[Current design and cement mantle thickness in hip arthroplasty : Theory and analysis of register data]

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 5‑year revision rates were reported and analyzed. For the research, the focus was on the Exeter, C‑Stem, 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, C‑Stem 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 5‑year 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.

Efficacy of an Antibiotic Loaded Ceramic-Based Bone Graft Substitute for the Treatment of Infected Non-Unions

The treatment of non-unions is often complicated by segmental bone defects and bacterial colonization. Because of the limited availability of autologous bone grafts, tissue engineering focuses on antibiotic-loaded bone graft substitutes. HACaS+G is a resorbable calcium sulphate-hydroxyapatite loaded with gentamicin. The osteoinductive, osteoconductive, and anti-infective effect of HACaS+G has already been demonstrated in clinical studies on patients with chronic osteomyelitis. However, especially for the treatment of infected non-unions with segmental bone defects by HACaS+G, reliable clinical testing is difficult and sufficient experimental data are lacking. We used an already established sequential animal model in infected and non-infected rat femora to investigate the osteoinductive, osteoconductive, and anti-infective efficacy of HACaS+G for the treatment of infected non-unions. In biomechanical testing, bone consolidation could not be observed under infected and non-infected conditions. Only a prophylactic effect against infections, but no eradication, could be verified in the microbiological analysis. Using µ-CT scans and histology, osteoinduction was detected in both the infected and non-infected bone, whereas osteoconduction occurred only in the non-infected setting. Our data showed that HACaS+G is osteoinductive, but does not have added benefits in infected non-unions in terms of osteoconduction and mechanical bone stability, especially in those with segmental bone defects.

Does Kinematic Alignment Increase Polyethylene Wear Compared With Mechanically Aligned Components? A Wear Simulation Study

BACKGROUND

Kinematic alignment is an alternative approach to mechanical alignment. Kinematic alignment can restore the joint line to its prearthritic condition, and its advocates have suggested it may be associated with other benefits. But this alignment approach often results in tibial components that are placed in varus and femoral components that are placed in valgus alignment, which may result in an increased risk of component loosening because of wear. Like malaligned implant components, kinematically aligned knee implants could increase wear in vivo, but we lack comparative data about wear behavior between these approaches.

QUESTIONS/PURPOSES

(1) Do the different alignment approaches (kinematic, mechanical, and purposefully malaligned components) result in different wear rates in a wear simulator? (2) Do the different alignment approaches lead to different worn areas on the polyethylene inserts in a wear simulator? (3) Do the different alignment approaches result in different joint kinematics in a wear simulator?

METHODS

Mechanical alignment was simulated in a force-controlled manner with a virtual ligament structure according to the International Organization for Standardization (ISO 14243-1) using a knee wear simulator. To simulate kinematic alignment, flexion-extension motion, internal-external torque, and the joint line were tilted by 4°, using a novel mechanical setup, without changing the force axis. The setup includes bearings with inclinations of 4° so that the joint axis of 4° is determined. To verify the angle of 4°, a digital spirit level was used. To simulate malalignment, we tilted the implant and, therefore, the joint axis by 4° using a wedge with an angle of 4° without tilting the torque axes of the simulator. This leads to a purposefully malaligned tibial varus and femoral valgus of 4°. For each condition, three cruciate-retaining knee implants were tested for 3.0 x 10 6 cycles, and one additional implant was used as soak control. Gravimetric wear analyses were performed every 0.5 x 10 6 cycles to determine the linear wear rate of each group by linear regression. The wear area was measured after 3.0 x 10 6 cycles by outlining the worn areas on the polyethylene inserts, then photographing the inserts and determining the worn areas using imaging software. The joint kinematics (AP translation and internal-external rotation) were recorded by the knee simulator software and analyzed during each of the six simulation intervals.

RESULTS

Comparing the wear rates of the different groups, no difference could be found between the mechanical alignment and the kinematic alignment (3.8 ± 0.5 mg/million cycles versus 4.1 ± 0.2 mg/million cycles; p > 0.99). However, there was a lower wear rate in the malaligned group (2.7 ± 0.2 mg/million cycles) than in the other two groups (p < 0.01). When comparing the total wear areas of the polyethylene inserts among the three different alignment groups, the lowest worn area could be found for the malaligned group (716 ± 19 mm 2 ; p ≤ 0.003), but there was no difference between kinematic alignment and mechanical alignment (823 ± 19 mm 2 versus 825 ± 26 mm 2 ; p > 0.99). Comparing the AP translation, no difference was found between the mechanical alignment, the kinematic alignment, and the malalignment group (6.6 ± 0.1 mm versus 6.9 ± 0.2 mm versus 6.8 ± 0.3 mm; p = 0.06). In addition, the internal-external rotation between mechanical alignment, kinematic alignment, and malalignment also revealed no difference (9.9° ± 0.4° versus 10.2° ± 0.1° versus 10.1° ± 0.6°; p = 0.44).

CONCLUSION

In the current wear simulation study, the wear rates of mechanical alignment and kinematic alignment of 4° were in a comparable range.

CLINICAL RELEVANCE

The results suggest that kinematic alignment with up to 4° of component inclination may give the surgeon confidence that the reconstruction will have good wear-related performance when using a modern cruciate-retaining implant. The malaligned group had the lowest wear rate, which may be a function of the smaller worn area on the inserts compared with the other two alignment groups. This smaller articulation area between the femoral condyles and polyethylene insert could increase the risk of delamination of malaligned components over longer test durations and during high-load activities. For that reason, and because malalignment can cause nonwear-related revisions, malalignment should be avoided. Further in vitro and clinical studies must prove whether the wear simulation of different alignments can predict the wear behavior in vivo.

Insights into Imprinting: How Is the Phenomenon of Tribocorrosion at Head-Neck Taper Interfaces Related to Corrosion, Fretting, and Implant Design Parameters?

BACKGROUND

Wear and corrosion at modular neck tapers in THA can lead to major clinical implications such as periprosthetic osteolysis, adverse local tissue reactions, or implant failure. The material degradation processes at the taper interface are complex and involve fretting corrosion, third-body abrasion, as well as electrochemical and crevice corrosion. One phenomenon in this context is imprinting of the head taper, where the initially smooth surface develops a topography that reflects the rougher neck taper profile. The formation mechanism of this specific phenomenon, and its relation to other observed damage features, is unclear. An analysis of retrieved implants may offer some insights into this process.

QUESTIONS/PURPOSES

(1) Is imprinting related to time in situ of the implants and to the taper damage modes of corrosion and fretting? (2) Are implant design parameters like neck taper profile, stem material, or head seating associated with the formation of imprinting? (3) Is imprinting created by an impression of the neck taper profile or can a different mechanistic explanation for imprinting be derived?

METHODS

Thirty-one THAs with cobalt-chromium-molybdenum-alloy (CoCrMo) heads retrieved between 2013 and 2019 at revision surgery from an institutional registry were investigated. Inclusion criteria were: 12/14 tapers, a head size of 36 mm or smaller, time in situ more than 1 year, and intact nonmodular stems without sleeve adaptors. After grouping the residual THAs according to stem type, stem material, and manufacturer, all groups of three or more were included. Of the resulting subset of 31 retrievals, nine THAs exhibited a still assembled head-neck taper connection. The median (range) time in situ was 5 years (1 to 23). Two stem materials (21 titanium-alloy and 10 stainless steel), three kinds of bearing couples (11 metal-on-metal, 13 metal-on-polyethylene, and seven dual-mobility heads), and two different neck taper profiles (six wavy profile and 25 fluted profile) were present in the collection. Four THAs exhibited signs of eccentric head seating. The 31 investigated THAs represented 21% of the retrieved THAs with a CoCrMo alloy head during the specified period.At the head tapers, the damage modes of corrosion, fretting, and imprinting were semiquantitatively rated on a scale between 0 (no corrosion/fretting/imprinting) and 3 (severe corrosion/fretting/imprinting). Corrosion and fretting were assessed applying the Goldberg score, with the modification that the scale started at 0 and not at 1. Imprinting was assessed with a custom scoring system. Rating was done individually at the proximal and distal head taper half and summed to one total damage score for each retrieval and damage mode. Correlations between the damage modes and time in situ and between the damage modes among each other, were assessed using the Spearman rank order correlation coefficient (ρ). Associations between imprinting and implant design parameters were investigated by comparing the total imprinting score distributions with the Mann-Whitney U-test. Metallographically prepared cross-sections of assembled head-neck taper connections were examined by optical microscopy and disassembled head and neck taper surfaces were assessed by scanning electron microscopy (SEM).

