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Background: This study aimed to assess the radiographic proximal humerus bony adaptations to stress shielding and associated clinical outcomes following stemless total shoulder arthroplasty. Methods: A retrospective review of all patients who underwent stemless total shoulder arthroplasty surgery at our centre from 2010 to 2020 was performed. Results: In total, 115 stemless total shoulder arthroplasty utilising a single implant design with a minimum one-year follow-up were identified over a 10-year period. The median follow-up was 3.5 years (range: 1–8.9 years). Evidence of stress shielding was observed in 20 cases (17%), (9 mild (8%), 0 moderate (0%), 11 severe (9%). No significant differences were seen between stress shielding and gender, body mass index, post-operative range-of-motion, patient satisfaction, or Oxford shoulder score. No significant differences were seen between the operative technique and stress shielding. No cases had evidence of humeral lucency. In total, 24 cases (21%) had evidence of glenoid lucency of Lazarus grade 0–3. No cases had Lazarus grades 4 or 5. There was no association between stress shielding and humeral lucency, glenoid lucency, or revision procedure. Discussion: Stress shielding in this study occurred at lower rates than anticipated following stemless total shoulder arthroplasty and was not associated with radiographic evidence of lucency, revision procedures, or adverse effect on clinical outcome measures. [ABSTRACT FROM AUTHOR]

Directed Energy Deposition (DED), a metal additive manufacturing technique, shows promise for future orthopaedic applications, especially in bone plate manufacturing. The need for patient-specific solutions in orthopaedics is growing, driven by the limitations of traditional bone plates made from stainless steel or titanium alloys and the rising incidence of complex fractures. This paper explores the design of orthopaedic bone plates using Generative Design (GD) and Topological Optimization (TO), aimed at eventual production through DED. By focusing on design, the research addresses challenges like stress shielding, caused by the modulus disparity between conventional plate materials and natural bone. Significant findings include mass reductions of 43.7% and 44.2% for GD designs GD1 and GD2, respectively, and a 36% reduction for the TO design TO1, enhancing biomechanical performance with improved strain values. The findings demonstrate GD's effectiveness in generating anatomically congruent implants, showcasing advancements in personalized care and fracture treatment. The integration of GD and DED within the Design for Additive Manufacturing (DfAM) framework offers a promising pathway for future research focused on refining patient-specific designs and manufacturing processes, aligning with the evolving needs of orthopaedic treatments. [ABSTRACT FROM AUTHOR]

This paper conceptualises an understanding of advanced manufacturing methods to develop 3D-printed metallic orthopaedic implants, including a brief discussion on post-process machining. The significance of Metallic Additive Manufacturing (MAM) and its practicality for industrial applications is discussed through a juxtaposition with conventional casting and machining approach. Different alloys and suitable MAM techniques are thoroughly reviewed to determine optimum operating conditions. Although MAM can produce near-net shape parts, post-processing is an unavoidable requirement to improve surface quality and dimensional accuracy. A comparative study is presented, highlighting the importance of machining for post-processing in terms of cost savings and performance. Different materials are evaluated aiming to overcome problems associated with existing orthopaedic implants. The consequence of bone-implant mechanical mismatch leading to stress shielding and inadequate corrosion properties obstructing biodegradability are explored in detail. The effect of additive manufacturing parameters on mechanical, corrosion, and surface properties including biocompatibility is analysed. Evidence of MAM's advantages over conventional manufacturing approaches, such as the use of functionally graded lattices and patient-specific customised designs, is also presented. Finally, for future studies, a two-way approach is conceptualised with material selection and manufacturing process control in progressions of implant development using MAM. [ABSTRACT FROM AUTHOR]

Porous metallic prosthesis components can now be manufactured using additive manufacturing techniques, and may prove beneficial for promoting bony ingrowth, for accommodating drug delivery systems, and for reducing stress shielding. Using finite element modeling techniques, 36 scenarios (three porous stems, three bone densities, and four held arm positions) were analysed to assess the viability of porous humeral stems for use in total shoulder arthroplasty, and their resulting mechanobiological impact on the surrounding humerus bone. All three porous stems were predicted to experience stresses below the yield strength of Ti6Al4V (880 MPa) and to be capable of withstanding more than 10 million cycles of each loading scenario before failure. There was an indication that within an 80 mm region of the proximal humerus, there would be a reduction in bone resorption as stem porosity increased. Overall, this study shows promise that these porous structures are mechanically viable for incorporation into permanent shoulder prostheses to combat orthopedic infections. [ABSTRACT FROM AUTHOR]

A significant proportion of revisions after reverse shoulder arthroplasty (RSA) is attributed to the humeral component. The purpose of this study is to evaluate the radiographic and clinical outcomes of the hybrid humerus technique for RSA using a Grammont-style humeral prosthesis in an onlay fashion with metaphyseal bone impaction grafting technique and undersized stem to avoid humeral stress shielding, notching, and loosening. This is a prospective case series of patients who underwent RSA using the hybrid humerus technique with a minimum 2-year follow-up. Key steps of this technique include the use of undersized Grammont-style stem, impaction bone grafting of the proximal 5 cm of the humerus, and adjusting the height and offset of the stem depending on the patient stature, desired lateralization and distalization, and joint and soft tissue tension. Radiographic assessments were performed immediately after surgery, and at 1 and 2 years after surgery. These included assessment of metaphyseal and diaphyseal filling ratio, cortical narrowing, radiolucent lines, cortical lucencies, spot welding, scapular notching, and stem alignment. Preoperative and 2-year postoperative clinical assessments included American Shoulder and Elbow Surgeons score, Constant-Murley Score, University of California Los Angeles score, visual analog scale for pain, and active range of motion. Correlation between the filling ratios and clinical outcomes were also evaluated. Sixty-one patients were included in the study. The average metaphyseal and diaphyseal filling ratio on the postoperative X-ray was 0.66 and 0.54, and 0.67 and 0.54 at 2 years, respectively. Stress shielding was graded as none in 24 (40.7%), mild in 33 (55.9%), and moderate in 2 (3.4%). No stem had a change in position of more than 5°. At 2 years of follow-up, no humeral implant loosening was noted, with only 2 (3.4%) of the stems at risk of loosening. Thirty-nine (66.1%) had no notching, 14 (23.7%) were graded as mild, and 6 (10.2%) had moderate signs of notching. All clinical assessments significantly improved at 2 years (P <.001), with a weak negative correlation between visual analog scale and metaphyseal filling ratio (r = −0.268, P =.036) but none between diaphyseal filling ratio and clinical outcomes. The hybrid humerus technique of metaphyseal bone grafting with a low filling ratio stem presents a promising solution for reducing humeral complications in RSA. This technique demonstrates a low incidence of stress shielding and loosening, with excellent clinical outcomes at 2 years. [ABSTRACT FROM AUTHOR]

