Modular Hip Research Articles

A Retrospective Single-Center Study of 23 Patients to Compare Gait Before and After Total Hip Arthroplasty Using the S-ROM Modular Hip System.

BackgroundThis retrospective study used the Harris hip score (HHS) and range of motion (ROM) to compare gait before and after total hip arthroplasty using the modular S-ROM® hip prosthesis in 23 patients treated at a single center.Material/MethodsFor this study, 23 patients with severe hip deformity, who were treated with a total hip replacement using the S-ROM® modular hip system by DePuy® in the period from 2003 until 2008, underwent a 3-dimensional gait analysis before and after surgery. Values were compared with a validated data set of healthy subjects. Gait analysis took place using 8 infrared cameras (50 Hz), 2 force platforms of Advanced Medical Technology, Inc. (AMTI)®, and the Vicon® 512 system. The HHS and ROM of the hip joint were determined preoperatively and postoperatively. The follow-up period was 16.7±15.2 months.ResultsA healthy gait pattern is characterized by an even stride length of both legs in relation to body height and relative symmetry of certain gait phases. These characteristics are influenced by the range of motion of the hip joint and by pelvic tilt.Symmetry could be achieved postoperatively in the stance phase and in the single-leg stance phase. However, the gait phases could not normalize. HHS and ROM improved postoperatively.ConclusionsThe findings from this retrospective study showed that ROM and HHS significantly improved following THA with the S-ROM® hip prosthesis, but that gait did not completely return to normal.

Driving electrochemical corrosion of implanted CoCrMo metal via oscillatory electric fields without mechanical wear

Decades of research have been dedicated to understanding the corrosion mechanisms of metal based implanted prosthetics utilized in modern surgical procedures. Focused primarily on mechanically driven wear, current fretting and crevice corrosion investigations have yet to precisely replicate the complex chemical composition of corrosion products recovered from patients’ periprosthetic tissue. This work specifically targets the creation of corrosion products at the metal on metal junction utilized in modular hip prosthetics. Moreover, this manuscript serves as an initial investigation into the potential interaction between implanted CoCrMo metal alloy and low amplitude electrical oscillation, similar in magnitude to those which may develop from ambient electromagnetic radiation. It is believed that introduction of such an electrical oscillation may be able to initiate electrochemical reactions between the metal and surrounding fluid, forming the precursor to secondary wear particles, without mechanically eroding the metal’s natural passivation layer. Here, we show that a low magnitude electrical oscillation (≤ 200 mV) in the megahertz frequency (106 Hz) range is capable of initiating corrosion on implanted CoCrMo without the addition of mechanical wear. Specifically, a 50 MHz, 200 mVpp sine wave generates corrosion products comprising of Cr, P, Ca, O, and C, which is consistent with previous literature on the analysis of failed hip prosthetics. These findings demonstrate that mechanical wear may not be required to initiate the production of chemically complex corrosion products.

The different failure modes of the connecting elements of the modular hip arthroplasty revision stem Revitan

IntroductionFracture of the femoral stem is the cause of ~1 % of revisions after total hip arthroplasty. The risk increases intrinsically with modularity, whereby modularity is particularly useful in revision arthroplasty. We present 7 cases of failure of a specific modular, tapered, fluted, titanium alloy Revitan stem and analyse the different failure modes. MethodsRetrospective review of all Revitan stems revised at our institutions due to implant failure and analysis of clinical presentation, diagnostic workup, and failure mode. The retrieved components were analyzed by optical and scanning electron microscopy. ResultsA total of 7 cases were included. There was a significant time lag between symptom onset and correct diagnosis. Conventional radiographs and low-dose CT scans (CT scout imaging) were decisive for diagnosis. All failures occurred at the level of the connection between the proximal component and the distal part of the stem. Three different failure modes were identified: loosening of the proximal component, fatigue fracture of the connection pin, and distal loosening of the connection pin. No alterations of the microstructure or deviation from manufacturing specifications regarding dimensions were observed. Failure was caused by mechanical overload. ConclusionConventional radiographs are the mainstay in identifying failed modular stems. Repeated radiographs and low-dose CT scans may be helpful additions. No single modification of the connection will address all possible failure modes. Modularity of revision stems offers advantages up until insertion of the definitive stem. Monoblock definitive stems might overcome the potential mechanical weaknesses of modularity and should be considered in relatively young, heavy and active patients.

