Aim. Periprosthetic joint infection (PJI) is a complication of total joint arthroplasty that typically requires revision surgery for treatment. Systemic antibiotics are usually held prior to surgery to improve yield of intraoperative cultures. However, recent studies suggest that preoperative aspirations have a high concordance with intraoperative cultures, which may allow surgeons to initiate antibiotic treatment earlier. The purpose of the study was to investigate the effect of Pre-surgical systemic antibiotic therapy on the bacterial burden within the periprosthetic space and systemic immune reaction. Method. PJI was induced with MSSA (Xen36) S. aureus in the right knee of 16-week old, female, C57BL6 mice using a previously validated murine model. Mice were randomized to three groups (n=8, each): control; Vanc, receiving systemic vancomycin (110mg/kg, SQ, twice daily); or VancRif receiving vancomycin same as in Vanc group, plus rifampin (12mg/kg dose, IV, once daily). Following 2 weeks of treatment, mice were euthanized and periprosthetic bone, soft tissue and the implant were harvested. Bacterial burden, colony forming units (CFUs), was quantified in soft tissue, tibial bone, and on the implant. Specifically, tissues were homogenized and serially plated for CFUs, while the implant was sonicated and then plated for CFUs. The host immune response was analysed through weighing inguinal and iliac lymph nodes and through measuring serum amyloid A (SAA). Non-parametric pairwise group comparisons of the three outcome measures were performed using a Mann-Whitney U test. Results. VancRif, the combined treatment significantly reduced bacterial burden in the periprosthetic soft tissue, bone, and implant compared to control (p<0.001) and Vanc alone (p<0.001). While not significant, Vanc alone did reduce bacterial load as compared to control. The ipsilateral weight of the iliac lymph nodes was significantly reduced in Vanc and VancRif mice compared to controls (p<0.001), was well as in VancRif versus Vanc alone (p<0.001). Interestingly, SAA levels did not significantly differ among all groups. During tissue harvesting, minimal purulence was observed in antibiotic treatment groups, unlike controls. Conclusions. Treating active PJI with vancomycin alone decreases periprosthetic bacterial loads and reduces the local immunological response. This effect is significantly enhanced with the combined rifampin use. These findings could suggest that when culture positive PJI is diagnosed, pre-surgical treatment with antibiotics may decrease immunosuppression and soft tissue infiltration, leading to a better chance of infection cure with subsequent surgical debridement. Histological investigations and repeat experiments involving subsequent surgical treatment are underway. Acknowledgements. Funding comes from internal institutional grants

Aim. The time to onset of symptoms after fracture fixation is still commonly used to classify fracture-related infections (FRI). Early infections (<2 weeks) can often be treated with debridement, systemic antibiotics, irrigation, and implant preservation (DAIR). Late infections (>10 weeks) typically require implant removal as mature, antibiotic-tolerant biofilms have formed. However, the recommendations for delayed infections (2–10 weeks) are not clearly defined. Here, infection healing and bone healing in early and delayed FRI is investigated in a rabbit model with a standardized DAIR procedure. Method. Staphylococcus aureus was inoculated into 17 rabbits after plate osteosynthesis in a humerus osteotomy. The infection developed either one week (early group, n=6) or four weeks (delayed group, n=6) before a standardized DAIR procedure and microbiological analysis were performed. Systemic antibiotics were administered for six weeks (two weeks: Nafcillin+Rifampin, four weeks: Levofloxacin+Rifampin). A control group (n=5) also underwent a revision operation (debridement and irrigation) after four weeks, but received no antibiotic treatment. Rabbits were euthanized seven weeks after the revision operation. Bone healing was assessed using a modified radiographic union score for tibial fractures (mRUST). After euthanasia, a quantitative microbiological examination of the entire humerus, adjacent soft tissues, and implants was performed. Results. All animals were infected at the time of revision surgery, with the bacterial load in the early group (especially in soft tissues) being greater than in the delayed group and control group. This indicates infiltration of bacteria into areas that are more difficult to reach after four weeks of debridement. The infection was eradicated in all animals in both the early and delayed groups at euthanasia, but not in the control group (CFU median (IQR): 2.1×10. 7. (1.3×10. 7. -2.6×10. 7. ). The osteotomy healed in the early group, while bone healing was significantly impaired in both the delayed group and control group (mRUST median (IQR): early group: 16 (14–16), delayed group: 7.5 (6–10), control: 7 (5.5–9); early vs. delayed: p=0.0411, early vs. control p=0.0065). Conclusion. The maturation of the infection between the first and fourth week does not affect the success of infection eradication in this rabbit FRI model. However, bone healing appears to be impaired with increasing duration of infection

