Aims. To report our experience with trunnion corrosion following metal-on-polyethylene total hip arthroplasty, in particular to report the spectrum of presentation and determine the mean time to presentation. Patients and Methods. We report the presenting symptoms and signs, intraoperative findings, and early results and complications of operative treatment in nine patients with a mean age of 74 years (60 to 86). The onset of symptoms was at a mean of seven years (3 to 18) after index surgery. Results. Patients presented with a variety of symptoms including pain, limp and rash. The preoperative mean serum cobalt level was 7.1 ppb (2.2 to 12.8) and mean serum chromium level was 2.2 ppb (0.5 to 5.2). Metal artifact reduction sequence (MARS) MRI showed fluid collection and possible pseudotumour formation in five hips, fluid collection in two hips, and synovitis/debris in one hip, with no MRI in one patient. Acetabular revision was performed in three patients, six patients underwent liner and head exchange only. The postoperative metal levels decreased in all patients: mean cobalt 0.5 ppb (0 to 1.8) and mean chromium 0.9 ppb (0 to 2.6) at a mean of five months (3 to 8) postoperatively. Seven patients had good pain relief and no complications at one year. There were two major complications requiring reoperation: acute infection at six weeks, for which the patient required two-stage reimplantation; and recurrent dislocation, for which the patient was revised to a dual mobility component. Conclusion. Trunnion corrosion in metal-on-polyethylene THA has a range of presenting symptoms, and may present later than previously described. A high index of suspicion is warranted, and serum cobalt and chromium levels are recommended for diagnosis. Patients should be counselled about possible postoperative complications. Cite this article: Bone Joint J 2018;100-B:898–902

Aims. To present a surgically relevant update of trunnionosis. . Materials and Methods. Systematic review performed April 2017. Results. Trunnionosis accounts for approximately 2% of the revision total hip arthroplasty (THA) burden. Thinner (reduced flexural rigidity) and shorter trunnions (reduced contact area at the taper junction) may contribute to mechanically assisted corrosion, exacerbated by high offset implants. The contribution of large heads and mixed metallurgy is discussed. Conclusion. Identifying causative risk factors is challenging due to the multifactorial nature of this problem. Cite this article: Bone Joint J 2018;100-B(1 Supple A):44–9

Modular femoral stems offer surgeons great flexibility in biomechanical configuration during total hip replacement (THR) however introduce a taper-trunnion articulation known to be a source of additional wear debris through crevice, fretting and galvanic corrosion with mixed material combinations. This study aimed to investigate the influence of the trunnion bearing surface combination on the revision rate following primary total hip replacement (THR). All patients who underwent THR using an Exeter V40 cemented stainless steel stem and monobloc cemented polyethylene acetabular component (uncemented cups excluded to standardise the acetabular bearing surface and fixation) between January 2003 and December 2019 were extracted from the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man. The primary exposure was the head substrate used corresponding to the trunnion bearing. Time-to-event was determined by duration of implantation from primary surgery to revision with cases censored at death or end of available follow-up. Multivariable Cox proportional hazard models were used to identify predictors of all cause revision, adjusted for age, sex, American Association of Anaesthesiologists (ASA) grade, body mass index, surgical indication (osteoarthritis or other), and femoral head size. 229,870 THR were identified (66% female, mean age 73.4 years (SD 9.1) with the majority (91%) performed for osteoarthritis of which 4,598 were revised. Mean time from primary to revision or censoring was 6.8 years (SD 4.0). Multivariable modelling showed CoCr/SS trunnions were associated with a significantly higher risk of revision (hazard ratio (HR) 1.31 (95%CI 1.15 to 1.48, p<0.0001) as compared to SS/SS (reference). Both Alumina/SS (HR 0.74 (0.65 to 0.84), p<0.0001) and Zirconia/SS (HR 0.61 (0.49 to 0.74), p<0.0001) were associated with a significantly lower risk of revision. Ceramic heads on an Exeter stem were associated with significantly improved survivorship compared to metal heads in primary THR. CoCr/SS trunnion articulations had the poorest survivorship which may be contributed to by trunnionosis

