Objectives. An ongoing prospective study to investigate failing metal-on-metal hip prostheses was commenced at our centre in 2008. We report on the results of the analysis of the first consecutive 126 failed mated total hip prostheses from a single manufacturer. Methods. Analysis was carried out using highly accurate coordinate measuring to calculate volumetric and linear rates of the articular bearing surfaces and also the surfaces of the taper junctions. The relationship between taper wear rates and a number of variables, including bearing diameter and orientation of the acetabular component, was investigated. Results. The measured rates of wear and distribution of material loss from the taper surfaces appeared to show that the primary factor leading to taper failure is the increased lever arm acting on this junction in contemporary large-diameter metal-on-metal hip replacements. Conclusions. Our analysis suggests that varus stems, laterally engaging taper systems and larger head diameters all contribute to taper failure

Objectives. This study aimed to characterise and qualitatively grade the severity of the corrosion particles released into the hip joint following taper corrosion. Methods. The 26 cases examined were CoC/ABG Modular (n = 13) and ASR/SROM (n = 13). Blood serum metal ion levels were collected before and after revision surgery. The haematoxylin and eosin tissue sections were graded on the presence of fibrin exudates, necrosis, inflammatory cells and corrosion products. The corrosion products were identified based on visible observation and graded on abundance. Two independent observers blinded to the clinical patient findings scored all cases. Elemental analysis was performed on corrosion products within tissue sections. X-Ray diffraction was used to identify crystalline structures present in taper debris. Results. The CoC/ABG Modular patients had a mean age of 64.6 years (49.4 to 76.5) and ASR/SROM patients had a mean age of 58.2 years (33.3 to 85.6). The mean time in situ for CoC/ABG was 4.9 years (2 to 6.4) and ASR/SROM was 6.1 years (2.5 to 8.1). The blood serum metal ion concentrations reduced following revision surgery with the exception of Cr levels within CoC/ABG. The grading of tissue sections showed that the macrophage response and metal debris were significantly higher for the ASR/SROM patients (p < 0.001). The brown/red particles were significantly higher for ASR/SROM (p < 0.001). The taper debris contained traces of titanium oxide, chromium oxide and aluminium nitride. Conclusion. This study characterised and qualitatively graded the severity of the corrosion particles released into the hip joint from tapers that had corrosion damage. Cite this article: S. Munir, R. A. Oliver, B. Zicat, W. L. Walter, W. K. Walter, W. R. Walsh. The histological and elemental characterisation of corrosion particles from taper junctions. Bone Joint Res 2016;5:370–378. DOI: 10.1302/2046-3758.59.2000507

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

Taper corrosion and fretting have been associated with oxide layer abrasion and fluid ingress that contributes to adverse local tissue reactions with potential failure of the hip joint replacement. [1,2]. Both mechanisms are considered to be affected by the precise nature of the taper design. [3]. Indeed relative motion at the taper interface that causes fretting damage and wear effects, such as pistoning and rocking, have been described following analysis of implants at retrieval. [4,5]. However, there is much less reported about the mechanisms that allow the fluid ingress/egress at the taper interface which would drive corrosion. Thus the aim of the present study was to investigate the effect of trunnion design on the gap opening and taper relative motions under different load scenarios and taper designs. A 3-D finite element model of a 40mm CoCr modular femoral head and a Ti6Al4V trunnion was established in Abaqus CAE/2018. Femoral head and trunnion geometries were meshed with an element (C3D8) size of 0.17mm. Tapers were assembled by simulating a range of impact forces (AF); taper interface behaviour was evaluated under physiological forces and frictional moments simulated during walking activity. [6]. , assuming different coefficients of friction (CF), Figure 1. The output involved the total and normal relative motion of the surfaces at the taper interface. The model predicted for a taper mismatch of 0.36° which, when combined with an assembly force of 2kN, generated the largest taper gap opening (59.2mm) during walking, Figure 2. In all trunnion designs the largest normal relative motion coincided with heel strike in the gait cycle (0–5%). The taper gap and normal relative motions were related to the initial taper lock area. Furthermore, the direction of the total motion was different in all three taper mismatches, with a shift in the direction towards the normal of the surface as the taper mismatch increased, Figure 3. By contrast, the direction of the normal relative motions did not change with different trunnion designs. Contact patterns were asymmetrical and contact areas varied throughout the walking activity; contact pressure and the largest taper gap were located on the same side of the taper, suggesting toggling of the trunnion. The relationship between taper gap opening and initial taper lock contact area suggests that the taper contact area functions as a fulcrum in a lever mechanism. Large taper mismatches create larger relative motions that will not only create more wear and fretting damage but also larger normal relative motions. This may allow fluid ingress into the taper interface and/or the egress of fluid along with any metal wear particles into the body. This increased understanding of the taper motion will result in improved designs and ultimately taper performance. For any figures or tables, please contact the authors directly

