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Biodegradable materials such as WE43 magnesium are of great interest for bone tissue engineering applications. This research paper presents a novel manufacturing methodology (i.e., Joining Stacking based Laser Micro-Spot Welding (JS-LMSW)) for produce tubular WE43 Magnesium scaffolds. The proposed methodology consists of laser-cut tailored geometries joined and stacked using laser micro-spot welding to form a porous structure (scaffold). The relationship between microstructure and mechanical properties of the manufactured WE43 magnesium scaffolds is summarized in this paper. Additionally, the manufactured scaffolds were dimensionally and morphologically characterized, and the obtained results are close to the designed values (relative errors of ∼ 1.04%, 0.93%, 0.83%, and 1.53% for length, width, height, and interconnected porosity, respectively). Compressive testing was conducted on the scaffolds for axial and transversal loading conditions and, micro-hardness was evaluated in the micro spot welds. The obtained results indicated that the developed WE43 magnesium scaffold features bone-like mechanical properties. The elastic modulus range of cancellous bone is between 0.01 and 0.90 GPa compared to WE43 magnesium scaffold́s elastic modulus between 0.07 and 0.41 GPa for transversal and axial conditions, respectively. Hardness results showed values between 74 HV and 80 HV in the fusion zone and heat-affected zone, respectively. This novel methodology opens a new path for the construction of complex geometries such as scaffolds.

Hydroxyapatite (HA) coatings have been widely used for improving the bone-implant interface (BII) bonding of the artificial joint prostheses. However, the incidence of prosthetic revisions due to aseptic loosening remains high. Porous materials, including three-dimensional (3D) printing, can reduce the elastic modulus and improve osseointegration at the BII. In our previous study, we identified a porous material with a sintered bionic trabecular structure with in vitro and in vivo bio-safety as well as in vivo mechanical safety. This study aimed to compare the difference in osseointegration ability of the different porous materials and HA-coated titanium alloy in the BII. We fabricated sintered bionic trabecular porous titanium acetabular cups, 3D-printed porous titanium acetabular cups, and HA-coated titanium alloy acetabular cups for producing a hip prosthesis suitable for beagle dogs. Subsequently, the imaging and histomorphological analysis of the three materials under mechanical loading in animals was performed (at months 1, 3, and 6). The results suggested that both sintered bionic porous titanium alloy and 3D-printed titanium alloy exhibited superior performances in promoting osseointegration at the BII than the HA-coated titanium alloy. In particular, the sintered bionic porous titanium alloy exhibited a favorable bone ingrowth performance at an early stage (month 1). A comparison of the two porous titanium alloys suggested that the sintered bionic porous titanium alloys exhibit superior bone in growth properties and osseointegration ability. Overall, our findings provide an experimental basis for the clinical application of sintered bionic trabecular porous titanium alloys.

Arthroplasty is commonly performed to treat advanced osteoarthritis or other degenerative joint conditions; however, it can also be considered for young patients with severe joint damage that significantly limits their functionality and quality of life. Young patients are still at risk of aseptic mobilization and bone resorption due to the phenomenon of stress shielding that causes an uneven distribution of tensions along the femoral contact surface prosthesis. This phenomenon can be limited by choosing the material of the prosthesis appropriately or by varying its stiffness, making sure that its mechanical behavior simulates that of the femur as much as possible. The aim of this study is to evaluate the mechanical strength of a prosthesis optimized both in shape and material and compare the results with a standard titanium prosthesis. Methods: Through three-dimensional modeling and the use of finite element method (FEM) software such as ANSYS, the mechanical behavior of traditional prosthesis and prosthesis optimized topologically respecting the ASTM F2996-13 standard. Results: With topological optimization, there is a stress reduction from 987 MPa to 810 MPa with a mass reduction of 30%. When carbon fiber is used, it is possible to further reduce stress to 509 MPa. Conclusions: The reduction in stress on the femoral stem allows an optimal distribution of the load on the cortical bone, thus decreasing the problem of stress shielding.

BACKGROUND: Excessive wear of the tibial insert and aseptic loosening of the prosthesis were the main reasons for the failure of the knee prosthesis after total knee arthroplasty. Owing to the large variation of mechanical strength between prosthesis and bone, it would lead to stress shielding on bone, and then induce aseptic loosening of prosthesis. OBJECTIVE: To analyze the stress response of cancellous bone in proximal tibia after functionally graded materials (FGMs) tibial prosthesis implantation by finite element method. METHODS: Two FGMs with different porosity parameters (FGM I and FGM III) were designed using titanium-hydroxyapatite composite. The other was prepared by titanium-ideal bone repairing material and named FGM II. The porosity parameters of FGM I were 0.1, 1 and 1, and the porosity parameters of FGM II and FGM III were 0.4, 0 and 1. A three-dimensional finite element model of total knee arthroplasty was established, and the stress distributions of FGM and titanium alloy tibial prostheses were analyzed by Abaqus software under three working conditions of 0° extension, 30° and 60° flexion. RESULTS AND CONCLUSION: (1) The maximum Von Mises stresses of FGM tibial prostheses were significantly lower than those of titanium alloy tibial prosthesis, and the stresses at the contact zone between the cancellous bone and the stem end were significantly reduced in FGM tibial prostheses groups. (2) According to the stress curve and average stress of the cancellous bone of the tibia along different paths, the stresses of the cancellous bone of the proximal tibia were increased in FGM tibial prostheses groups compared with titanium alloy tibial prostheses, under different working conditions. Specifically, FGM I was increased by 5.4%-17.3%; FGM II was increased by 1.0%-13.5%; and FGM III was increased by 1.6%-15.4%. (3) The results illustrated that FGM prostheses could increase the stress on the cancellous bone of the proximal tibia and reduce the stress shielding effect of the proximal tibia. Therefore, the risk of aseptic loosening was decreased and the availability of the prosthesis was prolonged. Specifically, FGM I tibial prosthesis was the best among the three kinds of FGM prostheses. [ABSTRACT FROM AUTHOR]

Polypropylene meshes used in pelvic organ prolapse (POP) repair are hampered by complications. Most POP meshes are highly unstable after tensioning ex vivo , as evidenced by marked deformations (pore collapse and wrinkling) that result in altered structural properties and material burden. By intentionally introducing collapsed pores and wrinkles into a mesh that normally has open pores and remains relatively flat after implantation, we reproduce mesh complications in vivo. To do this, meshes were implanted onto the vagina of rhesus macaques in nondeformed (flat) vs deformed (pore collapse +/− wrinkles) configurations and placed on tension. Twelve weeks later, animals with deformed meshes had two complications, (1) mesh exposure through the vaginal epithelium, and (2) myofibroblast proliferation with fibrosis – a mechanism of pain. The overarching response to deformed mesh was vaginal thinning associated with accelerated apoptosis, reduced collagen content, increased proteolysis, deterioration of mechanical integrity, and loss of contractile function consistent with stress shielding – a precursor to mesh exposure. Regional differences were observed, however, with some areas demonstrating myofibroblast proliferation and matrix deposition. Variable mechanical cues imposed by deformed meshes likely induce these two disparate responses. Utilizing meshes associated with uniform stresses on the vagina by remaining flat with open pores after tensioning is critical to improving outcomes. Pain and exposure are the two most reported complications associated with the use of polypropylene mesh in urogynecologic procedures. Most meshes have unstable geometries as evidenced by pore collapse and wrinkling after tensioning ex vivo , recapitulating what is observed in meshes excised from women with complications in vivo. We demonstrate that collapsed pores and wrinkling result in two distinct responses (1) mesh exposure associated with tissue degradation and atrophy and (2) myofibroblast proliferation and matrix deposition consistent with fibrosis, a tissue response associated with pain. In conclusion, mesh deformation leads to areas of tissue degradation and myofibroblast proliferation, the likely mechanisms of mesh exposure and pain, respectively. These data corroborate that mesh implantation in a flat configuration with open pores is a critical factor for reducing complications in mesh-augmented surgeries. [Display omitted] [ABSTRACT FROM AUTHOR]

