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.

Neuromuscular function and fatigue resistance of the plantar flexors following short-term cycling endurance training

Previously published studies on the effect of short-term endurance training on neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC) and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after 8 weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100, 100–200 ms) and iMVC of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave), peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that cycling endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue resistance.

Prospective multi-centre study on a composite ceramic femoral component in total knee arthroplasty: Five-year clinical and radiological outcomes

BACKGROUND

Enhanced wear resistance of ceramics in general and improved mechanical characteristics of composite ceramics in terms of strength and resistance meet the demands for application in TKA. The aim of this prospective international multi-centre study was to evaluate the 5-year clinical and radiological outcomes of an unconstrained TKA with a composite ceramic femoral component.

METHODS

A total of 107 patients (109 knees) underwent TKA with the MULTIGEN-PLUS Ceramic Knee at seven centres in three European countries. Clinical and radiological assessments were performed preoperatively and postoperatively at 3, 12, 24 and 60 months, using HSS, WOMAC, SF-36 and standardised radiographs.

RESULTS

Mean HSS and WOMAC increased significantly from 55.1±11.5 (21-83) and 48.1±16.6 (3-90) preoperatively to 85.6±9.6 (49-98) and 73.3±20.4 (17-100) at 60 months. Mean SF-36 showed significant improvements in patients' quality of life (49.1±17.6 (12-96) preoperatively versus 67.7±23.1 (12-100) at 60 months). Non-progressive radiolucent lines (<1 mm) were observed around the femoral component in four cases. Neither implant migration nor loosening were registered. Kaplan-Meier survivorship was 96.0% at 60 months (92.1-100%, CI 95%).

CONCLUSIONS

Five-year implant survival rate of the ceramic knee is comparable to other metallic and ceramic unconstrained TKA systems. Although the assessment of long-term implant survivorship is still pending, the ceramic implants represent a promising solution for patients with allergies against metallic components and furthermore for the general osteoarthritis population due to enhanced wear resistance.

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.

[Influence of surgeon experience in total hip arthroplasty. Dependence on operating time and complication risk]

BACKGROUND

As a consequence of limited personnel and financial resources, the increase in total hip arthroplasties places higher demands on orthopedic surgeons.

OBJECTIVES

In order to maintain high quality treatment, the correlation between surgical experience, duration of surgery and risk of complications was examined.

MATERIAL AND METHODS

The surgery time and, if applicable, complications (until discharge from hospital) of 1129 total hip arthroplasties over a period of 4 years were evaluated retrospectively.

RESULTS

The group of most experienced surgeons needed an average time of 53.2 ± 17.6 min for each implantation, followed by moderately experienced surgeons (74.5 ± 25.5 min) and less experienced surgeons (80.8 ± 21.9 min). Of all included cases, a total of 41 complications until discharge from hospital occurred. The number of complications increased with duration of surgery, whereby the risk of complications was significantly lower for shorter surgery times conducted by the most experienced surgeons as well as moderately experienced surgeons. The complication risk of less experienced surgeons remained constant independent of surgery duration.

CONCLUSION

These results underline the recommendations of the German Endocert system, which determine a minimum number of total joint arthroplasties as a quality indicator not only for hospitals but also for individual surgeons.

Positive impact of IGF-1-coupled nanoparticles on the differentiation potential of human chondrocytes cultured on collagen scaffolds

PURPOSE

In the present study, silica nanoparticles (sNP) coupled with insulin-like growth factor 1 (IGF-1) were loaded on a collagen-based scaffold intended for cartilage repair, and the influence on the viability, proliferation, and differentiation potential of human primary articular chondrocytes was examined.

METHODS

Human chondrocytes were isolated from the hyaline cartilage of patients (n=4, female, mean age: 73±5.1 years) undergoing primary total knee joint replacement. Cells were dedifferentiated and then cultivated on a bioresorbable collagen matrix supplemented with fluorescent sNP coupled with IGF-1 (sNP-IGF-1). After 3, 7, and 14 days of cultivation, cell viability and integrity into the collagen scaffold as well as metabolic cell activity and synthesis rate of matrix proteins (collagen type I and II) were analyzed.

