Introduction. Post cam structure, which is the main structure of posterior-stabilized design (PS), is useful to realize the intrinsic stability of a knee prosthesis replaced for a case with the severe degeneration. A large size post might, however, shorten the range of knee motion. On the other hand, retrieval studies sometimes reveal the ultrahigh molecular weight polyethylene (UHMWPE) deformation or severe failure of the tibial post of PS knee. Strength of a tibial post of available design is obviously insufficient to prevent the severe deformation. Therefore, minimally required size of the post should be clarified for polyethylene inserts. In the present study, we performed finite element (FE) analysis assumed the mechanical conditions of a tibial post in a PS knee and aimed to design criterion of a post of polyethylene insert of a knee prosthesis. Method. The shape of one commercially available knee prosthesis was referred as a posterior-stabilized knee prosthesis. The contour of the metallic femoral component was traced and digitized by hand. The contour of the UHMWPE insert was digitized by a micro computed tomography apparatus. Three dimensional finite elements were generated by a modeling software (Simpleware, Ltd. UK) as total 83000 four-noded tetrahedral elements. The bottom of the tibial insert was fully constrained. Load on femoral component was assumed to realize the tibial post impingement under several kinds of knee motions. Posterior load 100 N or 500N at the 10 degree hyperextension, anterior load 500N or 1000N during 120 degree flexion were applied (Fig. 1). The software of FE analysis was LS-DYNA ver.971 (Livemore Software Technology Corp. USA). The hardware was Endeaver Pro-4500 (EPSON Corp. Japan). The distributed values of von Mises stress and plastic strain of the tibial post were shown as the results of the analysis. Results. At the 10 degree hyperextension, the maximum values of von Mises stress and plastic strain of anterior aspect of tibial post were 26.0 MPa, 0.054 at posterior load 100 N., 35.3 MPa, 0.383 at posterior load 500N, respectively (Fig. 2). At 120 degree flexion, these values of posterior aspect of tibial post were 27.6 MPa, 0.086 at anterior load 500 N, 32.1 MPa, 0.208 at anterior load 1000N, respectively (Fig. 3). Plastic deformation has occurred on the contact area, as shown in Fig. 2, 3. Discussion. Our results showed that large plastic deformation may occur in the anterior or the posterior aspect of a tibial post by impingement during common exercises like running, climbing up, or squatting. In the femoro-tibial articulation, the true-stress decreases with increase in load because the compressive deformation can widen the contact area on the UHMWPE. The true-stress in the tibial post, however, increases with increase in load because bending and tensile deformation reduces the section area. Therefore, the design criterion of tibial post of PS knee prosthesis including the size of the post must be revised the safety coefficient that realize the sufficiently lower stress generated in the tibial post than the yield stress of UHMWPE

Introduction. Post cam is useful to realize the intrinsic stability of a posterior-stabilized (PS) knee prosthesis replaced for a case with the severe degeneration. Some retrieval studies reveal the ultrahigh molecular weight polyethylene (UHMWPE) deformation or severe failure of the tibial post of PS knee. Strength of the tibial post of available design is obviously insufficient to prevent the severe deformation. The large size post might, however, shorten the range of knee motion. Therefore, minimally required size of the post should be clarified for polyethylene inserts. In the present study, we performed finite element (FE) analysis assumed the mechanical conditions of a tibial post in a PS knee and aimed to design criterion of a post of polyethylene insert of a knee prosthesis. Method. The shape of three commercially available knee prostheses, product A, B, and C was referred as PS knee prosthesis. The contour of the metallic femoral component and the UHMWPE insert were digitized by a computed tomography apparatus. Three dimensional finite elements were generated by modeling software (Simpleware, Ltd. UK) as four-node tetrahedral elements. In FE analysis, we used LS-DYNA ver.971 (Livemore Software Technology Corp. USA) as the software and Endeaver Pro-4500 (EPSON Corp. Japan) as the hardware. These bottoms of the tibial insert were fully constrained. The value of 30MPa was defined as yield stress of UHMWPE. 500N posterior load was applied to each femoral component at 10 degree hyperextension. Then, 1000N anterior load at 120 degree flexion, after tibial insert was located 10 degree internal rotation (Fig. 1). These loads were assumed to realize the two types of tibial post impingement under several kinds of knee motions. The distributed values of von Mises stress and plastic strain on the tibial post were shown as the results of the analysis. Results. At the 10 degree hyperextension, these maximum values of von Mises stress were 24.5, 3.23, 27.09MPa on anterior aspect of tibial post of the product A, B, and C, respectively (Fig. 2). These plastic strains were 0.045, 0.001, 0.064. At the 120 degree flexion, these maximum values of von Mises stress were 33.67, 4.53, 27.03MPa on posterior aspect of the product A, B, and C, respectively (Fig. 3). These plastic strains were 0.28, 0.004, 0.061. The stress of product A was higher than yield stress of UHMWPE. The strain was obviously higher than that of product B and C. Discussion. Our results showed that plastic deformation may occur in the posterior aspect of a tibial post by impingement during common exercises like climbing up, or squatting. In the femoro-tibial articulation, the true-stress decreases with increase in load because the compressive deformation can widen the contact area on the UHMWPE. The true-stress in the tibial post, however, increases with increase in load because bending and tensile deformation reduces the section area. Therefore, the design criterion including the post size must be revised the safety coefficient which realizes that the generated stress in the tibial post is sufficiently lower than the yield stress of UHMWPE

