Aim. Bacterial identification in musculoskeletal infection is sometimes difficult and treatment strategy difficult facing unknown pathogen agent. We wonder if the delay of incubation and the preservation conditions of the samples between surgical procurement and subculture on plates have an influence. Method. 25 cm³ bone fragments were obtained from femoral heads retrieved during hip arthroplasty and excluded for bone transplant donation. Informed consent was obtained from the donor for research purpose. The study was approved by the Ethic Committee (N°B403201317725). Bone fragments were immersed for 30 minutes under gently agitation (140 RPM) at 35°C in a physiologic solution (negative control) or two solutions with two concentrations of staphylococcus epidermidis (0.5 Mc Farland or 1.5× 108 bacteria and 7.5×102 bacteria). Bone samples were separated and preserved at room temperature or at 4°C until seeded on Petri Plates to observe the influence of preservation conditions. Samples were plated after different delays (T0, T30min, T1H, T2H, T4H, T6H, T8H, T12H, T16H, T24H et T48H) to observe the influence of delay of culture. Experiments were repeated 5 times. When culture was positive, results were expressed with the number of colony. Results. We observed a regular diminution of number of colonies with the delay of culture. The number of colony goes to zero after 40 hours when the samples have been preserved at room temperature. Differences were not significant between preservation at room temperature and at 4°C for delay inferior to 04 hours but become significant for higher delay of culture in favor of low temperature preservation. With a low bacterial bioburden, no colony was recovered after a delay of 06 hours. False positive results were observed in 4% of the negative control. Conclusions. This experimental model demonstrates the negative influence of delay of culture and preservation at room temperature if the culture is delayed for more than 04 hours. The negative influence is more critical when facing low bacterial bioburden as it is generally the case in musculoskeletal infections. Our model do not included biofilm embedded bacteria and is limited to a staphylococcus epidermidis strain. The results could be worse with anaerobic bacteria. Some inhibition due to antibi prophylaxis given to patient just before hip arthroplasty could have negatively influence the results. This study stresses the importance of a rapid seeding of bacterial samples to improve bacterial identification. Procedures should be in place to transfer rapidly samples to the lab and process them immediately

Aim

To demonstrate the effect of location of the split of the plaster on the raised intercompartmental pressure in the volar and dorsal compartments.

Aim. The utilization of silver as an anti-infective agent is a subject of debate within the scientific community, with recurring discussions surrounding its biocompatibility. Presently, galvanic silver coating finds widespread clinical application in mitigating infection risks associated with large joint arthroplasties. While some instances have linked this coating to sporadic cases of localized argyria, these occurrences have not exhibited systematic or functional limitations. To address concerns regarding biocompatibility, a novel approach has been devised for anti-infective implant coatings: encapsulating silver nitrate within a biopolymer reservoir for non-articulating surfaces. This poly-L-lactic acid layer releases silver ions gradually, thereby circumventing biocompatibility concerns. Method. Female C57BL/6 mice were utilized as an experimental model, with 6x2 mm Ti6Al4V discs, coated with or without the biopolymer-protected silver coating, implanted subcutaneously on both sides of the vertebrae. Daily blood samples were collected, and serum was analyzed for C-reactive protein (CRP) and silver concentration. After three days, histopathological analyses were conducted on the surrounding soft tissue pouch. Results. Maximum CRP levels in the silver group (4.80 mg/L; Median: 3.29 mg/L; IQR: 2.38 to 3.73) did not significantly differ from the control group (4.58 mg/L; Median: 2.93 mg/L; IQR: 1.91 to 3.78) over the study period. Silver levels in serum 24 hours post-implantation were 64 µg/L (IQR: 35 to 78) and decreased subsequently over three days to 23 µg/L (IQR: 13 to 28). Histopathological examinations revealed a similarly strong expression of inflammation signs in tissue samples from the two groups. Conclusions. Despite evidence of local inflammation indicated by CRP and histopathological analysis, no significant difference was observed between the coated and uncoated groups. This suggests that any inflammation may be attributed to the implantation procedure rather than silver influence. Furthermore, silver levels remained below the toxic limit, indicating the efficacy of the biopolymer-protected reservoir in aiding biocompatibility. This study underlines the potential of biopolymer-protected silver reservoirs in enhancing the safety profile of anti-infective silver implant coatings, warranting further investigation into their clinical application

