Roentgen Stereophotogrammetric Analysis (RSA) is the gold standard for measuring implant micromotion thereby predicting implant loosening. Early migration has been associated with the risk of long-term clinical failure. We used RSA to assess the stability of the Australian designed cementless hip stem (Paragon TM) and now report our 5-year results. Fifty-three patients were prospectively and consecutively enrolled to receive a Paragon hip replacement. Tantalum beads were inserted into the bone as per RSA protocol and in the implant. RSA x-rays were taken at baseline 1–4 days post-surgery, at 6 weeks, 6 months, 12 months, 2 years, and 5 years. RSA was completed by an experienced, independent assessor. We reported the 2-year results on 46 hips (ANZJS 91 (3) March 2021 p398) and now present the 5-year results on 27 hips. From the 2-year cohort 5 patients had died, 8 patients were uncontactable, 1 patient was too unwell to attend, 5 patients had relocated too far away and declined. At 5 years the mean axial subsidence of the stem was 0.66mm (0.05 to 2.96); the mean rotation into retroversion was 0.49˚ (−0.78˚ to 2.09˚), rotation of the stem into valgus was −0.23˚ (−0.627˚ to 1.56˚). There was no detectable increase in subsidence or rotation between 6 weeks and 5 years. We compared our data to that published for the Corail cementless stem and a similar pattern of migration was noted, however greater rotational stability was achieved with the Paragon stem over a comparable follow-up period. The RSA results confirm that any minor motion of the Paragon cementless stem occurs in the first 6 weeks after which there is sustained stability for the next 5 years. The combination of a bi-planar wedge and transverse rectangular geometry provide excellent implant stability that is comparable to or better than other leading cementless stems

Aim. Debridement and implant retention (DAIR) is a valuable option for treating periprosthetic joint infection (PJI), provided that the criteria of the Infectious Diseases Society of America guidelines are fulfilled. The inflammation caused by infection and the surgical impact of DAIR may influence implant stability. In this study, we investigated the sequelae of DAIR on implant survival after total hip arthroplasty (THA). Method. THAs from our database implanted between 1984 and 2016 were included in a retrospective double-cohort study. THAs were exposed (DAIR cohort) or not exposed to DAIR (control cohort). The control cohort comprised patients matched 3:1 to the DAIR cohort. The outcome—implant failure over time—was evaluated for (i) revision for any reason, (ii) aseptic loosening of any component, and (iii) radiographic evidence of loosening. Results. Fifty-seven THAs (56 patients) were included in the DAIR cohort and 170 THAs (168 patients) in the control cohort. The mean follow-up periods in the DAIR and control cohorts were 6.1 (SD 4.7) and 7.8 (SD 5.5) years, respectively. During follow-up, 20 (36%) patients in the DAIR cohort and 54 (32%) in the control cohort died after a mean of 4.1 (SD 4.7) and 7.2 (SD 5.4) years, respectively. Revision for any reason was performed in 9 (16%) DAIR THAs and 10 (6%) control THAs (p = 0.03) and for aseptic loosening of any component in 5 (9%) DAIR THAs and 8 (5%, p = 0.32) control THAs, respectively. Radiological analysis included 56 DAIR THAs and 168 control THAs. Two (4%) stems and 2 (4%) cups in the DAIR cohort and 7 (4%) and 1 (0.6%) in the control cohort, respectively, demonstrated radiological signs of failure (p = 1). Conclusions. THAs exposed to DAIR were revised for any reason more frequently than were THAs in the control cohort. The difference in revisions for aseptic loosening was not statistically significant. There was no statistically significant difference in radiographic evidence of loosening of any component between cohorts

Patients undergoing revision surgery of a primary total hip arthroplasty often exhibit bone loss and poor bone quality, which make achieving stable fixation and osseointegration challenging. Implant components coated in porous metals are used clinically to improve mechanical stability and encourage bone in-growth. We compared ultra-porous titanium coatings, known commercially as Gription and Porocoat, in an intra-articular model by press-fitting coated cylindrical implants into ovine femoral condyles and evaluating bone in-growth and fixation strength 4, 8 and 16 weeks post-operatively.

Bilateral surgery using a mini-arthrotomy approach was performed on twenty-four Dorset-Rideau Arcott rams (3.4 ± 0.8 years old, 84.8 ± 9.3 kg) with Institutional Animal Care Committee approval in accordance with the Canadian Council on Animal Care. Cylindrical implants, 6.2 mm in diameter by 10 mm in length with surface radius of curvature of 35 mm, were composed of a titanium substrate coated in either Porocoat or Gription and press-fit into 6 mm diameter recipient holes in the weight-bearing regions of the medial (MFC) and lateral (LFC) femoral condyles. Each sheep received 4 implants; two Gription in one stifle (knee) and two Porocoat in the contralateral joint. Biomechanical push-out tests (Instron ElectroPuls E10000) were performed on LFCs, where implants were pushed out relative to the condyle at a rate of 2 mm/min. Force and displacement data were used to calculate force and displacement at failure, stiffness, energy, stress, strain, elastic modulus, and toughness. MFCs were fixed in 70% ethanol, processed undecalcified, and polished sections, approximately 70 µm thick (Exakt Micro Grinding system) were carbon-coated. Backscattered electron images were collected on a scanning electron microscope (Hitachi SU3500) at 5 kV and working distance of 5 mm. Bone in-growth within the porous coating was quantified using software (ImageJ). Statistical comparisons were made using a two-way ANOVA and Fisher's LSD post-hoc test (Statistica v.8).

