Background and aim. Recent proposals have been introduced to modify stem design and/or femoral fixation in total hip replacement (THR). New designs need to consider previous design features and their results. The aim of this study has been to evaluate the clinical and radiological results of six different designs of tapered uncemented stems implanted in our Institution. Methods. 1918 uncemented hips were prospectively assessed from 1999 to 2011 (minimum follow-up of five years for the unrevised hips). All hips had a 28 or 32 mm femoral head and metal-on-polyethylene or alumina-on-alumina bearing surface. Six uncemented femoral designs that shared a femoral tapered stem incorporating a coating surface were included in the study. The different design features included the type of coating, metaphyseal filling, and sectional shape. Results. Intra-operative proximal femoral crack was 6.7% in one of the designs (p=0.01), univariate analysis showing a lower risk of crack in the other designs. The position of the stem was neutral in 80% of the cases for all designs. Femoral canal filing was related to the stem design (p<0.001 at the three levels) and to the femoral level assessed (subset alpha=0.005). Twelve stems were revised for aseptic loosening (6 from two different designs). The survival rate for femoral aseptic loosening at 15 years was 96.6% (95% CI 93.8 to 99.4) for one of these two designs ad 97.4% (95% CI95.5 to 99.6) for the other. Regression analysis showed that stem design was the only factor related to aseptic loosening when adjusted for femoral canal filling (at the three levels) stem position (neutral or not) and femoral type (cylindrical or not). Conclusion. Tapered uncemented stems consistently provide excellent bone fixation. New designs need to avoid changing successful features and concentrate on the less successful aspects

This study compared the pullout forces of the initial implantation and the “cement-in-cement” revision technique for short and standard-length (125 mm vs. 150 mm) Exeter. ®. V40 femoral stems used in total hip arthroplasty (THA). The idea that the pullout force for a double taper slip stem is relative to the force applied to the femur and that “cement-in-cement” revision provides the same reproduction of force. A total sample size of 15 femoral stems were tested (Short, n = 6 and Standard, n = 9). 3D printed fixtures for repeatable sample preparation were used to minimize variance during testing. To promote stem subsidence and to simulate an in vivo environment, the samples were placed in an incubator at 37°C at 100% humidity and experienced a constant compressive loading of 1335 N for 14 days. The samples underwent a displacement-controlled pullout test. After the initial pullout test, “cement-in-cement” revision will be performed and tested similar to the initial implantation to observe the efficacy of the revision technique. To compare the pullout forces between the two groups, a Kruskal-Wallis test using a significance level of 0.05 was conducted. The mean maximum pullout force for the short and standard-length femoral stems were 3939 ± 1178 N and 5078 ± 1168 N, respectively. The Kruskal-Wallis test determined no statistically significant difference between the two groups for the initial implantation (p = 0.13). The “cement-in-cement” revision pullout force will be conducted in future testing. This study demonstrated the potential use of short stem designs for THA as it provides similar levels of fixation as the standard-length femoral stem. The potential benefits for using a short stem design would be providing similar load transfer to the proximal femur, preserving proximal metaphyseal femoral bone in primary replacement, and reducing the invasiveness during revision

