Introduction. Cementless stems are fixed to the surrounding bone by means of mechanical press-fit. Short-, mid-, and long term outcomes are good for this type of fixation despite that only a part of the stem surface is in contact with the surrounding bone. Several studies show that the contact ratio achieved after surgery between the stem and the surrounding bone ranged between 15% and 60%. Then, only a part of the stem-bone interface presents a press-fit. The rest of the stem-bone interface is only in contact or presents an interfacial gap inherent to the surgical technique. Therefore, this study aimed to investigate the difference in the primary stability of a cementless stem between a press-fit combined with contact and a press-fit combined with gap achieved after the surgery. Materials & Methods. A finite element study was carried out on a composite bone implanted with a femoral stem and subjected to physiological loading simulating stair climbing [1]. All materials were defined as isotropic homogeneous. The stem-bone interface was divided into 4 areas: the superior plasma spray, the inferior plasma spray, the polished surface of the stem in contact with the cancellous bone, and the plasma spray surface of the stem in contact with the cortical bone. Each contact area can be either in contact with a press-fit, either in contact without press-fit or can present a gap. This result in a total of 28 cases: 14 where there is a press-fit combined with contact and 14 cases where there is a press-fit combined with gap. Results. When 1 press-fit is combined with 3 contacts, the average micromotion reaches 26µm. The average micromotion increases up to 47µm (+45%) when 1 press-fit is combined with 3 gaps. The detailed results can be seen on Figure 1. When 2 press-fits are combined with 2 contacts, the average micromotion reaches 28µm. The average micromotion increases up to 36µm (+29%) when 2 press-fit are combined with 2 gaps. The detailed results can be seen on Figure 2. When 3 press-fits are combined with 1 contact, the average micromotion reaches 31µm. The average micromotion increases up to 34µm (+9%) when 3 press-fits are combined to 1 gap. The detailed results can be seen on Figure 3. Discussion. As expected, micromotion predicted when press-fit is combined with contact is lower than when press-fit is combined with gap. However, the average micromotion increases with the increase of press-fit when combined with contact (from 26µm to 31µm (+19%)). The increase of the press-fit area combined with contact lead to a slightly increase of the micromotion. Conversely, the average micromotion decreases with the increase of press-fit when combined with gap (from 47µm to 34µm (−28%)). This is due to the increase of the press-fit area, and then the gap has a lesser effect. This study also shows that the difference in the micromotion between press-fit when combined with contact and press-fit when combined with gap decreases with the increase of the press-fit

INTRODUCTION. Reaming of the acetabular cavity prior to cementless cup implantation aims to create a defined press-fit between implant and bone. The goal is to achieve full implant seating with the desired press-fit to reduce the risk of early cup loosening and the risk of excessive cup deformation. Current research concentrated on the spherical deviations of the reamed cavity compared to the reamer size, but the direct relationship between nominal press-fit, reamer geometry, cavity shape and bone-implant contact has not yet been investigated. The aim of this study was to determine the influence of the reaming process, the surface coating, and the implantation force on the achieved press-fit situation. METHODS. Fresh-frozen porcine acetabulae (n = 20) were prepared and embedded. Hemispherical reamers were used and the last reaming step was performed using a vertical drilling machine to ensure a proper alignment of the cavity axis. A hand-guided 3D laser scanner was used (HandySCAN 700, Creaform) to determine the reamer geometry and the cavity shape. Press-fit cups with two different surface coatings (Ø44 mm, Porocoat/Gription, DePuy Synthes) were implanted using a drop tower. The Porocoat cup was implanted with impacts from lower drop heights (low implantation force) and press-fits of 1 mm and 2 mm. The Gription cup, exhibiting a rougher surface, was implanted with low and high implantation forces and a press-fit of 1 mm. Bone-implant contact was analysed by the registration of the cup and cavity surface models, scanned prior to implantation, to the scan of the implanted cup. The cup surface was divided in areas with and without contact to the surrounding cavity. Overhang indicates that there was no adjacent cavity surface surrounding the implanted cup. The transition between contact and a gap at the cup dome was defined as contact depth and used as indicator for the cup seating. RESULTS. The peripheral cavity diameter was on average 0.94 ± 0.29 mm smaller than the reamer diameter due to the sub-hemispherical distribution of the cutting blades. This led to an increased effective press-fit in the peripheral area of the cavity. The contact area between cup and bone increased with the implantation force (p = 0.008) and ranged from 13.1 % to 27.8 %. The contact depth was larger for the smoother Porocoat coating (p = 0.008), a press-fit of 2 mm (p = 0.008) and a higher implantation force (p = 0.008). DISCUSSION. This study shows that, assuming similar implantation forces, an increased surface roughness of the cup coating increases the risk of an insufficient cup seating. For a given press-fit, higher implantation forces would be necessary to fully seat the cup in order to enhance the bone-implant contact. Implantation of a cup without a defined nominal press-fit could increase the contact area; however a high reaming accuracy and an increased friction coefficient of the cup coating are required to compensate for a reduction in initial fixation strength caused by reduced radial compressive forces. For any figures or tables, please contact authors directly

