INTRODUCTION. Additive manufacturing (3D printing) is used to create porous surfaces that promote bone ingrowth in an effort to improve initial stability and optimize long-term biological fixation. The acetabular cup that was studied is manufactured with titanium alloy powder via electron beam melting. Electron beam melting integrates the porous and solid substrate rather than sintering a porous coating to a solid surface. The 3D-printed acetabular cup's high surface coefficient of friction (up to 1.2), combined with its geometry, creates a predictable press-fit in the acetabulum, improving initial mechanical stability and ultimately leading to reproducible biologic fixation. The objective of this study was to evaluate the early clinical outcomes and implant fixation of this 3D-printed acetabular cup in total hip arthroplasty (THA). METHODS. Four hundred twenty-eight subjects from 8 US and international research sites underwent primary THA with the 3D-printed acetabular cup. All sites received IRB approval prior to conducting the study, and all participants signed the informed consent. Screw usage and number used during surgery were used as a surrogate measurement for initial implant fixation. Clinical performance outcomes included pre- and post-operative Harris Hip Scores (HHS) and Oxford Hip Scores (OHS), patient satisfaction, and revision assessment. 215 patients had a minimum 1-year post-operative follow-up visit. Student t-tests were used to identify significant mean differences (p<0.05). RESULTS. Acetabular screws were used in 206 of 428 cases (48.1%); 85.9% used 1 screw, 12.6% used 2 screws, and 1.5% used 3 screws. For patients with a 1-year post-operative visit, the HHS improved by 49.8 points to 91.9 from 42.1, and the OHS improved by 27.7 points to 44.4 from16.7. Patient satisfaction scores at the 1-year post-operative visit were 9.7±0.7 (n=94). There was no significant difference between genders with regard to BMI, the 1-year post-operative HHS, OHS, or patient satisfaction scores. However, the males were significantly younger (59.8 vs. 62.9 years) and had significantly higher pre-operative HHS (45.7 vs. 37.9) and OHS scores (17.8 vs. 15.3). There were 9 revisions reported. DISCUSSION. For initial implant fixation, compared to a similar, non-3D-printed acetabular cup in the same product line, the 3D-printed cup used significantly fewer screws per case (n=1 for 85.9% cases vs. n=2 for 85.7% of cases) in a fewer percentage of cases (48.1% vs. 70.4%), suggesting greater initial stability and “scratch fit”. The 3D-printed acetabular cup also displayed positive early clinical results as evidenced by the pronounced improvement in clinical outcome scores from the pre-operative visit to the 1-year post-operative visit. These 1-year improvements are better than moderate clinically important improvements reported in the literature (40.1 points for HHS). Patient satisfaction scores were also excellent (9.7/10). There were nine revisions; however, four of these were due to patient falls and one was due to infection. SIGNIFICANCE. The 3D-printed acetabular cup evaluated in this study demonstrated improved implant fixation and positive early clinical outcomes for THA

Clinically applied methods of assessing implant fixation and implant loosening are of sub-optimal precision, leading to the risk of unsecure indication of revision surgery and late recognition of bone defects. Loosening diagnosis involving measuring the eigenfrequencies of implants has its roots in the field of dentistry. The changing of the eigenfrequencies of the implant-bone-system due to the loosening state can be measured as vibrations or structure-borne sound. In research, vibrometry was studied using an external shaker to excite the femur-stem-system of total hip replacements and to measure the resulting frequencies by integrated accelerometers or by ultrasound. Since proper excitation of implant components seems a major challenge in vibrometry, we developed a non-invasive method of internal excitation creating an acoustic source directly inside the implant. In the concept proposed for clinical use, an oscillator is integrated in the implant, e.g. the femoral stem of a total hip replacement. The oscillator consists of a magnetic or magnetisable spherical body which is fixed on a flat steel spring and is excited electromagnetically by a coil placed outside the patient. The oscillator impinges inside the implant and excites this to vibrate in its eigenfrequency. The excitation within the bending modes of the implant leads to a sound emission to the surrounding bone and soft tissue. The sound waves are detected by an acoustic sensor which is applied on the patient's skin. Differences in the signal generated result from varying level of implant fixation. The sensor principle was tested in porcine foreleg specimens with a custom-made implant. Influence of the measurement location at the porcine skin and different levels of fixation were investigated (press-fit, slight loosening, advanced loosening) and compared to the pull-out strength of the implant. Evaluation of different parameters, especially the frequency spectrum resulted in differences of up to 12% for the comparison between press-fit and slight loosening, and 30% between press-fit and advanced loosening. A significant correlation between the measured frequency and the pull-out strength for different levels of fixation was found. Based on these findings, an animal study with sensor-equipped bone implants was initiated using a rabbit model. The implants comprised an octagonal cross-section and were implanted into a circular drill hole at the distal femur. Thereby, definite gaps were realized between bone and implant initially. After implantation, the bone growth around the implant started and the gaps were successively closed over postoperative period. Consequently, since the tests had been started with a loose implant followed by its bony integration, a reverse loosening situation was simulated. In weekly measurements of the eigenfrequencies using the excitation and sensor system, the acoustic signals were followed up. Finally, after periods of 4 and 12 weeks after implantation, the animals were sacrificed and pull-out tests of the implants were performed to measure the implant fixation. The measured implant fixation strengths at the endpoint of each animal trial were correlated with the acoustic signals recorded

