Ti-6Al-4V is the most common alloy used for orthopaedic implants. Its popularity is due to low density, superior corrosion resistance, good osseointegration and lower elastic modulus when compared to other commonly used alloys such as CoCrMo and stainless steel. In fact, the use of Ti64 has even further increased lately since recent controversy around adverse local tissue reactions and implant failure related to taper corrosion of CoCrMo alloy. However, implants made from Ti64 can fail in some cases due to fatigue fracture, sometimes related to oxide induced stress corrosion cracking or hydrogen embrittlement, or preferential corrosion of the beta phase. Studies performed with Ti-6Al-4V do often not consider that the alloy itself may have a range of characteristics that can vary and could significantly impact the implant properties. These variations are related to the material microstructure which depends not only on chemical composition, but also the manufacturing process and subsequent heat treatments. Different microstructures can occur in implants made form wrought alloys, cast alloys, and more recently, additive manufactured (AM) alloys. Implant alloy microstructure drives mechanical and electrochemical properties. Therefore, this study aims to analyse the microstructure of Ti-6Al-4V alloy of additive manufactured and conventional retrieved orthopaedic implants such as acetabular cups, tibial trays, femoral stem and modular neck by means of electron backscatter diffraction (EBSD). Microstructural features of interest include grains shape and size, phase content and distribution, preferred grain orientation (texture), alloying elements distribution (homogenization) and presence of impurities. Additionally, we demonstrate the direct impact of different microstructural features on hardness. We analysed 17 conventional devices from 6 different manufacturers, 3 additive manufactured devices from 2 different manufactures and 1 control alloy (bar stock). The preliminary results showed that even though all implants have the same chemical composition, their microstructural characteristics vary broadly. Ti64 microstructure of conventional alloys could be categorized in 3 groups: equiaxed grains alloys (Fine and Coarse), bimodal alloys and dendritic alloys. The additive manufactured implants were classified in an additional group on its own which consists of a needle-like microstructures - similar to Widmanstätten patterns, Fig. 1, with a network of β phase along α phase grains. Furthermore, AM alloys exhibited residual grain boundaries from the original β grains from the early stage of the solidification process, Fig. 2. These characteristics may have implication on the fatigue and corrosion behaviour. In addition, it we observed inhomogeneous alloying element distribution in some cases, Fig. 3, especially for the additive manufactured alloys, which also may have consequences on corrosion behaviour. Finally, the hardness testing revealed that the implants with large grain size, such as AM alloys, exhibit low hardness values, as expected, but also the amount of beta phase correlated positively with lower hardness. Grain aspect ratio and beta phase grain size correlated positively with higher hardness. In summary, we found that common Ti64 implants can exhibit a broad variety of different alloy microstructures and the advent of AM alloys introduces an entirely new category. It is imperative to determine the ideal microstructure for specific applications.
The use modular total hip arthroplasty is associated with potentially serious local and systemic complications. Each modular interface introduces a source for wear particle generation. Research suggests the etiology of wear particle generation and subsequent corrosion begins with mechanical fretting and disruption of the protective oxide layer leading to release of metal ions at the taper interface. The purpose of this study was to conduct three dimensional (3D) surface scans of the mating surfaces of the neck-stem taper to identify features that may contribute to the fretting and surface corrosion. Eighteen modular hip implant components (9 stems and 9 necks) received 3D surface scans to examine the neck-stem taper junction. The study analyzed the neck-stem taper in an as assembled condition so relative surface positions and surface features could be studied. The 9 stems and 9 necks were scanned using an optical scanner. The implant image volume was resolved to a point spacing of 0.5 mm. Measurements were made to determine the normal distance between the surfaces of the neck taper as seated in the stem slot. These measurements were used to produce a color map of the contact proximity between the neck and stem surfaces (Figure 1). Circumferential surface points from the neck and stem at corresponding taper axis heights were used to create surface contour plots to identify surface shape variation and contact. The angle measurements and neck seated depth were analyzed by regression.Introduction
