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

Aims. It is important to analyze objectively the hammering sound in cup press-fit technique in total hip arthroplasty (THA) in order to better understand the change of the sound during impaction. We hypothesized that a specific characteristic would present in a hammering sound with successful fixation. We designed the study to quantitatively investigate the acoustic characteristics during cementless cup impaction in THA. Methods. In 52 THAs performed between November 2018 and April 2022, the acoustic parameters of the hammering sound of 224 impacts of successful press-fit fixation, and 55 impacts of unsuccessful press-fit fixation, were analyzed. The successful fixation was defined if the following two criteria were met: 1) intraoperatively, the stability of the cup was retained after manual application of the torque test; and 2) at one month postoperatively, the cup showed no translation on radiograph. Each hammering sound was converted to sound pressures in 24 frequency bands by fast Fourier transform analysis. Basic patient characteristics were assessed as potential contributors to the hammering sound. Results. The median sound pressure (SP) of successful fixation at 0.5 to 1.0 kHz was higher than that of unsuccessful fixation (0.0694 (interquartile range (IQR) 0.04721 to 0.09576) vs 0.05425 (IQR 0.03047 to 0.06803), p < 0.001). The median SP of successful fixation at 3.5 to 4.0 kHz and 4.0 to 4.5 kHz was lower than that of unsuccessful fixation (0.0812 (IQR 0.05631 to 0.01161) vs 0.1233 (IQR 0.0730 to 0.1449), p < 0.001; and 0.0891 (IQR 0.0526 to 0.0891) vs 0.0885 (IQR 0.0716 to 0.1048); p < 0.001, respectively). There was a statistically significant positive relationship between body weight and SP at 0.5 to 1.0 kHz (p < 0.001). Multivariate analyses indicated that the SP at 0.5 to 1.0 kHz and 3.5 to 4.0 kHz was independently associated with the successful fixation. Conclusion. The frequency bands of 0.5 to 1.0 and 3.5 to 4.0 kHz were the key to distinguish the sound characteristics between successful and unsuccessful press-fit cup fixation. Cite this article: Bone Jt Open 2024;5(3):154–161

Aims. It is important to analyze objectively the hammering sound in cup press-fit technique in total hip arthroplasty (THA) in order to better understand the change of the sound during impaction. We hypothesized that a specific characteristic would present in a hammering sound with successful fixation. We designed the study to quantitatively investigate the acoustic characteristics during cementless cup impaction in THA. Methods. In 52 THAs performed between November 2018 and April 2022, the acoustic parameters of the hammering sound of 224 impacts of successful press-fit fixation, and 55 impacts of unsuccessful press-fit fixation, were analyzed. The successful fixation was defined if the following two criteria were met: 1) intraoperatively, the stability of the cup was retained after manual application of the torque test; and 2) at one month postoperatively, the cup showed no translation on radiograph. Each hammering sound was converted to sound pressures in 24 frequency bands by fast Fourier transform analysis. Basic patient characteristics were assessed as potential contributors to the hammering sound. Results. The median sound pressure (SP) of successful fixation at 0.5 to 1.0 kHz was higher than that of unsuccessful fixation (0.0694 (interquartile range (IQR) 0.04721 to 0.09576) vs 0.05425 (IQR 0.03047 to 0.06803), p < 0.001). The median SP of successful fixation at 3.5 to 4.0 kHz and 4.0 to 4.5 kHz was lower than that of unsuccessful fixation (0.0812 (IQR 0.05631 to 0.01161) vs 0.1233 (IQR 0.0730 to 0.1449), p < 0.001; and 0.0891 (IQR 0.0526 to 0.0891) vs 0.0885 (IQR 0.0716 to 0.1048); p < 0.001, respectively). There was a statistically significant positive relationship between body weight and SP at 0.5 to 1.0 kHz (p < 0.001). Multivariate analyses indicated that the SP at 0.5 to 1.0 kHz and 3.5 to 4.0 kHz was independently associated with the successful fixation. Conclusion. The frequency bands of 0.5 to 1.0 and 3.5 to 4.0 kHz were the key to distinguish the sound characteristics between successful and unsuccessful press-fit cup fixation. Cite this article: Bone Jt Open 2024;4(3):154–161