Aim. Implant infections caused by Staphylococcus aureus are difficult to treat due to biofilm formation, which complicates surgical and antibiotic treatment. Herewith we introduce an alternative approach using monoclonal antibodies (mAbs) targeting S. aureus and provide the biodistribution and specificity in a mouse implant infection model. Methods. 4497-IgG1targeting S. aureus Wall Teichoic Acid was labeled to Indium-111 using “CHXA” as a chelator. SPECT-CT scans were performed at 24, 72 and 120 hours after administration in Balb/cAnNCrl mice with a subcutaneous implant pre-colonized with biofilm of S. aureus. Biodistribution over the various organs of this labelled antibody was visualized and quantified using SPECT-CT imaging and compared to uptake at the target tissue with implant infection. Results. Uptake of the . 111. In-4497 mAbs (half-life 59 hours) at the infected implant gradually increased from 8.34%ID/g at 24 hours to 9.22%ID/g at 120 hours. Uptake at the heart/blood pool decreased over time from 11.60 to 7.58%ID/g whereas the uptake in other organs decreased from 7.26 to less than 4.66%ID/g at 120 hours. Conclusion. 111. In-4497 mAbs was found to specifically detect S. aureus and its biofilm with excellent and prolonged accumulation at the colonized implant site. Therefore, it holds great promise as a drug delivery system for diagnostic and bactericidal treatment of biofilm. However, high activity in the blood pool must be considered as it could pose a risk to healthy tissue

Aim. In severe cases of postoperative spinal implant infections (PSII) multiple revision surgeries may be needed. Little is known if changes of the microbiological spectrum and antibiotic resistance pattern occur between revision surgeries. Therefore, the aim of this study was to analyze the microbiological spectrum and antibiotic resistance pattern in patients with multiple revision surgeries for the treatment of PSII. Furthermore, changes of the microbiological spectrum, distribution of mono vs. polymicrobial infections, and changes of the antimicrobial resistance profile in persistent microorganisms were evaluated. Method. A retrospective analysis of a prospectively maintained single center spine infection database was performed with a minimum follow-up of 3 years. Between 01/2011 and 12/2018, 103 patients underwent 248 revision surgeries for the treatment of PSII. Overall, 20 patients (6 male/14 female) underwent 82 revisions for PSII (median 3; range 2–12). There were 55/82 (67.1%) procedures with a positive microbiological result. Microbiological analysis was performed on tissue and implant sonication fluid. Changes in microbial spectrum and antibiotic resistance pattern between surgeries were evaluated using Chi-Square and Fisher's exact test. Results. In total, 74 microorganisms (83.3% gram-positive; 10.8% gram-negative) were identified. The most common microorganisms were Staphylococcus epidermidis (18.9%) and Cutibacterium acnes (18.9%). All S. epidermidis identified were methicillin-resistant (MRSE). Overall, there were 15/55 (27.3%) polymicrobial infections. The microbiological spectrum changed in 57.1% (20/35) between the revision stages over the entire PSII period. In 42.9% (15/35) the microorganism persisted between the revision surgeries stages. Overall, changes of the antibiotic resistance pattern were seen in 17.4% (8/46) of the detected microorganisms comparing index revision and all subsequent re-revisions. Moreover, higher resistance rates were found for moxifloxacin and for ciprofloxacin at first re-revision surgery compared with index PSII revision. Resistances against vancomycin increased from 4.5% (1/23) at index PSII revision to 7.7% (2/26) at first re-revision surgery. Conclusions. Changes of the microbiological spectrum and the resistance pattern can occur in patients with severe PSII who require multiple revision surgeries. It is important to consider these findings in the antimicrobial treatment of PSII. The microbiological analysis of intraoperative tissue samples should be performed at every revision procedure for PSI

