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Objective To analyze the influence of total hip arthroplasty (THA) on the process of proximal femoral bone remodeling by using the Wolff bone remodeling theory. Methods According to control equation of bone remodeling, the program of bone remodeling was written in Python language. Preoperative femur model and postoperative femur and prosthesis finite element models were established respectively in ABAQUS software. The process of bone reconstruction before and after THA operation was compared to analyze the effect of prosthesis implantation on mechanical properties of the femur in the middle and long term after THA operation. Results The stress in proximal femur continued to decrease after prosthesis implantation, and the stress site was transferred from the femoral head to the prosthesis, resulting in an obvious stress shielding phenomenon. Bone loss in the stress shielding area was serious. The femoral shaft cortical bone became thinner and the stress shielding was relieved. The medial side at the bottom of the prosthesis was compressed, and the stress was significantly higher than that of the lateral side, where the bone was unevenly distributed. Conclusions After THA operation, obvious stress shielding occured at proximal medial side of the femur, leading to bone loss and prosthesis loosening. The difference in stress levels on both sides at the bottom of the prosthesis resulted in an uneven bone distribution, causing the discordance between the prosthesis and the femur, as well as postoperative pain in the middle part of the thigh.
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Objective To evaluate biomechanical properties of the personalized titanium alloy short femoral prosthesis by finite element analysis. Methods Based on the validated femoral finite element model, the base of the femoral neck was simulated, and by inserting different short femoral prostheses, four total hip replacement (THR) models, namely, the SMF stem model (Model A), BE1 stem model (Model B), MINI stem model (Model C) and personalized stem model (Model D) were established, respectively. The same loads and constraints were applied to four groups of models, and the von Mises stress distribution and deformation were calculated and analyzed, so as to compare mechanical stability of each model. Results The deformation of all THR models was smaller than that of the femur model under physiological state. The deformation of Model B was close to that of Model C, and the deformation of Model A was close to that of Model D. The peak stress of Model C was higher than that of the other 3 models, reaching 9555 MPa. The overall stress trend was Model C > Model B > Model D> Model A > Model under physiological state. Conclusions The peak stress, stress distribution of personalized short femoral stem were similar to that of SMF stem, with reasonable stress distribution, small stress shielding of the proximal femur, minimum overall deformation and shear stress of the prosthesis, and its effectiveness and stability could meet the requirements of human biomechanics, which could provide references for joint surgeons and prosthesis researchers.
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BACKGROUND: Fracture fixation and surgical procedures have a very important impact on the final outcome of fracture healing, but the adverse outcome of fracture healing is the result of the combined action of surgical procedures and a series of four-dimensional space events. OBJECTIVE: To explore the four-dimensional space events in fracture healing. METHODS: China National Knowledge Infrastructure and Medline were retrieved, with the key words of “fracture healing, femoral fracture, stress shielding, fracture and blood flow” in Chinese and English. Retrieval of relatively macroscopic factual descriptions corresponds to the four-dimensional space events of fracture healing process, including logically supported and refuted evidence. Combined with literature review, the main four-dimensional space events after fracture fixation were analyzed. RESULTS AND CONCLUSION: The main four-dimensional space events after fracture fixation include blood flow tides, mechanical and biological impulses, grinding disc effect of small gap in hard tissue, stress shielding effect and four-dimensional space drift effect of internal fixation material. Fractures and surgical trauma are accompanied by months of super-compensatory blood flow tides, so there is no ischemia in the macro-level after fracture surgery, but the grinding disc effect will occur in the small gap of hard tissue under unstable condition, resulting in contusion injury and micro-ischemia in the fracture gap. Stress shielding effect caused by too strong fixation is an important reason for refracture after internal fixation removal and bone atrophy and thinning after internal fixation. The small axial drift of plate fixation screw may have important theoretical significance. It has “intelligent” axial dynamic effect, which can make the stress shared by plate gradually decrease with the healing of fracture. Discussing the four-dimensional space events of fracture healing will provide basic logic for the regulation of fracture healing and distraction osteogenesis.