First-time revision acetabular components have a 36% re-revision rate at 10 years in Australia, with subsequent revisions known to have even worse results. Acetabular component migration >1mm at two years following revision THA is a surrogate for long term loosening. This study aimed to measure the migration of porous tantalum components used at revision surgery and investigate the effect of achieving press-fit and/or three-point fixation within acetabular bone. Between May 2011 and March 2018, 55 patients (56 hips; 30 female, 25 male) underwent acetabular revision THR with a porous tantalum component, with a post-operative CT scan to assess implant to host bone contact achieved and Radiostereometric Analysis (RSA) examinations on day 2, 3 months, 1 and 2 years. A porous tantalum component was used because the defects treated (Paprosky IIa:IIb:IIc:IIIa:IIIb; 2:6:8:22:18; 13 with pelvic discontinuity) were either deemed too large or in a position preventing screw fixation of an implant with low coefficient of friction. Press-fit and three-point fixation of the implant was assessed intra-operatively and on postoperative imaging. Three-point acetabular fixation was achieved in 51 hips (92%), 34 (62%) of which were press-fit. The mean implant to host bone contact achieved was 36% (range 9-71%). The majority (52/56, 93%) of components demonstrated acceptable early stability. Four components migrated >1mm proximally at two years (1.1, 3.2, 3.6 and 16.4mm). Three of these were in hips with Paprosky IIIB defects, including 2 with pelvic discontinuity. Neither press-fit nor three-point fixation was achieved for these three components and the cup to host bone contact achieved was low (30, 32 and 59%). The majority of porous tantalum components had acceptable stability at two years following revision surgery despite treating large acetabular defects and poor bone quality. Components without press-fit or three-point fixation were associated with unacceptable amounts of early migration

Aims. Periprosthetic fracture and implant loosening are two of the major reasons for revision surgery of cementless implants. Optimal implant fixation with minimal bone damage is challenging in this procedure. This pilot study investigates whether vibratory implant insertion is gentler compared to consecutive single blows for acetabular component implantation in a surrogate polyurethane (PU) model. Methods. Acetabular components (cups) were implanted into 1 mm nominal under-sized cavities in PU foams (15 and 30 per cubic foot (PCF)) using a vibratory implant insertion device and an automated impaction device for single blows. The impaction force, remaining polar gap, and lever-out moment were measured and compared between the impaction methods. Results. Impaction force was reduced by 89% and 53% for vibratory insertion in 15 and 30 PCF foams, respectively. Both methods positioned the component with polar gaps under 2 mm in 15 PCF foam. However, in 30 PCF foam, the vibratory insertion resulted in a clinically undesirable polar gap of over 2 mm. A higher lever-out moment was achieved with the consecutive single blow insertion by 42% in 15 PCF and 2.7 times higher in 30 PCF foam. Conclusion. Vibratory implant insertion may lower periprosthetic fracture risk by reducing impaction forces, particularly in low-quality bone. Achieving implant seating using vibratory insertion requires adjustment of the nominal press-fit, especially in denser bone. Further preclinical testing on real bone tissue is necessary to assess whether its viscoelasticity in combination with an adjusted press-fit can compensate for the reduced primary stability after vibratory insertion observed in this study. Cite this article: Bone Joint Res 2024;13(6):272–278

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 and Objective. The patients with a total hip arthroplasty is growing in world manly in Europe and USA, and this solution present a high success at 10years in several orthopaedic registers. The application of total press-fit hip fixation presents the most used solution, but presents some failures associated to the acetabular component fixation, associated to the load transfer and bone loss at long term. The aim of this work is to investigate the influence of different acetabular bone loss in the strain distribution in iliac bone. To evaluate implant fixation, an experimental study was performed using acetabular press-fit component simulating different acetabular bone loss and measuring the strain distribution. Materials and Methods. The experimental samples developed was based in an iliac bone model of Sawbones supplier and a acetabular component Titanium (Stryker) in a condition press-fit fixation and was implanted according surgical procedure with 45º inclination angle and 20º in the anteversion angle. Were developed five models with same initial bone, one with intact condition simulating the cartilage between bones and four with different bone loss around the acetabular component. These four models representing the evolution of bone support of acetabular components presented in the literature. The evolution of bone loss was imposed with a CAD CAM process in same iliac bone model. The models were instrumented with 5 rosettes in critical region at the cortical bone to measure the strain evolution along the process. Results. The results of strain gauges present the influence of acetabular component implantation, reducing the bone strains and presented the effect of the strain shielding. The acetabular component works as a shield in the load transfer. The critical region is the posterior region with highest principal strains and the strain effect was observed with different bone loss around acetabular component. The maximum value of principal strain was observed in the intact condition in the anterior region, with 950μ∊. In the posterior superior region, the effect of bone loss is more important presenting a reduction of 500% in the strains. The effect of bone loss is presented in the strains induced with acetabular implantation, in the first step of implantation the maximum strain was 950μ∊ and in the last model the value was 50μ∊, indicating lower press-fit fixation. Conclusions. The models developed allows study the effect of bone loss and acetabular implant fixation in the load transfer at the hip articulation. The results presented a critical region as the anterior-superior and the effect of strain shielding was observed in comparison with intact articulation. The results of press-fit fixation present a reduction of implant stability along bone loss. The process of bone fixation developed present some limitation associated to the bone adhesion in the interface, not considered. Acknowledgement. This work was supported by POCI-01-0145-FEDER-032486,– FCT, by the FEDER, with COMPETE2020 - (POCI), FCT/M

