Alexander Paulus

Inflammatory response against different carbon fiber-reinforced PEEK wear particles compared with UHMWPE in vivo.

Poly(ether ether ketone) (PEEK) and its composites are recognized as alternative bearing materials for use in arthroplasty because of their mechanical properties. The objective of this project was to evaluate the biological response of two different kinds of carbon fiber-reinforced (CFR) PEEK compared with ultra-high molecular weight polyethylene (UHMWPE) in vivo as a standard bearing material. Wear particles of the particulate biomaterials were injected into the left knee joint of female BALB/c mice. Assessment of the synovial microcirculation using intravital fluorescence microscopy as well as histological evaluation of the synovial layer were performed 7 days after particle injection. Enhanced leukocyte-endothelial cell interactions and an increase in functional capillary density as well as histological investigations revealed that all tested biomaterials caused significantly (P < 0.05) increased inflammatory reactions compared with control animals (injected with sterile phosphate-buffered saline), without any difference between the tested biomaterials (P > 0.05). These data suggest that wear debris of CFR-PEEK is comparable with UHMWPE in its biological activity. Therefore, CFR-PEEK represents an alternative bearing material because of its superior mechanical and chemical behavior without any increased biological activity of the wear particles, compared with a standard bearing material.

Influence of design and bearing material on polyethylene wear particle generation in total knee replacement

Periprosthetic osteolysis is one of the main reasons for revision of arthroplasty. The osteolytic reaction is influenced by the dose, size and shape of the wear particles. For arthroplasty, a low number and biologically less active particles are required. This is the first study which analyzes the impact of different knee designs, combined with crosslinked polyethylenes (sequentially irradiated and annealed as well as remelted techniques), on the amount, size and shape of particles. Overall, six material combinations, four of them with crosslinked polyethylene (XPE) and two of them with ultra-high molecular weight polyethylene (UHMWPE) inserts, including fixed and mobile bearings, were tested in a knee joint simulator. After isolation nearly 100,000 particles were analyzed in size, shape and number by scanning electron microscopy and image analysis. For all the designs, the wear was predominantly smooth and granular with few fibrillar particles. The Scorpio design with the X3 insert, the Natural Knee II design with the Durasul insert and the LCS design, also combined with a crosslinked polyethylene insert, generated statistically significant (P<0.05) lower particle numbers. The particle size was independent of the radiation dose. The wear generated by the LCS knee design (XPE and UHMWPE) had a higher percentage fraction of particles >1microm in size (equivalent circle diameter). The NexGen design, tested with the Prolong insert, showed a high number of particles in the biologically active size range compared with the other crosslinked designs, which could be a predictor for higher biological reactivity.

Elevated cytokine expression of different PEEK wear particles compared to UHMWPE in vivo

Due to their mechanical properties, there has been growing interest in poly-ether-ether-ketone (PEEK) and its composites as bearing material in total and unicompartmental knee arthroplasty. The aim of this study was to analyze the biological activity of wear particles of two different (pitch and PAN) carbon-fiber-reinforced- (CFR-) PEEK varieties in comparison to ultra-high-molecular-weight-polyethylene (UHMWPE) in vivo. The authors hypothesized no difference between the used biomaterials. Wear particle suspensions of the particulate biomaterials were injected into knee joints of Balb/c mice, which were sacrificed after seven days. The cytokine expression (IL-1β, IL-6, TNF-α) was analyzed immunohistochemically in the synovial layer, the adjacent bone marrow and the articular cartilage. Especially in the bone marrow of the two CFR-PEEK varieties there were increased cytokine expressions compared to the control and UHMWPE group. Furthermore, in the articular cartilage the CFR-PEEK pitch group showed an enhanced cytokine expression, which could be a negative predictor for the use in unicondylar knee systems. As these data suggest an increased proinflammatory potential of CFR-PEEK and its composites in vivo, the initial hypothesis had to be refuted. Summarizing these results, CFR-PEEK seems not to be an attractive alternative to UHMWPE as a bearing material, especially in unicompartmental knee arthroplasty.

Principles of tribological analysis of endoprostheses

For the tribological characterization of artificial joints, various experimental methods are currently available. However, the in vitro test conditions applied are only comparable in a limited way and transferability to the in vivo situation is also restricted. This is due to the different wear simulation concepts used and partly insufficient simulation of clinical worst case situations. In the present paper current scientific methods and procedures for tribological testing of artificial joints are presented. In addition, the biological effects of wear products are described enabling clinicians to challenge tribological studies and to facilitate specific interpretation of scientific results taking the clinical situation into account.

