Femoral stress distribution in fully hydroxyapatite-coated cementless versus polished cemented stems with identical geometry: a thermoelastic stress analysis

Thermoelastic stress analysis (TSA) was used to evaluate stress changes over the entire surface of a specimen. This study aimed to assess the relationship between femoral stress distribution, analysed using TSA and changes in bone mineral density (BMD) after total hip arthroplasty (THA). Stress changes in the simulated bone before and after taper-wedge stem insertion were measured using the TSA. Stress changes were compared with BMD changes around the stem 1 year after surgery in a THA patient (58 hips) with the same taper-wedge stem. Subsequently, we compared the correlation between stress changes and BMD changes. TSA revealed significant stress changes before and after stem insertion, with prominent alterations in the proximal medial region. The BMD changes at 1 year post-THA exhibited a 15%-25% decrease in the proximal zones, while Zones 2-6 showed a -6% to 3% change. Notably, a strong positive correlation (0.886) was found between the stress change rate and BMD change rate. This study demonstrated a high correlation between femoral stress distribution assessed using TSA and subsequent BMD changes after THA. The TSA method offers the potential to predict stress distribution and BMD alterations postsurgery, aiding in implant development and clinical assessment. Combining TSA with finite element analysis could provide even more detailed insights into stress distribution. Case series (with or without comparison).

This study investigates the stress distribution in beam-like structures composed of triply periodic minimal surface (TPMS) fabricated through additive manufacturing. Two topologies, Schwarz Primitive and Gyroid, were analyzed using a hybrid numerical–experimental approach combining Finite Element (FE) simulation and Thermoelastic Stress Analysis (TSA). Those methods were used to examine flexural behavior under static and dynamic loading conditions respectively. FE simulations revealed distinct stress distributions: the Gyroid structure exhibited localized regions with higher stress, while the Schwarz Primitive displayed a more uniform stress distribution. TSA, a non-contact, full-field technique sensitive to dynamic loading, confirmed these patterns, showing good agreement with the FE predictions. A three-point bending test was also conducted to provide further validation of mechanical performance. The results highlight the influence of TPMS geometry on stress distribution and show that integrating FE and TSA provides a reliable investigation of architected materials. This is, to the authors’ best knowledge, the first attempt to apply TSA to TPMS lattices, enabling full-field experimental validation of numerically predicted stress distributions. This framework offers promising potential for the design and validation of functionally graded and mechanically efficient components in structural, biomedical, and aerospace applications.

Purpose: The aim of this study was to evaluate the stress distribution in a synthetic femur that was implanted with a fully hydroxyapatite-coated stem using thermoelastic stress and finite element analyses, and to clarify the differences in the stress distributions between these two methods. Methods: Thermoelastic stress analysis is a stress-analysis technique that employs the thermoelastic effect. Sinusoidal vertical loads were applied to the head of the stem placed on the synthetic femur, and surface stress distribution images were acquired using an infrared stress measurement system. The finite element model for the synthetic femur and stem were set up similarly to the thermoelastic stress analysis experiment, and vertical load was applied to the head of the stem. Surface stress distribution and stress values obtained via these two methods were compared. Results: Thermoelastic stress analysis showed that compressive and tensile stresses were distributed from the proximal femur to the diaphysis, not only on the medial and lateral surfaces, but also on the anterior and posterior surfaces. However, finite element analysis showed that compressive stress was not distributed on the anterior and posterior surfaces of the femoral intertrochanter. The stress values of thermoelastic stress analysis tended to be higher in the proximal femur than that obtained via the finite element analysis. Conclusions: The surface stress distribution obtained by these two methods were different specifically in the proximal femur. Our results imply that thermoelastic stress analysis has a better potential than finite element analysis to show the surface stress distribution that reflects the stem design.

