The impact of stem fixation method on Vancouver Type B1 periprosthetic femoral fracture management

Introduction: Our understanding of the impact of the stem fixation method in total hip arthroplasty (THA) on the subsequent management of periprosthetic femoral fractures (PFF) is still limited. This study aimed to investigate and quantify the effect of the stem fixation method, i.e., cemented vs. uncemented THA, on the management of Vancouver Type B1 periprosthetic femoral fractures with the same plate. Methods: Eight laboratory models of synthetic femora were divided into two groups and implanted with either a cemented or uncemented hip prosthesis. The overall stiffness and strain distribution were measured under an anatomical one-legged stance. All eight specimens underwent an osteotomy to simulate Vancouver type B1 PFF’s. Fractures were then fixed using the same extramedullary plate and screws. The same measurements and fracture movement were taken under the same loading conditions. Results: Highlighted that the uncemented THA and PFF fixation constructs had a lower overall stiffness. Subsequently, the mechanical strain on the fracture plate for the uncemented construct was higher compared to the cemented constructs. Conclusion: PFF fixation of a Vancouver type B1 fracture using a plate may have a higher risk of failure in uncemented THAs.

Influence of the taper on the fretting wear of the femoral stem-femoral head taper junction in total hip prosthesis

Purpose The purpose of this paper is to study the roughness effect on the fixation of taper junction components and surfaces wear in terms of taper surface design. The roughness of the femoral heads’ taper and of the femoral stems’ trunnions can influence the fretting wear of the taper junction. Design/methodology/approach It was analysed whether a microgrooved taper surface of the femoral stem trunnion improves the fixation and reduces the wear rate at the taper junction of the hip prosthesis. Two models have studied: a femoral head with a smooth tapered surface combined with a microgrooved stem trunnion and a femoral head with a smooth tapered surface combined with a trunnion that had a smooth surface of the tapered. To compare the wear evolution between these two models, a computerised finite element model of the wear was used. Findings The results obtained after analysis carried out during millions of loading cycles showed that the depth of the linear wear and the total material loss were higher for the femoral heads joined with microgrooved trunnions. The main conclusion of this paper is that the smooth surfaces of the taper and of the trunnions will ensure a better fixation at the taper junction, and therefore, will reduce the volumetric wear rates. Originality/value A higher fixation of the taper junction will reduce the total hip prosthesis failure and, finally, it will improve the quality and durability of modular hip prostheses.

Combined and hybrid marker models for radiostereometry assessment of polyethylene liner motion in dual mobility hip prosthesis: a proof-of-concept study

Background Investigation of polyethylene liner movement in total hip arthroplasty requires bead-marking for radiographic visibility of the liner. However, occlusion of markers poses a challenge for marker registration in radiographs. Methods The polyethylene of a dual mobility acetabular system was marked with twelve 1-mm tantalum markers (four groups of three markers) using a custom-made drill guide. Liner motion in a phantom and a patient was investigated with dynamic radiostereometry analysis (dRSA) at 1-year follow-up and static radiostereometry analysis (sRSA) postoperatively and at 1- and 2-year follow-up. A combined marker configuration (CMC) model was calculated from the registered positions of the liner markers and the femoral head in several images. Furthermore, the CMC model and the theoretic marker positions from computer-assisted models of the drill guide were combined in a hybrid model. Results The CMC model included eleven markers in the phantom and nine markers in the patient, which was sufficient for dRSA. Liner movement in the phantom followed liner contact with the femoral neck, while liner movement in the patient was independent. The hybrid model was necessary to determine liner orientation in sRSA recordings, which clearly changed from postoperative to 1- and 2-year follow-up even though the patient was positioned similarly. Conclusion Polyethylene liner motion in dual mobility hip prosthesis can be assessed with CMC models in dRSA recordings. In sRSA, the liner position between follow-ups is unpredictable and analysis requires inclusion of all markers in the model, accomplished with a hybrid marker model. Trial registration ClinicalTrials.gov [NCT02301182], 25 October 2015.

Modularity of total hip prosthesis and its tribological implications

Purpose The study aims to analyze the fretting phenomenon, manifested at the taper junctions of modular total hip prostheses (THP). Modularity of prostheses implies the micro-movement occurrence. Fractures can arise as a result of the fretting cracking of the prostheses components, affecting durability of modular THPs. Fretting corrosion is associated with the decrease in the clinical acceptance of hip modular implants. Design/methodology/approach Starting from the fretting phenomenon influence on modularity, monoblock THPs and prostheses with modular femoral head recovered from some review surgeries were investigated. Modular prostheses have a taper junction femoral head – femoral stem neck. Investigation consisted in the analysis of fretting wear and fretting corrosion, of the femoral heads’ taper and of the femoral stems’ trunnions. Findings The main result was that the micro-movement that provokes the fretting of the femoral head-femoral stem taper junction analyzed does not have the same direction. It is manifesting in the direction of the axis of the femoral head taper, around this axis or as a composed movement. The authors suspect that this is due to the different design of the taper. In this way, the inclination of the stem’s trunnion into the head hole has a different angular misalignment and may cause greater damages of the taper. Originality/value This result can be a starting point from the improvement of the future taper junctions design that will improve the quality, durability and modularity of THPs.

