Biomechanical research of medial femoral circumflex vascularized bone-grafting in the treatment of early-to-mid osteonecrosis of the femoral head: a finite element analysis
Authors: Zhang Yingkai , Wang Xinyuan , Jiang Chang , Hua Bingxuan , Yan Zuoqin 
Published: October 2022

Abstract
Purpose
Hip preservation therapy of early ONFH (Osteonecrosis of the femoral head) has emerged as one of the hot areas of research. We have optimized the procedure of traditional MFCVBG (medial femoral circumflex vascularized bone grafting) by using specialized surgical tools and used the finite element analysis to guide the implantation position of the bone flap during surgery and validate the biological mechanical stability of the modified MFCVBG.

Methods
This study was based on the data of a male patient with left hip (ARCO stage IIB, JIC type C) hormonal ONFH. Harris score (HHS), anteroposterior and lateral hip radiographs, frog position hip radiographs and SPECT/CT of femoral head flow imaging were performed postoperatively to evaluate clinical efficacy. The patient’s CT data were used to establish upper femur finite element model of the normal group, osteonecrosis group and postoperative group, respectively. The force on the femoral structure of each group was analyzed under four different loads in the gait cycle of 0.5 times the body weight (0.5 G, standing on two feet), 2.75 G (standing on one foot), 4 G (walking with the middle foot on the ground) and 7 G (walking with the toe off the ground) to validate the biological mechanical stability of the modified MFCVBG, predict femoral head collapse risk, simulate of the different healing conditions of postoperative bone flap, and analyze the postoperative effect of non-ideal surgical model.

Results
According to the follow-up results, the bone flap and the inner wall of decompression channel healed well, no osteonecrosis progression, no local collapse or micro-fracture occurred in the femoral head, and the articular surface was intact and the necrosis was well repaired. According to the result of the finite element analysis, compared with the osteonecrosis group, the overall stress and displacement peak of the upper femur and the cortical bone stress peak of the femoral head in the postoperative group and normal group were significantly reducing; modified MFCVBG can significantly improve the biomechanical stability of necrotic femoral head and reduce the risk of femoral head collapse; there was no obvious abnormal stress distribution in the greater trochanter and intertrochanter region after the flap was removed; the bone flap of the complete removal of necrotic focus + long bone flap group was directly placed at the bottom of the decompression passage, and the bone flap cortical bone can provide substantial mechanical support; in theory, patients can try to reduce the load with crutches or walking aids and carry out appropriate flat activities to effectively promote the early postoperative recovery.

Conclusions
The modified MFCVBG resulted in good efficacy, safety and feasibility. The necrotic focus should be completely removed during the operation, and the long bone flap should be placed directly under the subchondral bone. For patients with better bone healing ability, a more positive attitude can be taken to promote early postoperative weight-bearing.