Aim. Analysis of microbiological spectrum and resistance patterns as well as the clinical outcome of patients who underwent a Debridement, antibiotics and implant retention (DAIR) procedure in the early phase following failed two-stage exchange arthroplasty of the knee and hip. Method. Of 312 patients treated with two-stage exchange arthroplasty between January 2011 and December 2019, 16 (5.1%) patients (9 knee, 7 hip) underwent a DAIR procedure within 6 months following second stage. We retrospectively analyzed the microbiological results as well as changes in the microbiological spectrum and antibiotic resistance patterns between stages of two-stage exchange arthroplasties and DAIR procedures. Patient's re-revision rates after a minimum follow-up of 12 months following DAIR procedure were evaluated. Moreover, differences between knee and hip and between infected primary total joint replacement (TJRs) and infected revision TJRs as well as patient's host factors and microbiological results regarding the outcome of DAIR were analyzed. Results. In 7/16 (43.8%) patients the first and second stage procedure was culture positive, in 5/16 (31.2%) patients the first and second stage procedure was culture negative and in 4/16 (25%) patients the first stage procedure was culture positive, and the second stage procedure was culture negative. Moreover, 6 (37.5%) out of 16 DAIR procedures showed a positive microbiological result. In 5/7 (71.4%) patients with culture positive second stage procedure a different microorganism compared to first stage procedure was detected. In 6/6 (100%) patients with culture positive DAIR procedure, the isolated microorganisms were not detected during first or second stage procedure. An additional re-revision surgery was necessary in 4/16 (25%) patients after a median time of 31 months (range, 12 to 138 months) at a mean follow up of 63.1 ± 32 months following DAIR procedure. Highest re-revision rates were found in patients with culture positive second stage procedures (3/7 [42.9%]) and patients with culture positive DAIR procedures (2/6 [33.3%]). Conclusions. DAIR procedure seems to be a useful early treatment option following failed two-stage exchange arthroplasty. The re-revision rates were independent of different combinations of culture positive and culture negative first and second stage procedures. The high number of changes in the microbiological spectrum needs to be considered in the treatment of PJI

Combined Partial Knee Arthroplasty (CPKA) is a promising alternative to Total Knee Arthroplasty (TKA) for the treatment of multi-compartment arthrosis. Through the simultaneous or staged implantation of multiple Partial Knee Arthroplasties (PKAs), CPKA aims to restore near-normal function of the knee, through retention of the anterior cruciate ligament and native disease-free compartment. Whilst PKA is well established, CPKA is comparatively novel and associated biomechanics are less well understood. Clinically, PKA and CPKA have been shown to better restore knee function compared to TKA, particularly during fast walking. The biomechanical explanation for this superiority remains unclear but may be due to better preservation of the extensor mechanism. This study sought to assess and compare extensor function after PKA, CPKA, and TKA. An instrumented knee extension rig facilitated the measurement extension moment of twenty-four cadaveric knees, which were measured in the native state and then following a sequence of arthroplasty procedures. Eight knees underwent medial Unicompartmental Knee Arthroplasty (UKA-M), followed by patellofemoral arthroplasty (PFA) thereby converting to medial Bicompartmental Knee Arthroplasty (BCA-M). In the final round of testing the PKA implants were removed a posterior-cruciate retaining TKA was implanted. The second eight received lateral equivalents (UKA-L then BCA-L) then TKA. The final eight underwent simultaneous Bi-Unicondylar Arthroplasty (Bi-UKA) before TKA. Extensor efficiencies over extension ranges typical of daily tasks were also calculated and differences between arthroplasties were assessed using repeated measures analysis of variance. For both the medial and lateral groups, UKA demonstrated the same extensor function as the native knee. BCA resulted in a small reduction in extensor moment between 70–90° flexion but, in the context of daily activity, extensor efficiency was largely unaffected and no significant reductions were found. TKA, however, resulted in significantly reduced extensor moments, leading to efficiency deficits ranging from 8% to 43% in flexion ranges associated with downhill walking and the stance phase of gait, respectively. Comparing the arthroplasties: TKA was significantly less efficient than both UKA-M and BCA-M over ranges representing stair ascent and gait; TKA showed a significant 23% reduction compared to BCA-L in the same range. There were no differences in efficiency between the UKAs and BCAs over any flexion range and TKA efficiency was consistently lower than all other arthroplasties. Bi-UKA generated the same extensor moment as native knee at flexion angles typical of fast gait (0–30°). Again, TKA displayed significantly reduced extensor moments towards full extension but returned to the normal range in deep flexion. Overall, TKA was significantly less efficient following TKA than Bi-UKA. Recipients of PKA and CPKA have superior functional outcomes compared to TKA, particularly in relation to fast walking. This in vitro study found that both UKA and CPKA better preserve extensor function compared to TKA, especially when evaluated in the context of daily functional tasks. TKA reduced knee extensor efficiency by over 40% at flexion angles associated with gait, arguably the most important activity to maintain patient satisfaction. These findings go some way to explaining functional deficiencies of TKA compared to CPKA observed clinically