Aim. The aim of this study is to evaluate if the gentamycin elution from bone cement is influenced by the timing of application of the antibiotic powder. Method. This was an experimental in vitro study that compared the elution properties of different formulation of gentamycin from a commercially available hip, knee and shoulder cement spacers. Four different experimental models were prepared. Five different spacers were prepared for each experimental mode and for each joint. We compared four different formulation of cement spacers: spacer #1, in which the spacer was prepared with a premixed bone-cement antibiotic mixture; spacer #2, in which the spacer was prepared by adding antibiotic powder to the bone cement at the time of spacer preparation; spacer #3, in which the spacer was prepared as spacer #2 but was stored for two months before starting the experiment; spacer #4, in addition to the gentamycin, other two antibiotics (tobramycin and vancomycin) were added to the bone cement. Gentamycin concentration was documented at seven intervals of time: T0 = 0h, T1 = 1h, T2 = 24h, T3 = 1W, T4 = 2W, T5 = 1M, T6 = 3M and T7 = 6M. The gentamycin elution at each interval of time was evaluated by using a T-student test. Results. Spacer #2, in which the gentamycin powder was added to the bone cement at the time of spacer preparation showed the higher gentamycin elution at each interval of time observed. In addition, Spacer #1, in which gentamycin powder was premixed with the bone cement showed a higher gentamycin elution when compared with spacer #3, in which the spacers were stored for two months to simulate the preformed spacers. Lastly, the addition of different antibiotic to the bone cement increases the gentamycin elution from the spacers (as demonstrated by spacer #4 model). Conclusions. a higher gentamycin elution was observed if spacer was prepared at the time of surgery when compared with preformed spacer. Lastly, our study confirmed the synergistic effect of adding one or more antibiotics with the aims to increase gentamycin elution

Introduction. Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was to develop an experimental model which would simulate the clinical revision hip scenario and to determine the effects of alendronate coating on porous tantalum on gap filling and bone ingrowth in the experimental model. Methods. Thirty-six porous tantalum plugs were implanted into the distal femur, bilaterally of 18 rabbits for four weeks. There were 3 groups of plugs inserted; control groups of porous tantalum plugs (Ta) with no coating, a 2nd control group of porous tantalum plugs with micro-porous calcium phosphate coating, (Ta-CaP) and porous tantalum plugs coated with alendronate (Ta-CaP-ALN). Subcutaneous fluorochrome labelling was used to track new bone formation. Bone formation was analysed by backscattered electron microscopy and fluorescence microscopy on undecalcified histological sections. Results. The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 124%, 232% and 170% respectively in Ta-CaP-ALN compared with the uncoated porous tantalum (Ta) controls, which was statistically significant. The contact length of new bone formation on porous tantalum implants in Ta-CaP-ALN was increased by 700% (8-fold) on average compared with the uncoated porous tantalum (Ta) controls. Discussion. Alendronate coated porous tantalum significantly modulated implant bioactivity compared with controls. This study has demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth, which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss, the addition of alendronate as a surface coating would enhance biological fixation of the implant and promote the healing of bone defects