Introduction. Approximately 2,000 Skeletal transcutaneous osseointegration (STOI) procedures have been performed worldwide as of 2020, more than half of which have been performed by the Osseointegration Group of Australia using a press-fit technique with either ILP or OPL implant designs. Despite the consistently demonstrated clinical benefits, concerns regarding potential complications following STOI have slowed its widespread adoption. As more patients are followed for a longer period of time, longitudinal studies have confirmed complication rates are very acceptable, similar to those of total ankle and total elbow replacements. One of the major risk category is implant removal. The primary goal of this study was to investigate the complications and technical issues associated with transtibial osseointegration implant removal due to any cause. The focus here will be on the press-fit ILP and OPL implants, including the indications for removal and patient outcomes following removal. Materials & Methods. A review of our osseointegration registry between November 2010 and March 2022 was performed. Inclusion criteria were patients who have undergone removal of a transtibial osseointegration implant due to any cause. Selected patients either had a follow-up of at least two years or had their index osseointegration surgery at least two years prior to when the study was performed. Patients who have had osseointegration at other anatomic levels, and patients who underwent simultaneous total knee replacement with transtibial osseointegration were excluded from the registry search. Results. There were a total of 148 transtibial osseointegration procedures performed during the study period, with 97 (65.5%) performed in males and 51 (34.5%) performed in females. The average age at first stage osseointegration procedure is 50.4 years (range 16.8–87.9, SD 14.1). In the study cohort of 22 cases requiring implant removals, 12 (54.5%) were male and 10 (45.5%) were female. The average age at first stage osseointegration procedure in this cohort is 51.3 (range 37.4–82.6, SD 10.7) and average BMI 30.3 (range 21.9–40.9, SD 5.8). Although men comprised the majority of removals, women had a greater relative risk (Fisher exact test p=0.032). The average duration from time of STOI to removal was 2.6 years (range 0.1–6.8, SD 1.9) within this 11.5 year follow-up period. The most frequent indication was infection (54.6%, n=12) followed equally by pain (13.6%, n=3), aseptic loosening (13.6%, n=3) and implant fracture (13.6%, n=3), and lastly failure to integrate (4.6%, n=1). Conclusions. Of the 22 removals, 12 were reimplanted at the same anatomical level (10 were reimplanted within 6 months, 1 within 12 months, and 1 within 24 months). 11 of these cases currently wear their prosthetic legs for more than 13 hours daily. 1 case was recently reimplanted and still completing their loading program. Of the patients who were not reimplanted at the same anatomical level, 1 required proximal amputation with transfemoral osseointegration. 3 patients converted to traditional socket prostheses (TSP) due to pain, and 1 underwent proximal amputation and converted to TSP due to infection. 3 cases are currently awaiting transtibial osseointegration reimplantation, and 1 patient was deceased. 1 patient was lost to follow-up

Introduction. Osseointegration has been established as a promising approach for the reconstruction of amputated limbs, particularly for amputees suffering from traditional socket prosthesis (TSP). While Osseointegration was originally developed with a screw fixation design, several Osseointegration devices adopting a modern press-fit design have also been introduced. In this study, medium-term outcomes for patients with the two most common press-fit osseointegration implant used worldwide are analysed. Materials and Methods. This is a cross-sectional analysis containing a cohort of Osseointegration patients treated in several centres worldwide. We analyzed a total of 93 patients with an average follow-up time of 6.52 years. Functional, Mobility and patient reported outcomes were collected pre-operatively and during follow-up. All postoperative adverse events (infection, revision surgery, fractures, and implant failures) were also analyzed. Results. Crude analysis of the data indicated that all 93 patients continue to use their osseointegrated prosthesis. Significant improvements for all outcome measures were observed. However, several adverse events including 19 implant revisions, 8 periprosthetic fractures and 43 surgical debridements were also reported. A detailed analysis was performed on each adverse event type to evaluate possible causes. Conclusions. At 5 years post-surgery, Osseointegration continues to provide amputees with improvements on function and quality of life which were previously unattainable with socket prosthesis. However, the benefits are accompanied with a relatively high risk of adverse events. Further research in standardizing clinical practice and the development of better implant may offer a reduction to these risks

Introduction. The number of total hip replacements (THR) increased around 3.5% by year in last decade. Osteoarthritis is the most important disease in the hip, with a prevalence of 10% in the older population (>85 years), according to the Swedish THA Register. THR have been increasing in last years, mainly in young patients between 45 to 59 years old. This type of patients needs a long term solution to prevent hip revision. Two commercial solutions for young patients, the resurfacing prosthesis and press fit one, were analysed in the present study by experimental and numerical models. Methods. Two synthetic left models of composite femur (Sawbones. ®. , model 3403), which replicates the cadaveric femur, and two composite pelvic bones were used to introduce two Comercial models of Hip resurfacing (Birmingham model) and Press-fit stem (Laffit Selft –locking stem press-fit model). The commercial hip stems were chosen according to the femurs head size (resurfacing) and the femur size to press-fit Hip stem. Then, they were introduced by an experimented surgeon. The experimental set-up was applied according to a system defined previously by Ramos et al. (2013). Numerical models were implemented by replicating the experimental tests. A 3D scanning was used to identify the stem position in each model. The properties of cortical and cancel bone and hip prosthesis were also taken into account by these models. Contact was established in the interfaces for both press-fit solutions. The femur rotates distally and Pelvic moves up and down according model changes, in order to guarantee models with the same boundary conditions. Results. The numerical models were already validated experimentally using different loading conditions. Results from numerical models, present different distribution in the two commercial solutions in comparison to intact articulation (Figure 1). The medial aspect is the most critical in the femur. The resurfacing hip presents a closer behavior than the intact femur at proximal region. The press-fit hip presents a strain reduction in proximal region, which promotes the bone loss observed in clinical cases. The changes in the contact Hip joint for commercial solutions modify strain distribution distally, in all femur aspects. The press fit solution increase the bending in medial aspect