Introdution:. Over the last years research has focused on attempts to achieve better fixation in knee prosthesis by improving cementing techniques and prosthetic designs; thus prosthetic fixation is critical while loosening at the bone-cement interface is still an important matter for the orthopaedic surgeon. Material and Method:. In the present study, we evaluated in vivo displacement of both total and unicompartimental knee prosthesis implanted on 73 patients by collecting data from RSA associated to the conventional X-rays and clinical follow-ups; we were able to reach only 18 patients (2 males and 16 females) for the actual follow up because of death or other diseases occurred on the other patients over the years (mean age at the time of surgery 68, range 27–83). Results:. As shown in Fig 1 there is an evident increase of MPTM during time and this is an effect of the implant wear. Comparing this trend with a early stability MPTM, after a stabilization of the implant during the first 2 years, we can define a plateau of normal working and after it a degenerative curve. Fig 2 shows the trend of the patient as KSS score. It is evident the pre- to post- operative increase of the curves. After it there is a valley during the normal activity, that is not evident as MPTM modification and then a trend of degeneration starting from 8–10 years of follow-up. Conclusions:. Our study highlighted the trend of a prosthesis during all of is life. The RSA device guarantees a very good image quality and the implant life curves became very accurate. Further studies are going to better characterize that curves and correlation between migration and clinical scores at long term follow up

INTRODUCTION. Total knee arthroplasty (TKA) is one of the most successful and beneficial treatments for osteoarthritic knees. We have developed posterior-stabilized (PS) total knee prosthesis for Asian patients, especially Japanese patients, and have used it since November, 2010. The component was designed based on the CT images of osteoarthritic knees, aiming to achieve deep flexion and stability. The purpose of this study was to analyze in- vivo kinematics of this new prosthesis. METHODS. We analyzed a total of 28 knees implanted with PS TKAs: Fourteen knees with the new PS prosthesis (group A), and the other fourteen knees with a popular PS prosthesis as a control group (group B). Preoperative data of both groups were not significantly difference. Flat-panel radiographic knee images were recorded during five static knee postures including full extension standing, lunge at 90° and maximum flexion, and kneeling at 90° and maximum flexion. The three-dimensional position and orientation of the implant components were determined using model-based shape matching techniques. The results of this shape-matching process have standard errors of approximately 0.5° to 1.0° for rotations and 0.5 to 1.0 mm for translations in the sagittal plane. Unpaired t-tests were used for statistical analysis and probability values less than 0.05 were considered significant. RESULTS. The maximum implant flexion angles tended to be greater in group A than group B (Fig. 1a), averaging 117±8° and 109 ± 14° in lunge (p=0.054), and 119 ± 7° and 110 ± 14° in kneeling (p=0.061), in Groups A and B respectively. Femoral external rotation was significantly smaller in group A than group B (Fig. 1b), averaging 7±7° and 10±5° mm in lunge (p<0.05), and 6±7° and 8±3° in kneeling (p<0.05). The medial condylar AP translations were greater in group A than group B (Fig. 1c), averaging −7±3mm and −3±3mm in lunge (p<0.05), and −6±2mm and −4±3mm in kneeling (p<0.05), respectively. Lateral condylar AP translations were not significantly different between the two groups except at 90° kneeling (Fig. 1d). DISCUSSION. Both implants are designed to achieve deep flexion, preventing edge loading until 155° flexion. Post/cam engagement occurs at 75° flexion in both system and the implant shapes are similar. Positive correlations have been reported between increasing femoral posterior translation and greater maximum knee flexion. The cam/post design of the new implant is configured to provide approximately 8mm of posterior femoral translation at 120° flexion which, on average, was slightly greater than observed in the control knees. Slightly greater lunge and keeling flexion in knees with the new design may be a manifestation of this greater posterior femoral translation. Previous studies have failed to demonstrate axial rotation as a predictor of greater flexion. Likewise, our data do not show a relationship between axial rotation and maximum flexion. The new TKA designed for Asian knees appears to perform comparably to a traditional high-flexion PS design, but may show some improvement in functional flexion due to greater posterior femoral translation