Background: We created patient-based 3D finite-element (FE) models that simulate the congruent-arc Latarjet (CAL) and traditional Latarjet (TL) procedures and then compared their stress distribution patterns with different arm positions and glenoid defects. Methods: The computed tomography data of 10 adult patients (9 men and 1 woman, ages: 18–50 years) were used to develop the 3D FE glenohumeral joint models. Twenty-five and 35% bony defects were created on the anterior glenoid rim, and the coracoid process was transferred flush with the glenoid by the traditional and congruent-arc techniques using two half-threaded screws. A load was applied to the greater tuberosity toward the center of the glenoid, and a tensile force (20 N) was applied to the coracoid tip along the direction of the conjoint tendon. The distribution patterns of the von Mises stress in the traditional and congruent-arc Latarjet techniques were compared. Results: The mean von Mises on the graft was significantly greater for the TL technique than for the CAL. While the von Mises stress was greater in the distal medial part of the graft in the TL models, a higher stress concentration was observed in the distal lateral edge of the coracoid graft in the CAL models. The proximal medial part of the graft exhibited significantly lower von Mises stress than the distal medial part when compared according to technique, defect size, and arm position. Increasing the glenoid defect from 25 to 35% resulted in a significant increase in stress on the lateral side of the graft in both models. Conclusion: The stress distribution patterns and stress magnitude of the coracoid grafts differed according to the procedure. Due to placing less stress on the proximal–medial part of the graft, the CAL technique may lead to insufficient stimulation for bone formation at the graft–glenoid interface, resulting in a higher incidence of graft osteolysis. Clinical relevance The CAL technique may lead to a higher incidence of graft osteolysis. Level of evidence: Basic Science Study; Computer Modeling. [ABSTRACT FROM AUTHOR]

Lattice structures are porous materials with interconnected porosity and non-stochastic pore distribution that present unique properties. Recently, additive manufacturing (AM) has driven attention to the production of lattice structures since it provides a direct-from-CAD production, tailoring their mechanical properties by controlling their unit cell type, pore size, strut size, and porosity. However, the mechanical behavior of these structures is yet to be understood, as surface post-processing is needed for the biomedical application (ASTM F3335) and manufacturing deviations and defects imply different results from the CAD projected models. In this work, three different types of Ti-6Al-4 V ELI lattice structures were projected and produced by powder bed fusion AM technique. The surface structures were cleaned using pickling, and as-built and pickled structures were compared using scanning electron microscopy (SEM), optical microscopy (OM), and Archimedes' principle. Mechanical compressive tests were conducted on the surface-cleaned lattice structures, and fractured surfaces were analyzed by SEM. Finally, finite element analysis (FEA) was made to understand the stress distribution during compression. The results show that pickling is successful in removing adhered powder particles from lattice structures' outer and inner surfaces, as it also reduces surface roughness and defects, which may act as stress raisers. The compressive tests along with fracture analysis show that fracture behavior cannot be predicted using Maxwell's criterion in 3D and FEA can be a better tool to predict fracture behavior. These results show that classifications of lattice structures made by AM in stretch or bending-based need further research. [ABSTRACT FROM AUTHOR]

Background: The high rate of aseptic loosening of cemented stems has led to their frequent use in endoprosthetic reconstruction. However, problems, such as stem breakage and stress shielding at the insertion site, remain. The Japanese Musculoskeletal Oncology Group (JMOG) has developed Kyocera Modular Limb Salvage System (KMLS) cementless stems with a unique tapered press-fit and short fixation design. This study aimed to clarify the short-term postoperative outcomes of this prosthesis and validate the stem design.Methods: One hundred cases of KMLS cementless stems (51 male patients; median age, 49 years; mean follow-up period, 35 months), with a minimum follow-up of 2 years, for the proximal femur (PF), distal femur (DF), and proximal tibia were prospectively registered for use. Prosthesis survival, complication rates, postoperative functional, and radiographical evaluation were analyzed. Complications or failures after insertion of the KMLS endoprostheses were classified into five types and functional results were analyzed according to the MSTS scoring system at postoperative 1 year. The diaphyseal interface and anchorage were graded by the ISOLS system at postoperative 2 years.Results: The overall prosthesis survival rates at 2 and 4 years were 88.2 and 79.6%, respectively. The prosthesis-specific survival rate excluding infection and tumor recurrence was 90.2 and 87.9%, respectively. Younger age (p = 0.045) and primary tumor (p = 0.057) were associated with poor prognosis of prosthesis-specific survival excluding infection and tumor recurrence. Complications were observed in 31 patients, 13 patients underwent revision surgery. The mean MSTS functional score at 1 year postoperatively was 68%. Early implant loosening was significantly more common in the DF (p = 0.006) and PF/DF straight stem (p = 0.038). The ISOLS radiographic evaluation at 2 years after surgery revealed good bone remodeling and anchorage in most cases (bone remodeling: 90% / excellent and good, anchorage: 97% / excellent and good).Conclusions: Tumor endoprosthesis long-term fixation to the diaphysis of the lower extremity remains challenging. The KMLS cementless stem with a unique tapered press fit design showed good short-term results in maintaining bone stock. To prevent early loosening, a curved stem should be used in PF and DF, but long-term follow-up is necessary. [ABSTRACT FROM AUTHOR]

Purpose: The aim of this study was to evaluate the mechanical stimuli transfer at the bone-implant interface via stress and strain energy density transfer parameters. This study also aimed to investigate the effect of different implant stiffness and parafunctional loading values on the defined mechanical stimuli transfer from the implant to the surrounding bone. Methods: A three-dimensional finite element model of two-piece threaded dental implant with internal hexagonal connection and mandibular bone block was constructed. Response surface method through face-centred central composite design was applied to examine the influence of two independent factors variables using three levels. The analysis model was fitted to a second-order polynomial equation to determine the response values. Results: The results showed that the implant stiffness was more effective than the horizontal load value in increasing the stress and strain energy density transfers. The interaction between both factors was significant in decreasing the likelihood of bone resorption. Decreasing the implant stiffness and horizontal load value led to the increased stress transfer and unexpected decrease in the strain energy density, except at the minimum level of the horizontal load. The increase in the implant stiffness and horizontal load value (up to medium level) have increased the strain energy transfer to the bone. Conclusions: The stress and strain energy density were transferred distinctively at the bone--implant interface. The role of both implant stiffness and parafunctional loading is important and should be highlighted in the preoperative treatment planning and design of dental implant. [ABSTRACT FROM AUTHOR]

Background: Total knee arthroplasty (TKA) tibial baseplate thickness, metallurgy, and implant fixation with cement may influence stress shielding. The purpose of the present study is to compare bone mineral density of 2 cemented and press-fit TKA designs with differing tibial baseplate thicknesses and metallurgy over a 2-year period to assess for changes in stress shielding.Methods: One-hundred one TKAs were performed in this Institutional Review Board-approved, prospective study. There were 4 cohorts: DePuy Attune cemented and press-fit, and Stryker Triathlon cemented and press-fit. The Attune tibial baseplate was thicker; both cemented tibial and femoral components were cobalt-chromium. The DePuy Attune press-fit had a cobalt-chromium sintered bead porous coating while the Stryker Triathlon was 3-dimensional printed highly porous titanium alloy. All patients had quantitative dual-energy X-ray absorptiometry scans performed at baseline (4-6 weeks postoperatively) and at 1 and 2 years postoperatively. Stress shielding was evaluated by comparing percent change in bone mineral density in 11 radiographic zones over 2 years.Results: Over a 2-year period, there were no differences in stress shielding on the tibial side in either cemented or press-fit between Stryker Triathlon and DePuy Attune; however, there were differences on the femoral side. The press-fit tibial components of the Stryker Triathlon and DePuy Attune had either similar or less stress shielding over a 2-year period compared to their cemented counterparts.Conclusion: This study comparing 2 TKA implants with differing tibial tray thickness did not find significant differences in tibial stress shielding between designs. There was a difference in stress shielding on the femoral side between designs, suggesting that longer term follow-up is warranted. [ABSTRACT FROM AUTHOR]