RESULTS

The number of vital cells increased over 14 days of cultivation, and the cells were able to infiltrate the collagen matrix (up to 120 μm by day 7). Chondrocytes cultured on the collagen scaffold supplemented with sNP-IGF-1 showed an increase in metabolic activity (5.98-fold), and reduced collagen type I (1.58-fold), but significantly increased collagen type II expression levels (1.53-fold; P=0.02) after 7 days of cultivation compared to 3 days. In contrast, chondrocytes grown in a monolayer on plastic supplemented with sNP-IGF-1 had significantly lower metabolic activity (1.32-fold; P=0.007), a consistent amount of collagen type I, and significantly reduced collagen type II protein expression (1.86-fold; P=0.001) after 7 days compared to 3 days.

CONCLUSION

Collagen-based scaffolds enriched with growth factors, such as IGF-1 coupled to nanoparticles, represent an improved therapeutic intervention for the targeted and controlled treatment of articular cartilage lesions.

Influence of three different preservative techniques on the mechanical properties of the ovine cortical bone

PURPOSE

Preservative treatments are necessary for disinfection and long term storage when dealing with biological tissue. Freezing is a gold standard but infectious risk can only be eliminated by using chemical fluids that may alter the mechanical properties, depending on their composition. Therefore, we experimentally evaluated the influence of freezing and of two commonly used preservative fluids (formalin and alcohol) on the intrinsic mechanical properties of ovine cortical bone samples, compared to purely fresh samples.

METHODS

Prismatic specimens were prepared from the sheep's metacarpal bones and were divided into four groups (fresh, fresh-frozen, formalin and alcohol). All samples underwent four-point-bending; fresh samples were tested immediately, preserved samples were tested after 14 days. Bending modulus, bending strength, yield strength and energy absorption for the elastic and plastic region were determined.

RESULTS

Significant differences were found for the plastic energy absorption for formalin (-41%) and alcohol (+37%) preservation com- pared to fresh samples. Formalin preservation revealed embrittlement of the cortical bone samples and alcohol preservation revealed higher ability of plastic energy absorption.

CONCLUSIONS

Our results indicate that freezing has no influence on the mechanical properties of the ovine cortical bone. Preservation with chemical fluids (formalin and alcohol) showed no influence on the elastic properties but it was observed for the ability of plastic energy absorption. Therefore, these methods seem to be suitable for preservation without evident altering of the elastic mechanical properties.

[Reimbursement in psychiatry and psychosomatics: proof of concept for a system based on daily costs]

BACKGROUND

In Germany a new reimbursement system for psychiatry and psychosomatics is under development. Based on total costs of each case from selected hospitals and day clinics, in 2013 the Institute for the Hospital Remuneration System (InEK) proposed to reimburse the hospital costs daily with step-wise decreasing remuneration, mainly depending on the ICD-10 diagnosis, duration of stay and some complicating factors (PEPP grouper). It is controversial whether this degressive system will result in an inadequate remuneration of patients with longer duration of severe symptoms, such as suicidality in depression or autoaggressive behavior in borderline personality disorder and will eventually lead to advantages for acutely ill patients with short duration of stay compared to chronically ill patients.

OBJECTIVES

This study formulated and tested an alternative remuneration system (proof of concept) mainly based on an analysis of daily cost data instead of the total costs of each case.

MATERIAL AND METHODS

The study is based on 147,749 treatment days from 4,633 cases of patients with psychotic disorders (PEPP-PA03) in 6 hospitals. As possible cost separating factors the study analyzed days with and without intensive psychiatric care, 1 to 1 care, psychological diagnostics, magnetic resonance imaging (MRI), acute crisis intervention, age at admission, the first days of treatment and day of discharge.

