Aims. The risk of mechanical failure of modular revision hip stems is frequently mentioned in the literature, but little is currently known about the actual clinical failure rates of this type of prosthesis. The current retrospective long-term analysis examines the distal and modular failure patterns of the Prevision hip stem from 18 years of clinical use. A design improvement of the modular taper was introduced in 2008, and the data could also be used to compare the original and the current design of the modular connection. Methods. We performed an analysis of the Prevision modular hip stem using the manufacturer’s vigilance database and investigated different mechanical failure patterns of the hip stem from January 2004 to December 2022. Results. Two mechanical failure patterns were identified: fractures in the area of the distal fluted profile (distal stem fracture) and failure of the modular taper (modular fracture). A failure rate of 0.07% was observed for distal stem fracture, and modular fracture rates of 1.74% for the original and 0.013% for the current taper design. Conclusion. A low risk of mechanical failure for both fracture types was observed compared to other known complications in revision hip arthroplasty. In addition, the data show that a design change did significantly reduce the risk of a modular fracture. Cite this article: Bone Joint J 2024;106-B(2):151–157

The vast majority of total hip replacements (THR) implanted today enable modularity by means of a tapered junction; based on the Morse taper design introduced for cutting tools in the 19. th. Century . 1. Morse-type tapers at the head-stem junction provide many benefits, key for a successful surgical outcome such as wider component selection and restoration of better biomechanics . 2. However, moving from mono-block to modular designs has not been without its issues. Fluid ingress and motion at the interface has led to a complex multifactorial degradation mechanism better known as fretting-corrosion . 3. Fretting-corrosion products created at the junction are commonly associated with adverse local tissue reactions . 4. . There is a wide variation in the taper junction of THR differing quite significantly from Morse's original design. Performance of the taper junction has been found to vary with different designs . 5,6. However, there is still a lack of common understanding of what design inputs makes a ‘good’ modular taper interface. The aim of this study was to better understand the links between implant design and fretting-corrosion initially focussing on the role of angular mismatch between male and female taper. A combination of experimental approaches with the aid of computational models to assist understanding has been adopted. A more descriptive understanding between taper design, engagement, motion and fretting-corrosion will be developed. Three different sample designs were created to represent the maximum range of possible angular mismatches seen in clinically available THR modular tapers (Matched: 0.020 ±0.002 °, Proximal: 0.127 ±0.016 °, Distal: −0.090 ±0.002 °). Head-stem components were assembled at 2 kN. Motion and fretting-corrosion at the interface was simulated under incremental uniaxial sinusoidal loading between 0.5–4 kN at 8 intervals of 600 cycles. The different types of motions at the interface was measured using a developed inductance circuit composed of four sensing coils, digital inductance converter chip (LDC1614, Texas Instruments, US) and microcontroller (myRIO, National Instruments, US). Fretting-corrosion was measured using potentiostatic electrochemical techniques with an over potential of +100 mV vs OCP (Ivium, NL). Complimentary finite element (FE) models were created in Ansys (Ansys 19.2, US). Under uniaxial loading, the ‘matched’ modular taper assemblies corroded most and allowed the greatest pistoning motion due to a seating action. ‘Distal’ and ‘proximal’ engaged modular tapers showed reduced corrosion and seating when compare to the ‘matched’ components. However the kinetics of corrosion and motion were interface dependent. It is hypothesized, and complimented by FEA analysis, that lower initial contact stress in the ‘matched’ modular tapers allows for greater subsidence and depassivation of the oxide layer and higher corrosion. ‘Matched’ modular tapers allowed less rotational and toggling motions compared to mismatched tapers, suggesting a reduced mismatch might perform better once the heads have seated over time. Future work involves tests conducted under a surgically relevant impaction force and physiological loading kinematics to develop this descriptive link between taper design, engagement and performance