Purpose: Some patients show severe humeral bone stress shielding even one year after press-fit humeral stem, which can be a risk factor for implant durability. This study compared humeral stress shielding and clinical outcomes between high and low filling ratio (HFR and LFR) stems in primary reverse shoulder arthroplasty (RSA).Methods: From 2015 to 2020, 104 patients who underwent RSA with a non-cemented standard-length humeral stem were examined. The humeral stems included large press-fit stems (HFR group, 53 patients) or small non-press-fit stems with autogenous cancellous bone grafting (LFR group, 51 patients). The radiologic and clinical outcomes were compared between the groups one year post-operatively.Results: One patient in the LFR group with early infectious dislocation was excluded from the 1-one year evaluation. No stress shielding was observed in 27/50 (54.0%) and 5/53 (9.4%) of patients in the LFR and HFR groups, while 3/50 (6%) and 19/53 (35.8%) patients showed high-stress shielding, respectively. However, the stem alignment change, subsidence, complications and evidence of loosening did not differ between the groups. The final range-of-motion and functional scores were significantly poorer in the LFR group than those in the HFR group, although the difference was minimal.Conclusion: Even at one year follow-up, patients receiving LFR stems with autogenous bone grafting had significantly less humeral stress shielding compared to patients with HFR stem with press-fit in primary RSA, without compromising stem stability. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to compare the periprosthetic BMD changes around Tri‐Lock "Bone Preserving Stem" with the other two common and longer stems (Corail and Summit) after THA. Methods: It was a retrospective cohort study followed patients underwent the total hip arthroplasty from January 2013 to December 2015. They were selected and followed from January 2013 to Janaury 2020. Patients without osteoporosis underwent hip replacements with three aimed stems were included. Among the 138 patients included, 49 patients received the Tri‐Lock stem, 44 patients received the Corail stem, and 45 patients received the Summit stem. The periprosthetic BMD changes evaluated by the Dual energy X‐ray absorptiometry (iDXA) measurement according to the seven Gruen zones was the primary outcome. The Radiographic changes including spot welds, pedestal sign and grade of stress shielding was evaluated by the consecutive hip images. Einzel‐Bild‐Roentgen‐Analyze‐femoral component analysis (EBRA‐FCA) was used to measure the stem migration at 5 years postoperatively. Patient‐reported outcomes (PROMs) and adverse events were assessed and compared in three groups. Finally, the subgroups for the periprosthetic BMD changes, radiological and clinical outcomes were made based on the age, gender and length of follow‐up. Results: A total of 138 patients were retrospectively followed for an average of 4.66 years. Excepting the different stems used in three groups, the age, gender and other characteristics of patients included were similar between groups. There was no significant difference between the three groups in periprosthetic BMD changes over postoperative 5 years. The Summit stem shown more BMD loss in Gruen zone 1 compared with the Tri‐Lock and Corail stems without significant difference (7.49%, −1.89% and −2.62%, respectively, P = 0.42). And the most prominent BMD loss was found in Gruen zone 7 for all three stems (−12.60%, −11.84%, and −9.56%, respectively, P = 0.91). The spot weld was significantly more common around the Corail stem, while there was no difference in the stem migration between three groups. Patient reported outcomes (PROMs) were significantly improved compared with the preoperative values. Regarding the rate of postoperative complications, two patients underwent the dislocation and 25 patients sometimes felt mild to moderate thigh pain. Subgroup analysis showed that female patients older than 50 years lost more BMD and had lower clinical scores, while the stem stability was not good enough in male patients. Conclusions: The Tri‐Lock Bone Preserving Stem did not show significant difference in periprosthetic BMD changes compared with the other two conventional longer stems at 5 years after THA. [ABSTRACT FROM AUTHOR]

In shoulder arthroplasty, bone resorption around the stem can lead to stem loosening and makes surgery difficult at the time of revision. Proximal bone resorption after reverse shoulder arthroplasty can cause instability because of a decrease of deltoid wrapping effect. As factors of the stem itself, such as stem coating, shape, length, and use of bone cement, may also affect bone resorption, a single-stem model should be used to compare bone resorptions between different pathologies and surgical procedures. However, to date, a few reports have compared these differences in detail using a single-stem model. Therefore, we investigated the prevalence and location of humeral bone resorption in a single-stem model. The study included 100 shoulders that underwent anatomical total shoulder arthroplasty (TSA) or humeral head replacement (HHR) with a single uncemented humeral stem from 2008 to 2018. The patients were 31 men and 69 women. The mean age at surgery was 72.9 years (range, 41-86 years). The patients were divided into three groups: especially, 25, 61, and 14 shoulders received TSA for primary osteoarthritis without rotator cuff tears (TSA group), HHR using an anatomical head with rotator cuff repair for cuff tear arthropathy (CTA) (HHR group), and HHR using a CTA head without rotator cuff repair (CTA group), respectively. Patients were monitored for a mean of 56 months (range, 12-98 months). The location of bone resorption was divided into seven zones as follows: zone 1, greater tuberosity; zone 2, lateral diaphysis; zone 3, lateral diaphysis beyond the deltoid tuberosity; zone 4, tip of the stem; zone 5, medial diaphysis beyond the deltoid tuberosity; zone 6, medial diaphysis; and zone 7, calcar region. The degree of bone resorption was classified from grade 0 to 4. Bone resorption of grade 3 or higher was significantly more frequent at the greater tuberosity in the HHR and CTA groups (P <.001 and P <.001, respectively) than that in the TSA group. Grade 4 bone resorption was significantly more frequent in the CTA than that in the TSA and HHR groups in zone 1 (P =.016 and P =.041, respectively). The state of attachment of the rotator cuff to the greater tuberosity might affect bone resorption at the greater tuberosity, such as the greater tuberosity after shoulder arthroplasty. In cases of shoulder arthroplasty for arthropathy with rotator cuff tear, performing rotator cuff repair might prevent bone resorption. Level IV; Prognosis Study [ABSTRACT FROM AUTHOR]

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Total hip Arthroplasty (THA) is performed every year at a very high frequency to improve the quality of life of thousands of patients all over the globe. Nevertheless, the expected service life of such surgery remains unsuitable for patients under 50 years old. This is mainly related to stress shielding and the potential adverse tissue reaction to some of the elements of the market-dominant implant materials. In this research, functionally graded (FG) implant designs of several titanium alloys layered with hydroxyapatite (HA) are proposed to provide lower implant stiffness compared to a solid stem to approach the requirements of human bone. Moreover, TNZT (Ti35Nb7Zr5Ta), and TMZF (Ti12Mo6Zr2Fe) second-generation titanium alloys are studied as a replacement for the famous Ti6Al4V alloy to avoid the adverse tissue reactions related to aluminum and vanadium elements. The different FG models are numerically tested using a 3D finite element simulation after virtual implantation in a femur bone under the dynamic load of a patient descending stairs. In the numerical study, the variation in stress distribution and strain energy in a femur bone is assessed for different FG hip stems as well as the axial stiffness of the hip stems. Results indicated an increase in strain energy and von Mises stress in the cortical and cancellous bones using FG hip stems. Additionally, the axial stiffness is reduced for all FG hip stems relative to the commercial Ti6Al4V hip stem.

Objective To investigate whether the periprosthetic bone environment could be affected by activity during the early rehabilitation period after primary total hip arthroplasty (THA) and to evaluate the safety and efficacy of activity during the early rehabilitation period. Methods This random clinical trial was conducted from January 2017 to July 2017. A total of 22 selected patients with advanced osteonecrosis of the femoral head (ONFH) who underwent primary unilateral THA were randomized (1:1) to a high activity level group (HA group) or a low activity level group (LA group). The HA group included nine men and two women, aged 53.18 ± 13.29 years. The LA group included five men and six women, aged 55.73 ± 11.73 years. The intervention was different postoperative daily walking distances guided by researchers: 1727.27 ± 564.08 m 0–2 months and 4272.73 ± 904.53 m 3–6 months postoperation for the HA group and 909.09 ± 583.87 m 0–2 months and 2409.09 ± 1068.13 m 3–6 months postoperation for LA group. The primary outcomes were radiographic evaluation (prosthetic stability and stress shielding based on the Engh scale) and bone mineral density (BMD) with a femoral prosthesis (individual and intergroup comparison using seven Gruen zones) at 6 months postoperatively. Secondary outcomes were set to confirm the safety and efficacy of activity during early rehabilitation, including day 1 erythrocyte sedimentation rate (ESR), day 1 hypersensitive C‐reactive protein (CRP), length of hospital stay (LOS), and the Harris hip score (HHS) at discharge, 2 months postoperatively, and 6 months postoperatively. Results Patients were followed up for 6 months after surgery. Regarding primary outcomes, all prostheses were assessed as stable, with bone in‐growth. There were no adverse events in any cases. The HA group had a higher incidence of stress shielding than the LA group, but there was no statistical significance (63.64% vs 18.18%; P > 0.05). The degree of stress shielding had a different distribution for the two groups (P 0.05). The HHS on day of discharge was higher in the HA group than in the LA group (60.73 ± 5.37 points vs 51.18 ± 8.05 points, P 0.05) and 6 months (90.45 ± 5.24 points vs 91.55 ± 4.03 points, P > 0.05). Conclusion High activity levels during early rehabilitation after primary THA accelerate the process of bone remodeling and aggravate stress shielding, with no significant benefits for functional recovery.