Reverse shoulder arthroplasty (RSA) has extended its indications in recent years to include complex proximal humerus fractures (PHFs) in elderly patients. The traditional approach in cases of PHF has been to cement the stem but, as in orthopedic surgery, the current trend in PHF is to avoid cementing the humeral stem as well. We evaluated 63 patients (representing 63 shoulders) who underwent RSA with uncemented stem after acute fracture of the proximal humerus. We analyzed the clinical and radiological outcomes, as well as medium-term complications, using two different prosthesis models. The mean postoperative follow-up period was 21-23 months, and the mean age of the patients was 74.5 years. The average Constant Score was 56.94 points; there were no statistical significant differences in Constant Score depending on the prosthesis model used. No cases of aseptic loosening were observed. However, there was evidence of stress-shielding in prostheses with diaphyseal fixation, although this phenomenon did not appear to have functional or clinical consequences for the patients. Intraoperative complications occurred in 6.35% of cases, and postoperative complications were noted in 4.92%. Based on the results of this study, we can affirm that the use of RSA with cementless stems in PHF can be a safe alternative, providing satisfactory clinical, functional, and radiographic results in the short term without the need to use cement in their fixation. The choice of prosthesis model may influence the occurrence of radiographic phenomena but does not seem to affect clinical outcome. [ABSTRACT FROM AUTHOR]

Stress shielding is a problem for traditional metal bone fixation plates made of magnesium and titanium alloys. This problem can be solved by using composite materials with a low elastic modulus. This study analyzed the effect of carbon fiber reinforced PEEK (CFRP) composites on stress shielding under static loading using finite element simulations. Callus formation times relative to the healing period were gradually imposed according to the elapsed time, considering 1% and 75% as healing stages. The Inventor© 3D CAD 2024 software was used for modeling, and the ANSYS© FEA R2023 software was used for analysis. The results showed that metal fixation plates made of titanium and magnesium alloys transferred less stress to the bone than the CFRP fixation plate. In particular, the use of the CFRP fixation plate resulted in a higher peak stress and a more uniform stress field in the bone, especially in the bone-plate contact area, where the risk of stress shielding is higher in the 1% and 75% healing phases. [ABSTRACT FROM AUTHOR]

Metals, ceramics, and polymers are commonly used as orthopedic implant materials. Conventionally, Cobalt Chromium (CoCr) alloys, Titanium (Ti) alloys, Alumina (Al2O3) ceramic, Hydroxyapatite (HA), and Polyetheretherketone (PEEK) are used. Bone resorption owing to stress shielding is one of the reasons for the failure of total ankle replacement (TAR). The stiffness mismatch between the tibia bone and the implant is responsible for stress shielding. It is hypothesized that stress shielding can be reduced by tailoring the implant material similar to the tibia bone by using functionally graded materials (FGMs). The aim of the study is to understand the effect of FGMs on the stress shielding of the tibia bone for TAR. Finite element (FE) models were prepared for, the natural bone, and the implanted bone with the tibial component made from CoCr alloy, Ti alloy, Al2O3 ceramic, FGM of Al2O3 ceramic at the bottom and PEEK at the top, and FGM of Ti at the bottom and HA at the top. Material properties for FGMs were assigned using Ansys APDL code. The results indicated that the highest stress shielding was present in the Al2O3 ceramic model. Whereas, the least stress shielding was in the Ti + HA FGM model. This implies that the stress shielding and subsequently the bone resorption can be reduced by using the FGMs. Thus, FGMs are advantageous when compared to conventional implant materials in order to reduce stress shielding. [ABSTRACT FROM AUTHOR]

Orthopaedic trauma is a predominant cause of patient mortality and prompt surgical interventions. The locking compression plate (LCP) is widely regarded as a gold standard in treating bone fractures. However, current fixation materials, such as 316 L stainless steel (316 L SS) and titanium (Ti) alloys induce stress shielding. A novel design approach is considered to design the next generation of bone plates to minimize stress shielding through design for additive manufacturing principles. Embedding of 316 L SS sheets within the bone plate structure has improved the mechanical properties by 200% compared with PLA-only plate, resulting in a flexural modulus of 9.3 GPa, which is closer to the cortical bone range of 10–25 GPa. In contrast, commercial plates measured 51 GPa for Ti and 112 GPa for 316 L SS. The novel plates showed to have a lower economic and environmental impact than commercial ones. Additively manufactured bone plates are more sustainable and cost-effective than current commercial ones.

Objectives: The purpose of this study was to compare two different designs of three-dimensional osteosynthesis plates for their suitability in the treatment of mandibular angle fractures in terms of sufficient fracture healing and concomitant complications. Materials and methods: Retrospectively a total of 54 patients with 56 mandibular angle fractures were evaluated. Two different types of three-dimensional plates from the Medartis Trilock system were analyzed: (A) Square design plate (☐-plate) with a thickness of 1.0 mm, and (B) triangular-shaped 3D-plate (△-plate) with a thickness of 1.3 mm. Patient demographics, fracture mechanism and intraoperative details were recorded during an average follow-up period of 1 year. Results: The utilization of △-plates was observed to entail a considerably lengthier surgical time in contrast to ☐-plate systems (P = 0.037). The application of △-plate showed a tendency of higher incidence of major complications than ☐-plate (P = 0.06), as evidenced by the occurrence of non-union in 2 out of 22 cases, resulting in higher surgical revision rate for △-plate (P = 0.027). Conclusion: Sufficient treatment of mandibular angle fractures is feasible by using 1.0 mm thick, square shaped three-dimensional plate systems. The use of thicker three-dimensional osteosynthesis plates seems to significantly increase the operating time and complication rates, whereby the geometry of the plate seems to have an influence. Clinical relevance: The plate design could have an impact on treatment outcomes of mandibular angle fractures. Trial registration number: Not applicable. [ABSTRACT FROM AUTHOR]

Abstract Background In recent years, the use of tapered-wedge short stems has increased due to their ability to preserve bones and tendons. Surgical techniques occasionally result in a varus position of the stem, which is particularly pronounced in short stems. Although the varus position is not clinically problematic, there are reports of an increased incidence of stress shielding and cortical hypertrophy. Thus, we evaluated and examined the acceptable range of varus angles using finite element analysis. Methods Patients diagnosed with osteoarthritis of the hip joint who had undergone arthroplasty were selected and classified into three types [champagne-flute (type A), intermediate (type B), and stovepipe (type C)]. Finite element analysis was performed using Mechanical Finder. The model was created using a Taperloc microplasty stem with the varus angle increased by 1° from 0° to 5° from the bone axis and classified into seven zones based on Gruen’s zone classification under loading conditions in a one-leg standing position. The volume of interest was set, the mean equivalent stress for each zone was calculated. Results A significant decrease in stress was observed in zone 2, and increased stress was observed in zones 3 and 4, suggesting the emergence of a distal periosteal reaction, similar to the results of previous studies. In zone 2, there was a significant decrease in stress in all groups at a varus angle ≥ 3°. In zone 3, stress increased from ≥ 3° in type B and ≥ 4° in type C. In zone 4, there was a significant increase in stress at varus angles of ≥ 2° in types A and B and at ≥ 3° in type C. Conclusion In zone 2, the varus angle at which stress shielding above Engh classification grade 3 may appear is expected to be ≥ 3°. Distal cortical hypertrophy may appear in zones 3 and 4; the narrower the medullary cavity shape, the smaller the allowable angle of internal recession, and the wider the medullary cavity shape, the wider the allowable range. Long-term follow-up is required in patients with varus angles > 3°.