Introduction. Hip stem taper wear and corrosion is a multifactorial process involving mechanical, chemical and biological damage modes. For the most cases it seems likely that the mechanically driven fretting wear is accompanied by other damage modes like pitting corrosion, galvanic corrosion or metal transfer. Recent retrieval studies have reported that the taper surface topography may affect taper damage resulting from fretting and corrosion [1]. Therefore, the current study aimed to examine effects of different taper topography parameters and material combinations on taper mechanics and results regarding wear and corrosion have been investigated. Materials and Methods. Combined experimental and numerical studies were conducted using titanium, cobalt-chromium and stainless steel generic tapers (Figure1). Uniaxial tensile tests were performed to determine the mechanical properties of the materials examined. For the taper studies macro-geometry of ceramic ball heads (BIOLOX. ®. delta) and tapers were characterized using a coordinate measuring machine, and assembly experiments according to ISO7206-10 were conducted up to 4kN. Before and after loading, taper subsidence was quantified by assembly height measurements. Taper micro-geometry, taper surface deformation, and contact area were determined by profilometry. Initial numerical studies determined coefficients of friction for the three material combinations. Macro- and micro-geometries of the tapers were modelled, and taper subsidence and assembly load served as boundary conditions. Further studies used simplified models to examine effects of varying profile depths and angular gaps on surface deformation, taper subsidence, contact area, engagement length and pull-off force. Results. Largest coefficient of friction and pull-off forces were calculated for steel (µ=0.32), cobalt-chromium revealed the lowest with µ=0.18. Titanium showed largest deformations and taper subsidence throughout all calculations (Figure2, Figure3). Taper subsidence, engagement length and deformations increased with increasing profile depth while contact area decreased. Pull-off forces were almost constant for different profile depths while they increased for increasing angular gaps. Taper subsidence and deformations also increased with increasing angular gap while engagement length decreased and contact area almost remained constant. Discussion. In order to decrease wear and corrosion micromotions should be minimized. Therefore, smaller angular gaps and smaller profile depths seems to be beneficial since deformation and taper subsidence are reduced. Literature data confirmed the results for different angular gaps showing that a larger angular gap is associated with larger amounts of micromotion and wear [2, 3]. Additionally, larger angular gaps and larger profile depths result in larger plastic deformation facilitating subsurface crack initiation and propagation. A large angular gap may also facilitate particle release [4]. Larger pull-off forces can indicate larger resistance against micromotion. Therefore, steel may tend to later develop fretting-corrosion in situ. However, among the metals examined steel also showed the largest equivalent plastic strain. This study is limited to pairings involving ceramic heads. These can help mitigating fretting corrosion resulting from micromotion between ball head and cobalt-chromium or titanium alloy tapers [5]. However, future studies will include other ball head materials. In conclusion, this study showed that taper surface topography affects taper mechanics and is important in terms of wear and corrosion