Introduction. Unicompartmental knee arthroplasty (UKA) currently experiences increased popularity. It is usually assumed that UKA shows kinematic features closer to the natural knee than total knee arthroplasty (TKA). Especially in younger patients more natural knee function and faster recovery have helped to increase the popularity of UKA. Another leading reason for the popularity of UKA is the ability to preserve the remaining healthy tissues in the knee, which is not always possible in TKA. Many biomechanical questions remain, however, with respect to this type of replacement. 25% of knees with medial compartment osteoarthritis also have a deficient anterior cruciate ligament [1]. In current clinical practice, medial UKA would be contraindicated in these patients. Our hypothesis is that kinematics after UKA in combination with ACL reconstruction should allow to restore joint function close to the native knee joint. This is clinically relevant, because functional benefits for medial UKA should especially be attractive to the young and active patient. Materials and Methods. Six fresh frozen full leg cadaver specimens were prepared to be mounted in a kinematic rig (Figure 1) with six degrees of freedom for the knee joint. Three motion patterns were applied: passive flexion-extension, open chain extension, and squatting. These motion patterns were performed in four situations for each specimen: with the native knee; after implantation of a medial UKA (Figure 2); next after cutting the ACL and finally after reconstruction of the ACL. During the loaded motions, quadriceps and hamstrings muscle forces were applied. Infrared cameras continuously recorded the trajectories of marker frames rigidly attached to femur, tibia and patella. Prior computer tomography allowed identification of coordinate frames of the bones and calculations of anatomical rotations and translations. Strains in the collateral ligaments were calculated from insertion site distances. Results. Knee kinematics and collateral ligament strains were quite close to the native situation after both UKA and ACL reconstruction for all motor tasks. Nevertheless, some statistically significant differences were detected, which may be relevant clinically and biomechanically. In general, insertion of a UKA led to a knee joint which was somewhat less adducted (Figure 3), with a medial femoral condyle located slightly higher, confirming previously published findings [2]. These effects were slightly reduced both after cutting as well as after reconstructing the ACL. The joint became somewhat less stable in the AP direction after insertion of a UKA and this instability persisted not only after cutting but even after reconstructing the ACL

Background. Alignment and soft tissue (ligament) balance are two variables that are under the control of a surgeon during replacement arthroplasty of the knee. Mobile bearing medial unicompartmental knee replacements have traditionally advocated sizing the prosthesis based on soft tissue balance while accepting the natural alignment of the knee, while fixed bearing prosthesis have tended to correct alignment to a pre planned value, while meticulously avoiding overcorrection. The dynamic loading parameters like peak adduction moment (PKAM) and angular adduction Impulse (Add Imp) have been studied extensively as proxies for medial compartment loading. In this investigation we tried to answer the question whether correcting static alignment, which is the only alignment variable under the control of the surgeon actually translates into improvement in dynamic loading during gait. We investigated the effect of correction of static alignment parameter Hip Knee Ankle (HKA) angle and dynamic alignment parameter in coronal plane, Mean Adduction angle (MAA) on 1st Peak Knee Adduction Moment (PKAM) and Angular Adduction Impulse (Add Imp) following medial unicompartmental knee replacements. Methods. Twenty four knees (20 patients) underwent instrumented gait analysis (BTS Milan, 12 cameras and single Kistler force platform measuring at 100 Hz) before and after medial uni compartmental knee replacement. The alignment was measured using long leg alignment views, to assess Hip Knee Ankle (HKA) angle. Coronal plane kinetics namely 1st Peak Knee Adduction Moment (PKAM) and angular adduction impulse (Add Imp)- which is the moment time integral of the adduction moment curve were calculated to assess medial compartment loading. Single and multiple regression analyses were done to assess the effect of static alignment parameters (HKA angle) and dynamic coronal plane alignment parameters (Mean Adduction Angle – MAA) on PKAM and Add Imp. Results. 12 knees had mobile bearing prosthesis implanted while the other 12 had fixed bearing prosthesis. The mean correction for HKA angle was 2.78 degrees (SD ± 1.32 degrees). There was no significant difference in correction of alignment (HKA) between mobile bearing and fixed bearing groups. MAA and HKA angles were significant predictors of dynamic loading parameters, PKAM and Add Imp (p<0.05). Correction of HKA angle was found to be a better predictor of dynamic loading. We assessed the percentage improvement in loading (%ΔPKAM & %ΔAdd. Imp) and its relationship to correction of HKA (Δ HKA) angle Correction of alignment in the form of HKA (Δ HKA) angle was found to be a very strong predictor of improvement of loads (R = 0.90 for %ΔAdd. Imp and R = 0.50 for %Δ PKAM). Conclusion. Correction of alignment (HKA Angle) predicts improvement in loads through medial compartment of knee. One degree correction resulted in 7% improvement of load through the medial unicompartmental knee replacement