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BACKGROUND: Tendon is a special connective tissue that can transmit the force generated by the muscle to the bone through the enthesis. The occurrence of tendinopathy is closely related to the mechanical characteristics of tendon and enthesis and its micro-structure, but the specific mechanism still remains controversial OBJECTIVE: To summarize the micro-structure of tendon and en thesis, the biomechanical characteristics of tendon, the healing and repair of tendon injuries, and the biomechanical factors related to chronic tendinopathy. METHODS: CNKI, VIP, CBM, WanFang, PubMed and Embase databases were searched. The articles concerning micro-structure of tendon and enthesis, relationship between tendinopathy/enthesis and stress, and biomechanical mechanisms of tendinopathy/enthesis were selected. RESULTS AND CONCLUSION: The biomechanical properties of tendon and enthesis are closely related to their microstructures. The biomechanical properties of tendon are reduced due to the damage of their microstructures in the process of repair. The occurrence and development of chronic tendinopathy are related to the microstructures and biomechanical characteristics of enthesis. Compression load and stress shielding of enthesis may play a key role, but further high-quality studies on the specific mechanism are still required.
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Objective To explore the anti-osteoporosis effect of bisphosphonates on repairing injured vertebrae after thoracolumbar fracture internal fixation through a randomized controlled study. Methods Eighty-four patients with thoracolumbar fracture treated by orthopaedic internal fixation in Department of Orthopaedics, Nanjing General Hospital from Jun. 2014 to Jun. 2015 were included, and the patients were divided into the bisphosphonate treatment group (n=42) and control group (n=42) by random number method. The patients in both groups were given the routine anti-osteoporosis drugs such as calcitriol and calcium carbonate D3 after surgery; in addition, the patients in the bisphosphonate treatment group were also given alendronate sodium D3 tablets (each containing alendronate sodium 70 mg, 1 tablet per week), while the control group received a placebo. The bone mineral density (BMD) in thoracolumbar vertebral injury area of patients in the two groups was measured and compared at 1 month, 3 months, 6 months and 1 year after surgery. Results The BMD values of patients in two groups were significantly decreased immediately after reset compared with preoperation, and then they were increased continuously in follow-up. There was no significant difference in BMD between the two groups at 1 month or 3 months after sursery (P>0.05), while the BMD in the bisphosphonate treatment group was significantly higher than that in the control group at 6 months and 1 year after surgery (P<0.05). Conclusion Bisphosphaonate drugs can accelerate the repair of vertebral osteoporosis after thoracolumbar fracture internal fixation, showing a good clinical application value.
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Objective By studying biomechanical responses of the femur-prosthesis-tibia complex under normal standing condition after tumor-type hinged knee arthroplasty, to investigate the cause of femoral perforation in patients after knee arthroplasty, so as to provide a theoretical basis for optimal design and manufacturing of tumor-type hinged artificial knee prosthesis. Methods By coupling CT and 3D optical scanning, the finite element model of the subject-specific femur-prosthesis-tibia complex was established and was validated regarding its availability, so as to analyze stress distribution and stress shielding phenomenon of the complex in standing position. Results (1) Under the loading state of standing, the stress on the femur was significantly larger than that on the tibia, and presented an evident concentration phenomenon. The proximal 1/3 of femoral shaft presented a larger stress, with a stress shielding effect. (2) As the model was based on geometry and bone characteristics of the patient in clinic, the location of femur stress concentration was close to that of femur perforation in the patient, which indicated that femur injury behavior might occur when its own gravity was applied such as the patient condition. Conclusions After implantation of the tumor-type hinged artificial knee prosthesis, the prosthesis marrow needle goes deep into marrow cavities, which brings certain pressure to the marrow cavities even under normal standing condition. The produced stress shielding effect and the match of the prosthesis marrow needle to the marrow cavity are all likely to cause stress concentration on the femur, even make femur crack or perforation, and eventually affect the surgery quality. Thus, the prosthesis design should be carefully optimized before surgery in order to reduce or avoid such phenomenon that is related to the postoperative complication rate.