Histopathological Analysis of PEEK Wear Particle Effects on the Synovial Tissue of Patients

Introduction. Increasing interest developed in the use of carbon-fiber-reinforced-poly-ether-ether-ketones (CFR-PEEK) as an alternative bearing material in knee arthroplasty. The effects of CFR-PEEK wear in in vitro and animal studies are controversially discussed, as there are no data available concerning human tissue. The aim of this study was to analyze human tissue containing CFR-PEEK as well as UHMWPE wear debris. The authors hypothesized no difference between the used biomaterials. Methods and Materials. In 10 patients during knee revision surgery of a rotating-hinge-knee-implant-design, synovial tissue samples were achieved (tibial inserts: UHMWPE; bushings and flanges: CFR-PEEK). One additional patient received revision surgery without any PEEK components as a control. The tissue was paraffin-embedded, sliced into 2 μm thick sections, and stained with hematoxylin and eosin in a standard process. A modified panoptical staining was also done. Results. A “wear-type” reaction was seen in the testing and the control group. In all samples, the UHMWPE particles were scattered in the tissue or incorporated in giant cells. CFR-PEEK particles were seen as conglomerates and only could be found next to vessels. CFR-PEEK particles showed no giant-cell reactions. In conclusion, the hypothesis has to be rejected. UHMWPE and PEEK showed a different scatter-behavior in human synovial tissue.

Comparison of ropivacaine and fentanyl toxicity in human fibroblasts

Introduction Although ropivacaine and fentanyl are commonly administered intra-articularly after knee or shoulder arthroscopy for postoperative pain control, there are no studies investigating the toxicity of ropivacaine and fentanyl on human fibroblasts (hF). Material and methods Human fibroblasts were seeded in monolayer triple flasks at a density of 104 cells/cm2 and plated into 96 plates at a density of 5000 cells per well. After fully aspirating the culture medium 200 µl of ropivacaine or fentanyl in its corresponding concentration or culture medium only was added to each well. After 30 min ropivacaine or fentanyl was removed and fresh culture medium was added. Fibroblast mitochondrial activity and apoptosis marker level were evaluated after 1 h, 24 h and 7 days. Results We found a significant decrease in mitochondrial activity after 7 days when exposed to 0.5% ropivacaine. Mitochondrial activity after 1 h, 24 h and 7 days was significantly decreased when fibroblasts were exposed to 0.05% fentanyl. Also, a significant decrease in mitochondrial activity was observed 1 h after exposure to 0.025% fentanyl. Cell viability remained unchanged at any other point in time. A significant increase of caspase-3, as a marker of apoptosis, was only present after exposure to 0.5% ropivacaine after 7 days. Conclusions These data suggest that both drugs have a concentration-dependent effect on mitochondrial activity in hF in vitro. This effect is more pronounced with fentanyl. Because the cytotoxicity of fentanyl, without the anticipated increase of caspase-3 as an apoptosis marker, remains unclear, we cannot support fentanyl as an alternative to ropivacaine.

Grundlagen zur tribologischen Analyse von Endoprothesen

For the tribological characterization of artificial joints, various experimental methods are currently available. However, the in vitro test conditions applied are only comparable in a limited way and transferability to the in vivo situation is also restricted. This is due to the different wear simulation concepts used and partly insufficient simulation of clinical worst case situations. In the present paper current scientific methods and procedures for tribological testing of artificial joints are presented. In addition, the biological effects of wear products are described enabling clinicians to challenge tribological studies and to facilitate specific interpretation of scientific results taking the clinical situation into account.

PMMA Third-Body Wear after Unicondylar Knee Arthroplasty Decuples the UHMWPE Wear Particle Generation In Vitro

Introduction. Overlooked polymethylmethacrylate after unicondylar knee arthroplasty can be a potential problem, since this might influence the generated wear particle size and morphology. The aim of this study was the analysis of polyethylene wear in a knee wear simulator for changes in size, morphology, and particle number after the addition of third-bodies. Material and Methods. Fixed bearing unicondylar knee prostheses (UKA) were tested in a knee simulator for 5.0 million cycles. Following bone particles were added for 1.5 million cycles, followed by 1.5 million cycles with PMMA particles. A particle analysis by scanning electron microscopy of the lubricant after the cycles was performed. Size and morphology of the generated wear were characterized. Further, the number of particles per 1 million cycles was calculated for each group. Results. The particles of all groups were similar in size and shape. The number of particles in the PMMA group showed 10-fold higher values than in the bone and control group (PMMA: 10.251 × 1012; bone: 1.145 × 1012; control: 1.804 × 1012). Conclusion. The addition of bone or PMMA particles in terms of a third-body wear results in no change of particle size and morphology. PMMA third-bodies generated tenfold elevated particle numbers. This could favor an early aseptic loosening.

Can Salter osteotomy correct late diagnosed hip dysplasia: A retrospective evaluation of 49 hips after 6.7 years?