Aim. Fungal periprosthetic joint infections are difficult to treat and often associated with a limited outcome for patients. Candida species account for approximately 90% of all fungal infections. In vivo biofilm models play major role to study biofilm development, morphology, and regulatory molecules for bacteria. However, in vivo modeling of biofilm-associated fungi models are very rare. Furthermore, due to ethical restrictions, mammalian models are replaced with other alternative models in basic research. Recently, we have developed insect infection model G. mellonella larvae to study implant associated biofilm infections with bacteria. This model organism was not used for fungi biofilm infection yet. Thus, we aimed to establish G. mellonella as in vivo model to study fungal implant infections using Candida albicans as model organism and to test anti-fungal medication. Method. Titanium and Stainless steel K-wires were cut into small pieces with size of 4mm. For the infection process, implants were pre-incubated in specified fungal growth culture Candida albicans at 1×10. 7. CFU/ml for 30 min at 150 rpm shaking conditions. Later, these implants were washed with 10ml PBS and implanted in the larvae as mentioned. To analyze the susceptibility of the implant-associated fungal infections towards anti fungal compounds, the larvae were treated with amphotericin B, fluconazole and voriconazole after 24h of implantation. The effect of anti-fungal compounds was measured in terms of survival observation for 5 days and fungal load in larvae on 2. nd. day. To reveal the fungal biofilm formation on implant, the implants were removed on day 3 and processed for SEM analysis. Results. Pre-incubated K-wire caused the Candida infection and observed the death of the larvae. The treatment with antifungal compounds recovered the larvae from the implant-infection, except in case of Voriconazole. However, the recovery with treatment of anti fungal compounds was not effective as the larvae with planktonic infection, which highlights typical biofilm phenotype. Further, the treatment with anti-fungal compounds with Amphotericin B and Fluconazole reduced the fungal load in larvae tissue. The SEM analysis revealed the formation fungal biofilm with hyphae and spores associated with larvae tissue on implant surface. Conclusions. The results from survival analysis, antifungal treatment and SEM analysis are very promising to use of G. mellonella as in vivo model to study fungal infections on implanted materials. Our study highlights the use of G. mellonella larvae as alternative in vivo model to study implant-associated fungal infections that reduces the use of the higher mammals

Aims

Delayed postoperative inoculation of orthopaedic implants with persistent wound drainage or bacterial seeding of a haematoma can result in periprosthetic joint infection (PJI). The aim of this in vivo study was to compare the efficacy of vancomycin powder with vancomycin-eluting calcium sulphate beads in preventing PJI due to delayed inoculation.