Uncemented metal-on-polyethylene total hip arthroplasties (THAs) have had a modular cobalt-chrome alloy head since their introduction in the early 1980's. Retrieval analysis studies and case reports in the early 1990's first reported corrosion between the femoral stem trunnion (usually titanium alloy) and cobalt-chrome alloy femoral head. However, then this condition seemed to disappear for about two decades? There are now numerous recent case series of this problem after metal-on-polyethylene THA, with a single taper or dual taper modular femoral component. Metal ion elevation, corrosion debris, and effusion are caused by mechanically assisted crevice corrosion (MACC). These patients present with diffuse hip pain, simulating trochanteric bursitis, iliopsoas tendinitis, or even deep infection. Trunnion corrosion, with adverse local tissue reaction, is a diagnosis of exclusion, after infection, loosening, or fracture. The initial lab tests recommended are: ESR, CRP, and serum cobalt and chromium ions. With a metal-on-polyethylene THA, a cobalt level > 1ppb is abnormal. Plain radiographs are usually negative, but may show calcar osteolysis or acetabular erosion or cyst. MARS MRI may be the best imaging study to confirm the diagnosis. Hip aspiration for culture and cell-count may be necessary. The operative treatment is empiric, with debridement, and head exchange with a ceramic head-titanium sleeve (or oxidised zirconium head) placed on the cleaned trunnion. The femoral component may have to be removed if there is “whole trunnion failure”. This usually relieves the symptoms, but the complication rate of this procedure may be high

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 release of metallic debris can promote many adverse tissue reactions, as metallosis, necrosis, pseudotumors and osteolysis . 1–3. This debris is mainly generated by the fretting-corrosion mechanism due to the geometric difference in the head-stem interface . 4. Retrieval and in silico analysis showed the roughness of the stem-head interface appears to play an important role in the volume of material lost and THA failure . 5–7. The technical standard ISO 7206-2 recommends the measurement of average roughness (Ra) and max height of the profile (Rz) to control the quality of the surface finish of articulating surfaces on THA implants. However, despite the importance of the trunnion roughness, there is no specific requirement for this variable on the referred technical standard. The present study carried out a surface finish analysis of the trunnion of hip stems from five distinct manufacturers. Methods. Four stems (n = 4) from five (5) distinct manufacturers (A, B, C, D, and E) were used to evaluate the roughness of the trunnion. All the stems are similar to the classical Exeter stem design, with a 12/14 taper and a polished body surface. The roughness of trunnions was evaluated according to ISO 4287 and ISO 13565-2. The total assessment length was 4.8 mm with 0.8 mm cut-off. The first and last 8.33% of assessment length were not considered. The measurements of all samples were made in a rugosimeter with 2 µm feeler ITP (Völklingen, Germany), the velocity of 0.5 mm.s. -1. , and a force of 1.5 mN. The calibration was made at 20 ºC and relative humidity at 50%. The Kruskal Wallis with post hoc Nemenyi test was used to evaluate the difference of Ra among the manufacturers. The confidence level was set at 5%. Results and Discussion. The analysis of surface finish revealed different roughness among the manufactures (p < 0.005), with Ra between 0.061 µm to 3.184 µm and Rz varying of 0.41 µm to 12.69 µm. The manufacturers A and E had a Ra (2.587±0.050 µm and 3.146±0.031µm) of the trunnion similar to founded by Panagiotidou et al (2013). Within such range, the trunnion has shown a high presence of pit . 8. The manufacturer C, on the other hand, had the best surface finish of the trunnion (Ra = 0.069±0.010 µm and Rz = 0.505 ± 0.076 µm). This more smooth surface might increase the taper strength, reduce the shear stress and the susceptibility to the fretting-corrosion damage . 4,8. . Conclusion. The results were worrying because there is great variability of roughness among the manufacturers with the occurrence of trunnions with roughness too high. Nevertheless, the ISO technical standard does not recommend any procedure or minimum parameters acceptable for the surface finish of the trunnion. The revision of ISO 7206-2 would guarantee better control of trunnion roughness to reduce the amount of metallic debris and increase the safety of THA implants. Additional research is needed to determine a target value for this variable. For any figures or tables, please contact authors directly