BACKGROUND Surgical treatment of late diagnosed development dysplasia of the hip (DDH) remains challenging with several methods being described. We therefore retrospectively evaluated the outcome of Salter innominate osteotomy (SIO) in patients with fully-grown bone, to evaluate whether this surgical procedure allows sufficient acetabular correction. MATERIAL AND METHODS Between 2004-2012 SIO had been performed in 45 patients (49 hips) with late diagnosed DDH. The evaluation included pre- and postoperative radiographs (n=49), the complication rate (n=49) and the clinical outcome (WOMAC, HHS, UCLA) (n=34). RESULTS Mean age at surgery was 27.6 (16-51) with a follow-up of 6.7±2.7 (0.9-11.0) years. Radiologically, a good acetabular correction with a significant improvement of the Center Edge angle (15.4° to 34.9°), sharps angle (45.7° to 32.0°) and migration percentage (33.2% to 14.4%) (p<0.001) was found. Clinical results revealed a WOMAC of 13.9±13.3, UCLA of 7.8±2.1 and HHS of 85.0±11.8. Complications were noted for 10 patients (20%) with 7 (14%) requiring revision. CONCLUSION The results demonstrated that SIO achieved a satisfying acetabular correction and good clinical results in late diagnosed DDH. It therefore might be an option in some cases, although periacetabular osteotomy techniques are currently preferable used as they allow a wider range of acetabular correction. LEVEL OF EVIDENCE IV, retrospective observational study.

Possibilities and limits of modern polyethylenes. With respect to the application profile

ZusammenfassungHintergrundPolyethylen ist nach wie vor eines der wichtigsten Materialien für den gelenkersetzenden Chirurgen. Dabei halfen die klinischen Resultate der letzten Jahrzehnte, dieses Material zu einem High-Tech-Werkstoff weiter zu entwickeln. Fortschritte in der Entwicklung neuer Materialien müssen mit Bewährtem abgewogen werden, um den Patienten bestmöglichst und individuell zu versorgen.Ziel der ArbeitDem Leser wird ein Überblick über Historie und aktuelle Anwendungsprofile des Werkstoffs „ultra-high molecular weight polyethylene“ (UHMWPE) in der Hüft- und Knieendoprothetik gegeben.Material und MethodenUnter Zuhilfenahme der aktuellen Literatur werden die Neuentwicklungen im Bereich des Werkstoffs UHMWPE, auch im Hinblick auf die biologische Aktivität des Abriebs, die besondere Biomechanik des Kniegelenks sowie alternative Hart-Hart-Gleitpaarungen in der Hüfte im Hinblick auf die Implantatsicherheit dargestellt.ErgebnisseDie Problempunkte, den Werkstoff Polyethylen betreffend, sind mittlerweile gut erkannt, die Nachteile des Werkstoffs UHMWPE konnten durch konsequente Materialforschung stetig verringert werden, sodass sich nach und nach auch in klinischen Studien die modernen Polyethylene als verlässlich einsetzbar zeigen.DiskussionTrotzdem ist das Verbesserungspotenzial bis heute immer noch nicht ausgeschöpft. Jede weitere Entwicklung muss umfangreich biomechanisch und biologisch getestet werden, bevor sie in vivo einsetzbar ist. Nach wie vor sind Langzeitergebnisse entscheidend, um einen Werkstoff als sicher gelten zu lassen.AbstractBackgroundPolyethylene is still one of the most important materials in the field of hip and knee arthroplasty. The clinical results of the last decades have helped to further develop polyethylene into a high-tech material. Progress in the development of new materials must be compared with the tried and tested ones to provide optimal and most individual patient care.ObjectivesThis article gives an overview of the history and current application profile of the material ultra-high molecular weight polyethylene (UHMWPE) in hip and knee arthroplasty.Material and methodsWith the aid of the current literature, new developments in the field of the material UHMWPE, also with respect to the biological activity of wear, the particular biomechanics of the knee joint as well as alternative hard-hard bearing surfaces in the hip, are represented in terms of implant safety.ResultsThe problems concerning polyethylene are now well recognized. The disadvantages of the material UHMWPE could be consistently reduced based on material research so that modern polyethylenes have gradually been shown in clinical trials that they can be reliably used.ConclusionDespite this the potential for improvement has still not yet been fully exploited. Any further development must be extensively tested both biomechanically and biologically before the material can be used in vivo. Long-term results are still necessary before a material can be accepted as being clinically safe.BACKGROUND Polyethylene is still one of the most important materials in the field of hip and knee arthroplasty. The clinical results of the last decades have helped to further develop polyethylene into a high-tech material. Progress in the development of new materials must be compared with the tried and tested ones to provide optimal and most individual patient care. OBJECTIVES This article gives an overview of the history and current application profile of the material ultra-high molecular weight polyethylene (UHMWPE) in hip and knee arthroplasty. MATERIAL AND METHODS With the aid of the current literature, new developments in the field of the material UHMWPE, also with respect to the biological activity of wear, the particular biomechanics of the knee joint as well as alternative hard-hard bearing surfaces in the hip, are represented in terms of implant safety. RESULTS The problems concerning polyethylene are now well recognized. The disadvantages of the material UHMWPE could be consistently reduced based on material research so that modern polyethylenes have gradually been shown in clinical trials that they can be reliably used. CONCLUSION Despite this the potential for improvement has still not yet been fully exploited. Any further development must be extensively tested both biomechanically and biologically before the material can be used in vivo. Long-term results are still necessary before a material can be accepted as being clinically safe.