Aims. This study aims to enhance understanding of clinical and radiological consequences and involved mechanisms that led to corrosion of the Precice Stryde (Stryde) intramedullary lengthening nail in the post market surveillance era of the device. Between 2018 and 2021 more than 2,000 Stryde nails have been implanted worldwide. However, the outcome of treatment with the Stryde system is insufficiently reported. Methods. This is a retrospective single-centre study analyzing outcome of 57 consecutive lengthening procedures performed with the Stryde nail at the authors’ institution from February 2019 until November 2020. Macro- and microscopic metallographic analysis of four retrieved nails was conducted. To investigate observed corrosion at telescoping junction, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) were performed. Results. Adjacent to the nail’s telescoping junction, osteolytic changes were observed in bi-planar radiographs of 20/57 segments (35%) after a mean of 9.5 months (95% confidence interval 7.2 to 11.9) after surgery. A total of 8/20 patients with osseous alterations (40%) reported rest and ambulation pain of the lengthened segment during consolidation. So far, 24 Stryde nails were retrieved and in 20 (83%) macroscopic corrosion was observed at the nail’s telescoping junction. Before implant removal 11/20 radiographs (55%) of lengthened segments with these 20 nails revealed osteolysis. Implant retrieval analysis by means of SEM showed pitting and crevice corrosion. EDX detected chromium as the main metallic element of corrosion. Conclusion. Patients are exposed to the risk of implant-related osteolysis of unclear short- and long-term clinical consequences. The authors advocate in favour of an early implant removal after osseous consolidation. Cite this article: Bone Joint Res 2021;10(7):425–436

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

Introduction. Ring breakage is a rare but significant complication requiring revision surgery and prolonging the course of treatment. We have encountered three cases with Taylor Spatial Frames (TSF) with breakage at the half ring junction of the distal ring. This experimental study examines the strains produced at different locations on the distal ring during loading and the effects of altering the construct in order to develop techniques to minimise the risk of breakage. Materials and Methods. We mounted different TSF constructs on tibia sawbone models. Construct 1 reproducing the configuration of cases where failure was seen, Construct 2 with different wire and half pin configuration and construct 3 with the distal ring rotated 60 degrees. Strain Gauges were attached to different locations and measurements were collected during loading. Statistical analysis was subsequently performed. Results. The highest strain values were recorded at the half ring junction of constructs 1,2 (>600 microstrains in tension). Rotating the ring 60 degrees significantly reduces the strain observed at the half ring junction (300 microstrains) (p=.000). Strain is increased in areas close to where a half pin attaches to the ring. Conclusions. The highest strains are observed in the half ring junction as the two half rings are subjected to different modes of loading. This area is at higher risk of failure as the thickness of the half rings is halved and their second moment of area significantly reduced. Positioning this junction close to the half pin frame interface increases the strain produced. This interface is dictated by the safe zone in the mid-distal diaphysis of the tibia. Rotating the distal ring 60 degrees has a protective effect by significantly reducing the strain. This simple technical tips should be taken into consideration in order to reduce the risk of breakage at the half ring junction

Wear debris associated with CoCr bearings has been implicated in the development of adverse soft tissue reactions and pseudotumors following THA with large metal heads and following hip resurfacing. Additional concerns have been raised regarding trunion fretting and corrosion. Most recently, the neck-stem junction of some modular femoral stem designs have come under additional scrutiny. We undertook a review of patients who had undergone THA with a proximal modular junction stem design in order to ascertain the state of the junction in early follow up. We examined the records of all patients in our practice who had undergone uncomplicated, unilateral THA with the ARC stem (OmniLife Science, East Taunton, MA, USA) between April 2010 and April 2012. Office records, radiographs and laboratory data were included. Serum or blood cobalt and chromium ion levels were obtained at the one-year post-op visit or later or if the patient had unexpected pain. The test obtained (serum or blood) was dependent on the lab performing the study. In the study period 100 patients met the inclusion criteria and had metal ion levels available for review. No patient required revision for adverse soft tissue reaction or elevated metal ion levels. Cobalt levels fell with the normal lab ranges in the majority of patients with a very small percentage demonstrating levels slightly above the normal range. Chromium levels all fell within the expected normal range. One patient had a neck exchange for mechanical reasons at 8 weeks following primary THA. This patient went on to develop elevated serum cobalt levels and a large hip effusion. The hip was revised at one year to a non-modular stem. A modular proximal stem offers the advantages of addressing variable anatomy and allowing less soft tissue dissection. Some designs have enjoyed success while others have been withdrawn from the market due to fatigue failure, dissociation or metal-associated adverse reactions. Modular junction designs vary greatly which can impact their inherent stability and their ability to resist micro-motion. In this patient group the junction has shown good stability in early follow up as judged by clinical and laboratory data. Cobalt levels were all normal or well below the range considered suspicious for adverse reaction. Chromium levels all fell within the normal range. A case of an exchanged neck with retention of the stem was associated with high cobalt levels. We discuss several junction designs and their characteristics