Existing implants used with Total Knee Arthroplasty (TKA), Total Hip Arthroplasty (THA), and other joint reconstruction treatments, have displayed premature failures and frequent needs for revision surgery in recent years, particularly with young active patients who represent more than 55% of all joint reconstruction patients. Bone cement and stress shielding have been identified as the major reasons for premature joint failures. A breakdown of the cement may happen, and revision surgery may be needed because of the aseptic loosening. The significant mismatch of stiffness properties of patient trabecular bones and metallic implant materials in joint reconstruction surgery results in the stress shielding phenomenon. This could lead to significant bone resorption and increased risk of bone fracture and the aseptic loosening of implants. The present project introduces an approach for development of customized cellular structures to match the mechanical properties and architecture of human trabecular bone. The present work aims at fulfilling the objectives of the introduced approach by exploring new designs of customized lattice structures and texture tailored to mimic closely patients’ bone anisotropic properties and that can incorporate an engineered biological press-fit fixation technique. The effects of various lattice design variables on the mechanical performance of the structure are examined through a systematic experimental plan using the statistical design of experiments technique and analysis of variance method. All tested lattice designs were explored under realistic geometrical, biological, and manufacturing constraints. Of the four design factors examined in this study, strut thickness was found to have the highest percent contribution (41%) regarding the structure stiffness, followed by unit cell type, and cell size. Strut shape was found to have the lowest effect with only 11% contribution. The introduced solution offers lattice structure designs that can be adjusted to match bone stiffness distribution and promote bone ingrowth and hence eliminating the phenomenon of stress shielding while incorporating biological press-fit fixation technique.

BACKGROUND: The treatment of distal tibial comminuted fractures with soft tissue injury has always been challenging. The new retrograde tibial nailing and supercutaneous locking plate are important treatment methods, but their strain and stress shielding at the fracture end during different periods of fracture healing and different load conditions have not been reported. OBJECTIVE: To explore the biomechanical stability of retrograde tibial nailing and supercutaneous locking plate in different periods of fracture healing by finite element analysis to offer a scientific foundation for clinical application and rehabilitation exercise. METHODS: The finite element model of distal tibial comminuted fracture was established by utilizing the CT data of the tibia from a 40-year-old healthy male. Retrograde tibial nailing, supercutaneous locking plate, and callus models were assembled in accordance with the principle of fracture fixation. The finite element analysis was performed using ANSYS software to compare the displacement of the fracture end, the stress shielding of the tibia, the stress of the callus, and the stress distribution of the tibia and the fixation device during different periods of fracture healing. RESULTS AND CONCLUSION: (1) The relative displacement of the tibial fracture decreased gradually with the healing of the fracture, and the displacement decreased significantly after 3 months. At 0 and 1 months after operation, the vertical displacement and total displacement of the supercutaneous locking plate group were higher than those in the retrograde intramedullary nail group. The Z-axis displacement (horizontal medial and lateral displacement) of the two fixation methods was more obvious than the X-axis and Y-axis, and the Z-axis displacement of supercutaneous locking plate group was the most obvious. The maximum Z-axis displacement of the two fixation methods was located on the outside of the tibia, and the minimum displacement was located on the inside of the tibia. (2) The stress shielding rate at different periods of fracture healing gradually decreased with time. The stress shielding rate of the retrograde intramedullary nail was higher than that of the supercutaneous locking plate at different stages of fracture healing. After 3 months, the stress shielding rate of the supercutaneous locking plate was reduced to about 4%, and the stress shielding rate of the retrograde intramedullary nail was reduced to about 40%. (3) The stress of the stress concentration site of the callus in the two fixation methods increased with the increase of the load, and the stress of the callus in the supercutaneous locking plate group was always greater than that in the retrograde intramedullary nail group. The maximum stress distribution of the callus was approximately equally distributed among the two modes of fixation, both in the lateral portion of the tibia. (4) As the fracture healed, the maximum stress of the tibia in the two groups decreased gradually, and the stress in the supercutaneous locking plate group was always greater than that in the retrograde intramedullary nail group. The average stress of the maximum stress area of the tibia in the supercutaneous locking plate group under 1 500 N load was 285 MPa, while that in the retrograde intramedullary nail group was 26 MPa. (5) As the fracture healed, the stress of the fixation device in the two groups decreased gradually, and the stress in the supercutaneous locking plate group was significantly higher than that in the retrograde intramedullary nail group. After 3 months, the stress of the two fixation devices decreased significantly. (6) It is indicated that in the early stage of fracture healing, the strain on the fracture end in the retrograde intramedullary nail group is small, and the maximum stress of the tibia is moderate, allowing early loaded. The fractured ends in the supercutaneous locking plate group had too large strain and too large maximum stress of the tibia, which needed to be partially loaded under protection and could not be fully loaded. In the middle and late stages of fracture healing, the tibial retrograde intramedullary nail and the supercutaneous locking plate could be completely loaded, and the stress shielding rate of the supercutaneous locking plate was significantly lower than the tibial retrograde intramedullary nail. [ABSTRACT FROM AUTHOR]

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. 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). 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). 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. [ABSTRACT FROM AUTHOR]

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. 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. 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. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

BACKGROUND: With social progress, the incidence rate of knee osteoarthritis is getting higher and higher in the face of the rapidly developing aging problem in the social population, and the number of total knee replacement operations is gradually increasing. OBJECTIVE: To study the relationship between prosthesis size and stress shielding by improving the tibial prosthesis base. METHODS: A female patient with severe knee osteoarthritis was selected. Based on Mimics, through extracting the bone structure of the knee joint and simulating the total knee replacement surgery, osteotomy, positioning, and implantation operations were carried out to establish the geometric modeling of the total knee replacement prosthesis (including the femoral prosthesis, tibial bracket, and tibial pad), and improve the design of the tibial prosthesis base, analyze the effect of different tibial prosthesis bases on stress shielding of surrounding bone tissue. RESULTS AND CONCLUSION: (1) Compared with single-stem tibial intramedullary stem prosthesis, the design of four-post tibial intramedullary stem prosthesis created a certain degree of stress shielding around the short stem. However, compared with a thicker single long stem, this stress shielding effect was significantly reduced, and the load was evenly distributed among the four short stems, so there was no stress concentration at the bottom of the pile. (2) The design with a rectangular hole in the middle not only provided relatively good stability, but also helped to reduce stress shielding of cancellous bone to a certain extent, with a reduction rate of 77.5%. (3) Compared with a single-stem tibial intramedullary stem prosthesis, both the four-post tibial intramedullary stem prosthesis and the four-post tibial intramedullary stem prosthesis with a hole in the middle have good stability, which can reduce stress shielding to a certain extent without causing stress concentration, providing theoretical guidance for the design of the tibial intramedullary stem. [ABSTRACT FROM AUTHOR]

The fabrication of Ti-Mg composite biomaterials was investigated using spark plasma sintering (SPS) with varying Mg contents and sintering pressures. The effects of powder mixing, Mg addition, and sintering pressure on the microstructure and mechanical properties of the composite materials were systematically analyzed. Uniform dispersion of Mg within the Ti matrix was achieved, confirming the efficacy of ethanol-assisted ball milling for consistent mixing. The Young's modulus of the composite materials exhibited a linear decrease with increasing Mg content, with Ti-30vol%Mg and Ti-50vol%Mg demonstrating reduced modulus values compared to pure Ti. Based on density measurements, compression tests, and Young's modulus results, it was determined that the sinterability of Ti-30vol%Mg saturates at a sintering pressure of approximately 50 MPa. Moreover, our immersion tests in physiological saline underscore the profound significance of our findings. Ti-30vol%Mg maintained compressive strength above that of cortical bone for 6-to-10 days, with mechanical integrity improving under higher sintering pressures. These findings mark a significant leap towards the development of Ti-Mg composite biomaterials with tailored mechanical properties, thereby enhancing biocompatibility and osseointegration for a wide range of biomedical applications. [ABSTRACT FROM AUTHOR]