RESULTS

The imprinting damage score increased with time in-situ (ρ = 0.72; p < 0.001) and the corrosion damage score (ρ = 0.63; p < 0.001) but not with the fretting damage score (ρ = 0.35; p = 0.05). There was no difference in total imprinting score comparing neck taper profiles or stem materials, with the numbers available. Eccentric head seating had elevated total imprinting score (median 6 [interquartile range 0]) compared with centric seating (median 1 [2]; p = 0.001). Light optical investigations showed that imprinting can be present on the head taper surfaces even if the depth of abraded material exceeds the neck taper profile height. SEM investigations showed bands of pitting corrosion in the imprinted grooves.

CONCLUSION

The microscopic investigations suggest that imprinting is not an independent phenomenon but a process that accompanies the continuous material degradation of the head taper surface because of circular damage on the passive layer induced by grooved neck tapers.

CLINICAL RELEVANCE

Material loss from head-neck taper connections involving CoCrMo alloy heads is a source of metal ions and could potentially be reduced if hip stems with smooth neck tapers were used. Surgeons should pay attention to the exact centric seating of the femoral head onto the stem taper during joining of the parts.

[Partial or full component exchange in hip revision? : The relevance of off-label use and 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.

EFORT recommendations for off-label use, mix & match and mismatch in hip and knee arthroplasty

Off-label use is frequently practiced in primary and revision arthroplasty, as there may be indications for the application of implants for purposes outside the one the manufacturers intended.

Under certain circumstances, patients may benefit from selective application of mix & match. This can refer to primary hip arthroplasty (if evidence suggests that the combination of devices from different manufacturers has superior results) and revision hip or knee arthroplasty (when the exchange of one component only is necessary and the invasiveness of surgery can be reduced).

Within the EFORT ‘Implant and Patient Safety Initiative’, evidence- and consensus-based recommendations have been developed for the safe application of off-label use and mix & match in primary as well as revision hip and knee arthroplasty.

Prior to the application of a medical device for hip or knee arthroplasty off-label and within a mix & match situation, surgeons should balance the risks and benefits to the patient, obtain informed consent, and document the decision process appropriately.

Nevertheless, it is crucial for surgeons to only combine implants that are compatible. Mismatch of components, where their sizes or connections do not fit, may have catastrophic effects and is a surgical mistake.

Surgeons must be fully aware of the features of the components that they use in off-label indications or during mix & match applications, must be appropriately trained and must audit their results.

Considering the frequent practice of off-label and mix & match as well as the potential medico-legal issues, further research is necessary to obtain more data about the appropriate indications and outcomes for those procedures.

Cite this article: EFORT Open Rev 2021;6:982-1005. DOI: 10.1302/2058-5241.6.210080

Cement debonding behaviors of the various tibial components of the ATTUNE knee system and its predecessors: Is a cement-in-cement revision an alternative?

BACKGROUND

Aseptic loosening remains one of the most common causes of revision of the tibial component for total knee arthroplasty. A stable bond between implant and cement is essential for appropriate long-term results. The aim of our in vitro study was to investigate the maximum failure load of tibial ATTUNE prosthesis design alternatives compared with a previous design. In addition, cement-in-cement revision was considered as a potential strategy after tibial component debonding.

METHODS

The experimental investigations of the maximum failure load of the implant-cement interface were performed under optimal conditions, without potential contamination. We compared the designs of the tibial components of the ATTUNE, ATTUNE S+ and P.F.C. Sigma. In addition, we investigated the cement-in-cement revision for the ATTUNE knee system replacing it with an ATTUNE S+.

RESULTS

The maximum failure load showed no significant difference between P.F.C. Sigma and ATTUNE groups (P = 0.087), but there was a significant difference between the P.F.C. Sigma and the ATTUNE S+ groups (P < 0.001). The analysis also showed a significant difference (P < 0.001) between the ATTUNE and the ATTUNE S+ groups for the maximum failure load. The ATTUNE S+ cement-in-cement revision group showed a significant higher failure load (P < 0.001) compared with the P.F.C. Sigma and ATTUNE groups. No significant differences (P = 1.000) were found between the ATTUNE S+ cement-in-cement and ATTUNE S+ group.

CONCLUSION

Based on these results, we found no design-specific evidence of increased debonding risk with the ATTUNE and ATTUNE S+ components compared with the P.F.C Sigma. Furthermore, the cement-in-cement revision seems to be an alternative for the revision surgery.

Wear and damage in retrieved humeral inlays of reverse total shoulder arthroplasty-where, how much, and why?

BACKGROUND

Polyethylene (PE) wear and material degradation have been reported as complications in reverse total shoulder replacements (rTSAs). In this regard, scapular notching is associated with more clinical complications. Therefore, the purposes of the study were to quantify the linear and volumetric wear, as a measure for the amount of removed material, and to qualitatively assess the PE damage modes to describe the material degradation in retrieved rTSA humeral PE inlays that contribute to failure of shoulder replacements. Furthermore, this study aimed to evaluate the effect of scapular notching on PE wear and rim damage of the humeral components.

METHODS

The total study population of 39 humeral inlays contains 2 cohorts that were used for the damage mode analysis and for the wear analysis, respectively. The extent and presence of wear damage modes in 5 defined zones were assessed by a grading system for all PE joint replacements. For quantitative wear analysis the most frequent design (n = 17) was chosen. Using a coordinate-measuring machine and postprocessing software, volumetric wear measurements for the retrieved humeral PE inlays were undertaken. Furthermore, prerevision radiographs were analyzed for scapular notching. Finally, retrieval findings were correlated with clinical and radiographic data to consider the effect of notching and to identify risk of failures for these prostheses.

RESULTS

Damage on the rim of the humeral PE inlays was more frequent and severe than on the intended articulation surface. Irrespective of the damage mode, the inferior rim zone sustained the greatest amount of wear damage followed by the posterior zone. Burnishing, scratching, pitting, and embedded particles are most likely to occur in the articular surface area, whereas surface deformation, abrasion, delamination and gross material degradation are predominantly present in the inferior and posterior rim zones. The retrieved inlays exhibited a mean volumetric wear rate of 296.9 mm³/yr ± 87.0 mm³/yr. However, if the notched and non-notched components were compared, a significant higher volumetric wear rate (296.5 ± 106.1 mm³/yr) was found for the notched components compared to the non-notched group (65.7 ± 7.4 mm³/yr). Generally, there was a significantly greater incidence of damage and greater amount of wear if scapular notching occurred.

CONCLUSION

The notched components showed a 5-fold increase in PE wear rate. Therefore, scapular notching has a strong effect on PE damage and wear. If scapular notching can be clinically avoided, the PE wear performance is in a similar magnitude as found for hip and knee replacements.