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Objective To investigate biomechanical properties of the femur during slow walking and stair climbing before and after total hip replacement (THA), so as to provide theoretical basis for optimal design and manufacturing of the prosthetic hip. Methods The 3D finite element model of hip femur was established and validated first, and the stress distributions and stress shielding rates during slow walking and stair climbing before and after THA were calculated. Results During slow walking, the stress increased gradually from the proximal femur to the distal femur, reaching the maximum 90.6 MPa at the lower part of the femur before THA. A stress shielding phenomenon occurred on the femur after THA, but the stress amplitude decreased, with the maximum stress reaching 82.5 MPa. The maximum shielding rate appeared near the greater trochanter of the proximal femoral prosthesis and the total stress shielding rate reached 14.9%-99.0%. In addition, excessive stress concentration occurred at the prosthetic neck. Meanwhile, the stress distribution during stair climbing had a similar regular pattern as that appeared during slow waling, but with a more obvious stress shielding effect. Conclusions The greater stress shielding of the proximal femur and the excessive stress concentration on the prosthetic hip during stair climbing will both influence the THA surgery quality, so patients should minimize the movement involving large joint angle after THA.
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Objective To investigate the variation of stress distributions on proximal femur after hip resurfacing arthroplasty (HRA) by using three-dimensional (3D) finite element method. Methods The 3D finite element model of proximal femur was reconstructed based on 64-slice spiral CT scan image data. Both the stress distributions on proximal femur after metal-on-metal HRA and normal proximal femur were studied, so as to analyze the biomechanical environment changes after HRA. Results After HRA, the superior, anterior, rear and inferior area of the proximal femoral head showed significant stress shielding, with peak stress of 0.60, 0.57, 0.66, 0.79 MPa, respectively, and stress shielding rate of 99.80%, 99.16%, 98.92%, 96.66%, respectively. Increased stress occurred in most regions of the distal femoral head, while stress shielding appeared only in rear area of the distal femoral head, with stress shielding rate of 4.92%. Increased stress occurred in anterior region of the proximal femoral neck, while stress shielding appeared in the superior, inferior and rear area of the proximal femoral neck, with shielding rate of 16.48%, 22.75% and 7.83%, respectively. Increased stress also occurred in inferior area of the distal femoral neck, while the remaining area showed stress shielding. The stress in greater trochanter increased by 9.22%, and the stress shielding rate for lesser trochanter area and basal area of femoral neck were 2.49% and 14.44%, respectively. Conclusions Stress distributions on most regions of proximal femur after HRA were similar to that on normal femur, and the stress transfer was close to physiological status, which could effectively avoid obvious stress shielding in proximal femur and preserve bone mass, which could contribute to normal physiological activity of patients.
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PURPOSE: We evaluated the clinical and radiological results of patients who received the cementless VerSys fiber metal tapered stem for total hip arthroplasty. MATERIALS AND METHODS: Thirty seven hip joint replacements(31 patients) were evaluated over a minimum four year period following the procedure with an average follow-up period of 56 months(48-96 months). The mean patient age was 47.9 years old. Clinical results were analyzed using Harris hip scores, incidence of thigh pain and radiographic analysis was used to assess fixation of the stem, stress shielding, cortical hypertrophy and radiolucent lines around the femoral stem. RESULTS: The average Harris hip score was 90.7 points(82-99 points). Thigh pain was noticed in 6 hips(16%). Proximal femoral bone resorption by stress shielding was observed in 32 hips(86.5%). Cortical hypertrophy was noticed in 16 hips(43.2%) and was statistically correlated with stress shielding of 2nd degree or more according to the Engh classification. Stable bone ingrowth at the last follow-up was seen in 36 hips(97.2%). CONCLUSION: Cementless total hip arthroplasty using the cementless VerSys fiber metal tapered stem demonstrated excellent midterm clinical results as well as excellent radiologic results for stable fixation and endosteal new bone formtion. However, long term follow-up evaluation will be required because of the high rates of proximal bone resorption by stress shielding.