The stem and the rasp for cemented arthroplasty are typically designed to obtain a cement mantle 2–5 mm thick. However, sometimes a line-to-line cementation is preferred, where the femoral cavity is prepared with the same dimension as the actual stem. There are contrasting reports [1,2] about the suitability of this technique to withstand the long-term fatigue loads. While the theoretical geometry allows no space for the cement, a sort of cement mantle is formed as the cement penetrates in the spongy bone. The scopes of this study were: 1) developing a dedicated in vitro method to test line-to-line cementation; 2) assessing if a short, polished hip stem designed for a standard cementation can be safely cemented line-to-line. In order to perform long-term mechanical in vitro tests, composite bones must be used, as cadaveric bones cannot withstand millions of loading cycles [3]. For this study, the Sawbones Mod. 3406-4 were chosen: they feature an open-cell polyurethane core simulating low-density spongy bone. Post-implantation x-rays confirmed that a relevant cement-bone interdigitation was obtained. Four femurs were prepared with a CoreHip (Aesculap) with regular cement mantle (Regular). Another 4 femurs were rasped to the same rasp size, and implanted with line-to-line cementation with a larger stem (Line-to-line). The implanted femurs were subjected to an accelerated test derived from a validated protocol [3] which replicates the most demanding motor tasks of 24 years of patient activity. Implant elastic micromotions and permanent migrations were measured throughout the test. The implants were then sectioned and treated with dye penetrants to highlight the cement cracks. Elastic and permanent motions did not show any loosening trend, and never exceeded few micrometers. As expected, some damage was visible in the cement mantles after test completion, for both types of implantation (similar to retrieved cement mantles surrounding stable implants [3]. The cement damage was similar in all specimens. No sign of major disruption was visible, neither within the Regular nor in the Line-to-line specimens: in fact, the cracks were limited in length, did not seem to cross the entire mantle thickness, and did not result in any loose cement fragments. The cracks in the line-to-line implants showed the same position and distribution compared to those found in the regular implants, but were slightly longer in some specimens. This in vitro study confirmed the feasibility of simulating line-to-line cementation in vitro. Our results suggest that a stem designed for a regular cement mantle could induce slightly more damage when implanted line-to-line, but no significant trend toward loosening

Coronoid fractures account for 2 to 15% of the cases with elbow dislocations and usually occur as part of complex injuries. Comminuted fractures and non-unions necessitate coronoid fixation, reconstruction or replacement. The aim of this biomechanical study was to compare the axial stability achieved via an individualized 3D printed prosthesis with curved cemented intramedullary stem to both radial head grafted reconstruction and coronoid fixation with 2 screws. It was hypothesized that the prosthetic replacement will provide superior stability over the grafted reconstruction and screw fixation. Following CT scanning, 18 human cadaveric proximal ulnas were osteotomized at 40% of the coronoid height and randomized to 3 groups (n = 6). The specimens in Group 1 were treated with an individually designed 3D printed stainless steel coronoid prosthesis with curved cemented intramedullary stem, individually designed based on the contralateral coronoid scan. The ulnas in Group 2 were reconstructed with an ipsilateral radial head autograft fixed with two anteroposterior screws, whereas the osteotomized coronoids in Group 3 were fixed in situ with two anteroposterior screws. All specimens were biomechanically tested under ramped quasi-static axial loading to failure at a rate of 10 mm/min. Construct stiffness and failure load were calculated. Statistical analysis was performed at a level of significance set at 0.05. Prosthetic treatment (Group 1) resulted in significantly higher stiffness and failure load compared to both radial head autograft reconstruction (Group 2) and coronoid screw fixation, p ≤ 0.002. Stiffness and failure load did not reveal any significant differences between Group 2 and Group 3, p ≥ 0.846. In cases of coronoid deficiency, replacement of the coronoid process with an anatomically shaped individually designed 3D printed prosthesis with a curved cemented intramedullary stem seems to be an effective method to restore the buttress function of the coronoid under axial loading. This method provides superior stability over both radial head graft reconstruction and coronoid screw fixation, while achieving anatomical articular congruity. Therefore, better load distribution with less stress at the bone-implant interface can be anticipated. In the clinical practice, implementation of this prosthesis type could allow for early patient mobilization with better short- and long-term treatment outcomes and may be beneficial for patients with irreparable comminuted coronoid fractures, severe arthritic changes or non-unions

Recent NICE guidance recommends use of a well proven cemented femoral stem for hip hemiarthroplasty in management of fractured neck of femur. The Exeter Trauma Stem (ETS) has been designed based on the well proven Exeter hip stem. It has a double taper polished stem design, proclaimed to share geometry and surface finish with the Exeter hip. This study investigated the surface finish of the two stems in order to investigate the hypothesis that they were different. Two ETS and two Exeter stems were examined using a profilometer with a sensitivity of one nanometer. Macroscopic visual inspection showed that the two Exeter stems had significantly smoother surface finish than the ETS stems. The roughness average (RA) values on the ETS stems were approximately an order of magnitude higher than those of the Exeter stems, mean of 0.235μm compared with 0.025μm (p<0.0001). This difference in surface finish has implications for the biomechanical functioning of the stem. Previous change of the Exeter stem to a matt surface-finish in 1976 resulted in a significant increase in stem failure rates and an understanding of the importance of the polished surface-finish in order to function within a taper-slip philosophy. By changing the surface finish in the ETS stem, longevity of the implant may similarly be affected. Clinical results have yet to be published demonstrating this. We recommend the manufacturer reconsiders the surface finish of the ETS stem to ensure it functions as well as the Exeter primary stem with which it shares a design philosophy

