Prosthesis Stem Research Articles

Optimization Design and SLM Manufacturing of Porous Titanium Alloy Femoral Stem.

In order to solve the loosening problem caused by stress shielding of femoral stem prostheses in clinical practice, an optimization design method of a personalized porous titanium alloy femoral stem is proposed. According to the stress characteristics of the femur, the porous unit cell structures (TO-C, TO-T, TO-B) under three different loads of compression, torsion, and bending were designed by topology optimization. The mechanical properties and permeability of different structures were studied. Combined with the porous structure optimization, a personalized radial gradient porous titanium alloy femoral stem was designed and manufactured by selective laser melting (SLM) technology. The results show that the TO-B structure has the best comprehensive performance among the three topologically optimized porous types, which is suitable for the porous filling structure of the femoral stem, and the SLM-formed porous femoral stem has good quality. The feasibility of the personalized design and manufacture of porous titanium alloy implants is verified, which can provide a theoretical basis for the optimal design of implants in different parts.

Does the calcar femorale affect the position of uncemented short stems?

Metaphyseal-stabilised short stems rely on sufficient metaphyseal fixation and are inserted by following the medial cortex. This type of stem is used extensively in our institution, and we observed on occasion unintended implant positioning with an increased distance between the implant and the medial cortex. A bony structure within the proximal femur which was first described in 1874 and named the calcar femorale, coincides with this phenomenon.The aim of this study was to investigate the impact of the calcar femorale on the position of a metaphyseal-stabilised short stem. The frequency of cases with an increased distance between medial cortex and the implanted short stem was analysed in 52 consecutive patients. Additionally, we performed an anatomical CT study with 60 cadaveric femora to obtain more detailed information on the anatomy of the calcar femorale. Detailed measurements regarding the calcar femorale and its relationship to the proximal femur were obtained. From this, we derived implications for the implantation of a short stem prosthesis. In 50% of all cases, we found an increased gap between the stem and the medial cortex. An increased gap did not significantly affect stem size, position, or subsidence rate, but in cases with an increased gap we found fewer stems with a radiologically optimum fit. The calcar could be identified in all 60 cadavers. The calcar femorale angle showed a high correlation with the mechanical antetorsion (0.87, p = 0.02) and the functional antetorsion (0.86, p = 0.05) of the femur. The calcar femorale is a consistent anatomical structure which may be the cause for an increased gap medial to the short stem in 50% of our cases. It limits the intramedullary space and influences both stem size and orientation. The CF angle which correlates with femoral antetorsion may influence the anteversion of the stem.

Collum Femoris-Preserving Hip Stem: Clinical and Radiographical Results from a Medium-Term, Multi-Centric Study in a Latin American Population

Background: There is a lack of information related to the medium-term results of short stem prosthesis in the Latin-American population. This study represents the longest follow-up results of the CFP prosthesis in the Latin-American population. Methods: Two-hundred fifty-five patients treated with anatomic neck preserving from June 2013 to June 2020 were enrolled in the current study. The mean follow-up was 81 (60-96) months. All the subjects were available for the follow-up examination at a minimum of 5 years after surgery. Clinical results were assessed using Oxford Hip Score (OHS). Radiologic assessment was performed at each follow-up. Results: Follow-up was 81 (60-96) months. Two-hundred fifty-five patients were contacted. The patients with hip dysplasia were operated with the CFP stem in 10.2% of all cases; with regards to the Dorr classification of the proximal femur, type 1: 9.8%; type 2: 88.6% and type 3: 1.6%. The overall prosthesis survival was 96.1%. The functional results were OHS pre: 9.1 (3-35), post: 44.4 (27-48). Conclusion: The surgeries with CFP stem have excellent clinical results. The main indication of this short stem is primary hip osteoarthritis; nevertheless, we have some experience in dysplastic hips with good clinical results and survivorship. The results are comparable in terms of survivorship when this stem is implanted in Dorr 1, 2 and 3; however, we had a limitation, the sample was not comparable in the three groups. The overall survivorship, the functional scales and the radiographical results in the Latin-American population are comparable with literature reported around the world. Level of Evidence: Level III

The Wagner Cone Stem for Atypical Femoral Anatomy in Total Hip Arthroplasty: A Report of 320 Cases with Minimum 5-Year Follow-up.