[Typing and particle analysis of squeaking hip endoprostheses : First histopathological analysis to examine the squeaking pathogenesis of ceramic-on-ceramic bearings]

BACKGROUND

Since the use of ceramic-on-ceramic (CoC) hip endoprostheses complications in the form of squeaking noises have occasionally occurred.

OBJECTIVES

This is the first histopathological analysis of the synovia-like interface membrane (SLIM) of ceramic squeaking hip endoprostheses with the aim to gain new insights into the squeaking pathogenesis.

MATERIALS AND METHODS

Seven CoC hip endoprostheses with squeaking pathogenesis are analyzed by SLIM consensus classification, particle algorithm, CD3 quantification, semiquantitative CD68 macrophages, Oil-Red positive macrophages, hemosiderin evaluation and in two cases by energy dispersive X‑ray spectroscopy (EDX).

RESULTS

In 1733 hip joint prosthesis pathology cases, a squeaking revision incidence of 0.40% was determined. In addition to SLIM type I (1/7), only SLIM type IV (6/7) was detected. 4/7 CoC cases showed combinations of micro, macro and, for the first time, supramacro (166.5 µm) ceramic wear particles. The EDX analysis confirmed the ceramic and an additional metallic abrasion. Increased focal concentrated low inflammatory markers (CD3/CD68) with hemosiderin (5/7) and lipid depositions (Oil-Red positive macrophages) (6/7) occurred.

CONCLUSIONS

A pathogenetic connection between SLIM type I/IV and squeaking can be assumed. SLIM types showed a partly light microscopic ceramic particle-dependent, partly independent predominantly low-grade inflammation. Hemosiderin and Oil-Red positive macrophages are signs of synovial tissue damage and indicate biomechanical misload (impingement) and dysfunction as cause of the squeaking pathogenesis.

Amorphous Carbon Coatings for Total Knee Replacements-Part II: Tribological Behavior

Diamond-like carbon coatings may decrease implant wear, therefore, they are helping to reduce aseptic loosening and increase service life of total knee arthroplasties (TKAs). This two-part study addresses the development of such coatings for ultrahigh molecular weight polyethylene (UHMWPE) tibial inlays as well as cobalt-chromium-molybdenum (CoCr) and titanium (Ti64) alloy femoral components. While the deposition of a pure (a-C:H) and tungsten-doped hydrogen-containing amorphous carbon coating (a-C:H:W) as well as the detailed characterization of mechanical and adhesion properties were the subject of Part I, the tribological behavior is studied in Part II. Pin-on-disk tests are performed under artificial synovial fluid lubrication. Numerical elastohydrodynamic lubrication modeling is used to show the representability of contact conditions for TKAs and to assess the influence of coatings on lubrication conditions. The wear behavior is characterized by means of light and laser scanning microscopy, Raman spectroscopy, scanning electron microscopy and particle analyses. Although the coating leads to an increase in friction due to the considerably higher roughness, especially the UHMWPE wear is significantly reduced up to a factor of 49% (CoCr) and 77% (Ti64). Thereby, the coating shows continuous wear and no sudden failure or spallation of larger wear particles. This demonstrated the great potential of amorphous carbon coatings for knee replacements.

The effect of surgical suture material on osteoclast generation and implant-loosening

Background: Implant loosening - either infectious or aseptic- is a still a major complication in the field of orthopaedic surgery. In both cases, a pro-inflammatory peri-prosthetic environment is generated by the immune system - either triggered by bacteria or by implant wear particles - which leads to osteoclast differentiation and osteolysis. Since infectious cases in particular often require multiple revision surgeries, we wondered whether commonly used surgical suture material may also activate the immune system and thus contribute to loss of bone substance by generation of osteoclasts. Methods: Tissue samples from patients suffering from infectious implant loosening were collected intraoperatively and presence of osteoclasts was evaluated by histopathology and immunohistochemistry. Further on, human monocytes were isolated from peripheral blood and stimulated with surgical suture material. Cell supernatant samples were collected and ELISA analysis for the pro-inflammatory cytokine IL-8 was performed. These experiments were additionally carried out on ivory slices to demonstrate functionality of osteoclasts. Whole blood samples were incubated with surgical suture material and up-regulation of activation-associated cell surface markers CD11b and CD66b on neutrophils was evaluated by flow cytofluorometry analysis. Results: We were able to demonstrate that multinucleated giant cells form in direct vicinity to surgical suture material. These cells stained positive for cathepsin K, which is a typical protease found in osteoclasts. By in vitro analysis, we were able to show that monocytes differentiated into osteoclasts when stimulated with surgical suture material. Resorption pits on ivory slices provided proof that the osteoclasts were functional. Release of IL-8 into cell supernatant was increased after stimulation with suture material and was further enhanced if minor amounts of bacterial lipoteichoic acid (LTA) were added. Neutrophils were also activated by surgical suture material and up-regulation of CD11b and CD66b could be seen. Conclusion: We were able to demonstrate that surgical suture material induces a pro-inflammatory response of immune cells which leads to osteoclast differentiation, in particular in combination with bacterial infection. In conclusion, surgical suture material -aside from bacteria and implant wear particles- is a contributing factor in implant loosening.

Bacterial Biofilm Components Induce an Enhanced Inflammatory Response Against Metal Wear Particles

Purpose

Aseptic implant loosening is still a feared complication in the field of orthopaedics. Presumably, a chronic inflammatory response is induced by wear particles, which leads to osteoclast generation, bone degradation and hence loosening of the implant. Since it has been demonstrated in the literature that most implants are in fact colonized by bacteria, the question arises whether aseptic implant loosening is truly aseptic. The aim of this study was to investigate a possibly enhanced inflammatory response to metal wear particles in the context of subclinical infection.

Patients and Methods

Tissue samples were collected intra-operatively from patients undergoing implant-exchange surgery due to aseptic loosening. Histopathological analysis was performed, as well as gene expression analysis for the pro-inflammatory cytokine Interleukin-8. By a series of in vitro experiments, the effect of metal wear particles on human monocytes, polymorphonuclear neutrophiles and osteoblasts was investigated. Additionally, minor amounts of lipoteichoic acid (LTA) and the bacterial heat shock protein GroEL were added.

Results

Histopathology of tissue samples revealed an accumulation of metal wear particles, as well as a cellular infiltrate consisting predominately of mononuclear cells. Furthermore, high expression of IL-8 could be detected in tissue surrounding the implant. Monocytes and osteoblasts in particular showed an increased release of IL-8 after stimulation with metal wear particles and in particular after stimulation with bacterial components and wear particles together.

Conclusion

We were able to show that minor amounts of bacterial components and metal wear particles together induce an enhanced inflammatory response in human monocytes and osteoblasts. This effect could significantly contribute to the generation of bone-resorbing osteoclasts and hence implant-loosening.

IgY Targeting Bacterial Quorum-Sensing Molecules in Implant-Associated Infections

Background: Implant-associated infections are still a major complication in the field of orthopedics. Bacteria can form biofilms on implant surfaces, making them more difficult to detect and treat. Since standard antibiotic therapy is often impaired in biofilm infections, particular interest is directed towards finding treatment alternatives. Biofilm-formation is a well-organized process during which bacteria communicate via quorum-sensing molecules (QSM). The aim of this study was to inhibit bacterial communication by directing avian IgY against specific QSM. Methods: Chicken were immunized against the following QSM: (1) AtlE, a member of the autolysin family which mediates attachment to a surface in Staphylococcus epidermidis; (2) GroEL, the bacterial heat shock protein; (3) PIA (polysaccharide intercellular adhesion), which is essential for cell–cell adhesion in biofilms. Staphylococcus epidermidis biofilms were grown and inhibition of biofilm-formation by IgYs was evaluated. Additionally, human osteoblasts were cultivated and biocompatibility of IgYs was tested. Results: We were able to demonstrate that all IgYs reduced biofilm-formation, also without prior immunization. Therefore, the response was probably not specific with regard to the QSM. Osteoblasts were activated by all IgYs which was demonstrated by microscopy and an increased release of IL-8. Conclusions: In conclusion, avian IgY inhibits biofilm-formation, though the underlying mechanism is not yet clear. However, adverse effects on local tissue cells (osteoblasts) were also observed.

