Hip Stem Research Articles

Metaphyseal anchoring short stem hip arthroplasty provides a more physiological load transfer: a comparative finite element analysis study

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

A piezoelectric energy harvesting concept for an energy-autonomous instrumented total hip replacement

To improve the clinical outcome of total hip replacements (THRs), instrumented implants with sensory functions for implant monitoring and diagnostics or actuators for therapeutic measures are a promising approach. Therefore, an adequate energy source is needed. Batteries and external power supplies bring shortcomings e.g. limited lifetime or dependency on external equipment. Energy harvesting has the clear benefit of providing continuous and independent power for fully autonomous implants. Our present study evaluates by means of finite element analysis (FEA) the capabilities of a concept of a piezoelectric energy harvesting system (ring shaped multilayer piezoelectric element of 5 mm diameter and 2.5 mm height) integrated in a femoral hip stem. The deformations from a modified load-bearing implant are used to generate electric power for various instrumentation purposes. Besides the expected amount of converted energy, the influence on the stress distribution of the instrumented implant is analysed. The results show that the local stress increase for the modified implant geometry does not exceed the stress of the original reference model. The maximum generated open circuit voltage of 11.9 V can be processed in standard energy harvesting circuitry whereas an average power output amounts up to 8.1 µW. In order to increase the electric power in an upcoming design optimization, a sensitivity analysis is performed to identify the most important influencing parameters with regard to power output and implant safety.

Influence of different anteversion alignments of a cementless hip stem on primary stability and strain distribution

BackgroundStem anteversion in total hip arthroplasty is well known to have a high impact on dislocation, but empirical data regarding the clinical and biomechanical influence is lacking. Therefore, we evaluated the impact of different anteversion alignments on the primary stability and strain distribution of a cementless stem. MethodsThe cementless CLS Spotorno stem was implanted in 3 different groups (each group n = 6, total n = 21) with different anteversion alignments: reference anteversion (8°), +15° torsion in anteversion (+23°), −15° torsion in retroversion (−7°) using composite femurs (Sawbones). Primary stability was determined by 3-dimensional micromotions using a dynamic loading procedure simulating walking on level ground. Additionally, surface strains were registered before and after stem insertion in the 3 different groups, using one composite femur for each group (total n = 3). FindingsThe micromotion measurements did not show a significant difference between the 3 evaluated alignments. Moreover, determination of the strain distribution did also not reveal an obvious difference. InterpretationThis biomechanical study simulating walking on level ground indicates that there is no considerable influence of stem ante−/retroversion variation (±15°) on the initial stability and strain distribution when evaluating the cementless CLS Spotorno in composite femora.

Comparison of Resistive and Optical Strain Measurement for Early Fracture Detection

Abstract To increase learning success in surgical training, physical simulators are supplemented by measurement technology to generate and record objective feedback and error detection. An opportunity to detect fractures following hip stem implantation early can be measurement of occurring strains on bone surface. These strains can be determined while using strain gauges, digital image correlation (DIC) or photoelasticity. In this research strain gauges and DIC were compared regarding their suitability as strain measurement tools for use in physical simulators. Therefore a testing method was described to replicate the implantation of a hip stem. Testing devices modelled on a realistic prosthesis were pressed into prepared porcine femora in a two-step procedure with a material testing machine. The local strains occurring on bone surface were determined using an optical measurement system for DIC and strain gauges. The initial fractures in the tested femora are located medial-anterior in most cases (73,6%). With increasing indentation depth of the test device, the strains on bone surface increase. Comparing the local strains determined by DIC and strain gauges consistencies in curves are noticeable. Maximal determined strains before fracturing amount to 0,69% with strain gauges and 0,75% with DIC. In the range of the fracture gap, strain gradients are determined by using DIC. However the detected surfaces are of low quality caused by gaps and motion artefacts. The results show strains on bone surfaces for early fracture detection are measurable with strain gauges and DIC. DIC is assessed as less suitable compared to strain gauges. Furthermore strain gauges have greater level of integration and economic efficiency, so they are preferred the use in surgical training simulators.

