BACKGROUND:Developmental dysplasia of hip causes groin pain in patients with prolonged activity or standing due to the presence of deformities of the acetabulum and femoral head in terms of structure,size and orientation,and if not effectively treated,patients' normal activities will be severely limited.OBJECTIVE:Finite element model of the hip joint of solid-liquid biphase fiber reinforced cartilage based on FEBio was established to explore the biomechanical properties of the cartilage for patients with developmental dysplasia of hip and the normal hip joint.METHODS:A patient with developmental dysplasia of hip and a normal volunteer were chosen to build their left hip models including left pelvis,left femur,and cartilage attached thereto. The solid-liquid biphase fiber reinforced cartilage of normal hip was verified to be effective. The cartilage equal contact stress,fluid pressure,solid effective stress,and fluid support rate differences between the developmental dysplasia of hip patients hip and the normal one in the case of one leg of static load (2130 N) were compared after establishing finite element models of developmental dysplasia of hip patients.RESULTS AND CONCLUSION:(1) Compared with the finite element results of the normal hip model,the cartilage contact position of developmental hip dysplasia patient hip showed obvious edge contact,the peak contact stress (3.86 Mpa) and peak fluid pressure (3.76 Mpa) were both higher than normal hip model. (2) After 1500 s (stable load-bearing capacity),peak contact stress and peak fluid pressure in both models decreased,but the cartilage contact position of developmental hip dysplasia patient hip moved from the edge of cartilage to the center,and fluid support rate decreased from 97.41％ to 91.08％. The fluid support rate in normal hip was decreased by 0.58％ from 95.24％ to 94.66％. (3) It is indicated that under the physiological load of standing on one leg,the cartilage of developmental dysplasia of hip patients showed obvious edge load,and the decrease of peak contact stress,fluid pressure,and fluid formation rate was greater than that of normal cartilage. Considering the solid-liquid biphasic fiber reinforcement characteristics of cartilage,it is of great clinical significance to evaluate the biomechanical properties of hip cartilage in developmental dysplasia of hip patients,to understand the pathophysiological mechanism of developmental dysplasia of hip,and make preoperative plan.

BACKGROUND:Developmental dysplasia of hip causes groin pain in patients with prolonged activity or standing due to the presence of deformities of the acetabulum and femoral head in terms of structure,size and orientation,and if not effectively treated,patients' normal activities will be severely limited.OBJECTIVE:Finite element model of the hip joint of solid-liquid biphase fiber reinforced cartilage based on FEBio was established to explore the biomechanical properties of the cartilage for patients with developmental dysplasia of hip and the normal hip joint.METHODS:A patient with developmental dysplasia of hip and a normal volunteer were chosen to build their left hip models including left pelvis,left femur,and cartilage attached thereto. The solid-liquid biphase fiber reinforced cartilage of normal hip was verified to be effective. The cartilage equal contact stress,fluid pressure,solid effective stress,and fluid support rate differences between the developmental dysplasia of hip patients hip and the normal one in the case of one leg of static load (2130 N) were compared after establishing finite element models of developmental dysplasia of hip patients.RESULTS AND CONCLUSION:(1) Compared with the finite element results of the normal hip model,the cartilage contact position of developmental hip dysplasia patient hip showed obvious edge contact,the peak contact stress (3.86 Mpa) and peak fluid pressure (3.76 Mpa) were both higher than normal hip model. (2) After 1500 s (stable load-bearing capacity),peak contact stress and peak fluid pressure in both models decreased,but the cartilage contact position of developmental hip dysplasia patient hip moved from the edge of cartilage to the center,and fluid support rate decreased from 97.41％ to 91.08％. The fluid support rate in normal hip was decreased by 0.58％ from 95.24％ to 94.66％. (3) It is indicated that under the physiological load of standing on one leg,the cartilage of developmental dysplasia of hip patients showed obvious edge load,and the decrease of peak contact stress,fluid pressure,and fluid formation rate was greater than that of normal cartilage. Considering the solid-liquid biphasic fiber reinforcement characteristics of cartilage,it is of great clinical significance to evaluate the biomechanical properties of hip cartilage in developmental dysplasia of hip patients,to understand the pathophysiological mechanism of developmental dysplasia of hip,and make preoperative plan.