Background: In recent years, the use of tapered-wedge short stems has increased due to their ability to preserve bones and tendons. Surgical techniques occasionally result in a varus position of the stem, which is particularly pronounced in short stems. Although the varus position is not clinically problematic, there are reports of an increased incidence of stress shielding and cortical hypertrophy. Thus, we evaluated and examined the acceptable range of varus angles using finite element analysis. Methods: Patients diagnosed with osteoarthritis of the hip joint who had undergone arthroplasty were selected and classified into three types [champagne-flute (type A), intermediate (type B), and stovepipe (type C)]. Finite element analysis was performed using Mechanical Finder. The model was created using a Taperloc microplasty stem with the varus angle increased by 1° from 0° to 5° from the bone axis and classified into seven zones based on Gruen’s zone classification under loading conditions in a one-leg standing position. The volume of interest was set, the mean equivalent stress for each zone was calculated. Results: A significant decrease in stress was observed in zone 2, and increased stress was observed in zones 3 and 4, suggesting the emergence of a distal periosteal reaction, similar to the results of previous studies. In zone 2, there was a significant decrease in stress in all groups at a varus angle ≥ 3°. In zone 3, stress increased from ≥ 3° in type B and ≥ 4° in type C. In zone 4, there was a significant increase in stress at varus angles of ≥ 2° in types A and B and at ≥ 3° in type C. Conclusion: In zone 2, the varus angle at which stress shielding above Engh classification grade 3 may appear is expected to be ≥ 3°. Distal cortical hypertrophy may appear in zones 3 and 4; the narrower the medullary cavity shape, the smaller the allowable angle of internal recession, and the wider the medullary cavity shape, the wider the allowable range. Long-term follow-up is required in patients with varus angles > 3°. [ABSTRACT FROM AUTHOR]

Total hip arthroplasty is one of the most common and successful orthopaedic operations. Occasionally, periprosthetic osteolysis associated with stress shielding occurs, resulting in a reduction of bone density where the femur is not properly loaded and the formation of denser bone where stresses are confined. To enhance proximal load transfer and reduce stress shielding, approaches, including decreasing the stiffness of femoral stems, such as carbon fibre-reinforced polymer composites (CFRPCs), have been explored through novel modular prostheses. The purpose of the present study was to analyse, by the finite element analysis (FEA) method, the effect that the variation of material for the distal part of the femoral stem has on stress transmission between a modulable prosthesis and the adjacent bone. Methods: Through three-dimensional modelling and the use of commercially available FEA software Ansys R2023, the mechanical behaviour of the distal part of the femoral stem made of CFRPC or Ti-6Al-4V was obtained. A load was applied to the head of the femoral stem that simulates a complete walking cycle. Results: The results showed that the use of a material with mechanical characteristics close to the bone, like CFRPC, allowed for optimisation of the transmitted loads, promoting a better distribution of stress from the proximal to the distal part of the femur. This observation was also found in some clinical studies in literature, which reported not only an improved load transfer with the use of CFRPC but also a higher cell attachment than Ti-6Al-4V. Conclusions: The use of a material that has mechanical properties that are close to bone promotes load transfer from the proximal to the distal area. In particular, the use of CFRPC allows the material to be designed based on the patient's actual bone characteristics. This provides a customised design with a lower risk of prosthesis loss due to stress shielding. [ABSTRACT FROM AUTHOR]

Existing implants used with Total Knee Arthroplasty (TKA), Total Hip Arthroplasty (THA), and other joint reconstruction treatments, have displayed premature failures and frequent needs for revision surgery in recent years, particularly with young active patients who represent more than 55% of all joint reconstruction patients. Bone cement and stress shielding have been identified as the major reasons for premature joint failures. A breakdown of the cement may happen, and revision surgery may be needed because of the aseptic loosening. The significant mismatch of stiffness properties of patient trabecular bones and metallic implant materials in joint reconstruction surgery results in the stress shielding phenomenon. This could lead to significant bone resorption and increased risk of bone fracture and the aseptic loosening of implants. The present project introduces an approach for development of customized cellular structures to match the mechanical properties and architecture of human trabecular bone. The present work aims at fulfilling the objectives of the introduced approach by exploring new designs of customized lattice structures and texture tailored to mimic closely patients' bone anisotropic properties and that can incorporate an engineered biological press-fit fixation technique. The effects of various lattice design variables on the mechanical performance of the structure are examined through a systematic experimental plan using the statistical design of experiments technique and analysis of variance method. All tested lattice designs were explored under realistic geometrical, biological, and manufacturing constraints. Of the four design factors examined in this study, strut thickness was found to have the highest percent contribution (41%) regarding the structure stiffness, followed by unit cell type, and cell size. Strut shape was found to have the lowest effect with only 11% contribution. The introduced solution offers lattice structure designs that can be adjusted to match bone stiffness distribution and promote bone ingrowth and hence eliminating the phenomenon of stress shielding while incorporating biological press-fit fixation technique. [ABSTRACT FROM AUTHOR]

The stem of the reverse shoulder arthroplasty (RSA) used in this study population relies on diaphyseal anchorage. The surgical strategy was to insert the largest possible stem size to achieve an adequate press-fit fixation resulting in a high diaphyseal filling ratio (FR). However, for different reasons, a high FR was sometimes not achievable. The aim of this study was to analyze the effect of different FR (high/medium/low) on clinical and radiographic outcome (ie, subsidence and humeral peri-implant bone resorption), complications, and revision surgeries after RSA. One hundred ninety nine patients were included and analyzed for clinical and radiologic outcome at a mean follow-up of 31.8 months after RSA. Diaphyseal humeral stem FR were measured directly postoperative and patients were divided into a low (N = 67), medium (N = 66), or high (N = 66) FR group. Humeral component complications and revision surgeries were measured as primary end points. Constant-Murley Score, range of motion, and the Subjective Shoulder Value were analyzed for clinical outcome. Periprosthetic bone resorption, radiolucent lines, shaft subsidence, and change in shaft alignment were measured for radiologic outcome. Two intraoperative fractures were seen in the high FR group (3%) and none in the other groups. There was no clinical humeral component loosening and no correlation could be found between FR and revision surgery. No differences were found between the low, medium, or high FR groups regarding range of motion, Subjective Shoulder Value, and absolute and relative Constant-Murley Scores (P >.05). Bone resorption was significantly more present in the high FR group, compared to the low FR ratio group, 4.5 (standard deviation ± 2.2) vs. 6.4 (standard deviation ± 1.8), respectively (P <.001). However, no difference could be observed regarding radiolucent lines, shaft subsidence, or shaft alignment changes between the 3 groups. High humeral diaphyseal stem FR in RSA is associated with more humeral bone resorption and might increase the risk for intraoperative stem fractures, compared to medium and low humeral diaphyseal stem FR. However, the FR does not have an effect on functional outcome or radiographic loosening signs after a mid-term follow-up of 31.8 months. [ABSTRACT FROM AUTHOR]