First-time revision acetabular components have a 36% re-revision rate at 10 years in Australia, with subsequent revisions known to have even worse results. Acetabular component migration >1mm at two years following revision THA is a surrogate for long term loosening. This study aimed to measure the migration of porous tantalum components used at revision surgery and investigate the effect of achieving press-fit and/or three-point fixation within acetabular bone. Between May 2011 and March 2018, 55 patients (56 hips; 30 female, 25 male) underwent acetabular revision THR with a porous tantalum component, with a post-operative CT scan to assess implant to host bone contact achieved and Radiostereometric Analysis (RSA) examinations on day 2, 3 months, 1 and 2 years. A porous tantalum component was used because the defects treated (Paprosky IIa:IIb:IIc:IIIa:IIIb; 2:6:8:22:18; 13 with pelvic discontinuity) were either deemed too large or in a position preventing screw fixation of an implant with low coefficient of friction. Press-fit and three-point fixation of the implant was assessed intra-operatively and on postoperative imaging. Three-point acetabular fixation was achieved in 51 hips (92%), 34 (62%) of which were press-fit. The mean implant to host bone contact achieved was 36% (range 9–71%). The majority (52/56, 93%) of components demonstrated acceptable early stability. Four components migrated >1mm proximally at two years (1.1, 3.2, 3.6 and 16.4mm). Three of these were in hips with Paprosky IIIB defects, including 2 with pelvic discontinuity. Neither press-fit nor three-point fixation was achieved for these three components and the cup to host bone contact achieved was low (30, 32 and 59%). The majority of porous tantalum components had acceptable stability at two years following revision surgery despite treating large acetabular defects and poor bone quality. Components without press-fit or three-point fixation were associated with unacceptable amounts of early migration

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: Uncemented proximally filling porous-coated femoral components must be designed with an optimal level of press-fit. Excessive press-fit yields higher femoral stress which can result in periprosthetic femoral fracture (PPFx), whereas insufficient femoral stress can lead to a lack of initial mechanical stability, which “is necessary to achieve bone ingrowth into the porous surface” (. Manley P.A. et. al., . J Arthroplasty. 10. :. 63. –73, . 1995. ) of the implant. An optimal press-fit design should also provide an accurate and repeatable femoral stem seating height in all patients. A battery of cadaveric tests, physical “bench-top” tests, and finite element analyses (FEA) should be used in order to both quantitatively and qualitatively optimize a femoral press-fit design. In this study, a method is proposed to quantitatively rank candidate press-fit stem designs relative to successful predicates based on stem seating height and PPFx risk by recreating impact loading applied during surgery through a controlled “bench-top” model. Methods: Three press fit candidate designs A, B & C and two clinically successful predicate proximal fit and fill stems (Secur-Fit™ Max (Fit & Fill 1) and Meridian. ®. TMZF. ®. (Fit & Fill 2), Stryker, Mahwah NJ) were evaluated. Five foam cortical shell Sawbones. ®. femur samples (Item# 1130, Pacific Research Laboratories, Inc., Vashon, WA) were prepared for each press-fit design. A stem impactor was attached to the stem and then the stem was hand inserted in the femur. Then the construct was mounted in the drop tower using a vice and initial drop height was set to generate approximately 5500 N of impaction force when fully seated. Each stem was serially impacted until stable then step loaded until PPFx occurred. The height above/below the medial resection plane was measured after each impaction. Results: All press-fit designs had an initial stable seating height within the desired range without causing PPFx, using an average impaction load of 5341 N. All of the press-fit designs required, on average, roughly a 200% increase in impact load (10925 N) to cause PPFx. The press-fit deign which ranked first based on seating height accuracy, defined as the design closest to zero at stable, was Design C at −0.02 mm countersunk. Design A with a standard deviation of 0.09 mm ranked first for repeatability, defined as the design with the smallest standard deviation at stable. Finally the press-fit design which ranked first for lowest PPFx risk, defined as the design that is most countersunk prior to PPFx, was Fit & Fill 1 at 6.30 mm countersunk. Discussion: This controlled “bench-top” impact loading model successfully showed that it can quantitatively evaluate stem seating height and PPFx risk for several different femoral press-fit designs. In order to determine the optimal design, each press-fit design was ranked with equal weight given to seating height and fracture risk. Using this test method one design alternative, press-fit Design C, ranked first as the optimal combination of seating height accuracy and consistency with a low risk of PPFx. A limitation of this impaction model is that it does not directly predict PPFx rate, it only quantifies risk of fracture. Another limitation is that this model does not simulate all of the variably that is inherent to actual patient bone types. This test is one step in a battery of tests, including cadaveric evaluation and FEA, which should be used in order to optimize a femoral press-fit design

