Assessment of Wear and Corrosion at the Taper Junction of Modular Total Hip Replacements

The concept of modularity in primary and revision total hip arthroplasty is well established. Whilst modern modular femoral components offer surgeons the flexibility to tailor the size, offset and biomaterials of the femoral head, neck and stem to the anatomy of the patients hip, they do present an additional interface and therefore a potential source of wear and corrosion. There is increasing global awareness of adverse reactions to metal debris and elevated serum metal ion concentrations following the use of third-generation modular metal-on-metal total hip arthroplasties. In some instances the high incidence of these complications can be attributed to corrosion at the head-neck interface. In 2011 published clinical data highlighted the early revision rate of thirdgeneration metal-on-metal modular hip replacements and consequently, in February 2012 the British Orthopaedic Association recommended that large head metal-on-metal hip replacements no longer be implanted. Although severe corrosion of the taper is identified most commonly in association with larger diameter femoral heads, there is emerging evidence of varying levels of corrosion observed in retrieved components with smaller diameter femoral heads and other material combinations such as metal on polyethylene and ceramic on polyethylene. In my thesis a systematic retrieval analysis has been completed in order to understand the contribution of material wear at the modular junction compared to the wear at the bearing surface. Furthermore in-vitro dynamic experimental approaches were adopted utilising in-situ electrochemistry in order to investigate the factors that contribute to enhanced wear and corrosion at the head-neck junction and ultimately lead to the early failure of modular hip replacements. Retrieval analysis of failed large head metal-on-metal prostheses (>36mm head diameter) indicated that about 1/3rd of total wear can be attributed to material loss at the taper junction. Experimental investigations indicated that neck taper rough surface finish and reduced engagement length contribute to enhanced fretting corrosion at the modular junction, a finding that points to concern associated with their current use in orthopaedics. Increased frictional torque and bending moment both of which can be associated with large diameter heads and high offsets may also increase the susceptibility of mechanically assisted crevice corrosion at the taper junction, an effect which may be diminished with the use of ceramic heads. Additionally it would appear that regardless of engagement length, surface roughness or material combination an assembly force of greater than 4kN reduces the amount of corrosion. From the findings presented in this thesis all tapers tested exhibited evidence of mechanically assisted crevice corrosion. Although this may be unavoidable it may be reduced if certain parameters associated with implant design are taken into consideration during implant selection

Material Loss at the Taper Junction of Retrieved Large Head Metal-on-Metal Total Hip Replacements

It has been speculated that material loss, either as corrosion or wear, at the head–stem taper junction is implicated in the high revision rates reported for metal-on-metal total hip replacements. We measured the volume of material loss from the taper and bearing surfaces of retrieved devices, and investigated the associations with blood metal ion levels and the diagnosis of a cystic or solid pseudotumor. The median volumes of material lost from the female and male taper surfaces were 2.0 and 0.29 mm3, respectively, while the median volumes of wear from the cup and head bearing surfaces were 1.94 and 3.44 mm3, respectively. Material loss from the female taper was similar to that from the acetabular bearing surface (p ¼ 0.55), but significantly less than that from the femoral bearing surface (p < 0.001). Material loss from the male taper was less than that from both bearing surfaces (p < 0.001). Multivariable analysis demonstrated no significant correlations between the volume of material lost from the taper surfaces and either blood cobalt or chromium ions, or the presence of pseudotumor. While a substantial volume of material is lost at the taper junction, the clinical significance of this debris remains unclear

Neuron-specific proteasome activation exerts cell non-autonomous protection against amyloid-beta (Aβ) proteotoxicity in Caenorhabditis elegans

Proteostasis reinforcement is a promising approach in the design of therapeutic interventions against proteinopathies, including Alzheimer's disease. Understanding how and which parts of the proteostasis network should be enhanced is crucial in developing efficient therapeutic strategies. The ability of specific tissues to induce proteostatic responses in distal ones (cell non-autonomous regulation of proteostasis) is attracting interest. Although the proteasome is a major protein degradation node, nothing is known on its cell non-autonomous regulation. We show that proteasome activation in the nervous system can enhance the proteasome activity in the muscle of Caenorhabditis elegans. Mechanistically, this communication depends on Small Clear Vesicles, with glutamate as one of the neurotransmitters required for the distal regulation. More importantly, we demonstrate that this cell non-autonomous proteasome activation is translated into efficient prevention of amyloid-beta (Αβ)-mediated proteotoxic effects in the muscle of C. elegans but notably not to resistance against oxidative stress. Our in vivo data establish a mechanistic link between neuronal proteasome reinforcement and decreased Aβ proteotoxicity in the muscle. The identified distal communication may have serious implications in the design of therapeutic strategies based on tissue-specific proteasome manipulation