Introduction. The failure rate of Total Hip Replacement (THR) has been shown to be strongly influenced by the nature of the articulating interfaces, with Metal-on-Metal (MoM) articulations having three times the failure rate of Metal-on-Polyethylene (MoP) components. It has been postulated that this observation is related to edge wear and increased bearing torque of large MoM heads, which would lead to increased loading and wear at the head taper junction and, subsequently, to the release of metal ions and corrosion products. This suggests that taper wear and corrosion should not be as prevalent in large head MoP implants as in large head MoM implants. This study was undertaken to test the hypotheses that: (i) MoM implants exhibit higher rates of corrosion and fretting at the head taper junction than MoP implants, and that (ii) the severity of corrosion and fretting is greater in components of larger head diameter. Materials and Methods. Our study included 90 modular implants (41 MoM; 49 MoP) retrieved during revision hip arthroplasties performed between 1992 and 2012. Only retrievals with head diameters greater than 32 mm were included, and trunnion sizes ranged from 10/12 mm to 14/16 mm with 12/14 mm being the most common size. The stem trunnion and head taper surfaces were examined under stereomicroscope by a single observer. Each surface was scored for both corrosion (using a modified Goldberg scoring system) and fretting (using the standard Goldberg scoring system). For both the trunnion and head tapers, the student's t-test was used to determine if differences exist in the severity of corrosion or fretting between the MoM and MoP groups and between different head sizes of the same articulation type. Results. Overall, there was no significant difference in the severity of corrosion or fretting damage of femoral head taper surfaces or in the fretting of stem trunions between articulation types (p values: 0.245 to 0.733) or head sizes (p values: 0.333 to 0.680). However, corrosion damage of the trunions did vary with the type of articulation (p = 0.0069) and with head size (p = 0.0145). MoP trunnions were found to have significantly more corrosion damage than MoM trunnions at head diameters greater than 40 mm (p = 0.005). Discussion. The surprising conclusion of this study is that the severity of trunnion corrosion in MOP articulations, which surpassed the tribo-corrosion of MOM joints, especially when the prosthetic head size exceeded 40 mm. This conclusion is consistent with the presence of moderate to severe third-body damage in many large diameter polyethylene liners which would lead to a large increase in the frictional torques generated during hip motion. In addition, only part of the loading of the trunnion arises from increased frictional torque. The increase in head size, especially in designs with an offset head center, will lead to increased toggling, and accelerated wear and corrosion of the taper junction, independent of the bearing surface material

Introduction. The Morse taper was adapted into orthopaedics as a connecting junction in total hip replacements. The benefit of modular systems includes the adjustment of leg length, offset and the ability to remove the head for acetabular exposure during revision surgery. The design of the Morse taper facilitates the intimate contact of the conical trunnion of the femoral stem (male component), with the conical bore of the femoral head (female component). Design consideration for tapers involve physical parameters (angle, length, diameter and contact points), and manufacturing finish (surface characteristics). Orthopaedic trunnion tapers are not standardized and vary in length, taper angle and base dimension. Variations in the design and surface characteristics of the trunnion, which directly reflects on the interface at the taper junction can influence the likelihood of subsequent wear, corrosion and ultimately effect longevity of the implant. Methods and Materials. We studied 11 clean un-used commercial stems from five different companies (DePuy, Stryker, Biomet, Wright Medical, Smith and Nephew). Trunnion surface was scanned with an optical profilometer (Bruker ContourGT-I 3D Optical Microscope (Karlsruhe, Germany), an interference microscopes with the capability to analyse 3 dimensional topographical features of materials. Three measurements of each trunnion were taken on the anterior surface at the proximal, mid-point, and distal segments. Each region scan was conducted under a 20x objective with the scan length of 1000 um and a back scan of 500 um. Results. Four of the eleven hip stems demonstrated a smooth surface finish and the remaining seven had a distinct threaded surface with the Corail and the SROM surface topography shown in figure 1. All the analysed trunnion surfaces had a Sa value than Sz value (p < 0.05), indicating each trunnion surface consists of repetitive peak heights and valley depth across the scanned surface area shown in figure two. The higher Sa parameter for the threaded trunnions indicates a rougher overall surface due to a recurring threads pattern. The mean dominant thread heights of the trunnions varied from 12.91 μm on the Profemur to 3.24 μm on the SecurFit Max. The Silent, Summit and the Tri-Lock stems demonstrated a variation in thread heights on their respective surfaces. The Summit stem also demonstrated variability in the pitch of its threads which was not seen on the other threaded stems. The Silent had the widest pitch at 0.304 μm whilst the Profemur had the narrowest pitch at 0.13 μm. Conclusion. Threaded trunnion surfaces for different stems are not uniformly patterned and demonstrate variability in thread height and pitch. These differences could affect micro motion at the taper junction, influencing corrosion and fretting. The study is limited in its capacity as only one stem of each type was analysed, therefore any variation between same stem designs cannot be commented on