Introduction

Total shoulder arthroplasty is the fastest growing joint replacement in recent years, with projected compound annual growth rates of 10% for 2016 through 2021 – higher than those of both the hip and knee combined. Reverse total shoulder arthroplasty (RTSA) has gained particular interest as a solution for patients with irreparable massive rotator cuff tears and failed conventional shoulder replacement, for whom no satisfactory intervention previously existed. As the number of indications for RTSA continues to grow, so do implant designs, configurations, and fixation techniques. It has previously been shown that continuous implant migration within the first two years postoperatively is predictive of later loosening and failure in the hip and knee, with aseptic loosening of implant components a guaranteed cause for revision in the reverse shoulder. By identifying implants with a tendency to migrate, they can be eliminated from clinical practice prior to widespread use. The purpose of this study is to, for the first time, evaluate the pattern and magnitude of implant component migration in RTSA using the gold standard imaging technique radiostereometric analysis (RSA).

The Rizzoli Orthopaedic Institute has been involved in RSA since 1998. During last 25 years, several investigations have been carried on to evaluate both implant fixation and poliethylene deformation in unicompartmental and total knee replacements. Nevertheless, RSA has also been used to investigate the relative micromotions and the kinematic modifications in cadaveric models of ankles with ligamentous injuries. RSA evaluation has demonstrated that in a particular TKR implant, with mobile half-bearings, the threshold for loosening was 1.3° for rotation about the longitudinal axis and 0.5 mm for medio-lateral translation. Moreover, RSA has revealed cold flow to be concentrated in the posterior region of the medial half-bearing. This has lead to further improvement in polyethilene and implant design. RSA has also demonstrated that in all-poly tibial UKR, poliwear does not impair tibial component fixation and that deformation of the all-poly tibial component is strictly correlated to implant loosening. Moreover, RSA has been used to investigate stress-inducible displacement of the tibial component in all-poly UKRs. It has been demonstrated that rotations around the transverse axis of the knee joint are the most common form of stress-inducible displacement, while stress-induced translations are negligible. Moreover, stress-inducible translational displacement has reached significantly higher values for those patients with unexplained painful UKR, despite no sign of loosening on conventional radiographic and standard supine RSA evaluations. Further application of RSA has focused on the kinematic evaluation of poliethilene motion pattern modifications throughout a 3 years follow-up period after a mobile-bearing TKR. Patients have been investigated in weight-bearing conditions and results demonstrated that longitudinal rotations and medio-lateral translations tended to increase at last follow-up, while sagittal translations dod not show any significant modification over time. At present, a new device has been installed at the Istituto Ortopedico Rizzoli. It was specifically designed and made for RSA, static and fluoroscopic. This device can work both in mono- and bi-planar configuration as required by the RSA protocols. Moreover it is able to acquire image stacks in order to study the in-vivo and real time kinematics of a joint. he theoretical biomechanical resolution of a static RSA followup tests is 0.2 mm for translation and 0.3° for rotation. In fluoroscopic configuration the theoretical resolution is 1 mm for translation and 1° for rotations, depending on the used frame rate and on the joint movement speed. A kinematic comparison of different prosthetic designs is currently ongoing, to evaluate different motion patterns under dynamic weight-bearing conditions and to compare them with passive kinematics acquired intra-operatively using a navigation system

Introduction

Aseptic loosening is one of the highest causes for revision in total knee arthroplasty (TKA). With growing interest in anatomically aligned (AA) TKA, it is important to understand if this surgical technique affects cemented tibial fixation any differently than mechanical alignment (MA). Previous studies have shown that lipid/marrow infiltration (LMI) during implantation may significantly reduce fixation of tibial implants to bone analogs [1]. This study aims to investigate the effect of surgical alignment on fixation failure load after physiological loading.