Background. Surgical site infection following spine surgery is associated with increased morbidity, mortality and increased cost for the health care system. The reported pooled incidence is 3%. Perioperative antibiotic prophylaxis is a key factor in lowering the risk of acquiring an infection. Previous studies have assessed perioperative cefuroxime concentrations in the anterior column of the cervical spine with an anterior surgical approach. However, the majority of surgeries are performed in the posterior column and often involve the lumbar spine. Accordingly, the objective was to compare the perioperative tissue concentrations of cefuroxime in the anterior and posterior column of the same lumbar vertebra using microdialysis in an experimental porcine model. Method. The lumbar vertebral column was exposed in 8 female pigs. Microdialysis catheters were placed for sampling in the anterior column (vertebral body) and posterior column (posterior arch) within the same vertebra (L5). Cefuroxime (1.5 g) was administered intravenously over 10 min. Microdialysates and plasma samples were continuously obtained over 8 hours. Cefuroxime concentrations were quantified by Ultra High Performance Liquid Chromatography Tandem Mass Spectrometry. Microdialysis is a catheter-based pharmacokinetic tool, that allows dynamic sampling of unbound and pharmacologic active fraction of drugs e.g., cefuroxime. The primary endpoint was the time with cefuroxime above the clinical breakpoint minimal inhibitory concentration (T>MIC) for Staphylococcus aureus of 4 µg/mL as this has been suggested as the best predictor of efficacy for cefuroxime. The secondary endpoint was tissue penetration (AUC. tissue. /AUC. plasma. ). Results. Mean T>MIC 4 µg/mL (95% confidence interval) was 123 min (105–141) in plasma, 97 min (79–115) in the anterior column and 93 min (75–111) in the posterior column. Tissue penetration (95% confidence interval) was incomplete for both the anterior column 0.48 (0.40–0.56) and posterior column 0.40 (0.33–0.48). Conclusions. Open lumbar spine surgery often involves extensive soft tissue dissection, stripping and retraction of the paraspinal muscles which may impair the local blood flow exposing the lumbar vertebra to postoperative infections. A single intravenous administration of 1.5 g cefuroxime resulted in comparable T>MIC between the anterior and posterior column of the lumbar spine. Mean cefuroxime concentrations decreased below the clinical breakpoint MIC for S. aureus of 4 µg/mL after 123 min (plasma), 97 min (anterior column) and 93 min (posterior column). This is shorter than the duration of most lumbar spine surgeries, and therefore alternative dosing regimens should be considered in posterior open lumbar spine surgeries lasting more than 1.5 hours

Introduction. Initial stability of cementless total knee arthroplasty (TKA) tibial trays is necessary to facilitate biological fixation. Previous experimental and computational studies describe a dynamic loading micromotion test used to evaluate the initial stability of a design. Experimental tests were focused on cruciate retaining (CR) designs and walking gait loading. A FEA computational study of various constraints and activities found CR designs during walking gait experienced the greatest micromotion. This experimental study is a continuation of testing performed on CR and walking gait to include a PS design and stair descent activity. Methods. The previously described experimental method employed robotic loading informed by a custom computational model of the knee. Different TKA designs were virtually implanted into a specimen specific model of the knee. Activities were simulated using in-vivo loading profiles from instrumented tibia implants. The calculated loads on the tibia were applied in a robotic test. Anatomically designed cementless tibia components were implanted into a bone surrogate. Micromotion of the tray relative to the bone was measured using digital image correlation at 10 locations around the tray. Three PS and three CR samples were dynamically loaded with their respective femur components with force and moment profiles simulating walking gait and stair descent activities. Periods of walking and stair descent cycles were alternated for a total of 2500 walking cycles and 180 stair descent cycles. Micromotion data was collected intermittently throughout the test and the overall 3D motion during a particular cycle calculated. The data was normalized to the maximum micromotion value measured throughout the test. The experimental data was evaluated against previously reported computational finite element model of the micromotion test. Results. The maximum average micromotion was on the CR design during walking gait. The greatest CR micromotion during stair descent was 67% of the maximum. The maximum micromotion in the PS design was 55% of the CR walking maximum and occurred during stair descent. The next highest PS value was 52% during walking. The absolute difference in these values was under 3 µm. The majority of the PS micromotion values around the tray were less than 50% that of the maximum micromotion of the CR design. Discussion. The experimental continuation of this investigation into cementless tray stability aligned with computational results in this model. The computational model predicted the PS tray would have 50% of the micromotion of the CR design, which was close to the experimental test. For CR, the computational rank order for walking and stair descent was also the same in the experimental follow-up. Future work in this investigation will include continued validation of the computational and experimental models, including more designs. Further exploration into accounting for patient and surgical variability should be explored. For any figures or tables, please contact authors directly