The rate of failure of primary total hip arthroplasty in patients with osteonecrosis of the femoral head is higher than that in patients with osteoarthritis. The purpose of this prospective study was to document the clinical and radiographic results of arthroplasty with so-called third-generation cementing and the results of second-generation cementless total hip arthroplasty in ninety-eight consecutive patients with osteonecrosis of the femoral head. Fifty patients who had had simultaneous bilateral total hip arthroplasty with a cemented stem in one hip and a cementless stem in the other and forty-eight patients who had had a unilateral total hip arthroplasty with a cementless stem were included in the study. A cementless acetabular component was used in all hips. The presumed cause of the osteonecrosis was ethanol abuse in fifty-seven patients, unknown in twenty-seven, fracture of the femoral neck in nine, and steroid use in five. There were eighty men and eighteen women. The mean age at the time of the arthroplasty was 47.3 years (range, twenty-six to fifty-eight years). Clinical and radiographic evaluations were performed preoperatively; at six weeks; at three, six, and twelve months; and yearly thereafter. The average duration of follow-up was 9.3 years. The average Harris hip scores in the group treated with unilateral arthroplasty (97 points) and the group treated with bilateral arthroplasty (94 points) were similar at the time of final follow-up. They were also similar between the group treated with cement (mean, 96 points) and that treated without cement (95 points). No component had aseptic loosening in either group. In one hip, a cemented femoral stem (2%) and a cementless cup were revised because of infection. Two cementless stems (2%) were revised because of fracture of the proximal part of the femur with loosening of the stem. Annual wear of the polyethylene liner averaged 0.22 mm in the group treated with cement (a zirconia head) and 0.14 mm in the group treated without cement (a cobalt-chromium head). The prevalence of osteolysis in zones 1 and 7 of the femur was 16% in the group treated with cement and 24% in the group treated without cement. Advancements in surgical technique and better designs have greatly improved the long-term survival of cemented and cementless implants in young patients with osteonecrosis of the femoral head. Although there was no aseptic loosening of the components, a high rate of linear wear of the polyethylene liner and a high rate of osteolysis in these high-risk young patients remain challenging problems.

Cement fixation for total hip arthroplasty (THA) remains a controversial topic. While cemented stems are associated with lower risk of periprosthetic fractures (PPF), cementless stems may offer superior biological fixation. This study analyzed peri-operative and short-term outcomes of cemented vs. cementless stem fixation in THA. A retrospective review was conducted on 15,012 patients who underwent primary elective THA at an academic medical center from 2011 to 2021. Of these patients, 429 were cemented. Patients were stratified into 3 age cohorts (25-69, 70-79 and ≥ 80 years). Cemented stem patients were 1:1 propensity-score matched to cementless stem patients for baseline characteristics. Perioperative and short-term outcomes were compared. The mean operative time for cemented cases was significantly longer across all age cohorts (25-69, P = 0.005; 70-79, P < 0.001; ≥80, P < 0.001). In the 70-79 and ≥ 80 cohorts, cemented patients demonstrated a significantly shorter length of stay (LOS) compared to cementless patients (2.2 vs. 2.6 days, P = 0.017; 3.0 vs. 3.4, P = 0.041, respectively). In the 70-79 and ≥ 80 cohorts, cemented patients were significantly more likely to be discharged home when compared to cementless patients (88.2 vs. 80.5%, P = 0.031; 64.0 vs. 54.2%, P = 0.046, respectively). Across age cohorts, there were no differences in all-cause revision rates (Cohort 1: 5.4% vs. 1.1%, P = 0.108; Cohort 2: 3.0% vs. 1.8%, P = 0.362; Cohort 3: 1.8% vs. 1.2%, P = 0.714). The ≥ 80 cohort demonstrated increased rates of PPF in the cementless cohort compared to cemented (1.2 vs. 0%, P = 0.082, respectively), but it did not reach significance. Patient age has a substantial impact on perioperative outcomes following cemented versus cementless stem THA. Patients > 70 with a cemented femoral stem had improved perioperative outcomes such as shorter LOS, increased discharge to home and reduced rates of PPF compared to their cementless stem counterparts. Patient age should be considered prior to selecting a stem fixation strategy. III, Therapeutic Study.

What's New in Hip Replacement.