A new experimental method to simulate dynamic crevice corrosion in modular hip arthroplasty

A new method was developed to study the complex corrosion mechanism found in modular hip arthroplasty, i.e., dynamic crevice corrosion. Short wear events followed by rest times were applied in a conformal tribocontact to simulate different activity levels. Likewise, stepped potentiostatic polarization testing and electron microscopy were used to compare dynamic (continuous and interrupted) and static conditions. Results showed that 316L stainless steel underwent severe corrosion under the dynamic setting. The findings reproduced the extent and morphology of attack found in a retrieved implant. Thus, the new method could be used to investigate the corrosion susceptibility of modular hip arthroplasty.

Use of a modular hip dual-mobility articulation in patients with high risk of dislocation: a relatively small-sized acetabulum in Asian patients may limit its use

BackgroundDual-mobility hip component is widely used in Europe and North America, because it effectively reduces hip dislocation in primary and revision total hip arthroplasties. However, reports were limited on the use of dual-mobility articulation in Asian populations.PurposeThe aim of this retrospective study was to review the use of modular dual-mobility hip articulation in Asian patients with the high risk factor for hip dislocation. We also discussed the potential concern on the use of dual-mobility articulation in Asian patients.MethodsFrom Jan 2018 to June 2019, 17 patients were included in this study. The mean age of the patients was (73.8 ± 9.5) years (range: 57–88 years). The mean size of acetabular cup and modular DM liner were (49.5 ± 3.4) mm (range, 46–58 mm) and (40.7 ± 3.4) mm (range, 38–48 mm), respectively. The mean follow-up period was (15.8 ± 3.9) months (range, 11–24 months). The primary outcome was the rate of hip dislocation. The secondary outcomes included the Harris Hip Score. Differences were considered statistically significant at p < 0.05.ResultsHip dislocation, loosening, peri-prosthetic fractures, or intra-prosthetic dislocation was not found in the series. The mean preoperative and postoperative Harris Hip Scores were 42.2 ± 17.2 (range, 15–80) and 74.7 ± 13.5 (range, 52–97), respectively, giving a mean improvement of 32.5 ± 17.2 (range, 4–72). The improvement was statistically significant (p < 0.05).ConclusionsIn Asian patients with high risk of hip dislocation, the use of modular dual-mobility hip component produces promising outcomes without hip dislocation, but the relatively small-sized acetabulum may limit it widespread application in other populations worldwide.Trial registrationHKUCTR-2913.

A novel approach for a modular taper junction in hip stems using turn-milling

The durability of hip endoprostheses depends on a variety of influences. Besides the use of biocompatible materials, premature implant failures can occur that require complex revision surgeries. Since hip endoprostheses are characterized by a modular system, their interfaces are a frequent cause of failure. Consequently, the occurrence of micromotion at the modular taper junction can cause the release of metal particles and ions due to fretting corrosion. In this publication, the adhesive strength of the taper junction of modular hip endoprostheses is examined. In order to improve the tapers bearing area, the surface structures of the femoral stem taper were modified by different manufacturing processes and mechanically examined in a torsion test. In this case, especially turn-milling was applied which causes a structured surface topography due to the kinematic conditions.

Medium Term Radiographic and Clinical Outcomes Using a Modular Tapered Hip Revision Implant.

BackgroundThe rate of revision hip arthroplasty surgery is rising. Surgeons must use implants with proven outcomes to help overcome the technical challenges faced during revision surgery. However, outcome studies using these implants are limited. The aim of this study is to investigate the radiographic and clinical outcomes of the Stryker Restoration stem, the most commonly used hip revision stem in the United Kingdom (UK).MethodsA retrospective review of a single surgeon case series was performed. Immediate postoperative radiographs were analyzed for offset and leg length discrepancy. Radiographic evidence of subsidence was assessed using follow-up radiographs. Kaplan-Meier survival analysis was applied using explantation and reoperation as endpoints. Patient-reported outcomes were measured using the Oxford Hip Score and EQ-5D-5L.ResultsOne hundred ninety-eight cases were identified. Mean follow-up duration was 51.8 months (range: 24-121). Stem survival during this period was 98%. Reoperation for any reason was 13%. Mean subsidence was 4.18 mm. Analysis of variance testing showed no difference in mean subsidence between revision indications. Mean offset and leg length discrepancies were measured at 4.5 mm and 4.3 mm, respectively. The mean Oxford Hip Score for participants was 27.6.ConclusionsThis series demonstrates excellent implant survival, with radiographic parameters for reconstruction and subsidence levels comparable to those in the existing literature. The tapered modular hip revision stem provides surgeons with the intraoperative flexibility to overcome some of the anatomical difficulties encountered during revision surgery; this is reflected in the radiographic and clinical outcomes of the cohort in this study.