Aim. Open fractures still have a high risk for fracture-related Infection (FRI). The optimal duration of perioperative antibiotic prophylaxis (PAP) for open fractures remains controversial due to heterogeneous guidelines and highly variable prophylactic regimens in clinical practice. In order to provide further evidence with which to support the selection of antibiotic duration for open fracture care, we performed a preclinical evaluation in a contaminated rabbit fracture model. Method. A complete humeral osteotomy in 18 rabbits was fixed with a 7-hole-LCP and inoculated with Staphylococcus aureus (2×106 colony forming units, CFU per inoculum). This inoculum was previously shown to result in a 100% infection rate in the absence of any antibiotic prophylaxis. Cefuroxime was administered intravenously in a weight adjusted dosage equivalent to human medicine (18.75 mg/kg) as a single shot only, for 24 hours (every 8 hours) and for 72 hours (every 8 hours) in separate groups of rabbits (n=6 per group). Infection rate per group was assessed after two weeks by quantitative bacteriological evaluation of soft tissue, bone and implants. Blood samples were taken from rabbits preoperatively and on days 3, 7 and 14 after surgery to measure white blood cell count (WBC) and C-reactive protein (CRP) levels. Results. Duration of PAP had a significant impact on the success of antibiotic prophylaxis. The single shot regimen completely failed to prevent infection. All samples (soft tissue, implant and bone) from this group displayed high numbers of bacteria. Additionally, abscesses were present in two of six rabbits. The 24-hour regimen showed a reduced infection rate (1 out of 6 rabbits infected), but only the 72-hour course was able to prevent FRI in all animals in our model. After an initial postoperative peak on day three, CRP levels then decreased to baseline (approx. 30 µg/ml) in the 24h-group and 72h-group, but remained significantly higher in the single shot group at day 7 and 14 (p<0.05). Conclusions. When contamination with high bacterial loads is likely (e.g. in an open fracture situation), a 72-hour course of intravenous cefuroxime appears to be superior in preventing FRI compared to a single shot or 24-hour antibiotic regimen. Acknowledgements. This work was funded by AOTrauma

Aim. Treatment regimens for fracture-related infection (FRI) often refer to the classification of Willenegger and Roth, which stratifies FRIs based on time of onset of symptoms. The classification includes early (<2 weeks), delayed (2–10 weeks) and late (>10 weeks) infections. Early infections are generally treated with debridement and systemic antibiotics but may not require implant removal. Delayed and late infections, in contrast, are believed to have a mature biofilm on the implant, and therefore, treatment often involves implant removal. This distinction between early and delayed infections has never been established in a controlled clinical or preclinical study. This study tested the hypothesis that early and delayed FRIs respond differently to treatment comprising implant retention. Method. A complete humeral osteotomy in 16 rabbits was fixed with a 7-hole-LCP and inoculated with Staphylococcus aureus. The inoculum size (2×106 colony forming units per inoculum) was previously tested without antibiotic intervention to result in infection of all animals persisting for at least 12 weeks.4 The infection was allowed to develop for either 1 (early group) or 4 (delayed group) weeks (n= 8 per group) after bacterial inoculation. At these time points, treatment involved debridement and irrigation of the wound (no implant removal) and quantitative bacteriological evaluation of the removed materials. Systemic antibiotics were administered according to a common clinical regimen (2 weeks: rifampin + nafcillin, followed by 4 weeks: rifampin + levofloxacin). After an additional one-week antibiotic washout period, animals were euthanized and a quantitative bacteriology of soft tissue, implant (after sonication) and bone was performed. Results. Greater numbers of bacteria were recovered by debridement and irrigation in the early group compared with the delayed group, which may indicate retraction of the infection in the delayed stage. Treatment was successful in both the early and delayed group: all animals in both groups were infection free at euthanasia. Furthermore, all osteotomies had healed, although animals in the delayed group displayed irregular callus formation. Conclusions. In both groups, treatment successfully eradicated the infection, suggesting that, at least in this model, the maturity of the infection does not impact upon treatment success within the first four weeks. Acknowledgements. This work was funded by AOTrauma

