Introduction. There have been increased concerns with trunnion fretting and corrosion and adverse local tissue reactions (ALTR) in total hip arthroplasty. We report on 11 catastrophic trunnion failures associated with severe ALTR requiring urgent revision arthroplasty. Methods. We retrospectively reviewed 10 patients with gross trunnion failure (n=11) and an additional 3 patients with impending trunnion failure. Results. All patients presented to the emergency department with severe pain, an inability to bear weight, and dramatic radiographs demonstrating implant failure. Patients were an average of 7.8 years from the initial index procedure. Implants were a cementless component with metal on polyethylene bearing from a single manufacturer with a 36mm femoral head size and a range of extended offset of 2.5 to 5.5 and neck length of +0 (n=1), +5 (n=5), and +10 (n=5). The implant was used during a limited time (2.5 years) by single surgeon in our practice using a posterior approach, with the last implant placed 7 years ago. Prior to revision, serum cobalt levels were elevated, typically more than chromium levels. Radiographs demonstrated failure of the implant with a dissociation of the head from the taper and large radiolucent fluid collections from the metal debris (Fig 1). Intraoperative findings and magnetic resonance imaging confirmed a diagnosis of ALTR with loss of abductors, and severe material loss from the taper (Fig 2). We estimate a conservative incidence of catastrophic trunnion failure in our series to be 2.2% (n = 636 total implanted). A femoral revision with a modular Wagner stem was performed, and when necessary the acetabulum was revised secondary to destruction of the locking mechanism from mechanical wear. Discussion and Conclusion. ALTR can occur in patients with catastrophic failure of their trunnion. Radiographs are dramatic. Serum metal ion levels and magnetic resonance imaging is comparable to adverse local tissue reaction in metal on metal bearing surfaces, corrosion at the head neck taper, and corrosion of dual modular taper stems. The initiating events leading to this mechanism of trunnion failure is unknown. We observed trunnion failure at large head sizes and at increased femoral head offsets. Other groups have reported an association of trunnion failure at increased neck length and head size with a variety of manufacturers. Based on our experience, we have been able to identify impending failure based on subtle radiographic criteria and elevated metal ion levels. A failure rate of 2% at 7.8 years is non-trivial. Impending trunnion failure should be considered as a possible diagnosis in a painful total hip arthroplasty with unknown etiology. Serum metal ion levels and magnetic resonance imaging should be obtained as part of the initial evaluation

Introduction:. The addition of neck-stem modularity of femoral components allowed for increased versatility in controlling stability, head center, and limb length in total hip arthroplasty (THA). Recent reports of neck-stem corrosion, complicated by adverse local tissue reaction, have raised concern and prompted further patient evaluation for revision arthroplasty. Methods:. This was a single center, retrospective case series of thirteen hips in twelve patients. The cohort included eight women and four men, with an average age of 69.5 years (range 50–82), who underwent primary THA with a dual-taper femoral component with a titanium alloy stem, cobalt-chromium (CoCr) alloy modular neck and CoCr alloy head. Patients were followed an average of 34.3 months postsurgical (range 24–38.5 months). Each patient underwent serologic studies including metal ion levels, and Metal Artifact Reduction Sequence (MARS) magnetic resonance imaging (MRI) or Ultrasound. All patients were then referred for fluoro-assisted hip aspiration. Four patients underwent revision surgery. Results:. Ten of thirteen hips were symptomatic at the time of evaluation. ESR and CRP were normal in all patients. Serum Cobalt was elevated in 10/12 patients, with an average serum Cobalt level 4.16 mcg/L (range 1.7–9.4). Serum Chromium levels were normal in all patients. MRI was completed in eleven of twelve patients, with abnormal findings consistent with adverse local tissue reaction in nine hips. Three hips were normal by MRI. One patient had an abnormal ultrasound. Hip aspirations were positive in nine hips, negative in three, and indeterminate in one. Asymptomatic hips (3/13) all had elevated cobalt levels, and 2/3 had positive MRI and aspirates. One patient had a normal MRI and a negative aspirate. Of ten symptomatic hips, eight had elevated cobalt. 7/10 had an abnormal MRI, 2/10 a normal MRI, and 1 abnormal Ultrasound. 5/10 had aspirates that were consistent with the MRI. One aspirate was indeterminate. Four symptomatic patients had discrepancies between MRI findings and aspiration (negative MRI with positive aspirate, or vice versa); one patient had normal labs and MRI, but a positive aspirate, and was noted to have extensive adverse local tissue reaction at revision. Discussion:. Patients with dual-taper femoral stems are at risk of neck-stem corrosion and adverse local tissue reactions. The workup of these patients should include serologic studies as well as advanced imaging with MRI or Ultrasound. Hip aspiration may be a useful adjunct in identifying underlying soft tissue destruction in patients with normal or indeterminate labs or advanced imaging