The effect of an advanced porous surface morphology on the mechanical performance of an uncemented femoral knee prosthesis was investigated. Eighteen implants were inserted and then pushed-off from nine paired femurs (Left legs: advanced surface coating; right legs: Porocoat® surface coating as baseline). Bone mineral density (BMD) and anteroposterior dimension were measured, which both were not significantly different between groups. The insertion force was not significantly different, but push-off force was significantly higher in the advanced surface coating group (P = 0.007). BMD had direct relationship with the insertion force and push-off force (p < 0.001). The effect of surface morphology on implant alignment was very small. We suggest that the surface properties create a higher frictional resistance thereby providing a better inherent stability of implants featuring the advanced surface coating

Introduction

Revision of total knee endoprostheses (TKA) is increasing in number and causes rising healthcare costs. For constrained prostheses, the use of intramedullar femoral stems is standard. However, there is a big variety of available stem types with regard to length, type of fixation (cemented vs. hybrid) and fixation area (diaphyseal vs. metaphyseal). The aim of this biomechanical study was to investigate the primary stability of revision TKA with different stem types and different femoral bone defects, to find out whether smaller or shorter stems may achieve sufficient stability while preserving bone for re-revision.

INTRODUCTION. Computer-aided systems have been developed recently in order to improve the precision of implantation of a total knee replacement (TKR). Several authors demonstrated that the accuracy of implantation of an unicompartmental knee replacement (UKR) was also improved. Minimal invasive techniques have been developed to decrease the surgical trauma related to the prosthesis implantation. The benefits of minimal-incision surgery might include less surgical dissection, less blood loss and pain, an earlier return to function, a smaller scar, and subsequently lower costs. However, there might be a concern about the potential of minimal invasive techniques for a loss of accuracy. Navigation might help to compensate for these difficulties. Mobile bearing prostheses have been developed to decrease the risk of polyethylene wear. The benefits might be a better survival and less bone loss during revisions. However, these prosthesis are technically more demanding, and involve the specific risk of bearing luxation. Again, navigation might help to compensate for these difficulties. MATERIAL AND METHODS. We wanted to combine the theoretical advantages of the three different techniques by developing a navigated, minimal invasive, mobile bearing unicompartmental knee prosthesis. 160 patients have been operated on at our institution with this system. The 81 patients with more than 2 year follow-up have been re-examined. Complications have been recorded. The clinical results have been analyzed according to the Knee Society Scoring System. The subjective results have been analyzed with the Oxford Knee Questionnaire. The accuracy of implantation has been analyzed on post-operative antero-posterior and lateral long leg X-rays. The 2-year survival rate has been calculated. RESULTS. We observed 8 complications related to the implant or the operative technique: 2 cases of meniscus instability (1 revision to TKR, 1 bearing exchange); 2 cases of tibia loosening (revised to TKR), 2 cases of femoral loosening (revised to TKR), 1 case of lateral disease progression (revised to TKR), 1 case of unexplained pain syndrome (revised to TKR). The mean Knee Score was 93 points, 44% had the maximum of 100 points, and only 10% have less than 85 points. The mean pain score was 48 points/50. The mean flexion angle was 128°, and 60% had at least 130° of knee flexion. The mean Function Score was 97 points, 84% have the maximum of 100 points, and only 5% had less than 85 points. The mean Oxford Knee Questionnaire score was 19 points (best result: 12 points, worst result: 60 points). Expected limb axis correction was obtained in 77% of the cases. 62% of the cases had an optimally implanted prosthesis for all studied criteria. The 2-year survival rate was 97%. DISCUSSION. Most of the revision cases were related to technical difficulties during the development phase. Fixation of the implant has been improved, and some imprecise steps of the software have been corrected. Since these changes occurred, no severe early complication related to implant or software has been observed. The current implant is considered reliable, and the current minimal invasive navigated technique is considered reliable as well

Aim

To describe the management of PJI due to S. aureus in CRIOAcs in 2019 and to particularly focus on the evaluation of the efficacy of DAIR regarding control of infection and risk factors for failure up to 12 months.