Introduction. Improper seating during head/stem assembly can lead to unintended micromotion between the femoral head and stem taper—resulting in fretting corrosion and implant failure. There is no consensus—either by manufacturers or by the surgical community—on what head/stem taper assembly method maximizes modular junction stability in total hip arthroplasty (THA). A 2018 clinical survey found that orthopedic surgeons prefer applying one strike or three, subsequent strikes when assembling head/stem taper. However, it has been suggested that additional strikes may lead to decreased interference. Additionally, the taper surface finish—micro-grooves—has been shown to affect taper interference and may be influenced by assembly method. Objective. The objective of this study was to employ a novel, micro-grooved finite element (FEA) model of the hip taper interface and assess the role of head/stem assembly method—one vs three strikes—on modular taper junction stability. Methods. A two-dimensional, axisymmetric model representative of a CoCrMo femoral head taper and Ti6Al4V stem taper was created using median geometrical measurements taken from over 100 retrieved implants. Surface finish—micro-grooves—of the head/stem taper were modeled using a sinusoidal function with amplitude and period corresponding to median retrieval measurements of micro-groove height and spacing, respectively (“smooth” stem taper: height=2µm, spacing=50µm; “rough” stem taper: height=11µm, spacing=200µm; head taper: height=2µm, spacing=50µm). All models had a 3’ (0.05°), proximal-locked angular mismatch between the tapers. To simulate modular assembly during surgery, multiple dynamic loads (4kN, 8kN, and 12kN) were applied to the femoral head taper as either one or three sequence of strikes. The input load profile (Figure 1) used for both cases was collected from surgeons assembling an experimental setup with a three-dimensional load sensor. Models were assembled and meshed in ABAQUS Standard (v 6.17) using four-node linear hexahedral, reduced integration elements. Friction was modeled between the stem and head taper using surface-to-surface formulation with penalty contact (µ=0.2). A total of 12 implicit, dynamic simulations (3 loads x 2 assembly sequences x 2 stem taper surface finishes) were run, with 2 static simulations at 4kN for evaluating inertial effects. Outcome variables included contact area, contact pressure, equivalent plastic strain, and pull-off force. Results. As expected, increasing assembly load led to increased contact area, pressures, and plasticity for both taper finishes. Rough tapers exhibited less total contact area at each loading level as compared to the smooth taper. Contact pressures were relatively similar across the stem taper finishes, except the 3-strike smooth taper, which exhibited the lowest contact pressures (Figure 2) and pull-off forces. The models assembled with one strike exhibited the greatest contact pressures, pull-off forces, and micro-groove plastic deformation. Conclusion. Employing 1-strike loads led to greater contact areas, pressures, pull-off forces, and plastic deformation of the stem taper micro-grooves as compared to tapers assembled with three strikes. Residual energy may be lost with subsequent assembly strikes, suggesting that one, firm strike maximizes taper assembly mechanics. These models will be used to identify the optimal design factors and impaction method to maximize stability of modular taper junctions. For any figures or tables, please contact authors directly

Periprosthetic femoral fracture (PFF) is a potentially devastating complication after total hip arthroplasty, with historically high rates of complication and failure because of the technical challenges of surgery, as well as the prevalence of advanced age and comorbidity in the patients at risk. This study describes the short-term outcome after revision arthroplasty using a modular, titanium, tapered, conical stem for PFF in a series of 38 fractures in 37 patients. The mean age of the cohort was 77 years (47 to 96). A total of 27 patients had an American Society of Anesthesiologists grade of at least 3. At a mean follow-up of 35 months (4 to 66) the mean Oxford Hip Score (OHS) was 35 (15 to 48) and comorbidity was significantly associated with a poorer OHS. All fractures united and no stem needed to be revised. Three hips in three patients required further surgery for infection, recurrent PFF and recurrent dislocation and three other patients required closed manipulation for a single dislocation. One stem subsided more than 5 mm but then stabilised and required no further intervention. . In this series, a modular, tapered, conical stem provided a versatile reconstruction solution with a low rate of complications. Cite this article: Bone Joint J 2015;97-B:1031–7