The Wagner Cone Prosthesis was designed to address complex femoral deformities during total hip arthroplasty (THA), but its mid-term component survivorship and functional outcomes remain undetermined. The objectives of this study were to determine the implant survivorship, patient satisfaction, functional outcomes, osseointegration as seen radiographically, implant subsidence, and complications of THA using the Wagner Cone Prosthesis stem at intermediate-term follow-up. This study involved 302 patients with proximal femoral deformities, including developmental hip dysplasia and Legg-Calvé-Perthes disease, who underwent a total of 320 primary THAs using the Wagner Cone Prosthesis. The average age at the time of surgery was 49.4 ± 14.5 years (range, 18.8 to 85.6 years). Patient satisfaction was recorded using a self-administered questionnaire assessing satisfaction in 4 domains. The University of California at Los Angeles (UCLA) activity score, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Oxford Hip Score (OHS), the Forgotten Joint Score (FJS), radiographic outcomes, and complications were recorded. The mean follow-up time was 10.1 years (range, 5.2 to 15.5 years). Survivorship of the Wagner Cone Prosthesis was 98.7% (95% confidence interval [CI]: 97.2% to 100%) with stem revision as the end point and 95.8% (95% CI: 93.5% to 98.2%) with reoperation for any reason as the end point at 10 years postoperatively. In total, 3 stems were revised: 2 for infection and 1 for chronic hip dislocation. The median patient satisfaction score was 95 (interquartile range [IQR], 80 to 100), median UCLA score was 6 (IQR, 6 to 7), median WOMAC score was 18 (IQR, 16 to 22), median OHS was 40 (IQR, 36 to 47), and median FJS was 80 (IQR, 76 to 88) at the time of final follow-up. All Wagner Cone stems that were not revised showed radiographic evidence of osseointegration, with a mean stem subsidence of 0.9 ± 0.8 mm at the most recent follow-up. The use of the Wagner Cone Prosthesis stem in patients with complex femoral anatomy undergoing primary THA is associated with excellent component survivorship, high levels of patient satisfaction, good functional outcomes, and reliable osseointegration with minimal stem subsidence as seen on radiographs at intermediate-term follow-up. Therapeutic Level IV . See Instructions for Authors for a complete description of levels of evidence.

Comparison of Short Uncemented Metaphyseal Stem and Long-Stem Reverse Shoulder Arthroplasty in Proximal Humerus Fractures: Preliminary Study at 2-Year Follow-Up.

Introduction: In the last few years, short metaphyseal-socket prosthetic humeral stems have been introduced for reverse shoulder arthroplasty (RSA). A short stem may have advantages in humeral force distribution, reducing shear stress and preserving bone stock, keeping in mind the need for possible future revision surgery. The main objective of our study was to validate the use of a short stem prosthesis in the surgical treatment of humeral fractures by comparing clinical and radiological outcomes of our studied implant with those obtained with the use of traditional long-stem implants. Methods: In this multicentric, controlled prospective study, 125 patients with proximal three- or four-fragment humerus fractures were selected and treated with RSA. A short stem was used in group A (n = 53, mean age: 75.6 ± 5.6 years old), and a long stem was used in group B (n = 72, mean age: 71.76 ± 3). Active range of motion (ROM), Constant score (CS), Quick DASH, American Shoulder and Elbow Surgeons Shoulder (ASES) score, and Visual Analog Scale (VAS) scores were collected and analyzed at 2 years mean follow-up, as well as humeral and glenoid bone resorption (sum Inoue scores and Sirveaux scores were used). Results: No statistically significant differences were observed between group A and B in ROM, Constant score (51.69 ± 15.8 vs. 53.46 ± 15.96, p > 0.05), Quick DASH (31.5 ± 21.81 vs. 28.79 ± 13.72, p = 0.85), ASES (82.53 ± 17.79 vs. 84.34 ± 15.24, p = 0.57), or the VAS (0.53 ± 1 vs. 0.56 ± 1.07, p = 0.14) at the final follow-up. No statistically significant differences were found in the radiographic parameters between the two groups. No statistically significant differences were found for the average degree of humeral and glenoid bone resorption either. Conclusions: The use of a short metaphyseal-socket stem can be considered a safe, effective, and feasible option in reverse shoulder arthroplasty for treating proximal humerus fractures. Our results are encouraging, with no statistically significant differences identified between the proposed treatment and traditional long stems.