Trunnion corrosion in metal-on-polyethylene THA is poorly understood, with multifactorial etiology, and the patients present with “hip pain”. We analysed the presenting symptoms and signs, intraoperative findings and the early results and complications of operative treatment. One surgeon treated 9 patients (6 male, 3 female), mean age 74 years, with the onset of symptoms at a mean of 7 years (range 3–18) after index surgery. The taper size was 12/14 in seven, 14/16 in one, and 6 degree in one hip. The preoperative mean cobalt level was 7.1 ppb (range, 2.2–12.8) and mean chromium level was 2.2 ppb (range, 0.5–5.2). MARS MRI showed fluid collection and pseudotumor in 5, fluid collection only in two, and synovitis/debris in one hip. In one patient, there was no preoperative MRI. There were a myriad of clinical presentations: thigh rash alone in one; diffuse leg pain and hip rash in one; acute pseudo-sepsis in one; iliopsoas tendinitis and diffuse rash in one; trochanteric bursitis in one; groin pain only in one; thigh-buttock pain in two; and diffuse hip pain and limp in one patient. Intraoperatively, 6 patients had liner and ceramic (or oxidized zirconium) head exchange only. Three patients had concurrent acetabular revision: one for broken locking mechanism; one because liner was unavailable, and one had acetabular loosening. The postoperative metal levels decreased in all patients: mean cobalt 0.5 ppb (range, 0–1.8) and mean chromium 0.9 ppb (range, 0–2.6). Seven patients had good pain relief and no complications. There were two major complications requiring reoperation: acute infection at 6 weeks and patient required 2-stage reimplantation; and second patient had recurrent dislocation and was revised to a dual mobility component. Trunnion corrosion in metal-on-polyethylene THA has several clinical presentations, including local skin rash, iliopsoas tendinitis, and other limb dysfunction. There should be a high index of suspicion and serum cobalt/chromium levels are recommended for diagnosis. The patients should be counseled about possible postoperative complications

There is renewed concern surrounding the potential for corrosion at the modular head-neck junction to cause early failure in modern hip implants. Although taper corrosion involves a complex interplay of many factors, previous studies have correlated decreasing flexural rigidity of the femoral trunnion with an increased likelihood of corrosion at retrieval. A multicenter retrieval analysis of 85 modular femoral stems was performed to calculate the flexural rigidity of various femoral trunnions. Stems were implanted between 1991–2012 and retrieved between 2004–2012. There were 10 different taper designs from 16 manufacturers. Digital calipers were used to measure taper geometries by two independent observers. Mean flexural rigidity was 262 Nm. 2. , however there was a wide range of values among the various stems spanning nearly an order of magnitude between the most flexible (80 Nm. 2. ) and most rigid (623 Nm. 2. ) trunnions, which was due in part to the taper geometry and in part to the material properties of the base alloy. There was a modest but significant negative correlation between flexural rigidity of the trunnion and release date of the stem. This wide variability in flexural rigidity may predispose particular stem designs to an increased risk of corrosion at the modular head-neck taper, and may in part explain why taper corrosion is being seen with increasing frequency in modern hip arthroplasty

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.

