segment (1225 N) was significantly stronger than the fibula flap (p < 0.01). There was no significant difference between the mean maximum forces at fracture for the whole femurs (3978 N), femurs with 35% segmental osteotomies (3604 N), and femurs with 40% segmental osteotomies (3493 N, p =ߙ0.87). A significant change occurred in the fracture pattern of the femurs following the osteotomies. The whole femurs consistently fractured at the femoral neck, while the osteotomized femurs consistently fractured obliquely from the proximal end of the osteotomy.

A segment consisting of 40% of the circumference of the distal femur exceeds the structural strength of a fibula flap. This femur flap may be an alternative to the fibula flap. Taking such a flap appears to change the structural integrity of the femur such that intramedullary rod or equivalent fixation of the femur may be prudent following harvest of this flap.