Aims

The aim of this study was to analyze the prevalence of culture-negative periprosthetic joint infections (PJIs) when adequate methods of culture are used, and to evaluate the outcome in patients who were treated with antibiotics for a culture-negative PJI compared with those in whom antibiotics were withheld.

Osteoarthritis (OA) is the fastest growing global health problem, with a total joint replacement being the only effective treatment for patients with end stage OA. Many groups are examining the use of bone marrow or adipose derived mesenchymal stem cells (MSCs) to repair cartilage, or modulate inflammation to promote healing, however, little efficacy in promoting cartilage repair, or reducing patient symptoms over temporary treatments such as micro-fracture has been observed. There is a growing body of literature demonstrating that MSCs derived from the synovial lining of the joint are superior in terms of chondrogenic differentiation and while improvements in clinical outcome measures have been observed with synovial MSCs, results from clinical studies are still highly variable. Based on our results, we believe this variability in clinical studies with MSCs results in part from the isolation, expansion and re-injection of distinct MSCs subtypes in normal vs. OA tissues, each with differing regenerating potential. However, it remains unknown if this heterogeneity is natural (e.g. multiple MSC subtypes present) or if MSCs are influenced by factors in vivo (disease state/stage). Therefore, in this study, we undertook an ‘omics’ screening approach on MSCs from normal and OA knee synovial tissue. Specifically, we characterized their global proteome and genomic expression patterns to determine if multiple MSC from normal and OA joints are distinct at the protein/gene expression level and/if so, what proteins/genes are differentially expressed between MSCs derived from normal and OA synovial tissue. Synovium tissue was collected from OA patients undergoing joint replacement and normal cadaveric knees. The in vitro adipogenic, chondrogenic and osteogenic differentiation potential of the MSCs was analyzed via qPCR and histology. Fully characterized MSC populations where then analyzed through an unbiased shotgun proteomics, and microarray analysis. Synovial MSCs isolated from both OA and normal knees demonstrated similar multipotent differentiation capacity. Likewise, both OA and normal MSCs display the typical MSCs cell surface marker profile in vitro (CD90+, CD44+, CD73+, CD105+). Using shotgun proteomics, 7720 unique peptides corresponding to 2183 proteins were identified and quantified between normal and OA MSCs. Of these 2183 proteins, 994 were equally expressed in normal and OA, MSCs, 324 were upregulated in OA MSCs (with 50 proteins exclusively expressed in OA MSCs), 630 proteins were upregulated in normal MSCs (with 16 proteins exclusively expressed in normal MSCs). Microarray analysis of normal and OA MSCs demonstrated a similar result in where, 967 genes were differentially expressed between normal and OA MSCs, with 423 genes upregulated in OA, and 544 genes upregulated in normal MSCs. In this project, we have demonstrated that although normal and OA synovial derived MSCs demonstrate similar multipotent differentiation potential and cell surface markers expression, these cells demonstrated significant differences at the molecular level (protein and gene expression). Further research is required to determine if these differences influence functional differences in vitro and/or in vivo and what drives this dramatic change in the regulatory pathways within normal vs. OA synovial MSCs

Aim. The purpose of this work is to study whether there is or not, in the case of an aseptic arthroplasty exchange, a relationship between positive cultures and an early periprosthetic joint infection. Method. We carried out a retrospective review of our cases of aseptic exchange arthroplasties of hip, knee and shoulder performed between January 2007 and December 2015. The follow-up period was, in average, from 1 to 9 years, and in all the cases perioperative cultures were evaluated. Results. The number of arthroplasties reviewed was 183, corresponding to 180 patients. Seventy-six cultures were positive for one or more microorganisms. Staphylococcus epidermidis was the microorganism most isolated followed by other Coagulase Negative Staphylococci. Five cases (6.58%) were followed by an acute infection. In three of these cases (60%) the previous culture were positive, but only in one single case, one of the microorganisms isolated after the infection was the same as the isolated previously. Conclusions. Perioperative cultures in aseptic exchange arthroplasties seems not to have any value as infection predictor. Neither the previous isolated microorganisms, in case of postoperative infection, have any value as a predictor of the etiological agent

