Introduction. The use of Additive Manufacturing (AM) to 3D print titanium implants is becoming widespread in orthopaedics, particularly in producing cementless porous acetabular components that are either custom-made or off-the-shelf; the primary design rationale for this is enhanced bony fixation by matching the porosity of bone. Analysis of these retrieved components can help us understand their performance; in this study we introduce a non-destructive method of the retrieval analysis of 3D printed implants. Material and methods. We examined 11 retrieved 3D printed acetabular cups divided into two groups: “custom-made” (n = 4) and “off-the-shelf” (n = 7). A macroscopic visual analysis was initially performed to measure the area of tissue ongrowth. High resolution imaging of each component was captured using a micro-CT scanner and 3D reconstructed models were used to assess clinically relevant morphometric features of the porous structure: porosity, porous structure thickness, pore size and strut thickness. Optical microscopy was also used as a comparison with microCT results. Surface morphology and elemental composition of the implants were investigated with a Scanning Electron Microscope (SEM) coupled with an Energy Dispersive X-ray Spectroscope (EDS). Statistical analysis was performed to evaluate possible differences between the two groups. Results. We found a spread of tissue coverage, median of 81% (23 – 95), with a trend with time in situ. Custom implants showed a higher spread of porosity, with median value of 74.11% (67.94 – 81.01), due to the presence of differently designed porous areas. Off-the-shelf cups had median porosity of 72.49% (66.67 – 73.07), but there was no significant difference between the two groups (p = 0.164). There was a significant difference in the thickness of the porous structure of the two groups, which were 3.918 mm (3.688 – 4.102) and 1.289 mm (1.235 – 1.364), respectively (p = 0.006). SEM output showed specific morphological features of 3D printed object; EDS analysis suggested that no chemical modifications occurred in vivo, with elemental ratios (Ti/Al = 14; Ti/V = 21; Al/V = 1.51) comparable to previously published results. Conclusion. This is one of the first retrieval studies of 3D printed orthopaedic implants. We introduced a method for the investigation of these components and micro-CT scanning enabled the non-destructive assessment of the porous structure. This work represents the first step in understanding the performance of 3D printed implants

Introduction. Thermally treated 1st generation highly crosslinked polyethylenes (HXLPE) have demonstrated reduced penetration and osteolysis rates, however, concerns still remain with respect to oxidative stability and mechanical properties of these materials. To address these concerns, manufacturers have introduced the use of antioxidants to quench free radicals while maintaining the mechanical properties of the HXLPE. Two common antioxidants are α-tocopherol (Vitamin-E) and pentaerythritol tetrakis (PBHP). These may be either mixed prior to consolidation, or diffused throughout the polymer after consolidation and irradiation. In vitrostudies have shown that these materials are oxidatively stable and have improved mechanical properties compared to 1st generation HXLPEs; however, few studies have investigated the in vivo performance of anti-oxidant stabilized HXLPE. The purpose of this study was to investigate the revision reasons, oxidation, and mechanical properties of retrieved short-term anti-oxidant HXLPE. Methods. Between 2010 and 2015, 73 anti-oxidant HXLPE components were collected as a part of an IRB approved, multi-institutional retrieval analysis program during routine revision surgery. Of the seventy-three components, 30 (41%) were acetabular liners, whereas, 43 were tibial inserts. The components were fabricated from three different materials: Vitamin-E Diffused HXLPE (n=30; E1, Biomet), Vitamin-E Blended (n = 41; Vivacit-E, Zimmer) and PBHP blended (n = 2, AOX, DePuy). The hip and knee components were implanted for 0.7 ± 0.8 years (Range: 0.0–2.25 years) and 0.8 ± 1.1 years (Range: 0.0–4.5 years), respectively. Implantation time, patient weight, age, gender, and activity levels were similar between hip and knee components (Table 1). For oxidation analysis, thin slices (∼200μm) were taken from medial condyle and central eminence of the tibial inserts or the superior/inferior axis from hip components. The slices were boiled in heptane for six hours to extract lipids absorbed in vivo. 3-millimeter FTIR line scans were taken perpendicular to the surface of interest, according to the ASTM F2102. Mechanical properties were assessed using the small punch test (ASTM F2183). Forty-three explants were available for destructive testing. Results. The predominant revision reasons were loosening, instability, and infection (Figure 1). Oxidation was low in both the hip and knee components (Mean OI≤0.1; Figure 2). For both tibial inserts and acetabular liners, there was no correlation between implantation time and oxidation indices (p>0.05). In the tibial inserts, the AP face had slightly higher oxidation indices than the articulating surface (Mean difference = 0.04; p=0.03). There was no difference in ultimate load between hips and knees at the surface (p=0.14) or the subsurface (p=0.38). Discussion. This study analyzed the revision reasons, oxidative stability, and mechanical properties of short-term retrieved 2nd generation HXLPE. The observations of this study show that anti-oxidant infused HXLPE exhibited low oxidative indices (Mean OI<0.1). There was no difference observed in the mechanical properties of these materials between hip and knee applications. However, this study is limited by short implantation times. This is unavoidable because the materials have only recently become clinically available. The data presented serves as a benchmark for future studies when longer-term retrieved implants become available