Background. It is still controversial whether “labral tear” in the pelvis or “pincer type's femoroacetabular impingement syndrome” should be considered a pathologic lesion, and whether they cause the early onset of osteoarthritis in the pelvis. Hypothesis. The disruption of chondrolabral junction causes degenerative change on hip joint, and the disruption of the vessel tissue to the labrum induces the rapidly progressive degeneration of outside in osteoarthritis changes. Methods. Femoral acetabulum has been escaped from the chondrolabral junction and expanded to the acetabulum inside or outward. Therefore we report the cases. Results. We found cases which has chondrolabral junction disruptive slippage, and disruption of the vessel tissue and inverted or everted labral pathologic lesion, which we named COLADIS, chondrolabral junction disruptive slippage. Conclusion. COLADIS (chondrolabral junction disruptive slippage) caused symptoms on patient's hip, and may be the pre-pathologic lesion of early osteoarthritis

Introduction. The gastrocnemius tendon extends from the musculotendinous junction proximally to the conjoint junction with soleus distally. The morphology of the junction has not, to our knowledge, been described previously. Lengthening of the gastrocnemius tendon is a standard surgical procedure in surgery for cerebral palsy. The aims of the study were to describe the morphology of the conjoint junction and to identify the location of the gastrocnemius tendon relative to palpable bony landmarks to assist with incision planning. Methods. Twenty-one embalmed adult cadaveric specimens were dissected to document the morphology of the conjoint junction. The location of the gastrocnemius tendon was measured relative to the distance between the palpable bony landmarks of the calcaneus and the head of the fibula. Results. The conjoint junction morphology was transverse in 9/21 (43%), oblique in 6/21 (29%), and arcuate as an inverted ‘U’ in 4/21 legs (19%) and ‘U’ shaped in 2/21 legs (9%). On the medial side of the leg the gastrocnemius tendon was located between 35% and 43% of the distance between the calcaneus and fibula head. The corresponding distances for the midline were 39% and 56% and for the lateral side 40% and 50%. Conclusion. The morphology of the conjoint junction varied in the specimens studied. An indication of the site of the gastrocnemius tendon relative to identifiable bony landmarks may help in incision planning either for open or endoscopic gastrocnemius lengthening

Introduction. Ion analysis has been used as one of the key indicators to assess the performance of MoM devices in patients. Modular devices, in particular having larger overall surface area (the stem and sleeve), and locking interfaces (head – bore, sleeve- taper and sleeve-bore, stem-taper surfaces) than other MoM devices are expected to release greater number of ions. Concerns have been expressed that the ion release at the taper junction might be a potential cause leading to the failure of the implant [Garbuz et al, 2010]. The aim of this study was to look into the wear and the associated ion release from the taper junction and the articulating surface of modular devices. Method. For the first time a novel design has been used to isolate the taper junction on modular devices on the hip simulators in order to compare the wear at the taper junction and articulating surface. The taper junction has been isolated in a small gaiter, while the head and cup were contained in a large gaiter. CoCrMo sleeves having an offset of +8 mm have been used on 50 mm modular heads along with Ti6Al4V stems. The acetabular components were standard BHR cups. Three devices (Smith & Nephew, UK) have been tested with newborn calf serum as a lubricant (in the large gaiter) and also as the medium containing the taper junction (in the small gaiter). The serum samples from the articulating surface and taper junction were analysed using HR-ICPMS. The locking interfaces at the taper junction have been left intact throughout the duration of the test. Both the head and the cup have been tested under anatomical conditions using the standard implant development centre's (IDC) profile for 2 million cycles (Mc). The lubricant was newborn calf serum with 0.2% sodium azide diluted with de-ionised water to achieve protein concentration of 20 mg/ml. The flexion/extension was 30°/15° and the internal/external rotation was ±10°. The force was Paul-type stance phase loading with a maximum load of 3 kN and a standard ISO swing phase load of 0.3 kN. The frequency was 1 Hz, with an 8 hour stop after every 16 hours of testing. Results and discussion. The ion analysis results from the articulating surface expressed in cumulative volume showed a biphasic wear trend at 0.96 ± 0.15 mm. 3. (0.5 Mc) and 1.05 ± 0.13 mm. 3. (2 Mc). The ion analysis results obtained for the samples from the small gaiter are (1.83 ± 0.35) x 10. −3. mm. 3. at 0.5 Mc and (4.52 ±0.83) x 10. −3. mm. 3. (2 Mc). On comparison, the ion release from the taper junction is 100 fold lower than that from the articulating surface. It should be noted that the ion release from the taper junction can be influenced by the material, tolerance, surface finish and design of the taper joint. Conclusion. The ion release associated with the taper junction is extremely low when compared with the ion release from the articulating surface