A Crevice Corrosion Model for Biomedical Trunnion Geometries and Surfaces Feature.

Modular hip joint implants were introduced in arthroplasty medical procedures because they facilitate the tailoring of patients’ anatomy, the use of different materials in one single configuration, as well as medical revision. However, in certain cases, such prostheses may undergo deterioration at the head–neck junctions with negative clinical consequences. Crevice-corrosion is commonly invoked as one of the degradation mechanisms acting at those junctions despite biomedical alloys such as Ti6Al4V and CoCr being considered generally resistant to this form of corrosion. To verify the occurrence of crevice corrosion in modular hip joint junctions, laboratory crevice-corrosion tests were conducted in this work under hip joint-relevant conditions, i.e., using similar convergent crevice geometries, materials (Ti6Al4V and CoCr alloys vs. ceramic), surface finish, NaCl solution pHs (5.6 and 2.3), and electrochemical conditions. A theoretical model was also developed to describe crevice-corrosion considering relevant geometrical and electrochemical parameters. To verify the model, a FeCr alloy, known to be sensitive to this phenomenon, was subjected to the crevice-corrosion test in sulfuric acid. The experiments and the model predictions clearly showed that, in principle, crevice corrosion of Ti6Al4V or CoCr is not supposed to occur in typical crevices formed at the stem-neck junction of hip implants.

Taper junctions in modular hip joint replacements: What affects their stability?

BackgroundAlthough taper junctions are beneficial in the reconstruction of hip joints, some clinical concerns like the formation of adverse local tissue reactions have recently emerged. These reactions are associated with wear and corrosion products from the interface of insufficient taper connections regarding strength. Commonly used tapers vary in their geometric and topographical design parameter. Therefore, this study aims to evaluate interactions between design and surgical related parameters to the taper connection strength. MethodsIn this study, the effect of the taper contact situation, surface roughness and head material in combination with assembly force on the taper connection strength were assessed using torque-off tests. Furthermore, the type of use in terms of single-use or re-use of the stem taper was investigated. ResultsThe study showed that the impaction force is the predominant factor that determines the taper strength followed by the type of use and the head material. The contact situation seems to slightly influence the determined torque-off moment, whereas the surface topography of the stem taper obviously plays a minor role for the taper connection strength. ConclusionClinical users should be aware that an increased assembly force will strengthen the stability of the taper junction, whereas care should be taken when reusing hip stems with metal heads as this may decrease their connection strength.

산업 노동자의 들기 작업 시 허리 통증을 예방하기 위한 수동 모듈형 외골격 시스템 개발

This paper deals with the development of a passive modular hip exoskeleton system aimed at preventing musculoskeletal low back pain, which commonly occurs in heavy weight transport workers, by improving back muscle strength. The passive exoskeleton system has the advantage of being lightweight, making it suitable for modular exoskeleton systems. The cam and spring actuator designed in this study was applied to the passive modular exoskeleton system to build human hip and lumbar muscle strength. In order to evaluate the effectiveness of the passive modular exoskeleton system, a test was performed in which a subject lifted a 15 kg weight three times in a stoop posture, using heart rate measurement and Borg scale recording. According to the results, all subjects showed 26.83% lower maximum heart rate and 34.73% lower average heart rate than those who did not wear the system, and Borg scale evaluation result was lower. All subjects wore this system and did not experience back pain during the experiment. Through this study, we validated the effectiveness of the passive modular exoskeleton system and proved that this system can build the strength of industrial workers and be a solution to prevent musculoskeletal lumbar disease.

