The primary stability of a cementless PEEK femoral component is sensitive to BMI: A population-based FE study.

The use of polyetheretherketone (PEEK) for cementless femoral total knee arthroplasty (TKA) components is of interest due to several potential advantages, e.g. the use in patients with metal hypersensitivity. Additionally, the stiffness of PEEK closer resembles the stiffness of bone, and therefore, peri-prosthetic stress-shielding may be avoided. When introducing a new implant material for cementless TKA designs, it is important to study its effect on the primary fixation, which is required for the long-term fixation. Finite element (FE) studies can be used to study the effect of PEEK as implant material on the primary fixation, which may be dependent on patient factors such as age, gender and body weight index (BMI). Therefore, the research objectives of this study were to investigate the effect of PEEK vs cobalt-chrome (CoCr) and patient characteristics on the primary fixation of a cementless femoral component. 280 FE models of 70 femora were created with varying implant material and gait and squat activity. Overall, the PEEK models generated larger peak micromotions than the CoCr models. Distinct differences were seen in the micromotion distributions between the PEEK and CoCr models for both the gait and squat models. The micromotions of all femoral models significantly increased with BMI. Neither gender nor age of the patients had a significant effect on the micromotions. This population study gives insights into the primary fixation of a cementless femoral component in a cohort of FE models with varying implant material and patient characteristics.

The Effect of Patient-Related Factors on the Primary Fixation of PEEK and Titanium Tibial Components: A Population-Based FE Study.

Polyetheretherketone (PEEK) is of interest as implant material for cementless tibial total knee arthroplasty (TKA) components due to its potential advantages. One main advantage is that the stiffness of PEEK closely resembles the stiffness of bone, potentially avoiding peri-prosthetic stress-shielding. When introducing a new implant material for cementless TKA designs, it is essential to study its effect on the primary fixation. The primary fixation may be influenced by patient factors such as age, gender, and body mass index (BMI). Therefore, the research objectives of this finite element (FE) study were to investigate the effect of material (PEEK vs. titanium) and patient characteristics on the primary fixation (i.e., micromotions) of a cementless tibial tray component. A total of 296 FE models of 74 tibiae were created with either PEEK or titanium material properties, under gait and squat loading conditions. Overall, the PEEK models generated larger peak micromotions than the titanium models. Differences were seen in the micromotion distributions between the PEEK and titanium models for both the gait and squat models. The micromotions of all tibial models significantly increased with BMI, while gender and age did not influence micromotions.

The sensitivity of the stiffness and thickness of a titanium inlay in a cementless PEEK femoral component to the micromotions and bone strain energy density.

Polyetheretherketone (PEEK) has been proposed as alternative material for total knee arthroplasty implants due to its low stiffness, which may reduce stress-shielding. In cementless fixation, a proper primary fixation is required for long-term fixation. Previous research showed that the lower stiffness of a cementless PEEK femoral component results in larger micromotions at the implant-bone interface compared to a cobalt-chrome femoral component. A titanium inlay on the PEEK implant surface may improve the primary fixation while maintaining the favourable stiffness properties. Therefore, the effect of thickness and stiffness of a titanium inlay on the primary fixation and stress-shielding was investigated. A finite element model of the femur and femoral component was created with five titanium inlay variants. The micromotions and strain energy density (SED) were quantified as outcome measures. The distal thin - proximal thick variant showed the largest resulting micromotions (51.2 µm). Relative to the all-PEEK femoral component, the addition of a titanium inlay reduced the micromotions with 30 % to 40 % without considerably affecting the stress-shielding capacity (strain energy difference of 6 % to 10 %). Differences in micromotions (43.0-51.2 µm) and SED between the variants were relatively small. In conclusion, the addition of a titanium inlay could lead to a reduction of the micromotions without substantially affecting the SED distribution.

A FE study on the effect of interference fit and coefficient of friction on the micromotions and interface gaps of a cementless PEEK femoral component.