Biomechanical evaluation of the bone-implant interface revealed that by 16 weeks, Gription-coated implants exhibited higher force (2455±1362 N vs. 1002±1466 N, p=0.046) and stress (12.60±6.99 MPa vs. 5.14±7.53 MPa, p=0.046) at failure, and trended towards higher stiffness (11510±7645 N/mm vs. 5010±8374 N/mm, p=.061) and modulus of elasticity (591±392 MPa vs. 256±431 MPa, p=0.61). Similarly, by 16 weeks, bone in-growth in Gription-coated implants was approximately double that measured in Porocoat (6.73±3.86 % vs. 3.22±1.52 %, p=0.045). No statistically significant differences were detected at either 4 nor 8 weeks, however, qualitative observations of the exposed bone-implant interface, made following push-out testing, showed more bony material consistently adhered to Gription compared to Porocoat at all three time points. High variability is attributed to implant placement, resulting from the small visual window afforded during surgery, unique curvatures of the condyles, and presence of the extensor digitorum longus tendon which limited access to the LFC.

Ultra-porous titanium coatings, know commercially as Gription and Porocoat, were compared for the first time in a challenging intra-articular ovine model. Gription provided superior fixation strength and bone in-growth, suggesting it may be beneficial in hip replacement surgeries where bone stock quality and quantity may be compromised.

Glenoid bone grafting in reverse total shoulder arthroplasty (RTSA) has emerged as an effective method of restoring bone stock in the presence of complex glenoid bone loss, yet there is limited published evidence on efficacy. The aim of this study was to conduct an analysis of clinical and radiographic outcomes associated with glenoid bone grafting in primary RTSA. Patients who underwent a primary RTSA with glenoid bone grafting were retrospectively identified from the databases of two senior shoulder surgeons. Inclusion criteria included minimum of 12 months clinical and/or radiographical follow up. Patients underwent preoperative clinical and radiographic assessment. Graft characteristics (source, type, preparation), range of movement (ROM), patient-reported outcome measures (Oxford Shoulder Scores [OSS]), and complications were recorded. Radiographic imaging was used to analyse implant stability, graft incorporation, and notching by two independent reviewers. Between 2013 and 2021, a total of 53 primary RTSA procedures (48 patients) with glenoid bone grafting were identified. Humeral head autograft was used in 51 (96%) of cases. Femoral head allograft was utilised in two cases. Depending on the morphology of glenoid bone loss, a combination of structural (corticocancellous) and non-structural (cancellous) grafts were used to restore glenoid bone stock and the joint line. All grafts were incorporated at review. The mean post-operative OSS was significantly higher than the pre-operative OSS (40 vs. 22, p < 0.001). ROM was significantly improved post-operatively. One patient is being investigated for residual activity-related shoulder pain. This patient also experienced scapular notching resulting in the fracturing of the inferior screw. One patient experienced recurrent dislocations but was not revised. Overall, at short term follow up, glenoid bone grafting was effective in addressing glenoid bone loss with excellent functional and clinical outcomes when used for complex bone loss in primary RTSA. The graft incorporation rate was high, with an associated low complication rate

Gram-negative prosthetic joint infections (GN-PJI) present unique challenges in management due to their distinct pathogenesis of biofilm formation on implant surfaces. To date, there are no animal models that can fully recapitulate how a biofilm is challenged in vivo in the setting of GN-PJI. The purpose of this study is to establish a clinically representative GN-PJI in vivo model that can reliably depict biofilm formation on titanium implant surface. We hypothesized that the biofilm formation on the implant surface would affect the ability of the implant to be osseointegrated. The model was developed using a 3D-printed, medical-grade titanium (Ti-6Al-4V), monoblock, cementless hemiarthroplasty hip implant. This implant was used to replace the femoral head of a Sprague-Dawley rat using a posterior surgical approach. To induce PJI, two bioluminescent Pseudomonas aeruginosa (PA) strains were utilized: a reference strain (PA14-lux) and a mutant strain that is defective in biofilm formation (DflgK-lux). PJI development and biofilm formation was quantitatively assessed in vivo using the in vivo imaging system (IVIS), and in vitro using the viable colony count of the bacterial load on implant surface. Magnetic Resonance Imaging (MRI) was acquired to assess the involvement of periprosthetic tissue in vivo, and the field emission scanning electron microscopy (FE-SEM) of the explanted implants was used to visualize the biofilm formation at the bone-implant interface. The implant stability, as an outcome, was directly assessed by quantifying the osseointegration using microCT scans of the extracted femurs with retained implants in vitro, and indirectly assessed by identifying the gait pattern changes using DigiGaitTM system in vivo. A localized prosthetic infection was reliably established within the hip joint and was followed by IVIS in real-time. There was a quantitative and qualitative difference in the bacterial load and biofilm formation between PA14 and DflgK. This difference in the ability to persist in the model between the two strains was reflected on the gait pattern and implant osseointegration. We developed a novel uncemented hip hemiarthroplasty GN-PJI rat model. This model is clinically representative since animals can bear weight on the implant. PJI was detected by various modalities. In addition, biofilm formation correlated with implant function and stability. In conclusion, the proposed in vivo GN-PJI model will allow for more reliable testing of novel biofilm-targeting therapetics

