Finite element analysis of biomechanical variation of subchondral bone in osteoarthritis and effect of diphosphonate therapy / 中华创伤杂志

ABSTRACT

Objective To observe the biomechanical changes of subchondral bone in the early stage of knee joint instability and effect of diphosphonate therapy so as to investigate the role of the early biomechanical changes of subchondral bone in the onset and development of osteoarthritis (OA).Methods Sixty healthy male New Zealand white rabbits were assigned to model group (n =24),diphosphonate group (n =24) and control group (n =12) according to random number table.Joint destabilization by anterior cruciate ligament transection of the right knee of the rabbits was performed to induce OA models.Rabbits in diphosphonate group received subcutaneous injection of 0.01 mg/kg diphosphonate (risedronate) per day,and isotonic saline solution of the same volume was subcutaneously given to rabbits in model and control groups.Half the animals in each group were killed by aeroembolism at postoperative 4 weeks and 12 weeks respectively.Surgical knee joint with preservation of each 2 cm bone above and below joint surface was dissected to perform gross scoring.Thereafter,two-dimensional image profile was achieved by Micro-CT examination and converted into Ansys for limit element analysis after fitting in Mimics software.Results At four weeks,bone volume fraction (BVF),elastic modulus (EM),reaction force (RF),and mean Von Mises stress were all declined in three groups,the lowest level in the model group (P ＜ 0.01).The diphosphonate group also had lower levels than the control group,with insignificant difference.Bone mineral density (BMD) in the model group was obviously declined in contrast with the diphosphonate and control groups (P ＜ 0.01),but there were no significant difference between the diphosphonate group and the control group.At 12 weeks,the model group showed higher level of BVF and BMD,but lower level of EM,RF and Von Mises stress in comparison with the control and diphosphonate groups (P ＜ 0.01).EM,RF,and Von Mises stress were lower in the diphosphonate group than those in the control group as well,but the difference was statistically insignificant.The model group showed that BVF,BMD,EM,RF,and Von Mises stress at 12 weeks were improved from those at 4 weeks (P ＜ 0.01).Conclusions Biomechanical properties of subchondral bone are affected in the early stage of knee joint instability and a notable decrease of EM is observed in the early stage,followed by an enhancement in late stage.It means that the biomechanical changes of subchondra,l bone in the early stage of knee joint instability may be connected with the bone resorption resulting from abnormal stress.On the contrary,diphosphonate may markedly improve EM of subchondral bone through inhibiting bone resorption.