Aim. Propionibacterium acnes (PA) is an important cause of shoulder prosthetic joint infections (SPJIs) for which the optimal treatment has not yet been determined. Rifampicin and Levofloxacin both showed not benefit in recent experimental models of PA-SPJIs. We describe herein the experience of five different medical French centers in order to assess factors associated with patient's outcome with special emphasize on antibiotic regimens. Method. A multicentric retrospective study was performed, on consecutive patients with PA – related SPJIs diagnosed on the basis of at least 2 or more positive cultures of either per-operative or joint aspiration and clinical history compatible with a PJI according to the current guidelines. All patients had surgical management, followed by systemic antibiotic therapy. Remission was defined as an asymptomatic patient with functioning prosthesis at the last contact. Results. Fifty-nine patients of mean age 66.2 ± 10.5 years were included. Most patients were at least ASA 2 (66%), 8 (14%) diabetes mellitus, 3 (5%) had neoplasia. Fourteen patients (24%) had acute, 34 (58%) subacute, and 11 late infections (19%). The mean delay from symptoms of infection to surgery was 89 ± 141 days (1–660). Surgical management consisted in implant exchange in 40 (68%) patients. Antibiotic treatment included mainly clindamycin (49%), levofloxacin (44%) and rifampin (17%), with a mean duration of 52.3 ± 31.9 days. The mean follow-up duration was 540 days ± 488 (range 12 ™ 1925). Forty-five patients were in remission (76%) in this study, 8 patients had a relapsing infection (14%), 1 a recurrence (2%) and 5 a superinfection ™ i.e, due to a different pathogen − (8%). In monovariate analysis, rifampicin/levofloxacin treatment was significantly associated with failure (p=0.038). In multivariate analysis, levofloxacin use and implants retention were significantly related to failure (p=0.02 and p=0.003, respectively). Conclusions. Our results suggest that implant retention and levofloxacin use are two independents factors of failure in patients treated for PA – related SPJIs

Shear plane non unions: biomechanical study and clinical application using an all wire Illizarov frame. 60 degree osteotomy of plastic tibiae were stabilised using four different Ilizarov frame configurations. Models were loaded and shear displacement measured at the fracture site. The optimum frame design was identified and used in clinical practice. The transfracture locked olive wire frame model offered the least displacement in the experimental model This frame model was used in two patients with shear plane non unions and both healed satisfactorily Both displacements had previously failed to unite with standard frame constructs. Transfracture locked olive wire frame design is useful in the treatment of tibial non unions with shear plane

Purpose. Twelve case reports of distal femur fractures as post-operative complications after anterior cruciate ligament (ACL) reconstruction have been described in the literature. The femoral tunnel has been suggested as a potential stress riser for fracture formation. The recent increase in double bundle ACL reconstructions may compound this risk. This is the first biomechanical study to examine the stress riser effect of the femoral tunnel(s) after ACL reconstruction. The hypotheses tested in this study are that the femoral tunnel acts as a stress riser to fracture and that this effect increases with the size of the tunnel (8mm versus 10mm) and with the number of tunnels (one versus two). Method. Femoral tunnels simulating single bundle (SB) hamstring graft (8 mm), bone-patellar tendon-bone graft (10 mm), and double bundle (DB) ACL reconstruction (7mm, 6 mm) were drilled in fourth generation saw bones. These three experimental groups and a control group consisting of native saw bones without tunnels, were loaded to failure. Result. All fractures occurred through the tunnels in the double tunnel group whereas fractures did not consistently occur through the tunnels in the single tunnel groups. The mean fracture load was 6145 N 471 N in the native group, 5691 N 198 N in the 8 mm single tunnel group, 5702 N 282 N in the 10 mm single tunnel group, and 4744 N 418 N in the double tunnel group. The mean fracture load for the double tunnel group was significantly different when compared to native, 8 mm single bundle, and 10 mm single bundle groups independently (p value = 0.0016, 0.0060, and 0.0038 respectively). No other statistically significant differences were identified. Conclusion. An anatomically placed femoral tunnel in single bundle ACL reconstruction in our experimental model was not a stress riser to fracture, whereas the two femoral tunnels in double bundle ACL reconstruction significantly decreased load to failure. The results support the sparcity of reported peri-ACL reconstruction femur fractures in single femoral tunnel techniques. However, the increased fracture risk in double bundle ACL reconstruction is a cause for concern and may impact patient selection