INTRODUCTION. The restoration of the anatomical hip rotation center (HRC) has a major influence on the longevity of hip prostheses. Deviations from the HRC of the anatomical joint after total hip arthroplasty (THA) can lead to increased hip joint forces, early wear or loosening of the implant. The contact conditions of acetabular press-fit cups after implantation, including the degree of press-fit, the existence of a polar gap and cup orientation, may affect the HRC restoration, and therefore implant stability. The aim of this study was to determine the influence of acetabular press-fit, polar gap and cup orientation on HRC restoration during THA. METHODS. THAs were performed by an experienced orthopaedic surgeon in full cadaveric models simulating real patient surgery (n=7). Acetabular cups with a Porocoat™ (n=3) and Gription™ surface coating (n=4) were implanted (DePuy Synthes, Leeds, UK). Computed tomography (CT) scans prior to surgery, as well as after reaming and implantation of press-fit cups were used to calculate the HRC displacement. After aligning the pelves in the anterior pelvic plane, 3D reconstruction of the HRC at each stage was performed by fitting spheres to the femoral head, the reamed cavity and the inserted cup. 3D surface models of the cups were generated using a laser scanner and were registered to the CT images. The effective press-fit was calculated using the diameters of spheres, fitted to the cavity prior to cup insertion and to the outer cup coating. The polar gap was defined as the difference between the outer cup surface and the subchondral bone at the cup pole. Anteversion and abduction angles were calculated as difference between the cup planes and the sagittal and transverse plane, respectively. RESULTS. A medial (6.4±1.6mm), superior (5.1±1.5mm) and posterior (3.0±1.4mm) displacement of the HRC after reaming was measured. A significant inferior shift of the HRC could be measured after cup implantation (p=0.043). No significant influence of the coating design on the HRC shift could be observed. The shift of the HRC back towards the anatomical HRC was highly correlated to the degree of polar gap (R. 2. =0.928, p<0.001) and a trend towards an association with effective press-fit was observed (R. 2. =0.536, p=0.061). The cup angles had no influence on the shift of the HRC, but a high variability in cup anteversion (20.7° to 61.8°) was observed. DISCUSSION. The study suggests that increasing the press-fit and polar gap improves the restoration of the anatomical HRC. Since increasing the degree of press-fit could also lead to higher stresses and an increased fracture risk, future work will study how the acetabular contact conditions influence both primary implant stability and fracture risk, in order to establish an optimal HRC reconstruction to maximize implant longevity

Background. Radial head arthroplasty (RHA) is a popular method of treatment for complex fractures of the radial head. The purpose of this study was to investigate patient outcomes and radiographic findings associated with a single anatomical monopolar press-fit radial head system commonly used for the treatment of radial head fractures. Methods. A retrospective review of prospectively collected data was performed for a consecutive series of patients treated with RHA between November 2007 and April 2014. Patients with a minimum of 12-month follow-up were included. Most recent radiographs were evaluated for loosening, stress shielding, and instability. Post-operative motion and outcomes were reported at most-recent follow-up. Results. At an average follow-up of 30 months, 7 of the 17 patients (41%) demonstrated radiographic loosening. Six of the 10 patients (60%) without loosening demonstrated stress shielding (average 6mm). Functional outcome scores included a mean ASES of 74, MEPS of 87, VAS Pain of 1, VAS Function of 8 and SANE of 79. Average flexion-extension arc was 13°–138°, and average pronation-supination was 77°–76° (Figure 1). Of the patients with radiographic loosening, 86% had undergone RHA with an associated ligamentous injury of the elbow. Satisfaction among patients was high, as no patient reported an unsatisfactory outcome. Conclusions. The use of an anatomic, press-fit monopolar RHA in the management of acute complex radial head fractures has yielded excellent clinical outcomes despite high rates of radiographic loosening and stress shielding. Press-fit RHA in the setting of ligamentous injury warrants further investigation due to a high rate of implant loosening observed

Introduction. Modeling the press-fit that occurs in Total Hip Arthroplasty (THA) cementless implants is crucial for the prediction of micromotion using finite element analysis (FEA). Some studies investigated the effect of the press-fit magnitude and found a direct influence on the micromotion [1,2]. They assumed in their model that press-fit occurs throughout the prosthesis. However [3] found using computed tomography measurement that only 43% of the stem-bone interfaces is really in contact. The aim of this study is to investigate the press-fit effect at the stem-bone interface on the implant micromotion. Methods. Finite element analysis (FEA) was performed on a Profemur® TL implanted into a Sawbones®. The implant orientation was validated in a previous study [4]. All materials were defined as linear isotropic homogeneous. FEA was carried out for the static loading conditions defined by [5] simulating walking fastly. Frictional contact between the bone and the prosthesis was assumed all along the prosthesis with a coefficient μ set to 0, 63 for the plasma spray (Fig. 1a) and 0,39 for the polished surface (Fig. 1b) [6]. Firstly, FEA was performed without press-fit (Fig. 2a) and then press-fit was simulated with an interference of 0,05 mm [2] between stem and bone in specific areas: superior (Fig. 2b), intermediate (Fig. 2c), inferior (Fig. 2d), and cortical alone (Fig. 2e) and finally over the entire surface in contact with the bone. The press-fit effect at the stem-bone interface on the micromotion was investigated. Measurement of the micromotion was realised on different points located on the plasma spray surface by calculating the difference between the final displacement of the prosthesis and the final displacement of the bone. Results. When press-fit is applied along the entire stem-bone interface, micromotion is lower than 10 μm. In the case when no press fit is simulated, micromotion is in the range of 11 μm and 48 μm. When press-fit is included where only cortical bone is (small areas mid-way proximal and medial part), micromotion is in the range of 17 μm and 30 μm. When the press-fit is included where inferior cancellous bone is (more distal), micromotion is between 9 μm and 38 μm. When the press-fit is included in the intermediate cancellous bone (mid-way), micromotion is between 1 μm and 47 μm. Finally, when press-fit is involved in the superior cancellous bone (more proximal) alone, micromotion is in the range of 4 μm and 12 μm. The results are shown on Fig. 3. Discussion. The maximum stem-bone interface micromotions calculated in this study always remain lower than 50 μm. [7] shows that interfacial micromotion greater than 40 μm produces only partial ingrowth. This indicates that in our study, in all cases investigated the primary stability was not compromised. In general, press-fit increased the primary stability. Our results indicate that press-fit in the proximal area improves widely the primary stability of this prosthesis, especially if the implant is in direct contact with cortical and cancellous bone