A Post-industrial Walk in Genk. Engaging with heritage through participatory design

status: Published onlin

Epidemiology and management of chronic thromboembolic pulmonary hypertension: experience from two expert centers

Objectives: Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare, distinct pulmonary vascular disease, and therefore, there is a lack of data regarding its clinical presentation, diagnosis, and management at a national basis. We aimed to describe the demographics and management of patients with CTEPH in Northern Greece. Methods: We conducted a retrospective, observational study by a joint collaboration between two pulmonary hypertension expert centers in Greece, and the study included patients diagnosed with CTEPH. The patient population was divided into two groups depending on their operability. Results: Overall, 27 consecutive patients were included (59% female, mean age 59.3±15.1 years). Dyspnea and fatigue were the most common presenting symptoms. History of pulmonary embolism was present in 82%. Of patients, 18 (67%) were assessed as operable, of whom 10 (55%) finally underwent pulmonary endarterectomy (PEA). There were no differences in symptoms, WHO functional class, 6-min walking test distance, and hemodynamics between the operable and nonoperable groups. At the end of follow-up, all non-operable and operable patients who did not receive surgical treatment were treated with at least one pulmonary hypertension-specific drug. Conclusion: This is the first report that presents data of patients diagnosed with CTEPH in Greece. The percentage of patients who underwent surgical treatment is lower but approaches the reported rates in large registries. Considering that PEA is a relatively safe and potentially curative surgical procedure, we emphasize the need for establishing a designated PEA center in Greece. Keywords: Chronic thromboembolic pulmonary hypertension, pulmonary endarterectomy, registry, riocigua

Epidemiology and management of chronic thromboembolic pulmonary hypertension: experience from two expert centers

Objectives: Chronic thromboembolic pulmonary hypertension (CTEPH) is a rare, distinct pulmonary vascular disease, and therefore, there is a lack of data regarding its clinical presentation, diagnosis, and management at a national basis. We aimed to describe the demographics and management of patients with CTEPH in Northern Greece. Methods: We conducted a retrospective, observational study by a joint collaboration between two pulmonary hypertension expert centers in Greece, and the study included patients diagnosed with CTEPH. The patient population was divided into two groups depending on their operability. Results: Overall, 27 consecutive patients were included (59% female, mean age 59.3±15.1 years). Dyspnea and fatigue were the most common presenting symptoms. History of pulmonary embolism was present in 82%. Of patients, 18 (67%) were assessed as operable, of whom 10 (55%) finally underwent pulmonary endarterectomy (PEA). There were no differences in symptoms, WHO functional class, 6-min walking test distance, and hemodynamics between the operable and nonoperable groups. At the end of follow-up, all non-operable and operable patients who did not receive surgical treatment were treated with at least one pulmonary hypertension-specific drug. Conclusion: This is the first report that presents data of patients diagnosed with CTEPH in Greece. The percentage of patients who underwent surgical treatment is lower but approaches the reported rates in large registries. Considering that PEA is a relatively safe and potentially curative surgical procedure, we emphasize the need for establishing a designated PEA center in Greece. Keywords: Chronic thromboembolic pulmonary hypertension, pulmonary endarterectomy, registry, riociguat

Component Size Mismatch Of Metal On Metal Hip Arthroplasty: An Avoidable Never Event

Recent advances in hip replacement design, in particular the trend towards greater modularity in hip systems, have increased the risk of component size mismatch (CSM). CSM occurs when incorrectly sized femoral heads and acetabular cups are coupled together or when the dimensions of the paired stem trunnion and head differ to that intended by the manufacturer. CSM is a serious, preventable patient safety incident of which the true prevalence is unknown as many cases are not detected. Retrieval analysis of failed MOM hip implants may offer a better understanding of how often CSM occurs and how it affects the integrity of the implant