Background. Intraoperative balancing of total knee arthroplasty (TKA) can be accomplished by either more prevalent but less predictable soft tissue releases, implant realignment through adjustments of bone resection or a combination of both. Robotic TKA allows for quantifiable precision performing bone resections for implant realignment within acceptable final component and limb alignments. Objective. To provide a direct comparison of patient reported outcomes between implant realignment and traditional ligamentous release for soft tissue balancing in TKA. Methods. IRB approved retrospective single surgeon cohort study of prospectively collected operative and clinical data of consecutive patients that underwent TKA with a single radius design utilizing kinematic sensors to assess final balance with or without robotic assistance allowing for a minimum of 12 months clinical follow up. Operative reports were reviewed to characterize the balancing strategy. In surgical cases using robotic assistance, pre-operative plan changes that altered implant placement were included in the implant realignment group. Any patient that underwent both implant realignment and soft tissue releases was analyzed separately. Kinematic sensor data was utilized to quantify ultimate balance to assure that each cohort had equivalent balance. Patient reported outcome data consisting of Knee Society- Knee Scores (KS-KS), Knee Society- Function Scores (KS-FS), and Forgotten Joint Scores (FJS) were prospectively collected during clinical follow up. Results. 182 TKA were included in the study. 3-Month clinical follow up was available for 174/182 knees (91%), 1-Year clinical follow up was available for 167/182 knees (92%) and kinematic sensor data was available for 169/182 knees (93%). Kinetic sensor data showed that on average all of the balancing subgroups achieved clinically equivalent balance. Use of robotic-arm assistance provided the tools and confidence to decrease from ligament release only in 40.8% of non-robotic cases to 3.8% in the robotic group, and the use of component realignment alone increased from 23.7% in the non-robotic cases to 48.1% in the robotic TKA group. KS-KS, KS-FS and FJS scores showed improvements in outcomes at both the 3-month and 1-year time points in the implant realignment cohort compared to the ligamentous release cohort. KS-KS, KS-FS, and FJS at 1-year were 1.6, 7.6, and 17.2 points higher respectively. While none of the comparisons reached statistical significance, KS-FS at 1 year showed a statistically and clinically significant difference (MCID 6.1–6.4) increase of 7.7 points in the implant realignment cohort compared to the ligamentous cohort. The 1-year trend can be further explained by the outperformance (MCID increase of 6.4 points) of the implant realignment robotic cohort at 1-year compared to the non-robotic ligamentous cohort. Conclusions. Directly comparing TKA patients balanced with implant realignment alone versus ligamentous release alone versus combined technique, a trend toward clinical improvement above a minimally clinical significant difference in KS-FS scores benefiting the implant realignment technique was seen at both 3-months and 1-year post-operatively. We hypothesize that the benefit of implant realignment is achieved through decreased soft tissue trauma as well as potentially greater predictability and sustainability of soft tissue balance than with soft tissue releases alone

Background. Intraoperative balancing can be accomplished by either more prevalent but less predictable soft tissue releases, implant realignment through adjustments of bone resection or a combination of both. There is no published study directly comparing these methods. Objective. To provide a direct comparison between implant realignment and traditional ligamentous release for soft tissue balancing in total knee arthroplasty using both objective kinematic sensor data to document final balance and patient reported outcomes. Methods. IRB Approved retrospective cohort study of prospectively collected data comparing kinematic sensor data and patient reported outcomes for all consecutive patients that underwent TKA utilizing kinematic sensors with or without robotic assistance performed between August 2012 to April 2017 to allow for a minimum of 12 months clinical follow up. Results. 107 knees met inclusion criteria. Component realignment was utilized more frequently in the robotic surgical technique cohort than the non-robotic, non-navigated cohort due to the increased precision in implant realignment possble. Although KSS and FJS scores showed equivalent outcomes at both the 3-month and 1-year time points, KSS-Function scores at 1-year showed a statistically and clinically significant increase of 11.89 points in the implant realignment cohort compared to the ligamentous release cohort. Conclusions. A statistically and clinically significant improvement in KSS-Function scores benefiting the implant realignment technique was seen at 1-year post-operatively. This may suggest a benefit to using implant realignment as the ideal balancing strategy in total knee arthroplasty. Further longitudinal studies with increased number of cases should increase statistical power which is needed to further confirm the suggested benefits of the implant realignment balancing technique

Aims

The STRYDE nail is an evolution of the PRECICE Intramedullary Limb Lengthening System, with unique features regarding its composition. It is designed for load bearing throughout treatment in order to improve patient experience and outcomes and allow for simultaneous bilateral lower limb lengthening. The literature published to date is limited regarding outcomes and potential problems. We report on our early experience and raise awareness for the potential of adverse effects from this device.