Introduction. Gram-negative prosthetic joint infections (GN-PJI) present unique challenges in management due to their distinct pathogenesis of biofilm formation on implant surfaces. The purpose of this study is to establish a clinically representative GN-PJI model that can reliably recapitulate biofilm formation on titanium implant surface in vivo. We hypothesized that biofilm formation on an implant surface will affect its ability to osseointegrate. Methods. The model was developed using 3D-printed titanium hip implants, to replace the femoral head of male Sprague-Dawley rats. GN-PJI was induced using two bioluminescent Pseudomonas aeruginosa strains: a reference strain (PA14-lux) and a mutant biofilm-defective strain (ΔflgK-lux). Infection was monitored in real-time using the in vivo imaging system (IVIS) and Magnetic Resonance Imaging (MRI). Bacterial loads on implant surface and in periprosthetic tissues were quantified utilizing viable-colony-count. Field-emission scanning-electron-microscopy of the explanted implants was used to visualize the biofilm formation at the bone-implant-interface. The implant stability, as an outcome, was directly assessed by quantifying the osseointegration in vitro using microCT scan, and indirectly assessed by identifying the gait pattern changes using DigiGait. TM. system in vivo. Results. Localized infection was established within the hip joint and was followed by IVIS in real-time. There was a quantitative and qualitative difference in the bacterial load and biofilm formation between PA14-lux and ΔflgK-lux. This difference in the ability to persist in the model between the two strains was reflected in the gait pattern and implant osseointegration. Conclusions. We developed a novel uncemented hip hemiarthroplasty, GN-PJI rat model. To date, the proposed in vivo biofilm-based model is the most clinically representative for GN-PJI since animals can bear weight on the implant and poor osseointegration correlates with biofilm formation. In addition, localized PJI was detected by various modalities. Clinical Relevance. The proposed in vivo GN-PJI model will allow for more reliable testing of novel biofilm-targeting therapeutics

Introduction. Loosening of the baseplate is one of the most common causes of failure in Reverse Shoulder Arthroplasty. To allow osteo-integration to occur and thus provide long-term stability, initial screws fixation plays a pivotal role. In particular, tightening torque and force of nonlocking screws are two parameters that are considered to have a clear impact on implant stability, yet the relation is not fully understood. For this reason, this study aims to define an experimental set-up, to measure force and torque in artificial bone samples of different quality, in order to estimate ranges of optimal surgical values and give guidelines to maximize screw fixation and therefore initial implant stability. Methods. A custom-made torque sensor (Figure 1a) was built and calibrated using a lever deadweight system. To measure the compression force generated by the screw head, three thin FlexiForce sensors (Tekscan, South Boston, US) were enclosed between two 3D printed plates with a central hole to allow screw insertion (Figure 1b). The tightening force, represented by the sum of the three sensors, was calibrated using a uniaxial testing machine (Zwick/Roell, Ulm, Germany). Multiple screw lengths (26mm, 32mm and 47mm) were selected in the protocol. Synthetic bone blocks (Sawbones; Malmö, Sweden) of 20 and 30 PCF were used to account for bone quality variation. To evaluate the effect of a cortical bone layer, for each density three blocks were considered with 0 mm (no layer), 1.5 mm and 3 mm of laminate foam of 50 PCF. The holes for the screws were pre-drilled in the same way as in the operation room. For each combination of screw dimensions and bone quality, ten measurements were performed by acquiring the signal of the insertion torque and tightening force until bone breaking. Results. The typical output signal shows a maximum in the torque and force measurements, corresponding to bone breaking. After failure, a drop in the torque is visible, while a residual force remains present. For the base case (20 PCF), both torque and force show increasing mean values with longer screws, passing from 0.39 Nm (26mm) to 1.12 Nm (47mm) and from 180 N (26mm) to 419 N (47mm) respectively. Similar patterns were observed when the cortical layer was present or the bone quality was increased. Discussion. The findings of this study demonstrate that tightening force and torque are strongly impacted by bone quality and screw length. As main outcome, the maximum torque values could be used in clinical practice as a safety threshold for the surgeon. Compression force could also be used as input parameter in stability predictions of numerical models. Since only bone substitute was used, future research should include the extension to cadaveric bones. For any figures or tables, please contact authors directly