Summary Statement. Proximal femoral bony deficits present a surgical and biomechanical challenge to implant longevity in revision hip arthroplasty. This work finds comparable primary stability when a distally fixing tapered fluted stem was compared with a conical design in cadaveric tests. Introduction. Proximal bony deficits complicate revision hip surgery and compromise implant survival. Longer distally fixing stems which bypass such defects are therefore required to achieve stability compatible with bony ingrowth and implant longevity. Aims. It is hypothesised that a tapered stem will provide superior rotational stability to a conical design. This work therefore aims to compare the primary stability and biomechanical properties of a new design of tapered fluted modular femoral stem (Redapt®, Smith & Nephew) with that of a conical fluted stem (Restoration®, Stryker). Materials & Methods. 7 Pairs of cadaveric femora were obtained according to strict inclusion/exclusion criteria. Each underwent dual energy x-ray absorptiometry and calibration plain-film radiographs were taken. Digital templating was performed using TraumaCad (Voyant Health, Brainlab) to determine implant sizing. Both stems are fluted, modular and manufactured from titanium. The control stem (Restoration) featured a straight conical design and the investigation stem (Redapt) a straight tapered design. Implantation was performed by a revision arthroplasty surgeon familiar with both systems. Proximal bone deficiency was reproduced using an extended trochanteric osteotomy with removal of metaphyseal bone before reattaching the osteotomy. Primary stability in the axial, sagittal and coronal planes was assessed using micromotion transducers (HBM, Darmstadt, Germany) and also by Radiostereometric Analysis (RSA). RSA employs simultaneous biplanar radiographs to measure relative movement. Two 1mm tantalum beads were mounted on the prosthesis with the centre of the femoral head taken as the third reference point. Beads were placed proximally in the surrounding bone as rigid body markers. Each bone was potted according to the ISO standard for fatigue testing and cyclically loaded at 1Hz for at least 3 increments (750–350N, 1000–350N, 1500–350N) for 1000 cycles. RSA radiographs were taken at baseline and on completion of each cycle. A strain analysis was concurrently performed using a PhotoStress® (Vishay Precision Group, Raleigh, USA) photoelastic coating on the medial femoral cortex. Each bone was loaded intact and then with the prosthesis in-situ at 500N increments until strain fringes were identified. Once testing was completed, the stems were sectioned at the femoral isthmus and data is presented on the cross-sectional fit and fill observed. Results. Both stem designs showed comparable primary stability with all stems achieving clinically acceptable micromotion (<150 μm) when loaded at body weight. A larger proportion of the control stems remained stable as loading increased to x2-3 body weight. Transducer-recorded migration appeared greatest in the axial plane (y axis) with negligible distal movement in the coronal or sagittal planes. Point motion analysis (RSA) indicated most movement to be in the coronal plane (x-axis) whereas segment motion analysis showed rotation about the long axis of the prosthesis to be largest. Photoelastic strain patterns were transferred more distally in both designs, however substantial stress shielding was also observed. Discussion/Conclusion. Both designs achieved adequate distal fixation and primary stability under representative clinical loading conditions. This work supports the continued use of this novel stem design for revision surgery in the presence of extensive proximal bone loss