Objective To investigate the effects of patient bone mass differences on the stability of unicondylar knee arthroplasty(UKA)prostheses.Methods A UKA finite element model was established to quantify the effects of five different bone quality conditions on the proximal tibial von Mises stress,bone-prosthesis fixation interface contact stress,and bone-prosthesis fixation interface micromotion,using the medial knee force and joint motion predicted by the individualized UKA musculoskeletal multibody dynamics model as boundary conditions.Results The influences of bone strength on the proximal tibia von Mises stress and bone-prosthesis fixation interface contact stress were not obvious,and the difference in peak values of the proximal tibia von Mises stress between two groups of models with the largest difference in bone strength was not more than 5％,and the difference in peak values of the bone-prosthesis fixation interface contact stress was only 2.37 MPa.However,the influence of bone strength on the bone-prosthesis fixation interface micromotion was significant,and the weaker bones were more prone to cause the bone-prosthesis fixation interface micromotion.However,bone strength had a significant effect on the bone-prosthesis fixation interface micromotion,and weak bone was more likely to cause changes in the bone-prosthesis fixation interface micromotion.Compared to patients with the neutral bone quality,the prosthesis fixation interface micromotion increased by 84.67％at 20％gait cycles for patients with the weakest bone quality.Conclusions UKA patients with a weaker bone quality have a higher risk of prosthesis loosening.It is recommended that surgeons should carefully choose their surgical strategy in order to reduce the rate of postoperative revision in UKA.

Prosthesis loosening is the leading cause of postoperative revision in unicompartmental knee arthroplasty (UKA). The deviation of medial and lateral translational installation of the prosthesis during surgery is a common clinical phenomenon and an important factor in increasing the risk of prosthesis loosening. This study established a UKA finite element model and a bone-prosthesis fixation interface micromotion prediction model. The predicted medial contact force and joint motion of the knee joint from a patient-specific lower extremity musculoskeletal multibody dynamics model of UKA were used as boundary conditions. The effects of 9 femoral component medial and lateral translational installation deviations on the Von Mises stress of the proximal tibia, the contact stress, and the micro-motion of the bone prosthesis fixation interface were quantitatively studied. It was found that compared with the neutral position (a/A of 0.492), the lateral translational deviation of the femoral component significantly increased the tibial Von Mises stress and the bone-prosthesis fixation interface contact stress. The maximum Von Mises stress and the maximum contact stress of the fixation interface increased by 14.08% and 143.15%, respectively, when a/A was 0.361. The medial translational deviation of the femoral component significantly increased the bone-prosthesis fixation interface micro-motion. The maximum value of micromotion under the conditions of femoral neutral and medial translation deviation was in the range of 20-50 μm, which is suitable for osseointegration. Therefore, based on considerations such as the micromotion range suitable for osseointegration reported in the literature, the risk of reducing prosthesis loosening, and factors that may induce pain, it is recommended that clinicians control the mounting position of the femoral component during surgery within the safe range of 0-4 mm medial translation deviation.
Humans ; Arthroplasty, Replacement, Knee/methods* ; Finite Element Analysis ; Biomechanical Phenomena ; Knee Prosthesis ; Tibia/surgery* ; Femur/surgery* ; Stress, Mechanical ; Prosthesis Failure ; Knee Joint/surgery* ; Prosthesis Design