Blood Metal Ion Release After Primary Total Knee Arthroplasty: A Prospective Study

Objectives

To investigate the course of in vivo blood metal ion levels in patients undergoing primary total knee arthroplasty (TKA) and to investigate potential risk factors associated with metal ion release in these patients.

Methods

Twenty‐five patients with indication for TKA were included in this prospective study. Whole blood metal ion analysis was performed pre‐operatively and at 1 week, 6 weeks, 3 months, 6 months, and 12 months postoperatively. Clinical scores were obtained using the American Knee Society Score (AKSS) and the Oxford Knee Score (OKS) at each follow‐up and patientsʼ activity levels were assessed by measuring the mean annual walking cycles at 12 months follow‐up. Anteroposterior and lateral radiographs of the operated knee were evaluated postoperatively and at 12‐month follow‐up with regard to implant position and radiological signs of implant loosening. Correlation analysis using multivariate linear regression was performed to investigate the influence of different variables (age, gender, functional scores, number of walking cycles, and body mass index [BMI]) on blood cobalt ion concentrations.

Results

Mean metal ion levels of cobalt, chromium, molybdenum, and titanium were 0.28 μg/L (SD, 0.14), 0.43 μg/L (SD, 0.49), 0.62 μg/L (SD, 0.45), and 1.96 μg/L (SD, 0.98), respectively at 12‐month follow‐up. Mean cobalt ion levels significantly increased 1‐year after surgery compared to preoperative measurements. There was no statistically significant increase of mean metal ion levels of chromium, titanium, and molybdenum at 1‐year follow‐up. Overall, metal ion levels were low and no patient demonstrated cobalt ion levels above 1 μg/L. Postoperative radiographs demonstrated well‐aligned TKAs in all patients and no signs of osteolysis or implant loosening were detected at 1‐year follow‐up. Both the AKSS and OKS significantly improved during the course of the study up to the final follow‐up. Multivariate regression analysis did not show a statistically significant correlation between the tested variables and blood cobalt ion concentrations.

Conclusion

A statistically significant increase of mean cobalt ion concentration at 1‐year follow‐up was found in this cohort of patients with well‐functioning TKA, although overall blood metal ion levels were relatively low. Despite low systemic metal ion concentrations seen in this cohort, the local effects of increased metal ion concentrations in the periprosthetic environment on the long‐term outcome of TKA should be further investigated.

Long-Term Results of a Second-Generation, Small-Diameter, Metal-On-Metal Bearing in Primary Total Hip Arthroplasty at 14-year Follow-Up

(1) Background: The objective of the present study was to review the clinical and radiological results of a small-head, MoM bearing in primary THA and to determine blood metal ion levels at long-term follow-up. (2) Methods: We retrospectively evaluated the clinical and radiological results of 284 small-diameter, MoM 28-mm Metasul THA at a mean follow-up of 14.5 years, and measured blood metal ion concentrations in 174 of these patients. (3) Results: After 14 years, survival free for revision due to any reason was 94%. Proximal femoral osteolysis was seen in 23% of hips, and MRI demonstrated ARMD in 27 of the 66 investigated hips (41%). Mean cobalt, chromium, and titanium ion concentrations were 0.82 µg/L (range 0.22-4.45), 1.51 µg/L (0.04-22.69), and 2.68 µg/L (0.26-19.56) in patients with unilateral THA, and 2.59 µg/L (0.43-24.75), 2.50 µg/L (0.26-16.75), and 3.76 µg/L (0.67-19.77), respectively in patients with bilateral THA. Twenty-nine percent of patients showed cobalt or chromium ion levels > 2 µg/L. (4) Conclusions: Despite good clinical long-term results, increased blood metal ion levels (cobalt or chromium > 2 µg/L) were found in approximately one-third of asymptomatic patients, and proximal femoral osteolysis and ARMD were frequently seen in this cohort. Blood metal ion analysis appears helpful in the long-term follow-up of these patients in order to identify individuals at risk. In accordance with contemporary consensus statements, symptomatic patients with elevated metal ion levels and/or progressive osteolysis should be considered for additional CT or MARS MRI to determine the extent of soft tissue affection prior to revision surgery. Further studies are necessary to investigate the clinical relevance of ARMD in asymptomatic patients with small-head, MoM THA.

Backside wear, particle migration and effectiveness of screw hole plugs in acetabular hip joint replacement with cross-linked polyethylene

In total hip arthroplasty, osteolysis of the acetabulum often occurs at the backside of cups in the area of screw holes, indicating a clinically relevant amount of polyethylene (PE) wear particles in this area. In order to avoid a possible migration of wear particles to the acetabulum-bone, screw hole plugs are provided for some implant systems. The aims of this study were to quantitatively determine backside wear and to investigate the migration behaviour of articulation-related wear particles in a cup system with open and closed screw holes by plugs. Titanium cup systems with backside holes for screw fixations were sinusoidally loaded with 2.7 kN. The articulation area was separated from the backside area of the cup. A defined amount of articulation-generated particles was added to the fluid of the articulation chamber. The fluids in the two chambers were separately filtered after 2 × 10⁶ cycles for a particle analysis. Backside wear with noticeably small (65.6 ± 4.2 nm) and round PE particles was identified. With both open and closed screw holes, a migration of the articulating wear particles from the articulation area behind the cup could be observed. Backside wear was estimated to be below 1% of the articulated wear. Screw hole plugs did not effectively prevent the migration of PE wear particles behind the investigated cups. STATEMENT OF SIGNIFICANCE: Backside wear occurs in a proven cup-system. Furthermore, it was quantitatively observed that articulation-generated wear products could migrate from the articulating area along the cup/liner-interface through the screw holes behind the cup. An almost unimpeded particle migration to the acetabulum-bone, in conjunction with very small backside wear particles, could produce a clinically relevant amount of PE with respect to pelvic lysis. These findings highlight the importance of management to avoid particle migration in artificial hip cups. Therefore, primarily the use of screw hole plugs, as far as available for the respective cup-system, is recommended. The aim of avoiding particle migration by plugs, but also by using a sophisticated anchoring mechanism between cup and PE liner should continue in future.

Impact of Electrocautery on Fatigue Life of Spinal Fusion Constructs-An In Vitro Biomechanical Study

Instrumentation failure in the context of spine surgery is attributed to cyclic loading leading to formation of fatigue cracks, which later propagate and result in rod fracture. A biomechanical analysis of the potential impact of electrocautery on the fatigue life of spinal implants has not been previously performed. The aim of this study was to assess the fatigue life of titanium (Ti) and cobalt-chrome (CoCr) rod-screw constructs after being treated with electrocautery. Twelve spinal constructs with CoCr and Ti rods were examined. Specimens were divided into four groups by rod material (Ti and CoCr) and application of monopolar electrocautery on the rods’ surface (control-group and electrocautery-group). Electrocautery was applied on each rod at three locations, then constructs were cyclically tested. Outcome measures were load-to-failure, total number of cycles-to-failure, and location of rod failure. Ti-rods treated with electrocautery demonstrated a significantly decreased fatigue life compared to non-treated Ti-rods. Intergroup comparison of cycles-to-failure revealed a significant mean decrease of almost 9 × 10⁵ cycles (p = 0.03). No CoCr-rods failed in this experiment. Electrocautery application on the surface of Ti-rods significantly reduces their fatigue life. Surgeons should exercise caution when using electrocautery in the vicinity of Ti-rods to mitigate the risk of rod failure.