Where Are We Now? Total hip arthroplasty is one of the most successful operations in the field of orthopaedic surgery. In fact, Lermonth et al. [4] called THA “the operation of the century” in 2007. Of course, that statement is still up for debate. What cannot be questioned is that the life expectancy of our patient population is getting higher. Because of this, the survival analysis of cemented stems beyond 20 years followup is very important. Cemented stems have shown good long-term results with low revision rates at 15- and 20-year followup. However, the survival of cemented stems is influenced by several femoral-stem characteristics and operative factors including stem geometry, material properties, surface roughness, cementing technique, cement mantle thickness and stem position [1, 6]. The current study by Bedard and colleagues addressed the results of cemented stems with a followup of more than 20 years. All relevant articles in the literature with followups of more than 20 years were analyzed, leading to 4343 cemented polished stems and 360 matte stems achieving this minimum followup. According to the results of this analysis, stems with a rough surface finish did not perform as well as polished stems. However, this study included only two different series of matte stems. Where Do We Need To Go? Although studies [2, 7, 8] support the idea that increased surface roughness in certain stem designs such as the Müller and the Exeter stems leads to higher loosening rates, the more-general question of which surface finish is best (rough, matte, or polished) cannot be considered answered for all cemented stems. Indeed, the complex interplay of confounding factors like surface roughness, stem geometry, and cement mantle geometry and quality (homgeneous or inhomogeneous) should keep us from generalizing what we know about a few stem designs compared with all others. It may be that surface roughness has a higher influence on stem survival for straight Müller-type stems with inhomogeneous cement mantle thicknesses than it does on straight Exeter-type stems or anatomical stems with more homogeneous cement mantles. This hypothesis may be supported by results from the Swedish Hip Arthroplasty Register [5], which indicated better results for the anatomical cemented Lubinus SPII stem with rough surface compared to the Müller stem with rough surface and the Charnley stem with a polished surface. The Norwegian Arthroplasty Register showed similar survival rates beyond 10 years for the matte anatomical Lubinus SPII stem and the polished Charnley stem [3]. Additionally, the inhomogeneous cement mantle of Müller-type stems may result in higher revision rates compared to Exeter- and Lubinus-type stems with homogenious cement mantles [5]. How Do We Get There? We will need to get more-specific data from available sources. Registries, as they start to capture more data from imaging studies, may allow us to compare stems of similar design but different surface finishes, and perhaps even to perform subanalyses based on the quality of the cement mantle. The differences in survivorship between these selected groups, even in shorter followup periods, will be even more evident in long-term followup studies. If there are no differences in the survival curves at 10 and 15 years, additional studies with longer followup would be helpful. Studies with longer followup could potentially discover the importance of surface roughness for each specific design and cement mantle of cemented stems.

Controversy exists regarding the safety of bilateral simultaneous total hip arthroplasty, in part because of the potentially higher prevalence of pulmonary fat embolism. The purpose of the present study was to determine if unilateral and bilateral simultaneous total hip arthroplasty procedures resulted in different prevalences of fat embolization, different degrees of hemodynamic compromise, or different levels of hypoxemia or mental status changes. One hundred and fifty-six consecutive patients undergoing primary total hip arthroplasty were prospectively enrolled in the study. The study group included fifty patients undergoing bilateral simultaneous total hip arthroplasty and 106 patients undergoing unilateral total hip arthroplasty. One hundred hips were treated with a cemented stem, and 106 were treated with a cementless stem. Arterial and right atrial blood samples were obtained before implantation (baseline); at one, three, five, and ten minutes after implantation of the acetabular and femoral components; and at twenty-four and forty-eight hours after the operation. Arterial blood pressure, right atrial pressure, arterial oxygen tension, and carbon-dioxide tension were also monitored at these times. The presence of lipid and cellular contents of bone marrow was determined. The prevalence of fat embolism was not significantly different between the groups managed with bilateral and unilateral total hip arthroplasty or between the groups managed with cemented and cementless stems. Similarly, the prevalence of bone-marrow-cell embolization was not significantly different between the groups managed with bilateral and unilateral total hip arthroplasty or between the groups managed with cemented and cementless stems. Patients with bone-marrow-cell embolization had a significantly lower arterial oxygen tension (p = 0.022) and oxygen saturation (p = 0.017) than did patients without bone-marrow-cell embolization on the first postoperative day. Four patients with bone-marrow cells in the blood samples that were obtained from the right atrium on the first postoperative day had development of diffuse encephalopathy with confusion and agitation that lasted for about twenty-four hours. The prevalence of fat and bone-marrow-cell embolization was similar in the groups managed with bilateral simultaneous and unilateral total hip arthroplasty as well as in the groups managed with cemented and cementless stems.