Abstract Stress shielding and aseptic loosening are complications of short stem total hip arthroplasty, which may lead to hardware failure. Stems with increased porosity toward the distal end were discovered to be effective in reducing stress shielding, however, there is a lack of research on optimized porous distribution in stem’s coating. This study aimed to optimize the distribution of the coefficient of friction of a metaphyseal femoral stem, aiming for reducing stress shielding in the proximal area. A finite element analysis model of an implanted, titanium alloy short-tapered wedge stem featuring a porous coating made of titanium was designed to simulate a static structural analysis of the femoral stem's behavior under axial loading in Analysis System Mechanical Software. For computational feasibility, 500 combinations of coefficients of friction were randomly sampled. Increased strains in proximal femur were found in 8.4% of the models, which had decreased coefficients of friction in middle medial areas of porous coating and increased in lateral proximal and lateral and medial distal areas. This study reported the importance of the interface between bone and middle medial and distal lateral areas of the porous coating in influencing the biomechanical behavior of the proximal femur, and potentially reducing stress shielding.

Arthroplasty is generally used to treat advanced osteoarthritis or other degenerative joint diseases. However, it can also be considered in younger patients with severe joint damage that seriously limits their function and quality of life. Young patients are at risk of aseptic mobilization and bone resorption due to the uneven distribution of stress on the contact surface between the prosthesis and the femur that generates the stress-shielding phenomenon. To overcome this occurrence, it is necessary to use biocompatible materials with a stiffness that is similar to bone. Composite hip prostheses, consisting of continuous fiber-reinforced polymers, play a progressively key role in the development of prosthetic devices. Composite materials can be designed more carefully than monolithic stems (single-phase materials such as metals), allowing for the development of more effective tissue substitutes. Our purpose of this review was to analyze the state of the art in the use of carbon femoral prostheses. In particular, the major mechanical properties of reinforcement (fiber) and matrix were outlined with their applications in the prosthetic field.

ABSTRACTA natural fiber-reinforced composite from a locally available false banana plant is developed for a prosthesis socket application. Four batches of composite samples are fabricated by arranging the longitudinal uniformly distributed unidirectional false banana fibers in four orientations (0°, 90°, ±45°, 0°/90o). The composites’ mechanical and physical properties, such as tensile strength, compression strength, flexural strength, impact resistance, and the effect of chemical treatment on water absorption, are investigated. The results are compared with E-glass fiber-reinforced polymer matrix composite. The false banana fiber-polymer composites with a 0° fiber orientation have a tensile strength of 86.81 MPa, less than 9% lower than E-glass-fiber composites (95.44 MPa), and an impact resistance of 6.25 J, 10% higher compared to the E-glass fiber polymer composites (5.70 J). In addition, the treated false banana fiber-polymer composite absorbed 70% less water than the untreated false banana fiber-polymer composite. It is observed that the fiber treatment has increased the polymer–fiber interaction and the interface strength of the false banana fiber-polymer composites.

Stress shielding and aseptic loosening are complications of short stem total hip arthroplasty, which may lead to hardware failure. Stems with increased porosity toward the distal end were discovered to be effective in reducing stress shielding, however, there is a lack of research on optimized porous distribution in stem’s coating. This study aimed to optimize the distribution of the coefficient of friction of a metaphyseal femoral stem, aiming for reducing stress shielding in the proximal area. A finite element analysis model of an implanted, titanium alloy short-tapered wedge stem featuring a porous coating made of titanium was designed to simulate a static structural analysis of the femoral stem's behavior under axial loading in Analysis System Mechanical Software. For computational feasibility, 500 combinations of coefficients of friction were randomly sampled. Increased strains in proximal femur were found in 8.4% of the models, which had decreased coefficients of friction in middle medial areas of porous coating and increased in lateral proximal and lateral and medial distal areas. This study reported the importance of the interface between bone and middle medial and distal lateral areas of the porous coating in influencing the biomechanical behavior of the proximal femur, and potentially reducing stress shielding. [ABSTRACT FROM AUTHOR]

The increase of revision surgeries in hip replacement procedure in Colombian young adult population can be addressed by a new design of femoral stem that reduces stress shielding. A new femoral stem was designed using topology optimization as a design aid to reduce the mass in the femoral stem and its overall stiffness, combined with the theoretical, computational, and experimental assessment of the new design that complies with a static and fatigue safety factor greater than one. The new femoral stem design can be used as a design tool to reduce the number of revision surgeries caused by stress shielding. [ABSTRACT FROM AUTHOR]

Introduction: The purposes of this study were to analyze and compare the functional outcomes and radiological changes around the press-fit humeral components in two contemporary medialized reverse total shoulder arthroplasty (RTSA) systems at a minimum of 5-year follow-up. Materials and methods: Between December 2003 and December 2015, 249 consecutive RTSAs were performed at our hospital. Of these, 68 primary uncemented RTSA met our inclusion criteria. The Constant-Murley score (CMS), the modified Constant score, a visual analog scale (VAS) and active shoulder range of motion (ROM) were measured pre- and postoperatively. Radiological assessment was performed by plain radiographs at a minimum of 5 years postoperatively. Results: At a mean follow-up of 80.2 months, there was no significant difference (p =.59) between the postoperative functional scores and range of motion of the two groups (Delta Xtend and Lima SMR). Radiological data of stress-shielding were observed in 38 patients (55.9%) being slightly more frequent in the Lima SMR group (21 patients) than in the Delta Xtend group (17 patients) (p =.62). Conclusions: Our study shows that the good functional results are similar between the two uncemented RTSA systems used and that they do not depend on the presence of radiological changes (stress-shielding) in the humeral stem at a minimum 5-year follow-up. [ABSTRACT FROM AUTHOR]

Long-segment instrumentation, such as Harrington rods, offloads vertebrae within the construct, which may result in significant stress shielding of the fused segments. The present study aimed to determine the effects of spinal fusion on bone density by measuring Hounsfield units (HUs) throughout the spine in patients with a history of Harrington rod fusion. Patients with a history of Harrington rod fusion treated at a single academic institution were identified. Mean HUs were calculated at 5 spinal segments for each patient: cranial adjacent mobile segment, cranial fused segment, midconstruct fused segment, caudal fused segment, and caudal adjacent mobile segment. Mean HUs for each level were compared using a paired-sample t test, with statistical significance defined by P < 0.05. Hierarchic multiple regression, including age, gender, body mass index, and time since original fusion, was used to determine predictors of midfused segment HUs. One hundred patients were included (mean age, 55 ± 12 years; 62% female). Mean HUs for the midconstruct fused segment (110; 95% confidence interval [CI], 100–121) were significantly lower than both the cranial and caudal fused segments (150 and 118, respectively; both P < 0.05), as well as both the cranial and caudal adjacent mobile segments (210 and 130, respectively; both P < 0.001). Multivariable regression showed midconstruct HUs were predicted only by patient age (−2.6 HU/year; 95% CI, −3.4 to −1.9; P < 0.001) and time since original surgery (−1.4 HU/year; 95% CI, −2.6 to −0.2; P = 0.02). HUs were significantly decreased in the middle of previous long-segment fusion constructs, suggesting that multilevel fusion constructs lead to vertebral bone density loss within the construct, potentially from stress shielding. [ABSTRACT FROM AUTHOR]