Abstract Background Limb salvage surgery (LSS) is the preferred method for treatment of patients with sarcomas and to a greater extent also to patients with metastatic bone disease. The aim of the present study was to evaluate the adaptive remodeling of the periprosthetic cortical bone after insertion of a tumor prosthesis with cemented stem. Methods A prospective study of 21 patients (F/M = 12/9), mean age 55 years (range 15–81) with metastatic bone disease (n = 9), sarcomas (n = 8) or aggressive benign tumors (n = 4) who underwent bone resection due to a tumor, and reconstruction with a tumor-prosthesis (Zimmer® Segmental 130 mm straight fluted cemented stem with trabecular metal (TM) collars) in the proximal femur (n = 10), distal femur (n = 9) or proximal tibia (n = 2). Measurements of bone mineral density (BMD) (g/cm2) were done postoperatively and after 3, 6, and 12 months using dual-energy X-ray absorptiometry. BMD was measured in 4 regions of interest around the cemented stem and in one region of interest 1 cm proximal from the ankle joint of the affected limb and measurement of the contralateral ankle was used as reference. Repeated measures ANOVA and students paired t-test was used to evaluate BMD changes over time. Results At 1-year follow-up, BMD decreased compared to baseline in all four regions of interest with a statistically significant bone loss of 8–15%. The bone loss was most pronounced (14–15%) in the 2 regions of interest closest to the trabecular metal (TM) collar and lowest (8%) adjacent to the tip of the stem. Conclusion After 1 year the decrease in bone mineral density of the ankle on the affected limb was 9% and the contralateral ankle was close to baseline, thus suggesting that the periprosthetic bone mineral density changes during follow-up, mainly are caused by stress shielding and immobilization. Trial registration The study was approved by the Scientific Ethical Committee of the Capital Region of Denmark (J. No. H-2-2014-105) and the Danish Data Protection Agency (J. No.: 2012–58-00004 ).

Abstract Background The procedure of femoral stem revision is challenging, and bone conservation with less stress shielding is a mandatory effort in these cases. Although there are several reports of stem revision with stems designed for primary total hip arthroplasty (THA), there is no report on stem revision with the Wagner cone prosthesis. Methods Between 1996 and 2008, 41 hips of 41 consecutive patients were subjected to femoral revision THA using the Wagner cone prosthesis. The mean age during revision surgery was 56.1 years, and the mean follow-up period was 14.8 years. The clinical results were evaluated, and the femoral component was assessed radiologically. Results The results showed that the average period from the first operation to revision THA was 8.0 years. Additionally, the mean Harris hip score improved from 52 points preoperatively to 83 points at the final follow-up. All stems showed bone integration in the radiological evaluation. A subsidence of more than 5 mm was observed in 3 out of 28 (10.7%) femoral stems. Two patients needed an acetabular revision for acetabular cup loosening during the follow-up period. Furthermore, one patient had recurrent dislocation and had to undergo revision surgery for soft tissue augmentation. Conclusions We achieved favorable clinical and radiological long-term outcomes in femoral stem revision using the Wagner cone prosthesis. This cementless femoral stem could be an option for femoral stem revision in cases with relatively good bone stock.

Magnesium-based alloys are relatively new materials for orthopedic implants. One common component that makes magnesium-based alloys biocompatible and chemically stable is the addition of minor compositions of rare earth metals like yttrium to anchor other chemically active components. From an orthopedic perspective, two goals are of primary concern. One is sufficient mechanical support to stabilize the fracture and reduce inflammation. Another is assistance for the transition of osteogenesis and intramembranous ossification for bone production and remodeling. To attain both goals and further improve the current magnesium-yttrium alloys, adding extra ingredients to improve osseointegration is a common and effective approach. By the nature of bone chemistry, calcium is the top choice as calcium is the key element in maintaining bone integrity and biochemical metabolism. In this study, the mechanical behaviors of a calcium-added magnesium-based alloy (Mg-Y 3.5 wt%) are investigated by experiments. This inventive idea for the natural source of calcium is obtained from chicken eggs due to their (1) cost-effective and abundant availability, and (2) naturally synthesized calcium carbonate along with a minor content of organic materials. The fabrication processes involved are the ball-milling of eggshells as an additive at 1, 3, and 5 wt%. into magnesium-yttrium alloys and resistance casting to form composites. Material characterization includes microstructural analysis by X-ray diffraction, morphological/elemental analysis via optical microscopy, field emission scanning electron microscopes, energy-dispersive X-ray spectroscopy, mechanical properties by uniaxial compression and Vickers microhardness tests. Experimental results supplemented by statistical and finite element analysis indicate that the new composite exhibits enhanced ductility; and the 3 wt% eggshell-added alloys show better reinforcement of mechanical properties among all samples with an ultimate compression strength of 161.19 MPa, maximum elongation of 17.53 %, and hardness of 457.48 (N/mm2). Note that the comparable mechanical strength of the composite to that of human bones could reduce the stress shielding on bones and further help the process of bone remodeling. [Display omitted] • Successful fabrication of Mg-Y with eggshell powders until 5 wt%. • Eggshell powders as additives enhance the ductility of Mg-Y alloys. • The core-shell structure of (Y 2 O 3 , Al 2 O 3)-CaCO 3 reinforces Mg matrix. [ABSTRACT FROM AUTHOR]

Periodic cellular materials such as body-centered cubic, face-centered cubic, and triply periodic minimal surfaces, have been used to construct scaffolds for bone tissue engineering. Their use is suboptimal for reasons like stress concentration at nodes, and/or poor anisotropy. Stochastic structures can mimic the bone microarchitecture with anisotropic mechanical properties. While several methods exist for generating stochastic structures, they face limitations like being computationally expensive, complex, or only applicable in specific cases. In this work, scaffolds are created using level set equations which permit spatially controllable porosity. A 3D volume is populated with random nodes, which segment the 3D volume into subdomains. Each subdomain is occupied with a basic architecture generated through level-set equations. All the architectures in the subdomains are then smoothly integrated at sub-domain boundaries to form the stochastic scaffold. Stainless steel stochastic scaffolds with porosities from 58% to 70% were fabricated and their mechanical characteristics, as well as cell viability, was assessed. Young’s modulus of the scaffolds ranges from 0.02 to 2 GPa, in the same range as that of trabecular bone, thus, mitigating stress shielding. In-vitro assay displayed a statistically significant osteoblast growth from Day 1 to Day 3 in 58%, 61%, and 64% porosity scaffolds.

Hip replacement femoral implants are made of substantial materials that all have stiffness considerably higher than that of bone, which can cause significant bone resorption secondary to stress shielding and lead to severe complications. The topology optimization design method based on the uniform distribution of material micro-structure density can form a continuous mechanical transmission route, which can better solve the problem of reducing the stress shielding effect. A multi-scale parallel topology optimization method is proposed in this paper and a topological structure of type B femoral stem is derived. Using the traditional topology optimization method (Solid Isotropic Material with Penalization, SIMP), a topological structure of type A femoral stem is also derived. The sensitivity of the two kinds of femoral stems to the change of load direction is compared with the variation amplitude of the structural flexibility of the femoral stem. Furthermore, the finite element method is used to analyze the stress of type A and type B femoral stem under multiple conditions. Simulation and experimental results show that the average stress of type A and type B femoral stem on the femur are 14.80 MPa, 23.55 MPa, 16.94 MPa and 10.89 MPa, 20.92 MPa, 16.50 MPa, respectively. For type B femoral stem, the average error of strain is −1682με and the average relative error is 20.3% at the test points on the medial side and the mean error of strain is 1281με and the mean relative error is 19.5% at the test points on the outside.