Introduction:. Isolated lateral compartment osteoarthritis (OA) occurs in 5–10% of knees with unicompartmental OA. Lateral unicompartmental knee arthroplasty has been limited in its prevalence due to challenging surgical technique issues. A robotic-arm assisted surgical technique has emerged as a way to achieve precise implant positioning which can potentially improve surgical outcomes. Methods:. 63 consecutive lateral unicompartmental knee arthroplasties were performed by a single surgeon with the use of a metal backed, cemented prosthesis installed with the three-dimensional intra-operative kinematics and haptic robotic guidance. The average age of the patient was 72.7 years (range: 59–87) and the average BMI was 27.2 (range: 19.0–38.6). The follow-up ranged from 2 months to 30 months. Results:. All patients recovered flexion to an average of 130° at 6 weeks post-operatively, compared to an average of 127° pre-operatively. There was one revision to a total knee at 26 months post-operatively for progression of OA to the patellofemoral compartment. Conclusion:. Early results of robotically guided lateral UKA are encouraging and provide evidence to show that lateral UKA is a viable option for patients with lateral OA disease. Three dimensional planning, intra-operative kinematic analysis and haptic robotic guidance provide a significant advantage over manual installation for lateral compartment arthroplasty of the knee. The significant anterior to posterior translation of the lateral femoral condyle along with the “screw-home” mechanism associated with the lateral compartment makes the tracking of the lateral compartment highly complex when retaining the cruciate ligaments. Intraoperative planning and adjustment of the preoperative plan provided only with this robotic system results in optimized lateral compartment kinematics. Further mid to long term studies are needed to determine survivorship as it compares to medial unicompartmental knee arthroplasty

Prosthetic joint infection continues to remain a diagnostic challenge for unhappy primary arthroplasty of hip and knees. There is increasing dependence upon alpha-defensin test to make key decisions like whether to revise or not & to decide between one-stage versus two-stage. Aim. This study aims to assess diagnostic accuracy of alpha-defensin test in determining prosthetic hip & knee infection and to provide guidance for appropriate use of this novel but expensive investigation. Methods. Retrospective review of all alpha-defensin investigated patients in an orthopaedic institute between February 2015 & March 2017 was performed. Clinical and radiological outcomes including re-infections, re-operations were analysed and alpha-defensin outcomes were compared with that of other available investigations. Results. Of total 52 tests performed (17 hips & 35 knees), 3 were positive. On comparison with intra-operative culture (gold standard), sensitivity is 100%. All suspected prosthetic hip infections have good clinical outcomes following their decisions being made based upon alpha-defensin test. Among the negative knee test results, 6 patients developed signs of infection in the post-operative period, 4 of which have been revised with washout, poly exchange or full revision. Conclusion. No single clinical investigation can accurately predict prosthetic joint infection in revision for suspected infection. Alpha-defensin test, however, is a useful adjunct to intra-operative surgeon's findings & pre-operative investigations to decide for crucial decisions like whether to revise or not & for deciding between single and two stage

The options for treatment of the young active patient with isolated symptomatic osteoarthritis of the medial compartment and pre-existing deficiency of the anterior cruciate ligament are limited. The indications for the unicompartimental knee prosthesis are selective. Misalignment femoral-tibia, varo-valgus angle more than 7°, over-weight, and knee instability were considered to be a contraindication. The potential longevity of the implant and levels of activity of the patient may preclude total knee replacement, and tibial osteotomy and unicompartmental knee arthroplasty are unreliable because of the ligamentous instability. Therefore, we combined reconstruction of the anterior cruciate ligament first and unicompartmental arthroplasty of the knee. We included in this study six patients, three males and three female, mean age 53.6 years, that presented only osteoarthritis of medial femoral condyle and ACL deficiency. In the first group included 2 patients, we performed arthroscopy ACL reconstruction with hamstring and unicompartimental knee prosthesis one-step, and in the second group included 4 patients, we performed the same surgical procedure in two-step. The clinical and radiological data at a minimum of 1.5 years at follow-up. We evaluated all patients with KOOS score, and IKDC score. At the last follow-up, no patient had radiological evidence of component loosening, no infection, no knee remainder instability. The subjective and objective outcome assessed with the scale documented satisfactory average results, both in patients of first group and in those of second group. ACL deficiency induced knee osteoarthritis for incorrect knee biomechanics, and all patients could be submit a total knee replacement. What method for preventing it? This combined surgical treatment seems to be a viable treatment option for young active patients with symptomatic arthritis of the medial compartment, in whom the anterior cruciate ligament has been ruptured. Future developments and more data are necessary for standardised surgical approach