Statement of Purpose. Mechanically assisted crevice corrosion of modular tapers continues to be a concern in total joint replacements as studies have reported increases in local tissue reactions. 1. Two surgical factors that may effect taper seating mechanics are seating load magnitude and orientation. In this study 12/14 modular taper junctions were seated over a range of loads and loading orientations. The goals of this study were to assess the effects of load magnitude and orientation on seating load-displacement mechanics and to correlate these to the pull-off load. Methods. Ti6Al4V 12/14 tapers and CoCrMo heads were tested axially at four seating load levels (n=5): 1-, 2-, 4- and 8- kN. Three orientation groups were tested at 4 kN (n=5), 0°, 10° and 20°. The load-displacement behavior during testing was captured using data acquisition methods and two non-contact eddy current sensors fixed to the neck, targeting head-neck relative motion (Micro-Epsilon). Loads were ramped (200 N/s) with a servohydraulic system from 0 N to peak load and held for 5s (Instron). Off-axis test samples were oriented in an angled fixture. Displacement and load data were recorded in LabView. Seating displacement was the distance traveled between 50 N and thepeak load. Axial tensile pull-off loads (5 mm/min) were applied until the locking ability of taper junctions failed. Statistical analysis was performed using ANOVA test (P<0.05). Results. Axial tests. Seating load-displacement behavior at different seating loads (Fig. 1) show consistent characteristic behavior. Displacements rise parabolically to the peak load reflecting elastic deformation and rigid-body motion. Unloading is elastic and the y-intercept of the unloading curves reflects seating displacement. Displacement and work of seating for the axial tests (Fig. 2a and 2b, respectively) show that both increase with seating magnitude. Displacement increases approximately linearly, while work increases parabolically with seating load. All groups are significantly different (P<0.05). Pull-off loads (Fig. 3) increase linearly with seating load. Pull-off loads are approximately 44% of the seating load. All loads are statistically different (P<0.05). Off-axis tests. Measured seating displacements were comprised of rigid-body and elastic motion. A stiffness-correction method removed elastic motion. 2. Displacement, work and pull-off at the different seating load orientations were not significantly affected (P>0.05, data not shown). Discussion. Static seating load magnitude and orientation effects on seating mechanics and pull-off loads simulating surgical assembly were quantitatively studied in an instrumented seating test method. Increased seating loads increased work of seating, seating displacement and pull-off load. Such seating plots may assist in better understanding of the design, material, and surgical factors associated with taper locking mechanics. Seating orientation to 20° offset did not significantly affect seating mechanics or pull-off loads. Pull-off loads were about 50% of the seating loads for all cases which is consistent with other work. 3. . Conclusions. Increased seating load magnitude increased seating displacement, work and pull-off loads in 12/14 tapers. Load orientation had no significant effect. For figures/tables, please contact authors directly.

Introduction:. There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with modular tapers in total hip replacements with a single combination of materials of modular tapers. Methods:. An inverted hip replacement setup was used (ASTM F1875-98). 28 mm Cobalt Chrome (CoCr) femoral heads were coupled with either full length (standard) or reduced length (mini) 12/14 Titanium (Ti) stem tapers. These Ti stem tapers had either a rough or smooth surface finish whilst all the head tapers had a smooth surface finish. Wear and corrosion of taper surfaces were compared after samples were sinusoidally loaded between 0.1 kN and 3.1 kN for 10 million cycles at 4 Hz. In test 1 rough mini stem tapers were compared with rough standard stem tapers whilst in test 2 rough mini stem tapers were compared with smooth mini stem tapers. Surface parameters and profiles were measured before and after testing. Electrochemical static and dynamic corrosion tests were performed between rough mini stem tapers and smooth mini stem tapers under loaded and non-loaded conditions. Results:. In test 1 following the mechanical loading test the surface roughness parameters on the head taper were significantly increased when they were coupled with the mini stem tapers compared to the standard stem tapers (p = 0.046). Similarly in test 2 the surface roughness parameters on the head tapers were significantly increased when mini rough stem tapers were used compared to smooth mini stem tapers (p = 0.04). Corrosion testing showed breaching of the passive film on the rough but not the smooth neck tapers. Conclusion:. This study has identified enhanced fretting corrosion at the modular taper junction associated with roughened surface finish and small neck tapers and points to the overall concern associated with the use of modular taper connections in orthopaedic implants. Crevice corrosion is identified as the predominant mechanism, with evidence of pitting in all rough mini neck tapers. The greatest wear and corrosion was in the plane where the greatest bending moments were generated, implicating fretting as a mechanism. The rough mini neck tapers have a reduced surface area at the interface and ultimately bending forces are concentrated here