Introduction

Aseptic acetabular component failure rates have been reported to be similar or even slightly higher than femoral component failure. Obtaining proper initial stability by press fitting the cementless acetabular cup into an undersized cavity is crucial to allow for secondary osseous integration. However, finding the insertion endpoint that corresponds to an optimal initial stability is challenging. This in vitro study presents an alternative method that allows tracking the insertion progress of acetabular implants in a non-destructive, real-time manner.

Introduction

Surgical techniques for implant alignment in total knee arthroplasty (TKA) is a expanding field as manufacturers introduce patient-specific cutting blocks derived from 3D reconstructions of pre-operative imaging, commonly MRI or CT. The patient-specific OtisMed system uses a detailed MRI scan of the knee for 3D reconstruction to estimate the kinematic axis, dictating the cutting planes in the custom-fit cutting blocks machined for each patient. The resulting planned alignment can vary greatly from a neutral mechanical axis. The purpose of this study was to evaluate the early fixation of components in subjects randomized to receive shape match derived kinematic alignment or conventional alignment using computer navigation. A subset of subjects were evaluated with gait analysis.

Introduction

Lateralizing the center of rotation (COR) of reverse total shoulder arthroplasty (rTSA) has the potential to increase functional outcomes of the procedure, namely adduction range of motion (ROM). However, increased torque at the bone-implant interface as a result of lateralization may provoke early implant loosening, especially in situations where two, rather than four, fixation screws are used. The aim of this study was to utilize finite element (FE) models to investigate the effects of lateralization and the number of fixation screws on micromotion and adduction ROM.

Dorr bone type is both a qualitative and quantitative classification. Qualitatively on x-rays the cortical thickness determines the ABC type. The cortical thickness is best judged on a lateral x-ray and the focus is on the posterior cortex. In Type A bone it is a thick convex structure (posterior fin of bone) that can force the tip of the tapered implant anteriorly – which then displaces the femoral head posteriorly into relative retroversion. Fractures in DAA hips have had increased fractures in Type A bone because of the metaphyseal-diaphyseal mismatch (metaphysis is bigger than diaphysis in relation to stem size). Quantitatively, Type B bone has osteoclastic erosion of the posterior fin which proceeds from proximal to distal and is characterised by flattening of the fin, and erosive cysts in it from osteoclasts. A tapered stem works well in this bone type, and the bone cells respond positively. Type C bone has loss of the entire posterior fin (stove pipe bone), and the osteoblast function at a low level with dominance of osteoclasts. Type C is also progressive and is worse when both the lateral and AP views show a stove pipe shape. If just the lateral x-ray has thin cortices, and the AP has a tapered thickness of the cortex a non-cemented stem will work, but there is a higher risk for fracture because of weak bone. At surgery Type C bone has “mushy” cancellous bone compared to the hard structure of type A. Tapered stems have high risk for loosening because the diaphysis is bigger than the metaphysis (opposite of Type A). Fully coated rod type stems fix well, but have a high incidence of stress shielding. Cemented fixation is done by surgeons for Type C bone to avoid fracture, and insure a comfortable hip. The large size stem often required to fit Type C bone causes an adverse-stem-bone ratio which can cause chronic thigh pain. I cement patients over age 70 with Type C bone which is most common in women over that age.

