[Current design and cement mantle thickness in hip arthroplasty : Theory and analysis of register data]. / Aktuelles Design und Zementmanteldicke in der Hüftendoprothetik : Theorie und Analyse der Registerdaten.

BACKGROUND: In this article, an overview and comparison of the most commonly used cemented hip stems, grouped into different stem types and cement mantle thickness, is given to see which combination performs well. METHODOLOGY: Revision rates of cemented stem types were categorized from the Endoprosthesis Register-Germany, and 3­ and 5­year revision rates were reported and analyzed. For the research, the focus was on the Exeter, C­Stem, MS-30, Excia, Bicontact, Charnley, Müller straight stem, Twinsys, Corail, Avenir, Quadra, and the Lubinus SP II stems. An important aspect was which stem is preferred to be implanted and which cementing technique is used with regard to the planned cement mantle thickness. In order to identify a trend in cemented hip arthroplasty, data from the Danish, Swedish, Norwegian, Swiss, New Zealand, English and Australian arthroplasty registers were also compared. RESULTS AND CONCLUSION: Most countries use cemented prostheses according to the taper slip principle (Exeter, MS30, C­Stem etc) or the composite beam (Charnley, Excia, Bicontact), which are implanted with a cement mantle thickness of 2-4 mm. However, a trend has emerged in Germany and Switzerland towards the line-to-line technique, with a planned cement mantle thickness of 1 mm (Twinsys, Corail, Avenir, Quadra), following the principle of the Müller straight stem prosthesis and the Kerboul-Charnley prosthesis, even though these are postulated to be "French paradoxes" in themselves. In the EPRD 5­year results, the newer line-to-line prostheses seem to perform slightly worse. The best results are achieved by the "MS 30" in Germany and the "Exeter" in England. These are polished straight stems with centralizer and subsidence space at the apex with a 2-4 mm cement mantle in good cementing technique.

[Partial or full component exchange in hip revision? : The relevance of off-label use and mix & match]. / Partieller oder vollständiger Wechsel in der Hüftrevisionsendoprothetik? : Bedeutung von Off-Label-Anwendung und Mix & Match.

Off-label use is frequently practiced in hip revision arthroplasty, as there may be indications for the application of implants for purposes outside the one the manufacturers intended (i.e. large bone and soft tissue defects, obesity). Patients may also benefit from selective application of mix & match in hip revision, when the exchange of one component only is necessary and the invasiveness of surgery can be reduced. Currently, there are no formal guidelines for these situations. Therefore, within a recent EFORT initiative, evidence- and consensus-based recommendations have been developed for the safe application of off-label use and mix & match in revision hip and knee arthroplasty.

Explant analysis and implant registries are both needed to further improve patient safety.

In the early days of total joint replacement, implant fracture, material problems and wear presented major problems for the long-term success of the operation. Today, failures directly related to the implant comprise only 2-3% of the reasons for revision surgeries, which is a result of the material and design improvements in combination with the standardization of pre-clinical testing methods and the post-market surveillance required by the legal regulation. Arthroplasty registers are very effective tools to document the long-term clinical performance of implants and implantation techniques such as fixation methods in combination with patient characteristics. Revisions due to implant failure are initially not reflected by the registries due to their small number. Explant analysis including patient, clinical and imaging documentation is crucial to identify failure mechanisms early enough to prevent massive failures detectable in the registries. In the past, early reaction was not always successful, since explant analysis studies have either been performed late or the results did not trigger preventive measures until clinical failures affected a substantial number of patients. The identification of implant-related problems is only possible if all failures are reported and related to the number of implantations. A system that analyses all explants from revisions attributed to implant failure is mandatory to reduce failures, allowing improvement of risk assessment in the regulatory process.

[Early assessment of the risk of later implantloosening using Roentgen Sterophotogrammetric Analysis (RSA)]. / Früherkennung des Risikos der späteren Implantatlockerung mittels der Röntgen Stereophotogrammetrischen Analyse (RSA).