Introduction. Corrosion at the modular junction of the femoral component in total hip arthroplasty (THA) was considered as a cause of adverse local tissue reaction in recent years. We reported three adverse local tissue reaction cases after total hip arthroplasty using the same modular neck stem in this study. Materials and Methods. We have been essentially using the same titanium modular neck stem system and the same combination bearing surface of 26mm cobalt chromium (CoCr) head and highly cross linked polyethylene line for primary total hip arthroplasty since November 2009. Three female showed adverse local tissue reaction and had additional surgical treatment after the THA. Results. Two patients showed asymptomatic focal osteolysis on X-ray at the Gruen zone 1 around three years after the THA (one case also showing pseudo tumor around lessor trochanter). One patient presented symptomatic deep vein thrombosis (DVT) suddenly four years after the surgery and was detected massive pseudo tumor around the hip in MRI. High serum cobalt level was detected in two pseud tumor cases (9.3 ng/ml in DVT case, 5.0 ng/ml in an osteolysis case). The patients had debridement of pseudo tumor and osteolysis. The 26mm CoCr head was replaced a delta ceramic head with a new neck and liner. Two osteolysis cases were grafted allogenic bone chips. Pathology specimens showed tissue necrosis. All retrieved head and neck component showed some corrosion only at the modular of head neck junction. High level of cobalt (2.43 mg/100g) and chromium (4.60 mg/100g) were detected in necrotic tissue of DVT case by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry) analysis. Discussion and Conclusion. This study showed adverse local tissue reaction could occur in spite of using small metal head and polyethylene bearing secondary to corrosion at the taper. It is thought that head neck junction corroded due to mechanically assisted crevice corrosion. An incidence of adverse local tissue reaction of this titanium modular stem might be lesser 0.2% (3/2600 over) in our institute. However, we began to stat new combination of bearing surfaces, ceramic head and polyethylene liner, even so extremely low incidence of adverse local tissue reaction derived from cobalt chromium alloy

Introduction. Neck-stem corrosion has been associated with Adverse Local Tissue Reaction (ALTR) in dual-taper femoral stems. Several diagnostic tests, of varying specificity and sensitivity, are used to identify ALTR. The purpose of this study was to document the clinical presentation, diagnostic workup and surgical findings in a large cohort of patients with dual modular stems, and use this information to propose an evaluation protocol that assists surgical decision-making. Methods. This is a single center, single surgeon's retrospective case series of 38 patients who underwent 42 primary total hip arthroplasty (THA) with a dual-taper femoral components between March 2010 and May 2011 The evaluation included clinical exam, hip radiographs, labs including serum metal ion levels, metal artifact reduction sequence magnetic resonance imaging (MARS MRI), and fluoroscopic hip aspiration with qualitative and quantitative assessment of synovial fluid. Each hip aspirate was classified into Class 1 (clear, <10cc), 2(brown, clear, >10cc), or 3 (cloudy, turbid, viscous). 20 patients to date have undergone revision THA. Results. 19/42 hips were symptomatic. Serum cobalt levels were elevated in 38/42 patients. 23/42 had abnormal MRI findings. MRI was able to identify abnormalities in 79% (15/19) of symptomatic patients and 35% (8/23) asymptomatic patients. Class 2 and 3 hip aspirates were associated with abnormal MRI (in 86% and 61%, respectively), elevated Cobalt, and a high rate of revision (71% and 72%, respectively). ESR and CRP were normal in most patients (76% and 66%, respectively). A small subset of patients (2/38) with symptoms, normal metal ion levels and normal MRI, had abnormal aspirates (Class 2 or 3) with extensive tissue necrosis at revision. Conclusion. The diagnosis of ALTR can be challenging and requires integrating data from several sources: clinical exam, radiographs, serum metal testing, MARS MRI and hip aspirations. Hip aspiration appears to be useful not only in excluding infection, as proposed in current literature, but also in identifying ALTR in patients with otherwise normal tests. Abnormal results on MARS MRI and/or hip aspiration appear to be most predictive of surgical pathology. Both should be included in the protocol to evaluate for underlying ALTR in patients with dual-taper femoral stems