Objectives: Periprosthetic bone fragility due to stress shielding (SS) can be a risk factor of periprosthetic fracture after cementless total hip arthroplasty (THA). We aimed to obtain epidemiological information on periprosthetic fragility fracture of the femur (PPFF) after THA. Methods: We retrospectively reviewed the medical records of 1062 hips that had undergone cementless THA. We evaluated the epidemiological data as well as the features of PPFFs. Results: Of the 1062 hips, 8 (0.8%) were diagnosed with PPFFs. The survival rates, with the occurrence of PPFF as the end point, were 99.2% and 97.6% at 10 and 16 years postoperatively, respectively. When patients were classified as having either mild or severe SS on radiographs 5 years postoperatively, there was no significant difference in the survival rate, with PPFF as the end point. Conclusions: In our cases, the incidence of PPFF after cementless THA was 0.8%. [ABSTRACT FROM AUTHOR]

The maximum stresses on a femoral stem must be known for selecting the right size and shape of the shaft cross-sectional area for reducing the stress shielding effect generated after the total hip arthroplasty (THA) surgical procedure. The methodology proposed in this study provides the tools to the designers of femoral stems and orthopedic surgeons to select the adequate femoral stem cross section, decreasing the stiffness of the stem, thus reducing the stress shielding effect in the patient bones. The first contribution is the theoretical development of the maximum static stress calculation for 12 different femoral stem models with the beam theory, followed by the comparison with the static finite element analysis (FEA) simulations and finally the experimental corroboration of one femoral stem model measuring the strain with linear strain gages and transform it to stresses, the three different approaches provide comparable results, with a maximum average error of less than 8.5%. The second contribution is the formulation of a new selection methodology based on maximum stresses in the femoral stem and the cross section area for decreasing the stress shielding effect, optimizing the area needed for withstand the loads and decreasing the overall stiffens of the stem. [ABSTRACT FROM AUTHOR]

Purpose: Short-stem prostheses in hip arthroplasty have emerged as an alternative to conventional stems, especially in younger patients. The purpose of this study was to compare functional and radiological results of a short metaphyseal fitting cementless stem versus a conventional stem implant, in patients younger than 60 years. Methods: All patients operated from January 2006 to April 2013 were included, obtaining a minimum follow-up of 7 years. Harris Hip Score (HHS) and SF-36 (quality of life) questionnaires were applied and the presence of "thigh pain" was specifically assessed. We also compared complication rate, revision rate and average prosthesis survival. Femoral stress shielding (Gruen scale), stem subsidence, varus-valgus tilt and implant stability (Engh scale) were also compared. Results: A total of 101 short-stem and 74 conventional arthroplasties were included, with an average follow-up of 9.82 (7–14) years. HHS functional score and SF-36 were excellent in both implants and no significant difference between them (p > 0.05) was found. However, "thigh pain" was present in 7 patients with conventional stems and none with short-stems (p < 0.001). The survival rate at 13 years was 99%, for both implants, and no significant differences were found between them (χ2(2) = 0.178; p = 0.673). Conventional stems had stress shielding at the greater trochanter in 72% of the cases and 43% at the calcar, being statistically superior (p < 0.001) to the stress shielding observed in the short stems. Conclusion: According to our results, this short-stem seems to allow preservation of bone stock, with decreased stress shielding and also a lower incidence of thigh pain compared to conventional stems. Level of Evidence: Level III retrospective comparative study. [ABSTRACT FROM AUTHOR]

Stress shielding is an important factor in the internal fixation of a fracture. To explore the regularity of stress shielding in internal fixation, a simplified model of a comminuted femoral shaft fracture bridged by a locking plate was established and finite element analysis was performed to analyze the load distribution between the plate and femur from the proximal end of the femur to the fracture line and investigate the stress shielding degree of the plate on the bone. The stress, deformation, and axial compressive force distribution of four internal fixation schemes under compression were obtained, and the stress shielding degrees on each section was calculated. To compare the regularity of stress shielding and flow distribution, the relationship between the compressive force increment and stress shielding degree was established. The normalized curves of compressive force increment with the plate section position were compared with the flow distribution in a Z-type manifold, a parallel pipe system similar to an internal fixation system in structure and working characteristics. For quantitative comparison, the similarity between normalized curves of the compressive force increment and simulated flow distribution was calculated. The regularity of load distribution along the section position of the plate was similar to the flow distribution in the Z-type manifold. Therefore, the flow distribution pattern of the Z-type manifold can be used to characterize the regularity of load distribution in internal fixation. This study provided a new method to characterize the stress shielding degree of a locking plate on bone. [ABSTRACT FROM AUTHOR]

This study focused on the design and the preparation method of a new biomaterial, Mg30Zn30Sn30Sr5Bi5 (at%) alloy, and its simulation and property analyses. Based on the comprehensive consideration of the preparation of high-entropy alloys, the selection of biomaterial elements, and the existing research results of common Mg-based materials, the atomic percentage of various elements, that is, Mg:Zn:Sn:Sr:Bi = 30:30:30:5:5, was determined. Using the theoretical methods of thermodynamic performance analysis and solidification performance analysis, the proposed composition was simulated and analyzed. The analysis results showed that the mechanical properties of the new material can meet the design requirements, and it can be prepared in physical form. XRD, SEM, PSD, compression tests, and other experimental tests were conducted on the material, and the alloy composition and distribution law showed various characteristics, which conformed to the "chaotic" characteristics of high-entropy alloys. The elastic modulus of the material was 17.98 GPa, which is within the 0–20 GPa elastic modulus range of human bone. This means that it can avoid the occurrence of stress shielding problems more effectively during the material implantation process. [ABSTRACT FROM AUTHOR]

Reducing stress shielding of stem-inserted femurs in total hip arthroplasty caused by the high stiffness of the stem is an emerging medical engineering issue. In this study, a numerical design optimization methodology lattice infill stem was developed to realize a stem, balancing the low stiffness and strength requirements. Two pairs of models and loading conditions were introduced for the stress shielding and strength criteria. The objective function was set as the weighted sum of the criteria. Its effective density distribution was optimized by handling the representative size of the lattice as a design variable, assuming that the so-called body-centered cubic lattice was the base shape of the lattice. In the optimization, the approximated model of the lattice was handled as a solid material with the effective physical properties of the lattice derived by the homogenization method. After optimization, the detailed lattice stem geometry was modeled based on the obtained optimal lattice distribution, and the actual performance was numerically evaluated. The developed stem increased the stress applied to the remaining femur by 32.4% compared with the conventional stem. [ABSTRACT FROM AUTHOR]

The purpose of this study is to design a patient-specific TMJ implant and study its behaviour under different loading conditions compared with natural intact TMJ. There are several diseases, which affect the proper growth and function of TMJ, and in some cases, TMJ injury results from accidents. To repair the TMJ, temporomandibular joint replacement or TJR surgery is performed. In this work, CT-scan data of the skull and mandible region with broken condylar head were used to study the biomechanical behaviour of the intact mandible and customized TMJ prostheses in order to design a patient-specific total TMJ implant. The customized TMJ implant was virtually studied under simulated loading conditions using finite element method (FEM) in ANSYS Workbench and then compared to the intact jaw-mandible for the combinations of two different biocompatible material models. It is observed that the natural TMJ has a higher deformation value as compared to the patient-specific TMJ implant due to the lower mechanical strength of bone relative to the Ti-6Al-4V and Co-Cr alloy. Hence, we can conclude that the designed custom TMJ implant is safe for the patient from the point of design perspective. [ABSTRACT FROM AUTHOR]

This review describes previous studies undertaken in the field of titanium alloy based human body implants, and the potential to be fabricated using one of the most disruptive technologies, i.e., additive manufacturing. Laser cladding is an emerging additive manufacturing technique and can produce implant materials directly from premixed alloy powders. Human body implants are specific materials that have to be manufactured according to the patient's requirements and titanium alloys have been the prime choice for patient-specific implants. However, stress shielding (a mechanical incompatibility) occurs in titanium alloys due to which a follow-up revision surgery needs to be performed. Therefore, numerous studies are being undertaken by researchers to find suitable alternatives to existing alloys. β-titanium alloys have proven to be more useful due to their stable microstructural and mechanical properties. In this article, useful fundamentals of laser cladding along with potential applications are discussed. An in-depth review on laser cladded titanium alloys, their in-vitro corrosion and wear behaviour is presented and useful alternatives are suggested. [ABSTRACT FROM AUTHOR]