Patients receiving reverse total shoulder arthroplasty (RTSA) often have osseous erosions because of glenohumeral arthritis, leading to increased surgical complexity. Glenoid implant fixation is a primary predictor of the success of RTSA and affects micromotion at the bone-implant interface. Augmented implants which incorporate specific geometry to address superior erosion are currently available, but the clinical outcomes of these implants are still considered short-term. The objective of this study was to investigate micromotion at the glenoid-baseplate interface for a standard, 3 mm and 6 mm lateralized baseplates, half-wedge, and full-wedge baseplates. It was hypothesized that the mechanism of load distribution from the baseplate to the glenoid will differ between implants, and these varying mechanisms will affect overall baseplate micromotion. Clinical CT scans of seven shoulders (mean age 69 years, 10°-19° glenoid inclinations) that were classified as having E2-type glenoid erosions were used to generate 3D scapula models using MIMICS image processing software (Materialise, Belgium) with a 0.75 mm mesh size. Each scapula was then repeatedly virtually reconstructed with the five implant types (standard,3mm,6mm lateralized, and half/full wedge; Fig.1) positioned in neutral version and inclination with full backside contact. The reconstructed scapulae were then imported into ABAQUS (SIMULIA, U.S.) finite element software and loads were applied simulating 15°,30°,45°,60°,75°, and 90° of abduction based on published instrumented in-vivo implant data. The micromotion normal and tangential to the bone surface, and effective load transfer area were recorded for each implant and abduction angle. A repeated measures ANOVA was used to perform statistical analysis. Maximum normal micromotion was found to be significantly less when using the standard baseplate (5±4 μm), as opposed to the full-wedge (16±7 μm, p=0.004), 3 mm lateralized (10±6 μm, p=0.017), and 6 mm lateralized (16±8 μm, p=0.007) baseplates (Fig.2). The half-wedge baseplate (11±7 μm) also produced significantly less micromotion than the full-wedge (p=0.003), and the 3 mm lateralized produced less micromotion than the full wedge (p=0.026) and 6 mm lateralized (p=0.003). Similarly, maximum tangential micromotion was found to be significantly less when using the standard baseplate (7±4 μm), as opposed to the half-wedge (12±5 μm, p=0.014), 3 mm lateralized (10±5 μm, p=0.003), and 6 mm lateralized (13±6 μm, p=0.003) baseplates (Fig.2). The full wedge (11±3 μm), half-wedge, and 3 mm lateralized baseplate also produced significantly less micromotion than the 6 mm lateralized (p=0.027, p=012, p=0.02, respectively). Both normal and tangential micromotion were highest at the 30° and 45° abduction angles (Fig.2). The effective load transfer area (ELTA) was lowest for the full wedge, followed by the half wedge, 6mm, 3mm, and standard baseplates (Fig.3) and increased with abduction angle. Glenoid baseplates with reduced lateralization and flat backside geometries resulted in the best outcomes with regards to normal and tangential micromotion. However, these types of implants are not always feasible due to the required amount of bone removal, and medialization of the bone-implant interface. Future work should study the acceptable levels of bone removal for patients with E-type glenoid erosion and the corresponding best implant selections for such cases. For any figures or tables, please contact the authors directly

Introduction. Polyetheretherketone (PEEK) has been proposed as an implant material for femoral total knee arthroplasty (TKA) components. Potential clinical advantages of PEEK over standard cobalt chrome alloys include modulus of elasticity and subsequently reduced stress shielding potentially eliminating osteolysis, thermal conduction properties allowing for a more natural soft tissue environment, and reduced weight enabling quicker quadriceps recovery. Manufacturing advantages include reduced manufacturing and sterilization time, lower cost, and improved quality control. Currently, no PEEK TKA implants exist on the market. Therefore, evaluation of mechanical properties in a pre-clinical phase is required to minimize patient risk. The objectives of this study include evaluation of implant fixation and determination of the potential for reduced stress shielding using the PEEK femoral TKA component. Methods and Materials. Experimental and computational analysis was performed to evaluate the biomechanical response of the femoral component (Freedom Knee, Maxx Orthopedics Inc., Plymouth Meeting, PA; Figure 1). Fixation strength of CoCr and PEEK components was evaluated in pull-off tests of cemented femoral components on cellular polyurethane foam blocks (Sawbones, Vashon Island, WA). Subsequent testing investigated the cemented fixation using cadaveric distal femurs. The reconstructions were subjected to 500,000 cycles of the peak load occurring during a standardized gait cycle (ISO 14243-1). The change from CoCr to PEEK on implant fixation was studied through computational analysis of stress distributions in the cement, implant, and the cement-implant interface. Reconstructions were analyzed when subjected to standardized gait and demanding squat loads. To investigate potentially reduced stress shielding when using a PEEK component, paired cadaveric femurs were used to measure local bone strains using digital image correlation (DIC). First, standardized gait load was applied, then the left and right femurs were implanted with CoCr and PEEK components, respectively, and subjected to the same load. To verify the validity of the computational methodology, the intact and reconstructed femurs were replicated in FEA models, based on CT scans. Results. The cyclic load phase of the pull-off experiments revealed minimal migration for both CoCr and PEEK components, although after construct sectioning, debonding at the implant-cement interface was observed for the PEEK implants. During pull-off from Sawbones the ultimate failure load of the PEEK and CoCr components averaged 2552N and 3814N respectively. FEA simulations indicated that under more physiological loading, such as walking or squatting, the PEEK component had no increased risk of loss of fixation when compared to the CoCr component. Finally, the DIC experiments and FEA simulations confirmed closer resemblance of pre-operative strain distribution using the PEEK component. Discussion. The biomechanical consequences of changing implant material from CoCr to PEEK on implant fixation was studied using experimental and computational testing of cemented reconstructions. The results indicate that, although changes occur in implant fixation, the PEEK component had a fixation strength comparable to CoCr. The advantage of long term bone preservation, as the more compliant PEEK implant is able to better replicate the physiological loads occurring in the intact femur, may reduce stress shielding around the distal femur, a common clinical cause of TKA failure. For any figures or tables, please contact the authors directly