Background. Adverse local tissue reactions (ALTR) in metal-on-polyethylene (MoP) total hip arthroplasty (THA) with head-neck taper corrosion is likely to be multifactorial involving implant and patient factors. However, there is a paucity of clinical data on implant parameters as predisposing factors in MoP head-neck taper corrosion. The aim of this study was to identify any potential implant factors associated with failed MoP THA due to head-neck taper corrosion. Methods. A total of 67 MoP THA patients in two groups was investigated: 1) ALTR (n=38) on MARS MRI and 2) non-ALTR (n=29) on MARS MRI. All patients had highly cross-linked polyethylene liners with cobalt-chromium femoral heads with a single head-neck modularity. Parameters compared between groups included: acetabular component orientation, femoral neck shaft angle, radiographic measurement of medial and vertical femoral offsets, limb length discrepancy, component size, femoral head offset, implant type, femoral stem alloy and taper design. Results. The occurrence of ALTR was associated with increased femoral head offset (non-ALTR vs. ALTR, 0.5 ± 3.7 vs. 4.1 ± 3.6, p = 0.008), increased radiographic femoral stem offset (35.9 ± 7.4 mm vs 40.7 ± 7.1mm, p = 0.018), and the use of TMZF alloy stems (p = 0.051). The presence of ALTR was significantly associated with higher cobalt (9.1 µg/L vs. 0.4µg/L, p=0.001) and chromium (2.6µg/L vs. 0.4µg/L). A significant correlation was identified between the serum cobalt level and the femoral stem offset (R=0.375, p=0.009). Conclusions. Although the occurrence of head-neck taper corrosion in MoP THA is likely to be an interplay between implant and patient factors, the results of this study identified increased femoral head and stem offset and the use of TMZF alloy stems as risk factors associated with clinically relevant ALTR due to head-neck taper corrosion in MoP THA patients. The study provides evidenced-based information in risk stratification of symptomatic MoP THA patients for head-neck taper corrosion. For any tables or figures, please contact the authors directly

High failure rates have been associated with large diameter metal-on-metal total hip replacements (MoM THR). However there is limited literature describing the outcomes following the revision of MoM THR for adverse local tissue reaction (ALTR). A total of 98 large diameter MoM THRs underwent revision for ALTR at our institution. The data was obtained from the clinical records and included the demographics, intra-operative findings of ALTR and post-operative complications. Any subsequent procedures and re-revision for any reason was analysed in detail. The clinical outcome was measured using functional outcome scores using the Oxford hip score (OHS), Western Ontario and McMaster Universities osteo-arthritis index (WOMAC) score and Short Form (SF12). The mean age of the patients at the time of revision was 58.2 yrs. At a mean follow-up of 3.9 years (1.0 to 8.6) from revision for ALTR, there were 15 hips (15.3 %) with post-operative complications and 8 hips (8 %) requiring re-revision. The Kaplan–Meier five-year survival rate for ALTR revision was 91 % (95% confidence interval 78.9 to 98.0). There were no statistically significant predictors of re-revision. The rate of postoperative dislocation following revision was 9.2% (9 hips). The post-operative functional outcome depends on the intra-operative findings of tissue destruction secondary to ALTR. The short term results following revision of large diameter MoM THR for ALTR are comparable with other reports in the literature. The use of constrained liners reduces the incidence of post-operative dislocation. There is an increased risk of postoperative instability following revision THR for ALTR. Early identification and intervention seems to be the logical approach in the management of patients with ALTR