Introduction. Mechanically assisted crevice corrosion (MACC) of head-neck modular taper junctions is prevalent in virtually all head neck tapers in use today. To date, no clear in vitro tests of design, material or surgical elements of the modular taper system have been reported that show which factors principally affect MACC in these tapers. Possible elements include seating load, head-neck offset, surface roughness, taper engagement length, material combination, angular mismatch, and taper diameter. The goals of this study were to use an incremental fretting corrosion test method. 1. to assess the above 7 elements using a design of experiments approach. The hypothesis is that only one or two principal factors affect fretting corrosion. Methods. A 2. 7-2. design of experiment test (7 factors, ¼ factorial, n=32 total runs, 16 samples per condition per factor) was conducted. Factors included: Assembly Force (100, 4000N), Head Offset (1.5, 12 mm), Taper Locking Position (Mouth, Throat), Stem Taper Length (0.44, 0.54 in), Stem Taper Roughness (Ground, Ridged), Taper Diameter (9/10, 12/14), and Stem Material (CoCrMo, Ti-6Al-4V). The heads were CoCrMo coupled with taper coupons (DePuy Synthes, Warsaw, IN). Test components were assembled wet and seated axially with 100 or 4000N assembly force. The assemblies were immersed in PBS and potentiostatically held at −50mV vs. Ag/AgCl. Incremental cyclic loads were applied vertically to the head at 3Hz until a 4000N maximum load was reached (See Fig. 1). Fretting currents at 4000 N cyclic load were used for comparisons while other parameters, including onset load, subsidence, micromotion and pull off load were also captured. Statistical analysis was performed using Pareto charts and Student's T-tests for single factor comparisons (P < 0.05 was statistically significant). Results. Average fretting corrosion currents at 4000 N cyclic load ranged from 0 to 23 µA for all test specimens. The primary factors that statistically affected fretting corrosion currents were head-neck offset (P<0.05) and assembly load (P<0.05). Test factors with the most significance are shown in the Pareto chart of effects (Fig 2). Assembly force, head offset, and the interaction between these two factors were the most significant effects (see Fig 3). All other factors had diminishing effects on fretting current. Note that there is a correlation between fretting currents and pull off load (Fig. 3c). A number of interactive effects were seen between factors on various output parameters (e.g., subsidence, pull off load, onset load) as well. Discussion. This work demonstrates that the principal factors affecting fretting corrosion are seating load and head-neck offset. Material combination, taper diameter, engagement length, roughness and angular mismatch were less significant effectors of fretting corrosion. This test assesses early fretting corrosion response but does not necessarily predict long-term performance where crevices and solution changes may be important. Significance. This work shows a relative comparison of the effects of multiple design, material and surgical elements on the early fretting corrosion behavior of modular tapers in vitro. Head offset and seating loads represent the most significant factors amongst those studied. For figures, please contact authors directly

Summary Statement. Fretting and corrosion has been identified as a clinical problem in modular metal-on-metal THA, but remains poorly understood in modern THA devices with polyethylene bearings. This study investigates taper damage and if this damage is associated with polyethylene wear. Introduction. Degradation of modular head-neck tapers was raised as a concern in the 1990s (Gilbert 1993). The incidence of fretting and corrosion among modern, metal-on-polyethylene and ceramic-on-polyethylene THA systems with 36+ mm femoral heads remains poorly understood. Additionally, it is unknown whether metal debris from modular tapers could increase wear rates of highly crosslinked PE (HXLPE) liners. The purpose of this study was to characterise the severity of fretting and corrosion at head-neck modular interfaces in retrieved conventional and HXLPE THA systems and its effect on penetration rates. Patients & Methods. 386 CoCr alloy heads from 5 manufacturers were analyzed along with 166 stems (38 with ceramic femoral heads). Metal and ceramic components were cleaned and examined at the head taper and stem taper by two investigators. Scores ranging from 1 (mild) to 4 (severe) were assigned in accordance with the semi-quantitative method adapted from a previously published technique. Linear penetration of liners was measured using a calibrated digital micrometer (accuracy: 0.001 mm). Devices implanted less than 1 year were excluded from this analysis because in the short-term, creep dominates penetration of the head into the liner. Results. The majority of the components were revised for instability, infection, and loosening. Mild to severe taper damage (score ≥2) was found in 77% of head tapers and 52% of stem tapers. The extent of damage was correlated to implantation time at the head taper (p=0.0004) and at the stem taper (p=0.0004). Damage scores were statistically elevated on CoCr heads than the matched stems (mean score difference=0.5; p<0.0001) and the two metrics were positively correlated with each other (ρ=0.41). No difference was observed between stem taper damage and head material (CoCr, ceramic) (p=0.56), nor was a correlation found between taper damage and head size (p=0.85). The penetration rate across different formulations of HXLPE was not found to be significantly different (p=0.07), and therefore grouped together for further analysis. Within this cohort, penetration rate was not found to be associated with head size (p=0.08) though a negative correlation with implantation time was noted (ρ=−0.35). When analyzed along with taper damage scores, a correlation was not observed between head taper damage scores and HXLPE penetration rates (p=0.51). Discussion. The results of this study do not support the hypothesis that 36+ mm ceramic or CoCr femoral heads articulating on HXLPE liners are associated with increased risk of corrosion among HXLPE liners when compared with smaller diameter heads. A limitation of this study is the semi-quantitative scoring technique, heterogeneity of the retrieval collection and short implantation time of the larger diameter heads. Because corrosion may increase over time in vivo, longer-term follow-up, coupled with quantitative taper wear measurement, will better assess the natural progression of taper degradation in modern THA bearings