Introduction. Wear debris induced osteolysis and loosening continue to be causes of clinical failure in total knee replacement (TKR). Laboratory simulation aims to predict the wear of TKR bearings under specific loading and motion conditions. However, the conditions applied may have significant influence on the study outcomes (1). The aim of this study was to examine the influence of femoral setup and kinematic inputs on the wear of a conventional polyethylene fixed bearing TKR through experimental and computational models. Methods. Six right Sigma CR fixed bearing TKRs (DePuy Synthes, Leeds, UK) with curved polyethylene inserts (GVF, GUR1020 UHMWPE) were tested in Prosim knee simulator (Simulator Solutions, UK). The femoral bearing was set up with the centre of rotation (CoR) on either on the distal radius of the implant (Distal CoR), as indicated by the device design, or according to the ISO specification (ISO CoR; ISO14243-3). The tests were conducted under ‘High Kinematics’ (2). It was necessary to reverse the direction of the anterior-posterior displacement for the tests conducted with the ISO centre of rotation to maintain the contact region within the insert surface (Reverse High Kinematics). Tests were conducted for three million cycles, lubricated with 25% bovine serum, with wear assessed gravimetrically. The computational wear model for the TKR was based on the contact area and an independent experimentally determined non-dimensional wear coefficient, previously validated against the experimental data (3). Results. Good agreement was found between our computational and experimental models (Figure 1). The effect of femoral setup (and adjusted input kinematics) was shown to be significant (ANOVA, p < 0.05), with lower wear under the ISO CoR conditions. The reduction in wear was approximately 49% compared with the Distal CoR. A comparison of the final wear scar area showed the scars to be smaller and located more anteriorly under the ISO CoR/Reverse High Kinematic conditions, compared with the distal CoR study (Figure 2). Discussion. The femoral setup was shown to have a significant impact on the computational and experimental wear rates, with the ISO CoR condition having approximately half the wear of the Distal CoR. It appears that through changing the centre of rotation (and subsequently the anterior-posterior direction) the relative motion and contact mechanics at the articulating surface are altered (1). This study highlights the significant influence test setup conditions may have on the wear of a. It is proposed that there is a need to examine TKR bearings under a broad range of conditions, rather than one study condition to fully assess wear performance