Implant loosening is one of the primary mechanisms of failure for hip, knee, ankle and shoulder arthroplasty. Many established implant fixation surfaces exist to achieve implant stability and fixation. More recently, additive manufacturing technology has offered exciting new possibilities for implant design such as large, open, porous structures that could encourage bony ingrowth into the implant and improve long-term implant fixation. Indeed, many implant manufacturers are exploiting this technology for their latest hip or knee arthroplasty implants. The purpose of this research is to investigate if the design freedoms offered by additive manufacturing could also be used to improve initial implant stability – a precursor to successful long-term fixation. This would enable fixation equivalent to current technology, but with lower profile fixation features, thus being less invasive, bone conserving and easier to revise. 250 cylindrical specimens with different fixation features were built in Ti6Al4V alloy using a Renishaw AM250 additive manufacturing machine, along with 14 specimens with a surface roughness similar to a conventional titanium fixation surface. Pegs were then pushed into interference fit holes in a synthetic bone material using a dual-axis materials testing machine equipped with a load/torque-cell (figure 1). Specimens were then either pulled-out of the bone, or rotated about their cylindrical axis before being pulled out to quantify their ability to influence initial implant stability. It was found that additively manufactured fixation features could favourably influence push-in/pull-out stability in one of two-ways: firstly the fixation features could be used to increase the amount pull-out force required to remove the peg from the bone. It was found that the optimum fixation feature for maximising pull-out load required a pull-out load of 320 N which was 6× greater than the least optimum design (54 N) and nearly 3× the maximum achieved with the conventional surface (120 N). Secondly, fixation features could also be used to decrease the amount of force required to insert the implant into bone whilst improving fixation (figure 2). Indeed, for some designs the ratio of push-in to pull-out was as high as 2.5, which is a dramatic improvement on current fixation surface technology, which typically achieved a ratio between 0.3–0.6 depending on the level of interference fit. It was also found that the additively manufactured fixation features could influence the level of rotational stability with the optimum design resisting 3× more rotational torque compared to the least optimum design. It is concluded that additive manufacturing technology could be used to improve initial implant stability either by increasing the anchoring force in bone, or by reducing the force required to insert an implant whilst maintaining a fixed level of fixation. This defines a new set of rules for implant fixation using smaller low profile features, which are required for minimally invasive device design

Introduction. The fixation of press-fit orthopaedic devices depends on the mechanical properties of the bone that is in contact with the implants. During the press-fit implantation, bone is compacted and permanently deformed, finally resulting in the mechanical interlock between implant and bone. For the development and design of new devices, it is imperative to understand these non-linear interactions. One way to investigate primary fixation is by using computational models based on Finite Element (FE) analysis. However, for a successful simulation, a proper material model is necessary that accurately captures the non-linear response of the bone. In the current study, we combined experimental testing with FE modeling to establish a Crushable Foam model (CFM) to represent the non-linear bone biomechanics that influences implant fixation. Methods. Mechanical testing of human tibial trabecular bone was done under uniaxial and confined compression configurations. We examined 62 human trabecular bone samples taken from 8 different cadaveric tibiae to obtain all the required parameters defining the CFM, dependent on local bone mineral density (BMD). The derived constitutive rule was subsequently applied using an in-house subroutine to the FE models of the bone specimens, to compare the model predictions against the experimental results. Results. The crushable foam model provided an accurate simulation of the experimental compression test, and was able to replicate the ultimate compression strength measured in the experiments [Figure 1]. The CFM was able to simulate the post-failure behavior that was observed in the experimental specimens up to strain levels of 50% [Figure 2]. Also, the distribution of yield strains and permanent displacement was qualitatively very similar to the experimental deformation of the bone specimens [Figure 3]. Conclusion. The crushable foam model developed in the current study was able to accurately replicate the mechanical behavior of the human trabecular bone under compression loading beyond the yield point. This advanced bone model enables realistic simulations of the primary fixation of orthopaedic devices, allowing for the analysis of the influence of interference fit and frictional properties on implant stability. In addition, the model is suitable for failure analysis of reconstructions, such as the tibial collapse of total knee arthroplasty. For any figures or tables, please contact the authors directly

Introduction. Although cementless press-fit femoral total knee arthroplasty (TKA) components are routinely used in clinical practice, the effect of the interference fit on primary stability is still not well understood. Intuitively, one would expect that a thicker coating and a higher surface roughness lead to a superior fixation. However, during implant insertion, a thicker coating can introduce more damage to the underlying bone, which could adversely influence the primary fixation. Therefore, in the current study, the effect of coating thickness and roughness on primary stability was investigated by measuring the micromotions at the bone-implant interface with experimental testing. Methods. A previous experimental set-up was used to test 6 pairs of human cadaveric femurs (47–60 years, 5 females) implanted with two femoral component designs with either the standard e.motion (Total Knee System, B. Braun, Germany) interference fit of 350 µm (right femurs) or a novel, thicker interference fit of 700 µm (left femurs). The specimens were placed in a MTS machine (Figure 1) and subjected to the peak loads of normal gait (1960N) and squat (1935N), based on the Orthoload dataset for Average 75. Varus/valgus moments were incorporated by applying the loads at an offset relative to the center of the implants, leading to a physiological mediolateral load distribution. Under these loads, micromotions at the implant-bone interface were measured using Digital Image Correlation (DIC) at different regions of interest (ROIs – Figure 1). In addition, DIC was used to measure opening and closing of the implant-bone interface in the same ROIs. Results. After comparing the micromotions and opening of the two implant designs, we found no significant differences between the standard and novel coating. Loading was a significant factor for both opening (P<0.0001) and micromotions (P=0.019), where the squat produced higher micromotions than gait. Opening was seen anteriorly (MA, LA), and was higher during squat. Closing was noticed distally (MD, LD), particularly during gait (Figure 2). During gait (Figure 3), the highest micromotions were found in the posterior condyles (CM, MP), followed by the medial anterior region (MA). For squat, the largest micromotions were in the anterior flange (ANT), followed by the distal regions (LD, MD). Discussion. In the current study, the primary stability of the same implant with two different coating thicknesses was evaluated. The results demonstrate that increasing the coating thickness does not automatically influence the primary stability of a femoral TKA component. This is likely due to abrasion and damage of the underlying trabecular during implant insertion, which also was observed in previous experiments. The exact relation between coating thickness or interference fit and primary implant stability still remains subject to debate. Obviously, the primary implant stability is compromised when the interference fit is too low. However, the current results suggest that there is a threshold beyond which further improvement of the fixation is not possible. The exact magnitude of this threshold is unknown, and may depend on coating characteristics and bone quality, and requires further evaluation, possibly utilizing a hybrid approach of experimental and computational techniques