Summary Statement. The current biomecahnical study demonstrated that the stemless peripheral leg humeral component prototype and central screw humeral component prototype achieved similar initial fixation as stemmed Global Advantage humeral component in terms of resultant micromotion in total shoulder arthroplasty. Introduction. A stemless humeral component may offer a variety of advantages over its stemmed counterpart, e.g. easier implantation, preservation of humeral bone stock, fewer humeral complications, etc. However, the initial fixation of a stemless humeral component typically depends on cementless metaphyseal press-fit, which could pose some challenges to the initial stability. Long-term success of cementless implants is highly related to osseous integration, which is affected by initial implant-bone interface motion. 1. The purpose of the study was to biomechanically compare micromotion at the implant-bone interface of three humeral components in total shoulder arthroplasty. Patients & Methods. Three humeral components were evaluated: Global Advantage, a central screw prototype, and a peripheral leg prototype. All components were the smallest sizes available. Global Advantage is a stemmed design. Both central screw prototype and peripheral leg prototype are stemless designs. Five specimens were tested for each design. Composite analogue humeral models were utilized to simulate the humeral bone. The cortical wall had a thickness of 3 mm and a density of 481 kg/m. 3. , while the cancellous density was 80 kg/m. 3. The model was custom fabricated to accommodate 40 mm humeral component and had a 45° resected surface and a square base to facilitate test setup. Each humeral component was implanted per its surgical technique. The construct was clamped in a vise with the humeral shaft angled at 27°. A MTS test system was employed to conduct the test. A sinusoidal compressive load from 157 N to 1566 N (2BW) was applied to the humeral component at 1 Hz for 100 cycles. The implant-bone interface micromotion was measured with a digital image correlation system which had a resolution of less than 1 micron. The micromotion measurement was transformed to 2 components: 1 was parallel and the other perpendicular to the humeral resection surface. Peak-valley micromotion from the last 10 cycles were averaged and utilised for data analyses. A one-way ANOVA and post-hoc Tukey tests were performed to compare the micromotion of different designs (α=0.05). Results. Micromotion of Global Advantage parallel to the resection (X-Axis) was significantly less than that of central screw prototype and peripheral leg prototype. Micromotion of peripheral leg prototype perpendicular to the resection (Y-Axis) was significantly less than Global Advantage and central screw prototype. There was no significant difference between different designs in resultant micromotion. Discussion/Conclusion. Clinical studies have shown that current stemless shoulder prosthesis yielded encouraging results in mid-term follow-ups. Particularly, the stemless Arthrex Eclipse humeral component, a central screw design, has been reported to have a secure bony fixation and ingrowth at an average of 23 months postoperatively. 4. The current study demonstrated that the stemless peripheral leg prototype and central screw prototype achieved similar initial fixation as stemmed Global Advantage in terms of resultant micromotion, and provided biomechanical evidence that stemless humeral components could have comparable initial stability to stemmed counterparts

Prosthesis migration and acetabular cup wear are useful short term measurement which may predict later implant outcome. However, the significance of the magnitude and pattern of the migration is very much dependent on the specific design studied. This study aimed to characterise patterns of migration by following four cemented femoral stem designs using Radiostereometry (RSA) within a prospective randomised longitudinal trial. 164 patients undergoing cemented femoral hip replacement for osteoarthritis were randomised to receive either an Exeter (Howmedica Stryker), Ultima Tapered Polished Stem (TPS) (Depuy), Ultima Straight Stem (USS) (Johnson and Johnson) or Elite Plus (Depuy) stem. Each subject received the OGEE PE cemented acetabular component (Depuy). RSA examinations were performed at 1 week and 6, 12, 18, 24 and 60 months post surgery. They were analysed using the UMRSA system (RSA Biomedical AB, Umea, Sweden), and our local geometric stem measurement software. 149 patients had RSA measurements available to 2 years, and 96 patients to 5 years. Differences were analysed using mixed linear modelling (SPSS). Median linear proximal cup wear rate reduced to a minimum of 0.02-0.06mm/year in year two. Between 2 and 5 years the wear rate increased, being significantly higher for the Elite. Cup migration was small but continuous. At 2 years it was median 0.3mm proximally, increasing to 0.5 mm at 5 years. Median rotations were less than 0.3 degrees. Proximal migration was positive and increasing at all time points for all stems. For the tapered polished designs, while the overall magnitude was significantly higher, the rate of migration significantly decreased, whereas for the other stem designs it did not. The TPS stem showed a tendency for posterior tilt which was significant compared to the other stems at 5 years. All stems tended to retroversion, with the USS significantly less than the others and the Elite showing and relative increase at 5 years. In summary migration patterns are characterised by the stem design, including where there were only small changes between designs. We are now testing measured migrations as predictors of outcome, and will continue to follow this group of patients to 10 years