Purpose: Endoprosthetic reconstruction of the distal femur is the preferred approach for patients undergoing resection of bone sarcomas. The traditional How-medica Modular Resection System, using a press-fit stem (HMRS or Kotz prosthesis, Stryker Orthopaedics, Mahwah, New Jersey, USA) has shown good long-term clinical success, but has also been known to incur complications such as stem fracture. The Restoration stem, as a part of the new Global Modular Resection System (GMRS, Stryker Orthopaedics, Mahwah, NJ, USA), is currently proposed for this same application. This stem has a different geometry and provides the advantage of decreased risk of fracture of the component. The goal of this study was to compare the HMRS and Restoration press-fit stems in terms of initial mechanical stability. Methods: Six matching pairs fresh frozen adult femora were obtained and prepared using a flexible canal reamer and fitted with either a Restoration or HMRS press-fit stem distally. All constructs were mechanically tested in axial compression, lateral bending, and torsion to obtain mechanical stiffness. Torque-to-failure was finally performed to determine the offset force required to clinically fail the specimen by either incurring damage to the femur, the stem, or the femur-stem interface. Results: Restoration press-fit stems results were: axial stiffness (average=1871.1 N/mm, SD=431.2), lateral stiffness (average=508.0 N/mm, SD=179.6), and torsional stiffness (average=262.3 N/mm, SD=53.2). HMRS stems achieved comparable levels: axial stiffness (average=1867.9 N/mm, SD=392.0), lateral bending stiffness (average=468.5 N/mm, SD=115.3), and torsional stiffness (average=234.9 N/mm, SD=62.4). For torque-to-failure, the applied offset forces on Restoration (average=876.3 N, SD=449.6) and HMRS (aver-age=690.5 N, SD=142.0) stems were similar. There were no statistical differences in performance between the two stem types regarding axial compression (p=0.97), lateral bending (p=0.45), or torsional stiffnesses (p=0.07). Moreover, no differences were detected between the groups when tested in torque-to-failure (p=0.37). The mechanism of torsional failure for all specimens was “spinning” (i.e. surface sliding) at the femur-stem interface. No significant damage was detected to any bones or stem devices. Conclusions: These results suggest that the Restoration and HMRS press-fit stems may be equivalent clinically in the immediate post-operative situation. Funding: Commerical funding Funding Parties: Stryker Orthopaedics

In acetabular revision press-fit cups usually are used in smaller defects and contact to the host bone should be more than 50 %. Due to the thin wall thickness and the surface design the cementless press-fit cup Allofit S has a specific characteristic during implantation. Therefore this cup was used for revision with greater acetabular defects and analysed in a prospective study. The press-fit in these cases was 4 mm and additional 2 or 3 screws into the Os ilium were used. 64 cups were were followed prospectively for 38.3 months with a minimum of 24 months and examined clinically (Harris-Hip-Score) and radiographically for migration (Method of Nunn et al.) and loosening (Method of Delee and Charnley). Corresponding to Nunn et al. and Blum et al., cup migration was defined to be a change of position greater than 3 mm or referring to Cordero-Ampuero et al. and Dickob et al. a change of inclination greater than 5 degrees. There were 25 revisions of the cup and 39 complete exchanges of the prosthesis due to 54 aseptic and 10 septic loosenings (two-step revision with spacer and cementless reimplantation). There were acetabular defects of type Paprosky 2A in 12 cases, of type 2B in 15 cases, type 2C in 19 cases, type 3A in 16 cases and type 3 B in 2 cases. The average age of the patients was 70.9 ± 8.9 years. The Harris-Hip-Score increased from 45.4 ± 14.9 points preoperatively to 81.8 ± 17.5 points one year and 82.3 ± 17.1 points two years postoperative. There was no loosing or significant migration of the cups. The Allofit S press-fit cup shows good result in cup revisions with greater acetabular defects when using a press-fit of 4 mm and additional 2 or 3 screws. In these cases it seems to be a good and cheeper alternative to specific implants like trabecular metal cups

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