Background:. Polyethylene wear in total knee arthroplasty (TKA) is influenced by patient, surgeon and implant factors. The objective of this study is to assess the effect of limb alignment, implant position and joint line position on the pattern of wear in posterior stabilized (PS) tibial inserts. Methods:. This was a retrieval analysis of 83 PS liners collected from patients who underwent revision surgery from 1999 to 2011. Inserts were divided into 16 zones and a microscopic analysis of surface damage was carried out. We determined overall damage with a scoring system. Pre-revisions radiographs were reviewed and analyzed for correlation with the wear profile. Results:. The mean age was 73 years old (range 45 to 96 years old) and the mean duration of implantation was 3.5 years (range 0.1 to 10.6 years). The most common reason for revision was infection (71%, 59 of 83 liners), followed by aseptic loosening (6%, 5 of 83 liners) and instability (6%, 5 of 83 liners). The most common mode of wear was burnishing, followed by abrasion and pitting. The total damage score was significantly higher in knees with postoperative varus alignment more than 3 degrees (p = 0.03). Postoperative varus alignment was associated with significantly more wear in the medial compartment (p = 0.03). The total damage score to the post was significantly more in knees with joint line elevation more than 5 mm (9.7 ± 3.9, compared to 6.5 ± 3.7 in knees with less joint line elevation) (p = 0.05). The most commonly affected compartment was the medial compartment. Conclusion:. Limb malalignment and implant malposition resulted in more wear in PS TKA

Retrieval analysis has been valuable in the assessment of in-vivo surface damage of orthopedic devices. Historically, subjective techniques were used to grade damage on the implant's surface. Microscopy improved the ability to localize and quantify damage, but cannot measure volumetric wear due to this damage. Laser scanning provides volumetric wear, but lacks image data. Recent techniques superimpose image data on laser scan data (photorendering) and combine the strengths of both methods. Our goal is to use such methods to improve our damage assessment and potentially correlate this assessment to volumetric wear. This project focused on two areas: image-stitching and photorendering. Image-stitching registers multiple images into large-scale high-resolution composites. Six total disc replacement components were imaged with a digital microscope (Moticam 2, Motic). Three sets were taken of each component: a single template at 10x zoom (1×1), a 4-image composite at 18x zoom (2×2), and a 9-image composite at 18x zoom (3×3). The 2×2 and 3×3 sets were image-stitched to resemble their template counterpart. Measurement error was defined using common pixels identified between the composite and template images for comparison with a semi-automated feature detection algorithm (Figure 1). For photorendering, a pilot study was performed on a single retrieved tibial bearing. The component was imaged with a digital microscope (VHX-2000, Keyence) under a 3D image-stitching setting, providing a high-resolution photo embedded with height values. MATLAB was used to convert the image into a photo-rendered point cloud approximating the surfaces. The component was then laser scanned, creating a 3D point cloud with resolution 0.127 mm. The photo-rendered point cloud data was registered to the laser scan data using an iterative closest point algorithm (Geomagic Studio, Geomagic). An analysis of all composite images showed a mean error of 0.221 mm. Figure 2 compares regions of images for the template, 2×2, and 3×3 composites. Zooming in shows the effect of the increased resolution contained in the composite. The 2×2 and 3×3 composites had mean errors of 0.231 mm and 0.209 mm, respectively; these were not significantly different. Comparisons among image types showed that components with less features exhibited larger errors during image-stitching. Figure 3 shows images resulting from each step of the photorendering process. The final image of the figure shows a qualitative result of our ability to photorender the tibial bearing surface of the component. While combining microscopy and laser scan data works anecdotally, further analyses must be performed to assure the robustness of the technique. The digital microscope's embedded image-stitching software is limited in its maximum field of view; we look to extend this by taking multiple scans and using in-house software to generate a composite of a whole implant. The improved resolution provided by microscopy offer an opportunity to automate damage assessment, yielding damage mapped images which can also be overlaid on laser scan data. This may provide a means to better quantify observed damage and yield meaningful correlations with volumetric loss due to wear