Unexpected varus deformity and concomitant metal ion release and MRI findings of modular-neck hip stems: descriptive RSA study in 75 hips with 8 years’ follow-up

Background and purpose — Modular-neck hip stems have been identified with corrosion-related problems from the neck–stem junction. We report an ongoing varus deformity of modular-neck hip stems with simultaneous metal ion release observed during a study comparing the migration of modular vs. standard hip stems. Patients and methods — We followed 50 patients with modular and 25 with standard neck stems using radiostereometry (RSA). At 5-year follow-up, we noted a compromised integrity of the modular stem with varus deformity in the neck–stem interface. Changes in head–tip distance as well as whole-blood ion concentration and MRI findings were analyzed. The modular stems were followed further up to 8 years. Results — The head–tip distance decreased continuously by 0.15 mm per year resulting in 1.2 (95% CI 1.0–1.4) mm at 8 years for modular stems, while for the standard stems at 5 years, the decrease was 0.09 (CI 0.0–0.2) mm or 0.02 mm/year. For the modular stems, the reduction in head–tip distance correlated to the increase in whole-blood cobalt concentration at 8 years but not to the MRI grading of tissue reactions. At 5 years, cobalt levels were 4.9 µg/L for modular stems and at 8 years 4.8 µg/L, whereas for standard stems this was 1.0 µg/L. After 8 years, 9 of 72 stems had been revised for different reasons, but only 1 with obvious adverse local tissue reaction (ALTR). Interpretation — We present a surprisingly large progressive deformation at the modular neck–stem junction, but so far without a definite clinical problem. Even the femoral head seems to show slight compression onto the taper over time. A high rate of revisions for the modular type of this stem has raised general concerns, and it has been recalled from the market.

Taper corrosion: a complication of total hip arthroplasty.

The focus on taper corrosion in modular hip arthroplasty increased around 2007 as a result of clinical problems with large-head metal-on-metal (MoM) bearings on standard stems. Corrosion problems with bi-modular primary hip stems focused attention on this issue even more.Factors increasing the risk of taper corrosion were identified in laboratory and retrieval studies: stiffness of the stem neck, taper diameter and design, head diameter, offset, assembly force, head and stem material and loading.The high variability of the occurrence of corrosion in the clinical application highlights its multi-factorial nature, identifying the implantation procedure and patient-related factors as important additional factors for taper corrosion.Discontinuing the use of MoM has reduced the revisions due to metal-related pathologies dramatically from 49.7% (MoM > 32 mm), over 9.2% (MoM ⩽ 32 mm) to 0.8% (excluding all MoM).Further reduction can be achieved by omitting less stiff Ti-alloys and large metal heads (36 mm and above) against polyethylene (PE).Standardized taper assembly of smaller and ceramic heads will reduce the clinical occurrence of taper corrosion even further. If 36 mm heads are clinically indicated, only ceramic heads should be used.Taper-related problems will not comprise a major clinical problem anymore if the mentioned factors are respected.Cite this article: EFORT Open Rev 2020;5:776-784. DOI: 10.1302/2058-5241.5.200013

Adaptive finite element simulation of fretting wear and fatigue in a taper junction of modular hip prosthesis

Modular taper junctions are commonly used in total hip arthroplasty to offer a wide range of intraoperative choices to surgeons. The damage at the taper surfaces can lead to the implant failure either by material removal (wear) or by cracks nucleation (fatigue). This paper presents a methodology based on the finite element approach to study both fretting wear and fatigue, taking into account their interaction in the modular taper. The modified Archard's law was employed to compute wear depth and the corresponding volume loss while the fatigue life was predicted using two critical plane fatigue parameters (Smith-Watson-Topper and Fatemi-Socie). An adaptive meshing technique was implemented to take into account the geometry changes and the material removal effect on fatigue life. The methodology developed was discussed and validated against available experimental data from the literature. In this case considered, a transition from a partial slip regime to a large slip one, which is mainly controlled by the contact slip amplitude, was found to reduce the fatigue life and a critical slip value was identified. This provides an efficient tool for an in-depth understanding of fretting in taper junctions and for future design.

Hip Revision Arthroplasty of Periprosthetic Fractures Vancouver B2 and B3 with a Modular Revision Stem: Short-Term Results and Review of Literature.