The Sensitivity Analysis in Topology Optimization of Hip Stem Prosthesis Using Finite Element Method

This paper discusses the results of the parameters employed sensitivity analysis in the optimization of hip stem prosthesis geometry using topology optimization techniques based on finite element methods. The study was carried out to examine the relationship of finite element parameters, such as mesh size and stress distribution, and topology optimization parameters, such as percent to retain, to the final geometry of the prosthesis stem. Topology optimization was performed using ANSYS software for hip stem prosthesis, a type of Anatomic Medullary Locking, made from titanium alloy. The results obtained from this study indicate that the selection of finite element parameters and topology optimization parameters will have a significant effect on the shape and geometry of the hip stem. The results of this analysis can be the basis for the development of hip stem shape and geometry through topology optimization techniques.

Investigation of Meshing Strategy on Mechanical Behaviour of Hip Stem Implant Design Using FEA

Abstract Hip joint is an important human joints system. The damaged hip joints need to be replaced with artificial hip joints. The Study of the hip joint is very costly therefore another calculation method is demanded to produce good result in acceptable time and cost. Considering this problem, a series of study to assess hip joint performance is conducted using numerical approach. Important parameter for example applied materials are used in the modelling by idealizing Ti-6Al-4V compared to SS 316 L, and stemlengthwas chosen to be 128 mm. ANSYS software was used to analyze models, and designed element size variations were set to be in range 1 to 2.5 mm. The magnitude of force was placed on the femoral head with an angle of 16 ∘ C from the vertical axis. Results showed that SS 316 L material has smaller deformation than Ti material. Whereas Central Processing (CP) time decreases in increasing element size for both materials. In addition, more variations in mesh size are needed to get more accurate convergent results.

Plasma Spray Deposition of HA-TiO2 on β-phase Ti-35Nb-7Ta-5Zr Alloy for Hip Stem: Characterization of Bio-mechanical Properties, Wettability, and Wear Resistance

In this work, a biomimetic coating of hydroxyapatite (HA)-and titania (TiO2) was deposited on low elastic β-phase Ti-35Nb-7Ta-5Zr (β-TNTZ) alloy by plasma spray deposition technique for orthopedic applications. The effect of TiO2 reinforcement on microstructure, mechanical properties, and bioactivity was investigated. The morphology, coating thickness, elemental composition, and phase composition of the developed coatings were characterized. The biomechanical behavior of the deposited coatings was investigated in terms of surface hardness, elastic modulus, and adhesion strength. It was found from the morphological investigation that the TiO2 reinforcement improves the microstructure and prevents the formation of defects in the coating. The biomimetic HA-TiO2 coated surface possessed pores, size ranging from 200 nm–600 nm that benefits the apatite growth and osseointegration. The EDS spectrum, mapping, and XRD analysis show that the deposited layer β-TCP, CaO, TTCP, TiO2 phases. The HA-TiO2 coating exhibits a very dense and thick layer of 100 µm–125 µm that exhibits excellent adhesion strength to offer mechanical interlocking to prevent delamination. The alloying of TiO2 improves the hardness from 1.67 GPa to 2.95 GPa that enhances the wear resistance. It was found that HA-TiO2 coating exhibits better hydrophilic and biocompatible surface as compared to HA-coating.

The influence of macro-textural designs over implant surface on bone on-growth: A computational mechanobiology based study

The longerterm secondary stability of an uncemented implant depends primarily on the quality and extent of bone in-growth or on-growth at the bone-implant interface. Investigations are warranted to predict the influences of implant macro-textures on bone on-growth pattern. Mechanoregulatory tissue differentiation algorithms can predict such patterns effectively. There is, however, a dearth of volumetric in silico study to assess the influence of macro-textures on bone growth. The present study investigated the influence of macro-textural grooves/ribs on changes in tissue formation at the bone-implant interface by carrying out a 3D finite element (FE) analysis. Three distinct macro-textures, loosely based on commercially viable hip stem models, were comparatively assessed for varying levels of interfacial micromotion. The study predicted elevated fibrogenesis and chondrogenesis, followed by a suppressed osteogenesis for higher levels of micromotion (60 μm and 100 μm), resulting in weak bone-implant interface strength. However, small judicious modifications in implant surface texture may enhance bone growth to a considerable extent. The numerical scheme can further be used as a template for more rigorous parametric and multi-scale studies.