Introduction

Mobility at insert-tray articulations in mobile bearing knee implant accommodates lower cross-shear at polyethylene (PE) insert, which in turn reduces wear and delamination as well as decreasing constraint forces at implant-bone interfaces. Though, clinical studies disclosed damage due to wear has occurred at these mobile bearing articulations. The primary goal of this study is to investigate the effect of second articulations bearing mobility and surface friction at insert-tray interfaces to stress states at tibial post during deep flexion motion.

Clinical outcomes for total knee arthroplasty (TKA) are sensitive to lower extremity alignment, implant positioning, and implant size. Accurate determination of femoral implant size is the focus of this paper. As existing methods (conventional instrumentation, preoperative images, navigation) can be limited by issues including inaccuracy, time required, exposure, and cost, this study assesses a novel method for determining femoral component size using navigation.

We used a commercially available navigation system (Exactech GPS, Blue Ortho, Grenoble, FR, with Total Knee V1.13 software). The system uses surface patches to collect small point clouds, and then computes points that match a given criteria (e.g. the most distal point). For femoral component sizing, the proposed method automatically defines a target area to be digitised on the anterior cortex.

To do this, the surgeon acquires anatomical landmarks (i.e., knee centre, distal condyles, etc.) for all femoral implant parameters but the size. The surgeon then moves the tip of the acquisition instrument near the anterior cortex, and the system computes the distance between the virtual posterior cut and the tip in real time. The theoretical implant size increases in real time as the instrument tip moves anteriorly and decreases as it moves posteriorly. The target area is displayed on the anterior cortex such that it covers all the bone in the medio-lateral direction, is centred on the most proximal part of the theoretical implant in the proximal-distal direction, and covers the current size plus or minus one size. As a result, the target area virtually moves in the proximal-distal direction as the surgeon moves the instrument tip closer to the anterior cortex surface. When the tip is in contact with the anterior surface, acquisition of the point cloud is performed. From a user point of view, the system does not move the target area relative to the bone on the display, but instead adjusts the relative position of the instrument tip, creating the impression that no matter the bone size, the target area does not move and the instrument tip is always guided to the right spot.

The method has been successfully implemented and used on more than 1,400 patients. A preliminary analysis on 189 surgical reports shows in 188 cases (99,5%) the proximal point of the selected implant is inside the target area (which means that the selected size is the one by default, plus or minus one).

We conclude the proposed method as implemented in the Exactech GPS has proven to be clinically effective. It can easily be extended to determination of other points when global criteria can be used to define an optimal area of digitisation determined from previously acquired data.

Over the past twenty years, the Low Contact Stress Rotating Platform (LCS RP) showed good results. Buechel and Pappas invented the Buechel-Pappas Knee (B-P Knee) system that is a modified version of the LCS system with different material (titanium), axial rotation limiting bar and improved conformity. The purpose of this prospective randomized study was to compare the 2-year clinical outcomes between two implants in the same patients who had been operated with bilateral TKAs. We prospectively enrolled 107 patients and 18 patients were lost to follow-up. Therefore, 89 patients (178 knees; mean age, 69.8±6.0years) were included in the study. The range of motion and clinical scores such as Knee Society score (KSS), Hospital for Special Surgery score (HSS) and Western Ontario and McMaster University (WOMAC) scores were measured preoperatively and postoperatively. At each follow-up, patients also complete a Likert scale questionnaire regarding subjective pain, lightness, left-right side preference (naturalness and satisfaction) and subjective instability. There were no significant differences in all preoperative variables between the two groups(P<.05). Mean follow-up period was 29.9±7.2 months. At the 2-year follow-up, mean value of flexion contracture, further flexion and range of motion were not significantly different between both groups. Also, there were no significant differences in the clinical scores and in side to side difference for the feeling of laterality between two groups(P<.05). After minimum 2-year follow-up, we found no differences in early clinical outcomes as well as subjective side to side difference between the LCS RP and B-P Knee system in this study.