Design, fabrication, and clinical characterization of additively manufactured tantalum hip joint prosthesis

Abstract The joint prosthesis plays a vital role in the outcome of total hip arthroplasty. The key factors that determine the performance of joint prostheses are the materials used and the structural design of the prosthesis. This study aimed to fabricate a porous tantalum (Ta) hip prosthesis using selective laser melting (SLM) technology. The feasibility of SLM Ta use in hip prosthesis was verified by studying its chemical composition, metallographic structure, and mechanical properties. In vitro experiments proved that SLM Ta exhibited better biological activities in promoting osteogenesis and inhibiting inflammation than SLM Ti6Al4V. Then, the topological optimization design of the femoral stem of the SLM Ta hip prosthesis was carried out by finite element simulation, and the fatigue performance of the optimized prosthesis was tested to verify the biomechanical safety of the prosthesis. A porous Ta acetabulum cup was also designed and fabricated using SLM. Its mechanical properties were then studied. Finally, clinical trials were conducted to verify the clinical efficacy of the SLM Ta hip prosthesis. The porous structure could reduce the weight of the prosthesis and stress shielding and avoid bone resorption around the prosthesis. In addition, anti-infection drugs can also be loaded into the pores for infection treatment. The acetabular cup can be custom-designed based on the severity of bone loss on the acetabular side, and the integrated acetabular cup can repair the acetabular bone defect while achieving the function of the acetabular cup.

Mid- to long-term periprosthetic bone density changes after cementless short stem hip arthroplasty in elderly: A clinical and radiological analysis

IntroductionShort stem prostheses were originally designed for younger and more active patients. In recent years, they have been increasingly offered to older patients. This study evaluates the mid-to long-term survival of a short stem prosthesis and the changes in periprosthetic bone density following implantation of a cementless short hip stem in patients over 60 years of age. Methods118 patients aged over 60 received short stem prostheses. Clinical examination included Harris Hip Score (HHS) and Hip Disability and Osteoarthritis Outcome Score (HOOS). 93 patients were followed clinically for at least five years. 53 patients underwent dual-energy x-ray absorptiometry (DXA) and radiographic evaluation. Follow-up intervals were preoperative and postoperative (t0), at approximately six months (t1), at approximately two years (t2), and at approximately five years or later (t3). ResultsOver a mean 6.7-year observation period for all 118 patients, one stem revision occurred due to a traumatic periprosthetic stem fracture. The five-year survival rate for the endpoint survival of the Metha® stem in 95 at-risk patients is 99.2%. HHS improved significantly from t0 55.3 ± 11.5 (range 30–79) to t3 95.3 ± 8.6 (range 57–100) at a mean of 8.0 years (p < 0.001). HOOS improved significantly in each subscale (p < 0.001). Bone mineral density (BMD) was available for review in 53 patients after a mean of 7.1 years. BMD increased from t0 to t3 in region of interest (ROI) 3 (+0.4%) and ROI 6 (+2.9%) and decreased in ROI 1 (−10.3%), ROI 2 (−9.8%), ROI 4 (−5.3%), ROI 5 (−3.4%) and ROI 7 (−23.1%). ConclusionsThe evaluated short stem prosthesis shows a remarkably high survival rate in elderly patients, accompanied by excellent clinical results. Load transfer measurements show a metaphyseal-diaphyseal pattern with a trend towards increased diaphyseal transfer over the period observed.

Assessing the influence of gastrocnemius reconstruction on stress distribution of femoral tumor rotating hinge knee prosthesis via finite element analysis.