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. Varus alignment in total knee replacement (TKR) results in a larger portion of the joint load carried by the medial compartment. [1]. Increased burden on the medial compartment could negatively impact the implant fixation, especially for cementless TKR that requires bone ingrowth. Our aim was to quantify the effect varus alignment on the bone-implant interaction of cementless tibial baseplates. To this end, we evaluated the bone-implant micromotion and the amount of bone at risk of failure. [2,3]. Methods. Finite element models (Fig.1) were developed from pre-operative CT scans of the tibiae of 11 female patients with osteoarthritis (age: 58–77 years). We sought to compare two loading conditions from Smith et al.;. [1]. these corresponded to a mechanically aligned knee and a knee with 4° of varus. Consequently, we virtually implanted each model with a two-peg cementless baseplate following two tibial alignment strategies: mechanical alignment (i.e., perpendicular to the tibial mechanical axis) and 2° tibial varus alignment (the femoral resection accounts for additional 2° varus). The baseplate was modeled as solid titanium (E=114.3 GPa; v=0.33). The pegs and a 1.2 mm layer on the bone-contact surface were modeled as 3D-printed porous titanium (E=1.1 GPa; v=0.3). Bone material properties were non-homogeneous, determined from the CT scans using relationships specific to the proximal tibia. [2,4]. The bone-implant interface was modelled as frictional with friction coefficients for solid and porous titanium of 0.6 and 1.1, respectively. The tibia was fixed 77 mm distal to the resection. For mechanical alignment, instrumented TKR loads previously measured in vivo. [5]. were applied to the top of the baseplate throughout level gait in 2% intervals (Fig.1a). For varus alignment, the varus/valgus moment was modified to match the ratio of medial-lateral force distribution from Smith et al. [1]. (Fig.1b). Results. For both alignments and all bones, the largest micromotion and amount of bone at risk of failure occurred during mid stance, at 16% of gait (Figs.2,3). Peak micromotion, located at the antero-lateral edge of the baseplate, was 153±32 µm and 273±48 µm for mechanical and varus alignment, respectively. The area of the baseplate with micromotion above 40 µm (the threshold for bone ingrowth. [3]. ) was 28±5% and 41±4% for mechanical and varus alignment, respectively. The amount of bone at risk of failure at the bone-implant interface was 0.5±0.3% and 0.8±0.3% for the mechanical and varus alignment, respectively. Discussion. The peak micromotion and the baseplate area with micromotion above 40 µm increased with varus alignment compared to mechanical alignment. Furthermore, the amount of bone at risk of failure, although small for both alignments, was greater for varus alignment. These results suggest that varus alignment, consisting of a combination of femoral and tibial alignment, may negatively impact bone ingrowth and increase the risk of bone failure for cementless tibial baseplates of this TKR design