Introduction. Trabecular Titanium is a biomaterial characterized by a regular three-dimensional hexagonal cell structure imitating trabecular bone morphology. Components are built via Electron Beam Melting technology in aone- step additive manufacturing process. This biomaterial combines the proven mechanical properties of Titanium with the elastic modulus provided by its cellular solid structure (Regis 2015 MRS Bulletin). Several in vitro studies reported promising outcomes on its osteoinductive and osteoconductive properties: Trabecular Titanium showed to significantly affect osteoblast attachment and proliferation while inhibiting osteoclastogenesis (Gastaldi 2010 J Biomed Mater Res A, Sollazzo 2011 ISRN Mater Sci); human adipose stem cells were able to adhere, proliferate and differentiate into an osteoblast-like phenotype in absence of osteogenic factors (Benazzo 2014 J Biomed Mater Res A). Furthermore, in vivo histological and histomorphometric analysis in a sheep model indicated that it provided bone in-growth in cancellous (+68%) and cortical bone (+87%) (Devine 2012 JBJS). A multicentre prospective study was performed to assess mid-term outcomes of acetabular cups in Trabecular Titanium after Total Hip Arthroplasty (THA). Methods. 89 patients (91 hips) underwent primary cementless THA. There were 46 (52%) men and 43 (48%) women, with a median (IQR) age and BMI of 67 (57–70) years and 26 (24–29) kg/m2, respectively. Diagnosis was mostly primary osteoarthritis in 80 (88%) cases. Radiographic and clinical evaluations (Harris Hip Score [HHS], SF-36) were performed preoperatively and at 7 days, 3, 6, 12, 24 and 60 months. Bone Mineral Density (BMD) was determined by dual-emission X-ray absorptiometry (DEXA) according to DeLee &Charnley 3 Regions of Interest (ROI) postoperatively at the same time-points using as baseline the measureat 1 week. Statistical analysis was carried out using Wilcoxon test. Results. Median (IQR) HHS and SF-36 improved significantly from 48 (39–61) and 49 (37–62) preoperatively to 99 (96–100) and 76 (60–85) at 60 mo. (p≤0.0001). Radiographic analysis showed evident signs of bone remodelling and biological fixation, with presence of superolateral and inferomedial bone buttress, and radial trabeculae in ROI I/II. All cups resulted radiographically stable without any radiolucent lines. The macro-porous structure of this biomaterial generates a high coefficient of friction (Marin 2012 Hip Int), promoting a firm mechanical interlocking at the implant-bone interface which could be already observed in the operating room. BMD initially declined from baseline at 7 days to 6 months. Then, BMD slightly increased or stabilized in all ROIs up to 24 months, while showing evidence of partial decline over time with increasing patient' age at 60 months, although without any clinical significance in terms of patients health status or implant stability. Statistical significant correlations in terms of bone remodeling were observed between groups of patients on the basis of gender and age (p≤0.05). No revision or implant failure was reported. Conclusions. All patients reported significant improvements in quality of life, pain relief and functional recovery. Radiographic evaluation confirmed good implant stability at 60 months. These outcomes corroborate the evidence reported on these cups by orthopaedic registries and literature (Perticarini 2015 BMC Musculoskelet Disord; Bistolfi 2014 Min Ortop)