Methods
Heterotopic ossification (HO) is a known complication following total hip arthroplasty, with increased incidence in certain patient populations. Current prophylaxis options include oral non-steroidal anti-inflammatory drugs (NSAIDs) and radiation therapy, but an optimal radiation protocol has yet to be clearly defined. We performed a randomized, double-blinded clinical trial in high-risk total hip arthroplasty patients to determine the efficacy of 400 cGy versus 700 cGy doses of radiation. 147 patients at high risk for HO undergoing total hip arthroplasty (THA) at Rush-St. Luke's- Presbyterian medical center were randomized to either a single 400 cGy or 700 cGy dose of radiation. High risk was defined as diagnosis of diffuse idiopathic skeletal hyperostosis (DISH), hypertrophic osteoarthritis, ankylosing spondylitis, or history of previous heterotopic ossification. Radiation was administered over a 14 × 6 cm area of soft tissue and given on the first or second post-operative day. A blinded reviewer graded anterior-posterior (AP) and lateral radiographs taken immediately post-operatively and at a minimum of 6 months post-operatively. Progression was defined as an increase in Brooker classification from the immediate post-operative to the long-term post-operative radiograph. Operative data including surgical approach, use of cemented implants, revision surgery, and post-operative range of motion data were also collected.Background
Methods
The purpose of this study was to investigate the stability of dual-taper modular hip implants following impaction forces delivered in varying directions as measured by the distraction forces required to disassemble the components. Distraction of the head-neck and neck-stem tapers of dual-taper modular implants with 0°, 8°, and 15° neck angles were measured utilizing a custom-made distraction fixture attached to a servohydraulic materials test machine. Distraction was measured after hand-pressing the components as well as following a simulated firm hammer blow impaction. Impacts to the 0°, 8°, 15° necks were directed axially in-line with the neck, 10° anterior, and 10° proximal to the axis of the neck, respectively.Background
Methods
Modularity in total hip arthroplasty offers many potential benefits, however the consequences of mechanically associated corrosion continue to be concerning. Micromotion and settling of the modular components at the taper interface are thought to contribute to the etiology of this problem. The purpose of this study was to investigate the effect of hammer blows delivered in different directions on the force transmitted to the head-neck and neck-stem interface in modular hip implants. One-hundred and forty-four impact tests were performed in six different directions: one on axis and five 10° off axis. Four different simulations were performed measuring the head-neck only and three different necks: 0°, 8°, and 15°. A constant height delivered on-axis hammer blows at a constant 4,500 Newton (N). Load cells positioned in the hammer and at the neck-stem junction transmitted voltage to an oscilloscope which measured forces.Introduction
Methods
Perioperative blood management remains a challenge during total hip and total knee arthroplasty (THA and TKA, respectively). The purpose of this study was to determine the impact of body mass index (BMI) on blood transfusion in THA and TKA. We retrospectively evaluated 2399 patients, of whom 896 underwent THA and 1503 had TKA. A variety of outcome variables were assessed for their relationship to BMI which was stratified using the World Health Organization (WHO) classification scheme (Normal <25 kg/m2, Overweight 25–30, and Obese >30). Increased BMI was found to be protective of blood transfusion in both THA and TKA patients. Among THA patients, transfusion rates were 34.8%, 27.6% and 21.9% for normal, overweight and obese categories respectively (p = 0.002). TKA transfusion rates were 17.3%, 11.4% and 8.3% for the same categorization of BMI (p = 0.002). No trends were identified for a relationship between BMI and deep vein thrombosis, pulmonary embolism, myocardial infarction, discharge location, length of stay, 30-day readmission rate and preoperative hemoglobin level. Elevated BMI was significantly associated with decreased age, increased Hemoglobin A1c, increased baseline creatinine, increased OR time, increased American Society of Anesthesiologists (ASA) score and increased estimated blood loss in both THA and TKA patients. There was a statistically significant trend toward increased deep surgical site infection in THA patients (p = 0.043).