Introduction. Taper corrosion and fretting has been identified to be a major problem in total hip replacement during the past years. Taper design and manufacturing are not been standardised, and therefore it can be assumed that the tapers vary among different implant manufacturers. This can lead to variable contact situations and stresses in the taper junction depending on the combination. It can be assumed that the taper strength will influence the occurrence and magnitude of micromotions which are known to influence corrosion. Therefore, the aim of this study was to assess the influence of the taper angle clearance on the taper connection strength. Material & Methods. For the investigation stem dummys with different taper angles were used that were manufactured from titanium alloy. The stem dummys were combined with ceramic heads with identically taper angles. Out of this, there were seven groups ranging from distal contact through full contact up to proximal contact. Three samples were used in each group and five repetitive measurements per samples were performed. All taper connections were impacted with different forces (1 kN, 3 kN, 6 kN and 10 kN) and afterwards an increasing torque was applied until the head disconnected. The maximal torque off value was used as a measure for the taper strength. Results. A greater taper clearance leads to a higher taper strength (Fig. 1). However, this effect is also influenced by the assembly force and becomes even stronger with higher assembly forces. When comparing a distal, full and proximal contact situation the full contact shows the lowest taper strength, whereas the distal contact situation leads to the highest taper strength. Discussion and conclusion. The design variability in taper connections influences its strength. A smaller contact area leads to higher local contact pressure. It is assumed that this increases local plastic deformations of the surface structure which is beneficial for this self-locking mechanism of the junction. However, the effect of the assembly force seems to overcome the effect of the taper clearance. Therefore taper junctions should be firmly connected in total hip replacements. Furthermore, surgeons should be aware that in a clinical case of a Mix & Match the taper strength may be reduced depending on the combined components. For figures/tables, please contact authors directly.

Introduction. Previous studies of retrieved CoCr alloy femoral heads have identified imprinting of the stem taper surface features onto the interior head bore, leading researchers to hypothesize that stem taper microgrooves may influence taper corrosion. However, little is known about the role of stem taper surface morphology on the magnitude of in vivo corrosion damage. We designed a matched cohort retrieval study to examine this issue. Methods. From a multi-institutional retrieval collection of over 3,000 THAs, 120 femoral head-stem pairs were analyzed for evidence of fretting and corrosion using a visual scoring technique based on the severity and extent of fretting and corrosion damage observed at the taper. A matched cohort design was used in which 60 CoCr head-stem pairs with a smooth stem taper were matched with 60 CoCr head-stem pairs having a micro-grooved surface, based on implantation time, flexural rigidity, apparent length of taper engagement, and head size. This study was adequately powered to detect a difference of 0.5 in corrosion scores between the two cohorts, with a power of 82% and 95% confidence. Both cohorts included CoCr and Ti-6-4 alloy femoral stems. A high precision roundness machine (Talyrond 585, Taylor Hobson, UK) was used to measure surface morphology and categorize the stem tapers into smooth vs. micro-grooved categories. Fretting and corrosion damage at the head/neck junction was characterized using a modified semi-quantitative adapted from the Goldberg method by three independent observers. This method separated corrosion damage into four visually determined categories: minimal, mild, moderate and severe damage. Results. Mild to severe damage (Fretting Corrosion Score ≥ 2) was observed in 75% of the 120 CoCr femoral heads (78% of the heads mated with micro-grooved stems (47/60), Fig. 1A) and 72% of the heads mated with smooth stems (43/60, Fig 1B). Fretting and corrosion damage was not significantly different between the two cohorts when evaluated at the CoCr femoral head bore (p =0.105, Mann Whitney test, Fig. 2A) or the male stem tapers (p =0.428, Fig. 2B). No implant or patient factors were associated with fretting corrosion; corrosion scores were not significantly associated with stem alloy in the two cohorts (p=0.669, Mann-Whitney test). Discussion. The results of this matched cohort retrieval study do not support the hypothesis that taper surfaces with micro-grooved stems exhibit increased in vivo fretting corrosion. We accounted for implant, patient, and clinical factors that may influence in vivo taper corrosion with the matched cohort design and by post hoc statistical analyses. However, this study is limited by the semi-quantitative method used for evaluating damage in these components. Therefore, additional research will be necessary to quantify the volume of metal release from these two cohorts. To view tables/figures, please contact authors directly