Background: Uncemented short stems have been shown to optimize load distribution on the proximal femur, reducing stress shielding and preserving bone mass. However, they may adversely affect the initial stability of the stems. To date, most research conducted on short stems has predominantly centered on uncemented stems, leaving a notable dearth of investigations encompassing cemented stems. Therefore, this study aimed to investigate the length of cemented stems on the transmission of femoral load patterns and assess the initial stability of cemented short stems. Method: A series of finite element models were created by gradient truncation on identical cemented stem. The impact of varying lengths of the cemented stem on both the peak stress of the femur and the stress distribution in the proximal femur (specifically Gruen zones 1 and 7) were assessed. In addition, an experimental biomechanical model for cemented short stem was established, and the initial stability was measured by evaluating the axial irreversible displacement of the stem relative to the cement. Result: The maximum von-Mises stress of the femur was 58.170MPa. Spearman correlation analysis on the shortened length and von-Mises stress of all nodes in each region showed that the p-values for all regions were less than 0.0001, and the correlation coefficients (r) for each region were 0.092 (Gruen Zone 1) and 0.366 (Gruen Zone 7). The result of the biomechanical experiment showed that the irreversible axial displacement of the stem relative to cement was -870μm (SD 430μm). Conclusion: Reducing the length of a cemented stem can effectively enhance the proximal load of the femur without posing additional fracture risk. Moreover, the biomechanical experiment demonstrated favorable initial stabilities of cemented short stems.

IntroductionDespite the increasing use of cementless stems in total hip arthroplasty, the cemented stem has played a valuable role in the armamentarium of orthopedic surgeons. This study aims to compare two types of Libra® stems SERF, one cemented (Libra® C) and the other cementless hydroxyapatite coated (Libra® HA) that were conducted to analyze the medium-term outcome regarding their behavior and longevity.MethodsThis is a retrospective study for patients who received primary total hip arthroplasty with Dual Mobility (DM) articulation in the period between January 2014 to January 2020 with a minimum of two years follow-up. Two-hundred hips have been identified in 196 patients. One hundred forty-three Libra® cementless versus fifty-seven Libra cemented stems were implanted and the outcome of these stems is reported. All procedures were performed through the posterior approach and cemented stems were selected for elderly patients with wide medullary canals Dorr Type C. The indications for the index procedure were fractures, avascular necrosis, rheumatoid, and osteoarthritis. One hundred thirty-nine cementless DM cups were used while sixty-one hips had cemented Novae stick cups. Radiological evaluation for cup and stem positions, cement mantle, and radiolucent lines was performed, besides clinical function using the Harris Hip Score.ResultsThe average age of patients was 60 ± 14.8. At the latest review, none of the cemented stems was revised or awaiting revision. One cementless stem was revised because of cortical perforation. Five intraoperative fractures were observed in the cementless group, but none of them needed revision or affected the stem stability. Readmission to theatre occurred in four patients to evacuate hematoma in two, a reduction of dislocation in one, and grafting bone lysis in one.ConclusionCemented stems have an important role in osteoporotic patients with wide medullary canals with excellent outcomes and minimal risk of fracture.Level of evidenceLevel IV.