INTRODUCTION. There is strong current interest to provide reliable treatments for one- and two-compartment arthritis in the cruciate-ligament intact knee. An alternative to total knee arthroplasty is to resurface only the diseased compartments with discrete compartmental components. Placing multiple small implants into the knee presents a greater surgical challenge than total knee arthroplasty, and it is not certain natural knee mechanics can be maintained. The goal of this study was to compare functional kinematics in cruciate-intact knees with either medial unicondylar (mUKA), mUKA plus patellofemoral (mUKA+PF), or bi-unicondylar (biUNI) arthroplasty using discrete compartmental implants with preparation and placement assisted by haptic robotic technology. METHODS. Nineteen patients with 21 knee arthroplasties consented to participate in an I.R.B. approved study of knee kinematics with a cruciate-retaining multicompartmental knee arthroplasty system. All subjects presented with knee OA, intact cruciate ligaments, and coronal deformity ranging from 7° varus to 4° valgus. All subjects received multicompartmental knee arthroplasty using haptic robotic-assisted bone preparation an average of 13 months (6–29 months) before the study. Eleven subjects received mUKA, five subjects received mUKA+PF, and five subjects received biUKA. Subjects averaged 62 years of age and had an average body mass index of 31. Combined Knee Society Pain/Function scores averaged 102 ± 28 preoperatively and 169 ± 26 at the time of study. Knee range of motion averaged −3° to 120° preoperatively and −1° to 129° at the time of the study. Knee motions were recorded using video-fluoroscopy while subjects performed step-up/down, kneeling and lunging activities. The three-dimensional position and orientation of the implant components were determined using model-image registration techniques (Fig. 1). The AP locations of the medial and lateral condyles were determined by computing a distance map between the femoral condyles and the tibial articular surfaces. RESULTS. Knee kinematics during maximum flexion kneeling and lunging showed tibial internal rotation, and posterior lateral condylar translation for all three treatments (Fig. 2). All knees showed femoral external rotation and posterior condylar translation with flexion during the step activity (Fig. 3). In all three activities, knees with mUKA and mUKA+PF arthroplasty showed the most femoral external rotation and posterior translation, and knees with biUKA showed the least. DISCUSSION. Knees with tricompartmental arthroplasty usually sacrifice one or both cruciate ligaments and also exhibit kinematics which differ from the normal knee. In particular, tibiofemoral rotations are almost always significantly less than the normal knee, and often the femur translates forward with flexion over some portion of the motion arc. In contrast, knees with accurately-placed uni- or bi-compartmental arthroplasty exhibited stable knee kinematics consistent with intact and functioning cruciate ligaments. The patterns and magnitudes of tibiofemoral motion were more similar to natural knees in the mUKA and mUKA+PF groups than commonly has been observed in knees with total knee arthroplasty. These results demonstrate the potential to restore or maintain closer-to-normal knee kinematics by retaining intact structures and compartments. Knees with an intact lateral compartment had kinematics closer to normal than those where both tibiofemoral compartments were diseased/replaced

Aim. When a prosthetic joint infection (PJI) is suspected, guidelines recommend performing periprosthetic samples, at least one for histopathological examination and 3 to 6 for microbiological culture. The diagnosis of infection is based on the presence of neutrophil granulocytes whose number and morphology can be variable, resulting in definition of “acute” inflammation. The acute inflammation of periprosthetic tissue is supportive of infection. Since 2007, in our hospital, for all patients with suspected PJI who underwent surgery, from each sample taken by the surgeon, one part has been sent to the pathologist and the other one to the microbiologist. Our aim was to compare histopathological to microbiological results from samples taken intraoperatively at the same site. Method. We conducted a retrospective study including all surgeries for which at least one couple “histopathology-culture” was found. Exclusion criterion was a history of antimicrobial treatment 2 weeks prior the surgery. Results. From July 2007 to April 2015, 309 surgeries for suspected PJI were performed in 181 patients. Median age of the study population was 70 years, 60% of patients were male, 45% had a history of joint infection. The location of arthroplasty was knee in 50% of cases and hip in 46%, ankle and shoulder in 4%. Surgery was performed within one month after the last prosthetic surgery in 15% of cases. According to the criteria from the Musculoskeletal Infection Society, 60% of cases should have been considered as having an infection. The median number of samples per surgery was 4 (IQR 3–5) for histopathological examination and 5 (IQR 4–6) for culture. Finally, 1247 couples “histopathology-culture” were available. Among them, histopathological examination showed acute inflammation in 292 cases (23%) and subacute inflammation in 327 cases (26%). Microorganisms considered to be pathogenic were found in 582 samples (47%). The presence of neutrophil granulocytes was well correlated with the presence of those microorganisms (OR=4.1; IC 95% 3.1–5.5). As expected, the highest correlation between acute inflammation and positive culture was observed for early infection (< 1 month) (OR = 9; 3.6–23.4) and Staphylococcus aureus infection (OR = 4.8; 3.3–7.0). There was no correlation between acute or low-grade inflammation and anaerobic or Candida infection. Conclusions. Our results confirmed histopathological examination is better correlated with culture in acute infection and/or infection due to highly virulent bacteria but must be interpreted with caution in case of chronic infection or infections due to microorganisms with low virulence