Machinability evaluation of titanium alloy Ti-6Al-4V obtained by EBM for functional part at medical application

The potential and advantages revealed by the application of 3D manufacturing techniques such as Electron Beam Melting (EBM) in the production of medical devices such as orthopaedic implants are increasing manly in custom made devices. However, the use of milling and turning operations are indispensable on surfaces where surface finish and dimensional accuracy have more demanding requirements. This work aims to evaluate the machinability of titanium alloy test samples submitted to turning operations, to obtain the geometry of a functional cone of the modular component of the hip prosthesis. The differences in cutting forces and surface finish obtained in the turning tests are compared between a wrought Ti-6Al-4V test sample and three obtained by EBM with different thicknesses. To perform the tests, a constant cutting speed of 60m/min was used, feed of 0.1 and 0.2mm/rev and ap of 0.15mm. The cutting forces were measured for each test, also the roughness was measured in the form of Ra, Rt and RzD in each test sample. From the results obtained, EBM test samples presented higher roughness values and lower resulting cutting forces. In both materials, the effect of feed rate is visible. When machining a cone, the passive force and the cutting force become the most influential forces. Generally, when the feed rate value was doubled, the resulting machining forces value increased up to about 50% for both types of materials and the Ra value to approximately 200%. The EBM technology as used form medical devices allow good quality surfaces as the wrought titanium alloy.

P039 Evolutionary course of Juvenile Idiopathic Arthritis

Background Juvenile idiopathic arthritis (JIA) is a heterogeneous group of rare conditions that begin before the age of 16. Seven categories have been defined by the International League of Associations for Rheumatology (ILAR) classification. The aim of our work is to describe the demographic, clinical, and radiological characteristics and therapeutic of patients with JIA. Materials and methods A retrospective, descriptive study of patients followed for AIJ in the rheumatology department of Mohamed LamineDebaghine during a period of 15 years (2005–2020). Patients were included if satisfied ILAR criteria. Results Ten patients with JIA were included, 5 of whom were females. The mean age of onset was 9.20 ± 3.15 (range: 5–14 years). The subtypes were as follows: 4 patients had RF-negative polyarthritis, one case had RF-positive polyarthritis, one with systemic arthritis form, 2 cases of oligoarthritis, 1 case of psoriatic arthritis, and enthesitis-related arthritis. Three children have coxitis. ACPA was positive in one case and antinuclear antibodies were negative. Eight patients have developed osteoarticular destruction. Pulmonary involvement was noted in a patient who had RF-positive polyarthritis. Corticosteroid therapy was prescribed in 9 patients, 5 of whom developed complications related to steroids, including growth retardation, which was observed in 3 cases. Nine JIA patients received methotrexate. The use of etanercept and IL-1 inhibitors were required in 7 and 1 cases, respectively. Corticosteroid infiltrations were performed in 9 patients. Total hip replacement was indicated in 3 patients. Conclusion Through our study, we note a predominance of the polyarticular form. Osteoarticular destruction seems to be frequent, particularly in the hip. The use of biotherapy and the total hip prosthesis proved the severity of juvenile idiopathic arthritis in our patients.

Quantitative Effect of Metal Artefact Reduction on CT-based attenuation correction in FDG PET/CT in patients with hip prosthesis

Background Metal artefact reduction (MAR) techniques still are in limited use in positron emission tomography/computed tomography (PET/CT). This study aimed to investigate the effect of Smart MAR on quantitative PET analysis in the vicinity of hip prostheses. Materials and methods Activities were measured on PET/CT images in 6 sources with tenfold activity concentration contrast to background, attached to the head, neck and the major trochanter of a human cadaveric femur, and in the same sources in similar locations after a hip prosthesis (titanium cup, ceramic head, chrome-cobalt stem) had been inserted into the femur. Measurements were compared between PET attenuation corrected using either conventional or MAR CT. In 38 patients harbouring 49 hip prostheses, standardized uptake values (SUV) in 6 periprosthetic regions and the bladder were compared between PET attenuation corrected with either conventional or MAR CT. Results Using conventional CT, measured activity decreased with 2 to 13% when the prosthesis was inserted. Use of MAR CT increased measured activity by up to 11% compared with conventional CT and reduced the relative difference with the reference values to under 5% in all sources. In all regions, to the exception of the prosthesis shaft, SUVmean increased significantly (p < 0.001) by use of MAR CT. Median (interquartile range) percentual increases of SUVmean were 1.4 (0.0–4.2), 4.0 (1.8–7.8), 7.8 (4.1–12.4), 1.5 (0.0–3.2), 1.4 (0.8–2.8) in acetabulum, lateral neck, medial neck, lateral diaphysis and medial diaphysis, respectively. Except for the shaft, the coefficient of variation did not increase significantly. Except for the erratic changes in the prosthesis shaft, decreases in SUVmean were rare and small. Bladder SUVmean increased by 0.9% in patients with unilateral prosthesis and by 4.1% in patients with bilateral prosthesis. Conclusions In a realistic hip prosthesis phantom, Smart MAR restores quantitative accuracy by recovering counts in underestimated sources. In patient studies, Smart MAR increases SUV in all areas surrounding the prosthesis, most markedly in the femoral neck region. This proves that underestimation of activity in the PET image is the most prevalent effect due to metal artefacts in the CT image in patients with hip prostheses. Smart MAR increases SUV in the urinary bladder, indicating effects at a distance from the prosthesis.