Background. We have often experienced a change of the tone of the hammering sound during the press-fit implantation of cementless acetabular components in total hip arthroplasty (THA). The tone of the impact sound before the press-fit of acetabular components seems to differ from the tone after the press-fit. This change of tone may depend on the accuracy of the fit of the acetabular component, or it may simply be a subjective perception. The aim of this study is to evaluate the impact sounds in the press-fit implantation of cementless acetabular components. Methods. The hammering sounds in press-fit implantation of acetabular components were studied intraoperatively in 22 patients (28 hips) who underwent primary THA for treatment of advanced osteoarthritis. All operations were performed via the direct anterior approach in a supine position. The hemispherical titanium-alloy acetabular component (TriAD; stryker) was implanted in all patients. A sound level meter (NA-28; RION) was used to record and analyze the sounds. The hammering sounds of the first three hits and last three hits were recorded as the “before press-fit” and “after press-fit” sound samples, respectively. A frequency analysis was then performed at the point of peak sound pressure in each sample. Results. The dominant frequency of the impact sounds was equal to or lower than 1 kHz in 20% of the before press-fit samples and 76% of the after press-fit samples, and equal to or higher than 4 kHz in 69% of the before press-fit samples and 21% of the after press-fit samples. The frequency of the impact sounds changed significantly (p<0.01) during the press-fit implantation. Conclusion. The frequency of the impact sound changed significantly during the press-fit implantation of cementless acetabular components. We conclude that an intraoperative evaluation of the impact sound might help to improve accuracy when implanting the acetabular component

Introduction. Uncemented press-fit cups provide bone fixation in primary total hip replacement (THR). However, sometimes screws are needed to achieve primary stability of the socket. We analyzed biomechanical factors related to press-fit in seven cup designs and assessed whether screw use provides similar loosening rates to those of the press-fit technique. Materials y Methods. From a series of 1,350 primary uncemented THRs using seven different press-fit cup designs (a dome loading hemispheric cup and bi- or tri- radius cups), we only analyzed the 889 diagnosed of primary osteoarthritis. All cases were operated by the same surgical team. The use of screws was decided intraoperatively based on cup stability according to the pull-out test. There were 399 female and 490 male patients with a mean age of 65 years old. The mean follow-up was 8.6 years (5–13 years). The reconstruction of the hip rotation center was evaluated according to Ranawat. Results. Screws were required in 223 (25.1%) of the surgeries: 35% of all dome-loaded cups and less frequently with other cup designs (range 18%-24%) (p<0.001) All hips showed good clinical results and radiological bone fixation. Screws were used more frequently in women (p<0.001). Adjusted multivariate analysis revealed that female patients (p<0.001, Odds Ratio (OR): 1.98; 95% Confidence Interval (CI) 1.34–2.95), hips with one of the hemispherical cup designs (p=0.01, OR: 2.51; 95% CI 1.33–5.33) and a greater distance to the rotation hip centre (p<0.001, OR: 1.25; 95% CI 1.15–1.35) had a higher risk for screw use. Every increase of 5 mm in this distance increased the risk of screw use by three (LI=2–4.5). Conclusions. Gender, cup design and reconstruction of the rotation center of the hip determine the primary stability of the cup in uncemented THR. The use of screws, when necessary, provides similar results than the press-fit technique

Introduction. The metal-backed patella was originally designed to address shortcomings found with cemented, all-polyethylene patellae. However, complications relating to an all-polyethylene patella were reported to account for up to half of all knee revisions. At the same time, good fixation with bone ingrowth was observed in both titanium and cobalt chromium porous-coated patellae. The advantages provided by using a metal-backed patella, such as uniform load sharing, decreased polyethylene deformation, and potential for biological fixation, may be unjustly outweighed by the fear of patellar component failure; high rates of failure have not been inherent to all metal-backed patella designs. Over the past decade, we have used a metal-backed patella design with excellent results that may be due largely to the design features of the component. Also, we believe there are certain selection criteria that should be strictly adhered to when implanting metal-backed patellae. Correct selection criteria and improved component design strongly indicate the use of press-fit metal-backed patellae. Methods. This single-center study was designed to conduct clinical and independent radiographic review of primary metal-backed, press-fit patella patients with a minimum five-year follow-up. Potential patients were recruited from a group of existing metal-backed patella patients within the principal investigator's medical practice. All patients recruited for this study were required to have undergone primary knee replacement surgery at least five years prior to clinical and radiographic evaluation. Patients were included if they had a diagnosis of noninflammatory degenerative joint disease. Patients with a BMI >40 were excluded from this study. Radiographic analysis was conducted by an independent reviewer according to the current Knee Society Total Knee Arthroplasty Roentgenographic Evaluation and Scoring System. Any radiographs that the reviewer deemed questionable were shown to a second independent orthopaedic surgeon for review, comment, and validation of observations. Kaplan-Meier survivorship was determined for all metal-backed patellae. For survival analysis, only knees with radiographic data were included (74 knees). KSS, WOMAC, and SF-36 scores were calculated also. Results. Seventy-four patients (88 knees) were enrolled in the study, 31 women (41.2%) and 43 men (58.1%). At the time of surgery, the average age was 59.7 years (range, 40–86 years), and the average BMI was 30.6 (range, 19.1–39.6). The breakdown of patients who completed the study and those who were lost to follow-up is shown in Table 1. One metal-backed patella was revised at 49 months for loosening at the bone/implant interface. Survivorship of the metal-backed patellae at minimum five-year follow-up was estimated to be 93.95% with bounds of 73.61% and 98.74%. No radiolucencies greater than 1 mm were observed in any radiographs (Fig. 1), with the exception of the one revision case. Conclusion. Our experience with this metal-backed patella design has been excellent. Failure does not occur due to dissociation of the plastic. As the porous coating is almost under constant compression, biological fixation is assured in most instances, as confirmed by our minimum five-year radiological results. Improved component design and adherence to the correct patient selection criteria absolutely indicate the use of press-fit metal-backed patellae