RESULTS AND DISCUSSION

Nearly all factors tested were shown to be statistically significant in separating daily hospital costs. Based on these findings an alternative calculation algorithm (TEPPconcret), which grouped the cases with respect to age, intensive care, 1 to 1 care, treatment days 1-4 and day of discharge, was formulated and tested. For psychotic disorders TEPPconcret with a basic rate complemented by daily add-on payments depending on the effort involved, is a serious alternative to the PEPP system and awaits further evaluation.

Evaluation of electric field distribution in electromagnetic stimulation of human femoral head

Electromagnetic stimulation is a common therapy used to support bone healing in the case of avascular necrosis of the femoral head. In the present study, we investigated a bipolar induction screw system with an integrated coil. The aim was to analyse the influence of the screw parameters on the electric field distribution in the human femoral head. In addition, three kinds of design parameters (the shape of the screw tip, position of the screw in the femoral head, and size of the screw insulation) were varied. The electric field distribution in the bone was calculated using the finite element software Comsol Multiphysics. Moreover, a validation experiment was set up for an identical bone specimen with an implanted screw. The electric potential of points inside and on the surface of the bone were measured and compared to numerical data. The electric field distribution within the bone was clearly changed by the different implant parameters. Repositioning the screw by a maximum of 10 mm and changing the insulation length by a maximum of 4 mm resulted in electric field volume changes of 16% and 7%, respectively. By comparing the results of numerical simulation with the data of the validation experiment, on average, the electric potential difference of 19% and 24% occurred when the measuring points were at a depth of approximately 5 mm within the femoral bone and directly on the surface of the femoral bone, respectively. The results of the numerical simulations underline that the electro-stimulation treatment of bone in clinical applications can be influenced by the implant parameters.

Comparative in vitro study on magnetic iron oxide nanoparticles for MRI tracking of adipose tissue-derived progenitor cells

Magnetic resonance imaging (MRI) using measurement of the transverse relaxation time (R2*) is to be considered as a promising approach for cell tracking experiments to evaluate the fate of transplanted progenitor cells and develop successful cell therapies for tissue engineering. While the relationship between core composition of nanoparticles and their MRI properties is well studied, little is known about possible effects on progenitor cells. This in vitro study aims at comparing two magnetic iron oxide nanoparticle types, single vs. multi-core nanoparticles, regarding their physico-chemical characteristics, effects on cellular behavior of adipose tissue-derived stem cells (ASC) like differentiation and proliferation as well as their detection and quantification by means of MRI. Quantification of both nanoparticle types revealed a linear correlation between labeling concentration and R2* values. However, according to core composition, different levels of labeling concentrations were needed to achieve comparable R2* values. Cell viability was not altered for all labeling concentrations, whereas the proliferation rate increased with increasing labeling concentrations. Likewise, deposition of lipid droplets as well as matrix calcification revealed to be highly dose-dependent particularly regarding multi-core nanoparticle-labeled cells. Synthesis of cartilage matrix proteins and mRNA expression of collagen type II was also highly dependent on nanoparticle labeling. In general, the differentiation potential was decreased with increasing labeling concentrations. This in vitro study provides the proof of principle for further in vivo tracking experiments of progenitor cells using nanoparticles with different core compositions but also provides striking evidence that combined testing of biological and MRI properties is advisable as improved MRI properties of multi-core nanoparticles may result in altered cell functions.

Examination of cross contamination risks between hospitals by external medical staff via cross-sectional intercept survey of hand hygiene

Introduction: Work in hospitals is supported by contributions of life sciences industry representatives (IR) in various ways of fields. Close contact between them, caretakers and patients is unavoidable, even in situations where hygiene is critical.

The present study investigates whether IR display comparable levels of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus (MRSA) contamination after being exposed to a shared environment for a minimum of 4 hours.

Material and methods: An anonymous survey to sample a group of healthcare professionals for traces of fingertip contamination was performed. We used dip slides (S. aureus and MRSA) to evaluate 311 healthcare professionals at the medical exhibition MEDICA. After applying exclusion criteria 298 participants remained valid, they consisted of 208 industry representatives, 49 nurses and 41 physicians.