Biomechanical Comparison of Periprosthetic Femoral Fracture Risk in Three Femoral Components in a Sawbone Model

BackgroundThe increasing use of orthopedic total hip arthroplasty implants has led to a consequent rise in the incidence of associated periprosthetic fractures (PPFs). Analysis of the National Joint Registry data showed the choice of cemented hip stem influenced the risk of a PPF occurring. However, the effect of implant design in relation to the risk of PPFs has not been investigated. MethodsThe main objective is to compare the biomechanics of PPFs as a failure of the Exeter V40, CPT, and DePuy C-Stem stems in a composite Sawbone model to identify whether a difference in the risk of fracture exists between them. Twenty-six Sawbones were divided into 3 groups, cemented with the Stryker Exeter, Zimmer CPT, or DePuy C-Stem and then torqued to fracture. ResultsWhen compared with the Exeter, the CPT- and C-Stem-implanted Sawbone models would sustain PPFs at a statistically significantly lower rotation to failure (20.1° and 26.7° vs 33.6°, P < .01) and torque to failure (124 Nm and 143 Nm vs 174 Nm, P < .01) values. The energy release rate at failure for the Exeter was significantly higher than that for the CPT and C-Stem (61.2 Nm vs 21.8 Nm and 38.6 Nm, P < .01), which led to more comminution. ConclusionThe CPT- and C-Stem-implanted femurs, although fracturing earlier, fractured in a simple pattern with less comminution. The differences in stem design mean higher stress at the critical point of failure in the CPT implanted femur compared with the Exeter and DePuy, which is likely the reason behind the observed increased risk of PPFs with the CPT implant.

The Migration Pattern of a Cementless Hydroxyapatite-Coated Titanium Stem under Immediate Full Weight-Bearing-A Randomized Controlled Trial Using Model-Based RSA.

(1) Background: High primary stability is important for the long-term survival of cementless femoral stems in total hip arthroplasty (THA). The objective of this study was to investigate the migration pattern of a hydroxyapatite-coated cementless hip stem developed for minimally invasive surgery using model-based radiostereometric analysis (RSA). (2) Methods: In this randomized controlled trial, 44 patients with an indication for cementless primary THA were randomly allocated to receive either the SL-PLUS MIA stem, developed for minimally invasive surgery, or the SL-PLUS stem (Smith & Nephew Orthopaedics, Baar, Switzerland) which served as a control group. Unlimited weight-bearing was permitted postoperatively in both groups. Model-based RSA was performed after six weeks and after 3, 6, 12 and 24 months postoperatively. (3) Results: Mean total stem subsidence at two-year follow-up was 0.40 mm (SD 0.66 mm) in the SL-PLUS group and 1.08 mm (SD 0.93 mm) in the SL-PLUS MIA group (p = 0.030). Stem subsidence occurred during the first six weeks after surgery, indicating initial settling of the stem under full weight-bearing. Both stem designs showed good osseointegration and high secondary stability with no further migration after initial settling. (4) Conclusions: Settling of a cementless straight femoral stem occurs during the first six weeks after surgery under full weight-bearing. Although initial stem migration was higher in the SL-PLUS MIA group, it had no influence on secondary stability. All implants showed good osseointegration and high secondary stability with no signs of implant loosening during this two-year follow-up period.