Introduction. Fatigue and wear at the head/stem modular junction of large diameter total hip replacements can be exacerbated as a result of the increase in frictional torque. In vivo, a “toggling,” anterior-posterior (A-P) movement of the head taper on the trunnion may facilitate corrosion in the presence of physiological fluids, leading to increased metal ion release. Clinically, metal ion release has been linked to the formation of pseudo tumours and tissue necrosis [1]. Aims. In this investigation, a large diameter metal on metal THR was tested on a rig designed to recreate the toggling motion at the head/stem junction. Post-test analyses are conducted to look for evidence of mechanical and corrosive damage. Methods and Materials. A 58 mm diameter metal head (12/14 taper) was assembled onto a sectioned Freeman stem affixed to custom designed rig that enabled both, axial loads and a frictional torque (for the AP toggle load) about the rotation of the femoral head to be applied as shown in Figure 1. A linear variable differential transformer (LVDT), which had a minimum resolution of 0.5 microns, was positioned in contact with the neck directly under the modular head to track A-P movements at the junction. An axial load of 150N with toggle loads varying between 100 (± 50N) and 200N (± 50N) at 1 Hz were run on 4 taper assemblies, 2 dry and 2 wet (incorporating a physiological fluid at the junction) between 400,000 and 600,000 cycles. Movement at the junction was recorded, followed by visual inspection and RedLux® surface profile analysis of the taper and trunnion. Results and Conclusion. The LVDT could successfully record movement at the junction. Initially (∼1000 cycles), the movement at the junction was found to be variable and between 5–10 microns, which can be attributed to the taper “bedding-in” on to the trunnion. The movement was then found to steadily increase before stabilising. The dry tapers recorded motion ranging between 5–15 microns, and between 10–20 microns for the wet taper. Visual inspection post testing showed minimal or no damage on the trunnion or taper surfaces on the dry tests. However, the trunnion and taper on the wet samples displayed marks and scratches on the surface (Figure 2). In addition, there was visible surface discolouration on both wet taper assemblies but none observed on the dry assemblies. This was further corroborated by Redlux topography measurements that also showed that material had been removed from both surfaces. The pilot study showed that A-P toggle movements at the junction could be produced by incorporating torque about the rotation of the head. Damage was evident on both the trunnion and taper surfaces, and discoloration was observed at the junction when fluid was introduced

Juvenile Osteochondritis dissecans (JOCD) in humans and subchondral cystic lesions (SCL) in horses (also termed radiolucencies) share similarities: they develop in skeletally immature individuals at the same location in the medial femoral condyle (MFC) and their etiology is only partially understood but trauma is suspected to be involved. JOCD is relatively uncommon in people whereas SCLs arise in 6% of young horses leading to lameness. Ischemic chondronecrosis is speculated to have a role in both osteochondrosis and SCL pathogenesis. We hypothesize that MFC radiolucencies develop very early in life following a focal internal trauma to the osteochondral junction. Our aims were to characterize early MFC radioluciencies in foals from 0 to 2 years old. Distal femurs (n=182) from Thoroughbred horses (n=91, 0–2 years old), presented for post-mortem examination for reasons unrelated to this study, were collected. Radiographs and clinical tomodensitometry were performed to identify lesions defined as a focal delay of ossification. Micro-tomodensitometry (m-CT) and histology was then performed on the MFCs (CT lesions and age-matched subset of controls). Images were constructed in 3D. The thawed condyles, following fixation, were sectioned within the region of interest, determined by CT lesion sites. Hematoxylin eosin phloxin and safran (HEPS) and Martius-Scarlet-Blue (MSB) stains were performed. Histological parameters assessed included presence of chondronecrosis, fibrin, fibroplasia and osteochondral fracture. An additional subset of CT control (lesion-free) MFCs (less 6 months old) were studied to identify early chondronecrosis lesions distant from the osteochondral junction. One MFC in clinical CT triages controls had a small lesion on m-CT and was placed in the lesion group. All m-CT and histologic lesions (n=23) had a focal delay of ossification located in the same site, a weight bearing area on craniomedial condyle. The youngest specimen with lesions was less than 2 months old. On m-CT 3D image analysis, the lesions seemed to progressively move in a craniolateral to caudomedial direction with advancing age and development. Seventy-four percent (n=17/23) of the lesions had bone-cartilage separation (considered to be osteochondral fractures) confirmed by the identification of fibrin/clot on MSB stains, representing an acute focal bleed. Fibroplasia, indicating chronicity, was also identified (74%, n=17/23). In four cases, the chondrocytes in the adjacent cartilage were healthy and no chondronecrosis was identified in any sections in the lesions. Nineteen cases had chondronecrosis and always on the surface adjacent to the bone, at the osteochondral junction. None of the subset of control specimens, less than 6 months old (n=44), had chondronecrosis within the growth cartilage. Early subchondral cystic lesions of the medial femoral condyle may arise secondary to focal internal trauma at the osteochondral junction. The presence of fibrin/clot is compatible with a recent focal bleed in the lesion. Medial femorotibial joint internal forces related to geometry could be the cause of repetitive trauma and lesion progression. In the juvenile horse, and potentially humans, the early diagnosis of MFC lesions and rest during the susceptible period may reduce progression and promote healing by prevention of repetitive trauma, but requires further study