After femoral oncological knee arthroplasty, some patients suffer from rotating axis fracture, which significantly impacts the life span of the rotating hinge knee (RHK) prosthesis. This research aimed to analyze the biomechanical response of anatomical gastrocnemius reconstruction and assess whether it could reduce the risk of rotating axis breakage by finite element (FE) analysis. A femur-prosthesis-tibia FE model was established using the data from CT scans. The mechanical properties of the RHK implant were quantitatively compared before and after gastrocnemius reconstruction at 6 angles: 10°, 20°, 30°, 40°, 50°, and 60°. Our results showed that gastrocnemius reconstruction effectively altered the stress distribution around the rotating axis, considerably relieving the stress in the fracture-prone region. In addition, the peak stress in the rotating axis, bending axis, prosthesis stem, and femoral condyles decreased variably. In distal femoral resection knee arthroplasty, the rebuilding of gastrocnemius substantially improved the stress distribution within the prosthesis, thereby having the potential to reduce the risk of prosthetic fracture and prolong the overall durability of the prosthesis.

Strains on the human femur after revision total knee arthroplasty: An in vitro study using digital image correlation.

Pain at the tip of the stem of a knee prosthesis (End-of-Stem Pain) is a common problem in revision total knee arthroplasty (TKA). It may be caused by a problematic interaction between stem and bone, but the exact biomechanical correlate is still unknown. On top of this, there is no biomechanical study investigating End-of-Stem Pain at the distal femur using human specimens. Aim of this study was to find out whether the implantation of a revision total knee implant leads to high femoral surface strains at the tip of the stem, which the authors expect to be the biomechanical correlate of End-of-Stem Pain. We implanted 16 rotating hinge knee implants into 16 fresh-frozen human femora using the hybrid fixation technique and comparing two reaming protocols. Afterwards, surface strains on these femora were measured under dynamic load in two different load scenarios (climbing stairs and chair rising) using digital image correlation (DIC) and fracture patterns after overcritical load were analysed. Peak surface strains were found at the tip of the stem in several measurements in both load scenarios. There were no significant differences between the two compared groups (different trial sizes) regarding surface strains and fracture patterns. We conclude that implantation of a long intramedullary stem in revision TKA can lead to high surface strains at the tip of the stem that may be the correlate of femoral End-of-Stem Pain. This finding might allow for a targeted development of future stem designs that can lead to lower surface strains and therefore might reduce End-of-Stem Pain. Digital Image Correlation proved valid for the measurement of surface strains and can be used in the future to test new stem designs in vitro.

Monte Carlo-based in-depth morphological analysis of medullary cavity for designing personalized femoral stem.

The design of femoral stem prostheses requires a precise understanding of the femoral marrow cavity. Traditional measurements of morphological parameters in the upper femur, particularly the medullary cavity and cortical region, are primarily based on coronal and sagittal axes, which may not fully capture the true three-dimensional structure of the femur. Propose a Monte Carlo-based method for a more comprehensive analysis of the femoral marrow cavity, using CT scans of femurs from a selected group of patients. The study aimed to define and calculate anatomically semantic morphological parameters to enhance the understanding of the femoral marrow cavity's anatomical morphological changes, ultimately improving the design and clinical selection of femoral stem prostheses. To enhance the accuracy of femoral stem prosthesis design, this study aims to develop a Monte Carlo-based method for a more comprehensive analysis of the femoral marrow cavity. The proposed method transforms the non-random problem of determining cross-sectional size into a random issue, allowing for the calculation of the size of the medullary cavity and cortical region. Anatomically semantic morphological parameters are then defined, calculated, and analyzed. The experimental results indicate that the newly defined parameters complement existing ones, providing a more rational scientific basis for understanding the anatomical morphological changes of the femoral marrow cavity. This research offers essential scientific theoretical support for improved morphologic research, design, and clinical selection of femoral stem prostheses. It holds significant importance and application value in clinical practice, contributing to a more accurate and comprehensive understanding of femoral anatomy for prosthetic design.