Although metal blocks have been widely used for reconstructing uncontained tibial bone defects, the influence of their elastic modulus on the stability of tibial prosthesis fixation remains unclear. Based on this, a finite element model incorporating constrained condylar knee (CCK) prosthesis, tibia, and metal block was established. Considering the influence of the post-restraint structure of the prosthesis, the effects of variations in the elastic modulus of the block on the von Mises stress distribution in the tibia and the block, as well as on the micromotion at the bone-prosthesis fixation interface, were investigated. Results demonstrated that collision between the insert post and femoral prosthesis during tibial internal rotation increased tibial von Mises stress, significantly influencing the prediction of block elastic modulus variation. A decrease in the elastic modulus of the metal block resulted in increased von Mises stress in the proximal tibia, significantly reduced von Mises stress in the distal tibia, decreased von Mises stress of the block, and increased micromotion at the bone-prosthesis fixation interface. When the elastic modulus of the metal block fell below that of bone cement, inadequate block support substantially increased the risk of stress shielding in the distal tibia and fixation interface loosening. Therefore, this study recommends that biomechanical investigations of CCK prostheses must consider the post-constraint effect, and the elastic modulus of metal blocks for bone reconstruction should not be lower than 3 600 MPa.
Knee Prosthesis ; Humans ; Finite Element Analysis ; Tibia/surgery* ; Elastic Modulus ; Arthroplasty, Replacement, Knee/methods* ; Stress, Mechanical ; Metals ; Prosthesis Design ; Knee Joint/surgery* ; Biomechanical Phenomena

Objective To investigate the effects of patient bone mass differences on the stability of unicondylar knee arthroplasty(UKA)prostheses.Methods A UKA finite element model was established to quantify the effects of five different bone quality conditions on the proximal tibial von Mises stress,bone-prosthesis fixation interface contact stress,and bone-prosthesis fixation interface micromotion,using the medial knee force and joint motion predicted by the individualized UKA musculoskeletal multibody dynamics model as boundary conditions.Results The influences of bone strength on the proximal tibia von Mises stress and bone-prosthesis fixation interface contact stress were not obvious,and the difference in peak values of the proximal tibia von Mises stress between two groups of models with the largest difference in bone strength was not more than 5％,and the difference in peak values of the bone-prosthesis fixation interface contact stress was only 2.37 MPa.However,the influence of bone strength on the bone-prosthesis fixation interface micromotion was significant,and the weaker bones were more prone to cause the bone-prosthesis fixation interface micromotion.However,bone strength had a significant effect on the bone-prosthesis fixation interface micromotion,and weak bone was more likely to cause changes in the bone-prosthesis fixation interface micromotion.Compared to patients with the neutral bone quality,the prosthesis fixation interface micromotion increased by 84.67％at 20％gait cycles for patients with the weakest bone quality.Conclusions UKA patients with a weaker bone quality have a higher risk of prosthesis loosening.It is recommended that surgeons should carefully choose their surgical strategy in order to reduce the rate of postoperative revision in UKA.

Objective To establish different sleep deprivation models in zebrafish to provide reproducible and practical modeling reference solutions for basic research on insomnia.Methods Zebrafish insomnia models were induced by two interventions:continuous light(150 Lux)and light plus caffeine.The zebrafish were divided randomly into control,light,caffeine(100 μmol/L),and combined light and caffeine groups.The locomotor ability of zebrafish in each group was observed using open field and circadian rhythm behavioral experiments.The expression and secretion of related sleep genes and the neurotransmitter 5-hydroxytryptamine(serotonin;5-HT)were detected using quantitative polymerase chain reaction and enzyme-linked immunosorbent assay,respectively.Results Sleep time,resting time(during the day),and sleep rounds were significantly reduced(P＜0.01 or P=0.01)and the distance traveled was significantly increased in the light group compared with the control group(P＜0.01).The resting time(daytime)and sleep rounds were increased in the combined and caffeine groups(P＜0.01)compared with the control group.There was no significant difference in the activity distance between the combined and caffeine groups(P＞0.05).The percentages of swimming distance and swimming time in the central area were decreased in the light group compared with the control group(P＜0.05),and were both decreased in the caffeine group compared with the light group(P＜0.01).HT receptor 1Aa(HTR1aa)mRNA expression at 6:00.and 12:00 was up-regulated in the light group compared with the control group(P＜0.05),but there was no significant difference in HTR1ab mRNA levels between the light group and the combined group(P＞0.05).5-HT secretion was decreased in the light group at 6:00(P＜0.01)and at 12:00 compared with the control group.5-HT levels were reduced in both the light and combined groups(P＜0.01),and secretion levels in the light and combined groups were still lower than in the control group at 18:00.(P＜0.01).Conclusions Light alone is the best intervention for modeling long-lasting insomnia in zebrafish larvae.The responsible mechanisms may be related to the HTR1aa gene as well as biological factors such as 5-HT.