Deposition of HA-TiO2 by plasma spray on β-phase Ti-35Nb-7Ta-5Zr alloy for hip stem: Characterization, mechanical properties, corrosion, and in-vitro bioactivity

This research work presents the deposition of titanium oxide (TiO2) reinforced hydroxyapatite (HA) on Ti-35Nb-7Ta-5Zr alloy by plasma spray deposition technique for Hip-stem application. The effect of TiO2 reinforcement (15 and 30 wt%) in HA has been studied on coatings morphology, microstructure, mechanical properties, corrosion resistance, and in-vitro bioactivity was investigated. The microstructure, elemental composition, and phase composition were characterized by FE-SEM, EDS, and XRD. The morphology analysis showed that of HA-coating contains micro-cracks and splats like structure with large globules. The reinforcement of TiO2 in HA improved the microstructure, prevents the formation of micro-cracks, and formed a dense structure. The cross-section morphology shows that HA-15%TiO2 (HA-Tx) and HA-30%TiO2 (HA-Ty) coatings (thickness 185–200 μm) were mechanically bonded with the substrate as compared HA-coatings, that helps in enhancing implant stability. Results also show that microhardness and adhesion strength of HA/TiO2 coatings improved with the reinforcement of TiO2 and HA-30%TiO2 possessed high micro-hardness and adhesion strength (1.35 GPa and 32.5 MPa) in comparison with HA-coating (0.63 GPa and 18.5 MPa). The electron dispersive spectroscopy (EDS) analysis and X-ray diffraction analysis (XRD) results show that HA-TiO2 coatings contain HA and TiO2 phases that prevent the formation of amorphous contents. In contrast, HA-coating contains amorphous content (CaO, β-TCP, and TTCP). The HA-TiO2 coatings exhibit excellent corrosion resistance as compared to HA-coating because of the presence of TiO2 lamellar structure in the HA matrix that acted as a barrier to corrosion and improves the corrosion resistance. The TiO2 reinforcement in HA/TiO2 coating not only increase the corrosion resistance but also help in promoting chemical integration of MG-63 osteoblastic cellular structure through the formation of apatite on the surface of the implant. Furthermore, the in-vitro bioactivity analysis results showed that Mg-63 osteoblastic cells have excellent adhesion and growth on the HA-30%TiO2 coated substrates.

Primary stability of a cementless modular revision hip stem in relation with the femoral defect size: A biomechanical study.

Cementless modular fluted hip stems are commonly used in revision arthroplasty. Nevertheless, there is a wide spectrum of recommendations concerning the minimum bone stock required to enable osseous ingrowth and implant-bone micromotions <100 µm. This experimental study investigated the primary stability of a tapered cementless fluted revision stem depending on different types of bone defects. Implant-bone interface movements with a bimodular stem were examined under cyclic axial and torsional loading using composite femora. In four degrees of freedom, the implant subsidence and micromotions were captured with linear variable differential transformers for the intact femora and seven different defects ranging from Paprosky type I to type IIIB. With a 7-cm length of intact diaphysis proximal to the isthmus (Paprosky IIIA), mean implant-bone micromotions of 66 µm occurred. An implant-bone contact zone of only 5 cm (Paprosky IIIA) resulted in micromotions notably over 100 µm and significantly increased subsidence (p < 0.05). With a Paprosky IIIB defect (3 cm of intact diaphysis) rotational instability occurred in all specimens. Aside from critically increased interfacial micromotions (>100 µm), rotational instability emerged as a mechanism of fixation failure when the implant-bone contact zone was only 5 cm or less. Hence, future studies investigating the implant fixation in the case of femoral bone defects should consider both axial and torsional loading. With regard to the clinical application, our data suggest maintaining 7 cm of diaphyseal implant-bone contact for a safe anchorage of cementless fluted hip revision stems.

Periprosthetic fracture fixation in Vancouver B1 femoral shaft fractures: A biomechanical study comparing two plate systems.