Increased failure rates due to metallic wear particle-associated adverse local tissue reactions (ALTR) is a significant clinical problem in resurfacing and total hip arthroplasty. Histological analysis and particle characterization are important elements for understanding the biological mechanisms of the reaction and different histological subtypes may have unique needs for longitudinal clinical follow-up and complication rates after revision arthroplasty. Consecutive patients (N=285 cases) presenting with ALTR from three major hip implant classes, metal-on-metal resurfacing and total hip arthroplasty (THA) and non-metal-on-metal THA with dual modular neck were identified from our prospective Osteolysis Tissue Database and Repository and 53 cases were selected for wear particle nano-analysis. Conventional histology: Tissue samples taken from multiple regions around the hip with extensive sampling performed at macroscopic examination were examined by light microscopy. Particle analysis: Tissue samples selected after frozen section evaluation for cellularity and particle content were examined by scanning electron microscopy (SEM), backscatter scanning electron microscopy (BSEM), BSEM-energy-dispersive X-ray spectroscopy (EDS) element mapping examination, transmission electron microscopy (TEM), TEM-EDS element mapping, and X-ray diffraction spectrometry (XRD) examination. ALTR encompasses three main histological patterns: 1) macrophage predominant, 2) mixed lymphocytic and macrophagic, and 3) predominant sarcoid-like granulomas. Duration of implantation and composition of periprosthetic cellular infiltrates was significantly different among the three implant types examined. Distinct differences in the size, shape, and element composition of the metallic particulate material were detected in each implant class, with correlation of the severity of the adverse reaction with element complexity of the particles. ALTR encompasses a diverse range of histological patterns, which are reflective of both the implant configuration independent of manufacturer and clinical features such as duration of implantation. Distinct differences in the metallic particulate material can contribute to explain the histological features of the ALTR and variability of performance of the implants. ALTR exhibits different histological patterns and is dependent on the characteristics of the wear particulate material of each implant class and host immunological reaction

Objectives

Modular dual-mobility (MDM) constructs are used to reduce dislocation rates after total hip replacement (THR). They combine the advantages of dual mobility with the option of supplementary acetabular screw fixation in complex revision surgery. However, there are concerns about adverse reaction to metal debris (ARMD) as a result of fretting corrosion between the metal liner and shell. Methods: The aim of this systematic review was to find and review all relevant studies to establish the outcomes and risks associated with MDM hip replacement. All articles on MDM THRs in the Medline, EMBASE, CINAHL, Cochrane Library, and Prospero databases were searched. A total of 14 articles were included. A random intercept logistic regression model was used for meta-analysis, giving estimated average values. Results: There were 6 cases of ARMD out of 1312 total. Estimated median incidence of ARMD from meta-analysis was 0.3% (95% CI 0.1 – 1.4%). Mean postoperative serum Cobalt was 0.81 μg/L (95% CI 0.33 – 1.29 μg/L), and Chromium was 0.77 μg/L (95% 0.35 – 1.19 μg/L), from 279 cases in 7 studies. Estimated median incidence of a serum cobalt or chromium ion measurement ≥1 μg/L was 7.9% (95% CI 3.5 – 16.8%), and ≥7 μg/L was 1.8% (95% CI 0.7 – 4.2%). Conclusions: ARMD is a rare but significant complication following total hip replacement using a MDM construct. Its incidence appears higher than that reported in non-metal-on-metal (MoM) hip replacements but lower than that of MoM hip replacements. MDM hip replacements are associated with raised serum metal ion levels postoperatively, but there was no correlation with worse clinical hip function within studies. Studies were poor quality and at high risk of confounding. Pending further work, MDM constructs should be used with caution, reserved for select cases at particularly high risk of dislocation.