Periprosthetic fractures Vancouver type B2/B3 after total hip arthroplasty (THA) is a challenging entity with increasing numbers. Limited data are available for this type of fracture treated with modular stems. Therefore, this study evaluated the outcome of Vancouver type B2/B3 fractures treated with a modular hip revision stem using a subproximal/distal anchorage and compared it to the current literature. A consecutive series of periprosthetic Vancouver type B2/B3 fractures treated with a modular revision stem was retrospectively (2013 - 2016) evaluated. Assessment included the clinical (HHS, pain, ROM) as well as the radiological outcome (subsidence, loosening, facture healing). In adddition, the surgical technique is described in detail and results are compared with the current literature. A total of 18 patients (female/male 12/6) with Vancouver B2/B3 (n = 12/6) fractures with a mean age of 75.5 (60 - 89) years were included. The revision stem was inserted via a modified transgluteal approach (n = 16) or classical transfemoral approach (n = 2). The mean follow-up was 18.5 months, with a mean Harris Hip Score of 72.5 ± 18.7 (35.0 - 99.0) points. The fracture healing rate was 94.4% (n = 17) with osseous integration according to Engh in all cases. Dislocations of the greater trochanter were recorded in seven patients (38.9%). According to Beals and Towers, all results were rated excellent or good. No implant-related failure or relevant subsidence during this time was observed. Major complications were observed in five patients with two periprosthetic joint infections and two cases of major revision surgery. This study assessing Vancouver B2/3 fractures shows reproducible, good, short-term results in terms of subsidence and clinical functional outcome by the use of a modular revision stem. The transfemoral approach together with the modular stem allows for a stable fixation and good fracture healing. However, our data and review of the literature also documents the difficulties and higher complication rate associated with Vancouver B2/3 fractures.

Long-Term Clinical and Radiological Outcomes of Primary Total Hip Arthroplasty with Modular Femoral Stem in Middle-Aged Asian Patients

BackgroundThere is insufficient information regarding the outcome of primary total hip arthroplasty (THA) with the modular femoral stem in middle-aged patients. This study aimed to assess long-term clinical and radiological outcomes of primary THA using the original or modified modular hip system (S-ROM) in middle-aged Asian patients. MethodsA retrospective review identified 98 primary THAs that used a modular stem and were undertaken between 1997 and 2009 in patients younger than 58 years, for whom at least 5 years of follow-up data were available. Clinical data and radiograph assessments were reviewed to analyze differences between the original and modified modular stem groups. ResultsThe mean patient follow-up duration was 148.3 months, and the follow-up ratio was 89.1%. The Kaplan–Meier analysis revealed that the survival rate of both stems was 98.9% at 10 years and 89.8% at 15 years. Although no statistically significant differences in the survival rate were observed between the stem designs, the original stem group had increased incidence of thigh pain compared with the modified stem group. In total, 12 and 54 hips showed change in stem alignment and osteolysis, respectively. ConclusionThe findings of this study show that the modular stems have a high survival rate, and results suggest positive outcomes among the Asian population over the long term. Although there were very few differences between the stem designs, the results suggest that the modified modular stem could prevent thigh pain and that selection of the implant based on the bone shape is important for THA.

Unusual Case of Acetabular Liner Dissociation Following Failure of Ceramic-OnCeramic Bearing Total Hip Arthroplasty: A Case Report

Modular hip implants can improve construct stability and the rate of volumetric wear in Total Hip Arthroplasty (THA), however, there is still a 0.2-10% risk of dislocation. We report the unusual case of a 54-year-old lady who presented with a dislocated migrated ceramic liner following a twisting injury. She had undergone a ceramic-on-ceramic THA five years earlier. This diagnosis of the dislocated liner was confirmed with computed tomography (CT) scanning. Review of National Joint Registry data showed ceramic-on-ceramic acetabular liner dissociation to be rarer than in those with metal-on-polyethylene (incidence 0.27 vs. 0.46 per 1000 prosthesis years). We suggest the liner may have migrated in retrograde along the iliopsoas. We recommend the use of cross-sectional imaging (CT) to assist in confirming the diagnosis and planning future surgery.

Risk factors and clinical manifestations of head-neck wear in artificial hip joints

At present, total hip arthroplasty (THA) is the primary treatment for hip diseases such as femoral head necrosis and developmental dysplasia of the hip. It has good effects in reducing pain and improving joint function. The appearance of modular hip prosthesis facilitates adjustment of limb length and femoral offset. However, the wear between the interface of hip prosthesis can lead to inflammatory pseudotumor, osteolysis and other adverse reactions. To explore the risk factors of wear between hip prosthesis interface is helpful to improve the design and manufacturing concept of the product, improve the product performance, help surgeons optimize the operation technology and reduce the impact of human factors on the wear of the prosthesis. Many literatures have reported the mechanism of wear between the head-acetabula interface of prosthesis. The mechanism of wear between the interfaces has been described relatively clearly. In addition to the head-acetabula interface, the wear between the head-neck interface is another major cause of unexplained pain around the joint and prosthesis loosening after hip replacement. Many factors affect head-neck wear. The design of prosthesis (such as prosthesis material and prosthesis taper), surgical technology (such as impact strength and prosthesis mismatch) and patient factors (such as age, gender and activity) have important impact on head-neck wear. Adverse reactions caused by head-neck wear have also been widely concerned. However, there is no considerable solution for wear prevention. Thus, we should optimize the design of prosthesis, improve the surgical technology, and guide the rehabilitation of patients to prevent wear. In order to improve the attention of joint surgeons, the present paper reviews the literatures and analyzes the risk factors of head-neck interface wear and the clinical manifestations caused by head-neck wear.