IntroductionPeriprosthetic fractures of the femur are an increasing problem in today's trauma and orthopaedic surgery. Owing to the hip stem, implant anchorage is very difficult in the proximal femur. This study compares two plate systems regarding their biomechanical properties and the handling in periprosthetic fracture fixation of the proximal femur.Materials and methodsUsing eight pairs of fresh, frozen human proximal femora the Locking Compression Plate/Locking Attachment Plate construct (LCP/LAP) (group I, DePuy Synthes) was compared to the new LOQTEQ® periprosthetic distal lateral femur plate (group II, AAP Implantate AG). After implantation of press fit femoral hip stems a Vancouver B1 fracture model was used. Biomechanical testing was performed by cyclic axial loading with a constant increment of 0.1 N/cycle starting from 750 N axial loading. Every 250 cycles an a.p. x-ray was done to evaluate failure.ResultsThe Group II showed significant higher axial stiffness (+42%) compared with Group I. In addition, Group II withstood significantly more load-cycles until failure (20%). The mode of catastrophic failure was plate breakage in Group II, whereas, in Group I, all plates showed an early bending followed by plate breakage.Discussion and conclusionBoth plate systems enable screw placement around hip stems. The hinge plate showed superior biomechanical results compared with the locking compression plate/locking attachment plate construct. Furthermore, the hinge plate offers variable hinges and variable angel locking making bicortical screw placement around hip stems more comfortable and safe.The translational potential of this articleThe results of this study can be directly transferred to patient care. With the innovative hinge plate, the surgeon has a biomechanically superior implant, which also offers improved options for screw placement compared to a standard locking plate.

The clinical outcome of the Metha short hip stem: a systematic scoping review.

Short femoral stems were designed to bridge the gap between conventional straight design stems and hip resurfacing prostheses in total hip arthroplasty (THA). A number of clinical trials have been recently conducted to assess the clinical and safety profile of the cementless, colarless, tapered Metha short hip stem in young or active middle-aged individuals. A systematic scoping review was conducted according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines. 4 reviewers independently conducted the search using the MEDLINE/PubMed database and the Cochrane Database of Systematic Reviews. These databases were queried with the terms "short" AND "hip" AND "stem". From the initial 773 studies we finally chose 12 studies after applying our inclusion-exclusion criteria. The number of operated hips that were included in these studies was 5048 (mean BMI range: 22.7-35.2, mean age range: 44.4-60.4 years, mean follow-up range: 2-9 years). The mean modified Coleman methodology score was 52.3/100, while it ranged from 31/100 to 63/100. All mean clinical outcome scores that were used in the studies illustrated significant postoperative improvement when compared with the respective initial values. The revision rate of the Metha stem for component-related reasons was 2.5%, while the rate of major complications not requiring revision of the Metha stem was 2.8%. The Metha stem performs well in young or active middle-aged THA patients. Further studies are required for the assessment of the long-term results.

Early stabilization of the uncemented Symax hip stem in a 2-year RSA study

Background and purpose — The uncemented Symax hip stem has shown early proximal ingrowth as result of the BONIT-hydroxyapatite (HA) coating and the distal DOTIZE surface treatment. We evaluated 2-year postoperative radiostereometric analysis (RSA) migration of the Symax hip stem in THA patients. We also investigated the correlation between migration at 4 weeks and clinical outcomes after 2 years.Patients and methods — Patients in a 2-year clinical follow-up single-centre RSA randomized controlled trial were randomized to 2 different cup designs. All 45 patients received a Symax hip stem. RSA migration patterns of the Symax hip stem is presented here as a single cohort. RSA examinations were performed postoperatively, but before weight-bearing, and subsequently after 1, 3, 6, 12, and 24 months. Clinical outcomes and radiographic evaluations were assessed 3, 6, 12, and 24 months postoperatively.Results — During the first 4 weeks, the Symax hip stem subsided, rotated into retroversion, and translated posteriorly, after which the migration ceased and the prosthesis stabilized. All clinical outcomes improved from preoperatively to 2 years. There was no clinically or statistically significant correlation between subsidence and retroversion at 4 weeks and clinical outcomes after 2 years.Interpretation — RSA evaluation of the uncemented Symax hip stem confirms that the design principles and coating properties lead to early stabilization of the stem, as early as 4 weeks postoperatively. There was no correlation between subsidence and retroversion at 4 weeks and clinical outcomes after 2 years. Based on the predictive potential of the RSA technique, we anticipate excellent long-term survival of this hip stem.

