Objectives. Screw plugs have been reported to increase the
Introduction. During revision surgery, the active electrode of an electrocautery device may get close to the implant, potentially provoking a flashover. Incidents have been reported, where in situ retained hip stems failed after isolated cup revision. Different sizes of discoloured areas, probably induced by electrocautery contact, were found at the starting point of the fracture. The effect of the flashover on the implant material is yet not fully understood. The aim of this study was to investigate the
Introduction. Laser marking of implants surfaces is necessary in order to provide traceability during revisions which will help identify product problems more quickly, better execute product recalls and improve patient safety. There are several methods of marking employed within the medical field such as chemical etching, electro pencil marking, mechanical imprinting, casting of markings, marking with vibratory type contact, ink jet, hot foil and screen printing. However, these methods have various drawbacks including marking durability or addition of potentially toxic chemical compounds. As a result laser marking has become the preferred identification process for orthopedic implants. Laser marking is known for its high visual quality, good reproducibility and precision. However there are concerns about the laser marking potential to affect fatigue life of a device. There is a limited number of research papers that studied the effect of laser marking on fatigue life of implants. The objective of the current study is to investigate the effects of laser marking on the fatigue life of titanium alloy material. Material and Methods. Two groups of four point bend specimens were used to investigate the effect of laser marking on the fatigue life. The first group comprised of the specimens without laser marking while the second group comprised of specimens with laser marking currently utilized for the implant surfaces. Prior to conducting the fatigue testing, a non-destructive X-ray diffraction (XRD) residual stress analysis was conducted to determine if the laser marking had introduced any residual stresses. Imaging analysis was also conducted to examine any potential surface damage on the test sample's surface. A servo-hydraulic test machine was used for the fatigue four point bend testing regime where the inner and outer spans were 30 mm and 90 mm respectively. All testing was conducted at a frequency of 10 Hz, a stress ratio R=0.1, and sine-wave loading in air. Testing was stopped at 10 Million cycles or at failure of the specimen. Results & Discussion. Figure 1 shows that laser marking process can create a fine network of surface cracks. Table 1 shows the results of residual stress measurements. Laser making introduced high tensile stresses on the components whereas “as machined” component without laser marking exhibited compressive stresses inherent due to machining. The result from the S-N curve testing is shown in Figure 2. The current laser marking components demonstrated 41% reduction in
We fatigue-tested a new resorbable composite screw (PLLA/tri-calcium phosphate) and a metal interference screw. We present average data and tolerance limits.
Means and standard deviations of pullout strength were compared. Log-log curves were fitted between force level and cycles to failure. LTLs were calculated.
We investigated a new intramedullary locking
nail that allows the distal interlocking screws to be locked to
the nail. We compared fixation using this new implant with fixation
using either a conventional nail or a locking plate in a laboratory
simulation of an osteoporotic fracture of the distal femur. A total
of 15 human cadaver femora were used to simulate an AO 33-A3 fracture
pattern. Paired specimens compared fixation using either a locking
or non-locking retrograde nail, and using either a locking retrograde
nail or a locking plate. The constructs underwent cyclical loading
to simulate single-leg stance up to 125 000 cycles. Axial and torsional
stiffness and displacement, cycles to failure and modes of failure
were recorded for each specimen. When compared with locking plate
constructs, locking nail constructs had significantly longer mean
fatigue life (75 800 cycles ( The new locking retrograde femoral nail showed better stiffness
and fatigue life than locking plates, and superior fatigue life
to non-locking nails, which may be advantageous in elderly patients. Cite this article:
The risk of mechanical failure of modular revision hip stems is frequently mentioned in the literature, but little is currently known about the actual clinical failure rates of this type of prosthesis. The current retrospective long-term analysis examines the distal and modular failure patterns of the Prevision hip stem from 18 years of clinical use. A design improvement of the modular taper was introduced in 2008, and the data could also be used to compare the original and the current design of the modular connection. We performed an analysis of the Prevision modular hip stem using the manufacturer’s vigilance database and investigated different mechanical failure patterns of the hip stem from January 2004 to December 2022.Aims
Methods