Modularity of femoral components has been widely accepted at the head neck junction, most commonly combining two unlike metals with only sporadic reporting of compatibility issues and corrosion. The development and introduction of a new and improved modular neck junction (Rejuvenate Modular Femoral component, Stryker Orthopedics) provided the option of fine-tuning leg lengths, offset and stability. The surgical technique did indeed provide the desired endpoints, however, the early recognition of problems with the junction causing corrosion and Adverse Local Soft Tissue Reaction (ALTR) and subsequent revision has led to the product being voluntarily withdrawn from the market. My experience as an early user of this stem is described in this manuscript providing a better early recognition and treatment of this potentially very destructive process. Methods. A retrospective review of one hundred and ninety one Rejuvenate Stems that were implanted between January 2010 and January of 2012. However, after March 2011, this stem was only used on those patients who had a rejuvenate stem on the contralateral side. They were all implanted through a mini posterior incision with the first 82 patients receiving a Tritanium cluster hole cup (Stryker Orthopedics) with between two and three screws. The remaining 109 patients had an ADM (Anatomic Dual Mobility, Stryker Orthopedics). All patients were allowed to bear weight as tolerated and were followed up with Xrays at six weeks and one year. Clinical visits were recorded at 2 weeks and 6 months postop. Additional follow up was scheduled every two years following the first annual visit. Results. One hundred and seventy four of the 191 hips were available for review at the one-year follow-up. Fourteen patients have undergone revision of the hip due to increased pain and formation of an avascular pseudo capsule due to corrosion at the neck stem junction. All patients have demonstrated a black flaky residue at the taper junction and all have had a large, tense effusion with a milky colored fluid. A neo caspsule has formed in all patients that appeared avascular and thickened. Seven of the eight tritanium cups in the revision cases were loose and required revision, while none of the ADM cups were loose. One patient has undergone two revisions since the initial cause of failure was not recognized and she subsequently developed pain within three months following placement of a new modular neck at the initial revision. One patient who underwent revision developed a deep infection and is currently on antibiotics but has not cleared the infection as of this writing. Conclusion. There has been catastrophic early failure of a modular femoral component due to corrosion at the neck stem junction during the very early stages of follow up. An intense reaction appears to begin early on, perhaps contributing to failure of bony ingrowth in certain cup designs but not others. Patients who develop early onset of discomfort progress to a poorly functioning hip that presents with pain, swelling and decreased ROM. These patients need to be assessed with serum ion levels, joint aspiration for infection and ion levels if possible. A MRI with MARS technology is useful in identifying joint fluid and neo caspsule expansion. These patients should be advised on the adverse reaction that can develop and revision of the hip should be expeditiously carried out

Background. Hip resurfacing has advantages for the young active patient with arthritis; maintaining a large range of motion, preserving bone stock, and reduced dislocation risk. However high serum metal ion levels with metal-on-metal resurfacing, and their clinical implications, has led to a decline in the use of hip resurfacing. Ceramic bearing surfaces display the lowest frictional torque and excellent wear rates. Recent developments have enabled large, strong ceramic materials to be used as resurfacing components. Any wear debris that is generated from these articulations is inert. However an all-ceramic hip resurfacing could be at risk of fracture at the head-stem junction. A new ceramic hip resurfacing system with a titanium-ceramic modular taper junction has been developed. The introduction of a taper introduces the potential for fretting corrosion; we sought to determine the extent of this in an in-vitro model, and compared this prosthesis to the conventional 12/14 titanium-cobalt chrome (Ti6Al4V-CoCr) taper junction. Methods. To simulate the gait cycle, sinusoidal cyclical loads between 300N-2300N, at a frequency of 3Hz, were applied to different head-neck offsets generating different bending moments and torques. The effect of increasing the bending moment and frictional torque were tested separately. Furthermore, the resurfacing head was mounted in a fixture held with just the stem, thus representing complete bone resorption under the head. 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, six neck lengths (short to xxx-long) of the Ti6Al4V-CoCr taper were compared to the standard neutral (concentric), and 3mm A/P offset stem options for the resurfacing design. To represent frictional torque, four increments of increasing torque (2-4-6-8Nm) were applied to both tapers. In a long term test with the resurfacing stem, the worst-case scenario of the eccentric offset option and 8Nm of torque were applied, and potentiostatic measurements were taken every million cycles, up to 10 million cycles. Results. For bending moment through the centre of the head, the standard neutral resurfacing taper displayed equivalent fretting current (1.35μA) compared to its conventional taper equivalent, the short 12/14 Ti6Al4V-CoCr taper (Fig. 1a). That was despite the bending moment through the resurfacing taper being higher due to the offset nature of its taper in relation to the centre of the head. For applied torque, the resurfacing taper displayed reduced average fretting current and average maximum fretting current when compared to the conventional taper (Fig. 1b), though this did not reach statistical significance (Kruskal-Wallis test). Under long term testing for worst-case bending and torque, the resurfacing taper displayed low fretting currents (<2μA and <5μA respectively) with no significant variance of the median values across 10 million cycles (Figs. 2 and 3). Conclusion. When compared to the gold-standard taper junction, the LIMA ceramic hip resurfacing displays equivalent fretting corrosion for bending moment and improved fretting corrosion for frictional torque. Across long term testing, stable and low fretting currents at this taper junction highlight its potential in clinical use