This study reports the mid-term results of a large bearing hybrid metal on metal total hip replacement (MOMHTHR) in 199 hips (185 patients) with mean follow up of 62 months. Clinical, radiological, metal ion and retrieval analysis were performed. Seventeen patients (8.6%) had undergone revision, and a further fourteen are awaiting surgery (defined in combination as failures). Twenty one (68%) failures were females. All revisions and ten (71%) awaiting revision were symptomatic. Twenty four failures (86%) showed progressive radiological changes. Fourteen revision cases showed evidence of adverse reactions to metal debris (ARMD). The failure cohort had significantly higher whole blood cobalt ion levels (p=0.001), but no significant difference in cup size (p=0.77), inclination (p=0.38) or cup version (p=0.12) compared to the non revised cohort. Female gender was associated with increased risk of failure (p=0.04). Multifactorial analysis demonstrated isolated raised Co levels in the absence of symptoms or XR changes were not predictive of failure (p=0.675). However the presence of pain (p<0.001) and XR changes (p<0.001) in isolation were significant predictors of failure. Wear analysis (n=5) demonstrated increased wear at the trunnion/head interface (mean out of roundness measurements 34.5 microns (normal range 8–10 microns) with normal wear levels at the articulating surfaces. Macroscopically corrosion was evident at the proximal and distal stem surfaces. Cumulative survival rate, with revision for any reason was 92.4% (95%CI: 87.4–95.4) at 5 years. Including those awaiting surgery, the revision rate would be 15.1% with 89.6% (95% CI: 83.9–93.4). Cumulative survival at 5 years. This MOMHTHR series has demonstrated unacceptable high failure rates with evidence of high wear at the head/trunnion interface and passive corrosion to the stem surface. Female gender was an independent risk factor of failure. Metal ion levels remain a useful aspect of the investigation work up but in isolation are not predictive of failure

Introduction. Antibiotic loaded polymethyle methacrylate spacers are commonly used in the management of septic hip replacements. Aim. The aim of this study was to determine wear patterns on the articulating surfaces of these spacers, as well as to determine the extent of PMMA particulate debris generation. Method. We took tissue specimens around the acetabulae in 12 cases at the time of the second stage procedure for septic total hip revisions. These were subjected to histological analysis to determine the extent of PMMA particulate debris contamination. We also performed a basic explant retrieval analysis of the articulating surfaces of the PMMA spacers to determine any specific wear patterns. Results. We found numerous PMMA particles in the acetabular soft tissues biopsied. The particle concentration was highest in the area of the acetabular fovea. We could also demonstrate specific wear patterns on the spacers that could be correlated with the generally mismatched articulating couple between the spacer and the bony acetabulum. We could also demonstrate some boney destruction present in the acetabulum with long-term spacer use. Conclusions. We concluded that significant amounts of PMMA particulate debris are generated by these articulating antibiotic spacers. The total volume of this debris may be determined by specific wear patterns on the spacers’ surfaces. We recommend a thorough debridement to decrease the PMMA particle load generated. Consideration in respect of the bearing surface implanted after the explantation of the PMMA spacer should take into account the effect of the debris on the bearing surfaces. We also make recommendations in respect of the design of these PMMA spacers

Objective

We explanted NeuFlex metacarpophalangeal (MP) joint prostheses to identify common features, such as position of fracture, and thus better understand the reasons for implant failure.