Aims. The aim of this study was to evaluate the suitability of the tapered cone stem in total hip arthroplasty (THA) in patients with excessive femoral anteversion and after femoral osteotomy. Methods. We included patients who underwent THA using Wagner Cone due to proximal femur anatomical abnormalities between August 2014 and January 2019 at a single institution. We investigated implant survival time using the endpoint of dislocation and revision, and compared the prevalence of prosthetic impingements between the Wagner Cone, a tapered cone stem, and the Taperloc, a tapered wedge stem, through simulation. We also collected Oxford Hip Score (OHS), visual analogue scale (VAS) satisfaction, and VAS pain by postal survey in August 2023 and explored variables associated with those scores. Results. Of the 58 patients (62 hips), two (two hips) presented with dislocation or reoperation, and Kaplan-Meier analysis indicated a five-year survival rate of 96.7% (95% CI 92.4 to 100). Mean stem anteversion was 35.2° (SD 18.2°) for the Taperloc stem and 29.8° (SD 7.9°) for the Wagner Cone stem; mean reduction from Taperloc to Wagner Cone was 5.4° (SD 18.8°). Overall, 55 hips (52 patients) were simulated, and the prevalence of prosthetic impingement was lower for the Wagner Cone (5.5%, 3/55) compared with the Taperloc (20.0%, 11/55) stem, with an odds ratio of 0.20 (p = 0.038). Among the 33 respondents to the postal survey (36 hips), the mean scores were VAS pain 10.9, VAS satisfaction 86.9, and OHS 44.7. A multivariable analysis revealed that reduction of stem anteversion from Taperloc to Wagner Cone was more favourable for VAS pain (p = 0.029) and VAS satisfaction (p = 0.002). Conclusion. The mid-term survival rate for THA using the Wagner Cone stem was high, which may be supported by a reduction in prosthetic impingement. The reduction in excessive stem anteversion by using a tapered cone stem was associated with reduced pain and increased patient satisfaction. Cite this article: Bone Jt Open 2024;5(10):858–867

Introduction. The femoral head/stem taper modular junction has several advantages; it also has the potential to result in fretting [1]. Stability of the taper junction is critical in reducing the risk associated with fretting. The purpose of this test was to measure the strength of various commercially available head-stem taper combinations under torsional loads to determine the effect of taper geometry and material on the strength of this taper junction. Methods and Materials. CoCr femoral heads were tested with trunnions that were machined with both a large and small taper geometry, replicating commercially available stem taper designs, V40 (small) and C (large) (Table-1, Stryker Orthopaedics, NJ). The femoral heads were assembled onto the trunnions with a 2 kN axial force. A multi-axis test frame (MTS Corp, MN) was used to test the head-trunnion combination by dynamically loading with a torque of ± 5Nm and a constant axial load of 2450N for 1000 cycles at 1.5 Hz (Figure 1). Samples were submerged in 25% diluted Alpha Calf Fraction Serum (Hyclone, UT). Upon completion of the dynamic test, a static torque to failure test was performed where the axial force of 2450N was maintained and the trunnion was rotated to 40° at a rate of 3°/sec. The torque required to rotate the trunnion by 1° was determined for each specimen. Also, the torsional resistance, defined as change in torque/change in angle in the linear region of the torque-angular displacement data curve, was calculated for all the specimens. A limitation associated with the static test was that at 1° rotation it was difficult to differentiate between rotation of the trunnion inside the femoral head and physical twisting of the trunnion. Specimen groups were compared with a single-factor ANOVA test and a Tukey post hoc test at 95% confidence level. Results. The dynamic test did not generate any rotation between the trunnion and the head. The difference in torque at 1° of rotation and torsional resistance was not statistically significant between any two specimen groups (Table 2, p > 0.05). Discussion. The results of this study indicate that neither taper surface area nor material have a significant effect on the strength of the taper junctions under torsional loads, within the range of designs and material combinations tested. Alternatively, the results suggest that taper junctions are appropriately designed to eliminate the effects of taper surface area and material on their strength. Previously in a similar test setup, it was determined that the average torque generated with CoCr femoral heads articulating against a press-fit acetabular shell/polyethylene liner assembly is 3.86 Nm [3]. In the present study, the trunnion-head combinations were cyclically loaded with 5 Nm of torque for 1000 cycles and the strength of the taper junction upon completion of the static test was at minimum six-times greater than the torque generated at the articulating surfaces