INTRODUCTION:. A discrepancy exists between biomechanical and clinical outcome studies when comparing cruciate-retaining (CR) versus posterior stabilized (PS) component designs. The purpose of this study is to re-evaluate experimental model results using half-body specimens with intact extensor mechanisms and navigation to evaluate PS and CR component gaps though an entire range of motion. METHODS:. A custom-designed knee testing apparatus was used for secure anchoring of the lower half of cadaver pelvic, allowing full range of knee motion and the application of traction throughout that range. Eight sequential testing regimens: were conducted with knee intact, with CR TKA in place, with PS TKA with quadriceps tendon in place, with PS TKA with sectioned quadriceps tendon in place, with and without traction at each stage. At each stage, a navigated knee system with dedicated software was used to record component gapping through a full range of motion from 0° to 120°. The amount of traction used was 22N. Each knee (n = 10) was taken through 6 full ranges of motion at every stage. At each stage, corroboration of navigation findings was attempted using a modified gap balancer to take static gap measurements at 0° and 90° with 12 in. lbs of torque was applied. RESULTS:. The difference in component gapping between CR and PS knees resulted in a range from −0.85 mm to 0.62 mm. The range of component gapping was from −0.67 mm to 0.70 mm with both constructs under 22N traction load. There was no significant difference between loaded and unloaded component gaps, and there were no statistically significant differences in component gapping between CR and PS knees throughout a full range of motion. Static flexion-extension gap measurements, were significantly different from previously published data, notably at in 90° flexion gap measurement. The comparison of the sectioned unloaded and sectioned loaded quadriceps tendon constructs gave a range of distraction of tibio-femoral gaps from 1.85 to 5.22 mm and 1.46 to 4.60 mm, respectively. These measurements were significantly increased over previously reported findings. CONCLUSION:. There was no significant difference between the CR and PS TKA designs with respect to component gapping when measured through a complete range of motion with an intact extensor mechanism. This data contradicts earlier results, obtained from less complete specimens, and correlates with clinical studies which show no gap differences in CR and PS knees. We conclude that the sectioned quadriceps tendon influences knee flexion-extension gaps in a PS TKA construct model. This finding suggests that intact extensor mechanisms may be required to perform proper kinematic studies of TKA, and this may be a contributing factor in the discrepancies observed between previous biomechanical and clinical outcome studies. Clinical Relevance: The findings of this study may solve the controversy regarding differences of the CR and PS TKA designs observed using biomechanical models

Experimental knee simulators for component evaluation or in vitro testing provide valuable insight into the mechanics of the implanted joint. The Kansas knee simulator (KKS) is an electro-hydraulic whole joint knee simulator, with five actuators at the hip, ankle and quadriceps muscle used to simulate a variety of dynamic activities in cadaveric specimens. However, the number and type of experimental tests which can feasibly be performed is limited by the need to make physical component parts, obtain cadaveric specimens and the substantial time required to carry out each test. Computational simulations provide a complementary toolset to experimental testing; experimental data can be used to validate the computational model which can subsequently be used for early evaluation and ranking of component designs. The objective of this study was to explore potential improvements to loading and boundary conditions in current computational/experimental models, specifically the KKS, in order to develop representations of several activities of daily living (ADLs) which reproduce in vivo knee joint loading measurements. An existing finite element model of the KKS was modified to extend the capability, and improve the fidelity, of the computational model beyond the experimental setup. An actuator to allow anterior-posterior (A-P) motion of the hip was included and used to prescribe relative hip-ankle A-P kinematics during the simulations. The quadriceps muscle, which in the experimental simulator consisted of a single quadriceps bundle with a point-to-point line of action, was divided into four heads of the quadriceps with physiological muscle paths. The hamstrings muscle, which was not present in the experiment, was represented by point-to-point actuators in four bundles. A flexible control system was developed which allowed control of the quadriceps and hamstrings actuators to match a knee flexion profile, similar to actuation of the experimental KKS, but also allowed control of the compressive tibiofemoral (TF) joint force, medial-lateral (M-L) load distribution, internal-external (I-E) torque and A-P load at the joint. A series of sensors, measuring all six load components on the medial and lateral compartments of the tibial insert, as well as knee flexion angle, were incorporated into the simulation. Instantaneous measurements from the sensors were fed to a control system, implemented within an Abaqus/Explicit user subroutine (Figure 1). The controller was used to drive actuators in the FE model to match target in vivo joint loading profiles, measured from telemetric patient data. The control system was applied to recreate in vivo loading conditions at the knee joint during three ADLs for three different subjects (Figure 2), with excellent agreement between simulation joint loading conditions and the target profiles; RMS differences were less than 1°, 80N, 2.5%, and 0.8Nm for knee flexion angle, compressive joint load, M-L load split and I-E torque, respectively, throughout the cycle for all three activities (Figure 3). The flexible nature of the control system ensures that it can be used to evaluate an expansive variety of ‘effect of’ studies, as well as to determine advanced loading profiles for the experimental simulator