Introduction:. Degradation of modular head-neck tapers was raised as a concern in the 1990s (Gilbert 1993). The incidence of fretting and corrosion among modern, metal-on-polyethylene and ceramic-on-polyethylene THA systems with 36+ mm femoral heads remains poorly understood. Additionally, it is unknown whether metal debris from modular tapers could increase wear rates of highly crosslinked PE (HXLPE) liners. The purpose of this study was to characterize the severity of fretting and corrosion at head-neck modular interfaces in retrieved conventional and HXLPE THA systems and its effect on penetration rates. Patients & Methods:. 386 CoCr alloy heads from 5 manufacturers were analyzed along with 166 stems (38 with ceramic femoral heads). Metal and ceramic components were cleaned and examined at the head taper and stem taper by two investigators. Scores ranging from 1 (mild) to 4 (severe) were assigned in accordance with the semi-quantitative method adapted from a previously published technique. Linear penetration of liners was measured using a calibrated digital micrometer (accuracy: 0.001 mm). Devices implanted less than 1 year were excluded from this analysis because in the short-term, creep dominates penetration of the head into the liner. Results:. The majority of the components were revised for instability, infection, and loosening. Mild to severe taper damage (score ≥2) was found in 77% of head tapers and 52% of stem tapers. The extent of damage was correlated to implantation time at the head taper (p = 0.0004) and at the stem taper (p = 0.0004). Damage scores were statistically elevated on CoCr heads than the matched stems (mean score difference = 0.5; p < 0.0001; Figure 2) and the two metrics were positively correlated with each other (ρ = 0.41). No difference was observed between stem taper damage and head material (CoCr, ceramic) (p = 0.56), nor was a correlation found between taper damage and head size (p = 0.85; Figure 3). The penetration rate across different formulations of HXLPE was not found to be significantly different (p = 0.07), and therefore grouped together for further analysis. Within this cohort, penetration rate was not found to be associated with head size (p = 0.08) though a negative correlation with implantation time was noted (ρ = −0.35). When analyzed with taper damage scores, a correlation was not observed between head damage scores and HXLPE penetration rates (p = 0.51). Discussion:. The results of this study do not support the hypothesis that 36+ mm ceramic or CoCr femoral heads articulating on HXLPE liners are associated with increased risk of corrosion among HXLPE liners when compared with smaller diameter heads. A limitation of this study is the semi-quantitative scoring technique, heterogeneity of the retrieval collection and short implantation time of the larger diameter heads. Because corrosion may increase over time in vivo, longer-term follow-up, coupled with quantitative taper wear measurement, will better assess the natural progression of taper degradation in modern THA bearings

Aims

The aim of this study was to develop a novel computational model for estimating head/stem taper mechanics during different simulated assembly conditions.

Tapered fluted titanium stems are increasingly used for femoral revision arthroplasty. They are available in modular and non-modular forms. Modularity has advantages when the bone loss is severe, the proximal femur is mis shapen or the surgeon is unfamiliar with the implant, but it introduces the risk of fracture of the stem at the junction between it and the proximal body segment. For that reason, and while awaiting intermediate-term results of more recently introduced designs of this junction, non-modularity has attracted attention, at least for straightforward revision cases.

We review the risks and causes of fracture of tapered titanium modular revision stems and present an argument in favour of the more selective use of modular designs.

Cite this article: Bone Joint J 2016;98-B(1 Suppl A):50–3.

Aims. Revision total hip arthroplasty in patients with Vancouver type B3 fractures with Paprosky type IIIA, IIIB, and IV femoral defects are difficult to treat. One option for Paprovsky type IIIB and IV defects involves modular cementless, tapered, revision femoral components in conjunction with distal interlocking screws. The aim of this study was to analyze the rate of reoperations and complications and union of the fracture, subsidence of the stem, mortality, and the clinical outcomes in these patients. Methods. A total of 46 femoral components in patients with Vancouver B3 fractures (23 with Paprosky type IIIA, 19 with type IIIB, and four with type IV defects) in 46 patients were revised with a transfemoral approach using a modular, tapered, cementless revision Revitan curved femoral component with distal cone-in-cone fixation and prospectively followed for a mean of 48.8 months (SD 23.9; 24 to 112). The mean age of the patients was 80.4 years (66 to 100). Additional distal interlocking was also used in 23 fractures in which distal cone-in-cone fixation in the isthmus was < 3 cm. Results. One patient (2.2%) died during the first postoperative year. After six months, 43 patients (93.5%) had osseous, and three had fibrous consolidation of the fracture and the bony flap, 42 (91.3%) had bony ingrowth and four had stable fibrous fixation of the stem. No patient had radiolucency around the interlocking screws and no screw broke. One patient had non-progressive subsidence and two had a dislocation. The mean Harris Hip Score increased from of 57.8 points (SD 7.9) three months postoperatively to 76.1 points (SD 10.7) 24 months postoperatively. Conclusion. The 2° tapered, fluted revision femoral component with distal cone-in-cone-fixation, combined with additional distal interlocking in patients with bony deficiency at the isthmus, led to reproducibly good results in patients with a Vancouver B3 fracture and Paprosky type IIIA, IIIB, and IV defects with regard to union of the fracture, subsidence or loosening of the stem, and clinical outcomes. Cite this article: Bone Joint J 2024;106-B(4):344–351