The purpose of this randomized controlled trial was to evaluate serum metal levels in patients undergoing total hip arthroplasty (THA) with a conventional compared to a modular dual-mobility bearing. Patients undergoing primary THA for osteoarthritis were randomized to receive either a modular dual-mobility or conventional polyethylene bearing. All patients received the same titanium acetabular and femoral component and a ceramic femoral head. Serum metal levels were drawn pre-operatively then annually for a minimum of two years postoperatively. An a priori power analysis determined that 40 patients (20 per cohort) were needed to identify a clinically relevant difference in serum cobalt of 0.35 ng/ml (ppb) at 90% power. Forty-six patients were randomized to a modular dual-mobility (n=25) or conventional bearing (n=21) with 40 at a minimum follow-up of two years. No differences in serum cobalt (mean 0.14 ppb [range, 0.075–0.29] vs. 0.20 ppb [range, 0.075–0.57], p=0.39) or chromium levels (mean 0.14 ppb [range, 0.05–0.50] vs. 0.12 ppb [range, 0.05–0.35], p=0.65) were identified between the modular dual-mobility and conventional cohorts, respectively. There was no statistically significant difference in serum Co or Cr at two years postoperatively in subjects implanted with a ceramic head and this particular dual mobility bearing in comparison to a ceramic head and a conventional acetabular component. While modest expected elevations in serum Co and Cr were observed in the dual mobility group, in no case did the Co level exceed the laboratory reference range nor the threshold of one part per billion that has been associated with adverse local tissue reactions to mechanically-assisted crevice corrosion

Distal neck modularity places a modular connection at a mechanically critical location. However, this is also the location that confers perhaps the greatest clinical utility. Assessment of femoral anteversion in 342 of our THR patients by CT showed a range from −24 to 61 degrees. The use of monoblock stems in some of these deformed femurs therefore must result in a failure to appropriately reconstruct the hip and have increased risks of impingement, instability, accelerated bearing wear or fracture, and adverse local tissue reaction (ATLR). However, the risks of failing to properly reconstruct the hip without neck modularity must be weighed against the additional risks introduced by neck modularity. There are several critical design, material, and technique variables that are directly associated with higher or lower incidences of problems associated with modular neck femoral components. These include modular neck length, design and material of both parts including the junction design, wall thickness of the receiving junction, assembly force, and bearing diameter and material. With regard to stem design and material, it has been clearly shown that the incidence of titanium neck fractures is higher in stems with a thinner wall-thickness of the receiving junction than in stems with a thicker wall-thickness. Moreover, titanium necks have been largely replaced with CoCr necks with significantly higher yield and fatigue strength. It remains to be seen if the introduction of CoCr necks will decrease or increase the risks associated with distal neck modularity. With respect to titanium necks, our experience has shown no adverse local tissue reaction, no fractures of short necks (0 of 370) and a 0.34% incidence of fractures in long necks (2/580) at 3 to 8 years following surgery. This lower incidence of neck fracture compared to other reports may relate to the relatively more rigid stem and thicker wall of the junction receiving the neck compared to other stems. With respect to CoCr modular necks, one device that mated the CoCr modular neck with a beta-titanium alloy femoral component has been shown to have a high incidence of ALTR and has been recalled. While the CoCr on Conventional Titanium Alloy modular neck experience has had a statistically significantly lower incidence of problems, we believe that we have identified two cases of ALTR. If that is the case, the CoCr neck experience may well have a higher incidence of problems that the Ti neck experience. In summary, placing a modular connection at the stem-neck junction has great clinical utility but this is a very design sensitive location. There are risks associated with the use of non-modular neck components that are incapable of properly reconstructing the spectrum of pathology that presents. This failure can lead to instability, impingement, and polyethylene fracture. Yet, the use of titanium modular necks has a small risk of component fracture while the use of cobalt-chrome modular necks may have a higher risk of adverse local tissue reaction. While the existence of a modular neck may offer great advantages at the time of primary reconstruction and of future revision, currently the risk/benefit for the use of these components is strongest in patients with more significant anatomical abnormalities or more complex revision settings