Introduction

Detailed analysis of retrieved total hip replacements (THRs) is valuable for assessing implant and material successes and failures. Reduction of bearing wear and corrosion and fretting of the head-neck trunnion is essential to implant durability and patient health. This research quantifies and characterizes taper and bearing surface damage on retrieved oxidized zirconium THRs.

Young osteoarthritic male patients have been considered the ideal candidates for Metal-on-Metal (MoM) hip resurfacing arthroplasty (HRA), based on generally good long term results. In contrast, hip resurfacing in young female patients has become controversial. Recently, one implant manufacturer withdrew 46mm and smaller components, citing poorer than expected 10 year outcomes in females with smaller HRAs. Whether this difference is related to gender or to component size is still debated. Possible reasons for higher failure rates reported in females include higher rates of hip dysplasia, poorer bone quality and the risk of higher wear in some smaller sized implants with low cup coverage angles.

We reviewed HRA revision specimens with the aim of comparing mode of failure, time to revision, femoral cement characteristics and acetabular bone attachment in specimens larger and smaller than 46mm and from male versus female patients.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in the form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from well functioning small diameter, with poorly functioning LHMOMTHR's using the above technique.

Aims. The aim of this study was to present the first retrieval analysis findings of PRECICE STRYDE intermedullary nails removed from patients, providing useful information in the post-market surveillance of these recently introduced devices. Methods. We collected ten nails removed from six patients, together with patient clinical data and plain radiograph imaging. We performed macro- and microscopic analysis of all surfaces and graded the presence of corrosion using validated semiquantitative scoring methods. We determined the elemental composition of surface debris using energy dispersive x-ray spectroscopy (EDS) and used metrology analysis to characterize the surface adjacent to the extendable junctions. Results. All nails were removed at the end of treatment, having achieved their intended lengthening (20 mm to 65 mm) and after regenerate consolidation. All nails had evidence of corrosion localized to the screw holes and the extendable junctions; corrosion was graded as moderate at the junction of one nail and severe at the junctions of five nails. EDS analysis showed surface deposits to be chromium rich. Plain radiographs showed cortical thickening and osteolysis around the junction of six nails, corresponding to the same nails with moderate – severe junction corrosion. Conclusion. We found, in fully united bones, evidence of cortical thickening and osteolysis that appeared to be associated with corrosion at the extendable junction; when corrosion was present, cortical thickening was adjacent to this junction. Further work, with greater numbers of retrievals, is required to fully understand this association between corrosion and bony changes, and the influencing surgeon, implant, and patient factors involved. Cite this article: Bone Jt Open 2021;2(8):599–610

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion/taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from small diameter with LHMOMTHR's. 3 groups of retrieval tapers were analysed (Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Group 3: 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. Both bearing surfaces and head tapers were measured for wear using the Redlux profiling non contact measurement system. Measurements included taper angle and 3D surface maps. Taper angles obtained with the Redlux method were compared to those obtained using CMM measurement on 3 parts. The Redlux profiling, including imprints, was also repeated 3 times to gauge potential errors. There was no difference in mean 12/14 taper angles between groups. There was no difference in volumetric and linear wear at the bearing surface between groups. Only the LHMOMs showed transfer of pattern from the stem to the internal head taper, with clear demarcation of the contact and damaged area between head taper and stem trunnion. 3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group alone. Discussion: Differences in appearance of the taper surface between LHMOMTHRs and MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure. Further work is required to fully qualify the Redlux method capabilities.

Introduction:

First generation highly crosslinked polyethylenes (HXPLEs) have proven successful in lowering both penetration and osteolysis rates. However, 1^st generation annealing and remelting thermal stabilization have been associated with in vivo oxidation or reduced mechanical properties. Thus, 2^nd generation HXLPEs were developed to improve oxidative stability while still maintaining material properties. Little is known about the in vivo clinical failure modes of these 2^nd generation HLXPEs.

The purpose of this study was to assess the revision reasons, wear, oxidative stability, and mechanical behavior of retrieved sequentially annealed Vitamin E diffused HXLPE in THA and TKA.