Finite Element Analysis of Different Artificial Hip Stem Designs Based on Fenestration under Static Loading

Permanent hip joint damage caused by calcification, aging, or accidents requires replacement using artificial hip joint replacement surgery. Among the biomaterial applications, the Total Hip Replacement (THR) method is the most successful. Many types of artificial hip joints are available in the commercial market. Various types of material and design can be selected to suit the needs of the patients. One of which is the design with fenestration type on the hip stem. In terms of materials, Titanium and stainless steel are the ones commonly used in hip joint replacement. In this paper, the effects of fenestration hip stem on mechanical behavior have been studied using the finite element analysis. Several hip designs, i.e., the hip joint without fenestration, hip joint with fenestration slot, hip joint with fenestration big loop, and hip joint with fenestration multi-loop, were considered in this study. All models were applied using Autodesk inventor model. Static structural analysis was performed using ANSYS to conclude at the best fenestration. Results showed that for Ti-6Al-4V material, design with many loop fenestration has the lowest stress than others, with the result obtained is 495.46 MPa. However, the artificial hip stem with slot fenestration has the smallest deformation with the least difference in value compared to other designs with distortion 0.54808 mm. In addition, the design that produced the higher stress von-Misses was big loop fenestration 526,28 MPa. In conclusion, it was found that all four designs indicated lesser stress values than the yield strength.

Design and prototyping of a novel low stiffness cementless hip stem

Present biocompatible materials that are suitable for load bearing implants have high stiffness compared to the natural human bone. This mechanical mismatch causes a condition known as stress shielding. The current trend for overcoming this problem is to use porous scaffold instead of solid implants to reduce the implant stiffness. Due to the wide spread of metal additive manufacturing machines, porous orthopaedic implants can be mass produced. In this regard, a porous scaffold is incorporated in the design of a low stiffness hip stem. A 3D finite element analysis is performed to evaluate the performance of the new stem with the patient descending the stairs. The results of the numerical study show that the proposed design improves stress and strain distributions in the proximal region which reduce the stress shielding effect. Finally, a prototype of the proposed design is produced using a 3D printer as proof of concept.

Design and prototyping of a novel low stiffness cementless hip stem

Design and prototyping of a novel low stiffness cementless hip stem

Is the strain pattern of conventional stems negatively affected by a previously short stem THA? An experimental study in cadavaric bone.

A short stem hip arthroplasty can be revised in many cases using a conventional stem. Furthermore, in some cases the implantation of a short stem is intended, but intraoperatively reasons may lead to the decision to implant a conventional stem after previous preparation of a short stem. In both cases it is questionable if the anchorage of a conventional stem is negatively affected by the previous preparation of a short stem. In clinical practice mid- or long-term follow up for these special cases hardly exist. The strain patterns for the conventional Bicontact stem in primary implantation and after preparation of the proximal femur for a METHA short stem were tested biomechanically in three pairs of cadaveric femora. The strain patterns for the conventional Bicontact after preparation of the METHA short stem were similar to conditions after testing the conventional stem in primary conditions. These data lead to the consequence that in clinical practise the implantation of a conventional stem after preparation of a short stem and even after revision of a short stem is possible without increased risk of loosening or long-term stress-shielding.

Long-term outcome after implantation of a nickel-containing cemented hip stem on the right in a patient with type IV sensitization to nickel sulphate.

Type IV allergies to nickel sulfate, potassium dichromate and/or cobalt chloride are supposed to be associated with aseptic loosening, pain or infections in patients with hip arthroplasty. However, there is debate on any causal relation between type IV sensitization to metals and any of these complications. We report on a patient with suspicion of pre-existing type IV sensitization to nickel sulfate and potassium dichromate who did not show any complications after hip arthroplasty.