BACKGROUND: Aseptic implant loosening is the most common cause of implant revisions in total hip and total knee arthroplasty. Roentgen Stereophotogrammetric Analysis (RSA) represents the current gold standard for the in-vivo assessment of implant fixation. PRESENT SITUATION: Long-term clinical trials have shown that continuous implant migration within the first two postoperative years correlates strongly with a later aseptic loosening. Thus, the implant migration measured with RSA can be regarded as a reliable surrogate marker for later implant loosening. Over the past 40 years, RSA has been continuously further developed, and the model-based RSA approach has reduced the effort involved since markers attached to implant are no longer needed. PERSPECTIVES: The RSA method is gaining importance in the certification process of new orthopaedic implants-for example, the Dutch Orthopedic Society has recommended phased-introduction and RSA studies for new hip implants. Furthermore, in the context of the new EU Medical Device Regulation (MDR), which took effect in May 2017, RSA gained relevance for investigating clinically unproven implants. Critics who associate MDR with hindering innovation can be countered in that the RSA method provides a predictive assessment of implant fixation after only two years of follow-up, which is significantly shorter than standard long-term clinical trials.

Modular tumor prostheses: are current stem designs suitable for distal femoral reconstruction? A biomechanical implant stability analysis in Sawbones.

INTRODUCTION: High loosening rates after distal femoral replacement may be due to implant design not adapted to specific anatomic and biomechanical conditions. MATERIALS AND METHODS: A modular tumor system (MUTARS®, Implantcast GmbH) was implanted with either a curved hexagonal or a straight tapered stems in eight Sawbones® in two consecutively generated bone defect (10 cm and 20 cm proximal to knee joint level). Implant-bone-interface micromotions were measured to analyze main fixation areas and to characterize the fixation pattern. RESULTS: Although areas of highest relative micromotions were measured distally in all groups, areas and lengths of main fixation differed with respect to stem design and bone defect size. Regardless of these changes, overall micromotions could only be reduced with extending bone defects in case of tapered stems. CONCLUSIONS: The tapered design may be favorable in larger defects whereas the hexagonal may be advantageous in defects located more distally.

Diagnostic guidelines for the histological particle algorithm in the periprosthetic neo-synovial tissue.

BACKGROUND: The identification of implant wear particles and non-implant related particles and the characterization of the inflammatory responses in the periprosthetic neo-synovial membrane, bone, and the synovial-like interface membrane (SLIM) play an important role for the evaluation of clinical outcome, correlation with radiological and implant retrieval studies, and understanding of the biological pathways contributing to implant failures in joint arthroplasty. The purpose of this study is to present a comprehensive histological particle algorithm (HPA) as a practical guide to particle identification at routine light microscopy examination. METHODS: The cases used for particle analysis were selected retrospectively from the archives of two institutions and were representative of the implant wear and non-implant related particle spectrum. All particle categories were described according to their size, shape, colour and properties observed at light microscopy, under polarized light, and after histochemical stains when necessary. A unified range of particle size, defined as a measure of length only, is proposed for the wear particles with five classes for polyethylene (PE) particles and four classes for conventional and corrosion metallic particles and ceramic particles. RESULTS: All implant wear and non-implant related particles were described and illustrated in detail by category. A particle scoring system for the periprosthetic tissue/SLIM is proposed as follows: 1) Wear particle identification at light microscopy with a two-step analysis at low (× 25, × 40, and × 100) and high magnification (× 200 and × 400); 2) Identification of the predominant wear particle type with size determination; 3) The presence of non-implant related endogenous and/or foreign particles. A guide for a comprehensive pathology report is also provided with sections for macroscopic and microscopic description, and diagnosis. CONCLUSIONS: The HPA should be considered a standard for the histological analysis of periprosthetic neo-synovial membrane, bone, and SLIM. It provides a basic, standardized tool for the identification of implant wear and non-implant related particles at routine light microscopy examination and aims at reducing intra-observer and inter-observer variability to provide a common platform for multicentric implant retrieval/radiological/histological studies and valuable data for the risk assessment of implant performance for regional and national implant registries and government agencies.