Introduction. The bearing surfaces of ceramic-on-ceramic (CoC) total hip replacements (THR) show a substantially lower wear rate than metal-on-polyethylene (MoP) THR in-vitro. However, revision rates for CoC THR are comparable with MoP. Our hypothesis that an explanation could be adverse reaction to metal debris (ARMD) from the trunnion led us to investigate the wear at both the bearing surfaces and the taper-trunnion interface of a contemporary CoC THR in an in-vitro study. Methods. Three 36mm CoC hips were tested in a hip simulator for 5 million cycles (Mc). BIOLOX. ®. delta ceramic femoral heads were mounted on 12/14 titanium (Ti6Al4V) trunnions. Wear of femoral heads, acetabular liners and trunnions was determined gravimetrically using the analytical balance. Roughness measurements (Sa) were taken on the articulating surfaces (pre and post-test) and on the trunnion surfaces (worn and unworn). Furthermore, Energy Dispersive X-ray Spectroscopy (EDX) was used to identify and quantify the wear debris present in the lubricant using scanning electron microscope (SEM). Results and Discussion. The total volumetric wear was 0.25 mm. 3. for CoC joints and 0.29 mm. 3. for titanium trunnions. The total wear volume of the titanium trunnions was in agreement with an explant study (Kocagoz et al, 2016, CORR) which quantified the volumetric material loss from retrieved trunnions with the total wear ranging from 0.0–0.74 mm. 3. The Sa values, pre-and post-test, for heads were 0.003 ± 0.002 and 0.004 ± 0.001 µm and for liners were 0.005 ± 0.001 and 0.005 ± 0.001 µm. Pre-and post-test measurements for Sa of heads (p = 0.184) and liners (p = 0.184) did not show a statistically significant change. The Sa of the trunnions on the unworn and worn areas showed a statistically significant decrease from 0.558 ± 0.060 to 0.312 ± 0.028 µm respectively (p < 0.001). Analysis of wear debris within the lubricant confirmed the presence of titanium. A recent clinical study (Matharu et al, 2016, BMC Musc Dis) found more ARMD in CoC hips than MoP hips. This is despite there being fewer metallic components in a CoC hip than a MoP hip. This in vitro study has shown that one source of metal debris in a CoC hip is the taper-trunnion junction. Conclusion. An explanation for wear related failures in ceramic-on-ceramic hip arthroplasty, despite the low wear arising at the articulating surfaces, may now exist; namely that titanium wear particles are generated from the trunnion. No other long-term hip simulator studies have measured wear at the taper-trunnion junction

Introduction. Metal-on-polyethylene (MoP) is the most commonly used bearing couple in total hip replacements (THRs). Retrieval studies (Cooper et al, 2012, JBJS, Lindgren et al, 2011, JBJS) report adverse reactions to metal debris (ARMD) due to debris produced from the taper-trunnion junction of the modular MoP THRs. A recent retrospective observational study (Matharu et al, 2016, BMC Musc Dis) showed that the risk of ARMD revision surgery is increasing in MoP THRs. To the authors' best knowledge, no hip simulator tests have investigated material loss from the taper-trunnion junction of contemporary MoP THRs. Methods. A 6-station anatomical hip joint simulator was used to investigate material loss at the articulating and taper-trunnion surfaces of 32mm diameter metal-on-cross-linked polyethylene (MoXLPE) joints for 5 million cycles (Mc) with a sixth joint serving as a dynamically loaded soak control. Commercially available cobalt-chromium-molybdenum (CoCrMo) femoral heads articulating against XLPE acetabular liners (7.5Mrad) were used with a diluted new-born-calf-serum lubricant. Each CoCrMo femoral head was mounted on a 12/14 titanium alloy trunnion. The test was stopped every 0.5Mc, components were cleaned and gravimetric measurements performed following ISO 14242-2 and the lubricant was changed. Weight loss (mg) obtained from gravimetric measurements was converted into volume loss (mm. 3. ) and wear rates were calculated from the slopes of the linear regression lines in the volumetric loss versus number of cycles plot for heads, liners and trunnions. Additionally, volumetric measurements of the head tapers were obtained using a coordinate measuring machine (CMM) post-test. The surface roughness (Sa) of all heads and liners was measured pre and post-test. At the end of the test, the femoral heads were cut and the roughness of the worn and unworn area was measured. Statistical analysis was performed using a paired-t-test (for roughness measurements) and an independent sample t-test (for wear rates). Results and Discussion. The mean volumetric wear rates for CoCrMo heads, XLPE liners and titanium trunnions were 0.019, 2.74 and 0.013 mm. 3. /Mc respectively. There was a statistically significant decrease (p<0.001) in the Sa of the liners post-test. This is in contrast to the femoral heads roughness in which no change was observed (p = 0.338). This head roughness result matches with a previous MoP in vitro test (Saikko, 2005, IMechE-H). The Sa of the head tapers on the worn area showed a statistically significant increase (p<0.001) compared with unworn, with an associated removal of the original machining marks. The mean volumetric wear rate of the head tapers obtained using the CMM (0.028 ± 0.016 mm. 3. /Mc) was not statistically different (p=0.435) to the mean volumetric wear rate obtained gravimetrically (0.019 ± 0.020 mm. 3. /Mc) for the femoral heads. Therefore, wear of the heads arose mainly from the internal taper. The mean wear rates of the CoCrMo taper and titanium trunnion are in agreement with a MoP explant study (Kocagoz et al, 2016, CORR). Conclusion. This is the first long-term hip simulator study to report wear generated from the taper-trunnion junction of MoP hips