Initial stability of cementless components in bone is essential for longevity of Total Hip Replacements. Fixation is provided by press-fit: seating an implant in an under-reamed bone cavity with mallet strikes (impaction). Excessive impaction energy has been shown to increase the risk of periprosthetic fracture of bone. However, if implants are not adequately seated they may lack the stability required for bone ingrowth. Ideal fixation would maximise implant stability but would minimise peak strain in bone, reducing the risk of fracture. This in-vitro study examines the influence of impaction energy and number of seating strikes upon implant push-out force (indicating stability) and peak dynamic strain in bone substitute (indicating likelihood of fracture). The ratio of these factors is given as an indicator of successful impaction strategy. A custom drop tower with simulated hip compliance was used to seat acetabular cups in 30 Sawbone blocks with CNC milled acetabular cavities. 3 impaction energies were selected; low (0.7j), medium (4.5j) and high (14.4j), representing the wide range of values measured during surgery. Each Sawbone was instrumented with strain gauges, secured on the block surface close to the acetabular cavity (Figure 1). Strain gauge data was acquired at 50 khz with peak tensile strain recorded for each strike. An optical tracker was used to determine the polar gap between the cup and Sawbone cavity during seating. Initially 10 strikes were used to seat each cup. Tracking data were then used to determine at which strike the cups progressed less than 10% of the final polar gap. This value was taken as number of strikes to complete seating. Tests were repeated with fresh Sawbone, striking each cup the number of times required to seat. Following each seating peak push-out forces of the cups were recorded using a compression testing machine. 10, 5 and 2 strikes were required to seat the acetabular cups for the low, medium and high energies respectively. It was found that strain in the Sawbone peaked around the number of strikes to complete seating and subsequently decreased. This trend was particularly pronounced in the high energy group. An increase in Sawbone strain during seating was observed with increasing energy (270 ± 29 µε [SD], 519 ± 91 µε and 585 ± 183 µε at low, medium and high energies respectively). The highest push-out force was achieved at medium strike energy (261 ± 46N). The ratio between push-out and strain was highest for medium strike energy (0.50 ± 0.095 N/µε). Push-out force was similar after 5 and 10 strikes for the medium energy strike. However push-out recorded at ten strikes for the high energy group was significantly lower than for 2 strikes (<40 ± 19 N, p<0.05). These results indicate that a medium strike energy with an appropriate number of seating strikes maximizes initial implant stability for a given peak bone strain. It is also shown that impaction with an excessive strike energy may greatly reduce fixation strength while inducing a very high peak dynamic strain in the bone. Surgeons should take care to avoid an excessive number of impaction strikes at high energy. For any figures or tables, please contact the authors directly

Recent introduction of short femoral implants has produced inconsistent outcomes. There have been reports of early aseptic failure as high as 30% within 2 years of implantation. This is in spite of the fact that these short components are shortened versions of existing successful non-cemented designs. The mode of initial fixation in non-cemented implants has been investigated. It has been demonstrated that long term survivability is dependent upon osseous integration; and that osseous integration requires secure initial implant fixation. Traditional non-cemented implants achieve initial fixation analogous to that of a nail in a piece of wood: friction and displacement (with resultant hoop stress). Initial fixation, of a traditional non-cemented femoral component, is directly proportional to surface area contact between the implant and endosteal bone and/or three point fixation. By reducing stem length, contact area may be significantly reduced, thereby increasing stresses over a smaller area of contact. The result of this is to potentially compromise fixation/implant stability against micromotion occurring in the early post-operative period. These stresses are most poorly resisted in flexion/extension and rotational planes about the long axis of the femur. In addition, force applied in an attempt to achieve initial fixation with a short stem may lead to an increased risk of periprosthetic fracture at the time of implantation. We propose that there is an alternative mode of initial fixation, a “rest fit”, that may avoid both the risk of femoral fracture as well as provide better initial implant stability. To assure a maximal initial fixation and resistance to post-operative stresses which may compromise initial implant stability and osseous integration, a short implant should have three distinct geometric features: a medial and lateral flare, a flat posterior surface and a proximal trapezoidal cross section. The first will provide stability against subsidence and varus migration, by resting upon the proximal femur. A flat posterior surface will maximize load transmission to the femur in flexon/extension activities; and an asymmetrical proximal cross-section will provide resistance against rotational stresses about the long axis of the femur during activities such as stairclimbing. Together these features have been throproughly evaluated by FEA and in vitro testing. We are reporting on the shoprt term follow up (2.5 years avg.) first 300 short stems which have employed a “rest fit”. There have been no aseptic failures or revisions for mechanical failure of these implants

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

Proximal humeral fractures occur frequently, with fixed angle locking plates often being used for their treatment. However, the failure rate of this fixation is high, ranging between 10 and 35%. Numerous variables are thought to affect the performance of the fixation used, including the length and configuration of screws used and the plate position. However, there is currently limited quantitative evidence to support concepts for optimal fixation. The variations in surgical techniques and human anatomy make biomechanical testing prohibitive for such investigations. Therefore, a finite element osteosynthesis test kit has been developed and validated - SystemFix. The aim of this study was to quantify the effect of variations in screw length, configuration and plate position on predicted failure risk of PHILOS plate fixation for unstable proximal humerus fractures using the test kit. Twenty-six low-density humerus models were selected and osteotomized to create a malreduced unstable three-part fracture AO/OTA 11-B3.2 with medial comminution which was virtually fixed with the PHILOS plate. In turn, four different screw lengths, twelve different screw configurations and five plate positions were simulated. Each time, three physiological loading cases were modelled, with an established finite element analysis methodology utilized to evaluate average peri-screw bone strain, this measure has been previously demonstrated to predict experimental fatigue fixation failure. All three core variables lead to significant differences in peri-screw strain magnitudes, i.e. predicted failure risk. With screw length, shortening of 4 mm in all screw lengths (the distance of the screw tips to the joint surface increasing from 4 mm to 8 mm) significantly (p < 0 .001) increased the risk of failure. In the lowest density bone, every additional screw reduced failure risk compared to the four-screw construct, whereas in more dense bone, once the sixth screw was inserted, no further significant benefit was seen (p=0.40). Screw configurations not including calcar screws, also demonstrated significant (p < 0 .001) increased risk of failure. Finally, more proximal plate positioning, compared to the suggested operative technique, was associated with reduced the predicted failure risk, especially in constructs using calcar screws, and distal positioning increased failure risk. Optimal fixation constructs were found when placing screws 4 mm from the joint surface, in configurations including calcar screws, in plates located more proximally, as these factors were associated with the greatest reduction in predicted fixation failure in 3-part unstable proximal humeral fractures. These results may help to provide practical recommendations on the implant usage for improved primary implant stability and may lead to better healing outcomes for osteoporotic proximal fracture patients. Whilst prospective clinical confirmation is required, using this validated computational tool kit enables the discovery of findings otherwise hidden by the variation and prohibitive costs of appropriately powered biomechanical studies using human samples