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

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

Background. Complications of metal-on-metal hip resurfacing, leading to implant failure, include femoral notching, neck fracture, and avascular necrosis. Revision arthroplasty options include femoral-only revision with a head, however mis-matching radial clearance could accelerate metal ion release. Alternatively, revision of a well-fixed acetabular component could lead to further bone loss, complicating revision surgery. We have developed a ceramic hip resurfacing system with a titanium-ceramic taper junction; taking advantage of the low frictional torque and wear rates that ceramic affords. Taking a revision scenario into account, the ceramic head has a deep female taper for the resurfacing stem, but also a superficial tapered rim. Should revision to this resurfacing be required, any femoral stem with a 12/14 taper can be implanted, onto which a dual taper adaptor is attached. The outer diameter of the taper adaptor then becomes the male taper for the superficial taper of the ceramic head; ultimately allowing retention of the acetabular component. In an in-vitro model, we have compared the fretting corrosion of this taper adaptor to existing revision taper options: a titanium-cobalt chrome (Ti-CoCr) taper junction, and a titanium-titanium sleeve-ceramic (Ti-Ti-Cer) taper junction. Methods. To simulate gait, sinusoidal cyclical loads between 300N-2300N, at a frequency of 3Hz was applied to different neck offsets generating different bending moments and torques. Bending moment and frictional torque were tested separately. An electrochemical assessment using potentiostatic tests at an applied potential of 200mV, was used to measure the fretting current (μA) and current amplitude (μA). In a short term 1000 cycle test with bending moment, four neck lengths (short to x-long) were applied. For frictional torque, four increments of increasing torque (2-4-6-8Nm) were applied. In a long-term test using the taper adaptor, the combination of worst-case scenario of bending and torque were applied, and fretting currents measured every million cycles, up to 10 million cycles. Results. Short-term test: When adjusting bending moment the taper adaptor displayed equivalent fretting currents for the short and medium neck lengths. Using the long neck the taper adaptor displayed a higher fretting current, though this was not significant (Kruskal-Wallis test). However, using the X-Long adaptor the fretting current was significantly higher than the other tapers (Fig. 1). Across the range of frictional torques, the taper adaptor displayed equivalent fretting currents to the Ti-CoCr single taper. The Ti-Ti-Cer displayed the lowest fretting currents but this was not significant when compared to the other combinations (Fig. 2). Long-term test: combining the worst case bending (X-Long) and torque (8Nm) showed consistent fretting currents and current amplitudes across 10 million cycles, with no significant variance of the median values (Fig. 3). Conclusion. Electro-chemical testing has highlighted caution if revision arthroplasty is performed using the X-Long taper adaptor. However for shorter neck lengths, fretting corrosion is comparable to existing revision tapers. The LIMA ceramic resurfacing arthroplasty is an integrated system and can be safely revised to a conventional hip system using a dual taper head, and taper adaptor

Aims. This study investigates head-neck taper corrosion with varying head size in a novel hip simulator instrumented to measure corrosion related electrical activity under torsional loads. Methods. In all, six 28 mm and six 36 mm titanium stem-cobalt chrome head pairs with polyethylene sockets were tested in a novel instrumented hip simulator. Samples were tested using simulated gait data with incremental increasing loads to determine corrosion onset load and electrochemical activity. Half of each head size group were then cycled with simulated gait and the other half with gait compression only. Damage was measured by area and maximum linear wear depth. Results. Overall, 36 mm heads had lower corrosion onset load (p = 0.009) and change in open circuit potential (OCP) during simulated gait with (p = 0.006) and without joint movement (p = 0.004). Discontinuing gait’s joint movement decreased corrosion currents (p = 0.042); however, wear testing showed no significant effect of joint movement on taper damage. In addition, 36 mm heads had greater corrosion area (p = 0.050), but no significant difference was found for maximum linear wear depth (p = 0.155). Conclusion. Larger heads are more susceptible to taper corrosion; however, not due to frictional torque as hypothesized. An alternative hypothesis of taper flexural rigidity differential is proposed. Further studies are necessary to investigate the clinical significance and underlying mechanism of this finding. Cite this article: Bone Jt Open 2021;2(11):1004–1016