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.

Finite Element Analysis and Biomechanical Testing of the New MiniMIS Short Stem

INTRODUCTION

In hip arthroplasty a trend towards short stem prostheses is observed. The aim of this study is to investigate the finite element analysis and biomechanical fatigue performance of a new short stem prosthesis.

METHODS

A finite element analysis was used to simulate the stresses during neck and stem loading according to the ISO standards. Numerical analysis with applied forces of up to 6 kN were performed in the vertical direction on a femoral neck-preserving stem (MiniMIS). During experimental testing, 10 million cycles with a maximum load of 5.34 kN using the worst case of a XL ceramic head (36 mm) were applied. This was followed by a Locati test, where the load was increased until failure of the stem.

RESULTS

For all stems, stress values below the limits according to the ISO 5832-3 standard (yield strength of 800 N/mm²) were calculated by the finite element analysis. In the biomechanical tests, the total number of 10 million cycles with a maximum load of 5.34 kN was reached in all cases without any visible signs of implant damage. The estimated load to failure after stem testing was 2.16 kN (required by ISO 7206-4: 1.2 kN) and after neck testing > 9.35 kN (required by ISO 7206-6: 5.4 kN).

SUMMARY

The presented finite element calculation and subsequent biomechanical testing show that the design of this stem meets the essential mechanical requirements given by the ISO and a material failure is not expected in all variants tested under the applied boundary conditions.

Particle analysis of shape factors according to American Society for Testing and Materials

Polyethylene wear is one of the major factors influencing the survivorship of joint replacements. Depending on the number, size and morphology of the polyethylene particles, biological responses of the periprosthetic soft tissue in terms of inflammatory processes can occur, leading to loosening of the implant. Various parameters are used to analyze wear particles, which are usually determined by examining scanning electron microscopy (SEM) images with a particle analysis program. In this study, three different software solutions for particle analysis (self-developed Particleanalyzer_HD, Leica QWin and ImageJ) were compared regarding particle number, size and morphology. These solutions were also compared to the American Society for Testing and Materials (ASTM) F1877-16 specifications regarding particle morphology. SEM image analysis revealed no differences for the equivalent circle diameter (p = 0.969). However, a significant difference was found for the aspect ratio between the Particleanalyzer_HD and the other two software solutions (p < 0.001) and between Leica QWin and the other two software solutions regarding the roundness (p < 0.001). Only the Particleanalyzer_HD showed an excellent agreement with the ASTM standard for both morphology parameters (intraclass correlation = 1.000). Only the Particleanalyzer_HD calculated the two morphology parameters according to the ASTM standard. A comparison of the particle morphology between different studies is barely possible, as different algorithms for particle analysis are used. It is strongly recommended that the calculation according to the ASTM standard is used to improve future comparability of findings from wear analysis studies. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:225-233, 2020.

Backside wear in acetabular hip joint replacement

INTRODUCTION

Besides head-insert articulation in hip joint replacements, micro-motions between the backside of assembled polyethylene acetabular liners and the metal cup may cause additional wear. Pelvic osteolysis frequently occurs in the region of screw holes, and cup loosening hints to clinically relevant amounts of polyethylene backside wear. It has yet to be confirmed whether backside wear particles differ in size and morphology compared to articulating wear. Previous methods have been limited to subjective assessment of backside surface damages without consideration of wear debris. The aim of this study was to develop and validate a method for quantitative in vitro measurements of polyethylene backside wear in artificial hip cups and to characterize these wear particles for the first time.

METHODS

Titanium cup-systems (Plasmafit®Plus7, Aesculap, UHMWPE liner) were sinusoidally loaded (2.5 kN) and a torque of 5 Nm was simultaneously applied. The front and rear side of the cup were separated to isolate backside wear. After 2 × 10⁶ cycles the surrounding fluid was filtered and a particle analysis was performed.

RESULTS

Backside wear had a particles size of 64.1 ± 1.9 nm and was verified as round and oval particles with partly rough outlines. An estimated total number of particles of 1.26 × 10⁹ ± 1.67 × 10⁸ per 10⁶ cycles was determined.

CONCLUSION

Backside wear was estimated to be several times lower than published values of articulating wear. However, polyethylene backside wear particles represented significantly smaller particles with partly roughened outlines than articulating wear particles and may therefore cause higher biological response in macrophage-mediated bone resorption compared to articulated particles.

STATEMENT OF SIGNIFICANCE

Within this study, an analytical method for quantitative measuring polyethylene backside wear of artificial hip cups was successfully developed and validated for the first time. It could be shown that backside wear is still present, even in modern cup-systems. These findings can be further used for investigations of the osteolytic potential of polyethylene particles, for evaluating and improving new implant systems and to evaluate the effectiveness of screw hole plugs to prevent the particle migration to the acetabulum.

The subchondral bone layer and glenoid implant design are relevant for primary stability in glenoid arthroplasty

BACKGROUND

Clinical studies suggest that reaming of the subchondral bone layer to achieve good implant seating is a risk factor for glenoid loosening. This study aims to evaluate (1) the importance of the subchondral bone layer and (2) the influence of the design of the glenoid component.

METHODS

Different techniques for preparation of an A1 glenoid were compared: (1) preserving the subchondral bone layer; (2) removal of the subchondral bone layer; (3) implantation of a glenoid component that does not adapt to the native anatomy. Artificial glenoid bones (n = 5 each) were used with a highly standardized preparation and implantation protocol. Biomechanical testing was performed during simulated physiological shoulder motion. Using a high-resolution optical system, the micromotions between implant and bone were measured up to 10,000 motion cycles.

RESULTS

At the 10,000 cycle measuring point, significantly more micromotions were found in the subchondral layer removed group than in the subchondral layer preserved group (p = 0.0427). The number of micromotions in the nonadapted group was significantly higher than in the subchondral layer preserved group (p = 0.0003) or the subchondral layer removed group (p = 0.0207).

CONCLUSION

Conservative reaming proved important to diminish the micromotions of the glenoid component. Implantation of a glenoid component that matches with the bony underlying glenoid can help to preserve the subchondral bone layer without sacrificing proper implant seating.

Influence of joint kinematics on polyethylene wear in anatomic shoulder joint arthroplasty

BACKGROUND

Despite the positive results in total shoulder arthroplasties (TSAs), a higher revision rate is documented compared with total hip and knee replacements. Wear is the possible main cause of TSA failure in the long-term. This study investigated the effect of joint kinematics and the influence of the rotator cuff on the polyethylene wear performance in an anatomic TSA.

METHODS

Lifting a load of 2 kg with an abduction/adduction of 0° to 90° was simulated for 2 × 10⁶ cycles as a primary motion using a fully kinematic joint simulator. A combined rotation in anteversion-retroversion of ±5° and ±10° was also simulated. The force in the superior-inferior direction and the axial joint compression were applied under force control based on in vivo data of the shoulder. A soft tissue restraint model was used to simulate an intact and an insufficient rotator cuff.

RESULTS

The highest wear rate in the intact rotator cuff group was 58.90 ± 1.20 mg/10⁶ cycles with a combined rotation of ±10°. When an insufficient rotator cuff was simulated, the highest polyethylene wear rate determined was 79.67 ± 4.18 mg/10⁶ cycles.