Introduction. Intimate bone-implant contact is a requirement for achieving stable component fixation and osseo-integration of porous-coated implants in TKA. However, consistently attaining a press-fit and a tight-fitting femoral component can be problematic when using conventional instrumentation. We present a new robotic cutting-guide system that permits intra-operative adjustment of the femoral resections such that a specified amount of press-fit can be consistently attained. System Description: A.R.T. (Apex Robotic Technology) employs a miniature bone-mounted robotic cutting-guide and flexible software that permits the surgeon to adjust the anterior and posterior femoral resections in increments of 0.25 mm per resection, allowing a maximum of 1.5mm of total added press in the AP dimension. Methods. The accuracy of guide-positioning and bone-cutting with A.R.T. was assessed in bench testing on synthetic bones (SAWBONES®) using an optical comparator. The individual guide locations for 16 femoral cut positioning sequences (80 guide positions in total) were measured. Femoral resections were performed with A.R.T. on eight sawbones (two per fit-adjustment setting) and the anterior-posterior dimensions of the final cut surfaces were also measured. Eight sawbones were prepared using conventional instrumentation (jigs) as controls: four with a 0 mm press-fit block and four with a +0.5 mm specially manufactured press-fit block. Results. The robotic guide-positioning error in the AP dimension was −0.04 ± 0.14mm (mean ± standard deviation, SD). The standard deviation in guide positioning for the distal, anterior chamfer and posterior chamfer resections was 0.03° and 0.17mm. The average error in the AP dimension between the targeted and measured cuts was −0.14±0.13mm with A.R.T. and 0.7±0.52mm with conventional blocks (p=0.021). Conclusions. A.R.T. guide positioning precision was found to be sub-degree and sub-millimetric, allowing for significantly more accurate and repeatable bone resections than conventional instrumentation

Introduction. The use of screws is frequent for additional fixation, however, since some disadvantages have been reported a cup press-fit is desirable, although this can not always be obtained. Cup primary intraoperative fixation in uncemented total hip replacement (THR) depends on sex, acetabular shape, and surgical technique. We analyzed different factors related to primary bone fixation of five different designs in patients only diagnosed with osteoarthritis, excluding severe congenital hip disease and inflammatory arthritis, and their clinical and radiological outcome. Materials y Methods. 791 hips operated in our Institution between 2002 and 2012 were included for the analysis. All cases were operated with the same press-fit technique, and screws were used according to the pull-out test. Two screws were used if there was any movement after the mentioned manoeuvres. Acetabular and femoral radiological shapes were classified according to Dorr et al. We analyzed radiological postoperative cup position for acetabular abduction angle, the horizontal distance and the vertical distance. Cup anteversion was evaluated according to Widmer and the hip rotation centre according to Ranawat. Results. Screws were required in 155 hips (19.6%) and were more frequently used in women and patients with a type A acetabulum (p<0.001, p=0.021, respectively). There were no differences among the different cups evaluated. The need for screws was more frequent in hips with a smaller version of the cup and with a distance greater than 2 mm to the approximate femoral head centre from the centre of the prosthetic femoral head (p=0.022, 0.012, respectively). Adjusted multivariate analysis revealed that female patients (p<0.001, Odds Ratio (OR): 2.063; 95% Confidence Interval (CI) 1.409–3.020), cups with a smaller version (p=0.012, OR: 0.966, 95% CI 0.94–0.992), and a greater distance to the rotation hip center (p<0.005, OR: 1.695; 95% CI 1.173–2.450) had a higher risk for screw use. No hips needed revision for aseptic loosening. Conclusions. Cup press-fit depends on gender and surgical technique in hips without significant acetabular abnormalities or inflammatory arthritis. Contemporary uncemented cups provide similar primary fixation and mid-term outcome