Aims. When performing revision total hip arthroplasty using diaphyseal-engaging titanium tapered stems (TTS), the recommended 3 to 4 cm of stem-cortical diaphyseal contact may not be available. In challenging cases such as these with only 2 cm of contact, can sufficient axial stability be achieved and what is the benefit of a prophylactic cable? This study sought to determine, first, whether a prophylactic cable allows for sufficient axial stability when the contact length is 2 cm, and second, if differing TTS taper angles (2° vs 3.5°) impact these results. Methods. A biomechanical matched-pair cadaveric study was designed using six matched pairs of human fresh cadaveric femora prepared so that 2 cm of diaphyseal bone engaged with 2° (right femora) or 3.5° (left femora) TTS. Before impaction, three matched pairs received a single 100 lb-tensioned prophylactic beaded cable; the remaining three matched pairs received no cable adjuncts. Specimens underwent stepwise axial loading to 2600 N or until failure, defined as stem subsidence > 5 mm. Results. All specimens without cable adjuncts (6/6 femora) failed during axial testing, while all specimens with a prophylactic cable (6/6) successfully resisted axial load, regardless of taper angle. In total, four of the failed specimens experienced proximal longitudinal fractures, three of which occurred with the higher 3.5° TTS. One fracture occurred in a 3.5° TTS with a prophylactic cable yet passed axial testing, subsiding < 5 mm. Among specimens with a prophylactic cable, the 3.5° TTS resulted in lower mean subsidence (0.5 mm (SD 0.8)) compared with the 2° TTS (2.4 mm (SD 1.8)). Conclusion. A single prophylactic beaded cable dramatically improved initial axial stability when stem-cortex contact length was 2 cm. All implants failed secondary to fracture or subsidence > 5 mm when a prophylactic cable was not used. A higher taper angle appears to decrease the magnitude of subsidence but increased the fracture risk. The fracture risk was mitigated by the use of a prophylactic cable. Cite this article: Bone Jt Open 2023;4(7):472–477

Periprosthetic femoral fractures (PFFs) remain a major concern following cementless total hip arthroplasty (THA). This study aimed to evaluate the association between different types of cementless tapered stems and the risk of postoperative PFF. A retrospective review of primary THAs performed at a single center from January 2011 to December 2018 included 3,315 hips (2,326 patients). Cementless stems were classified according to their design geometry using the system proposed by Radaelli et al. The incidence of PFF was compared between flat taper porous-coated stems (type A), rectangular taper grit-blasted stems (type B1), and quadrangular taper hydroxyapatite-coated stems (type B2). Multivariate regression analyses were performed to identify independent factors related to PFF. The mean follow-up duration was 61 months (range, 12‒139 months). Overall, 45 (1.4%) postoperative PFFs occurred. The incidence of PFF was significantly higher in type B1 stems than in type A and type B2 stems (1.8 vs. 0.7 vs. 0.7%; P=0.022). Additionally, more surgical treatments (1.7 vs. 0.5 vs. 0.7%; P=0.013) and femoral revisions (1.2 vs. 0.2 vs. 0%; P=0.004) were required for PFF in type B1 stems. After controlling for confounding variables, older age (P<0.001), diagnosis of hip fracture (P<0.001), and use of type B1 stems (P=0.001) were significant factors associated with PFF. Type B1 rectangular taper stems were found to have higher risks for postoperative PFF and PFF requiring surgical management than type A and type B2 stems in THA. Femoral stem geometry should be considered when planning for cementless THA in elderly patients with compromised bone quality