CONCLUSIONS

This study confirms a high dependency of the polyethylene wear behavior and dimension on the joint kinematics in total shoulder replacement. This can be explained by an increasing cross-shear stress on the polyethylene component. The results obtained indicate that additional combined kinematics are an indispensable part of wear tests on anatomic shoulder replacements.

Hard Chrome-Coated and Fullerene-Doped Metal Surfaces in Orthopedic Bearings

Metal-on-metal bearings for total hip replacements have been introduced as an alternative to polyethylene in young and more active patients. These have, however, been shown to be prone to implant malpositioning and have been limited by some specific design features. In that context, coatings present an option to increase wear resistance by keeping the high fracture strength of the metal substrate. A custom-made electroplating setup was designed for the coating of CoCr substrates using (a) an industrial standard chromium electrolyte; (b) a custom-made hexavalent chromium (Cr⁶⁺) electrolyte with a reduced chromium trioxide (CrO₃) content, both without solid additives and (c) with the addition of fullerene (C₆₀) nanoparticles; and (d) a trivalent chromium (Cr³⁺) electrolyte with C₆₀ addition. All coatings showed an increase in microhardness compared with the metal substrate. Trivalent coatings were thinner (10 µm) than the hexavalent coatings (23–40 µm) and resulted in increased roughness and crack density. Wear was found to be reduced for the hexavalent chromium coatings by 70–84% compared with the CoCr–CoCr reference bearing while the trivalent chromium coating even increased wear by more than 300%. The addition of fullerenes to the electrolyte did not show any further tribological effect.

Influence of humeral head material on wear performance in anatomic shoulder joint arthroplasty

BACKGROUND

The number of total shoulder arthroplasties has increased in the past years, with encouraging results. However, the survival of anatomic total shoulder arthroplasty (aTSA) is lower compared with that of knee and hip replacements. Wear-associated problems like loosening are well-known causes of long-term failure of aTSA. The main purpose of this study was to investigate the wear behavior of ceramic-polyethylene bearings compared with the standard metal-polyethylene bearings. Because there is a lack of valid experimental wear testing methods, the secondary aim was to develop a validated wear simulation.

METHODS

The wear assessment was performed using a force-controlled joint simulator for 3 × 10⁶ cycles, and polyethylene wear was assessed gravimetrically and by particle analysis. Kinetic and kinematic data were adopted from in vivo loading measurements and from several clinical studies on shoulder joint kinematics. The reaction of the rotator cuff was simulated on the basis of a virtual soft tissue model. As activity, an abduction-adduction motion of 0°-90° lifting a load of 2 kg superimposed by an anteversion-retroversion has been chosen.

RESULTS

The studied aTSA resulted in a polyethylene wear rate of 62.75 ± 1.60 mg/10⁶ cycles in combination with metallic heads. The ceramic heads significantly reduced the wear rate by 26.7% to 45.99 ± 1.31 mg/10⁶. There were no relevant differences in terms of the particle characteristics.

CONCLUSION

This is the first study that experimentally studied the wear behavior of aTSA based on patient-related and biomechanical data under load-controlled conditions. Regarding polyethylene wear, the analyzed aTSA could benefit from ceramic humeral heads.

Influence of implant length and bone defect situation on primary stability after distal femoral replacement in vitro

BACKGROUND

Aseptic loosening is the major reason for failure of distal femoral replacement using current modular megaprostheses. Although the same stems are used for proximal and distal replacement, survival rates in clinical studies with distal reconstruction were lower within the same system compared to proximal reconstruction. We analyzed whether primary stability as presupposition for long-term fixation can be achieved with a current tapered stem design. Additionally, we hypothesized that stem length affects primary stability depending on bone defect situations.

METHODS

A modular tumor system (Megasystem-C®, Link GmbH, Hamburg, Germany) with two different tapered stems (100 and 160mm) was implanted in eight Sawbones® in two consecutively created defect situations (10 and 20cm proximal to knee joint level). Primary rotational stability was investigated by measuring relative micromotions between implant and bone to identify the main fixation areas and to characterize the fixation pattern.

RESULTS

The fixation differed between the two stem lengths and with respect to both defect situations; however in each case the main fixation area was located at or close to the femoral isthmus. Highest relative micromotions were measured with the 160-mm stem at the distal end within small bone defects and at the proximal end when defects were increased.

CONCLUSIONS

The analyzed design seemed to create sufficient primary stability along the main fixation areas of the implant. Based on these results and with respect to oncologic or potential revision situations, we suggest the use of the shorter stem to be more favorable in case of primary implant fixation.

The Impact of Metal Ion Exposure on the Cellular Behavior of Human Osteoblasts and PBMCs: In Vitro Analyses of Osteolytic Processes

Osteolysis in the periprosthetic tissue can be caused by metallic wear particles and ions that can originate from implant surface corrosion. These products influence cellular behavior and stimulate the expression of proinflammatory cytokines. The purpose of this study was to evaluate the impact of CoCr29Mo6 ions on cell survival, differentiation, and cytokine expression in human osteoblasts and peripheral blood mononuclear cells (PBMCs). Thus, we exposed cells with a mixture of 200 µg/L ion solution and determined cell viability and apoptosis/necrosis. Gene expression analyses of osteoblastic and osteoclastic differentiation markers as well as pro-osteolytic mediators (IL-6, IL-8, TNF-α, MCP-1, MMP1, TIMP1) were performed. These markers were also investigated in mixed cultures of adherent and non-adherent PBMCs as well as in co-cultures of human osteoblasts and PBMCs. The ion solution induced necrosis in osteoblasts and PBMCs in single cultures. All examined mediators were highly expressed in the co-culture of osteoblasts and PBMCs whereas in the single cell cultures only IL-6, IL-8, and MMP1 were found to be stimulated. While the applied concentration of the CoCr29Mo6 ion solutions had only marginal effects on human osteoblasts and PBMCs alone, the co-culture may provide a comprehensive model to study osteolytic processes in response to Co and Cr ions.

Supramacroparticulate PE in 6 different joint endoprostheses localisations: An indicator for PE damage?

In the histopathological particle algorithm polyethylene (PE) particles with maximum lengths of more than 100μm - called PE supramacroparticles - are identified exclusively for knee joint and hip prostheses. However, a definitive characterisation, detection in all joint localisations and a causal clarification of the pathogenesis are lacking. In this study a total of 175 SLIM (synovial-like interface membrane) cases with PE supramacroparticles of knee joint prostheses (n=89), hip joint prostheses (n=44), ankle joint prostheses (n=36) and prostheses in three localisations of the upper extremities (n=6) were systematically investigated. The arithmetic mean of the particle length varied greatly within the prosthesis types. This had a significant positive correlation with the prosthesis lifetime and negative correlation with the date of implantation. It can be concluded that both the lifetime and the time of implantation have an influence on the particle length. The prostheses with supramacroparticulate damage moreover showed a clearly reduced survival rate compared with other data published on the prosthesis lifetime. The material wear therefore could not be attributed solely to the usual fatigue factors. Since loosening of the prostheses, decentring of the PE components or damage to the PE inlay existed in all cases, mechanical dysloading seems to be the most probable cause of PE supramacroparticle genesis. Due to the striking length and for demarcation from PE macroparticles, the term supramacroparticulate PE is proposed for a length of more than 100μm. In the extended histopathological particle algorithm supramacroparticulate PE has been included in the macroparticles category and should be taken into account and interpreted causally in histopathological diagnostics of joint prosthesis failure.

[Bearing selection in total hip arthroplasty]

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?]

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.