Hydroxyapatite-coated standard anatomical and customised femoral stems are designed to transmit load to the metaphyseal part of the proximal femur in order to avoid stress shielding and to reduce resorption of bone. In a randomised in vitro study, we compared the changes in the pattern of cortical strain after the insertion of hydroxyapatite-coated standard anatomical and customised stems in 12 pairs of human cadaver femora. A hip simulator reproduced the physiological loads on the proximal femur in single-leg stance and stair-climbing. The cortical strains were measured before and after the insertion of the stems. Significantly higher strain shielding was seen in Gruen zones 7, 6, 5, 3 and 2 after the insertion of the anatomical stem compared with the customised stem. For the anatomical stem, the hoop strains on the femur also indicated that the load was transferred to the cortical bone at the lower metaphyseal or upper diaphyseal part of the proximal femur. The customised stem induced a strain pattern more similar to that of the intact femur than the standard, anatomical stem

Background. The worldwide withdrawal of the DePuy Articular Surface Replacement (ASR) device in both its resurfacing and total hip replacement (THR) form on 26 August 2010, after 93,000 were implanted worldwide, has had major implications. The 2010 National Joint Registry for England and Wales quoted figures of 12-13% failure at five years; however these figures may be an underestimate. Patients and methods. In 2004 a single surgeon prospective study of the ASR bearing surface was undertaken. Presented are the Adverse Reaction to Metal Debris (ARMD) failure rates of the ASR resurfacing and ASR THR systems. The diagnosis of ARMD was made by the senior author and was based on clinical history, examination, ultrasound findings, metal ion analysis of blood and joint fluid, operative findings and histopathological analysis of tissues retrieved at revision. Acetabular cup position in vivo was determined using EBRA software. Mean follow up was 52 months (24-81) and 70 patients were beyond 6 years of the procedure at the time of writing. Kaplan Meier survival analysis was carried out firstly with joints designated ‘failure’ if the patient had undergone revision surgery or if the patient had been listed for revision. A second survival analysis was carried out with a failure defined as a serum cobalt concentration > 7microgrammes/L (MHRA guideline from MDA-2010-069). Full explant analysis was carried out for retrieved prostheses. Results. There were 505 ASR hips in total (418 resurfacings and 87 THRs). 657 metal ion samples were available at the time of writing including 152 repeats. Survival analysis using revision/listed for revision as end point (at 6 years): ASR resurfacing: 26.1% failure; ASR THR: 55.5% failure. Survival using ion analysis (at 5 years): ASR resurfacing: 50.1% failure; ASR THR: 66.5% failure. The median (range) volumetric wear rate of failed prostheses was 8.23mm3/year (0.51-95.5). Failure and high ion concentrations are linked to acetabular cup size, anteversion and inclination. Increased failure rates in THRs were due to wear at the taper junction of head and stem. Conclusion. Design flaws in the ASR have led to excessive wear and consequently catastrophic failure rates secondary to ARMD

The outcome of a cemented hip arthroplasty is partly dependent on the type of cement which is used. The production of an interface gap between the stem and the cement mantle as a result of shrinkage of the cement, may be a factor involved. Palacos R, Palacos LV (both with gentamicin), CMW 1, CMW 2, CMW Endurance (CMWE) and Simplex were prepared under vacuum and allowed to cure overnight in similar cylinders. The next day this volume was determined by the displacement of water. Shrinkage varied between 3.82% and 7.08% with CMWE having the lowest and Palacos LV the highest. This could be a factor to consider when choosing a cement for a shape-closed stem.

We have investigated the role of the penetration of saline on the shear strength of the cement-stem interface for stems inserted at room temperature and those preheated to 37°C using a variety of commercial bone cements. Immersion in saline for two weeks at 37°C reduced interfacial strength by 56% to 88% after insertion at room temperature and by 28% to 49% after preheating of the stem. The reduction in porosity as a result of preheating ranged from 71% to 100%. Increased porosity correlated with a reduction in shear strength after immersion in saline (r = 0.839, p < 0.01) indicating that interfacial porosity may act as a fluid conduit.