Revision surgeries for orthopaedic infections are done in two stages – one surgery to implant an antibiotic spacer to clear the infection and another to install a permanent implant. A permanent porous implant, that can be loaded with antibiotics and allow for single-stage revision surgery, will benefit patients and save healthcare resources. Gyroid structures can be constructed with high porosity, without stress concentrations that can develop in other period porous structures [1] [2]. The purpose of this research is to compare the resulting bone and prosthesis stress distributions when porous versus solid stems are implanted into three proximal humeri with varying bone densities, using finite element models (FEM). Porous humeral stems were constructed in a gyroid structure at porosities of 60%, 70%, and 80% using computer-aided design (CAD) software. These CAD models were analyzed using FEM (Abaqus) to look at the stress distributions within the proximal humerus and the stem components with loads and boundary conditions representing the arm actively maintained at 120˚ of flexion. The stem was assumed to be made of titanium (Ti6Al4V). Three different bone densities were investigated, representing a healthy, an osteopenic, and an osteoporotic humerus, with an average bone shape created using a statistical shape and density model (SSDM) based on 75 cadaveric shoulders (57 males and 18 females, 73 12 years) [3]. The Young's moduli (E) of the cortical and trabecular bones were defined on an element-by-element basis, with a minimum allowable E of 15 MPa. The Von Mises stress distributions in the bone and the stems were compared between different stem scenarios for each bone density model. A preliminary analysis shows an increase in stress values at the proximal-lateral region of the humerus when using the porous stems compared to the solid stem, which becomes more prominent as bone density decreases. With the exception of a few mesh dependent singularities, all three porous stems show stress distributions below the
Introduction. The
Fracture of contemporary femoral stems is a rare occurrence. Earlier THR stems failed due to design issues or post manufacturing heat treatments that weakened the core metal. Our group identified and analyzed 4 contemporary fractured femoral stems after revision surgery in which electrochemical welds contributed to the failure. All four stems were proximally porous coated titanium alloy components. All failures occurred in the neck region post revision surgery in an acetabular cup exchange. All were men and obese. The fractures occurred at an average of 3.6 years post THR redo (range, 1.0–6.5 years) and 8.3 years post index surgery (range, 5.5–12.0 years). To demonstrate the effect of electrocautery on retained femoral stems following revision surgery, we applied intermittent electrosurgical currents at three intensities (30, 60, 90 watts) to the polished neck surface of a titanium alloy stem under dry conditions. At all power settings, visible discoloration and damage to the polished neck surface was observed. The localized patterns and altered metal surface features exhibited were like the electrosurgically-induced damage priorly reported. The neck regions of all components studied displayed extensive mechanical and/or electrocautery damage in the area of fracture initiation. The use of mechanical instruments and electrocautery was documented to remove tissues in all 4 cases. The combination of mechanical and electrocautery damage to the femoral neck and stem served as an initiation point and stress riser for subsequent fractures. The electrocautery and mechanical damage across the fracture site observed occurred iatrogenically during revision surgery. The notch effect, particularly in titanium alloys, due to mechanical and/or electrocautery damage, further reduced the
Although 3D-printed porous dental implants may possess improved osseointegration potential, they must exhibit appropriate
Summary. Lumbar spinal specimens exhibited high
Introduction. Porous scaffolds for bone ingrowth have numerous applications, including correcting deformities in the foot and ankle. Various materials and shapes may be selected for bridging an osteotomy in a corrective procedure. This research explores the performance of commercially pure Titanium (CPTi) and Tantalum (Ta) porous scaffold materials for use in foot and ankle applications under simplified compression loading. Methods. Finite element analysis was performed to evaluate von Mises stress in 3 porous implant designs: 1) a CPTi foot and ankle implant (Fig 1) 2) a similar Ta implant (wedge angle = 5°) and 3) a similar Ta implant with an increased wedge angle of 20°. Properties were assigned per reported material and density specifications. Clinically relevant axial compressive load of 2.5X BW (2154 N) was applied through fixtures which conform to ASTM F2077–11. Compressive yield and
BACKGROUND. This scientific work is a non-interventional, experimental and prospective comparative study of two very high-viscosity PMMA bone cements: DePuy CMW 2G and Palacos® fast R+G. Reference product: Palacos® R+G. Fast-setting PMMA bone cements are used in the endoprothetics of the patella and knee (in Australia) and are also used to cement an artificial acetabulum (in the UK). Are there any differences regarding the characteristics of the two fast-setting PMMA bone cements?. MATERIALS AND METHODS. All cements were mixed as specified by the manufacturer and analysed on the following parameters: handling properties (mixing, waiting, working and hardening phase), powder/liquid-ratio, mechanical properties (ISO 5833:2002 and DIN 53435),