This study evaluates the potential for osseointegration and remodeling of customized dental implants made from Titanium-Hydroxyapatite Functionally Graded Material (Ti-HAP FGM) with optimized geometry, using the finite element method (FEM). The study utilized CT scan images to model and assemble various geometrical designs of dental implants in a mandibular slice. The mechanical properties of Ti-HAP FGMs were computed by varying volume fractions (VF) of hydroxyapatite (0–20%), and a bone remodeling algorithm was used to evaluate the biomechanical characteristics of the ultimate bone configuration in the peri-implant tissue. The findings of the FEA reveal that osseointegration improves with changes in the density and mechanical properties of the bone surrounding Ti-HAP implants, which are influenced by the varying VF of hydroxyapatite in the FGM. Increasing the hydroxyapatite fraction improves osseointegration, and appropriate length and diameter selection of Ti-HAP dental implants contribute to their stability and longevity. [Display omitted] [ABSTRACT FROM AUTHOR]

Arthroplasty is generally used to treat advanced osteoarthritis or other degenerative joint diseases. However, it can also be considered in younger patients with severe joint damage that seriously limits their function and quality of life. Young patients are at risk of aseptic mobilization and bone resorption due to the uneven distribution of stress on the contact surface between the prosthesis and the femur that generates the stress-shielding phenomenon. To overcome this occurrence, it is necessary to use biocompatible materials with a stiffness that is similar to bone. Composite hip prostheses, consisting of continuous fiber-reinforced polymers, play a progressively key role in the development of prosthetic devices. Composite materials can be designed more carefully than monolithic stems (single-phase materials such as metals), allowing for the development of more effective tissue substitutes. Our purpose of this review was to analyze the state of the art in the use of carbon femoral prostheses. In particular, the major mechanical properties of reinforcement (fiber) and matrix were outlined with their applications in the prosthetic field. [ABSTRACT FROM AUTHOR]

The design of humeral implants has evolved from the initial Grammont design, notably regarding the neck–shaft angle (NSA) and through the use of cementless prostheses. Stress shielding was frequently reported with cementless implants, the 2 main risk factors being humeral stem misalignment and high filling ratios. Our hypothesis was that standard length cementless stems with an NSA of 140° would facilitate good alignment with moderate filling ratios, thereby limiting stress shielding and ensuring good clinical outcomes. A single-center retrospective study was conducted of patients who underwent reverse total shoulder arthroplasty between January 2015 and August 2017, with at least 2 years' follow-up. Clinical evaluations included range of motion measurements and Constant and subjective shoulder values scores. Frontal alignment was assessed in terms of the angle (α) between axes of the stem and of the humerus. Filling ratios were measured in the metaphysis of the humerus, in the diaphysis, and at the distal end of the stem and considered excessive above 0.7. Stress shielding was evidenced radiographically by the observation of medial cortical narrowing, medial metaphysis thinning, lateral metaphysis thinning or under-the-baseplate osteolysis. Eighty-two shoulders were included and 70 had radiographic follow-up data available. The mean patient age was 78 years and 63/81 patients (78%) were female. The mean follow-up time was 39 ± 7 months. The mean α angle was 1.4° ± 0.9° and was less than 5° in all cases. The mean metaphyseal, diaphyseal, and distal filling ratios were 0.61 ± 0.06, 0.70 ± 0.08, and 0.64 ± 0.09, respectively. The mean Constant score improved from 28 ± 11 preoperatively to 64 ± 14 at last follow-up. The mean subjective shoulder values score at last follow-up was 81 ± 12. Seventy-nine percent of patients (55/70) had at least 1 form of stress-shielding related, which were not associated with clinical outcomes, apart from lateral metaphysis thinning, which was associated with lower active anterior elevation (mean, 106° ± 30° vs. 126° ± 28°; P =.01) and lower Constant scores (mean, 56 ± 17 vs. 65 ± 14; P =.06). The use of cementless reverse shoulder prostheses with a NSA of 140° was associated with good clinical outcomes at 2 years' follow-up. The prosthesis stem was correctly aligned with the humeral axis and the filling ratios were <0.7 in all cases. Stress-shielding was common but, apart from lateral metaphysis thinning, this had no impact on clinical outcomes. [ABSTRACT FROM AUTHOR]

The fluid flow dynamics on the porous scaffolds and their static responses on the adjacent bone are very crucial parameters for bone adaptation. Researchers are trying to develop different algorithms to design biomimetic porous scaffolds incorporating bone tissue engineering. In this present work, three types of biomimetic heterogeneous porous scaffolds (HPS) were designed with the help of the Voronoi tessellation method and Swarm Intelligence and those were analysed under fluid perfusion as well as under static loading conditions. In computational fluid dynamics (CFD) analysis, the wall shear stress (WSS) and the permeability of the porous scaffolds were compared to the natural trabecular bone to understand their hydrodynamic responses. In static analysis, the von Mises stresses of the Ti6Al4V scaffolds were checked to ensure no-yield condition. The strain energy density (SED) distributions were also studied on the neighbouring bone region of the femur greater trochanter to obtain stress shielding (SS) patterns and these findings were then compared with the natural trabecular bone at the same anatomical region. The outcome parameters, viz. the induced WSS, von Mises stress, the permeability, and SS of the scaffold, are found to be independent of the scaffold architecture. The von Mises stress and permeability increased with an increase in porosities, while the induced WSS and SS nature of the scaffolds showed the reverse trend. The results showed that the HPS designed based on the Swarm Intelligence incorporating Physarum Polycephalum algorithm offered the least SS level of 41.096 for 75% porous HPS, which may be considered the most promising result. Considering all the parameters, the novel designed scaffold based on Swarm Intelligence showed the most trabecular bone mimicking nature compared to the other scaffolds. [ABSTRACT FROM AUTHOR]

Orthodontic mini-implants are devices used for anchorage in various orthodontic treatments. We conducted a pilot study which aimed to observe preliminary trends regarding the impact of heat treatment on the elastic modulus of Ti6Al4V alloy and stainless steel 316L mini-implants. The initial phase involved testing the impact of heat treatment on the mechanical properties of Ti6Al4V alloy and stainless steel 316L mini-implants. Material and methods: Ten self-drilling mini-implants sourced from two distinct manufacturers (Jeil Medical Corporation® and Leone®) with dimensions of 2.0 mm diameter and 10 mm length were tested. They were separated into two material groups: Ti6Al4V and 316L. Using the CETRUMT-2 microtribometer equipment, indentation testing was conducted employing a diamond-tipped Rockwell penetrator at a constant force of 4.5 N. Results: Slight differences were observed in the elastic modulus of the Ti6Al4V alloy (103.99 GPa) and stainless steel 316L (203.20 GPa) compared to natural bone. The higher elastic moduli of these materials indicate that they are stiffer, which could potentially lead to stress-shielding phenomena and bone resorption. Heat treatment resulted in significant changes in mechanical properties, including elastic modulus reductions of approximately 26.14% for Ti6Al4V and 24.82% for 316L, impacting their performance in orthodontic applications. Conclusion: Understanding the effects of heat treatment on these alloys is crucial for optimizing their biomechanical compatibility and longevity in orthodontic treatment. To fully evaluate the effects of heat treatment on mini-implants and to refine their design and efficacy in clinical practice, further research is needed. [ABSTRACT FROM AUTHOR]