INTRODUCTION

In theory, Finite Element Analysis (FEA) is an attractive method for elucidating the mechanics of modular implant junctions, including variations in materials, designs, and modes of loading. However, the credence of any computational model can only be established through validation using experimental data. In this study we examine the validity of such a simulation validated by comparing values of interface motion predicted using FEA with values measured during experimental simulation of stair-climbing.

Aims. Uncemented implants are now commonly used at reimplantation of a two-stage revision total hip arthoplasty (THA) following periprosthetic joint infection (PJI). However, there is a paucity of data on the performance of the most commonly used uncemented femoral implants – modular fluted tapered (MFT) femoral components – in this setting. This study evaluated implant survival, radiological results, and clinical outcomes in a large cohort of reimplantation THAs using MFT components. Methods. We identified 236 reimplantation THAs from a single tertiary care academic institution from September 2000 to September 2020. Two designs of MFT femoral components were used as part of an established two-stage exchange protocol for the treatment of PJI. Mean age at reimplantation was 65 years (SD 11), mean BMI was 32 kg/m. 2. (SD 7), and 46% (n = 109) were female. Mean follow-up was seven years (SD 4). A competing risk model accounting for death was used. Results. The 15-year cumulative incidence of any revision was 24%. There were 48 revisions, with the most common reasons being dislocation (n = 25) and infection (n = 16). The 15-year cumulative incidence of any reoperation was 28%. Only 13 revisions involved the fluted tapered component (FTC), for a 15-year cumulative incidence of any FTC revision of 8%. Only two FTCs were revised for aseptic loosening, resulting in a 15-year cumulative incidence of FTC revision for aseptic loosening of 1%. Stem subsidence ≥ 5 mm occurred in 2% of unrevised cases. All stems were radiologically stable at most recent follow-up. Mean Harris Hip Score was 69 (SD 20) at most recent follow-up. Conclusion. This series demonstrated that MFT components were durable and reliable in the setting of two-stage reimplantation THA for infection. While the incidence of aseptic loosening was very low, the incidence of any revision was 24% at 15 years, primarily due to dislocation and recurrent PJI. Cite this article: Bone Joint J 2024;106-B(5 Supple B):125–132

We report our experience of revision total hip replacement (THR) using the Revitan curved modular titanium fluted revision stem in patients with a full spectrum of proximal femoral defects. A total of 112 patients (116 revisions) with a mean age of 73.4 years (39 to 90) were included in the study. The mean follow-up was 7.5 years (5.3 to 9.1). A total of 12 patients (12 hips) died but their data were included in the survival analysis, and four patients (4 hips) were lost to follow-up. The clinical outcome, proximal bone regeneration and subsidence were assessed for 101 hips.

The mean Harris Hip Score was 88.2 (45.8 to 100) after five years and there was an increase of the mean Barnett and Nordin-Score, a measure of the proximal bone regeneration, of 20.8 (-3.1 to 52.7). Five stems had to be revised (4.3%), three (2.9%) showed subsidence, five (4.3%) a dislocation and two of 85 aseptic revisions (2.3%) a periprosthetic infection.

At the latest follow-up, the survival with revision of the stem as the endpoint was 95.7% (95% confidence interval 91.9% to 99.4%) and with aseptic loosening as the endpoint, was 100%. Peri-prosthetic fractures were not observed.

We report excellent results with respect to subsidence, the risk of fracture, and loosening after femoral revision using a modular curved revision stem with distal cone-in-cone fixation. A successful outcome depends on careful pre-operative planning and the use of a transfemoral approach when the anatomy is distorted or a fracture is imminent, or residual cement or a partially-secured existing stem cannot be removed. The shortest appropriate stem should, in our opinion, be used and secured with > 3 cm fixation at the femoral isthmus, and distal interlocking screws should be used for additional stability when this goal cannot be realised.

Cite this article: Bone Joint J 2014;96-B:889–95.

