[Classification of prosthetic loosening and determination of wear particles]

A Comparison of Wear Patterns on Retrieved and Simulator-Tested Total Knee Replacements

Aseptic implant loosening is the most common reason for revision surgery after total knee replacement. This is associated with adverse biological reactions to wear debris from the articulating implant components. To predict the amount of wear debris generated in situ, standard wear testing of total knee replacement (TKR) is carried out before its clinical use. However, wear data reported on retrievals of total knee replacement (TKR) revealed significant discrepancies compared with standard wear simulator studies. Therefore, the aim of the present study was to compare the wear patterns on identical posterior-cruciate-retaining TKR designs by analyzing retrieved and experimentally tested implants. The identification and classification of wear patterns were performed using 21 retrieved ultra-high-molecular-weight-polyethylene (UHMW-PE) inserts and four sets of inserts of identical design and material tested in a knee wear simulator. These four sets had undergone different worst-case conditions and a standard test in a wear simulator according to ISO 14243-1. Macroscopic and microscopic examinations of the polyethylene inserts were performed, including the determination of seven modes of wear that correspond to specific wear patterns, the calculation of wear areas, and the classification of the damage over the whole articulating area. Retrieved and standard wear simulator-tested UHMW-PE inserts showed significant differences in wear area and patterns. The total wear areas and the damage score were significantly larger on the retrievals (52.3% versus 23.9%, 32.7 versus 22.7). Furthermore, the range of wear patterns found on the retrievals was not reproducible in the simulator-tested inserts. However, good correspondence was found with the simulator-tested polyethylene inserts under worst-case conditions (third body wear), i.e., deep wear areas could be replicated according to the in vivo situation compared with other wear test scenarios. Based on the findings presented here, standard simulator testing can be used to directly compare different TKR designs but is limited in the prediction of their in situ wear. Preclinical wear testing may be adjusted by worst-case conditions to improve the prediction of in situ performance of total knee implants in the future.

Validity of the Novel Radiological Classification System of the Distal Femur

OBJECTIVE

Aseptic loosening (AL) is among the most important causes of failure after total knee arthroplasty (TKA). However, while there are numerous underlying causes of AL, the morphometry of the distal femur and intramedullary canal has not been sufficiently demonstrated. This study aimed to show the interobserver and intraobserver reliability and validity of the Citak classification, which has been recently defined according to the morphometry of the distal femur and provides a risk factor definition for AL.

MATERIALS AND METHODS

A total of 200 patients whose standardized anteroposterior (AP) and lateral images of the knee joint were obtained between October 2019 and April 2020 were retrospectively evaluated in this study. Patients with a history of extra-articular deformity and knee surgery were excluded from the study. For AL, morphologies of the distal femur were identified by two observers using the new radiological classification system of the distal femur. Mean pairwise Cronbach's alpha coefficient was used to assess the intra- and interobserver agreement of the classification.

RESULTS

There was excellent interobserver agreement for the 20 cm proximal and 2 cm proximal to the lateral joint line (PLJL) and adductor tubercle (PAD), respectively. The mean Cronbach's alpha coefficient was 0.96 (range 0.764-0.944) for the PAD and 0.98 (range 0.734-0.929) for the PLJL. There was also an excellent intraobserver agreement, with 93% average pairwise percent agreement for the index group and 95.5% average pairwise percent agreement for the anatomical classification group.

CONCLUSIONS

The level of inter- and intraobserver agreement for the morphology of the distal femur was excellent in the new radiological classification system, which was shown to be beneficial in the planning of revision knee arthroplasty for AL. However, there is a need for further studies in order to make a correlation of the classification with specific intraoperative findings.

Physical and chemical characterization of Ag-doped Ti coatings produced by magnetron sputtering of modular targets

Silver-doped Ti films were produced using a single magnetron sputtering source equipped with a titanium target containing implemented silver modules under variation of bias voltage and substrate temperature. The Ti(Ag) films were characterized regarding their morphology, contact angle, phase composition, silver content and distribution as well as the elution of Ag(+) ions into cell media. SEM and AFM pictures showed that substrate heating during film deposition supported the formation of even and dense surface layers with small roughness values, an effect that could even be enforced, when a substrate bias voltage was applied instead. The deposition of both Ti and Ag was confirmed by X-ray diffraction. ICP-MS and EDX showed a clear correlation between the applied sputtering parameters and the silver content of the coatings. Surface-sensitive XPS measurements revealed that higher substrate temperatures led to an accumulation of Ag in the near-surface region, while the application of a bias voltage had the opposite effect. Additional elution measurements using ICP-MS showed that the release kinetics depended on the amount of silver located at the film surface and hence could be tailored by variation of the sputter parameters.