Wear testing of total hip replacements under severe conditions

Controlled wear testing of total hip replacements in hip joint simulators is a well-established and powerful method, giving an extensive prediction of the long-term clinical performance. To understand the wear behavior of a bearing and its limits under in vivo conditions, testing scenarios should be designed as physiologically as possible. Currently, the ISO standard protocol 14242 is the most common preclinical testing procedure for total hip replacements, based on a simplified gait cycle for normal walking conditions. However, in recent years, wear patterns have increasingly been observed on retrievals that cannot be replicated by the current standard. The purpose of this study is to review the severe testing conditions that enable the generation of clinically relevant wear rates and phenomena. These conditions include changes in loading and activity, third-body wear, surface topography, edge wear and the role of aging of the bearing materials.

Primary rotational stability of various megaprostheses in a biomechanical sawbone model with proximal femoral defects extending to the isthmus

PURPOSE

Fixation of proximal femoral megaprostheses is achieved in the diaphyseal isthmus. We hypothesized that after extended bone resection including the proximal part of the isthmus a reduced length of fixation will affect the stability and fixation characteristics of these megaprostheses. The aim of this study was to analyze in a validated sawbone model with extended proximal femoral defects which types of implants have sufficient primary stability to allow osteointegration and to describe their fixation characteristics.

METHODS

Four different cementless megaprostheses were implanted into 16 Sawbones with an AAOS type III defect after resection 11 cm below the lesser trochanter involving the proximal isthmus. To determine the primary implant stability relative micromotions between bone and implant were measured in relation to a cyclic torque of 7Nm applied on the longitudinal axis of the implant. We determined the fixation characteristics of the different implant designs by comparing these relative micromotions along the longitudinal stem axis.

RESULTS

In the tested sawbones all studied implants showed sufficient primary stability to admit bone integration with relative micromotions below 150 µm after adapting our results to physiologic hip joint loadings. Different fixation characteristics of the megaprostheses were determined, which could be explained by their differing design and fixation concepts.

CONCLUSIONS

Cementless megaprostheses of different designs seem to provide sufficient primary stability to bridge proximal femoral defects if the diaphyseal isthmus is partially preserved. In our sawbone model the different implant fixation patterns can be related to their stem designs. No evidence can be provided to favor one of the studied implants in this setting. However, femoral morphology is variable and in different isthmus configurations specific implant designs might be appropriate to achieve the most favorable primary stability, which enables bone integration and consequently long term implant stability.

Wear testing of moderate activities of daily living using in vivo measured knee joint loading

Resumption of daily living activities is a basic expectation for patients provided with total knee replacements. However, there is a lack of knowledge regarding the impact of different activities on the wear performance. In this study the wear performance under application of different daily activities has been analyzed. In vivo load data for walking, walking downstairs/upstairs, sitting down/standing up, and cycling (50 W & 120 W) has been standardized for wear testing. Wear testing of each activity was carried out on a knee wear simulator. Additionally, ISO walking was tested for reasons of comparison. Wear was assessed gravimetrically and wear particles were analyzed. In vivo walking produced the highest overall wear rates, which were determined to be three times higher than ISO walking. Moderate wear rates were determined for walking upstairs and downstairs. Low wear rates were determined for standing up/sitting down and cycling at power levels of 50 W and 120 W. The largest wear particles were observed for cycling. Walking based on in vivo data has been shown to be the most wear-relevant activity. Highly demanding activities (stair climbing) produced considerably less wear. Taking into account the expected number of loads, low-impact activities like cycling may have a greater impact on articular wear than highly demanding activities.

Experimental testing of total knee replacements with UHMW-PE inserts: impact of severe wear test conditions

Aseptic implant loosening due to inflammatory reactions to wear debris is the main reason for the revision of total knee replacements (TKR). Hence, the decrease in polyethylene wear particle generation from the articulating surfaces is aimed at improving implant design and material. For preclinical testing of new TKR systems standardized wear tests are required. However, these wear tests do not reproduce the entire in vivo situation, since the pattern and amount of wear and subsequent implant failure are underestimated. Therefore, daily activity, kinematics, implant aging and position, third-body-wear and surface properties have to be considered to estimate the wear of implant components in vivo. Hence, severe test conditions are in demand for a better reproduction of the in vivo situation of TKR. In the present article an overview of different experimental wear test scenarios considering clinically relevant polyethylene wear situations using severe test conditions is presented.

Loosening detection of the femoral component of hip prostheses with extracorporeal shockwaves: a pilot study

The diagnosis of aseptic loosening of hip implants is often challenging. A vibrational analysis of the bone-implant interface could be an alternative method to analyze the fixation of endoprostheses. We assessed an innovative and new approach for excitation by using extracorporeal shockwaves in this study. In three cadaver specimens total hip arthroplasty was performed bilaterally. Four different states of implant loosening were simulated. Three accelerometers were fixed at the medial condyle, the greater trochanter, and the crest of the ilium. The bone-implant compound was excited with highly standardized extracorporeal shock waves. Resonance spectra between 100 Hz and 5000 Hz were recorded. This technique permitted a good adaptation to varying soft tissue conditions. The main resonance frequency of the hip joints occurred at about 2000 Hz. The analysis of the measured spectra showed an interrelation between the state of loosening and the frequency values of the resonances. In case of a stem loosening, there were significant shifts of the resonance into the lower frequency area between 386 Hz and 847 Hz. With this novel technique the degree of stem loosening could be assessed in a soft tissue considering configuration. This study forms a first step for future establishment of a non-invasive, non-radiological and fast applicable diagnostic procedure for early detection of endoprostheses loosening before manifest presence of clinical signs.

Force-controlled dynamic wear testing of total ankle replacements

Currently, our knowledge of wear performance in total ankle replacements is limited. The aim of this study is to develop a scenario for force-controlled testing and wear testing of total ankle replacements. A force-controlled wear test was developed: based on cadaver measurements, the passive stabilization (ligaments and soft tissue) of the ankle joint was characterized and a restraint model for ankle stabilization was developed. Kinematics and kinetics acting at the replaced ankle joint were defined based on literature data and gait analysis. Afterwards, force-controlled wear testing was carried out on a mobile, three-component, total ankle replacement design. Wear was assessed gravimetrically and wear particles were analyzed. Wear testing resulted in a mean wear rate of 18.2±1.4mm(3)/10(6) cycles. Wear particles showed a mean size of 0.23μm with an aspect ratio of 1.61±0.96 and a roundness of 0.62±0.14. Wear testing of total ankle replacement shows that a relevant wear mass is generated with wear particles in a biologically relevant size range. The developed wear test provides a basis for future wear testing of total ankle replacements.

Synovial fluid replication in knee wear testing: an investigation of the fluid volume

Wear testing cannot replicate the variations in wear rates and wear mechanisms seen in vivo, which may be related to differences between in vivo and in vitro conditions. A considerable difference exists between the in vivo synovial fluid volume (few milliliter) and the in vitro substituted bovine serum volume (several hundred milliliter). The aim of this study was to analyze the effects of a reduced fluid volume on the wear behavior in a knee wear simulator study. Four wear tests with decreasing fluid volumes (250, 150, 75, and 45 ml) were carried out. Using a large fluid volume of 250 ml for wear testing resulted in a wear rate of 9.7±1.2 mm3/10(6)  cycles. Decreasing the fluid volume consecutively reduced the wear rate to down to 8.8±1.4 mm3/10(6) for 150 ml (p=1.00), 5.6±1.2 mm3/10(6) for 75 ml (p=0.01), and 1.0±0.2 mm3/10(6) cycles for 45 ml fluid volume (p≤0.01). Additionally, higher serum degradation and larger wear particles were observed with smaller fluid volumes used for testing. This study demonstrates the high relevance of the protein-based lubricant on the wear behavior and the technical limitation to replicate the synovial fluid in simulator tests. Wear testing should be carried out using larger fluid volumes (e.g., 250 ml) to generate physiological relevant wear masses.