Aloarthroplasty of the Hip After Pathological Fracture of the Right Femoral Neck and Right Femoral Dyaphysis and Osteosynthesis after Fracture of the Left Femoral Dyaphysis in 41-Year-Old Female Patient with Polyostotic Fibrous Dysplasia? Case Report

A 41-year- old female patient with pathological basicervical right femoral neck fracture and fractures of both femoral bones 15-20 cm distally from the small trochanter is presented. Skeletal scintigraphy was performed and multiple pathological accumulations of radioactive substances were found in almost the entire locomotor system. First, we implanted a partial biarticular hip prosthesis with long stem in right femur, and one year later osteosynthesis of the left femoral diaphysis was done. Pathohistological examination did not find tumor cells and polyostotic fibrous dysplasia also was not clear. Our patient had not problems with bones earlier and she was never treated for this disease, except surgery of femoral fractures. Today, 11 years later the patient is in good general state, she has no pain in her legs and fractures of femur bones healed completely. We did not find a case in literature that a two fractures of proximal right femur bone (femoral neck and proximal diaphysis) and fracture of the left femoral diaphysis were solved with long stem prosthesis, and osteosynthesis of another femoral bone in patient who, we believe, has fibrous dysplasia and was never treated for this disease.

Periprosthetic Comminuted High Energy Fracture of The Proximal Femur Three Months After Primary Total Hip Arthroplasty in Young Male. A Case Report

A 40 years old male patient had surgery on his right hip in 2010. when primary total cementless hip prosthesis was implanted because of posttraumatic arthrosis. Three months later he had a car accident and he got dislocation of the hip prosthesis with multiple femoral fractures of the proximal part of the femur around and below the femoral stem. The stem of the prosthesis was loose while acetaulum was stable. The patient had also fracture of the left acetabulum and ishial bone, without big dislocations. He underwent a new surgery on the right hip. Revisional long uncemented femoral stem was implanted, with cerclages and screws on multiple bone fragments. We met patient 8 years later with a very good function of his right hip. He has a problem with his left hip because of pseudarthrosis of the upper and lower part of the ischial bone. We think that this is an interesting case of periprosthetic femoral fracture, because of so many bone fragments around and below the femoral stem of the hip prosthesis, resulting in a very good function.

Current design and cement mantle thickness in hip arthroplasty : Theory and analysis of register data

In this article, an overview and comparison of the most commonly used cemented hip stems, grouped into different stem types and cement mantle thickness, is given to see which combination performs well. Revision rates of cemented stem types were categorized from the Endoprosthesis Register-Germany, and 3‑ and 5‑year revision rates were reported and analyzed. For the research, the focus was on the Exeter, C‑Stem, MS-30, Excia, Bicontact, Charnley, Müller straight stem, Twinsys, Corail, Avenir, Quadra, and the Lubinus SPII stems. An important aspect was which stem is preferred to be implanted and which cementing technique is used with regard to the planned cement mantle thickness. In order to identify atrend in cemented hip arthroplasty, data from the Danish, Swedish, Norwegian, Swiss, New Zealand, English and Australian arthroplasty registers were also compared. Most countries use cemented prostheses according to the taper slip principle (Exeter, MS30, C‑Stem etc) or the composite beam (Charnley, Excia, Bicontact), which are implanted with acement mantle thickness of 2-4 mm. However, atrend has emerged in Germany and Switzerland towards the line-to-line technique, with aplanned cement mantle thickness of 1 mm (Twinsys, Corail, Avenir, Quadra), following the principle of the Müller straight stem prosthesis and the Kerboul-Charnley prosthesis, even though these are postulated to be "French paradoxes" in themselves. In the EPRD 5‑year results, the newer line-to-line prostheses seem to perform slightly worse. The best results are achieved by the "MS30" in Germany and the "Exeter" in England. These are polished straight stems with centralizer and subsidence space at the apex with a2-4 mm cement mantle in good cementing technique.

Implications of ageing effects on thermal and mechanical properties of PMMA-based bone cement for THA revision surgery