INTRODUCTION

Revision total knee replacement (TKR) is a challenging procedure, especially because most of the standard bony and ligamentous landmarks used during primary TKR are lost due to the index implantation. However, as for primary TKR, restoration of the joint line, adequate limb axis correction and ligamentous stability are considered critical for the short- and long- term outcome of revision TKR. Navigation system might address this issue.

Femoral component fracture is a rarely reported but devastating complication of total knee arthroplasty. It has occurred most frequently with Whiteside Ortholoc II replacements uncemented knee replacements. Presentation may be with acute pain, progressive pain or returning deformity. It occurs more commonly in the medial condyle of the femoral component. It is rarely seen in cemented replacements.

All currently available literature describing fractures of condylar replacements, both cemented and uncemented. Predisposing factors include varus deformity either pre or post operatively. The mechanism of failure is thought to be failure of the infiltration of bone into the replacement. This is often due to polyethylene wear or metallosis causing abnormal tissue reaction with or without osteolysis.

We present the case of a fractured Press Fit Condylar (PFC) cemented implant (DePuy, Johnson&Johnson, Raynham, Massachusettes, USA) affecting the medial condyle. To our knowledge this is only the third reported case of fracture in a PFC implant, and the first in a cemented PFC implant.

Our patient was a 64 year old male who presented with unresolving knee pain post total knee arthroplasty, caused by fatigue fracture of the medial condyle of the femoral component. This was identified as loosening on plain radiographs and replaced with a revision prosthesis with a good post operative result. Given our aging population and with the increase of joint arthroplasty, this case sheds light on a potentially under recognised and increasingly important cause of knee pain following arthroplasty.

We have assessed the bone cuts achieved at surgery compared to the planned cuts produced during computer assisted surgery (CAS) using a CT free navigation system. In addition, two groups of matched patients were compared to assess the post-operative mechanical alignment achieved: 14 patients received a LCS total knee replacement (TKR) using the VectorVision module and 14 received a TKR using a conventional method of extramedullary alignment jigs The deviation in each plane (valgus-varus, flexion-extension and proximal-distal) was calculated.

For the tibia the mean deviation in the coronal plane was 0.21 degrees of Varus (SD = 1.37) and in the sagittal plane was 1.29 degrees of flexion (SD = 3.73) and 0.24 mm of resection distal to the anticipated cut (SD = 2.14). For the femur the mean deviation in the coronal plane was 0.88 degrees (SD = 2.2) of valgus and in the sagittal plane the mean deviation was 0.3 degrees (SD = 2.91) of extension. In the transverse plane there was a mean deviation of 0.07 degrees (SD = 1.57) of external rotation. There was mean deviation of 2.33 mm of proximal resection (SD = 2.9) and 1.05 mm of anterior shift (SD = 2.81).

On comparing the two groups, no statistically significant differences were found for the angles between the femoral component and the femoral mechanical axis, the tibial component and the tibial mechanical axis, the femoral and tibial mechanical axis and the femoral and tibial anatomical axis.

We have demonstrated variation in the true bone cuts obtained using computer assisted surgery from those suggested by the software and have not demonstrated significant improvement in post-operative alignment. Justification for the extra cost, time and morbidity associated with this technology must be provided in the form of improved clinical outcomes in the future.

INTRODUCTION

A preoperative planning for accurately predicting the size and alignment of the prosthetic components may allow to perform a precise, efficient and reproducible total knee replacement. The planning can be carried out using as a support digital radiographic images or CT images with three-dimensional reconstruction. Aim of this prospective study is to evaluate and compare the accuracy of two different types of pre-operative planning, in determining the size of the femoral and tibial component in total knee arthroplasty performed with Patient Specific Instrument (PSI). The two compared techniques were: digital radiography and “CT-Based”.

INTRODUCTION

Computer-aided systems have been developed recently in order to improve the precision of implantation of a total knee replacement (TKR). Several authors demonstrated that the accuracy of implantation of TKR was higher with the help of a navigation system in comparison to the conventional, manual technique. Theoretically, the clinical results and the survival rates should be improved. Our team was one of the first all over the world which decided to use routinely a navigation system for TKR.