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Humans , Arthroplasty , Bone Resorption , Follow-Up Studies , Hip , Hip Joint , Hypertrophy , Incidence , ThighABSTRACT
@# Objective To establish a new model of the Achilles tendon(AT) contraction by stress-shielding. Methods 8 SD rats were randomly divided into two groups, the normal control group and the experimental group. The ATs of the experimental group were stress-shielded by fixing the upper ankle joint in equines position using a cerclage and transecting the sciatic nerve. The control group received no treatment. All rats were killed three weeks later, and all the ATs of the left hind limbs of the experimental and normal control group were tested morphologically by transmission electron microscope (TEM). Results Compared to the normal control group, the collagen fibrils of the experimental tendons did not arrange very well. The number of tendon cells increased, and some of them were pycnotic. Some mitochondrias were swollen. The proportion of the smaller diameter collagen fibril became lager, and small and large fibrils did not distribute in even. Conclusion Our research is successful compared to the past researches and repeatable.
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PURPOSE: This study analyzed the differences in bone remodeling and stress shielding between cementless total hip arthroplasty and resurfacing arthroplasty by examining the serial bone mineral density around the prosthesis. MATERIALS AND METHODS: Fifty total hip arthroplasty procedures and 50 resurfacing arthroplasty procedures, which were performed between July 2002 and June 2003, were examined to this comparative study. The mean age at surgery was 44 years in the THA group and 36 years in the resurfacing arthroplasty group. The bone mineral density was measured by the DEXA at preoperation and 3 months, 6 months, 12 months after surgery in zone I-III of the acetabulum (classified by DeLee & Charnley) and zone I-VII of the femur (classified by Gruen), and the medial and lateral side of the femoral neck in the resurfacing arthroplasty group. RESULTS: In the acetabulum, zones I and II of both groups showed a significant decrease in the BMD 12 months after surgery but the level of bone loss in the resurfacing arthroplasty group was relatively small compared with those in the THA group. In the proximal femur, the overall amount of bone loss at 3, 6 and 12 months postoperatively were 0.7%, 5%, and 2.6% respectively, and those in zones I and VII at 12 months postoperatively in the THA group were 7.8% and 7.7%, respectively. In the BHR group, the overall bone loss in the proximal femur at 3, 6 and 12 months postoperatively were 5.8%, 4.4%, and 2.9%, respectively. However, those Gruen zones I and VII at 12 months postoperatively were 2.6% and 0.6%, respectively. CONCLUSION: The level of bone loss in Gruen zones I and VII of the resurfacing arthroplaty group was much lower, which suggests that resurfacing arthroplasty can prevent stress shielding and preserve the proximal bone stock around the femoral stem.
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Acetabulum , Arthroplasty , Arthroplasty, Replacement, Hip , Bone Density , Bone Remodeling , Femur Neck , Femur , Prostheses and ImplantsABSTRACT
PURPOSE: To report the results of hip arthroplasty using an uncemented hydroxyapatite (HA) coated anatomical Profile(R) femoral stem during a follow-up period of five to ten years. MATERIALS AND METHODS: Eighty-eight patients, ninety-nine cases of hip arthroplasty, who underwent surgery from May 1993 to February 1998, were reviewed clinically and radiographically. RESULTS: The mean Harris hip rating score was 54.4 preoperatively, which improved to 88.2 at the last follow up postoperatively. The radiographic evaluations revealed that endosteal new bone formation developed at Gruen zone 1 and 7 in all cases (100%) between 6 month and one year after surgery. Approximately 20 cases (20%) showed proximal osteoporosis due to profound stress shielding, and 83 cases (83.8%) showed distal cortical hypertrophy (zone 2, 6). These femoral remodelings correlated with the clinical results statistically. There was no aseptic loosening, but the polyethylene liner was changed only in one hip due to severe liner wear. CONCLUSION: This study indicate that the anatomical Profile(R) femoral stem can provide excellent initial stability and osseointegration. However, profound proximal bone loss was noted secondary to distal cortical hypertrophy in the long-term follow up. Therefore, other design concepts are needed, in which the femoral strain transfers more proximally rather than distally.