The use of a more compliant material, such as polyetheretherketone (PEEK), for a cementless femoral component is a potential solution to prevent aseptic loosening caused by peri-prosthetic stress-shielding. Long-term fixation of a cementless femoral component is achieved by a proper primary fixation of the bone-implant interface, which is influenced by the interference fit and frictional properties of the implant surface. This computational study investigates the sensitivity of micromotions and interface gaps of a cementless PEEK femoral component to the interference fit and coefficient of friction. 24 finite element models of the femur and femoral component were created with variations in implant material, interference fit and coefficient of friction. Peak loads of a jogging activity were applied on the models. Micromotions and interface gaps were both sensitive to the interference fit, coefficient of friction and implant material. Besides the implant material, the micromotions and interface gaps of the implant were most sensitive to the interference fit. Compared to the cobalt-chrome (CoCr) femoral component, the PEEK femoral component generated higher micromotions and interface gaps when equal interference fit and friction values were applied. However, increasing the interference fit and friction of the PEEK component resulted in micromotion values comparable with the CoCr component. This result leads to possibilities using cementless PEEK femoral components.

The diagnostic potential of low-field MRI in problematic total knee arthroplasties - a feasibility study.

PURPOSE: Low-field MRI, allowing imaging in supine and weight-bearing position, may be utilized as a non-invasive and affordable tool to differentiate between causes of dissatisfaction after TKA ('problematic TKA'). However, it remains unclear whether low-field MRI results in sufficient image quality with limited metal artefacts. Therefore, this feasibility study explored the diagnostic value of low-field MRI concerning pathologies associated with problematic TKA's' by comparing low-field MRI findings with CT and surgical findings. Secondly, differences in patellofemoral parameters between supine and weight-bearing low-field MRI were evaluated. METHODS: Eight patients with a problematic TKA were scanned using low-field MRI in weight-bearing and supine conditions. Six of these patients underwent revision surgery. Scans were analysed by a radiologist for pathologies associated with a problematic TKA. Additional patellofemoral and alignment parameters were measured by an imaging expert. MRI observations were compared to those obtained with CT, the diagnosis based on the clinical work-up, and findings during revision surgery. RESULTS: MRI observations of rotational malalignment, component loosening and patellofemoral arthrosis were comparable with the clinical diagnosis (six out of eight) and were confirmed during surgery (four out of six). All MRI observations were in line with CT findings (seven out of seven). Clinical diagnosis and surgical findings of collateral excessive laxity could not be confirmed with MRI (two out of eight). CONCLUSION: Low-field MRI shows comparable diagnostic value as CT and might be a future low cost and ionizing radiation free alternative. Differences between supine and weight-bearing MRI did not yield clinically relevant information. The study was approved by the Medical Research Ethics Committees of Twente (Netherlands Trial Register: Trial NL7009 (NTR7207). Registered 5 March 2018, https://www.trialregister.nl/trial/7009 ).

MRI as Diagnostic Modality for Analyzing the Problematic Knee Arthroplasty: A Systematic Review.

BACKGROUND: Various diagnostic modalities are available to assess the problematic knee arthroplasty. Visualization of soft-tissue structures in relation to the arthroplasty and bone remains difficult. Recent developments in MRI sequences could make MRI a viable addition to the diagnostic arsenal. PURPOSE: To review the diagnostic properties of MRI, to identify certain causes of complaints that may be directly related to implant failure of total (TKA) or unicompartmental knee arthroplasty (UKA); infection, loosening and wear, instability, malalignment, arthrofibrosis, or patellofemoral problems. STUDY TYPE: Systematic review. POPULATION: Twenty-three studies were included: 16 TKA, four UKA, and three cadaveric studies. Causes of knee arthroplasty complaints analyzed were; infection (three), loosening and wear (11), malalignment (five) and instability (four). FIELD STRENGTH AND SEQUENCES: No field strength or sequence restrictions. ASSESSMENT: PubMed, SCOPUS, and EMBASE were searched. Risk of bias was assessed using the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN) and the QUality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2). STATISTICAL TESTS: The results of the original research articles are stated. RESULTS: Fifteen studies assessed the reproducibility of analyzing infection, loosening and wear, and malalignment. Fourteen of 15 studies were deemed as adequate to good quality. Results showed a moderate to excellent agreement (ICC/K 0.55-0.97). Fourteen studies addressed the accuracy. For infection and loosening and wear the sensitivity and specificity estimates varied between 0.85-0.97 and 0.70-1.00, respectively. The accuracy for malalignment was excellent (r ≥ 0.81). For these studies QUADAS-2 analysis suggested few risks of bias. A meta-analysis was not possible due to the heterogeneity of the data. DATA CONCLUSION: This study supports that MRI can be used with overall reproducible and accurate results for diagnosing infection, loosening and wear, and malalignment after knee arthroplasty. Nonetheless, studies regarding the diagnosis of instability, arthrofibrosis or patellofemoral complaints using MRI are limited and inconclusive. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:446-458.