[Supramacroparticulate polyethylene in inflammation of synovial-like interface membranes: Characterization and suggested nomenclature]. / Supramakropartikuläres Polyethylen bei Entzündungen periprothetischer Membranen: Charakterisierung und Nomenklaturvorschlag.

BACKGROUND: The identification of particles of prosthesis material components in the histopathological diagnosis of synovialitis is of great importance in the evaluation of implant failure. MATERIALS AND METHODS: In histopathological particle algorithms, polyethylene (PE) particles with a maximum length of less than 100 µm are designated with the term macroparticles; however, a systematic investigation and characterization are lacking. RESULTS: In SLIM knee specimens (n = 24) a minimum value of 210 µm and a maximum value of 2100 µm were measured; the mathematical mean length varied between 235 µm and 1416 µm. In SLIM hip specimens (n = 11) the minimum value was 290 µm and the maximum value was 1806 µm; the mean length varied between 353 and 1726 µm. Because of this conspicuous size, and to distinguish from PE macroparticles, the designation PE supra-macroparticulate is suggested. This new terminology acknowledges the fact that these PE particles are visible under magnification (e.g., × 12.5) and also macroscopically. The particles were also indirectly proven as there were completely separate and optically clear, column-shaped cavities corresponding to the shape of the PE particles (PE vacuoles). The life of the prosthesis is highly variable at between 12 and 300 months. In all cases loosening of the prosthesis, misalignment of the PE components, and/or damage to the PE inlay occurred. CONCLUSION: The cause and existence of these supra-macroparticulate PE particles (more than 100 µm) is still unclear. A mechanical malfunction seems probable and should be discussed. In prostheses with short lives the proof of supra-macroparticulate PE in SLIM could be a sign of an early mechanical problem. In the wider histopathological particle algorithm supra-macroparticulate PE was considered to fall in the category of macroparticles and should be considered in the histopathological diagnosis of implant failure.

[Bearing selection in total hip arthroplasty]. / Wahl der richtigen Gleitpaarung in der Hüftendoprothetik.

Different bearing materials are available in total hip arthroplasty and it's the surgeon who has the choice between hard-on-soft, hard-on-hard and alternative materials. Ideally, the material selection should rely on evidence-based data regarding the wear performance, the incidence of revision surgery and other potential bearing-associated risk factors for the corresponding combinations of materials in the individual patient. While there are high-quality studies available for some materials, adequate data is lacking for other materials. Therefore, the current article aims to provide bearing selection criteria for the surgeon and to review the current literature regarding different combinations of bearing materials in total hip arthroplasty.

Increased antibiotic release and equivalent biomechanics of a spacer cement without hard radio contrast agents.

We compared a novel calcium carbonate spacer cement (Copal® spacem) to well-established bone cements. Electron microscopic structure and elution properties of the antibiotics ofloxacin, vancomycin, clindamycin, and gentamicin were examined. A knee wear simulator model for articulating cement spacers was established. Mechanical tests for bending strength, flexural modulus, and compressive and fatigue strength were performed. The electron microscopic analysis showed a microporous structure of the spacer cement, and this promoted a significantly higher and longer antibiotic elution. All spacer cement specimens released the antibiotics for a period of up to 50days with the exception of the vancomycin loading. The spacer cement showed significantly less wear scars and fulfilled the ISO 5833 requirements. The newly developed spacer cement is a hydrophilic antibiotic carrier with an increased release. Cement without hard radio contrast agents can improve tribological behaviour of spacers, and this may reduce reactive wear particles and abrasive bone defects.

[Modular Neck in Primary Total Hip Replacement--A Justifiable Risk?]. / Modulare Primärendoprothetik--Risiko gerechtfertigt?

Modular necks are considered as a treatment option in primary total hip replacement aiming to allow a variable reconstruction of the hip joint. Concerns are related to increased failure and complication rates which may be associated with the additional modular interface. This interface is frequently affected by corrosion processes which may initiate premature failure of the entire implant. In this study the risk of modular necks as a clinical treatment option is evaluated. Based on register data and clinical studies modular necks should only be used with strict limitations for general treatment in primary total hip replacement.

Revised histopathological consensus classification of joint implant related pathology.