Introduction:. Angular mismatch of the modular junction between the head and the trunion has been recognized as a contributing factor to fretting and corrosion of hip prostheses. Excessive angular-mismatch can lead to relative motion at the taper interface, and tribo-corrosion of the head-neck junction secondary to disruption of the passive oxide layer. Although manufacturing standards have been adopted to define acceptable tolerances for taper angles of mating components, recent investigations of failed components have suggested that stricter tolerances or changes in taper design may be necessary to avoid clinical failures secondary to excessive taper wear and corrosion. In this study we examine the effect of angular-mismatch on relative motion between the taper and bore subjected to normal gait load using finite element methods. Methods:. Computer simulations were executed using a verified finite element model (FEM), the results from which were determined to be consistent with literature. A stable, converging hexahedral mesh was defined for the trunnion (33648 elements) and a tetrahedral mesh for the femoral head (51182 elements). A friction-based sliding contact was defined at the taper-bore interface. A gait load of 1638N (2.34 × BW, BW = 700N) was applied at an angle of 30° to the trunnion axis (Figure 1) on an assembled FEM. A linear static solution was set up using Siemens NX-Nastran solver. Angular-mismatch was simulated by incrementing the conical half-angle of the bore to examine these cases: 0°, 0.005°, 0.010°, 0.015°, 0.030°, 0.050°, 0.075°, 0.100°, 0.200°and 0.300°. Results:. Relative interface micro-motion at the proximal-medial point of the taper demonstrated a lack of dependence upon angular-mismatch for tolerances up to 0.075° and a monotonic increase in micro-motion for higher tolerances (0.075–0.3 °; Figure 2). A similar trend was observed with respect to the average values of contact pressure, max von Mises stress and shear stress acting at the proximal-medial aspect of the taper (Figure 3). Non-linear correlation tests indicate a significant correlation (p < 0.0001) of mismatch angle with peak von Mises stress (r = 0.965) and relative micro-motion (r = 0.964). Discussion:. The FEA results corroborate the notion that high angular-mismatch tolerances have a deleterious effect of fretting at the trunnion-head interface. Although, stability of the implant did not appear to be compromised at relatively lower tolerances, the propensity for it is higher at higher mismatches. The simulation was, however, executed as a single-step static analysis ignoring the effect of cyclical loading often observed during gait. This abstract serves as a proof of concept to justify the further development of this FEA to study the effect of angular-mismatch tolerances on micro-motion at the trunnion-head interface. However, current results strongly indicate that tolerance for angular-mismatch can be more liberal without increasing the micro-motion and stresses at the trunnion-head interface. Significance: The effect of angular-mismatch suggests a threshold tolerance different from the industry accepted tolerance of 0.0167°. Mismatches smaller than 0.075° demonstrated only modest variation in the interface micro-motion. Additionally, the results corroborate recent clinical evidence that even with perfectly fit implants, the potential for interface micro-motion can lead to fretting-induced corrosion