Objective To study the effects of different posterior slope installations of unicompartmental knee arthroplasty(UKA)prostheses on the loading and motion of the knee joint and insert wear.Methods A combined approach involving the UKA musculoskeletal multibody dynamic,finite element,and wear prediction models was used to investigate the effects of five different posterior slope installation positions of the UKA prosthesis on the postoperative knee joint force and motion,insert contact stress,linear wear depth,and wear volume.Results At a 0° posterior slope,the maximum von Mises stress of the insert was 24.84 MPa,maximum contact stress was 47.61 MPa,and volumetric wear after 5 million cycles(MC)was 47.29 mm3.As the posterior slope angle of the UKA prosthesis increased,the internal rotation and posterior translation during the gait cycle increased,the medial joint force during the swing phase increased,the von Mises and contact stresses of the insert after 5 MC decreased significantly,and the wear area,maximum linear wear depth,and volumetric wear volume of the insert were consequently reduced.Compared to the 0° posterior slope,the linear wear depths of the insert at the 3°,5°,and 7° posterior slopes decreased by 17.8％,19.2％,and 20.6％,respectively.The volumetric wear volumes of the inserts decreased by 24.5％,30.9％,and 34.3％,respectively.Conclusions Installing a UKA prosthesis with a posterior slope exceeding 3° significantly increases internal rotation and posterior translation during the gait cycle,further reducing the articular volumetric wear of the polyethylene insert.

Objective To investigate the biomechanical effects of the backside design of tibial trays on the bone-prosthesis fixation interfaces in unicompartmental knee arthroplasty(UKA).Methods Finite element models of medial knee arthroplasty were constructed using a fixed UKA prosthesis.The knee joint load and joint motion under walking motion were considered as boundary conditions,and the differences in tibial von Mises stress,contact stress,and micromotion of the bone-prosthesis fixation interface of the UKA tibial trays with big keel,small keel,two-peg with fin,three-oblique peg,and three-upright peg types were compared.Results At the maximum medical knee force moment,compared to the two-peg with fin type,the tibial von Mises stress,contact stress,and micromotion of the bone-prosthesis fixation interface decreased by 8%and 15.9%and increased by 9.9%for the big keel type;decreased by 12.3%and increased by 7.5%and 0.9%for the small keel type;decreased by 10%,10.5%,and increased by 1.2%for the three-oblique peg type;and decreased by 7.7%,14.7%,and 1.6%for the three-upright peg type,respectively.However,the maximum micromotion of the bone-prosthesis fixation interface occurred at 21%of the gait cycle.Compared to the two-peg with fin type,the micromotion of the bone-prosthesis fixation interface increased by 11.6%for the big keel type,increased by 1.6%for the small keel type,decreased by 0.4%for the three-oblique peg type,and decreased by 2.3%for the three-upright peg type.Conclusions To improve the long-term fixation effects of tibial prostheses,it is recommended to focus on a two-upright peg with fin or small keel designs when UKA tibial trays are designed,which can effectively balance the stress transfer and interface micromotion,thereby ensuring prosthesis stability and reducing the risk of aseptic loosening.