Results: IR where engaged in hospitals, operating rooms and outpatient clinics (82%, 41.8%, 51.9% respectively). 65.9% of IR (vs. 48.8% physicians and 40.8% nurses) carried a microbiological burden ≥10⁴ CFU (colony forming units). Neither S. aureus (≥10⁴ CFU) in IR (40.9%) did show statistical differences in contamination patterns in comparison to physicians (43.9%, p=0.346) and nurses (36.7%, p=0.878) nor did MRSA (physicians p=0.579, nurses p=0.908). We were unable to differentiate transient from pre-existing permanent colonization.

Conclusion: Exposure to the same environment may result in similar hand contamination patterns of IR when compared caregivers. This supports the concern that industry representatives can cause cross infection between hospitals and hygiene sensitive areas like operation room, intensive care unit and central sterilization units particularly. Further study is required to clarify whether pre-existing bacterial colonization is an influencing factor and how industry is taking care of this to create a safe working environment for their employees, the customers and ultimately the patients.

[Failure analysis as basis for quality assurance strategies in implant technology]

BACKGROUND

Implant safety is a topic gaining more and more public interest. Implants are safety relevant medical devices which in the case of failure can lead to life-threatening situations.

OBJECTIVES

A well-founded failure analysis requires expert knowledge not only of materials and implant design but also a qualified explantation procedure and storage conditions.

METHODS

A selective literature search was carried out putting the main emphasis on implant failure analysis supplemented with own investigations.

RESULTS

The reasons for implant breakdown are mostly failures of materials and in the manufacturing process. In some cases false material combinations can lead to tribocorrosion effects under cyclic loading.

CONCLUSION

The increased level of knowledge gained from complex analyses of failed implants produces valuable evidence for better quality management.

The effect of continuous passive motion and sling exercise training on clinical and functional outcomes following total knee arthroplasty: a randomized active-controlled clinical study

BACKGROUND

The parallel-group randomized active-controlled clinical study was conducted to compare the effectiveness of two in-hospital range of motion (ROM) exercise programs following total knee arthroplasty (TKA). Continuous passive motion (CPM) is frequently used to increase ROM and improve postoperative recovery despite little conclusive scientific evidence. In contrast, a new active sling-based ROM therapy requires the activation of the knee joint muscles and dynamic joint stabilization. It was hypothesized that higher demands on muscle strength and muscle coordination during sling exercise training (ST) might be advantageous for early recovery following TKA.

METHODS

A total of 125 patients undergoing primary TKA were assessed for eligibility. Thirty-eight patients were randomly assigned to receive ST or CPM (control intervention) during hospital stay. Patients were assessed before TKA for baseline measurement (pretest), 1 day before discharge (posttest) and 3 months after TKA (follow-up). The passive knee flexion range of motion (pFL) was the primary outcome measure. Secondary outcome measures included active knee flexion range of motion, active and passive knee extension ROM, static postural control, physical activity, pain, length of hospital stay as well as clinical, functional and quality-of-life outcomes (SF-36, HSS and WOMAC scores). Data were analyzed according to the intention-to-treat principle. Differences between the groups were tested for significance by the unpaired Student's t test or an analysis of covariance (ANCOVA) adjusted for baseline, weight, sex, age, pain and physical activity.

RESULTS

A between-group difference could be determined at posttest. The pFL was significantly higher by 6.0° (95% CI 0.9 to 11.2°; P = 0.022) in the ST group. No difference between groups in pFL was documented at follow-up. Furthermore, no significant differences could be observed for any secondary outcome measure at posttest and follow-up.

CONCLUSIONS

ST seems to have a clinically relevant beneficial short-term effect on pFL compared to CPM. The results support the implementation of ST in rehabilitation programs following TKA.

LEVEL OF EVIDENCE

Therapy, level 2b.