Controversy has existed for decades over the role of fretting-corrosion in modular CoCr heads used with stems of CoCr vs Ti6Al4V. Since retrieval data on taper performance remains scant, we report here an18-year survivorship of a Ti6Al4V: CoCr combination (APR design; Intermedics Inc). Unique to this study were the threaded profiles present on both stem and head tapers (Fig. 1).

This female patient was revised for pain, osteolysis and recurrent hip dislocation at 17 years, 10 months. A prior MPE hip replacement performed for her severely dysplastic right hip had lasted 11 years. At this 2nd revision, the 28 mm CoCr head was found dislocated posteriorly and superiorly. Metallosis was evident in the tissues. The polyethylene liner showed extensive rim damage on both anterior and posterior aspects. The neck of her APR Revision stem (Intermedics Inc) had worn through the polyethylene rim and impinged on the metal cage. The cage was found loose, the liner had disassociated, and the peri-trochanteric areas were compromised by massive osteolysis. The femoral stem and head were removed together without disassembly. The femoral stem and acetabular construct were replaced by an ARCOS revision system using 36 mm head with a Freedom cup (cemented to Max-Ti cage; Biomet Inc.).

The complete femoral neck and head were bi-valved assembled in horizontal plane for direct imaging by interferometry and SEM (Fig. 1a). After sectioning the head separated from the stem. Quantitative imaging used 1 to 5 regions with 6-replicate measurements per region and differentiation into contact and non-contact zones (Fig. 1b). Visual corrosion mapping (3) was recorded digitally in 4 anatomical views (Figs 1b–f).

The thread profile on contact zone inside the head (Fig. 2a) had a pitch of approximately 40 μm and a peak-to-valley depth of 4 μm overall (Fig. 2b profile section of thread: PV = 2 μm). The thread profile on stem trunnion (Fig. 3a) had a pitch of approximately 125 μm and a peak-to-valley depth of 3.5 μm overall (Fig. 2b profile section of thread: PV = 1 μm). Thus the stem trunnion thread was much coarser than the head. Overall corrosion grading was judged very mild. Overall we were satisfied that this Ti6Al4V: CoCr combination taper junction with threaded interfaces had performed very well for 18 years. Nevertheless, our visual grading was subject to opinion and thus unrewarding. The continuing project will quantify the contacting and non-contacting regions of head and stem (Fig. 1b).

Introduction

Wear debris generation in metal-on-metal (MOM) total hip arthroplasty (THA) has emerged as a compelling issue. In the UK, clinically significant fretting corrosion was reported at head-taper junctions of MOM hip prostheses from a single manufacturer (Langton 2011). This study characterizes the prevalence of fretting and corrosion at various modular interfaces in retrieved MOM THA systems used in the United States.

Introduction

Titanium nitride (TiN) coatings are used in total hip arthroplasty to reduce friction of bearing couples or to decrease the allergic potential of orthopaedic alloys. Little is known about performance of currently manufactured implants, since only few retrieval studies were performed, furthermore they included a small number of implants manufactured over 15 years ago.