Long-term biological fixation and stability of uncemented acetabular implant are influenced by peri-prosthetic bone ingrowth which is known to follow the principle of mechanoregulatory tissue differentiation algorithm. A tissue differentiation is a complex set of cellular events which are largely influenced by various mechanical stimuli. Over the last decade, a number of cell-phenotype specific algorithms have been developed in order to simulate these complex cellular events during bone ingrowth. Higher bone ingrowth results in better implant fixation. It is hypothesized that these cellular events might influence the peri-prosthetic bone ingrowth and thereby implant fixation. Using a three-dimensional (3D) microscale FE model representing an implant-bone interface and a cell-phenotype specific algorithm, the objective of the study is to evaluate the influences of various cellular activities on peri-prosthetic tissue differentiation. Consequently the study aims at identifying those cellular activities that may enhance implant fixation. The 3D microscale implant-bone interface model, comprising of Porocast Bead of BHR implant, granulation tissue and bone, was developed and meshed in ANSYS (Fig. 1b). Frictional contact (µ=0.5) was simulated at all interfaces. The displacement fields were transferred and prescribed at the top and bottom boundaries of the microscale model from a previously investigated macroscale implanted pelvis model (Fig. 1a) [4]. Periodic boundary conditions were imposed on the lateral surfaces. Linear elastic, isotropic material properties were assumed for all materials. Young's modulus and Poisson's ratios of bone and implant were mapped from the macroscale implanted pelvis [4]. A cell-phenotype specific mechanoregulatory algorithm was developed where various cellular activities and tissue formation were modeled with seven coupled differential equations [1, 2]. In order to evaluate the influence of various cellular activities, a Plackett-Burman DOE scheme was adopted. In the present study each of the cellular activity was assumed to be an independent factor. A total of 20 independent two-level factors were considered in this study which resulted in altogether 24 different combinations to be investigated. All these cellular activities were in turn assumed to be regulated by local mechanical stimulus [3]. The mechano-biological simulation was run until a convergence in tissue formation was attained. The cell-phenotype specific algorithm predicted a progressive transformation of granulation tissue into bone, cartilage and fibrous tissue (Fig. 1c). Various cellular activities were found to influence the time to reach equilibrium in tissue differentiation and, thereby, attainment of sufficient implant fixation (Fig. 2, Table 1). Negative regression coefficients were predicted for the significant factors, differentiation rate of MSCs and bone matrix formation rate, indicating that these cellular activities favor peri-prosthetic bone ingrowth by facilitating rapid peri-prosthetic bone ingrowth. Osteoblast differentiation rate, on the contrary, was found to have the highest positive regression coefficient among the other cellular activities, indicating that an increase in this cellular activity delays the attainment of equilibrium in bone ingrowth prohibiting rapid implant fixation. To view tables/figures, please contact authors directly

The dual mobility design concept for acetabular components is intended to reduce the risk of dislocation and increase range of motion, but the wear pattern of this design is unclear and may have implications in implant fixation. Additionally, the solid back cups do not have the option for supplementary screw fixation, providing an additional smooth articulating surface for the liner to move against. The objective of this study was to assess cup fixation by measuring implant migration as well as proximal femoral head penetration to evaluate wear performance. Thirty subjects were recruited in a consecutive series prospective study and received dual mobility uncemented acetabular components with mobile bearing polyethylene liners through a direct lateral approach. Femoral stems were cemented or uncemented. All subjects had 28 mm femoral heads. The femur, acetabulum, and non-articulating surface of the mobile polyethylene liner were marked with tantalum beads. Radiostereometric analysis (RSA) exams were performed post-operatively and at 6 weeks, 3 months, 6 months, 1 year, 2 years, and 3 years. Oxford 12 Hip and Satisfaction questionnaire responses were recorded. Mobile bearing motion was assessed under fluoroscopy for a single case under loaded and unloaded conditions. Twenty-nine subjects (17 female) proceeded to surgery. Subjects were 63±11 years of age with BMIs of 28±4.7 kg/m2. Cup migration reached 0.16 ± 0.31 mm of proximal translation and 0.29±1.03 degrees of sagittal rotation at three years. A single individual had more than 3 degrees of cup rotation, occurring by 6 months and not substantially increasing after this time. Proximal translation was low for this subject. Wear of the highly cross-linked mobile bearings was 0.18 ± 0.30 mm of proximal femoral head penetration from 0 to 3 years. The mean wear rate from 1 to 3 years was 0.02 mm/year. One subject was an outlier for wear, with more than 1 mm of femoral head penetration at 1 year. However, wear did not increase after 1 year for this subject and cup migrations were below average for this individual. Similarly, the outlier for cup rotation had below average wear. Satisfaction (out of 100%) improved from 25±27% to 96±7% pre-operatively to 3 years post-operatively. Oxford 12 scores (best possible score of 48) improved from 21±7 to 43±7 over the same period. The fluoroscopic case study demonstrated visible motion of the mobile bearing during hip rotation tasks. The overall migration of the cup was low and demonstrated favorable patterns suggesting low risk of aseptic loosening. Wear rates are also within the expected range of 0 to 0.06 mm/year for highly cross-linked polyethylene. The combination of low subsidence and low sagittal rotations of the cup, and low wear of the polyethylene are favorable predictors of good long-term performance