Stress shielding of the proximal humerus following total shoulder arthroplasty (TSA) can promote unfavorable bone remodeling, especially for osteoporotic patients. The objective of this finite element (FE) study was to determine if a hollow, rather than solid, titanium stem can mitigate this effect for healthy, osteopenic, and osteoporotic bone. Using a population‐based model of the humerus, representative average healthy, osteopenic, and osteoporotic humerus FE models were created. For each model, changes in bone and implant stresses following TSA were evaluated for different loading scenarios and compared between solid versus hollow‐stemmed implants. For cortical bone, using an implant decreased von Mises stress with respect to intact values up to 34.4%, with a more pronounced effect at more proximal slices. In the most proximal slice, based on changes in strain energy density, hollow‐stemmed implants outperformed solid‐stemmed ones through reducing cortical bone volume with resorption potential by 11.7% ± 2.1% (p =.01). For cortical bone in this slice, the percentage of bone with resorption potential for the osteoporotic bone was greater than the healthy bone by 8.0% ± 1.4% using the hollow‐stemmed implant (p =.04). These results suggest a small improvement in bone‐implant mechanics using hollow‐stemmed humeral implants and indicate osteoporosis could exacerbate stress shielding to some extent. The hollow stems maintained adequate strength and using even thinner walls may further reduce stress shielding. After further developing these models, future studies could yield optimized implant designs tuned for varying bone qualities. [ABSTRACT FROM AUTHOR]

Nonabsorbable suture augmentation of ligament reconstruction has seen an increase in use over the past several years with the goal of protecting the newly reconstructed ligament while allowing early rehabilitation for a potential earlier return to activity and sport. By spanning the joint with a durable nonabsorbable suture, this construct shares the stress and load seen by the reconstructed ligament, thereby protecting it from forces that could result in an early failure during the early ligamentization phase of the tendon graft. However, stress shielding of the ligament via nonabsorbable suture augmentation is also a double-edged sword, as a reduction in the stress and load seen by the ligament during this healing phase may ultimately have an impact on the final strength and composition of the reconstructed ligament. Although the long-term effects of this stress shielding have yet to be studied or reported in human subjects, multiple biomechanical and animal studies have demonstrated overall changes in architecture, tensile strength, and mechanical properties of a stress-shielded autograft ligament reconstruction. [ABSTRACT FROM AUTHOR]

Background: Unloading of the proximal medial femoral cortex is usually associated with an increased bone strain at the distal part of the prosthesis, which may cause distal femoral cortical hypertrophy (CH). The objective of this study was to determine the factors that may be considered a predisposition to distal femoral CH and its effect on the stress shielding (SS) or durability of the fixation of the stem. Methods: A total of 240 total hip arthroplasties were performed between January 2006 and December 2016, with all hips implanted with a Bicontact stem. The minimum follow-up period was more than 2 years, and the mean follow-up period was 7.2 years. The radiographic outcome was assessed on an anteroposterior hip radiograph. CH and SS were assessed on postoperative radiographs in the Gruen zone. We defined CH that appeared in zone 3 or 5 as ‘the focal type’ and defined CH that appeared in zones 2, 3, 4, 5, and 6 as ‘the diffuse type.’ SS followed the procedures from the Engh classification. Results: CH was found in 72 hips (30% of the 240 hips), the focal type was found in 23 hips (9.6% of the 240 hips), and the diffuse type was found in 49 hips (20.4% of the 240 hips). SS was found in 41 hips (17.1% of 240 hips), including 32 hips with SS, which was found after the development of CH. One hip was from the focal-type CH and 31 hips were from the diffuse-type CH. SS, which is typically found in Engh classification types 1 and 2 developed in 13 hips, and SS, which is widely seen in Engh classification types 3 and 4 developed in 19 hips. All 19 hips with progressed SS were found after the diffuse-type CH had developed. In addition, among the 19 hips with progressed SS, Dorr type A was found in 0 hips, Dorr type B in 8 hips, and Dorr type C in 11 hips. Conclusions: According to the results of our radiological evaluation, development of the diffuse-type CH after total hip arthroplasty using Bicontact stems is one of the critical causes of the later development of SS and could be predicted to progress to SS. To prevent the development of the diffuse-type CH, the indication to choose a Bicontact stem for a Dorr type C with osteoporotic bone should be considered.

Abstract Background Aseptic loosening of distal femoral tumor implants significantly correlates with the resection length. We designed a new “sleeve” that is specially engaged in the metaphysis at least 5 cm proximal to the knee joint line to preserve as much bone stock as possible. This study investigates the influence of a metaphyseal sleeve on the stress-strain state of a bone tumor implant system in the distal femur. Methods Cortex strains in intact and implanted femurs were predicted with finite element (FE) models. Moreover strains were experimentally measured in a cadaveric femur with and without a sleeve and stem under an axial compressive load of 1000 N. The FE models, which were validated by linear regression, were used to investigate the maximal von Mises stress and the implanted-to-intact (ITI) ratios of strain in the femur with single-legged stance loading under immediate postoperative and osseointegration conditions. Results Good agreement was noted between the experimental measurements and numerical predictions of the femoral strains (coefficient of determination (R 2) ≥ 0.95; root-mean-square error (RMSE%) ≈ 10%). The ITI ratios for the metaphysis were between 13 and 28% and between 10 and 21% under the immediate postoperative and osseointegration conditions, respectively, while the ITI ratios for the posterior and lateral cortices around the tip of the stem were 110% and 119% under the immediate-postoperative condition, respectively, and 114% and 101% under the osseointegration condition, respectively. The maximal von Mises stresses for the implanted femur were 113.8 MPa and 43.41 MPa under the immediate postoperative and osseointegration conditions, which were 284% and 47% higher than those in the intact femur (29.6 MPa), respectively. Conclusions This study reveals that a metaphyseal sleeve may cause stress shielding relative to the intact femur, especially in the distal metaphysis. Stress concentrations might mainly occur in the posterior cortex around the tip of the stem. However, stress concentrations may not be accompanied by periprosthetic fracture under the single-legged stance condition.

This manuscript reviews the development of femoral stem prostheses in the biomedical field. After a brief introduction on the development of these prostheses and the associated problems, we describe the standard design of these systems. We review the different materials, constructions, and surfaces used in the development of femoral stems, in order to solve and avoid various problems associated with their use. Femoral stem prostheses have undergone substantial changes and design optimizations since their introduction. Common materials include stainless steel, cobalt–chromium alloy, titanium alloy, and composites. The structural development of femoral stem prostheses, including their length, shape, porosity, and functional gradient construction, is also reviewed. The performance of these prostheses is affected not only by individual factors, but also by the synergistic combination of multiple effects; therefore, several aspects need to be optimized. The main purpose of this study is to summarize various strategies for the material and construction optimization of femoral stem prostheses, and to provide a reference for the combined optimization of their performance. Substantial research is still needed to develop prostheses emulating the behavior of a real human femoral stem.

The bidirectional stiffness grading of orthopaedic plate has been investigated for internal fixation of transverse fracture in tibia bone. Highly porous cellular materials made of two types of cubic unit cells were designed. Their effective mechanical properties (elastic moduli and yield strengths) were computationally evaluated using finite element analysis. The Gibson-Ashby model was derived for elastic moduli and yield strengths of the cellular geometries. The modified cellular structure provided the desired minimum stiffness within the selected strut sizes. The developed structures were mapped to seven zones of the orthopaedic plate assigning the bidirectional stiffness grading (longitudinal direction). The effect of functional grading on mechanical stimulation through three stages of healing was studied. The results indicated less stress shielding and improvement in uniformity of distribution of equivalent stress around the newly formed bone. Thus, a functionally designed plate will offer a way to dynamically load the healing tissues by encouraging the patient for a regular walk and exercise. Hence, the generated mechanical signal will significantly help mechanically stimulated bone formation and remodeling in the fractured zone.

This study proposes a numerical approach for simulating bone remodeling in lumbar interbody fusion (LIF). It employs a topology optimization method to drive the remodeling process and uses a pixel function to describe the structural topology and bone density distribution. Unlike traditional approaches based on strain energy density or compliance, this study adopts von Mises stress to guide the remodeling of LIF. A novel pixel interpolation scheme associated with stress criteria is applied to the physical properties of the bone, directly addressing the stress shielding effect caused by the implanted cage, which significantly influences the bone remodeling outcome in LIF. Additionally, a boundary inverse approach is utilized to reconstruct a simplified analysis model. To reduce computational cost while maintaining high structural resolution and accuracy, the scaled boundary finite element method (SBFEM) is introduced. The proposed numerical approach successfully generates results that closely resemble human lumbar interbody fusion., (Copyright © 2024 by ASME.)