This extended classification of joint implant related pathology is a practical histopathologic classification based on defined morphological criteria covering the complete spectrum of pathohistologic changes in periprosthetic tissues. These changes may occur as a consequence of endoprosthetic replacement of large joints and may lead to a reduction in the prosthesis survival rate. We describe the established consensus classification of the periprosthetic membrane, in which aseptic and septic prosthetic loosening can be subdivided into four histological types, as well as histopathological criteria for additional significant pathologies including endoprosthetic-associated arthrofibrosis, particle-induced immunological, inflammatory and toxic mechanisms (adverse reactions), and bone tissue pathologies. These characteristic tissue alterations and their relationships are summarized in the extended classification. Since particle heterogeneity in periprosthetic tissue is high and particle identification is a necessary part of diagnosis, the identification of different types of particles is described in the histopathological particle algorithm. The morphological qualities of prosthetic material particles and the demarcation between abrasion and non-abrasion endogenous particles are also summarized. This feasible classification which is based on low cost standard tissue processing and examination and on well-defined diagnostic criteria is a solid platform for the histological diagnosis of implant associated pathologies providing a stable and reproducible tool for the surgical pathologist. Since this classification is suitable for standardized histopathological diagnostics, it might also provide a useful data set for joint arthroplasty registers, particularly for registers based on so-called routine data.

[Histopathological particle algorithm. Particle identification in the synovia and the SLIM]. / Histopathologischer Partikelalgorithmus. Partikelidentifikation in der Synovialis und in der SLIM.

BACKGROUND: In the histopathological diagnostics of synovitis and the synovium-like interface membrane (SLIM) the identification of crystals and crystal-like deposits and the associated inflammatory reactions play an important role. The multitude of endogenous crystals, the range of implant materials and material combinations, and the variability in the formation process of different particles explain the high morphological particle heterogeneity which complicates the diagnostic identification of diagnostic particles. STUDY DESIGN AND METHODS: A simple histopathological particle algorithm has been designed which allows methodological particle identification based on (1) conventional transmitted light microscopy with a guide to particle size, shape and color, (2) optical polarization criteria and (3) enzyme histochemical properties (oil red staining and Prussian blue reaction). These methods, the importance for particle identification and the differential diagnostics from non-prosthetic materials are summarized in the so-called histopathological particle algorithm. RESULTS: A total of 35 cases of synovitis and SLIM were analyzed and validated according to these criteria. Based on these criteria and a dichotomous differentiation the complete spectrum of particles in the SLIM and synovia can be defined histopathologically. CONCLUSION: For histopathological diagnosis a particle score for synovitis and SLIM is recommended to evaluate (1) the predominant type of prothetic wear debris with differentiation between microparticles, and macroparticles, (2) the presence of non-prosthesis material particles and (3) the quantification of particle-association necrosis and lymphocytosis. An open, continuously updated web-based particle algorithm would be helpful to address the issue of particle heterogeneity and include all new particle materials generated in a rapidly changing field.

Fixation of the shorter cementless GTS™ stem: biomechanical comparison between a conventional and an innovative implant design.

INTRODUCTION: Conventional cementless total hip arthroplasty already shows very good clinical results. Nevertheless, implant revision is often accompanied by massive bone loss. The new shorter GTS™ stem has been introduced to conserve femoral bone stock. However, no long-term clinical results were available for this implant. A biomechanical comparison of the GTS™ stem with the clinically well-established CLS(®) stem was therefore preformed to investigate the targeted stem philosophy. MATERIALS AND METHODS: Four GTS™ stems and four CLS(®) stems were implanted in a standardized manner in eight synthetic femurs. A high-precision measuring device was used to determine micromotions of the stem and bone during different load applications. Calculation of relative micromotions at the bone-implant interface allowed the rotational implant stability and the bending behavior of the stem to be determined. RESULTS: Lowest relative micromotions were detected near the lesser trochanter within the proximal part of both stems. Maximum relative micromotions were measured near the distal tip of the stems, indicating a proximal fixation of both stems. For the varus-valgus-torque application, a comparable stem bending behavior was shown for both stems. CONCLUSION: Both stems seem to provide a comparable and adequate primary stability. The shortened GTS™ design has a comparable rotational stability and bone-implant flexibility compared to a conventional stem. This study demonstrates that the CLS(®) stem and the GTS™ stem exhibit similar biomechanical behavior. However, a clinical confirmation of these experimental results is still required.