Background: Multisegmental pathologic autofusion occurs in patients with ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH). It may lead to reduced vertebral bone density due to stress shielding. Methods: This study aimed to determine the effects of autofusion on bone density by measuring Hounsfield units (HU) in the mobile and immobile spinal segments of patients with AS and DISH treated at a tertiary care center. The mean HU was calculated for five distinct regions—cranial adjacent mobile segment, cranial fused segment, mid-construct fused segment, caudal fused segment, and caudal adjacent mobile segment. Means for each region were compared using paired-sample t-tests. Multivariable regression was used to determine independent predictors of mid-fused segment HUs. Results: One hundred patients were included (mean age 76 ± 11 years, 74% male). The mean HU for the mid-construct fused segment (100, 95% CI [86, 113]) was significantly lower than both cranial and caudal fused segments (174 and 108, respectively; both p < 0.001), and cranial and caudal adjacent mobile segments (195 and 115, respectively; both p < 0.001). Multivariable regression showed the mid-construct HUs were predicted by history of smoking (−30 HU, p = 0.009). Conclusions: HUs were significantly reduced in the middle of long-segment autofusion, which was consistent with stress shielding. Such shielding may contribute to the diminution of vertebral bone integrity in AS/DISH patients and potentially increased fracture risk. [ABSTRACT FROM AUTHOR]

Stress shielding and osteolysis around the humeral stem after reverse shoulder arthroplasty causes loosening and periprosthetic fractures and reduces bone stock during revision surgery. In Japanese patients, who have relatively small bodies, different characteristics may exist regarding the occurrence of these changes compared with the characteristics of Westerners, who have relatively larger frames. The purpose of this multicenter study was to investigate the incidence and clarify the predictors of stress shielding and osteolysis in Japanese individuals who underwent reverse shoulder arthroplasty. The occurrence of stress shielding and osteolysis was investigated in 135 shoulders that had undergone reverse shoulder arthroplasty at least 2 years prior in five Japanese hospitals. During post-surgical follow-up, which was conducted every 3 months, the locations of the stress shielding occurrences, such as cortical thinning and osteopenia (which primarily occurred in zones 1, 2, and 7, where 1 is the greater tuberosity and 7 is the calcar part), spot weld, and condensation lines, were recorded. Cases without any abnormal findings on radiographs obtained up to ≥2 years after surgery were regarded as having no abnormalities. Finally, the predictors of cortical thinning and proximal humeral osteolysis were assessed using univariate and multivariate regression analyses. Cortical thinning and osteopenia occurred in 68 shoulders, a condensation line occurred in 37 shoulders, and spot weld occurred in 23 shoulders. In particular, greater tuberosity and calcar osteolysis occurred in 40 and 47 shoulders, respectively. Long stem, cementless stem, and a larger proximal filling ratio were independent predictors of cortical thinning and osteopenia, whereas a cementless stem, larger metaphysis diameter, and a larger proximal filling ratio were associated with proximal humeral osteolysis. The predictors of stress shielding and osteolysis included the use of long stems, cementless stems, larger proximal filling ratios, and larger metaphysis diameters. retrospective comparative study (Level III). [ABSTRACT FROM AUTHOR]

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Background: Newer generation humeral stem designs in total shoulder arthroplasty (TSA) are trending towards shorter lengths and uncemented fixation. The goal of this study is to report a 2-yr minimum clinical and radiographic outcomes of an uncemented short-stem press-fit humeral stem in anatomic total shoulder arthroplasty (ATSA) and reverse total shoulder arthroplasty (RTSA). Methods: A retrospective multicenter database review was performed of all patients who received an uncemented short-length press-fit humeral stem (Equinoxe Preserve humeral stem, Exactech, Inc., Gainesville, FL, USA) in ATSA and RTSA with a minimum two-year follow-up. The primary outcome was the prevalence of humeral stems at risk of radiographic loosening. Secondary outcomes included evaluation of functional outcome scores and prevalence of revision TSA for humeral stem loosening. Two blinded observers performed radiographic analyses, which included humeral stem alignment, canal filling ratio, radiolucent lines, stress shielding (calcar and greater tuberosity), and changes in component position (subsidence and stem shift). At risk stems were defined by the presence of one or more of the following: humeral stem with shifting or subsidence, scalloping of the humeral cortex, or radiolucent lines measuring 2 mm or greater in 3 or more zones. Results: 287 patients (97 ATSA and 190 RTSA) were included in this study. The mean follow-up was 35.9 (±6.1) months. There were significant improvements for all functional outcome scores (P

Hard tissues in the human body are damaged due to age, trauma, and bone diseases. Metal implants/prostheses are traditionally preferred to repair and treat these damaged tissues. Today, metals and their alloys meet the mechanical requirements of the musculoskeletal system well. However, the need to develop alternative composite materials has increased since metals are very stiff materials compared to bone. Problems such as stress shielding, and aseptic loosening can arise due to their high modulus of elasticity, and the need for secondary revision operations for such reasons. Also, the metal implant/prostheses should be removed after the healing that causes the undesirable secondary operation. In this study, polylactic acid (PLA) and hydroxyapatite (HA)-based composite materials were produced and their mechanical characteristics evaluated for possible implant applications. In addition, the PLA/HA composite materials stayed in Artificial Body Fluid (ABF) at different times, and the change in the mechanical properties were determined. PLA granules and HA powders were mixed in different ratios of weight (weight ratio 1:0, 9:1, 7:3, and 1:1) to produce 80 samples using the solvent casting technique. PLA was dissolved with chloroform in a magnetic stirrer at 200 rpm and room temperature, and then nano HA was added and mixed until homogeneity was achieved. After casting and drying, the samples were cut into appropriate standard sizes. The samples were subjected to biodegradability in-vitro test. In the results of this study, the modulus of elasticity increased with the increase of HA in the samples; however, the yield strength, ultimate strength, and yield strain of the samples decreased. In addition, it was observed that the existence of HA decreases the rate of degradation; therefore, the percentage of weakening in mechanical strength decreased in the measurements made at the end of the 15th day. According to these results, it was concluded that PLA/HA biodegradable composites can be developed to use as implant/prosthesis material.