Loosening and infection are the main reasons for revision surgery in total hip arthroplasty (THA). Removing partially detached cemented implant components during revision surgery remains challenging and poses the risk of periprosthetic bone damage.A promising approach for a gentler removal of partially detached prostheses involves softening the PMMA-based bone cement by heating it above its glass transition temperature (TG), thus loosening the implant-cement bond. It is assumed that the TG of PMMA-based bone cement decreases in-vivo due to the gradual absorption of body fluid. Reliable data on TG are essential to develop a heat-based method for removing cemented implant components during revision surgery.The effect of water absorption was investigated in-vitro by ageing PMMA-based bone cement samples for different periods up to 56 days in both Ringer's solution (37 °C) and air (37 °C and 30% humidity). Subsequently, the TG and Vicat softening temperatures of the samples were determined by differential scanning calorimetry and Vicat tests, respectively, according to prescribed methods.Over the entire ageing period, i.e. comparing one day of ageing in air and 56 days in Ringer's solution, the Vicat softening temperature dropped by 16 °C, while the TG dropped by 10 °C for Palacos® R PMMA-based bone cement. Water absorption over time correlated significantly with the Vicat softening temperature until saturation of the PMMA-based bone cement was reached.Based on the TG and Vicat softening temperature measurements, it can be assumed that in body-aged bone cement, an optimal softening can be achieved within a temperature range of 85 °C–93 °C to loosen the bond between the PMMA-based bone cement mantle and the prosthesis stem. These findings may pave the way for a gentler removal of the implant in revision THA.

Usefulness of modular neck adapter in partial hip revision.

Modular neck adapters allow different length and offset changes to reach a stable total hip arthroplasty (THA) and permit a quick partial hip revision procedure without removing the existing components. The literature is poor on this matter and about the long-term related outcomes. This narrative review summarizes the most recent literature about these devices as an option of surgical treatment in partial total hip arthroplasty revision (THAr) focusing on indications, clinical and radiological outcomes, and related complications. The narrative review of the current available literature was conducted in December 2022 through electronic database. The terms used were: "Head neck taper" OR "Merete BioBall" AND "revision Total Hip Arthroplasty (MeSH Terms)". The timeframe was limited between 01/01/2000 and 01/12/2022. The studies regarding the clinical use of the Merete BioBall® system in hip revision surgery were included, while all the papers concerning modular stem prosthesis were excluded. The surgical procedure is safe, quick and allows the surgeon to correct a well-fixed stem version, length and offset, besides retensioning soft tissues. Clinical and radiological outcomes are good with low complications rates. The modular neck adapter system seems to be a good surgical procedure for recurrent dislocation of THA, especially in case of a second THAr surgery. However, the main indication of adapter use remains the isolated acetabular cup revision. The related complications are rare: the worst is the re-dislocation due to an insufficient stem version and length correction. Re-dislocation rates reported in literature vary from 5.2% to 15%. Corrosion or fretting of the modular system are not reported in literature.

Development and Finite Element (FE) analysis of a novel short hip stem concept

IntroductionIn order to improve the anchorage behavior of short hip stems, this development project aims at designing a short hip stem concept that preserves the femoral neck and minimizes interference with the physiological stress distribution of the femur. The new design will be evaluated according to ISO 7206-4 which is the standard for testing Implants for surgery. MethodsBasic CAD models based on an established short stem prosthesis were created and evaluated using finite element analysis. The best design was further developed to achieve a more deformable stem while maintaining stability. The model was validated through in vitro testing. ResultsThe “H-Beam” short stem showed a higher degree of deformation of approximately 142–144% compared to the established short stem. The FE model had a relative error of 0.98% and 1.07% compared to the in vitro tests. An operating procedure was outlined for this new short stem design. DiscussionThe FE model is deemed valid due to small differences in comparison to in vitro testing. The short-stem prosthesis is more flexible and can be easily adapted to individual anatomy during surgery. The prosthesis length is similar to conventional prostheses, but the new stem design could allow better and faster osteointegration while preserving the cancellous bone structure.

Medium-term clinical and radiographic outcomes of a cementless prosthesis with a 140° neck–shaft angle in reverse total shoulder arthroplasty

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 78years and 63/81 patients (78%) were female. The mean follow-up time was 39±7months. 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.