Introduction. Corrosion of the femoral head-trunnion junction in modular hip components has become a concern as the corrosion products may lead to adverse local tissue reactions. A simple way to avoid trunnion corrosion is to manufacture the femoral head with a non-metallic material, such as ceramics that are widely. An alternative solution may lie in advanced polymers like polyaryletherketones (PAEKs). These thermoplastics have high mechanical strength necessary for use as femoral heads in hip arthroplasty, but they must be tested to ensure that they do not adversely affect the wear of the ultrahigh molecular weight polyethylene (UHMWPE) liner counterface. Pin-on-disc (POD) wear testing has been extensively used to evaluate the wear properties of UHMWPE prior to more extensive and costly analysis with joint simulators. We hypothesized that the wear of crosslinked UHMWPE would not be adversely affected in POD tests when articulated against an advanced thermoplastic counterface. Methods. 0.1 wt.% VitE blended UHMWPE stock was e-beam irradiated to 100, 125, 140, 160, and 175 kGy and machined into cylindrical pins for testing. An additional group of 100 kGy e-beam irradiated and melted UHMWPE (with no vitamin E) was also machined and tested. Three different counterface materials were tested: (1) Cobalt-chrome (CoCr) with a surface roughness (R. a. ) of <0.5 μm, (2) Biolox™ ceramic (CeramTec), and (3) Polyetheretherketone (PEEK), a member of the PAEK family (Fig 1). A bidirectional POD wear tester [1] was used to measure the wear rate of UHMWPE specimens, where the specimens moved in a 10 mm × 5 mm rectangular pattern under a Paul-type load curve [2] synchronized with the motion. The peak load of the loading curve corresponded to a peak contact pressure of 5.1 MPa between each UHMWPE pin specimen and the counterface disc. Each test was conducted at 2 Hz in undiluted bovine serum stabilized with ethylenediamine tetraacetate (EDTA) and penicillin. The pins were cleaned and weighed daily, and a wear rate was calculated at the end of each test by linear regression. Results. As expected, higher radiation doses led to lower wear rates against all counterface materials (Fig 2). The PEEK discs produced the lowest UHMWPE wear in each group and the CoCr discs produced the highest UHMWPE wear; however, the two UHMWPE groups with the lowest wear rates showed no difference between the three counterface materials. Conclusions. Even though the PEEK discs had visible machining marks – that is they were not polished to an implant surface finish – they still yielded the lowest wear rates for UHMWPE articulating against them when compared to the highly polished and smooth CoCr and ceramic materials. Implementing further steps to better the surface roughness of the PEEK counterface may yield even better wear rates. Using PEEK in femoral heads may alleviate issues with trunnion corrosion without increasing the incidence of osteolysis or other wear related issues. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

It is now well recognised that adverse local tissue reaction (so called pseudotumor or ALTR) may follow the use of metal-on-metal arthroplasty, the source of the metal being the primary bearing surface (the articulation itself) or a modular junction within the construct, such as the trunnion. This is more likely seen if a large femoral head has been used. We are aware of this risk and have implemented surveillance systems worldwide to facilitate its early diagnosis and prompt management. Less well known, and silent in its initial development, is adverse local reaction following metal-on-polyethylene hip replacement. Initially the problem is unknown to the patient and the surgeon. Typically there follows unexplained pain (due to synovitis), loss of motion, sometimes the development of a mass, followed by increasing dysfunction as the inflammatory, destructive process invades the surrounding soft tissues. Radiographic features are late to follow (focal osteolysis), unless cross-sectional imaging is considered (ultrasound and/or metal suppressed MRI) early in the process. Serum metal ions are an important adjunct in its diagnosis, and it is now acknowledged that the previously used level of 7 ppb is much higher than that required to recognise the entity. Typically there is a reverse of the usual CrCo ratio, and a recent study has suggested that a raised serum Co alone is adequate to assist in the diagnosis. Four important lessons have been learned at our center in recent years and will be demonstrated in this case-based presentation designed for surgeons in practice. It is hoped that the cases and supportive literature will prove useful in advancing the early diagnosis of this troublesome and often silent condition

Fracture of contemporary femoral stems is a rare occurrence. Earlier THR stems failed due to design issues or post manufacturing heat treatments that weakened the core metal. Our group identified and analyzed 4 contemporary fractured femoral stems after revision surgery in which electrochemical welds contributed to the failure.

All four stems were proximally porous coated titanium alloy components. All failures occurred in the neck region post revision surgery in an acetabular cup exchange. All were men and obese. The fractures occurred at an average of 3.6 years post THR redo (range, 1.0–6.5 years) and 8.3 years post index surgery (range, 5.5–12.0 years). To demonstrate the effect of electrocautery on retained femoral stems following revision surgery, we applied intermittent electrosurgical currents at three intensities (30, 60, 90 watts) to the polished neck surface of a titanium alloy stem under dry conditions.

At all power settings, visible discoloration and damage to the polished neck surface was observed. The localized patterns and altered metal surface features exhibited were like the electrosurgically-induced damage priorly reported.

The neck regions of all components studied displayed extensive mechanical and/or electrocautery damage in the area of fracture initiation. The use of mechanical instruments and electrocautery was documented to remove tissues in all 4 cases.