Introduction. Good outcomes in reverse shoulder arthroplasty (RSA) rely in part on stability of the humeral component. Traditionally humeral components have been cemented, however there has been recent interest in press-fit fixation of humeral components in RSA. Lateralization of the head center in RSA can impart larger moments on the humeral component than for anatomic reconstructions, increasing the importance of distal humeral canal preparation for implant stability. To date, the primary stability of any type of press-fit humeral prosthesis has been largely unexplored. The goal of this study is to evaluate the effect of over-reaming the distal humeral canal in a press-fit humeral component in RSA. Methods. Computed tomography (CT) data of the shoulder were obtained from 55 shoulders. Images were segmented to produce digital models of the humerus. Humeral components for RSA (2mm diameter size increments) were sized and placed per the surgical technique, including preparation of the humerus with the appropriate reamers (1mm increments). Finite element models for each specimen were created with heterogeneous bone properties derived from the CT scan. Pressfit between the bone and stem was resolved to quantify the initial contact pressure on the stem; each stem was then loaded at 566N oriented 20° lateral and 45° anterior. Overall motion of the stem was measured, as well as interfacial micromotion in the porous coating region (Fig. 1). The effect of line-to-line (L2L) reaming and over-reaming by 1 mm was evaluated using an unpaired Student's t-test, with significance defined at p<0.05. Results. Across all specimens, stem sizes 8 (n=3), 10 (n=25), 12 (n=20), 14 (n=2), and 16 (n=1) were used. Stem motion ranged from approximately 250–750μm; micromotion remained under 300μm (Fig. 2). Stem motion was significantly less for L2L reaming as compared to over-reaming for both size 10 (p=.008) and size 12 (p=.002) stems; micromotion was significantly less for size 12 (p=.002) stems. L2L reaming to a larger diameter stem resulted in significantly reduced stem motion (average 390μm versus 530μm, p<.001) and micromotion (average 53μm versus 135μm, p=.001) than over-reaming and using a smaller diameter stem. Stem rotation following L2L reaming was generally below 0.5°, and exceeded 0.75° when over-reaming. Discussion and Conclusion. Reaming of the humeral canal directly impacts the stability of humeral stems in RSA. Even with satisfactory proximal press-fit, over-reaming enables increased rotation of the stem under functional loading prior to cortical engagement, and results in increased micromotion. In cases in which the reamer and stem offerings result in over-reaming, L2L reaming to the next larger stem significantly reduces stem motion and micromotion. However, reaming up also removes distal cortical bone, and thus the strength of the prepared humerus must be considered. In conclusion, line-to-line reaming significantly reduces the micromotion of humeral stems as compared to over-reaming

Introduction. Total hip arthroplasty has seen a transition from cemented acetabular components to press-fit porous coated components. Plasma sprayed titanium implants are often press-fit with 1mm under-reaming of the acetabulum; however, as porous coating technologies evolve, the amount of under-reaming required for initial stability may be reduced. This reduction may improve implant seating due to lowered insertion loads, and reduce the risk of intraoperative fracture. The purpose of this study was to investigate the initial fixation provided by a high porosity coating (P2, DJO Surgical), and a plasma sprayed titanium coating under rim loading with line-to-line and 1mm press-fit surgical preparation. Methods. Five, 52mm high porosity acetabular cups (60% average porosity) and five 52mm plasma sprayed titanium coated cups were inserted into low density (0.24g/cc) biomechanical test foam (Pacific Research Laboratories). Foam test material was cut into uniform 90×90×40mm blocks. Reaming was performed using standard instrumentation mounted on a vertical mill. Cups were first inserted into foam blocks prepared with line-to-line (52mm) reaming. Following mechanical testing, cups were removed from the foam, cleaned, and inserted into foam blocks prepared with 1mm under reaming (51mm). In total 4 test conditions were evaluated:. Group A: P2 + line-to-line. Group B: Plasma sprayed + line-to-line,. Group C: P2 + 1mm under-reaming. Group D: Plasma sprayed + 1mm-under reaming. Acetabular cup impaction was carried out using a single axis servohydraulic test machine (Instron 8500). Cups were inserted at 1mm/s to a load of 5kN. Insertion load was calculated as a 0.1mm offset from the linear portion of the force/displacement curve; insertion energy was the area under the curve. Tangential rim loading was applied at 0.0254mm/s by a conical indenter to the implant rim. Load data were recorded at 1kHz. Cup displacement was recorded by a 3D, marker-based tracking system at 15Hz (DMAS, Spicatek). Six markers were attached to a disk secured in the acetabular cup (Figure 1). Yield failure was defined as 0.331o of angular displacement (150µm of relative displacement). Angular displacement was derived by calculating the normal vector of a best-fit plane based on marker centroids. Results. Under-reamed groups (C,D) showed statistically higher insertion loads and insertion energies than line-to-line groups (A,B), with group C requiring the highest insertion load. Despite greater ease of insertion, groups A and B attained comparable yield loads with group A statistically outperforming D. Group C attained the highest ultimate failure loads, outperforming A and D (Figure 2). Discussion. Implants with high porosity coating and line-to-line preparation required less effort for full seating and maintained yield and ultimate performance which exceeded, or was comparable to, plasma sprayed titanium coated implants in either under-reamed or line-to-line preparation. Limitations of this study include the use of a mill for foam block preparation and automated implant insertion. Initial results in three matched cadaveric acetabular pairs with line-to-line preparation indicate that the advantages of high porosity coating may be preserved in human tissue with average yield failure and ultimate failure load improvements of 108% and 73% respectively (Figure 3). Study is ongoing

Introduction. The hip joint is subjected to cyclic loading during activities of daily living and this can induce micromotion at the bone-implant interfaces of uncemented implants. Osseointegration, which is essential for long term implant survival, will occur when micromotion at these interfaces is below 40µm and may occur up to 150µm [1]. Studies investigating the micromotion of press-fit acetabular cups only report micromotions in one direction. Standard methods also maintain a static cup position throughout testing; usually at the angle of maximum resultant force during gait. Current methods therefore do not take into account the effect of motion of the hip on micromotion of the cup, nor do they investigate all six degree of freedom (DoF) of motion. The aim of this study was to assess press-fit cup micromotion in six DoF under physiological loading when the cup is held statically and moved in flexion-extension. Methods. A cementless acetabular cup (Trident, Stryker) was implanted into polyurethane foam blocks (Sawbones, density = 0.48g/cm³) with a 1mm press-fit. The blocks were manufactured to replicate important anatomical features, which model the acetabulum (Figure 1). A six DoF measurement system was rigidly attached to the bottom of the cup through the dome screw hole and micromotion was measured using six LVDT sensors (Figure 2). The micromotion of the cup was measured under three conditions. Firstly, the cup was tested statically at 30° flexion, representing heel strike during gait; secondly, under dynamic motion simulating gait (30° flexion to −15° extension; 0.5Hz); and finally, under dynamic motion simulating stair climb (45° flexion to −15° extension; 0.5Hz) [2]. For all conditions, the cup was cyclically loaded to a peak load of 2.0kN for 1000 cycles at 1Hz. The loading cycles were synchronised with the flexion-extension movement in order to achieve a loading peak at both heel strike and toe-off positions. Results. During all of the tests, micromotions in the medial-lateral and anterior-posterior directions, and the resultant of the anterior-posterior tilt, were above 40µm (Figure 2). When tested statically, the micromotions in the medial-lateral and in the anterior-posterior directions were similar in magnitude. However, when the cup was subjected to dynamic motion, the micromotion in the anterior-posterior direction increased substantially in magnitude. It was at its highest during simulated stair climb. The anterior-posterior tilt also increased substantially under dynamic motion. Discussion and Conclusions. This study is the first to measure the micromotion in six DoF of a press-fit acetabular cup under both physiological loading conditions and dynamic hip motion. The results indicate that, compared to static tests, the micromotion of the cup increases under dynamic hip motion. Results also showed that all DoF need to be considered when investigating micromotion of the cup as substantial micromotion was seen in more than one direction. Moving forwards, future pre-clinical tests investigating micromotion of press-fit acetabular cups should include dynamic motion and measure all DoF of the cup