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

Hybrid fixation of total joint arthroplasty has been an accepted form of surgical approach in multiple joints. Principles of implant fixation should focus on durability providing secure long-term function. To date there is no conclusive evidence that pressed fit humeral stem fixation has an advantage over well-secured cemented humeral fixation. In fact, need for revision arthroplasty due to inadequate implant fixation has almost universally revolved around failure of cement fixation and loosening of the glenoid component. A case will be made based on 30 years of experience of one surgeon performing total shoulder arthroplasty using secure modern cement fixation techniques of humeral components. More recently, over the last 10 years, extremely high rate of durable secure glenoid implant fixation has been achieved using tantalum porous anchorage with polyethylene glenoid components. This has resulted in no cases of loosening of glenoid fixation and only 1 case of glenoid component fracture with greater than 95% survivorship over a 10 year period. A combination of well cemented humeral stem and trabecular metal anchorage of the glenoid has provided durable lasting function in primary total shoulder arthroplasty

Olecranon Osteotomy is a common approach used in the management of intraarticular distal humerus fractures. Significant complication rates have been associated with this procedure, including non-union rates of 0–13% and implant removal rates between 12–86%. This study is a multicentre retrospective study involving the largest cohort of olecranon osteotomies in the literature, examining implant fixation types, removal rates and associated complications. Patients were identified between 2007 and 2017 (minimum one year follow-up) via Canadian Classification of Health Interventions (CCI) coding and ICD9/10 codes by our health region's data information service. CCI intervention codes were used to identify patients who underwent surgery for their fracture with an olecranon osteotomy. Reasons for implant removal were identified from a chart review. Our primary outcome was implant removal rates. Categorical data was assessed using Chi square test and Fischer's Exact test. Ninety-nine patients were identified to have undergone an olecranon osteotomy for treatment of a distal humerus fracture. Twenty patients had their osteotomy fixed with a plate and screws and 67 patients were fixed with a tension band wire. Eleven patients underwent “screw fixation”, consisting of a single screw with or without the addition of a wire. One patient had placement of a cable-pin system. Of patients who underwent olecranon osteotomy fixation, 34.3% required implant removal. Removal rates were: 28/67 for TBW (41.8%), 6/20 plates (30%), 0/1 cable-pin and 0/11 for osteotomies fixed with screw fixation. Screw fixation was removed less frequently than TBW p<.006. TBW were more commonly removed than all other fixation types p<.043. Screws were less commonly removed than all other fixation types p<.015. TBW were more likely to be removed for implant irritation than plates, p<.007, and all other implants p<.007. The average time to removal was 361 days (80–1503 days). A second surgeon was the surgeon responsible for the removal in 10/34 cases (29%). TBWs requiring removal were further off the olecranon tip than those not removed p=.006. TBWs were associated with an OR of 3.29 (CI 1.10–9.84) for implant removal if implanted further than 1mm off bone. Nonunion of the osteotomy occurred in three out of 99 patients (3%). K-wires through the anterior ulnar cortex did not result in decreased need for TBW removal. There was no relation between plate prominence and the need for implant removal. There was no association between age and implant removal. The implant removal rate was 34% overall. Single screw fixation was the best option for osteotomy fixation, as 0/11 required hardware removal, which was statistically less frequent than TBW at 28/67. Screw fixation was removed less frequently than TBW and screw fixation was less commonly removed than all other fixation types. Only 6/20 (30%) plates required removal, which is lower than previously published rates. Overall, TBW were more commonly removed than all other fixation types and this was also the case if hardware irritation was used as the indication for removal. Nonunion rates of olecranon osteotomy were 3%