Background. Restoration of physiologic rotational kinematics after total knee replacement has been difficult to achieve using modern dual M/L radius knee designs. This study was undertaken to determine whether a change in femoral shape substituting for the effect of the menisci in load sharing and motion accommodation would result in more normal rotational post arthroplasty kinematics. Methods. 17 knees reconstructed more than twelve months previously with a tricompartmental cemented knee replacement using a single F/E radius, miniscal substituting, a fixed bearing total knee were studied fluoroscopically while performing closed chain activities. The patients were studied during level gait, deep knee bending, rising from a chair, and kneeling. Images were converted from 2 to 3d and joint kinematics were measured using edge recognition softwear. Results. The highest levels of physiologic rotation were demonstrated during kneeling and squatting. The average knee flexion attained was 133 ± 6 degrees. Internal tibial rotation around a medial tibial axis was present in each knee. The average physiologic rotation observed was 13 degrees in both maneuvers. There was no visualized unloading or instability seen in any of the knees. Conclusions. These results suggest that incorporating a single M/L radius in both the femoral component and the tibial bearing can memic the function of the menisci in the normal knee: providing for unrestricted rotation while enhancing load distribution across the articular surface of the knee joint

INTRODUCTION. Ceramics are excellently suited for applications in arthroplasty, mainly total hip, knee and shoulder replacement. As the most prominent representative of this demanding type of material, BIOLOX. ®. delta is widely used and very successful in the market for more than 10 years. The ability of zirconia phase transformation (t-ZrO. 2. →m-ZrO. 2. ) in zirconia-platelet toughened alumina (ZPTA) ceramics is an indispensable prerequisite for their excellent mechanical properties. The degree of stabilization of the zirconia tetragonal phase at body temperature is essential for the desired toughening mechanism. Y. 2. O. 3. is the most widely used t-ZrO. 2. chemical stabilizer; also microstructure and grain size contribute to t-ZrO. 2. phase stabilization. Stabilization must be achieved such that no material degradation will occur in body environment, i.e. in aqueous liquid (synovia), which is known to potentially trigger phase transformation at the surface of ceramic components. In this study, it is shown how phase stabilization in BIOLOX. ®. delta as a reference material is excellently balanced by means of optimal mechanical performance and environmental stability. OBJECTIVES. To assess the influence of t-ZrO. 2. chemical stabilization on ZPTA properties, in terms of fracture toughness (i.e. the ability to resist crack extension), wear resistance and environmental stability. METHODS. Three ZPTA compositions with increasing yttria content (Y. 2. O. 3. /ZrO. 2. 2–4mol%) were produced and compared to the reference. Hardness and fracture toughness were assessed by Vickers indentation method. A micro scratch tester (CSM Instruments, Peseux Switzerland) loaded with a Rockwell C diamond tip with 50µm radius was used to assess the scratch resistance of the ceramic compositions. The scratch load was linearly increased from 0 to 30N, which simulates extremely heavy local wear conditions. The morphology and depth of the scratches as well as local damage has been analysed with a laser microscope (Olympus LEXT-OLS4000) and scanning electron microscope (Hitachi S4700). The hydrothermal aging resistance was measured by autoclaving the compositions up to 150 hours at 134°C and 2.2bar and the monoclinic zirconia volume fraction measured by XRD using the Garvie formula at each time interval (i.e. 0, 10, 50, 100 and 150h). Surface roughness after hydrothermal ageing was also evaluated by atomic force microscopy. RESULTS. As expected, t-ZrO. 2. stabilization improved with increasing yttria content. Consequently, hydrothermal aging resistance increased and fracture toughness decreased strongly to almost monolithic alumina values. The scratch resistance performances also decreased showing gradually lower critical load Lc1, where grain pull-out phenomenon appeared earlier with the higher zirconia stabilization composition. The materials kept almost the same hardness (about 18GPa). Surface roughness also remained unchanged for all compostions, even in extreme hydrothermal conditions. CONCLUSIONS. Higher tetragonal zirconia stabilization leads to the suppression of zirconia phase transformation toughening and consequently of low temperature degradation; annihilating almost all the improvements of ZPTA over the monolithic alumina material. It was demonstrated that the best performance is achieved by properly triggering the tetragonal zirconia transformation. This result is explaining the successful performance of BIOLOX. ®. delta bearing couples already observed in the clinical setting