Introduction. Frictional torque is generated at the hip joint during normal gait loading and motion [1]. This study investigated the effect of shell deformation due to press-fit on frictional torque generated at the articulating surfaces of cementless acetabular shells that incorporated fixed and dual mobility bearing designs. Materials and Methods. Figure 1 lists the study groups (minimum of n = 5). All groups were tested with a 50 mm Trident PSL shell (Stryker Orthopaedics, NJ) and a Ti6Al4V trunnion. Metal-on-Metal specimens were custom designed and manufactured, and are not approved for clinical use. The remaining groups consisted of commercially available products (Stryker Orthopaedics, NJ). All groups were tested with the shells in deformed and undeformed states. Deformed Setup: A two-point relief configuration was created in a polyurethane foam block (Figure 2) with a density of 30 lb/ft. 3. to replicate shell deformation due to press-fit [2]. The blocks were machined to replicate the press-fit prescribed in the shell's surgical protocol. Each shell was assembled into the foam block by applying an axial force at 5 mm/min until it was completely seated. Undeformed Setup: Each shell was assembled in a stainless steel block with a hemispherical cavity that resulted in a line-to-line fit with the shell OD. Frictional torque was measured using a physiologically relevant test model [3]. In this model, the specimen block was placed in a fixture to simulate 50° abduction and 130° neck angle (Figure 2). A 2450N side load was applied and the femoral head underwent angular displacement of ± 20° for 100 cycles at 0.75 Hz. The articulating surfaces were lubricated with 25% Alpha Calf Fraction Serum. Peak torque was observed towards the end or the beginning of each cycle where the velocity of the femoral head approaches 0 and the head changes direction. This torque is referred as maximum static frictional torque. Specimen groups were statistically compared with a single-factor ANOVA test and a Tukey post-hoc test at 95% confidence level. Paired t-tests were performed to compare individual groups in deformed and undeformed states. Results. Figure 3 contains the results. In both deformed and undeformed states, the MoM group exhibited the highest frictional torque whereas the MDM group had the lowest frictional torque. In both states, the difference in frictional torque between MoM vs. 28 mm–Fixed Bearing and MoM vs. MDM was statistically significant whereas the difference between 28 mm-Fixed Bearing and MDM was not statistically significant. Shell deformation due to press-fit did not have a significant effect on any of the groups. Discussion. This study evaluated the effect of press-fit on the frictional torque generated in various cementless acetabular systems using a physiologically relevant in-vitro test model. Results from this test suggest a trend towards lower frictional torque for dual mobility bearings, which is worthy of further investigation

INTRODUCTION. Combining novel diverse population-based software with a clinically-demonstrated implant design is redefining total hip arthroplasty. This contemporary stem design utilized a large patient database of high-resolution CT bone scans in order to determine the appropriate femoral head centers and neck lengths to assist in the recreation of natural head offset, designed to restore biomechanics. There are limited studies evaluating how radiographic software utilizing reference template bone can reconstruct patient composition in a model. The purpose of this study was to examine whether the application of a modern analytics system utilizing 3D modeling technology in the development of a primary stem was successful in restoring patient biomechanics, specifically with regards to femoral offset (FO) and leg length discrepancy (LLD). METHODS. Two hundred fifty six patients in a non-randomized, post-market multicenter study across 7 sites received a primary cementless fit and fill stem. Full anteroposterior pelvis and Lauenstein cross-table lateral x-rays were collected preoperatively and at 6-weeks postoperative. Radiographic parameters including contralateral and operative FO and LLD were measured. Preoperative and postoperative FO and LLD of the operative hip were compared to the normal, native hip. Clinical outcomes including the Harris Hip Score (HHS), Lower Extremity Activity Scale (LEAS), Short Form 12 (SF12), and EuroQol 5D Score (EQ-5D) were collected preoperatively, 6 weeks postoperatively, and at 1 year. RESULTS. The mean age is 62 years old (range 32 – 75), 136 male and 120 female, BMI 29.7. The preoperative FO and LLD of the operative hip were 43.5 mm (±9.0 mm) and 3.0 mm (±6.5 mm) compared to the native contralateral hip, respectively. The postoperative FO and LLD were 46.4 mm (±8.7 mm) and 1.6 mm (±7.6 mm) compared to the native contralateral hip, respectively. The change in FO on the operative side was 3.0 mm (±7.2 mm) (p<0.0001) and the change in LLD from preoperative to 6-weeks postoperative was 1.6 mm (±8.4 mm) (p=0.0052) (Figure 1), demonstrating the ability of this stem design to recreate normal hip biomechanics in this study. The HHS increased considerably from a preoperative score of 55.9 to 78.4 at 6 weeks and 92.7 at 1 year. Clinically significant improvements were also seen at 1 year in the LEAS (+2.3), SF12 PCS (+16.3), and EQ-5D TTO (+0.26) and the EQ-5D VAS (+15.7). DISCUSSION and CONCLUSION. This study demonstrated that recreation of normal anatomic leg length and offset is possible by utilizing a modern fit and fill stem that was designed by employing an advanced anthropomorphic database of CT scans. We hypothesize that when surgeons utilize this current fit and fill stem design, it will allow them to accurately recreate a patient's natural FO and leg length, assisting in the restoration of patient biomechanics. Summary Sentence. In this study, modern design methods of a press-fit stem using 3D modeling tools recreated natural femoral offset and leg length, assisting in the restoration of patient biomechanics