Fretting manifestations in total hip prosthesis

This paper analyses the fretting and fretting wear phenomena to the classical and modular hip prostheses. Theoretical and experimental manifestations are studied, at the interface of the femoral stem with the bone cement mantle, at the taper junction between the femoral stem and the femoral head of the prosthesis, as well as at the tapering of the femoral neck adapter’s connections with the stem and the femoral head. The aim of the paper is to highlight the modularization implications of the femoral component of the Total Hip Prosthesis, especially its tribological implications (fretting wear of modular junctions, fatigue and corrosion by fretting) which can contribute to wear and increasing ion concentrations of the metal in the blood, and the possibility of the femoral shaft fracture at the femoral head junction. Theoretical approach described, allows the “Archard” law implementation to predict the fretting wear. Experimental laboratory studies focused on the analysis of the tribological phenomena occurring at the taper junctions between the femoral head and neck, as well as the neck and femoral stem, highlighting the relevant qualitative tribological aspects. For this purpose, experimental junctions were fabricated and tested on a universal MTS mechanical machine, equipped with a fatigue testing device.

Short proximal components in modular revision stems carry a higher risk for stem fractures.

Fractures of modular hip revision stems are not uncommon. The current study examined implant-related factors on stem fracture. We hypothesised that in a modular stem the fracture risk is increased with the use of a short proximal implant component. Anonymised data of all 32 patients in Switzerland with a Revitan modular hip system who had a stem fracture were obtained from the manufacturer. Implant and patient data were compared with all components implanted in Switzerland during the same time interval. Between 2002 and 2017, 4834 Revitan stems were implanted, of which 32 fractured. A smaller size of the proximal stem component was significantly associated with a higher fracture risk (p < 0.001). Compared with the control group, the proportion of male patients was higher among the fracture cases, patients were younger, and they had a higher body weight (p < 0.001, respectively). The present study suggests that small proximal stem components increase the load at the modular junction due to size and lack of bony support. Surgeons should therefore avoid short proximal components so that the mid-stem junction lies as distally as possible and the risk of fracture is minimised.

Micromotion at the head-stem taper junction of total hip prostheses is influenced by prosthesis design-, patient- and surgeon-related factors

Taper junctions of modular hip prostheses are susceptible to fretting and crevice corrosion. Prevalence and significance increase for cobalt-chromium heads assembled on titanium-alloy stems. Retrieval and in-vitro studies have identified micromotion between the taper components to accelerate the corrosion process. The aim of this study was to identify the most critical factors contributing to increased micromotion, which is most likely influenced by design-, patient- and surgeon-related aspects. Micromotion between head and stem taper surfaces was measured for different taper surface topographies and load orientations. Consecutive visual images were recorded through windows in the head component. By image matching analysis the local micromotions at the taper junction between head and stem tapers were determined. To extend the findings to taper regions not visible through the windows, finite element models were generated. The models were further utilized to investigate the influence of head length, taper angle difference and assembly force on micromotion. Significantly higher micromotion (+20%) was found under varus loading (7.1 µm) in comparison to valgus loading (5.9 µm). Smooth and microgrooved stem tapers exhibited equal amounts of micromotion. The numerical model revealed head tilting and recurring taper contact changes in terms of cyclic engagement/disengagement during the loading sequences. Especially long heads (+240%) and low assembly forces (+53%) were found to substantially increase micromotion (from 2.7 µm to 9.3 µm and from 4.1 µm to 8.8 µm, respectively). This study accentuates the susceptibility of taper junctions to a variety of factors, which need to be appreciated in preoperative planning and surgical procedure to reduce the amount of micromotion and such minimize the risk of critical corrosion.