Purpose:. Starting February 2012, our institution changed from enoxaparin (Lovenox) to the Factor Xa inhibitor, rivaroxaban (Xarelto) for venous thromboembolism prophylaxis after primary total hip (THA) and total knee arthroplasty (TKA). The purpose of our study was to compare rates of venous thromboembolism and rates of major bleeding between these two medications when used for venous thromboembolism prophylaxis after primary THA and TKA. Methods:. A retrospective review was performed on 1795 patients who underwent THA or TKA at our institution between January 1, 2011 and December 31, 2012. Patients were excluded if they had a bilateral procedure, partial arthroplasty (hip hemiarthroplasty, unicompartmental knee arthroplasty), revision surgery, and cases designated as complex. Patients were excluded if they were on other anticoagulants (dabigatran, aspirin, clopidogrel, warfarin, heparin, fondaparinux), or if pre-operative creatinine was 1.2 or greater. After excluding these patients, there were 1089 patients included in the study. Chart review recorded demographics (age, gender), comorbidities (BMI, ASA, creatinine), surgery performed (primary THA or TKA), length of stay (LOS), venous thromboembolic events (deep venous thrombosis [DVT], pulmonary embolus [PE]), post-operative infections, and major bleeding events (stroke, post-operative bleeding requiring transfusion). Periprosthetic infection rates are also currently being reviewed. T-tests were used to compare continuous variables between treatment groups, and Chi-square tests were used to compare categorical variables between treatment groups (α = 0.05). Results:. There were 779 patients (71.5%) who received enoxaparin and 310 patients (28.5%) who received rivaroxaban during the study period. Demographics of the patients are presented in Table 1. A comparison of venous thromboembolism rates. Pre-operative creatinine was higher in the enoxaparin group (0.81 ± 0.19 vs. 0.72 ± 0.18, p < 0.001). With the numbers available for study, there were no demonstrable differences in DVT (p = 0.400, power = 0.125), PE (p = 0.679, power = 0.066), cerebrovascular events (p = 0.913, power = 0.049), or transfusion rates (p = 0.412, power = 0.121). Conclusion:. To our knowledge this is one of, if not the largest non-industry funded studies comparing these two medications. There were no statistically demonstrable differences between the enoxaparin and rivaroxaban groups in terms of venous thromboembolism or major bleeding complications

Introduction. The design and manufacture of patient specific implants at Hospital for Special Surgery (HSS) was started in the fall of 1976. The first implant designed and manufactured was an extra large total knee. This effort expanded to include all arthroplasty devices including hips, knees, shoulders and elbows along with fracture fixation devices. In the 1980s, the hospital was designing and manufacturing over 100 custom implants per year. This reduced significantly in the 1990s due to the introduction of modular total knee replacements. In 1996, HSS ceased manufacture due to rising costs and a greater regulatory burden. However, implants are still designed at HSS with manufacturing outsourced to commercial companies. Since 1976, the hospital has designed over 2500 implants. Patient Population. Currently, we design implants for ∼30 cases per year, hips, knees, and upper extremity devices (mainly elbow). We've seen an increase in acetabular revision cases over the last few years and now design about 10 revision acetabular components each year. Regulatory Challenges. Patient specific implants can be provided under a variety of regulatory pathways. Some have received 510(k) clearance as the manufacturer has provided a matrix of sizes; if the device fits within the matrix, the device can be supplied commercially. For devices that fall outside of the 510(k) pathway, the process is more complex. The 2012 FDA Safety and Innovation Act attempts to clarify the ambiguous nature of the prior statute in which the number of custom implants allowed of a specific type was unclear, setting the limit to 5 units per year of a particular device type. However, such a low number has led to rationing by the device manufacturers and even cessation of manufacturing of custom implants by one of the major companies. Another option available for obtaining patient specific implants is the Compassionate Use process. This process has been used, for example, when a patient needs a replacement of a part for a device that is not approved for use in the United States. The surgeon can request an exemption from FDA to use the part. To obtain this exemption, the surgeon must provide to FDA a justification letter explaining why using this device is in the best interests of the patient, a letter from a second surgeon who agrees with this conclusion, a letter from the implant company agreeing to manufacture the device, IRB approval from the institution where the device will be implanted, and consent from the patient. Though gathering this information can be time consuming, once the application is submitted, FDA has rapidly responded in providing exemptions (in less than two weeks). Conclusion. Even with the increase in modular components and the variety of devices in the commercial market, the need still exists for patient specific implants at HSS. The regulatory environment creates additional challenges to obtaining these devices. In spite of these challenges, we are able to provide the devices required for our patients