Prostheses designed with a mobile bearing polyethylene component allow an increased congruence between femoral and tibial gliding surface, and should decrease the risk of long-term polyethylene wear. We designed a prosthetic system with one of the highest congruence on the current market. These prostheses might be technically more demanding than more conventional designs, and involve specific complications like bearing luxation. Navigation systems might be helpful in this was as well.

In the present study, we wanted to test clinically the theoretic advantages of these three specific points of our system (navigated implantation, mobile bearing and increased congruence) with a five-year clinical and radiological follow-up.

Total Knee Arthroplasty (TKA) is an effective surgery performed for knee osteoarthritis. Despite this success up to 20% of patients are less than fully satisfied. Rotating platform (RP) bearings have demonstrated significant reduction in rates of wear in laboratory studies but thus far have failed to demonstrate a clinical difference compared to fixed bearing (FB) arthroplasty in patients. This may be due to studies limited by small sample size and single centre design. Additionally, no studies have utilised modern patient-reported outcome measures (PROMs) such as PKIP to investigate differences between these bearings. A non-randomised, prospective, multi-centre study was conducted across centres in Australia, United Kingdom and the United States from November 2012 to May 2015. Knee prosthesis included were the RP and FB models of the PFC Sigma Knee (Depuy, Synthes) and the ATTUNE Knee (Depuy, Synthes). Data was collected on pre-arthroplasty interventions, demographics and PROMs. PROMs included were the KOOS, OKS, EQ53DL and PKIP. Participants were followed-up for 2 years. A total of 1,718 patients were recruited across 27 centres. 959 participants underwent a FB TKA, 759 participants underwent a RP TKA. No significant difference was found between RP and FB in change from baseline at 2 years across any parameter in all PROMs investigated at 2 years. Body Mass Index pre-operatively was the biggest indicator of change from baseline at 2 years. Our data demonstrates similar improvements in the short-term in both RP and TKA across all PROMs. Patients reported similar scores in satisfaction, confidence, mobility and stability in the PKIP PROM for both RP and FB groups. We have not found any evidence to suggest that RP TKA is disadvantageous at 2 years, and this is reassuring for any surgeon looking to utilise this bearing type in practice. Our data does not demonstrate a clinical advantage in RP TKA over FB TKA at 2 years in any PROM

Aim. In 10% of the presumed aseptic hip or knee revisions, a low-grade infection is unexpectedly diagnosed based on the tissue samples taken during revision. Extended antimicrobial prophylaxis can possibly reduce the failure rate in cases of unexpected PJI, because the prophylaxis can be considered as early empiric treatment. In this randomized controlled study we analysed whether extended antimicrobial prophylaxis compared to a single dose is beneficial to improve the outcome of treatment in unexpected PJI in revision arthroplasty. Method. This study was nested in a randomized clinical trial comparing single-dose cefazolin with prolonged prophylaxis (15 doses of cefazolin over 5 days) for revision arthroplasty of the hip or knee. For this analysis, patients were included if an unsuspected PJI (defined as ≥2 positive intraoperative tissue samples with the same microorganism) was diagnosed. PJI treatment consisted of 12 weeks of a rifampicin-based regimen in Staphylococcal PJI, without removal of the prosthesis. We examined Infection characteristics and success of treatment after one year, defined as the absence of signs or treatment for PJI during follow-up. Results. After randomization of 662 patients, 68 unexpected PJI were diagnosed. In 5 cases no antimicrobial treatment was started. The success rate after one year follow-up for those who received PJI treatment was 96% (28/29) in the single dose group and 91% (31/34) in the extended prophylaxis group (p=1.00). The most frequently identified pathogens in unexpected PJI were Cutibacterium acnes (n=50) and Staphylococcus epidermidis (n=14). The causatives were susceptible for the cefazolin prophylaxis in 61 of the 63 cases. The interval between the stopped prophylaxis and the re-start of antimicrobial treatment was on average 10 days (SD 4) for the single dose and 5 days (SD 4) for the extended group. The mean duration of antimicrobial treatment was 83 days (SD 12) and did not differ between both groups (p=0.16). Conclusions. This is the first randomized controlled trial in which extended prophylaxis showed no benefit on the prosthesis survival for patients with an unexpected PJI after assumed aseptic revision of the hip or knee prosthesis. The results imply that extended prophylaxis should not be given as part of early empiric therapy