Cup-cage constructs are one of several methods commonly used to treat severe acetabular bone loss during contemporary revision total hip arthroplasty. The purpose of this study was to provide a long-term results of the technique with emphasis on implant survivorship, radiographic results, and clinical outcomes for both full and half cup-cage reconstructions. We identified 57 patients treated with a cup-cage reconstruction for major acetabular bone loss between 2002–2012. All patients had Paprosky Type 2B through 3B bone loss, with 60% having an associated pelvic discontinuity. Thirty-one patients received a full cup-cage construct, and 26 a half cup-cage. Mean age at reconstruction was 66 years, 75% were female, and the mean BMI was 27 kg/m. 2. Mean follow-up was 10 years. The 10-year cumulative incidences of any revision were 14% and 12% for the full and half cup-cage construct groups, respectively. Of the 9 revisions, 3 were for dislocation, 2 for aseptic loosening and construct failure (both were pelvic discontinuities), 1 for adverse local tissue reaction, and 1 for infection with persistent pelvic discontinuity. The 10-year cumulative incidences of revision for aseptic loosening were 4.5% and 5% for the full and half cup-cage constructs, respectively. Of the unrevised cases, incomplete and non-progressive zone 3 radiolucent lines were observed in 10% of patients in each group. Three patients experienced partial motor and sensory sciatic nerve palsies (2 in the full and 1 in the half cup-cage group). Both the full and half cup-cage cohorts demonstrated significantly improved Harris hip scores. Full and half cup-cage reconstructions for major acetabular defects were successful at 10 years in regards to acetabular fixation without appreciable differences between the two techniques. However, zone 3 radiolucent lines were not uncommon in association with discontinuities, and dislocation continues to be a problem

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction. Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to adverse local tissue reactions secondary to metal-on-metal bearing surfaces. While modularity in THR has demonstrable clinical benefits, modular junctions increase the risk of corrosion and the types of adverse soft tissue reactions seen in patients with accelerated metal release from metal-on-metal bearing THRs

There are numerous benefits of femoral head/neck modularity in both primary and revision surgery. Taper corrosion necessitating revision surgery was recognised decades ago, and there are concerns that the incidence is increasing. Variables in design, manufacturing, biomechanics, and modular head assembly have all been implicated. While the incidence of clinically significant taper corrosion is unknown, the adverse local tissue reaction (ALTR) does not appear to occur absent a cobalt chromium interface. The utilization of ceramic heads has increased in recent years. Domestically, more than 50% of femoral heads are now ceramic. This is due, at least in part, to a reduction in patient age at the time of surgery. A stronger influence, however, may be the concern for an adverse local tissue reaction (ALTR) due to taper corrosion with a cobalt chromium femoral head. Ceramic heads have a small risk of in-vivo fracture and cost more. Compared to cobalt chromium alloy, ceramic femoral heads wear less against UHMWPE, although the reduction may not be clinically significant when paired with a crosslinked polyethylene. In the Australian National Joint Replacement Registry, of the five bearing combinations with 14-year cumulative percent revision (CPR) data, the lowest is metal femoral heads with crosslinked polyethylene (5.4%). In-vivo taper assembly technique is variable and can play a role in clinical success or failure, regardless of the head material: taper corrosion with cobalt chromium heads, or fracture of ceramic heads. Standardization of head-neck taper assembly is desirable

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction. Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to adverse local tissue reactions secondary to metal on metal bearing surfaces. While modularity in THR has demonstrable clinical benefits, modular junctions increase the risk of corrosion and the types of adverse soft tissue reactions seen in patients with accelerated metal release from metal-on-metal bearing THRs

Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of modular tapers to mechanically assisted crevice corrosion (MACC), a combination of fretting and crevice corrosion, was subsequently introduced. Since that time, there have been numerous reports of corrosion at this taper interface, documented primarily in retrieval studies or in rare cases of catastrophic failure. We have reported that fretting corrosion at the modular taper may produce soluble and particulate debris that can migrate locally or systemically, and more recently reported that this process can cause an adverse local tissue reaction. Based on the type of tissue reaction and the presence of elevated serum metal ion levels, this process appears quite similar to adverse local tissue reactions secondary to metal on metal bearing surfaces. While modularity in THR has demonstrable clinical benefits, modular junctions increase the risk of corrosion and the types of adverse soft tissue reactions seen in patients with accelerated metal release from metal-on-metal bearing THRs