Introduction. Joint mechanics and implant performance have been shown to be sensitive to ligament properties [1]. Computational models have helped establish this understanding, where optimization is typically used to estimate ligament properties for recreation of physically measured specimen-specific kinematics [2]. If available, contact metrics from physical tests could be used to improve the robustness and validity of these predictions. Understanding specimen-specific relationships between joint kinematics, contact metrics, and ligament properties could further highlight factors affecting implant survivorship and patient satisfaction. Instrumented knee implants offer a means to measure joint contact data both in-vivo and intra-operatively, and can also be used in a controlled experimental environment. This study extends on previous work presented at ISTA [3], and the purpose here was to evaluate the use of instrumented implant contact metrics during optimization of ligament properties for two specimens. The overarching goal of this work is to inform clinical joint balancing techniques and identify factors that are critical to implant performance. Methods. Total knee arthroplasties were performed on 4 (two specimens modeled) cadeveric specimens by an experienced orthopaedic surgeon. An instrumented trial implant (VERASENSE, OrthoSensor, Inc., Dania Beach, FL) was used in place of a standard insert. Experimentation was performed using a simVITROTM controlled robotic musculoskeletal simulator (Cleveland Clinic, Cleveland, OH) to apply intra-operative style loading and measure tibiofemoral kinematics. Three successive laxity style tests were performed at 10° knee flexion: anterior-posterior force (±100 N), varus-valgus moment (±5 Nm), and internal-external moment (±3 Nm). Tibiofemoral kinematics and instrumented implant contact metrics were measured throughout testing (Fig. 1). Specimen-specific finite element models were developed for two of the tested specimens and solved using Abaqus/Explicit (Dassault Systèmes). Relevant ligaments and rigid bone geometries were defined using specimen-specific MRIs. Virtual implantation was achieved using registration and each ligament was modeled as a set of nonlinear elastic springs (Fig. 1). Stiffness values were adopted from the literature [2] while the ligament slack lengths served as control variables during optimization. The objective was to minimize the root mean square difference between VERASENSE measured tibiofemoral contact metrics and the corresponding model results (Fig. 1). Results and Discussion. The models for both specimens successfully recreated joint kinematics with average errors less than 4° in rotations, and 3 mm in translations (not shown). Minus a systematic offset in θ for specimen 3, AFD and θ contact kinematics also realized good agreement for both specimens (Fig. 2). Contact forces were generally over-predicted, though both specimens recreated the experimental trends (Fig. 2). The present work shows continued progress towards simulation based tools that can be used for both research and to support the clinical decision making process. A separate ISTA submission presents assessment of these model's predictive capacity, while future work will evaluate additional specimens, and explore the sensitivity to uncertainties in experimental and modeling parameters. Acknowledgements. This work was supported by Orthosensor Inc. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction:. There is substantial range in kinematics and joint loading in the total knee arthroplasty (TKA) patient population. Prospective TKA designs should be evaluated across the spectrum of loading conditions observed in vivo. Recent research has implanted telemetric tibial trays into TKA patients and measured loads at the tibiofemoral (TF) joint [1]. However, the number of patients for which telemetric data is available is limited and restricts the variability in loading conditions to a small subset of those which may be encountered in vivo. However, there is a substantial amount of fluoroscopic data available from numerous TKA patients and component designs [2]. The purpose of this study was to develop computational simulations which incorporate population-based variability in loading conditions derived from in vivo fluoroscopy, for eventual use in computational as well as experimental activity models. Methods:. Fluoroscopic kinematic data was obtained during squat for several patients with fixed bearing and rotating platform (RP) components. Anterior-posterior (A-P) and internal-external (I-E) motions of the TF joint were extracted from full extension to maximum flexion. Joint compressive loading was estimated using an inverse-dynamics approach. Previously-developed computational models of the knee, lower limb, and Kansas knee simulator were virtually implanted with the same design as the fluoroscopy patients. A control system was integrated with the computational models such that external loading at the hip and ankle were determined in order to reproduce the measured in vivo motions and compressive load (Fig. 1). Accuracy of the model in matching the in vivo motions was assessed, in addition to the resulting joint A-P and I-E loading. The external loading determined for a broader range of patients can subsequently be utilized in a force-controlled simulation to assess the robustness of implant concepts to patient loading variability. The applicability of this work as a comparative tool was illustrated by assessing the kinematics of two PS RP designs under three patient-specific loading conditions. Results:. External hip and ankle loading conditions were determined for each computational model that reproduced in vivo A-P, I-E and flexion-extension joint motions and estimated compressive load. For example, RMS accuracy of 0.4 mm, 0.2° and 0.7° were achieved for A-P, I-E and flexion, respectively (Fig. 1, 2). There was good agreement in both trend and magnitude of joint loads predicted from the externally-loaded models compared to telemetric measurements. Comparative analysis of two designs under multiple loading conditions illustrated variability in joint mechanics as a result of design factors and variation between subjects for the same design (Fig. 3). Discussion:. Pre-clinical evaluation of new devices under physiological joint loading conditions is crucial to robust functionality across the TKA population. The loads applied to a TKA system will affect fixation, wear, and functional performance. Harnessing in vivo kinematic data to develop population-based loading profiles will facilitate development of a platform for comprehensive design-phase evaluation of prospective designs. In addition, loading conditions for experimental simulators can be developed in order to test new devices under the range of variability likely to be encountered in vivo