[Different symptoms in patients with prostheses with metal-metal bearings]. / Unterschiedliche Erscheinungsbilder bei Patienten mit Metall-Metall-Gleitpaarungs-Prothesen.

Based on several clinical case examples, this article demonstrates the different symptoms and complications in patients fitted with prostheses with metal-on-metal (MoM) bearings. We recommend an annual clinical control for patients with MoM prostheses with a prosthesis head size of 36 mm or larger. In patients who have problems tests should be carried out to measure the metal ion levels of cobalt and chromium and the metal artifact-reduced sequence by magnetic resonance imaging (MRI) or if this is not possible an ultrasound investigation. The clinical investigations should specifically target asymptomatic local swellings or hardened sites and patients should be questioned on problems with general hypersensitivity reactions (skin rash), cardiomyopathy, neurological changes including sensory changes, renal function impairment and thyroid dysfunction.

[Histopathological differential diagnostics in context of joint implant allergic reactions]. / Histopathologische Differenzialdiagnostik bei gelenkimplantatallergischen Fragestellungen.

Total joint replacement has greatly increased over the last decades and so have endoprothesis-associated pathologies. European studies have shown a 10-year durability varying from 88% to 95%. By means of histopathology different pathogenetic synovial-like interface membrane (SLIM) patterns that lead to reduction of implant durability can be discerned, such as periprosthetic particles, bacterial infections and arthrofibrosis. Subsequently, SLIM types have been determined in a revised consensus classification including particle-induced type (type I) so-called non-septic loosening, infection type (type II) so-called septic loosening, combination type (type III) of bacterial and particle-induced types, indifferent type with mechanical and functional disorders (type IV), osseus pathologies (type V), arthrofibrotic type (type VI, endoprosthesis-associated arthrofibrosis) and allergic/immunological/toxic reactions to prosthesis material (type VII). Particles are characterized histopathologically according to the Krenn particle algorithm. In cases of severe lymphocyte/macrophage infiltration, necrosis, abrasion particle detection and granuloma formation, a toxic or allergic reaction to implant material should be considered. As a direct abrasion particle-induced toxicity cannot be differentiated from a particle-induced allergic type VII reaction to implant material, the histopathological diagnosis of toxic reaction to implant material or allergic reaction to implant material should be made with caution and only in association with immunological, allergic and clinical data. It is recommended that tissue samples should be arthroscopically taken from different regions: close to the prosthesis, distant from the prosthesis and from bone tissue. The pathologist should be given information concerning clinical, allergological and microbiological data.

[In vitro analysis of the impact of metal ions on human lymphocyte cultures]. / In-vitro-Analyse des Einflusses von Metallionen auf humane Lymphozyten.

The use of metal implants has become increasingly more frequent in all fields of medicine throughout the past decades. Numerous studies have demonstrated that metal ions released from these implants can be detected in body fluids remote from the implants. Although diseases directly linked to the release of these ions seem to be rare, the general public is unsettled. In this study we aimed to analyze the impact of molybdenum(V), cobalt(II), chromium(III) and nickel(II) ions on cell surface markers (CD25, CD38, CD69, CD95) and viability (7-AAD/AnnexinV) of human CD4+ T-lymphocytes in vitro. Cobalt(II) ions at a concentration of 1000 µg/l led to a significant suppression of lymphocyte activation markers while nickel(II), chromium(III) and molybdenum(V) did not show any significant impact on these lymphocyte activation markers. Cell viability was significantly reduced by all metal ions, whereas cobalt(II) led to the highest increase of apoptotic cells and was the only metal ion to significantly increase the necrosis rate. While the pathophysiological significance of these findings remains unclear, they are in favour of further research in this field.