How do gait frequency and serum-replacement interval affect polyethylene wear in knee-wear simulator tests?

Polyethylene wear (PE) is known to be a limiting factor in total joint replacements. However, a standardized wear test (e.g. ISO standard) can only replicate the complex in vivo loading condition in a simplified form. In this study, two different parameters were analyzed: (a) Bovine serum, as a substitute for synovial fluid, is typically replaced every 500,000 cycles. However, a continuous regeneration takes place in vivo. How does serum-replacement interval affect the wear rate of total knee replacements? (b) Patients with an artificial joint show reduced gait frequencies compared to standardized testing. What is the influence of a reduced frequency? Three knee wear tests were run: (a) reference test (ISO), (b) testing with a shortened lubricant replacement interval, (c) testing with reduced frequency. The wear behavior was determined based on gravimetric measurements and wear particle analysis. The results showed that the reduced test frequency only had a small effect on wear behavior. Testing with 1 Hz frequency is therefore a valid method for wear testing. However, testing with a shortened replacement interval nearly doubled the wear rate. Wear particle analysis revealed only small differences in wear particle size between the different tests. Wear particles were not linearly released within one replacement interval. The ISO standard should be revised to address the marked effects of lubricant replacement interval on wear rate.

Mechanical properties of a cemented porous implant interface

BACKGROUND

Revision arthroplasty often requires anchoring of prostheses to poor-quality or deficient bone stock. Recently, newer porous materials have been introduced onto the market as additional, and perhaps better, treatment options for revision arthroplasty. To date, there is no information on how these porous metals interface with bone cement. This is of clinical importance, since these components may require cementing to other prosthesis components and occasionally to bone.

METHODS

We created porous metal and bone cylinders of the same size and geometry and cemented them in a well-established standardized setting. These were then placed under tensile loading and torsional loading until failure was achieved. This permitted comparison of the porous metal/cement interface (group A) with the well-studied bone/cement interface (group B).

RESULTS

The group A interface was statistically significantly stronger than the group B interface, despite having significantly reduced depth of cement penetration: it showed a larger maximum tensile force (effect size 2.7), superior maximum tensile strength (effect size 2.6), greater maximum torsional force (effect size 2.2), and higher rotational stiffness (effect size 1.5).

INTERPRETATION

The newer porous implants showed good interface properties when cemented using medium-viscosity bone cement. The axial and rotational mechanical strength of a porous metal/cement interface appeared to be greater than the strength of the standard bone/cement interface. These results indicate that cementing of porous implants can provide great stability in situations where it is needed.

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.

CD4⁺CD25⁺/highCD127low/⁻ regulatory T cells are enriched in rheumatoid arthritis and osteoarthritis joints--analysis of frequency and phenotype in synovial membrane, synovial fluid and peripheral blood

INTRODUCTION

CD4⁺CD25⁺/highCD127low/⁻ regulatory T cells (Tregs) play a crucial role in maintaining peripheral tolerance. Data about the frequency of Tregs in rheumatoid arthritis (RA) are contradictory and based on the analysis of peripheral blood (PB) and synovial fluid (SF). Because Tregs exert their anti-inflammatory activity in a contact-dependent manner, the analysis of synovial membrane (SM) is crucial. Published reports regarding this matter are lacking, so we investigated the distribution and phenotype of Tregs in concurrent samples of SM, SF and PB of RA patients in comparison to those of osteoarthritis (OA) patients.

METHODS

Treg frequency in a total of 40 patients (18 RA and 22 OA) matched for age and sex was assessed by flow cytometry. Functional status was assessed by analysis of cell surface markers representative of activation, memory and regulation.

RESULTS

CD4⁺ T cells infiltrate the SM to higher frequencies in RA joints than in OA joints (P = 0.0336). In both groups, Tregs accumulate more within the SF and SM than concurrently in PB (P < 0.0001). Relative Treg frequencies were comparable in all compartments of RA and OA, but Treg concentration was significantly higher in the SM of RA patients (P = 0.025). Both PB and SM Tregs displayed a memory phenotype (CD45RO⁺RA⁻), but significantly differed in activation status (CD69 and CD62L) and markers associated with Treg function (CD152, CD154, CD274, CD279 and GITR) with only minor differences between RA and OA.

CONCLUSIONS

Treg enrichment into the joint compartment is not specific to inflammatory arthritis, as we found that it was similarly enriched in OA. RA pathophysiology might not be due to a Treg deficiency, because Treg concentration in SM was significantly higher in RA. Synovial Tregs represent a distinct phenotype and are activated effector memory cells (CD62L⁻CD69⁺), whereas peripheral Tregs are resting central memory cells (CD62L⁺CD69⁻).

[Different symptoms in patients with prostheses with metal-metal bearings]

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.

Wear in total knee arthroplasty--just a question of polyethylene?: Metal ion release in total knee arthroplasty

PURPOSE

Biological reactions against wear particles are a common cause for revision in total knee arthroplasty. To date, wear has mainly been attributed to polyethylene. However, the implants have large metallic surfaces that also could potentially lead to metal wear products (metal ions and debris). The aim of this study was to determine the local release of cobalt, chromium, molybdenum and titanium in total knee arthroplasty during a standard knee wear test.

METHODS

Four moderately conforming fixed-bearing implants were subjected to physiological loadings and motions for 5×10(6) walking cycles in a knee wear simulator. Polyethylene wear was determined gravimetrically and the release of metallic wear products was measured using high resolution-inductively coupled plasma-mass spectrometry.

RESULTS

A polyethylene wear rate of 7.28 ± 0.27 mg/10(6) cycles was determined and the cumulative mass of released metals measured 1.63 ± 0.28 mg for cobalt, 0.47 ± 0.06 mg for chromium, 0.42 ± 0.06 mg for molybdenum and 1.28 ± 0.14 mg for titanium.

CONCLUSION

For other metallic implants such as metal-on-metal total hip arthroplasty, the metal wear products can interact with the immune system, potentially leading to immunotoxic effects. In this study about 12 % by weight of the wear products were metallic, and these particles and ions may become clinically relevant for patients sensitive to these materials in particular. Non-metallic materials (e.g. ceramics or suitable coatings) may be considered for an alternative treatment for those patients.

Wear performance of ceramic-on-metal hip bearings

Ceramic-on-metal (CoM) bearings are considered to be a promising alternative to polyethylene-based bearings or hard-on-hard bearings (Ceramic-on-Ceramic (CoC) and Metal-on-Metal (MoM)). Although, CoM shows lower wear rates than MoM, in-vitro wear testing of CoM shows widely varying results. This may be related to limitations of wear-measuring methods. Therefore, the aim of this study was to improve the gravimetric measurement technique and to test wear behaviour of CoM bearings compared to CoC bearings. Level walking according to ISO-14242 was simulated for four CoM and four CoC bearings. Prior to simulation, errors in measurement of gravimetric wear were detected and improvements in measurement technique incorporated. The results showed no differences in mean wear rates between CoM and CoC bearings. However, the CoM bearings showed wear results over a wide range of wear performance. High reliability of wear results was recorded for the CoC bearings. Material transfer was observed on the ceramic heads of the CoM bearings. Therefore, for level walking a partial mixed or boundary lubrication has to be assumed for this type of bearing. CoM is a highly sensitive wear-couple. The reasons for the observed behaviour cannot be clarified from this study. Simulator studies have to be considered as an ideal loading condition. Therefore, high variations in wear rates as seen in this study, even at low levels, may have an adverse effect on the in-vivo wear behavior. Careful clinical use may be advisable until the reasons for the variation are fully clarified and understood.