Introduction. Wear and corrosion between head and stem tapers of modular hip implants have recently been related to clinical failures, possibly due to high friction moments in poorly lubricated joints [1–2]. In-vivo measurements have revealed reversing joint friction moments in the hip during a gait cycle [3], which may foster relative motion between the modular components. Blood, soft tissue or bone debris at the taper interface during assembly can lead to decreased stability or increased stress concentrations due to non-uniform loading [4]. The purpose of this study is to investigate the influence of taper contamination and the assembly force on the seating characteristic of the head on the stem incorporating realistic reversing joint friction moments. Methods. Cobalt chrome heads (M-SPEC, 36mm, +1.5mm; n=5) were assembled on titanium femoral stems (Corail 12/14, both components Depuy Synthes; n=5) by quasistatic axial push-on forces (F=0.5kN, 1kN, 2kN). Heads were modified by milling a flat plane, to which the joint load was applied alternately to point A and point B for 20 cycles to provide reversing moments (heel-strike FA=1971N, MA=5.4Nm; toe-off FB=807N, MB=4.6Nm; Fig. 1). All 6 degrees of freedom of relative displacement between head and stem were determined in the unloaded state and after each loading cycle. A coordinate measurement machine (accuracy ±2µm) was used to determine the components positions. Pull-off forces were measured after the last loading cycle. Each taper was tested in pristine condition and then contaminated with a bone chip (1.7±0.2mg). Results. Contaminated tapers exhibited significantly larger seating than clean samples for all assembly forces (p<0.001, Fig. 2). Higher assembly forces led to decreased translation and rotation (p<0.001). Pull-off forces remained constant (F=890±99N) and independent of assembly force (p=0.303), or contamination condition (p=0.192). No further seating of the head on the stem taper was seen for the 20th load cycle. Discussion. This study shows that contamination, even in very small quantities, can increase initial translation and rotation, which could initiate corrosion. This can be countered, to some extent by applying sufficiently high assembly forces. It is noted that no further seating was measurable by the 20th loading cycle for any assembly condition but this does not rule out increased cyclic motion, particularly in contaminated interfaces [5]. The final pull-off forces were independent of the magnitude of the assembly force but might rather be related to the maximum joint load, suggesting that the assembly force should be at least as great as the maximum joint load. To view tables/figures, please contact authors directly

Aims. United Classification System (UCS) B2 and B3 periprosthetic fractures in total hip arthroplasties (THAs) have been commonly managed with modular tapered stems. No study has evaluated the use of monoblock fluted tapered titanium stems for this indication. This study aimed to evaluate the effects of a monoblock stems on implant survivorship, postoperative outcomes, radiological outcomes, and osseointegration following treatment of THA UCS B2 and B3 periprosthetic fractures. Methods. A retrospective review was conducted of all patients who underwent revision THA (rTHA) for periprosthetic UCS B2 and B3 periprosthetic fracture who received a single design monoblock fluted tapered titanium stem at two large, tertiary care, academic hospitals. A total of 72 patients met inclusion and exclusion criteria (68 UCS B2, and four UCS B3 fractures). Primary outcomes of interest were radiological stem subsidence (> 5 mm), radiological osseointegration, and fracture union. Sub-analysis was also done for 46 patients with minimum one-year follow-up. Results. For the total cohort, stem osseointegration, fracture union, and stem subsidence were 98.6%, 98.6%, and 6.9%, respectively, at latest follow-up (mean follow-up 27.0 months (SD 22.4)). For patients with minimum one-year of follow-up, stem osseointegration, fracture union, and stem subsidence were 97.8%, 97.8%, and 6.5%, respectively. Conclusion. Monoblock fluted stems can be an acceptable modality for the management of UCS B2 periprosthetic fractures in rTHAs due to high rates of stem osseointegration and survival, and the low rates of stem subsidence, and revision. Further research on the use of this stem for UCS B3 periprosthetic fractures is warranted to determine if the same conclusion can be made for this fracture pattern. Cite this article: Bone Jt Open 2023;4(8):551–558