[Metal ion concentrations in patients with metal-metal bearings in prostheses]. / Metallkonzentrationen bei Patienten mit Metall-Metall-Gleitpaarungs-Prothese.

Increased wear leads to elevated systemic and local metal ion concentrations for patients treated with metal-on-metal bearings. The local metal ion content in the close environment of the joint replacement (e.g. joint aspirate or tissue) is several times higher compared to the systemic metal content (e.g. in blood or serum). As a result of increased metal ion levels, local and systemic effects, such as osteolysis, pseudotumors, sensitization or in rare cases toxicity may occur. Although the definition of a specific threshold to define clinical problems is difficult due to a lack of sensitivity, the systemic metal concentration is frequently measured clinically. Currently a threshold for cobalt and chromium between 4 µg/l and 7 µg/l is under debate. Very high levels (≥ 20 µg/l) or a steady increase over time should be a warning sign; however, metal ion levels should not be interpreted as a single diagnostic tool but rather in the entire context of the clinical, radiological and cross-sectional imaging, metal artefact reduction sequence (MARS) magnetic resonance imaging (MRI), ultrasound and computed tomography (CT) findings.

In vivo serum titanium ion levels following modular neck total hip arthroplasty--10 year results in 67 patients.

The objective of the present cross-sectional study was to determine in vivo titanium ion levels following cementless total hip arthroplasty (THA) using a modular stem system with different shapes for femoral canal fit and multiple neck options. A consecutive series of 173 patients (190 hips) who underwent cementless modular neck THA and a ceramic on polyethylene bearing with a median follow-up of 9 (7-13) years was evaluated retrospectively. According to a standardized protocol, titanium ion measurements were performed on 67 patients using high-resolution inductively coupled plasma-mass spectrometry. Ion levels were compared to a control group comprising patients with non-modular titanium implants (n=11) and to individuals without implants (n=23). Modular neck THA did not result in elevated titanium ion levels compared to non-modular THA. Compared to individuals without implants, both modular THA and non-modular THA showed elevated titanium ion levels. Absolute titanium ion levels, however, were comparatively low for both implants. The data suggest that the present modular stem system does not result in elevated systemic titanium ion levels in the medium term when compared to non-modular stems. Further longitudinal studies are needed to evaluate the use of systemic titanium ion levels as an objective diagnostic tool to identify THA failure and to monitor patients following revision surgery.

[Principles of tribological analysis of endoprostheses]. / 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.

Mobile-bearing lateral unicompartmental knee replacement with the Oxford domed tibial component: an independent series.

The Oxford mobile-bearing unicompartmental knee replacement (UKR) is an effective and safe treatment for osteoarthritis of the medial compartment. The results in the lateral compartment have been disappointing due to a high early rate of dislocation of the bearing. A series using a newly designed domed tibial component is reported. The first 50 consecutive domed lateral Oxford UKRs in 50 patients with a mean follow-up of three years (2.0 to 4.3) were included. Clinical scores were obtained prospectively and Kaplan-Meier survival analysis was performed for different endpoints. Radiological variables related to the position and alignment of the components were measured. One patient died and none was lost to follow-up. The cumulative incidence of dislocation was 6.2% (95% confidence interval (CI) 2.0 to 17.9) at three years. Survival using revision for any reason and aseptic revision was 94% (95% CI 82 to 98) and 96% (95% CI 85 to 99) at three years, respectively. Outcome scores, visual analogue scale for pain and maximum knee flexion showed a significant improvement (p < 0.001). The mean Oxford knee score was 43 (SD 5.3), the mean Objective American Knee Society score was 91 (SD 13.9) and the mean Functional American Knee Society score was 90 (SD 17.5). The mean maximum flexion was 127° (90° to 145°). Significant elevation of the lateral joint line as measured by the proximal tibial varus angle (p = 0.04) was evident in the dislocation group when compared with the non-dislocation group. Clinical results are excellent and short-term survival has improved when compared with earlier series. The risk of dislocation remains higher using a mobile-bearing UKR in the lateral compartment when compared with the medial compartment. Patients should be informed about this complication. To avoid dislocations, care must be taken not to elevate the lateral joint line.