The combination of mechanical and electrocautery damage to the femoral neck and stem served as an initiation point and stress riser for subsequent fractures. The electrocautery and mechanical damage across the fracture site observed occurred iatrogenically during revision surgery. The notch effect, particularly in titanium alloys, due to mechanical and/or electrocautery damage, further reduced the fatigue strength at the fractured femoral necks. While electrocautery and mechanical dissection is often required during revision THA, these failures highlight the need for caution during this step of the procedure in cases where the femoral stem is retained.

Adverse reaction to wear and corrosion debris is a cause for concern in total hip arthroplasty (THA). Modular junctions are a potential source of such wear products and are associated with secondary pseudotumour formation.

We present a consecutive series of 17 patients treated at our unit for this complication following metal-on-highly cross-linked polyethylene (MoP) THA. We emphasise the risk of misdiagnosis as infection, and present the aggregate laboratory results and pathological findings in this series.

The clinical presentation was pain, swelling or instability. Solid, cystic and mixed soft-tissue lesions were noted on imaging and confirmed intra-operatively. Corrosion at the head–neck junction was noted in all cases. No bacteria were isolated on multiple pre- and intra-operative samples yet the mean erythrocyte sedimentation rate was 49 (9 to 100) and C-reactive protein 32 (0.6 to 106) and stromal polymorphonuclear cell counts were noted in nine cases.

Adverse soft–tissue reactions can occur in MoP THA owing to corrosion products released from the head–neck junction. The diagnosis should be carefully considered when investigating pain after THA. This may avoid the misdiagnosis of periprosthetic infection with an unidentified organism and mitigate the unnecessary management of these cases with complete single- or two-stage exchange.

Cite this article: Bone Joint J 2015;97-B:1024–1030.

Aims

We present a case series of ten metal-on-polyethylene total hip arthroplasties (MoP THAs) with delayed dislocation associated with unrecognised adverse local tissue reaction due to corrosion at the trunnion and pseudotumour formation.

There is increasing global awareness of adverse reactions to metal debris and elevated serum metal ion concentrations following the use of second generation metal-on-metal total hip arthroplasties. The high incidence of these complications can be largely attributed to corrosion at the head-neck interface. Severe corrosion of the taper is identified most commonly in association with larger diameter femoral heads. However, there is emerging evidence of varying levels of corrosion observed in retrieved components with smaller diameter femoral heads. This same mechanism of galvanic and mechanically-assisted crevice corrosion has been observed in metal-on-polyethylene and ceramic components, suggesting an inherent biomechanical problem with current designs of the head-neck interface.

We provide a review of the fundamental questions and answers clinicians and researchers must understand regarding corrosion of the taper, and its relevance to current orthopaedic practice.

Cite this article: Bone Joint J 2016;98-B:579–84.

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

Aims. The aim of this study was to compare the design of the generic OptiStem XTR femoral stem with the established Exeter femoral stem. Materials and Methods. We obtained five boxed, as manufactured, implants of both designs at random (ten in total). Two examiners were blinded to the implant design and independently measured the mass, volume, trunnion surface topography, trunnion roughness, trunnion cone angle, Caput-Collum-Diaphyseal (CCD) angle, femoral offset, stem length, neck length, and the width and roughness of the polished stem shaft using peer-reviewed methods. We then compared the stems using these parameters. Results. We found that the OptiStems were lighter (p < 0.001), had a rougher trunnion surface (p <  0.001) with a greater spacing and depth of the machined threads (p < 0.001), had greater trunnion cone angles (p = 0.007), and a smaller radius at the top of the trunnion (p = 0.007). There was no difference in stem volume (p = 0.643), CCD angle (p = 0.788), offset (p = 0.993), neck length (p = 0.344), stem length (p = 0.808), shaft width (p = 0.058 to 0.720) or roughness of the polished surface (p = 0.536). Conclusion. This preliminary investigation found that whilst there were similarities between the two designs, the generic OptiStem is different to the branded Exeter design. Cite this article: Bone Joint J 2017;99-B:310–16