Mechanical wear and corrosion lead to the release of metal particulate debris and subsequent release of metal ions at the trunnion-taper surface. In order to quantify the amount of volume loss to ultimate locations in the surrounding joint space, finite element analysis of the modular head-stem junction is being carried out. The key purpose being to determine a set of optimum design changes that offer the least material loss at the taper-trunnion junction using optimization algorithms such as the gradient based local search (Sequential Quadratic Programming–SQP) and global search (Non-Dominated Sorting Genetic Algorithm-II–NSGA-II). In a broader sense, the principal goal is to work toward the minimization of wear debris produced in the hip joint, thereby resulting in a longer prosthetic lifetime. A numerical approach that simulates wear in modular hip prostheses with due consideration to the taper-trunnion junction on metal-on-metal contacts is proposed. A quasi-static analysis is performed considering realistic loading stages in the gait cycle, and nonlinear contact analysis is to be employed. The technique incorporates a measured wear rate as an input to the finite element model. The simulation of wear is performed by progressively changing nodal coordinates to simulate the wear loss that occurs during surface interaction. The geometry of the worn surface is updated under gait loading. With a given geometry and gait loading, the linear and volumetric wear increases with the number of gait cycles. The continuous wear propagation is discretized and an approximation scheme known as surrogates is to be developed using Artificial Neural Networks (ANN) to reduce the expensive computational simulations during optimization. The model is employed in the optimization schemes coded in MATLAB and linked to the finite element model developed in ANSYS batch mode. The objective function of the optimization problem is to minimize the volumetric wear at taper-trunnion interface under some constraints. By minimizing the volumetric wear, the chance of failure of modular hip implants is also minimized. The FE model developed to reproduce fretting wear is validated through in vitro wear simulations. The important taper design variables considered to have impact on the fretting corrosion performance include; medial-lateral offset, neck length, taper head diameter, trunnion length and diameter, included angle for the head/neck tapers, angle of mismatch or variation in taper trunnion angle, etc. It is expected from clinical outcomes that increased offset and large taper diameter has serious implications in the fretting corrosion behavior primarily because these variables control the bending stresses and strains along the length of the taper. During cyclic loading of the taper, the higher the strain range, the higher will be the relative micromotion at the point of engagement between the stem and head tapers. This research is carried out with the objective to optimize the effects of these geometrical factors at the mating taper interfaces. The developed models have great potentiality for accurate assessment of wear in a range of metal-on-metal (MoM) hip prostheses at the femoral head taper-trunnion junction while substantially reducing the wear and failure rate of prostheses

Introduction. Modern hip replacements all have encapsulated the design concept of proximal modularity. The factors contributing to the increased wear and corrosion at the taper junction are trunnion geometry, surface characteristics, head size, impaction forces, and material coupling. This study maps the inferior and superior region of the trunnion and bore to provide a visual identification of the corrosion severity. The corrosion/wear generated inferiorly and superiorly at the bore and trunnion will be quantified to understand how corrosion is affected by mechanical stresses in relation to anatomical orientation. Methodology. Three neck tapers generated from bar stock containing a threaded trunnion Ti-6Al-4V and 3× 32mm femoral heads (Co-Cr-Mo) with a +4 offset manufactured by Signature Orthopaedics were used within this study. Rectangular Rozzette strain gauges (Tokyo Sokki Kenkyujo Co., Ltd.) were adhered onto the inferior and superior sections of the neck section. The tapers were fatigued in accordance to ISO 7206 at 5Hz for 5 million cycles at 37 degrees Celsius in phosphate buffered saline. The tapers were sectioned from the center of the femoral head to split both trunnion and bore into superior and inferior components. SEM imaging of all surface areas for each component, per taper (4) was done under ×100 magnification. The images were used to quantify the corrosion present across the surface area using a MATLAB based program called Histomorph. To obtain a visual observation of the variation of corrosion across the bore and trunnion the proximal, medial, and distal regions were mapped together for both the superior and inferior sections. Results. The superior region of the trunnion had a dominant tensile strain in comparison to the inferior region, which had a dominant compressive strain. Corrosion/wear of the inferior section of the trunnion was significantly higher (p<0.05) in comparison to the superior section (Figure 1). The bore had more corrosion/wear on the superior side in comparison to the inferior side however the difference was not significant. The mapping of the trunnion shows corrosion/wear along the whole length of the inferior side and dominantly at the distal region for the superior side (Figure 2 & 3). The superior section of the trunnion had higher corrosion/wear damage across the center and distal regions of the trunnion. The subdivision of the superior section reveals that the majority of the distal section contains higher wear/corrosion damage. However the central region also has sufficient corrosion/wear extending across the width of the bore. Conclusion. The corroded regions have shown that the type of stress present on the regions of the taper junction determines the severity of corrosion. The inferior section of the trunnion under compressive stress has significantly (p<0.05) higher corrosion/wear in comparison to the superior section dominated by tensile stress