Finite element simulation of femoral stems lightweighted with re-entrant honeycomb lattice structure

Artificial hip joints are used to replace damaged or diseased natural joints. When the stress that is typically applied to the bone changes because the implant and bone are different in stiffness, a phenomenon known as stress shielding occurs. Stress shielding can lead to bone weakening through reduced density and aseptic loosening in the long term. Studies are ongoing to overcome this phenomenon through geometric design, the use of materials with a low modulus of elasticity, or latticed implants. In this study, the effect of lightening the hip prosthesis with lattice structures on stress shielding is investigated using finite element simulation. The femoral stem of a solid hip prosthesis was lightweighted, with a re-entrant honeycomb auxetic cellular lattice structure, and structural analysis was performed. Two different lattice orientations were used, and it was observed that the stress distribution was more homogeneous in both orientations. In these femoral stems, which can be easily produced using additive manufacturing methods, a volume reduction of up to 16% was achieved. The stress transmitted to the bone increased by more than 36%, depending on the orientation, which is a promising result for reducing the stress shield effect.

Ten-year follow-up and clinical outcome of a metaphyseal anchoring short hip stem prosthesis: a retrospective single-centre analysis.

Short stems for total hip arthroplasty are an alternative to traditional conventional long stems. Short stems are designed to facilitate minimal-invasive surgery, improve bone-stock preservation, and mimic a physiological load distribution. However, there is little evidence of the long-term outcome of short stems. This study aims to analyze the tenyear survival rates and clinical outcome of one specific metaphyseal short hip stem implant. We retrospectively analyzed the patient records of the patients who underwent a total hip arthroplasty with a monoblock partial collum sparing metaphyseal short hip stem prosthesis in 2008 and 2009 in our clinic. Patients were contacted, and clinical follow-up was recorded using the German version of the modified Harris Hip Score. Furthermore, complications, revision surgery, and post-operative radiographs were analyzed. Data from 339 primary implantations in 322 patients were retrieved. The mean follow-up was 10.6years. Seven patients underwent a revision. The tenyear survival rate with any revision surgery as the endpoint was 97.5%. The mean modified Harris Hip Score was 86 points (range 30 to 91 points). Five patients had an intraoperative fracture of the femur (1.6%). Two patients (0.6%) had a dislocation of the hip. The stem tip-to-cortex distance, measured in the anterior posterior view, was 2.6mm (range 0 to 8.3mm). The tenyear survival rate of our used monoblock partial collum sparing metaphyseal short hip stem implant is comparable to traditional stems for total hip arthroplasty.

PHYSICAL AND MATHEMATICAL MODELING OF THE DISTRIBUTION OF LOAD FORCES ON THE FEMINAL COMPONENT OF AN ENDOPROSTHESIS OF THE HIP JOINT UNDER REAL CONDITIONS

Determination of the factors causing the development of aseptic instability of endoprosthesis components is one of the main tasks of modern traumatology and orthopedics. It is important from a scientific and medical point of view to carry out physical and mathematical modeling of the distribution of load forces and their moments on the femoral component of a hip endoprosthesis. The purpose of the study: to conduct a physical and mathematical modeling of the distribution of load forces on the femoral component of a hip endoprosthesis under real conditions of incomplete axially symmetrical contact of the femoral component of the endoprosthesis and the femur, when the surface of the lower end of the endoprosthesis is not in contact with the surface of the bone. In the work, mathematical modeling of the distribution of point load forces and their moments on the contact surface between the femoral endoprosthesis stem and the bone marrow canal of the femur in real conditions is carried out. For qualitative estimates of point distributions of the load force, based on the analysis of previous results, an estimated empirical formula was obtained for these distributions: g(λ,λ1)=Р(λ,λ1) / 140λ7/2, in which the pressure Р(λ,λ1) is taken in kilograms per square centimeter (kg/cm2), and the point force g(λ,λ1) is in kilograms (kg). It was determined that the best, from the point of view of minimizing the harmful mechanical impact of the prosthesis on the femur, is the situation when the length of the prosthesis stem is not less than half the length of the femur (λ≥0.5). In this case, the values of the point load forces do not exceed 0.1 kg, at least for the length of the area of real contact, which is not less than half the length of the prosthesis stem (λ1≥0.5λ). It has been proven that the use of a prosthesis stem that is less than a third of the length of the femur is not advisable. Since already at the length of the prosthesis stem, which is 30 % of the length of the femur (λ=0.3), point loads increase rapidly and can reach from 0.55 to 1.5 kg depending on the length of the contact area. Such point loads are undesirable for the femur in the area of contact with the prosthesis in terms of the integrity of the femur.