The Effects Of LIPUS On Periprosthetic Osteolysis Induced By Polyethylene

BackgroundAlthough artificial joint replacement has achieved a great progress, its long-term life expectancy is still a difficult challenge in clinical practice. The polyethylene particle, which is the main material for joint liner, can activate osteoclast-macrophage system and cause periprosthetic osteolysis. Previous studies have demonstrated that the polyethylene is the main cause for revisions after primary total knee replacements. Of course some other materials are introduced to replace polyethylene, however, they all have different drawbacks. Till now, the polyethylene is still the main material for joint liner and widely used.The low intensity pulsed ultrasound(LIPUS) is a non-traumatic technique. It can penetrate surrounding surface organizations and has mechanical effects on related cells. It can accelerate the osteoblast differentiation, inhibit the osteoclast activation and process the bone healing. Clinical studies have confirmed LIPUS would help local bone healing. Some other studies also reported LIPUS could increase bone density in rats. Based on these, we consider, in the periprosthetic osteolysis process, LIPUS could also help bone forming process and inhibit the activation of osteoclast and finally inhibit bone osteolysis.Our experimental group has been long engaged in two aspects of the usage of LIPUS and prevention of periprosthetic osteolysis. This study is divided into four parts: in the first part, we successfully created polyethylene induced periprosthetic osteolysis model at the end of the rabbit femur; in the second part, we confirmed LIPUS could prevent or delay the periprosthetic osteolysis process in rabbit models; in the third part, we test the effect of LIPUS on in vitro cultured MC3T3osteoblast and discussed the possible mechanisms; and in the fourth part, we proposed a hypotheses that LIPUS may enhance the negative effect of oxygen radicals in the acute phase of fracture and suggest not applying LIPUS in the acute phase after fracture or surgery(within1week).Part I:The creation of periprosthetic osteolysis model at the distal part of rabbit femur.ObjectTo develop a simple periprosthetic osteolysis model in rabbits.MethodWe create the femur replacement model by drilling a bone tunnel from the patellofemoral joint aspect and inserting a steel bar. Then the polyethylene particle is injected during and after the operation to create the osteolysis model.16rabbits are used in this study, the femurs on one side are randomly chosen to create the replacement model(control group); the other sides are created the periprosthetic osteolysis model(study group). After3months, the periprosthetic shear strengths bone material density(BMD) and pathological images are analyzed and compared.Result sacrificing. The BMD (p=0.039),shear strength(p=0.017) are all lower in study group than in control group. The image analysis also shows the thickness of fibroblast layer is bigger (p=0.043, Z score=-2.023) and the shape of trabecular bone is worse in study group.ConclusionThe method used in our study can effectively create the periprosthetic osteolysis model at the distal part of rabbit femur. Part II:LIPUS would prevent the periprosthetic osteolysis model in rabbitsObjectStudy the effects of LIPUS on periprosthetic osteolysis process in rabbit femur.MethodWe create the periprosthetic osteolysis model by drilling a bone tunnel from the patellofemoral joint aspect, inserting a steel bar and injection of polyethylene particles(similar to Part I).16rabbits are used in this study. The femurs on one side are randomly chosen and treated by LIPUS(1.5MHZ,200mW/cm2,20min/day) for3months(study group); the other sides are not treated by LIPUS(control group). Then the rabbits are sacrificed and he periprosthetic shear strength,bone material density(BMD) and pathological images are analyzed.Result2rabbit dies from anesthesia and1rabbit has infection. The left13all live till sacrificing. The BMD (p=0.001) and shear strength (p=0.013) are all higher in study group than in control group. The image analysis also shows the thickness of fibroblast layer is smaller (p=0.043, Z score=-2.023) and the shape of trabecular bone is better in study group.ConclusionLIPUS could prevent or delay the periprosthetic osteolysis caused by polyethylene particles in rabbit femur. Partâ…¢:The effects of LIPUS on in vitro cultured MC3T3osteoblastsObjectStudy the effects of LIPUS in MC3T3osteoblasts in vitro.MethodWe culture MC3T3osteoblasts in vitro. They are divided into two groups:the study group is treated by LIPUS, and the control group is not. In the study group, the cells are cultured for24hours and treated by LIPUS for20minutes. Then the MTT OD value, cell counting and ALP activity value are tested.ResultThe MTT OD value (p=0.053) and cell counting (p=0.138) are higher in study group without statistical significance. The ALP activity value is higher in study group than in control group (p<0.01)ConclusionLIPUS could stimulate MC3T3osteoblast differentiation while its effect about proliferation is not obvious. Partâ…£:The hypotheses about negative effects of LIPUSObjectDiscuss the possible negative effects of LIPUS.MethodIn the early phase of a bone trauma,there are millions of oxygen radicals released by neutrophils in the injured area. The increased permeability of normal cell membranes by LIPUS make the concentration of oxygen radicals in these cells higher degree and make more damage to other healthy tissue cells. Here we proposed it may be better not to use LIPUS in the acute phase of a bone trauma(within one week after injury), and then it will be ok after the inflammative reaction has been weakened. Additionally, LIPUS would also enhance oxidative degeneration effect of oxygen radicals on the polyethylene linear after joint replacement.Result&ConclusionWe LIPUS has the possibility to enhance the negative effect of oxygen radicals in the acute phase of a bone trauma or surgery(within one week after injury). It would enhance the cell injury or oxidative degeneration of the polyethylene linear. And we also consider, the application of LIPUS is safe when the acute inflammative reaction has been weakened.