Constrained implants with intra-medullary fixation are expedient for complex TKA. Constraint is associated with loosening, but can correction of deformity mitigate risk of loosening?. Primary TKA's with a non-linked constrained prosthesis from 2010-2018 were identified. Indications were ligamentous instability or intra-medullary fixation to bypass stress risers. All included fully cemented 30mm stem extensions on tibia and femur. If soft tissue stability was achieved, a posterior stabilized (PS) tibial insert was selected. Pre and post TKA full length radiographs showed. i. hip-knee-ankle angles (HKAA). ii. Kennedy Zone (KZ) where hip to ankle vector crosses knee joint. 77 TKA's in 68 patients, average age 69.3 years (41-89.5) with OA (65%) post-trauma (24.5%) and inflammatory arthropathy (10.5%). Pre-op radiographs (62 knees) showed varus in 37.0%. (HKAA: 4. o. -29. o. ), valgus in 59.6% (HKAA range 8. o. -41. o. ) and 2 knees in neutral. 13 cases deceased within 2 years were excluded. Six with 2 year follow up pending have not been revised. Mean follow-up is 6.1 yrs (2.4-11.9yrs). Long post-op radiographs showed 34 (57.6%) in central KZ (HKKA 180. o. +/- 2. o. ). . Thirteen (22.0%) were in mechanical varus (HKAA 3. o. -15. o. ) and 12 (20.3%) in mechanical valgus: HKAA (171. o. -178. o. ). Three failed with infection; 2 after ORIF and one with BMI>50. The greatest post op varus suffered peri-prosthetic fracture. There was no aseptic loosening or instability. Only full-length radiographs accurately measure alignment and very few similar studies exist. No cases failed by loosening or instability, but PPF followed persistent malalignment. Infection complicated prior ORIF and elevated BMI. This does not endorse indiscriminate use of mechanically constrained knee prostheses. Lower demand patients with complex arthropathy, especially severe deformity, benefit from fully cemented, non-linked constrained prostheses, with intra-medullary fixation. Hinges are not necessarily indicated, and rotational constraint does not lead to loosening

Background. Bacteriophages are natural viruses of interest in the field of PJI. A paper previously reported the PhagoDAIR procedure (use of phages during DAIR) in three patients with PJI for whom explantation was not desirable. As the need to isolate the pathogen before surgery to perform phage susceptibility testing is a strong hindrance for the development of this procedure, we developed post-operative phage injections using ultrasound, in patients infected with S. aureus and/or P. aeruginosa who were eligible for the PhagoDAIR procedure, but for whom phages were not available at the time of surgery. Materials/Methods. We performed a single center, exploratory, prospective cohort study including patients with knee PJI who received phage therapy with ultrasound after performance of a DAIR or a partial prosthesis exchange. All patients had PJI requiring conservative surgery and suppressive antimicrobial therapy (SAT) as salvage procedure. Each case was discussed in multidisciplinary meetings in agreement with French health authority, based on the clinical presentation, and the phage susceptibility testing. The cocktail of highly concentrate active phages (5 mL; about 10. e. 9 PFU/mL) was extemporaneous prepared and administered three times directly into the joint using sonography (1 injection per week during 3 weeks) during the postoperative period, before switching antibiotics to SAT. Results. Seven patients received phages under sonography after the DAIR, and one after a partial exchange (mean age 71 years). All had resection prosthesis or constrained knee prosthesis. Among these seven patients, three were infected with S. aureus (including one MRSA), two were infected with P. aeruginosa (one was a multidrug-resistant isolate), one was infected with both S. aureus and P. aeruginosa and the last one was infected with MRSA, S. epidermidis and Corynebacterium spp.. All patients received a cocktail of active phages provided by Pherecydes Pharma targeting S. aureus or P. aeruginosa. No adverse event was recorded during or after the local injections. All patients were switched to SAT after a primary postoperative antimicrobial therapy of three months. Under SAT, the patient with S. epidermidis co-infection developed a relapse due to the S. epidermidis. With a mean follow-up of 13 months after surgery (from 9 to 24 months), the outcome was favorable for all patients without any sign of infection; none of them had abnormal pain, joint effusion or loosening. Conclusions. Postoperative administration of phages using sonography is a potentially useful procedure in patients with complex PJI for whom a conservative approach is desirable