Correct alignment of tibial and femoral components is one of the most important factors that determine favorable long-term results of total knee arthroplasty (TKA). Computer-assisted TKA allows for more accurate component positioning and continuous intraoperative monitoring of the alignment. However, the pinholes created by the temporally anchored pins used as reference points may cause problems. Here we report a case of tibial stress fracture that occurred after a TKA was performed with the use of a computer navigation system. Case report. The patient, a 76-year-old woman (height 157 cm, weight 73 kg and BMI 29.5 kg/m. 2. ) with bilateral knee osteoarthritis. The right knee was replaced first and recovered without complications. The left knee was replaced 2 weeks later. The patient underwent computer-assisted (Stryker Co., Allendale, NJ, USA), cemented, posterior cruciate ligament sacrificing replacement of the left knee (with a Zimmer Gender Solutions Knee). A midline skin incision was made and a 5.0 mm bicortical self-tapping anchoring pin was inserted 10 cm below the tibiofemoral joint line. The other anchoring pin was inserted into the femur at the same distance from the joint to the line. These pins were inserted bicortically, anterior to posterior. Femur and tibia resections were performed according to the light-emitting diode tracker on the navigation system and cutting jig. Femoral and tibial implants were fixed with cement. The anchoring screws were then removed after the fixation of all implants. For two weeks, the patient tolerated significant walking but experienced only vague pain and swelling at the site of the left proximal tibial area. Local heat or redness was not observed and inflammatory serological markers (erythrocyte sedimentation rate, c-reactive protein level and white blood cell count) were within normal limits. One week later the patient complained of more aggravated and persistent pain. The patient immediately had a radiography check-up which showed a long linear radiolucent line and cortical defect through the pinholes (Fig. 1A–D). Through close scrutiny of the radiographs taken immediately after and two weeks after the operation, it was realized that she had a tibial stress fracture resulting from a misplaced fixation pin (Fig. 2A, B). As a result, the patient wore a long leg splint and was instructed to avoid weight bearing for two weeks. She was then allowed to gradually put more weight after wearing along leg cast for four weeks. Clinically, a satisfactory outcome was reported by the patient with good recovery of her daily activities; crutches were no longer needed to walk after three months. Physical examination showed no tenderness and final ROM was 0–120 degrees. Radiography showed that the stress fracture was completely healed (Fig. 3A, B). Conclusively, we suggest that unicortical anchoring pins with a small diameter should be considered for use in the metaphyseal area and avoidance of transcortical drilling is recommended. Care should be taken to avoid stress fracture during rehabilitation in case of the development of pain after a pain-free period following computer assisted TKA

We performed a systematic review and meta-analysis to compare the efficacy of intermittent mechanical compression combined with pharmacological thromboprophylaxis, against either mechanical compression or pharmacological prophylaxis in preventing deep-vein thrombosis (DVT) and pulmonary embolism in patients undergoing hip or knee replacement. A total of six randomised controlled trials, evaluating a total of 1399 patients, were identified. In knee arthroplasty, the rate of DVT was reduced from 18.7% with anticoagulation alone to 3.7% with combined modalities (risk ratio (RR) 0.27, p = 0.03; number needed to treat: seven). There was moderate, albeit non-significant, heterogeneity (I² = 42%). In hip replacement, there was a non-significant reduction in DVT from 8.7% with mechanical compression alone to 7.2% with additional pharmacological prophylaxis (RR 0.84) and a significant reduction in DVT from 9.7% with anticoagulation alone to 0.9% with additional mechanical compression (RR 0.17, p < 0.001; number needed to treat: 12), with no heterogeneity (I² = 0%). The included studies had insufficient power to demonstrate an effect on pulmonary embolism.

We conclude that the addition of intermittent mechanical leg compression augments the efficacy of anticoagulation in preventing DVT in patients undergoing both knee and hip replacement. Further research on the role of combined modalities in thromboprophylaxis in joint replacement and in other high-risk situations, such as fracture of the hip, is warranted.