Introduction. We have carried out a 15 year survival analysis of a prospective, randomised trial comparing cemented with cementless fixation of press-fit condylar primary total knee replacements. Methods. A consecutive series of 501 PFC knee replacements received either cemented (219 patients, 277 implants) or cementless (177 patients, 224 implants) fixation. No patients were lost to follow up. Revision was defined as further surgery, irrespective of indication, that involved replacement of any of the three originally inserted components (Femur, Tibia, Patella). Results. Altogether 44 patients underwent revision surgery (24 cemented group Vs 20 cementless group). 11 cases were revised secondary to infection (7 cemented, 4 cementless, mean time to revision=5.1 years) and 26 were revised due to aseptic loosening (14 cemented, 12 cementless, mean time to revision=9.2 years). 7 cases were revised for other reasons (Instability, Anterior knee pain, polyethylene wear, patellar malallignment). For cemented knees 15-year survival=80.7% (95%CI, 71.5-87.4), 10-year survival=91.7 (95%CI, 87.1-94.8). For cemented knees 15-year survival=75.3% (95% CI, 63.5-84.3), 10-year survival=93.3% (95%CI, 88.4-96.2). When comparing the covariates (operation, sex, age, diagnosis, side), there was no significant difference between operation type (Hazard ratio=0.83 (95%CI, 0.45-1.52) p=0.545), side of operation (HR=0.58 (95%CI, 0.32-1.05) p=0.072), age (HR=0.97 (95%CI, 0.93-1.01) p=0.097), diagnosis (OA vs non OA, (HR=1.25 (95%CI, 0.38-4.12) p=0.718). However, there was a significant gender difference (Males vs Females, HR=2.48 (95%CI, 1.34-4.61) p=0.004). Conclusion. This single surgeon series, with no loss to follow up, provides reliable data of the revision rates of the most commonly used total knee replacement. The survival of the press-fit condylar total knee replacement remains good at 15 years irrespective of the method of fixation. This information is useful for strategic health authorities when establishing future requirements for revision knee surgery

Introduction. Although total hip replacement (THR) has been described as the operation of the century, there is still room for improvement. There is therefore continued effort for advanced implants and bearing surfaces, moreover so, for the younger patient with a longer life expectancy and increased needs. Objectives. This prospective case-series study aims to present the preliminary, minimum three-years, results of a novel uncemeted stem, the Leader StemÒ (Vadin Implants Ltd, London, U.K.). The Leader StemÒ is a titanium, tapered stem for immediate three-point fixation. There is a metaphyseal porous-coating with titanium microspheres for bone in-growth. It has anti-rotational ribs in the metaphyseal - diaphyseal junction to promote initial stability and a grit blasted diaphyseal region for bone on-growth. The distal tip is polished and shortened to minimize thigh pain, while the whole design and concept is one to eradicate stress shielding. Methods. Between June 2010 and May 2012 we operated on 20 males and 29 female patients (53 THRs, mean age 66±13 years). The diagnosis was osteoarthritis in 39 patients (41 THRs), developmental dysplasia in six patients (eight THRs), avascular necrosis in two patients (two THRs) and chondrolysis in two patients (two THRs). Operations were performed by the posterior approach by two hip surgeons. The bearing surface was ceramic on ceramic in six patients (eight THRs), metal on polyethylene in 22 patients (22 THRs) and ceramic on polyethylene in 21 patients (23 THRs). Patients' demographic data, Harris Hip Scores (HHS) and Oxford Hip Scores (OHS) were collected prospectively, preoperatively, postoperatively, and at six months intervals thereafter. Radiographic evaluation was performed on standard anteroposterior and lateral X-rays at the same time intervals. Results. At last follow-up, mean 50 months after surgery, no revision for any reason has been reported. Six patients were lost to follow-up and one deceased three years post-operatively from an unrelated reason with a stable and untroubled prosthesis. There was one periprosthetic fracture two years after the initial operation but with a stable prosthesis, which was treated with open reduction – internal fixation. Three patients had complained of thigh pain, which had resolved at last follow up. At the most recent follow-up, the average HHS improved from 33.9±13.6 preoperatively to 89.35±12.72 and OHS from 12.7±5.6 to 41.6±7.2. No clinical score was significantly correlated to any demographic index, but the latest HHS was well correlated to the pre-operative score (R=0.41, p=0.007). Radiographically, no radiolucent lines in any of the Gruen zones and no stem subsidence were observed at any time interval, while cortical hypertrophy was observed at the diaphyseal zone in two patients. Conclusions. This study showed that this new press-fit stem design had excellent short-term clinical and radiological results in all followed-up patients, irrespective of their age, gender, and body mass index. Longer follow-up is needed to evaluate its long-term survival and effectiveness