Purpose: This study aims to determine the stress shielding and other radiological outcomes of patients who underwent an uncemented reverse shoulder arthroplasty (RSA) with an anatomic proximal coated stem for complex proximal humeral fractures (PHF) with 3 or 4 parts at 2 years postoperatively. Methods: 37 shoulders underwent an uncemented RSA for PHF from November 2015 to February 2019 and were followed up for 2 years. A radiographic assessment of stress shielding, filling ratio, stem stability (radiolucent lines/subsidence/alignment), tuberosity healing and notch was performed. Results: The mean age at the time of surgery was 72 years (range, 61–85). Stress shielding was appreciated in 31 shoulders (83.8%). The most important characteristic of stress shielding is cortical resorption: Grade 3 resorption occurred in 3 shoulders (8.1%) and grade 4 in 23 (62.2%) as per the grading system defined by Inoue et al. (Inoue et al. in J Shoulder Elbow Surg 26:1984–1989, 2017). A high occurrence of bone resorption was observed in Gruen zones 2 (Lateral Stress shielding) and 7 (Medial Stress shielding). The mean distal filling ratio in patients without stress shielding was 78,48(SD 14,9), whereas in patients with stress shielding, it was slightly higher with a mean of 81,68% (SD 4,89). Tuberosity healing was found in 94.6% (35/37) of the shoulders. No patient had any radiolucent line. No notch was observed. Conclusion: At short-term follow-up, a high rate of tuberosity healing was achieved (94.6%) even though stress shielding was found in 83.8% (31/37) of the shoulders. Bone resorption was most frequently observed externally at zone 2 (Lateral stress shielding) and internally at zone 7 (Medial stress shielding). A higher filling ratio was associated with an increased occurrence of stress shielding. The uncemented anatomic humeral component did not result in early loosening. Level of evidence: IV; Case Series; Treatment study. [ABSTRACT FROM AUTHOR]

Introduction: To preserve humeral bone during RTSA, stems have been made shorter and cement avoided whenever possible. However, with the increased use of uncemented RTSA, a phenomenon comparable to the stress shielding of the hip has been described for the proximal humerus. The aim of this study was to investigate the influence of stem length and width on proximal humeral bone resorption after primary uncemented RTSA. Materials and methods: The prospective shoulder arthroplasty database of our institution was reviewed for all primary uncemented RTSAs from 2017 to 2020 in osteoarthritis and cuff tear arthropathy cases with > 2-year follow-up. We compared the clinical and the radiographic 2-year outcome of the short and standard length stems of the same prosthesis design. This allowed us to assess the effects of stem length and width with regard to stress shielding. Furthermore, we defined a cut-off value for the filling ratios to prevent stress shielding. Results: Fifty patients were included in the analysis, nineteen were in the short stem group (SHORT) and thirty-one in the standard stem group (STANDARD). After 2 years, SHORT showed a relative Constant Score of 91.8% and STANDARD of 98.3% (p = 0.256). Stress shielding was found in 4 patients (21%) in SHORT and in 16 patients (52%) in STANDARD (p = 0.03); it occurred more frequently in patients with higher humeral filling ratios (p < 0.05). The calculated cut-off to prevent stress shielding was 0.7 (± 0.03) for the metaphyseal and distal filling ratio. Conclusion: While short and standard stems for RTSA have good results after 2 years, we found a significant negative effect of higher length and width of the stem with regard to stress shielding. Even though the clinical effects of stress shielding have to be assessed, short stems should be chosen with a filling ratio at the metaphyseal and distal position below 0.7. Level of evidence (a retrospective case–control study): III. [ABSTRACT FROM AUTHOR]

Stress shielding (SS) around press-fit radial head arthroplasty (RHA) was recently reported as a cause of a new type of proximal radial neck resorption (PRNR). Very few studies have analyzed this phenomenon. No comprehensive classification is currently available. We thus decided to clinically and radiographically analyze 97 patients who underwent a press-fit RHA and who were followed up for a mean period of 72 months (range: 2–14 years). PRNR in the four quadrants of the radial neck was assessed. We designed a novel SS classification based on (1) the degree of resorption of the length of the radial neck and (2) the number of neck quadrants involved on the axial plane. The mean PRNR (mPRNR) was calculated as the mean resorption in the four quadrants. mPRNR was classified as mild (<3 mm), moderate (3 to 6 mm), and severe (>6 mm). Eighty-four percent of the patients presented PRNR. mPRNR was mild in 33% of the patients, moderate in 54%, and severe in 13%. In total, 6% of the patients with mild mPRNR displayed resorption in one quadrant, 18% displayed resorption in two quadrants, 4% displayed resorption in three quadrants, and 72% displayed resorption in four quadrants. All four quadrants were always involved in moderate or severe mPRNR, with no significant differences being detected between quadrants (p = 0.568). mPRNR has no apparent effect on the clinical results, complications, or RHA survival in the medium term. However, longer-term studies are needed to determine the effects of varying degrees of PRNR on implant failure. [ABSTRACT FROM AUTHOR]

This study aims to address the challenges associated with conventional metallic bone fixation plates in biomechanical applications, such as stainless steel and titanium alloys, including stress shielding, allergic reactions, corrosion resistance, and interference with medical imaging. The use of materials with a low elastic modulus is regarded as an effective approach to overcome these problems. In this study, the impact of different types of chopped carbon fiber-reinforced polyether ether ketone (CCF/PEEK) functionally graded material (FGM) bone plates on stress shielding under static and instantaneous dynamic loading was explored using finite element analysis (FEA). The FGM bone plate models were established using ABAQUS and the user's subroutine USDFLD and VUSDFLD, and each model was established with an equivalent overall elastic modulus and distinctive distributions. The results revealed that all FGM bone plates exhibited lower stress shielding effects compared to metal bone plates. Particularly, the FGM plate with an elastic modulus gradually increased from the centre to both sides and provided maximum stress stimulation and the most uniform stress distribution within the fractured area. These findings offer crucial insights for designing implantable medical devices that possess enhanced mechanical adaptability. [ABSTRACT FROM AUTHOR]

Hip implants face a significant challenge due to their limited lifespan, a concern amplified by the rising human life expectancy. Lattice structures have demonstrated the ability to provide precise control over geometry, thereby significantly enhancing implant performance. This paper introduces the development of graded additively manufactured Ti6Al4V lattice structures for orthopaedic implants. The objective focuses on developing a graded lattice unit cell design mirroring human bone properties, emphasising high surface curvature and design versatility to improve mechanical and biomedical properties, specifically osseointegration and stress shielding. The study involves modelling and grading simple cubic (SC) and body-centred cubic (BCC) lattice structures with various geometries and graded conditions and conducting compressive tests to identify the optimal configuration. The results showed that filleting was found to be the mechanical strength. On the other hand, BCC lattice structures demonstrated superior performance compared to SC structures. The optimised structure with a pore size of 400 µm provided an elastic modulus of 15.7 GPa, yield strength of 296 MPa and compressive strength of 530 MPa. This graded lattice design approach provides a promising technique for enhancing hip implant performance, offering potential improvements. [ABSTRACT FROM AUTHOR]

Conventional fixation plates permanently attached to the body can lead to complications, such as stress shielding and aseptic loosening, due to their contact with the bone, resulting in bone loss. The contact between these solid fixation plates and the bone surface inhibits blood flow, potentially leading to necrosis at the interface. To overcome this challenge, a porous implant featuring a gyroid lattice structure for humerus bone fixation is proposed. However, designing such an implant typically involves deterministic approaches, which do not account for uncertainties in design parameters, loadings on the plate, and additive manufacturing process parameters. Consequently, the actual conditions experienced by the plate may not be accurately modeled. Herein, both deterministic and probabilistic analyses of a porous implant with a gyroid lattice structure positioned on the humeral bone is conducted. The findings are compared to the failure probabilities of both the conventional fixation plate and the optimal plate derived from a previous study. The study reveals that uncertainties in design parameters significantly influence the plate's failure probability compared to deterministic analysis, emphasizing the importance of probability‐based analyses for a reliable plate design. [ABSTRACT FROM AUTHOR]