Self-centering dual-mobility total hip systems: Prediction of relative movements and realignment of different intermediate components

The increased jump distance against dislocation and the large range of motion due to the enlarged effective head diameter substantiate the use of dual-mobility systems in cases of total hip joint instability. For this type of total hip endoprostheses, an eccentric design of the outer bearing is assumed in order to provide a force-dependent self-centering mechanism and an improved joint stability against dislocation. The purpose of this study was to determine the relative movements and realignment of different intermediate components during various motion cycles as a result of the eccentric design. We established a validated mathematical model for eccentric dual-mobility systems, which allowed a comparison of relative movements, self-centering torque and overall frictional torque during four different activities in order to analyze their motion behavior in everyday life. In addition, the impact of different radial clearances on the dynamic performance of the self-centering mechanism was investigated. According to torque patterns and the validation experiment, the main articulation of eccentric dual-mobility systems was limited to the smaller inner bearing for the most daily life activities, i.e. the eccentric intermediate component remained in its current position and only with changing activity did the intermediate component realign clearly. However, an inappropriate dimensioning of the radial clearance could lead to a permanent realignment of the intermediate component during the motion cycles. In general, the self-centering mechanism of the intermediate component seems to have no negative influence on relative movements and wear propagation of dual-mobility cup systems if the clearance and eccentricity are appropriately dimensioned.

In vivo monitoring of implant osseointegration in a rabbit model using acoustic sound analysis

Implant osseointegration can currently only be assessed reliably post mortem. A novel method that relies on the principle of acoustic sound analysis was developed to enable examination of the longitudinal progress of osseointegration. The method is based on a magnetic sphere inside a hollow cylinder of the implant. By excitation using an external magnetic field, collision of the sphere inside the implant produces a sound signal. Custom-made titanium implants equipped thusly were inserted in each lateral femoral epicondyle of 20 New Zealand White Rabbits. Two groups were investigated: Uncoated, machined surface versus antiadhesive surface; and calcium phosphate-coated surface versus antiadhesive surface. The sound analysis was performed postoperatively and weekly. After 4 weeks, the animals were euthanized, and the axial pull-out strengths of the implants were determined. A significant increase in the central frequency was observed for the loose implants (mean pull-out strength 21.1 ± 16.9 N), up to 6.4 kHz over 4 weeks. In comparison, the central frequency of the osseointegrated implants (105.2 ± 25.3 N) dropped to its initial value. The presented method shows potential for monitoring the osseointegration of different implant surfaces and could considerably reduce the number of animals needed for experiments.

Evaluation of osseointegration of titanium alloyed implants modified by plasma polymerization

By means of plasma polymerization, positively charged, nanometre-thin coatings can be applied to implant surfaces. The aim of the present study was to quantify the adhesion of human bone cells in vitro and to evaluate the bone ongrowth in vivo, on titanium surfaces modified by plasma polymer coatings. Different implant surface configurations were examined: titanium alloy (Ti6Al4V) coated with plasma-polymerized allylamine (PPAAm) and plasma-polymerized ethylenediamine (PPEDA) versus uncoated. Shear stress on human osteoblast-like MG-63 cells was investigated in vitro using a spinning disc device. Furthermore, bone-to-implant contact (BIC) was evaluated in vivo. Custom-made conical titanium implants were inserted at the medial tibia of female Sprague-Dawley rats. After a follow-up of six weeks, the BIC was determined by means of histomorphometry. The quantification of cell adhesion showed a significantly higher shear stress for MG-63 cells on PPAAm and PPEDA compared to uncoated Ti6Al4V. Uncoated titanium alloyed implants showed the lowest BIC (40.4%). Implants with PPAAm coating revealed a clear but not significant increase of the BIC (58.5%) and implants with PPEDA a significantly increased BIC (63.7%). In conclusion, plasma polymer coatings demonstrate enhanced cell adhesion and bone ongrowth compared to uncoated titanium surfaces.