INTRODUCTION. The lifetime of total hip replacements (THR) is often limited by adverse local tissue reactions to corrosion products generated from modular junctions. Two prominent damage modes are the imprinting of the rougher stem topography into the smoother head taper topography (imprinting) and the occurrence of column-like troughs running parallel to the taper axis (column damage). It was the purpose of this study to identify mechanisms that lead to imprinting and column damage based on a thorough analysis of retrieved implants. METHODS. 776 femoral heads were studied. Heads were visually inspected for imprinting and column damage. Molds were made of each head taper and scanned with an optical coordinate measuring machine. The resulting intensity images were used to visualize damage on the entire surface. In selected cases, implant surfaces were further analyzed by means of scanning electron microscopy (SEM) and white light interferometry. The alloy microstructure was characterized for designs from different manufactures. RESULTS. 165 heads exhibited moderate to severe damage (modified Goldberg scale). Out of those heads 83% had imprinting and 28% exhibited column damage. In most cases with imprinting, the entire contact area between stem and head was affected (Figure 1). Several cases exhibited early signs of imprinting, usually starting on the distal-inferior and distal superior side. High resolution SEM imaging revealed that imprinting was a fretting driven process that was independent of the hardness and material of the stem and head. The SEM images showed that the main mechanism was surface fatigue under partial slip fretting. The generated wear debris was the primary driver of imprinting by three-body fretting. The effect was detrimental on the smoother head surface, but less severe on the rougher stem, where debris was pushed into the troughs of the machining mark topography. 90% of cases with column damage also exhibited imprinting. The other ten percent were either cases in which column damage was too extensive to identify imprinting, or the stem taper was smooth and therefore could not induce imprinting. Metallographic analysis showed that column damage was dictated by the alloy microstructure. Wrought alloy heads frequently exhibited banding related to slight alloy segregations. The process of column damage was entirely chemically driven with etching occurring along the banded microstructure eventually resulting in troughs that were several tens of micrometers deep (Figure 2). DISCUSSION. Imprinting and column damage are common damage modes in THR femoral heads. Imprinting is fretting (miro-motion) driven while column damage is caused chemically, but is also dictated by the alloy micro-structure. However, the results suggest that these two damage modes may be related. The damage process starts with local fretting slowly progressing to a large area of imprinting. The imprinting process leads to widening of the crevice, enabling joint fluid and biological constituents (protein, cells, etc.) to enter the taper interface. This change in local chemistry within a confined crevice environment can cause an etching process that leads to column damage, but only if the femoral head alloy has a banded microstructure

Purpose. We report our surgical management of a series of primary and metastatic tumours of the lumbosacral junction, highlighting different methods of fixation, outcome and complications. Method. Seven patients with primary and four with secondary tumours involving the lumbosacral junction underwent surgery. After tumour resection, iliolumbar fixation was performed in all but one case, using Galveston rods (4) or iliac screws (6). All constructs were attached proximally with pedicle screws. Cross links were used in all instrumented cases and autologous and allogenic bone graft applied. Results. There were no perioperative deaths. Mean operating time was 7.3 hours (range 3-18) and there was extensive blood loss (mean transfusion requirement 7.5 units, range 0-20). We estimate a transfusion requirement of approximately one unit per hour operating time. However, we noted no complications attributable to either blood loss or transfusions. Ambulation improved in 5, was unchanged in 5 and deteriorated in one. Neurological status deteriorated in 4 and remained static in the others. However in all but one case the neurological deficit was defined by the nature of proposed surgery. Mean survival from surgery for patients with metastatic disease was 9.5 months (3-18). At mean follow-up of 10 months (1-19 months), all patients with primary tumours were still alive without evidence of tumour recurrence. Extralesional excision, and therefore potentially curative surgery, was achieved in 4 cases where this was the primary goal of surgery (osteosarcoma, osteoblastoma, chordoma, embryonic rhabdomyosarcoma). There were no cases of metalwork failure. One patient has undergone revision surgery for pseudarthrosis. Conclusion. Sacral resection and iliolumbar reconstruction is a feasible treatment option in selected patients, offering potential cure. The fixation methods used by the authors restored lumbosacral stability, sufficient for pain relief and preserving ambulation and usually the predicted level of neurological function

Introduction. Recent reports implicate fretting corrosion at the head-stem taper junction as a potential cause of failure of some large diameter metal-on-metal (MOM) devices. Fretting observed at modular junctions is thought to be a type of ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to an increase in contact stresses and micromotions at the taper interface. These may include: intra-operative taper assembly, taper contamination by debris or body fluids, patient weight and ‘toggling’ of the head or increased frictional torque in a poorly functioning bearing. We adopted a finite element approach to model the head-taper junction, to analyze the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants. Materials and methods. Models of the Biomet Type-1 taper, a 60 mm head and a taper adaptor were created. These models were meshed with a mesh size based on a mesh density convergence study. Internal mesh coarsening was applied to reduce computational cost. Elastic-plastic material properties based on tensile tests were assigned to all titanium components. The contact conditions used in the FE analyses were validated against push-on and pull-off experiments, resulting in a coefficient of friction of 0.5. To analyze micromotions at the taper-adaptor connection, the models were loaded with 2300N (ISO 7206-4) and 5340N (ISO 7206-6), after being assembled with 2-4-15 kN, axially and under a 30º angle. This ISO standard is commonly used to determine endurance properties of stemmed femoral components. Micromotions and contact pressures were analyzed by scoring them to an average micromotion and average contact pressure for the surface area in contact. Results. For the higher loads (5340N) the average contact pressure decreased when a higher assembly force was used (Figure1a), as a result of the fact that the loads were distributed over a larger contact area. The average contact pressure increased when tested at the 30º angle. Figure1b shows that the average micromotion decreased when a higher assembly load is applied, except when the adaptor is assembled at a 30º angle. When assembled at a 30º angle with 15 kN the average micromotion is 1.5 times higher (11.1–7.4 µm). Discussion. The location and patterns of the micromotions were consistent with the patterns and locations of wear found on retrieved tapers described in the literature and those generated in an in vitro test model (Figure 2a-b). Increased impaction loads reduced the average amount of micromotion and therefore, fretting. For more realistic results, we intend to apply more complex loading regimes in future analyses, enabling to study the effect of phenomena such as edge loading and frictional torque. Moreover, the mechanical outcome as presented here will be used in a wear model, to simulate volumetric wear