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Humans , Arthroplasty , Durapatite , Follow-Up Studies , Hip , Hypertrophy , Osseointegration , Osteogenesis , Osteoporosis , PolyethyleneABSTRACT
As a main treatment instrument of limb fractures, the interlocking nail is used in two ways: dynamic fixation and static fixation. The former has less stress shielding but lower satiability. The latter is just the opposite. Therefore, static fixation is the main choice in clinic. But because of the higher stress shielding, complications take place frequently. This article is to discuss the relationship between micromovement and fracture healing, and calls for a new kind of interlocking nail which has micromovement function.
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PURPOSE: To investigate the annual change of bone mineral density (BMD) around the femoral stem and identified the factors that influence the stress shielding effect in patients who have received extensively porous coated cementless stem. MATERIALS AND METHODS: We reviewed seventy-four patients who were followed up for longer than three years after unilateral primary total hip replacement arthroplasty. The BMD was measured annually using a DEXA QDR 4500(R) on the proximal femur according at the Gruen zone. We analyzed the relationship between the results and the possible variates of periprosthetic bone remodeling. RESULTS: In first year after operation, the BMDs of all Gruen zone decreased significantly. From the second year, the BMDs in Gruen zones 1, 2, and 7 were decreased significantly, but those in Gruen zones 3, 5, and 6 were increased. After three years, the BMD showed no significant change. Among the examined variables including sex, patient's age, stem size, and preoperative Singh's index, stem size and age were found to have strong predictive value. CONCLUSION: Our findings suggest that periprosthetic BMD decreased in all areas over first postsurgical year. From the third year, the BMD stabilized.
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Humans , Arthroplasty , Arthroplasty, Replacement, Hip , Bone Density , Bone Remodeling , FemurABSTRACT
PURPOSE: This study was undertaken to compare the initial micromotion and stress shielding of a "fit and fill" stem to a "proximal fitting and distal tapered" stem in the early postoperative period using the load simulating single leg stance and stair climbing. MATERIALS AND METHODS: Using the data from 3-D human CT scan, authors developed two types of 3-dimensional finite element total hip replacement model of proximal femur, which were inserted with a "fit and fill" stem and a "proximal fitting and distal tapered" stem. The constructions of stems were based on the OmnifitTM stem (about 13,000 element & 20,000 nodes). We compared micromotion, maximal principal stress and strain energy of each stems. RESULTS: The results indicate that micromotion in a fit and fill stem were slightly lower than that of a tapered stem, especially in stair climbing over that in the single leg stance. The maximum principal stress on the cortex of femur was slightly higher in a tapered stem in the case of single leg stance, and 2 times higher in the case of stair climbing. Strain energy also was much higher in a tapered stem in both single leg stance and stair climbing gait. CONCLUSION: These findings indicate that a tapered stem design could provide more favorable biomechanical benefits rather than a fit & fill stem after cementless total hip replacement.
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Humans , Arthroplasty, Replacement, Hip , Femur , Gait , Hip Prosthesis , Hip , Leg , Postoperative Period , Tomography, X-Ray ComputedABSTRACT
Objective:To study the stress distribution dur i ng clenching and rigid internal fixation(RIF)of mandibular symphysis fracture. Methods:ANSYS software was used to establish the models of mandi bular symphysis fracture and the fracture treatment treat with RIF.The stress di stribution of mandibular symphysis fracture under different conditions were then analysed during different period of bone healthing. The value of stress shieldi ng rate was used to represent the level of stress shielding effects.Resu lts:The stress shielding rate decreased with the progression of fracture healing.The stress shielding rate produced by double plates fixation was higher than that by single plate.Stress shielding rate in the mandible fixed with tita nium plate was lower than that with steel plate.Conclusion:Minip late rigid internal fixation system may produce stress shielding effects when it is used to treat mandibular symphysis fractures. Stress shielding effects are a ffected by the attribute, the shape and the position of the plate.