The use of metal-on-metal (MOM) and modular total hip arthroplasty (THA) is associated with potentially serious complications including elevated serum metal ion levels, pseudotumor, cardiomyopathy and neurologic abnormalities. The primary aim of this analysis was to identify any associations between the presence of pseudotumor, serum metal ion levels, and specific dual modular implant components. We evaluated prospectively collected data from 49 patients, mean age 58.4 years, who underwent implantation of modular THA from 01/2004-01/2010. The collected data spanned a 5–11 year period from the time of index procedure. Serum metal ion levels, including titanium, cobalt and chromium, were collected in 2012 and 2015. Hip ultrasounds were performed on each patient by a trained musculoskeletal radiologist for evaluation of the presence of soft-tissue pseudotumor. Univariate nonparametric tests were used to compare the two groups: Fisher's exact tests for categorical variables, and Wilcoxon two-group tests for continuous variables. For the purposes of analysis, values that were below the level of detection (LOD) were set to half the LOD. All analyses were performed using SAS 9.4 (SAS Institute Inc, Cary, NC, USA). Statistical significance is set at p<0.05.Introduction
Methods
Total knee arthroplasty (TKA) is the definitive treatment for osteoarthritis of the knee. The primary goal of the operation is to minimize or eliminate pain associated with osteoarthritis and secondarily to regain functional mobility and stability around the knee joint in order improve overall quality of life. The vast majority of techniques utilized for this procedure involves removal of the anterior cruciate ligament (ACL). In a native knee the ACL is a primary stabilizing ligament and essential for providing proprioceptive feedback. In the absence of the ACL, the kinematics of the knee are compromised. In an effort to more accurately replicate normal knee stability, new implant designs have emerged which maintain an intact ACL. Described herein is a cadaveric study looking at ACL competency after implantation of a TKA in which the cruciate ligaments are preserved. Twenty fresh, frozen cadaveric knees were utilized in which the ACL was intact. Specimens were excluded if there was concern for ACL stability as determined by physical examination, direct visualization during the arthrotomy and a KT-1000 measurement of anterior tibial translation in millimeters at 67N and 89N of anterior force. Each KT-1000 measurement was repeated three times using three individual examiners at both force values for a total of six data points. Bicruciate retaining components were implanted into each knee using a medial parapatellar approach. After adequate sagittal and coronal balancing was obtained, the knee was reexamined using the KT-1000 protocol described above to assess for any changes in ACL competency. The ACL was then transected and the knee was examined for a third time with the same KT-1000 protocol. For statistical analysis, a 2-way repeated-measures ANOVA was utilized. Pairwise differences were assessed utilizing Fisher's least significant difference method.Introduction
Methods
Demand for total hip arthroplasty (THA) continues to rise and as such there is a concurrent presumed increase in the incidence of periprosthetic femoral fractures. Several studies have previously demonstrated differences in fixation technique and biomechanical advantages of various cerclage constructs in fixation of femoral periprosthetic fractures. The purpose of this study is to determine the most effective combination of cerclage materials and technique in fixation of of periprosthetic fractures during cementless THA. Thirty fourth generation synthetic femora were tested in axial compression and torsion. Femurs were placed in a standardized mount and a press fit hip prosthesis was implanted by one senior surgeon. After broaching but prior to implant placement, a band saw was used to create a Vancouver B1 fracture below the level of the lesser trochanter. The implant was then placed in the femur. Four different cerclage constructs were then created using two of the following: 1) hose clamp, 2) metallic cable, 3) synthetic cable, 4) monofilament wire. All cables were placed using tensioning devices to standardize final cerclage tension. Additional constructs were created increasing the number of cerclage cables/wires to three and then four, evenly spaced across the implant. Axial compression and torsion were assessed to failure for all constructs using standard Instrom testing criteria. Cost analysis was performed for each construct.Introduction:
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Starting February 2012, our institution changed from enoxaparin (Lovenox) to the Factor Xa inhibitor, rivaroxaban (Xarelto) for venous thromboembolism prophylaxis after primary total hip (THA) and total knee arthroplasty (TKA). The purpose of our study was to compare rates of venous thromboembolism and rates of major bleeding between these two medications when used for venous thromboembolism prophylaxis after primary THA and TKA. A retrospective review was performed on 1795 patients who underwent THA or TKA at our institution between January 1, 2011 and December 31, 2012. Patients were excluded if they had a bilateral procedure, partial arthroplasty (hip hemiarthroplasty, unicompartmental knee arthroplasty), revision surgery, and cases designated as complex. Patients were excluded if they were on other anticoagulants (dabigatran, aspirin, clopidogrel, warfarin, heparin, fondaparinux), or if pre-operative creatinine was 1.2 or greater. After excluding these patients, there were 1089 patients included in the study. Chart review recorded demographics (age, gender), comorbidities (BMI, ASA, creatinine), surgery performed (primary THA or TKA), length of stay (LOS), venous thromboembolic events (deep venous thrombosis [DVT], pulmonary embolus [PE]), post-operative infections, and major bleeding events (stroke, post-operative bleeding requiring transfusion). Periprosthetic infection rates are also currently being reviewed. T-tests were used to compare continuous variables between treatment groups, and Chi-square tests were used to compare categorical variables between treatment groups (α = 0.05).Purpose:
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