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

In an effort to understand the role of metal ion analysis and how it relates to revision surgery and implant wear, four revised MOM cases were reviewed. The first case was revised for acute infection and is representative of the low bearing wear predicted by MOM simulator studies. Two of the four cases had apparent anterior subluxation as a result of hip hyperextension occurring with long stride gaits. The last case is a true hypersensitivity response to CoCr ions. All four MOM prostheses were implanted by one surgeon and revised by the same surgeon approximately 6–8 years postoperatively. The implants had been positioned satisfactorily with inclination angles 45°–55° and anteversion angles 28°–42°. Patient A (76 y/o female) with bilateral MOM hip replacements, was revised at approximately 8 years due to infection and had moderately elevated ions at the time of revision surgery (Co = 5, Cr = 2.3, Ti = 4). Only the femoral head was retrieved in this case. Retrieval analysis identified a well defined main-wear zone and one polar stripe. The CMM indicated there was minimal wear overall (form factor = 11 μm). Patient B (33 y/o male) with bilateral MOM hip replacements, was revised at approximately 8 years due to pain, popping/catching sensations, and elevated ions (Co = 33, Cr = 17, Ti = 90). Intraoperatively, the implant was observed subluxing superiorly from the acetabular cup with anterior rotation of the leg. Both the femoral head and acetabular cup were retrieved. Retrieval analysis identified a well defined main-wear zone and multi-directional polar stripe formations similar to those reported on dislocated implants (Figure 1)[McPherson 2012, 2013]. The CMM indicated that overall wear was significant (form factor > 100 μm). Patient C (77 y/o female) was revised at approximately 6 years due to pain, suspected implant loosening, osteolytic cysts determined by CT, and highly elevated ions (co = 164, Cr = 45, Ti = 33). Intraoperatively, there was evidence of wear including darkly stained tissue and osteolytic cysts. Both the femoral head and acetabular cup were retrieved. Retrieval analysis identified a well defined main-wear zone and one polar stripe. CMM indicated considerable wear (head form factor > 200, cup form factor >300). Patient D (45 y/o female) was revised at approximately 6 years due to pain, apparent reactive response joint effusion, and moderately elevated ions (Co = 5, Cr = 6, Ti = 71). Only the femoral head was retrieved. Retrieval analysis identified a well defined main-wear zone and one polar stripe. Minimal wear was indicated by CMM (form factor = 21). These four cases demonstrate distinct failure models of MOM hips and their respective metal ion results. Due to the diversity of patient location, a variety of clinical labs were utilized for this patient population. Caution should be used in interpreting metal ion analysis, as there are still no standards. Figure 1: Retrieval analysis of stripe wear identified on femoral head from patient B. Figure 2: Femoral head from patient C showing broader polar stripe associated with anterior subluxation in comparison to narrow polar stripe found on femoral head from patient A

INTRODUCTION. Retrieval analysis is an important aspect of medical device development. Examination of retrieved devices allows device developers to close the design loop, understand the performance of devices, and validate assumptions made and methods used during preclinical testing. We provide an overview of the implant retrieval analysis performed at the Implant Research Center at Drexel University on reverse total shoulder systems retrieved after short to medium term implantation. METHODS. We have examined 18 reverse total shoulders, retrieved at revision surgery after short to mid-term implantation (average 1.4 years, maximum 3.3 years). The average age at revision was 71 years old (st dev 11 years). Our evaluations included analysis of glenosphere bearing surface damage, evaluation of tribocorrosion at the modular junctions, visual assessment of polyethylene humeral bearing surface damage, quantitative analysis of polyethylene wear. RESULTS and DISCUSSION. We observed that polyethylene wear of the humeral bearing surface (mode I) is limited in the short to medium term and that wear and damage of revised devices are dominated by unintentional contact and impingement of the inferior rim of the bushing (mode II damage). This was in agreement with a previously published analysis of a smaller cohort (Figure 1). Scratching and damage of the glenosphere was a common observation, particularly in patients with a history of instability. The observed increase in glenosphere roughness was similar to that reported in association with hip dislocation (Figure 2). Damage at the modular junctions was limited and dominated by fretting rather than corrosive damage. Mild to moderate fretting was commonly observed at the interface between the glenosphere and metaglene (Figure 3). These observations provide an increased understanding of device performance and potential failure modes. Further studies will be necessary to characterize the long term performance of reverse total shoulder systems

Irradiated, thermally stabilized, highly cross-linked UHMWPE bearings have demonstrated superior wear performance and improved in vitro oxidation resistance compared with terminally gamma-sterilized bearings, yet retrieval analysis reveals unanticipated in vivo oxidation in these materials. There has been little evidence to date that oxidation in these materials is leading to degradation of mechanical properties, but since oxidation has previously been shown to cause chain scission in other materials, there is the potential for oxidation to cause decreased molecular weight and crosslink density. The aim of this study was to determine whether measured in vivo oxidation in highly cross-linked tibial bearings corresponds with a decreasing crosslink density. Retrieval analysis for three tibial bearing materials reveals that crosslink density is decreasing following in vivo duration, and that the change in crosslink density is strongly correlated with oxidation. The results suggest that oxidation in highly cross-linked materials is causing chain scissions that may impact the material properties. If the correlation between oxidation and duration continues, then as longer duration, more oxidized devices are retrieved there is a potential for measurable mechanical property changes