The routine use of stems in revision TKA improves survival rates by enhancing the stability of the prosthesis. The ideal method of stem fixation (cemented or uncemented) in two-stage reimplantation remains controversial. The purpose of this study was to answer the following questions: (1) Are rerevision rates for aseptic loosening comparable between cemented stems and uncemented stems in two-stage reimplantation? (2) Is the reinfection rate comparable between antibiotic-impregnated cemented stems and uncemented stems for two-stage reimplantation? (3) Are there any differences in Knee Society radiographic scores between stem techniques? A retrospective analysis was performed in all patients who underwent two-stage reimplantation between 1990 and 2010 at Anderson Orthopaedic Research Institute (AORI) and OrthoCarolina (OC). One hundred fourteen patients with 228 stems met the inclusion criteria. Of these 228 stems, 102 stems were cemented and 126 stems were uncemented. The indication for stem fixation was largely institution specific; AORI used cementless stems 92% (118) of the time, whereas OC used a cemented stem 92% (92) of the time. A 2-year minimum radiographic and clinical followup was required for inclusion into the study. Radiographic evaluations were performed using a modification of the Knee Society radiographic score. Rerevision rates for aseptic loosening were comparable with three cemented and three cementless stem constructs. The reinfection rate was also comparable between cemented and cementless stems (p = 0.86). Using post hoc analysis, 32% of cemented stems were radiographically classified as loose or closely observe (33 of 102) compared with 17% of the cementless stem group (21 of 126; p = 0.006). Patients with good bone quality had a significantly lower rate of radiographic loosening compared with patients with poor bone quality (p = 0.01). There was no significant correlation with radiographic loosening and level of constraint (p = 0.90) or use of articulating versus static antibiotic spacer (p = 0.06). In this retrospective study, cementless diaphyseal-engaging stems had a lower rate of radiographic failure than did cemented stems in two-stage reimplantation. Reinfection rates remain similar despite the absence of antibiotic cement in the cementless constructs. At this time we believe the use of hybrid, cementless diaphyseal-engaging stems should be considered as a possible option at the time of reimplantation.

Total hip arthroplasty after failed fixation of a proximal femur fracture: Analysis of 59 cases of intra- and extra-capsular fractures

Thermoelastic stress analysis (TSA), performed on metallic components with a high diffusivity coefficient, seldom reaches adiabatic conditions. As a consequence, TSA results are affected by an attenuation whose entity varies locally, preventing the use of TSA as a reliable quantitative investigation means. The recovery of the adiabatic temperature and of the correct value of the first stress invariant, directly linked to it, can only be performed making an assumption on the local stress distribution. This article presents a method for automatically choosing, among a number of stress distribution functions, the one that performs the best correction of the raw TSA data. The implementation of this automatic correction procedure in a computer program allowed the point-by-point correction of whole TSA images.

In total hip arthroplasty (THA), the ideal stem length remains uncertain; different stem lengths are used in different cases or institutions. We aimed to compare the stress distributions of cementless tapered wedges and short stems in femurs with different femoral marrow geometries and determine the appropriate fit. Finite element models were created and analyzed using HyperMesh and LS-DYNA R11.1, respectively. The 3-dimensional shape data of the femurs were extracted from computed tomography images using the RETOMO software. Femurs were divided into 3 groups based on the Dorr classification. The computer-aided design data of cementless tapered wedge-type and short stems were used to select the appropriate size. In the finite element analysis, the loading condition of the femur was assumed to be walking. Volumes of interest (VOIs) were placed within the femur model at the internal and external contact points of the stem based on Gruen zones. The average stresses and strain energy density (SED) of the elements included in each VOI were obtained from the preoperative and postoperative models. The von Mises stress and SED distributions of the cementless tapered wedge and short stems were similar in their respective Dorr classifications. In both stems, the von Mises stress and SED after THA were lower than before THA. The von Mises stress and SED of the cementless tapered wedge stem were higher than those of short stems. Cementless tapered wedge-type stems tended to have lower rates of change than short stems; however, Dorr C exhibited the opposite trend. In the Dorr classification comparison, the von Mises stress and SED were greater for both stems in the order of Dorr C > Dorr B > Dorr A, from Zone 2 to Zone 6. In Dorr A and B, the short stem exhibited a natural stress distribution closer to the preoperative femur than the tapered wedge stem; however, in Dorr C, the short stem may have a greater effect on stress distribution, suggesting that it may cause greater effects, such as fracture in the early postoperative period, than other Dorr types.

TSA based evaluation of fatigue crack propagation in steel bridge members