INTRODUCTION. Adverse local tissue reactions (ALTR) and elevated serum metal ion levels secondary to fretting and corrosion at head-neck junctions in modular total hip arthroplasty (THA) designs have raised concern in recent years. Factors implicated in these processes include trunnion geometry, head-trunnion material couple, femoral head diameter, head length, force of head impaction at the time of surgery, and length of implantation. Our understanding of fretting and corrosion in vivo is based largely on the analysis of retrieved prostheses explanted for reasons related to clinical failure. Little is known about the natural history of head-neck tapers in well-functioning total hip replacements. We identified ten well-functioning THA prostheses retrieved at autopsy. We sought to determine the pull-off strength required for disassembly and to characterize fretting and corrosion apparent at the head-neck junctions of THAs that had been functioning appropriately in vivo. METHODS. Ten cobalt-chromium femoral stems and engaged cobalt-chromium femoral heads were retrieved at autopsy from 9 patients, after a mean length of implantation (LOI) of 11.3 ± 8 years (range 1.9–28.5). Trunnion design and material, femoral head material, size, and length, LOI, and patient sex were recorded (Table 1). Femoral heads were pulled off on a uniaxial load frame according to ASTM standards under displacement control at a rate of 0.05mm/s until the femoral head was fully disengaged from the trunnion. Mating surfaces were gently cleaned with 41% isopropyl alcohol to remove any extraneous debris. Femoral trunnions and head tapers were examined under a stereomicroscope by two independent graders to assess presence and severity of fretting and corrosion (method previously established). Trunnions and tapers were divided into 8 regions: anterior, medial, posterior, and lateral in both proximal and distal zones. Minimum possible damage score per hip was 32 (indicating pristine surfaces). The total possible score per hip was 128 (2 damage modes × 2 mating surfaces × 8 regions × max score of 4 per region). RESULTS. Mean pull-off force among all retrievals was 2446 ± 841 N (1655 – 4246 N). Mean pull-off force for 14/16 tapers (2998 ± 1298 N) was larger than for 12/14 tapers (2210 ± 531 N). Seven retrievals (70%) had no evidence of damage on either the stem or head component (Fig. 1). Three retrievals showed evidence of damage: (1) corrosion in one zone of the femoral head taper (score 33); (2) a circumferential ring of fretting in one zone of the stem trunnion (score 36); (3) circumferential rings of minor fretting in two regions of the stem trunnion (score 40). LOI for damaged retrievals was 16.3 ± 6 years, longer than that for undamaged retrievals (9.1 ± 9.1 years). CONCLUSION. THAs that had been well-functioning in vivo showed little evidence of fretting and corrosion. The presence of minor fretting and corrosion correlated with increased LOI. Mean pull-off force was 2446 +/- 841 N among the complete sample of ten THAs. Larger tapers were associated with greater average pull-off strength. Further investigation is required in order to clarify the clinical implications of these results

Introduction. Fretting corrosion at the taper interface has been implicated as a possible cause of implant failure. Using in-vitro testing, fretting wear observed at tapers of retrieved implants may be reproduced (Marriott, EORS-2014). In order to reduce time and cost associated with experimental testing, a validated finite element method (FE) can be employed to study the mechanics at the taper. In this study we compared experimental and representative FE simulations of an accelerated fretting test set-up. Comparison was made by between the FE wear score and volumetric material loss from the testing. Methods. Experimental test set-up: An accelerated wear test was developed that consistently reproduced fretting wear features observed in retrievals. Biomet stems with smooth 4° Type-1 tapers were combined with Ti6Al4V Magnum +9 mm adaptors using a 2 or 15 kN assembly force. The head was replaced with a custom head fixture to increase the offset and apply a torque at the taper interface. The stems were potted according to ISO 7206-6:2013. The set-up was submerged in a test medium containing PBS and 90gl-1 NaCl. The solution was pH adjusted to 3 using HCl and maintained at 37°C throughout the tests. For each assembly case, n=3 tests were cyclically loaded between 0.4–4 kN for 10 Million cycles. Volumetric wear measurements were performed using a Talyrond-365 roundness measurement machine. The FE model was created to replicate the experimental set up. Geometries and experimental material data were obtained from the manufacturer (Biomet). The same assembly forces of 2 and 15 kN were applied, and the same head fixture was used for similar offset and loading conditions. The 4 kN load was applied at the same angles in accordance with ISO 7206-6:2013. Micromotions and contact pressures were calculated, and based on these a wear score was determined by summation over all contact points. Results. The FE wear score showed a significant drop after an assembly force of 15 kN has been applied. The micromotion scores were similar, and the contact pressure was higher due to the larger assembly force. The volumetric wear measurements did not show a significant difference between the two assembly cases due to the large variation in measured values. A downward trend can be observed when applying higher assembly forces, similar to the trend seen at the FE wear score (figure 1, table1). Discussion. This study shows a correlation between experimental and FE simulation, however highlights the difficulty in validating a FE model with complex in-vitro experiments. Due to the nature of experimental testing, it is impossible to remove all sources of error associated with the set-up. The use of a single static load and the absence of fluids and corrosion processes means that the full mechanics of the wear process could not be fully replicated. Despite these deficiencies the general trends and wear patterns observed in the experimental setup were reproduced. Further studies will focus on including the interplay between the aforementioned properties, to provide a better simulation of the fretting processes occurring at the taper junction