Introduction. Total Hip Arthroplasty (THA) is currently one of the most widely performed surgical procedures in clinical orthopaedic practice. Despite the recorded number of uncemented implants has steadily increased in recent years, cemented fixation still remains the benchmark in THA, accounting for most of the procedures performed nowadays. The Friendly Short is a novel cemented short-stem that grants a less invasive and more bone conservative approach due to its shortened height and innovative cementing technique. It is indicated to treat elderly patients with the aim of preserving bone diaphysis while decreasing postoperative recovery times. Its instrument set allows to optimize the cement mantle thickness via an improved pressurization and stem centralization system. Objectives. Aim of this prospective study was to evaluate functional recovery and implant stability after THA with this cemented short-stem. Methods. Between June 2011 and October 2012, 96 consecutive patients (100 hips) underwent THA with the Friendly Short stem (Lima Corporate). All patients received DELTA-PF cups with UHMWPE cross-linked liners and CoCrMo femoral heads (Lima Corporate). A minimally invasive postero-lateral surgical approach was used in all cases. There were 60 women and 36 men, with a mean age and BMI of 72.6 ± 6.2 (59–85) years and of 26.6 ± 3.9 (18.7–35.6) kg/m2. Most patients were retired (87%) and led a moderately active lifestyle (79%). Underlying pathology was mostly primary coxarthrosis (94%), followed by aseptic necrosis (AVN) (4%) and post-traumatic osteoarthritis (2%). Radiographic and clinical evaluation (Harris Hip Score HHS, Oxford Hip Score OHS) were performed preoperatively, and postoperatively, at 45 days, and at 6, 12, and 24 months. Results. Mean HHS and OHS improved from 36.0 ± 11.3 (7–57) and 10.9 ± 4.9 (0–24) preoperatively, to 96.4 ± 6.1 (78–100) and 46.5 ± 3.1 (33–48) at 2 years. Most significant improvements were recorded already at 45 days after surgery, with a mean HHS of 78.6 ± 9.9 (27–100) and a mean OHS of 34.0 ± 7.4 (18–48). Despite old age, all patients reported remarkable early recovery, especially in terms of joint functionality [Mean flexion: preoperative 77.7 ± 11.1 (40–90), 101.7 ± 8.9 (70–110) at 45 days] and pain relief [Mean HHS pain domain: preoperative 9.6 ± 4.2 (0–20), 41.4 ± 3.6 (20–44) at 45 days); mean OHS pain sub-domain: preoperative 0.2 ± 0.5 (0–4), 3.4 ± 0.8 (1–4) at 45 days)]. X-rays demonstrated good implant stability thanks to optimal cement fixation; there was only 1 case of non-progressive 1-mm radiolucent lines, but no osteolytic areas, subsidence or loosening were observed. Absence of fatigue fractures in the cement mantle proved that there was good stress distribution. Acetabular cups were all stable: only 1 case of non-progressive 1-mm radiolucent lines was reported, but no case of either sclerosis or osteolysis was observed. No revision or implant failure occurred up to 2-year follow-up. Conclusions. Clinical and patient-subjective outcomes were very satisfactory, indicating a significant early functional recovery. Although longer follow-up is required, radiographic assessment demonstrated good implant stability already at 2 years as result of this innovative cementing technique

This is a minimum 15 year follow up of a cohort of 58 patients (30 men and 28 women) who underwent 62 non-cemented THR between 1998–2000 (54 unilateral, 4 bilateral), in whom an off-the-shelf “lateral flare” femoral component was implanted. These surgeries were performed by a single surgeon and have been followed continuously by that same surgeon. The mean age at the time of surgery was 60.4 yrs (52–74). There were no exclusions for osteoporosis or type “C” femoral geometry. Although some patients have deceased during these 15 years, there have been no stem failures, revisions or impending stem revisions at the time of follow up or at the time of death in those who have passed. Two patients have undergone revision of their acetabular liner for poly wear. There have been no complaints of thigh pain; and like the results seen in other series employing this stem design, there has been no evidence of bone loss due to stress shielding or subsidence of the femoral component in any of these patients. This mid-term follow up re-affirms the dynamic tension band model of hip biomechanics, upon which the “lateral flare” design is predicated. This model predicts that the proximal lateral femur can experience compression during the gait cycle and as such can be utilized as an additional base of support upon which the femoral component can rest. Rather than relying upon a traditional “press fit” technique to achieve initial implant stability, a technique which is highly dependent upon femoral geometry, bone quality and may risk fracture on implant seating, the “lateral flare” design permits a gentler, safer and more physiologic means of achieving initial implant stability necessary for osseous integration to occur. This alterantive terchnique has been termed a “rest fit”