Performance of the locking compression plate (LCP) is a multifactorial function. The control parameters of plating, such as geometries, material properties, and physical constraints of the LCP components, affect basic functions associated with the bone fixation, including the extent of stress shielding and subsequent bone remodeling, strength and stability of the bone‐LCP construct, and performance of secondary bone healing. The main objectives of this research were as follows: (1) to find the appropriate values of control parameters of an LCP construct to achieve the optimized performance throughout bone healing; and (2) to unravel relationships between LCP parameters and the LCP's performance. Different values for the plate/screw modulus of elasticity (E), plate width (W), plate thickness (T), screw diameter (D), bone‐plate offset (O), and screw configuration (C), as six control parameters, were considered at five different levels. Taguchi method was adopted to create trial combinations of control parameters and determining the best set of parameters, which can optimize the overall performance of the LCP. All design cases were analyzed using the finite element method. The optimal set of control parameters consisting of 150 GPa, 12 mm, 4 mm, 5.5 mm, 2 mm, and 123,678 were determined for E, W, T, D, O, and C, respectively. Furthermore, ANOVA was used to rank the most influential parameters on each function of the LCP fixation. In the overall performance of the LCP fixation, E, D, T, C, W, and O showed a contribution percentage of 46%, 22%, 10%, 11%, 8%, and 3%, respectively. [ABSTRACT FROM AUTHOR]

Femur bone fracture is mainly caused by sports injuries or accidents and has become serious attention in orthopedic trauma. The unique cortical bone microstructures and features contribute to complex fracture behavior. This paper presents the investigation of Type 2 and Type 3 arch-shaped microcrack penetration based on von Mises stress and stress intensity factor (SIF) parameters around the microcrack tips penetration in Haversian system cortical bones. The fracture model was constructed based on bone continuum mechanics theory named Kachanov theory of elastic interaction. It aims to determine the level of stress amplification and stress shielding for the transition of Type 2 to Type 3 for heterogeneous cortical bone fracture model. A total of eight microcrack extension points (CP1–8) were constructed based on 1-mm2 Haversian system model, subjected to the force of 10 N in Mode I and Mode II loading. Finite element (FE) analysis was then performed to evaluate the von Mises stress around the crack end tips and SIF under the assumption of bone damage, D < 1. The study found that the greatest von Mises stress value was observed at the CP4 (175.766 MPa) and CP8 (213.264 MPa) for Mode I loading and CP4 (106.037 MPa) for Mode II loading. In terms of fracture parameter, the critical SIF magnitude was peaked at CP4 (1272.8 MPa*m1/2) and CP8 (1369.0 MPa*m1/2) for Mode I loading and CP5 (402.29 MPa*m1/2) for Mode II loading. The results show that the transition of Type 2 (straight crack) to Type 3 (arch crack) microcrack penetration in Haversian system experienced the multilevel of stress amplification (CP1–CP4, CP6–8) and stress shielding (CP4–CP6) to represent the bone micro-damage level. [ABSTRACT FROM AUTHOR]

Abstract Background Short stem total hip arthroplasty (SHA) preserves femoral bone stock and is supposed to provide a more natural load transfer compared to standard stem total hip arthroplasty (THA). As comparative biomechanical reference data are rare we used a finite element analysis (FEA) approach to compare cortical load transfer after implantations of a metaphyseal anchoring short and standard stem in native biomechanical femora. Methods The subject specific finite element models of biomechanical femora, one native and two with implanted metaphyseal anchoring SHA (Metha, B. Braun Aesculap) and standard THA (CLS, Zimmer-Biomet), were generated from computed tomography datasets. The loading configuration was performed with an axial force of 1400 N. Von Mises stress was used to investigate the change of cortical stress distribution. Results Compared to the native femur, a considerable reduction of cortical stress was recorded after implantation of SHA and standard THA. The SHA showed less reduction proximally with a significant higher metaphyseal cortical stress compared to standard THA. Moreover, the highest peak stresses were observed metaphyseal for the SHA stem while for the standard THA high stress pattern was observed more distally. Conclusions Both, short and standard THA, cause unloading of the proximal femur. However, the metaphyseal anchoring SHA features a clearly favorable pattern in terms of a lower reduction proximally and improved metaphyseal loading, while standard THA shows a higher proximal unloading and more distal load transfer. These load patterns implicate a reduced stress shielding proximally for metaphyseal anchoring SHA stems and might be able to translate in a better bone preservation.

Background: Stress shielding of the humeral stem is a known complication in press-fit total shoulder arthroplasty (TSA), but there remain limited data on its prevalence and clinical impact in midterm follow-up. The purpose of this study was to determine the prevalence of humeral stem stress shielding and its impact on functional outcomes at minimum 5-year follow-up in standard length press-fit TSA. The hypothesis was that the presence of stress shielding at minimum 5-year follow-up would not affect functional outcome scores or range of motion (ROM). Methods: A multicenter retrospective review of primary TSAs performed with a press-fit standard length humeral stem. Functional outcome scores, ROM, and radiographs were reviewed at minimum 5-year follow-up. Prevalence of stress shielding was determined by presence of medial calcar osteolysis and adaptive changes. Function was assessed with the visual analog scale (VAS) pain score, Simple Shoulder Test (SST) score, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) score, and Single Assessment Numeric Evaluation (SANE) score, and ROM. Results: Forty-seven patients with 47 TSAs were available for follow-up at a mean of 79 months postoperation. Overall, 15 of 47 humeral stems had high adaptive change scores (31.9%), and 20 demonstrated medial calcar osteolysis (42.6%). Stems with evidence of stress shielding showed no significant change in SST, VAS, ASES, or SANE scores and minimal change in ROM measurements at minimum 5-year follow-up. Conclusion: Stress shielding is common at midterm follow-up in press-fit TSA but does not appear to affect functional outcomes.

Background: Humeral stem loosening has gained attention as it has been identified as a cause of revision surgery in reverse shoulder arthroplasty (RSA). In RSA, humeral stem revision is very difficult if there is humeral bone loss because of stress shielding. Some studies of humeral bone resorption after anatomic shoulder arthroplasty have been published, but there are few detailed reports of humeral bone resorption after RSA. This study aimed to investigate the prevalence of humeral bone resorption after RSA procedures and to evaluate the risk factors for bone resorption. Methods: This study included 48 shoulders that underwent RSA with an uncemented humeral stem from July 2014 to May 2017 and were followed up for more than 1 year. The prevalence of humeral bone resorption and risk factors were investigated. Logistic, multiple logistic, and multivariate logistic regression analyses were performed to evaluate the data. Results: Grade 0 bone resorption, the most advanced grade, occurred in 8 shoulders (16.7%); grade 1, in 0 (0%); grade 2, in 17 (35.4%); grade 3, in 14 (29.2%); and grade 4, in 9 (18.8%). A high occurrence of bone absorption was observed in zones 1, 2, and 7. Grade 4 bone resorption did not occur in zones 3, 5, and 6. Female sex and an onlay-type stem were significant independent risk factors for grade 4 bone resorption. Conclusions: Bone resorption was frequently observed in the greater tuberosity, lateral diaphysis, and calcar region. Significant risk factors included female sex and an onlay-type stem.

Human bone cells live in a complex environment, and the biomimetic design of porous structures attached to implants is in high demand. Porous structures based on Voronoi tessellation with biomimetic potential are gradually used in bone repair scaffolds. In this study, the mechanical properties and permeability of trabecular-like porous scaffolds with different porosity levels and average apertures were analyzed. The mechanical properties of bone-implant scaffolds were evaluated using finite element analysis and a mechanical compression experiment, and the permeability was studied by computational fluid dynamics. Finally, the attachment of cells was observed by confocal fluorescence microscope. The results show that the performance of porous structures can be controlled by the initial design of the microstructure and tissue morphology. A good structural design can accurately match the performance of the natural bone. The study of mechanical properties and permeability of the porous structure can help address several problems, including stress shielding and bone ingrowth in existing biomimetic bone structures, and will also promotes cell adhesion, migration, and eventual new bone attachment.

Bone cortical tissues reorganize and remodel in response to tensile forces acting on them, while compressive forces cause atrophy. However, implants support most of the payload. Bones do not regenerate, and stress shielding occurs. The aim is to analyze the biomechanical behavior of a lumbar cage to study the implant's stress shielding. The ASTM E-9 standard was used with the necessary adjustments to perform compression tests on lumbar and thoracic porcine spinal vertebrae. Twelve cases were analyzed: six with the metal prosthesis and six with the PEEK implant. A mathematical model based on the Hertz contact theory is proposed to assess the stress shielding for endoprosthesis used in spine pathologies. The lumbar spacer (screw) helps to reduce the stress shielding effect due to the ACME thread. The best interspinous spacer is the PEEK screw. It does not embed in bone. The deformation capability increases by 11.5% and supports 78.6 kg more than a system without any interspinous spacer.