A total of 38 patients with leprosy and localised nerve damage (11 median at the wrist and 37 posterior tibial at the ankle) were treated by 48 freeze-thawed skeletal muscle autografts ranging between 2.5 cm and 14 cm in length. Sensory recovery was noted in 34 patients (89%) and was maintained during a mean period of follow-up of 12.6 years (4 to 14). After grafting the median nerve all patients remained free of ulcers and blisters, ten demonstrated perception of texture and eight recognised weighted pins. In the posterior tibial nerve group, 24 of 30 repairs (80%) resulted in improved healing of the ulcers and 26 (87%) demonstrated discrimination of texture. Quality of life and hand and foot questionnaires showed improvement; the activities of daily living scores improved in six of seven after operations on the hand, and in 14 of 22 after procedures on the foot. Another benefit was subjective improvement in the opposite limb, probably because of the protective effect of better function in the operated side. This study demonstrates that nerve/muscle interposition grafting in leprosy results in consistent sensory recovery and high levels of patient satisfaction. Ten of 11 patients with hand operations and 22 of 25 with procedures to the foot showed sensory recovery in at least one modality.

We have prospectively studied the outcome of infections associated with implants which were retained and treated using a standardised antimicrobial protocol. Over a period of four years, we studied 24 consecutive patients who had symptoms of infection for less than one year, a stable implant, no sinus tract and a known pathogen which was susceptible to recommended antimicrobial agents. The infections involved hip prostheses (14), knee prostheses (5), an internal fixation device (4), and an ankle prosthesis (1).

Twenty patients had a successful outcome at a median follow-up of 3.7 years (1.8 to 4.7); four had failure of the implant after a median follow-up of 1.2 years (0.3 to 2.5). The probability of survival without failure of treatment was 96% at one year (95% confidence interval (CI) 88 to 100), 92% at two years (95% CI 80 to 100) and 86% at three years (95% CI 72 to 100).

Patients with a short-term infection but with a stable implant, no sinus tract and a known pathogen may be successfully treated by retention of the implant and the use of a standardised regimen of antimicrobial treatment.