Objectives: The purpose of this biomechanical study was to compare the mechanical properties of locked nails and screws made from either stainless steel or titanium alloy. Methods: The specially designed locked nails and screws with the same structures were made from either stainless steel or titanium alloy. The structural factors investigated included inner diameter and root radius for locking screws and outer diameter and nail hole size for locked nails. The mechanical properties investigated included bending stiffness,
Objectives. Opening wedge high tibial osteotomy (HTO) is an established surgical procedure for the treatment of early-stage knee arthritis. Other than infection, the majority of complications are related to mechanical factors – in particular, stimulation of healing at the osteotomy site. This study used finite element (FE) analysis to investigate the effect of plate design and bridging span on interfragmentary movement (IFM) and the influence of fracture healing on plate stress and potential failure. Materials and Methods. A 10° opening wedge HTO was created in a composite tibia. Imaging and strain gauge data were used to create and validate FE models. Models of an intact tibia and a tibia implanted with a custom HTO plate using two different bridging spans were validated against experimental data. Physiological muscle forces and different stages of osteotomy gap healing simulating up to six weeks postoperatively were then incorporated. Predictions of plate stress and IFM for the custom plate were compared against predictions for an industry standard plate (TomoFix). Results. For both plate types, long spans increased IFM but did not substantially alter peak plate stress. The custom plate increased axial and shear IFM values by up to 24% and 47%, respectively, compared with the TomoFix. In all cases, a callus stiffness of 528 MPa was required to reduce plate stress below the
Background. Titanium, in particular Ti6Al4V, is the standard material used in cementless joint arthroplasty. Implants are subjected to cyclic loading where fracture is the reason for re-operation in 1.5–2.4% of all revisions in total hip arthroplasty. In order to strengthen critical regions, surface treatments such as shot peening may be applied. A superficial titanium oxide layer is naturally formed on the surface as a protective film at ambient conditions. However, as its thickness is only in the range of several nanometers, it is prone to be destroyed by high loads - as present at the surface during bending - leading to an ‘oxidative wear’ in a corrosive environment [1]. The present study aims to evaluate the shot peening treatment on Ti6Al4V regarding its potential for cyclically loaded parts under a dry and a corrosive testing medium. Materials and Methods. Hour-glass shaped titanium specimens (Ti6Al4V) with a minimal diameter of 10 mm have been subjected to an annealing treatment at 620°C for 10h to remove initial residual stresses introduced during machining. Subsequently, a high-intensity shot peening treatment with cut wire followed by a low-intensity cleaning process with glass beads have been performed (Metal Improvement, Germany). Arithmetic mean roughness R. a. of the treated surfaces was measured (Mahr Perthometer M2, Germany). Residual stress depth profiles prior to and after shot peening have been measured by a Fe-filtered Co-K(alpha) radiation (GE Measurement&Control, USA) and calculated using the sin. 2. (psi) method.
We used the stainless steel cable grip system described by Dall and Miles in 1983 to fix trochanters in 40 hips after total arthroplasty with trochanteric osteotomy. The cable broke in 32.5% of the hips; the trochanter failed to unite in 37.5%. Significantly more cables broke when placed inside the femoral canal than when the cable was placed round the femoral shaft (58% as against 9.5%, difference p less than 0.01). The high incidence of breakage may have resulted from contact between the stainless steel cable and the titanium prosthesis, from the acute angulation, or because of the lower
There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines
Purpose: To perform a biomechanical comparison between an older established and a recently introduced technique, used in suturing semitendinosus quadrupled grafts. Methods: Flexor tendons were harvested from pigs giving a tendon of similar dimensions to semitendinosus. Specimens were prepared using an older established suturing method utilising a Bunnel ‘whip’ stitch (group A, 21 specimens), and a recently introduced(. 1. ) method where the tendon is sutured back on itself having an overlap of either 20mm or 30mm and forming a closed loop (group B, 40 specimens). In group A, a tibial fixation button was used and grafts were prepared as to have a common representative overall length. Consideration was given in mounting either end of these grafts in representative conditions. The lengths of Group B specimens were of comparable dimensions to group A, but were mounted by using custom-made grips incorporating roller bars. Tests were performed in a Dartec servohydraulic materials testing machine in fatigue and in single loading at various strain rates and by using physiological loading patterns and in physiological ambient conditions. Results: Group A specimens failed in a small load range of 200–250N and at the whipstitch, which snapped at the knot tied around the tibial button. Group B specimens failed either in the overlap region (for the shorter overlaps) or in mid-tendon substance (for longer overlaps). In general group A showed low