Aims. The purpose of this study is to report our updated results at a minimum follow-up of 30 years using a first generation uncemented tapered femoral component in primary total hip arthroplasty (THA). Methods. The original cohort consisted of 145 consecutive THAs performed by a single surgeon in 138 patients. A total of 37 patients (40 hips) survived a minimum of 30 years, and are the focus of this review. The femoral component used in all cases was a first-generation Taperloc with a non-modular 28 mm femoral head. Clinical follow-up at a minimum of 30 years was obtained on every living patient. Radiological follow-up at 30 years was obtained on all but four. Results. Seven femoral components (18%) required revision, and none for septic loosening. Four well fixed stems were removed during acetabular revision and three were revised for late infection. One femoral component (3%) was loose by radiological criteria. The mean Harris Hip Score improved from 47 points (SD 4.62) preoperatively to 83 points (SD 9.27) at final follow-up. With revision for any reason as the endpoint, survival of the femoral component was 80% (95% confidence interval (CI) 61% to 90%) at 32 years. With revision for aseptic loosing femoral component, survival was 99% (95% CI 93% to 99%). Conclusion. With regards to aseptic loosening, the Taperloc femoral component provides excellent fixation at a mean follow-up of 32 years. Cite this article: Bone Jt Open 2023;4(2):79–86

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

Taper corrosion and Trunionnosis are recognized as a major complication of hip replacement surgery presenting in a variety of clinical manifestations commonly referred to as Adverse Local Tissue Reactions. Metal debris is produced through Mechanically Assisted Crevice Corrosion with several implicating factors including mixed alloy components, taper design, head offset, femoral head size, and taper impaction techniques (including magnitude of force, control of alignment and environmental factors). Our project has focused singularly on taper impaction techniques and surgeon controlled factors, as we believe the process of head impaction unto a trunnion is non-standardized, which often times dooms the trunionn to failure. We have contemplated a standardization process, such that given the right tool, the surgeon can control the quality of the taper interlock, which may produce a “cold weld” or perfect taper interlock, eliminate micro motion, mechanically assisted crevice corrosion, and trunionnosis. We have considered four specific problems with current head to trunionn impaction techniques: 1. The magnitude of applied force is uncontrolled, haphazard, and non-standardized. 2. Non-axial application of force is the norm, which produces canting, leading to micro-motion and tribocorrosion. 3. The transfer of energy from the head to the trunionn interface is highly inefficient, such that the energy produced by the surgeon is mostly dissipated in a non-constrained system. 4. No in vitro studies exist to guide surgeons as to the magnitude of force required for a proper interlock. Regardless of the design, including taper angles, larger heads, offset heads, mixed alloy components, shorter and slimmer trunionns there is a widespread problem with the process of head impaction onto the trunionn and the engagement of the modular taper interface that dooms the trunionn interface to failure. The deficiencies noted in current techniques are addressed with a simple tool and minor modification of the femoral stem. We present a new concept/apparatus for head to trunionn taper assembly that fully controls the magnitude and direction of assembly force within a constrained, dry and contaminant free environment. This tool allows application of a perfectly axial and high insertional forces without risk of damage to the femoral stem/bone interface to obtain a cold weld and perfect taper interlock with no chance for canting, micro motion and tribocorrosion. The concept has been verified through several prototypes and can be adopted in order to standardize the process of taper assembly, making this procedure independent of surgeon skill and strength, and minimizing the incidence of trunionnosis

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

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. 1. 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. 2. 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 strength. Additionally, the taper surface finish—micro-grooves—has been shown to affect taper interference strength and may be influenced by assembly method. 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 FEA model representative of a CoCrMo femoral head taper and Ti6Al4V stem taper was created using median geometrical measurements taken from over 100 retrieved implants. 3. Surface finish—micro-grooves—of the head/stem taper were modeled using a sinusoidal function with amplitude and period corresponding to retrieval measurements of micro-groove height and spacing, respectively. Two stem taper micro-groove geometries— “rough” and “smooth”—were modeled corresponding to the median and 5. th. percentile height and spacing measurements from retrievals. All models had a 3' (0.05°), proximal-locked angular mismatch between the tapers. To simulate implant assembly during surgery, multiple dynamic loads (4kN, 8kN, and 12kN) were applied to the femoral head taper in a sequence of one or three 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 × 2 assembly sequences × 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 (Figure 3). 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 tables or figures, please contact the authors directly