Background. Cementless acetabular cups rely on press-fit fixation for initial stability; an essential pre-requisite to implant longevity. Impaction is used to seat an oversized implant in a pre-prepared bone cavity, generating bone strain, and ‘grip’ on the implant. In certain cases (such as during revision) initial fixation is more difficult to obtain due to poorer bone quality. This increases the chance of loosening and instability. No current study evaluates how a surgeon's impaction technique (mallet mass, mallet velocity and number of strikes) may be used to maximise cup fixation and seating. Questions/purposes. (1) How does impaction technique affect a) bone strain & fixation and b) seating in different density bones? (2) Can an impaction technique be recommended to minimize risk of implant loosening while ensuring seating of the acetabular cup?. Methods. A custom drop tower was used to simulate surgical strikes, seating acetabular cups into a synthetic bone model (Fig. 1). Strike velocity (representing surgeon strike level) and drop mass (representing mallet mass) were varied through representative low, medium and high levels. Polar gap between the implant and bone was measured using optical tracking markers. Strain gauges were used to measure acetabular rim strain. Following seating, cup pushout force was measured in a materials testing machine. Both measurements were used to quantify the level of fixation of the implant for two conditions: For the first, the cup was optimally seated (moving no more than 0.1mm on the previous strike, representing ideal conditions); For the second the cup was impacted 10 times (excessively impacted). Repeats (N = 5) were conducted in low and high density bone; a total of 180 tests. Results. For ideally impacted cups, increasing mallet mass and velocity improved fixation and reduced polar gap. However a phenomenon of bone strain deterioration was identified if an excessive number of strikes were used to seat a cup, resulting in loss of implant fixation. This effect was most severe in low density bone (Fig. 2). For high strike velocity and mallet mass, each excessive strike halved the measured bone strain (78 ± 7 με/strike). This reduced fixation strength from 630 ± 65 N (optimally seated) to just 49 ± 6 N at 10 strikes (Fig. 3). Discussion. These results identify a possible mechanism of loss of implant stability with excessive acetabular impaction. A high mallet mass with low strike velocity resulted in satisfactory fixation (442 ± 38 N) and polar gap (1 ± 0.1 mm) whilst minimizing the fixation deterioration due to excessive mallet strikes. Extreme caution must be exercised to avoid excessive impaction high velocity strikes in low density bone for any mallet mass. Conclusion & Clinical relevance. As it may be difficult for a surgeon to accurately infer when an implant is optimally seated, this study informs surgeons of the effects of different impaction techniques, particularly in lower density bones. For any figures or tables, please contact the authors directly

Purpose. Although the use of stems in revision total knee arthroplasty (RTKA) enhances survival by improving the stability of implant, questions as to the optimal fixation method as well as the vertical extent of the cement, remain unanswered. This study aimed 1) to determine the correlation between the vertical extent of cement and implant loosening; and 2) to determine the minimum cementing extent for a stable implant in revision TKA with a hybrid technique. Materials and Methods. We retrospectively analyzed 109 stemmed RTKAs with average follow-up of 63 months. In each case, a single varus-valgus constrained implant was used and fixed with a hybrid technique. During surgery, stem was partially covered with cement beyond stem-implant junction. Stability of implant was evaluated according to the modified Knee Society Radiographic Scoring System. Cementing extent was defined as length from implant base to the end of the radiopaque line around the stem. The correlation between the vertical cementing extent and implant stability was analyzed, and the minimal vertical cementing extent for a stable implant was evaluated with a scatter plot. Results. The vertical cementing extent was longer in stable implants (femur: P=.002, tibia:P=.007) and the correlation between the vertical cementing extent and implant stability was significant (femur:P<.001, tibia:P=.001). Logistic regression analysis found that the risk of loosening was 8.7 times higher if the cementing extent was less than 40mm (tibia=16.1 times). The minimal vertical cementing extent for a stable implant in femur was estimated to be 65mm for middle stem (40% of total implant length) and 50mm for long stem (25% of total implant length). For tibia, it was 55mm for middle stem (45% of total implant length) and 40mm for long stem (25% of total implant length). Conclusion. We confirmed that a negative correlation exists between the radiolucent line and the cementing extent in stemmed revision TKA with a hybrid fixation technique. We could expect a durable implant in revision TKA with a minimal vertical cementing extents and it was 65mm for the femur and 55mm for the tibia. Level of Evidence. IV, Cases series

Aims

Safety concerns surrounding osseointegration are a significant barrier to replacing socket prosthesis as the standard of care following limb amputation. While implanted osseointegrated prostheses traditionally occur in two stages, a one-stage approach has emerged. Currently, there is no existing comparison of the outcomes of these different approaches. To address safety concerns, this study sought to determine whether a one-stage osseointegration procedure is associated with fewer adverse events than the two-staged approach.