Aims. Taper corrosion has been widely reported to be problematic for modular total hip arthroplasty implants. A simple and systematic method to evaluate taper damage with sufficient resolution is needed. We introduce a semiquantitative grading system for modular femoral tapers to characterize taper corrosion damage. Methods. After examining a unique collection of retrieved cobalt-chromium (CoCr) taper sleeves (n = 465) using the widely-used Goldberg system, we developed an expanded six-point visual grading system intended to characterize the severity, visible material loss, and absence of direct component contact due to corrosion. Female taper sleeve damage was evaluated by three blinded observers using the Goldberg scoring system and the expanded system. A subset (n = 85) was then re-evaluated following destructive cleaning, using both scoring systems. Material loss for this subset was quantified using metrology and correlated with both scoring systems. Results. There was substantial agreement in grading among all three observers with uncleaned (n = 465) and with the subset of cleaned (n = 85) implants. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. Cleaning changed the average scores marginally using the Goldberg criteria (p = 0.290); however, using the VGS, approximately 40% of the scores for all observers changed, increasing the average score from 4.24 to 4.35 (p = 0.002). There was a strong correlation between measured material loss and new grading scores. Conclusion. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. This system provides potential advantages for assessing taper damage without requiring specialized imaging devices. Cite this article: Bone Joint Res 2023;12(3):155–164

Introduction. Modular tapered implants have been suggested as the optimal treatment in patients with severe femoral bone loss undergoing revision total hip arthroplasty (THA). The purpose of this study is to describe minimum 2 year follow up of patients treated with modular tapered prostheses for Paprosky type IIIB and IV femoral bone loss in revision THA. Methods. 44 Consecutive patients with Paprosky type IIIB (23) or IV (21) femurs undergoing revision total hip arthroplasty to cementless modular tapered prostheses were studied. Harris Hip Scores were obtained prior to revision on all patients except those presenting with acute implant failure or periprosthetic fracture. 10 Patients were deceased within 2 years of surgery; the remaining 18 were followed for an average of 42 months (range 25-69 months). Clinical outcomes were measured using the Harris Hip Score, and radiographs were assessed for signs of stem loosening or subsidence >4mm. Results. No further revisions were required in patients who were deceased within 2 years. In those with >2 year follow up, there were 4 additional revisions: 1 for infection, 2 for instability, and 1 for periprosthetic fracture. In patients with surviving implants, the mean Harris Hip Score improved from 33 (range 11-49) pre-operatively to 77 (range 55-100), and there was no radiographic evidence of loosening or subsidence at time of final follow up. Conclusions. These outcomes support the use of modular tapered implants as a safe and effective option for revision arthroplasty of type IIIB and IV femurs

Introduction. Corrosion products from modular taper junctions are a potent source of adverse tissue reactions after THR. In an attempt to increase the area of contact and resistance to interface motion in the face of taper mismatches, neck trunnions are often fabricated with threaded surfaces designed to deform upon assembly. However, this may lead to incomplete contact and misalignment of the head on the trunnion, depending upon the geometry and composition of the mating components. In this study we characterized the effect of different femoral head materials on the strength and area of contact of modular taper constructs formed with TiAlV trunnions. Materials and Methods. Three groups of 36mm femoral heads (CoCr, Biolox ceramic; Oxinium) and matching Ti-6Al-4V rods with 12/14 trunnions were selected for use in this study. The surface of each trunnion was coated with a 20nm layer of gold applied by sputter-coating in vacuo. Each head/trunnion pair was placed in an alignment jig and assembled with a peak axial impaction force of 2000N using a drop tower apparatus. After assembly, each taper was disassembled in a custom apparatus mounted in a mechanical testing machine (Bionix. MTS. After separation of the components, the surface of each trunnion was examined with backscattered electron microscopy to reveal the area of disruption of the original gold-coated surface. Images encompassing the entire surface of the trunnion were collected and quantified by image processing. Results. The force required to disassemble the Oxinium and Biolox heads from their mating tapers were 2153±104N and 2200±145N, respectively (p-=0.5359). In contrast, the average disassembly force of the CoCr-TiAlV couples was 47% less (1165±156N, p<0.0001). Direct contact between the trunnion and the femoral head was only present over 3.7±0.3% of the nominal surface area of the modular junctions and was limited to the crests of the threads. Contact area did not vary as a function of head composition (p>0.4). However, there were noticeable differences in terms of the distribution of contact between the head and the trunnion. CoCr heads typically had large spans of noncontact immediately below the apex of the taper and opposite each other at the trunnion base. Biolox heads tended to have complete contact at the apex but only extended down 30% of the taper and intermittently at the base. Oxinium heads had comparable complete contact areas to Biolox at the apex but unlike Biolox and CoCr, a uniform band of contact existed at the base. Conclusions. CoCr heads provided only half the resistance to disassembly of Biolox and Oxinium heads. The total area of direct head-trunnion contact is minimal and is not affected by head composition. The heads studied had characteristic patterns of interface contact. This may be due to variations in the geometry of the bores within each head combined with cocking of the femoral head during seating as the thread peaks are being deformed. For any figures or tables, please contact authors directly