Increasing pressure to use rapid recovery care pathways when treating patients undergoing total hip arthroplasty (THA) is evident in current health care systems for numerous reasons. Patient autonomy and health care economics has challenged the ability of THA implants to maintain functional integrity before achieving bony union. Although collared stems have been shown to provide improved axial stability, it is unclear if this stability correlates with activity levels or results in improved early function to patients compared to collarless stems. This study aims to examine the role of implant design on patient activity and implant fixation. The early follow-up period was examined as the majority of variation between implants is expected during this time-frame. Patients (n=100) with unilateral hip OA who were undergoing primary THA surgery were recruited pre-operatively to participate in this prospective randomized controlled trial. All patients were randomized to receive either a collared (n=50) or collarless (n=50) cementless femoral stem. Patients will be seen at nine appointments (pre-operative, < 2 4 hours post-operation, two-, four-, six-weeks, three-, six-months, one-, and two-years). Patients completed an instrumented timed up-and-go (TUG) test using wearable sensors at each visit, excluding the day of their surgery. Participants logged their steps using Fitbit activity trackers and a seven-day average prior to each visit was recorded. Patients also underwent supine radiostereometric analysis (RSA) imaging < 2 4 hours post-operation prior to leaving the hospital, and at all follow-up appointments. Nineteen collared stem patients and 20 collarless stem patients have been assessed. There were no demographic differences between groups. From < 2 4 hours to two weeks the collared implant subsided 0.90 ± 1.20 mm and the collarless implant subsided 3.32 ± 3.10 mm (p=0.014). From two weeks to three months the collared implant subsided 0.65 ± 1.54 mm and the collarless implant subsided 0.45 ± 0.52 mm (p=0.673). Subsidence following two weeks was lower than prior to two weeks in the collarless group (p=0.02) but not different in the collared group. Step count was reduced at two weeks compared to pre-operatively by 4078 ± 2959 steps for collared patients and 4282 ± 3187 steps for collarless patients (p=0.872). Step count increased from two weeks to three months by 6652 ± 4822 steps for collared patients and 4557 ± 2636 steps for collarless patients (p=0.289). TUG test time was increased at two weeks compared to pre-operatively by 4.71 ± 5.13 s for collared patients and 6.54 ± 10.18 s for collarless patients (p=0.551). TUG test time decreased from two weeks to three months by 7.21 ± 5.56 s for collared patients and 8.38 ± 7.20 s for collarless patients (p=0.685). There was no correlation between subsidence and step count or TUG test time. Collared implants subsided less in the first two weeks compared to collarless implants but subsequent subsidence after two weeks was not significantly different. The presence of a collar on the stem did not affect patient activity and function and these factors were not correlated to subsidence, suggesting that initial fixation is instead primarily related to implant design

INTRODUCTION. Modular knee implants are used to manage large bone defects in revision total knee arthroplasty. These implants are confronted with varying fixation characteristics, changes in load transfer or stiffen the bone. In spite of their current clinical use, the influence of modularity on the biomechanical implant-bone behavior (e.g. implant fixation, flexibility, etc.) still is inadequately investigated. Aim of this study is to analyze, if the modularity of a tibial implant could change the biomechanical implant fixation behavior and the implant-bone flexibility. MATERIAL & METHODS. Nine different stem and sleeve combinations of the clinically used tibial revision system Sigma TC3 (DePuy) were compared, each implanted standardized with n=4 in a total of 36 synthetic tibial bones. Four additional un-implanted bones served as reference. Two different cyclic load situations were applied on the implant: 1. Axial torque of ±7Nm around the longitudinal stem axis to determine the rotational implant stability. 2. Varus-valgus-torque of ±3,5Nm to determine the bending behavior of the stem. A high precision optical 3D measurement system allowed simultaneous measuring of spatial micromotions of implant and bone. Based on these micromotions, relative motions at the implant-bone-interface and implant flexibility could be calculated. RESULTS. Lowest relative micromotions were measured along the tibial base component and the sleeve; however, these motions varied depending on the implant construct used. Maximum relative micromotions were detected at the distal end of the implant for all groups, indicating a more proximal fixation of all modular combinations. Regarding varus-valgus-torque measurement, all groups showed a deviant flexibility behavior compared to the reference group. When referred to the un-implanted bone, implants without stems revealed the highest flexibility, whereas implants with shorter stems had lowest flexibility. DISCUSSION & CONCLUSION. All groups showed a more proximal fixation behavior; moreover, both extent and location of fixation could be influenced by varying the modular combination. Larger stems seemed to support a more distal fixation behavior, whereas the implant fixation moved proximal while extending the sleeve. Here the influence of the sleeve on fixation behavior seemed to be dominant compared to the influence of the stem. Concerning varus-valgus-torque, a strong connection between the used stem and implant-bone flexibility seemed to exist. In addition, the influence of the sleeve on flexibility seemed to be rather low. This study showed, that modularity can influence the biomechanical behavior of tibial implants. If these results can be transferred to other tibial implants still remains to be seen