Introduction. Modular neck (MN) components in total hip arthroplasty (THA) offer intraoperative flexibility, but adverse local tissue reactions (ALTR) due to tribocorrosion at modular junctions are a potential complication of such designs. Serum ion levels and metal artifact reduction sequence (MARS) MRI are used to assess ALTR following modular THA. This study investigates serum ion levels and MARS MRI findings in a series of hips with MN components and differing articulating surfaces. Methods. We retrospectively evaluated a cohort of 184 primary THAs in 159 patients implanted with a dual modular femoral stem by one surgeon from 2005–2013. 121 THAs had a cobalt-chromium neck component and non-metal-on-metal articulation, while 63 THAs had a titanium neck component and metal-on-metal (MoM) articulation. Serum ion levels were recorded for all patients. MARS MRI scans were read by musculoskeletal-trained radiologists. Pseudotumor grade and location were measured. Results. Serum cobalt levels as a function of time post-operatively demonstrated no correlation. In THAs with non-MoM articulation, pseudotumors were visualized in 13 of 54 (24.1%) initial MARS MRIs performed 1–40 months post-operatively compared to 5 of 67 (7.5%) performed 41–120 months post-operatively (p=0.02), and findings typically remained consistent across multiple MARS MRI scans. Pseudotumors were generally located lateral to the hip joint in hips with non-MoM articulation compared to anteromedial following MoM arthroplasty. In the cobalt-chrome MN group, cobalt levels were elevated in 11 of 20 (55%) of patients with pseudotumor compared to 15 of 19 (79%) in the MoM group. Conclusion. Generation of ALTR leading to pseudotumor formation is a concern with cobalt-chrome MN designs. Psuedotumor characteristics differ between patients with cobalt-chrome designs versus MoM articulation. Normal serum ion levels did not exclude the presence of a pseudotumor and routine MARS MRI should be included in follow-up of patients with cobalt-chromium MN prostheses

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

Periacetabular osteolysis in association with well-fixed cementless components was first recognised as a serious clinical problem in the early 1990s. By the mid-1990s, revision surgery for pelvic osteolysis secondary to polyethylene wear was the most common revision hip procedure performed. As a result, new bearing surfaces were introduced in hopes of reducing wear volume and thus reducing pelvic osteolysis. These included highly crosslinked polyethylene, ceramic-on-ceramic and metal-on-metal bearing surfaces. Metal-on-metal has for the most part been eliminated in conventional hip replacement because of the concerns centered around adverse local tissue reactions. Both highly crosslinked polyethylene and ceramic-on-ceramic bearings have been successful in limiting wear and all but eliminating clinically significant osteolysis. Multiple reports on highly crosslinked polyethylene have documented wear rates below the lysis threshold. No reports of revision for wear have been reported despite twenty years of in-vivo use. Of import to the surgeons, all manufacturers commonly used in North America have performed well. In addition, highly crosslinked polyethylene has been relatively insensitive to head size allowing the use of 36mm femoral heads routinely. Similar reports are noted with ceramic-on-ceramic bearings. However, highly crosslinked has dominated the North American market because it is a relatively forgiving bearing surface and comes at a lower cost. Currently, there is a trend towards the use of ceramic femoral heads – not because of wear concerns, but concerns related to taper corrosion and large cobalt-chrome femoral heads

Ceramic bearings are currently the most widely used alternative to metal-on-polyethylene bearings in total hip arthroplasty (THA). A workgroup at International Consensus Meeting (ICM) analyzed the potential link between the type of bearing surface and the subsequent periprosthetic joint infection (PJI), and found a higher incidence of PJI when using a metal-on-metal (MoM) bearing surface. A potential reason is that the failure of a MoM bearing surface can result in adverse local tissue reactions (ALTR), which might provide a favorable environment for bacterial proliferation. In the last few years, several observational studies including national registries, showed that metal-on-polyethylene (MoP) bearing surfaces are associated with a higher rate of infection following total hip arthroplasty (THA) compared to ceramic bearings, in particular with the use of ceramic-on-ceramic bearing (CoC) surfaces. After adjusting for selection bias and various confounding factors, patients treated with ceramic bearings experienced reduced risk of infection and MoP bearing surface is an independent risk factor correlating with higher incidence of PJI. The meta-analysis by Lee et al. comparing MoM with CoC cementless THA confirmed that the MoM is associated with a significantly higher revision rate than CoC group for any reason as well as for PJI. Furthermore, initial in-vitro studies have shown lower bacterial biofilm formation on ceramic bearing surfaces. Summarizing the current literature, ceramic bearings are associated with a lower risk of infection following THA

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