Biological activity and migration of wear particles in the knee joint: an in vivo comparison of six different polyethylene materials

Wear of polyethylene causes loosening of joint prostheses because of the particle mediated activity of the host tissue. It was hypothesized that conventional and crosslinked polyethylene particles lead to similar biological effects around the knee joint in vivo as well as to a similar particle distribution in the surrounding tissues. To verify these hypotheses, particle suspensions of six different polyethylene materials were injected into knee joints of Balb/C mice and intravital microscopic, histological and immunohistochemical evaluations were done after 1 week. Whereas the biological effects on the synovial layer and the subchondral bone of femur and tibia were similar for all the polyethylenes, two crosslinked materials showed an elevated cytokine expression in the articular cartilage. Furthermore, the distribution of particles around the joint was dependent on the injected polyethylene material. Those crosslinked particles, which remained mainly in the joint space, showed an increased expression of TNF-alpha in articular cartilage. The data of this study support the use of crosslinked polyethylene in total knee arthroplasty. In contrast, the presence of certain crosslinked wear particles in the joint space can lead to an elevated inflammatory reaction in the remaining cartilage, which challenges the potential use of those crosslinked polyethylenes for unicondylar knee prostheses.

Third-body abrasive wear of tibial polyethylene inserts combined with metallic and ceramic femoral components in a knee simulator study

AIM

Total knee arthroplasties have reached a high grade of quality and safety, but most often fail because of aseptic implant loosening caused by polyethylene wear debris. Wear is generated at the articulating surfaces, e.g. caused by third-body particles. The objective of this experimental study was to determine the wear of tibial polyethylene inserts combined with metallic and ceramic femoral components under third-body wear conditions initiated by bone cement particles.


METHODS AND MATERIALS

Wear testing using a cemented unconstrained bicondylar knee endoprosthesis (Multigen Plus CR knee system) was performed in a knee wear simulator. Tibial polyethylene inserts were combined with the identical femoral component design, but made of two different materials (cobalt-chromium and ceramic). Bone cement debris including zirconium oxide particles was added every 500,000 cycles between the articulating surfaces. After 5 million load cycles, the amount of wear was determined gravimetrically and compared with results from standard wear test conditions. The surfaces of tibial inserts were also analyzed.


RESULTS

The average gravimetrical wear of the tibial polyethylene inserts in combination with 
cobalt-chromium and ceramic femoral components under third-body wear conditions amounted to 31.88 ± 4.53 mg and 13.06 ± 1.88 mg after 5 million cycles, respectively, and was higher than under standard wear test conditions in both cases.


CONCLUSIONS

The wear simulator test demonstrates that wear of polyethylene inserts under third-body wear conditions, in combination with ceramic femoral components, was significantly lower than with metallic femoral components.

Hard implant coatings with antimicrobial properties

Infection of orthopaedic implants often leads to inflammation immediately after surgery and increases patient morbidity due to repetitive operations. Silver ions have been shown to combine good biocompatibility with a low risk of inducing bacterial resistance. In this study a physical vapour deposition system using both arc deposition and magnetron sputtering has been utilized to produce silver ion doped TiN coatings on Ti substrates. This biphasic system combines the advantages of silver induced bactericidity with the good mechanical properties of TiN. Crystallographic analysis by X-ray diffraction showed that silver was deposited as well in its elementary form as it was incorporated into the crystal lattice of TiN, which resulted in increasing hardness of the TiN-coatings. Elution experiments revealed a continuous release of Ag ions in phosphate buffered saline. The coatings showed significant inhibitory effects on the growth of Staphylococcus epidermidis and Staphylococcus aureus and practically no cell-toxicity in cytocompatibility tests.

Evaluation of madurahydroxylactone as a slow release antibacterial implant coating

Madurahydroxylactone (MHL), a secondary metabolite with antibacterial activity was evaluated for its suitability to generate controlled drug release coatings on medical implant materials. A smooth and firmly attached layer could be produced from a precursor solution on various metallic implant materials. In physiological salt solutions these coatings dissolved within a time period up to one week. A combination of MHL with a broad spectrum fluoroquinolone antibiotic was used to create a coating that was active against all bacterial strains tested. The time period during which the coating remained active against Pseudomonas aeruginosa was investigated. The results indicated a delayed drug release from single layer coatings in the course of seven days. MHL was biocompatible in cell culture assays and could after a delay even serve as a cell adhesion substrate for human or murine cells. The findings indicate a potential for MHL for the generation of delayed release antimicrobial implant coatings.

[Applications of molecular pathology in the diagnosis of joint infections]

The diagnosis of infections in patients with arthritis and/or joint prostheses requires interdisciplinary cooperation and the use of up-to-date methods. Massive bacterial infection can be identified by bacterial culture, and minimal infection can be detected by molecular pathological methods. These processes include specific enrichment of bacterial and fungal DNA, amplification, and identification of the DNA by gel electrophoresis, sequencing techniques, and chip technologies.Anamnesis (enteral or urogenital infection), the clinical picture (oligoarthritis), and further parameters (e.g., HLA B27 status) are important for the diagnosis of reactive arthritis. In many cases of reactive arthritis, molecular methods allow detection of bacterial DNA or RNA in synovial fluid or tissue. Molecular pathological methods allow the fast and reliable differential diagnosis of granulomatous synovialitis without prior cultivation of bacteria or fungi. The development of new molecular pathological methods for detecting bacterial and fungal nucleic acids will increase diagnostic accuracy.