Aging, tooth trauma, and pathological infections cause partial or total tooth loss, leading to the usage of dental implants for restoration treatments. As such, mechanical and tribological properties play an important role in the osseointegration and durability of these implants. Metallic and ceramic implants are shown to have mechanical properties much higher than the natural teeth structure, leading to stress shielding-related failure of an implant. Stress shielding occurs due to the difference in the elastic modulus between the implant material and the surrounding teeth structure, leading to bone loss and implant failure. The implant's properties (i.e., mechanical) should be as close as human teeth components. To achieve this, various materials and coatings are being developed and investigated. This review is a comprehensive survey of materials, manufacturing, coating techniques, and mechanical and tribological characterizations of dental implants, with a particular focus on polyetheretherketone (PEEK) as a potential alternative dental implant material. PEEK has mechanical properties similar to natural teeth, which make it a promising material for dental implants. The findings of this review suggest that PEEK offers superior biocompatibility, osseointegration, and wear resistance for implant applications. With the help of bioactive coatings, bone growth on the implant surface can be promoted. In addition, PEEK dental implants made using three-dimensional (3D) printing technology can significantly reduce the cost of implants, making them more affordable and increasing access to dental care, which can improve oral health significantly. In summary, this review highlights the potential of PEEK as a promising alternative dental implant material, and provides an overview of various techniques, testing, and future directions for PEEK dental implants., (Copyright 2023, Mary Ann Liebert, Inc., publishers.)

Background: The MoPyc radial head arthroplasty (RHA) is a monopolar implant with a pyrocarbon head that obtains rigid fixation via controlled expansion of the titanium stem. The aim of this study was to evaluate the short-term to midterm outcomes of MoPyc RHA., Materials and Methods: Between 2002 and 2021, 139 MoPyc RHA were implanted in 139 patients with a RH fracture. The mean follow-up was 5.9 years ± 3.5 (range 1-16). Range of motion, mean Mayo Elbow Performance Score (MEPS), Quick Disabilities of the Arm, Shoulder and Hand score, visual analog scale (VAS), radiographic outcome, and reason for failure were recorded., Results: The mean MEP, Quick Disabilities of the Arm, Shoulder and Hand, and VAS scores were 89.1 ± 2.2 (range, 45-100), 17.5 ± 16.7 (range, 0-78), and 0.8 ± 1.6 (range, 0-50), respectively. Stress shielding (SS) and osteolysis around the stem were identified in 92 (66%) and 20 (14%) patients. A total of 47 (29%) patients experienced at least 1 complication and 29 (21%) of them required re-intervention. Persistent stiffness (n = 12; 9%) was the most common complication. No painful loosening was noted. Osteolysis around the stem, presence of an autoexpanding stem, and overstuffing were associated with a lower MEPS and an increase in VAS (P < .05). SS was associated with an increase in MEPS (adjusted beta coefficients= 6.92; P < .001) and lower VAS (adjusted beta coefficients= -0.69; P = .016). The autoexpending stem increased the likelihood of SS after RHA (adjusted odds ratio = 1.49; P = .001)., Conclusions: A well-fixed MoPyc RHA provided satisfactory short to midterm outcomes, without painful loosening. However, the autoexpanding stem system was associated with poorer functional outcomes and increased the likelihood of SS., (Copyright © 2024 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

The conical stem tibial design of total ankle replacement (TAR) has high implant-bone micromotion. This may lead to aseptic loosening which can be avoided by improving the tibial design. The objective was to propose the best stem design parameters to reduce implant-bone micromotion along with minimizing stress shielding using an integrated Finite Element-Multi Criteria Decision Making (FE-MCDM) approach. FE models of implanted tibia bones were prepared by changing the height of the stem, the diameter of the stem, and the slant of the stem. Weighted Aggregated Sum Product Assessment (WASPAS), Technique for Order of Preference by Similarities to Ideal Solution (TOPSIS), Evaluation based on Distance from Average Solution (EDAS), and VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) MCDM techniques with equal weights for micromotion and stress shielding were considered. The micromotion and stress shielding were greater when the height of the stem was increased. Whereas, the increase in diameter and slant affected them marginally. The best-performing design was the Model with stem height 6 mm (diameter 6.4 mm and slant 4°) and after that was the Model with stem height 8 mm (diameter 6.4 mm and slant 4°), and then the Model with stem height 10 mm (diameter 6.4 mm and slant 4°). The height of the stem is the most important stem design parameter. Shorter height, moderate thickness, and moderate slanting stem designs are recommended., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background: We sought to assess if the medullary diameter to cortical width ratio (MD:CW), canal flair index (CFI), and canal fill (CF) of the proximal radius were associated with the presence of stress shielding (SS) after a MoPyC radial head arthroplasty., Materials and Methods: We conducted a retrospective, international, multicenter (4 centers) study. A total of 100 radial head arthroplasties in 64 women and 36 men with a mean age of 58.40 years ± 14.90 (range, 25.00-91.00) were included. Radiographic measurements, including MD:CW, CFI, CF, and postoperative SS were captured at a mean follow-up of 3.9 years ± 2.8 (range, 0.5-11)., Results: SS was identified in 60 patients. Mean preoperative MD:CW, CFI, and CF were 0.55 ± 0.09, 1.05 ± 0.18, and 0.79 ± 0.11, respectively. The presence of SS was significantly associated with MD:CW (adjusted odds ratio = 13.66; P = .001), and expansion of the stem (adjusted odds ratio = 3.78; P = .001). The amount of the SS was significantly correlated with expansion of the stem (aβ 4.58; P < .001)., Conclusions: Our study found that MD:CW was an independent risk factor of SS after MoPyc radial head arthroplasty. Autoexpansion of the MoPyc stem significantly increased the risk of SS and its extent. Further studies involving multiple implants designs are needed to confirm the preliminary observations presented in the current study., (Copyright © 2024 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)

Background: Humeral-sided complications account for up to 21% of all revision reverse total shoulder arthroplasty (RTSA) surgeries. Stress shielding with large bulky stems can lead to proximal bone resorption per Wolff law, complicating further surgeries. Previously published studies suggest that lowering the metaphyseal implant fill ratio can lead to fewer adaptive radiographic changes and decreased bone resorption. Inspired by these studies, cementless primary RTSA implantation technique with humeral matchstick autografts was proposed to augment cementless humeral constructs, foster the use of a smaller size stem, and create primary stability of the humeral implant even in osteoporotic or in-between size medullary canals. In this study, retrospective review of this cementless RTSA technique with short-term radiographic evaluation was performed., Methods: Forty-six nonconsecutive patients underwent primary RTSA with a short-stem cementless prosthesis (Stryker Ascend Flex) augmented by matchstick bone grafting from January to July 2020. Patient demographics were recorded, and follow-up radiographs were retrospectively reviewed to assess metaphyseal fill ratios and incidence of stress shielding at minimum 1-year follow-up. Discrepancies between templated and final stem sizes were recorded, along with all intraoperative and postoperative complications., Results: Of the 46 patients originally identified, there were 5 men and 41 women with a mean age of 71 years (standard deviation [SD] 7, range 53-88). Mean templated stem size was 4 (SD 2, range 1-8), whereas the mean final implant size was 2 (SD 1, range 1-3). Mean fill ratios were 0.76 (SD 0.06, range 0.54-0.89) along the metaphysis and 0.67 (SD 0.09, range 0.49-0.83) along the diaphysis. There were no intraoperative humeral fractures from implantation. All patients were available for radiographic follow-up with a mean of 19 months (SD 8, range 12-40). There were 3 cases (7%) of proximal humeral stress shielding, with average fill ratios of 0.857 and 0.807 in the metaphysis and diaphysis, respectively. There were 3 patients (7%) who underwent revision surgeries for baseplate failure and periprosthetic humeral fracture. There were no cases of early humeral loosening., Discussion: Matchstick autograft humeral augmentation is a simple, promising surgical technique with low intraoperative complication rates and good short-term radiographic outcomes. When the implant fill ratio is successfully reduced, there is a possible lower risk of humeral stress shielding. The authors believe this technique can help maximize implant stability in cementless shoulder arthroplasty and preserve humeral bone stock for future revision surgeries., (Copyright © 2024 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)