It is difficult for surgeons to make the decision on which design or material to use given multiple available options for total knee arthroplasty. Due to the complex interaction of soft tissue, implant position, patient anatomy, and kinematic demands of the patient, the prosthetic design of a knee device has traditionally been more important than materials. The purpose of this study was to examine the overall influence of both implant design and materials on volumetric wear rates in an in vitro knee simulator study for two knee designs. Two different designs (single radius and J-curve) with two highly crosslinked materials (Sequentially crosslinked and annealed PE (X3®, Stryker Orthopaedics, Mahwah, NJ) (7.5 kGy moderately crosslinked UHMWPE (XLPE, Smith and Nephew, Memphis, TN)) were evaluated. The two designs tested were the Triathlon® CR knee system (single radius design)(Stryker Orthopaedics, Mahwah, NJ) and the Legion™ Oxinium® CR knee system (J-curve design) (Verilast™, Smith and Nephew, Memphis, TN). Three inserts per condition were tested in this study. This comparison incorporates the effects of both materials and designs: different femoral component materials, different tibial bearing materials, and implant geometry (J-curve vs. single radius saggital profile). All devices were tested under ISO 14243-3 normal walking using an MTS knee simulator for a total of 5 million cycles. Standard test protocols were used for cleaning, weighing and assessing the wear loss of the tibial inserts (ASTM F2025). Soak control specimens were used to correct for fluid absorption with weight loss data converted to volumetric data (by material density). Statistical analysis was performed using the Student's t-test. Total volume loss results are shown in Figure 1. Test results show a 36% reduction (p<0.05) in volume loss and a 30% reduction (p<0.05) in wear rate for the single radius design compared to the J-curve design, respectively. All comparisons are statistically significant by the t-test method (p<0.05). Visual examination of all worn inserts revealed typical wear scars and features on the condylar surfaces, including burnishing. Results indicate superior wear resistance for the single radius system. This finding indicates that a combination of implant design and prosthesis material plays a significant role in knee wear rates. The in vitro low volumetric wear observed in the single-radius prosthesis could theoretically influence long term survivorship in vivo, and supports the potential for improved durability and long term wear performance for this design when compared to a J-curved femoral component. Longer term clinical evidence such as published studies or outcomes reported in the available joint registries will be needed to establish whether any material or design can achieve a 30-year or longer outcome

Aim. Implant-related infections, including peri-prosthetic joint infection (PJI) and infected osteosynthesis, are biofilm-related. Intra-operative diagnosis and pathogen identification is currently considered the diagnostic benchmark; however the presence of bacterial biofilm(s) may have a detrimental effect on pathogen detection with traditional microbiological techniques. Sonication and chemical biofilm debonding have been proposed to overcome, at least partially, this issue, however little is known about their possible economical impact. Aim of this study was to examine direct and indirect hospital costs connected with the routine use of anti-biofilm microbiological techniques applied to hip and knee PJIs. Method. In a first part of the study, the “Turn Around Time (TAT)” and direct costs comparison between a system to find bacteria on removed prosthetic implants. *. , a closed system for intra-operative tissue and implant sampling, transport and anti-biofilm processing, versus sonication has been performed. An additional analysis of the estimated indirect hospital costs, resulting from the diagnostic accuracy of traditional and anti-biofilm microbiological processing has been conducted. Results. Considering an average 5 samples per patient, processed separately with the sonication or pooled together, using the device. *. , the direct costs comparison shows a similar overall average estimated cost per patient when using sonication (€ 400.00) or the system to find bacteria on removed prosthetic implants. *. (€ 391.70). Indirect hospital costs of false positive or negative intra-operative pathogen identification can be estimated as, respectively, € 65,000 and € 90,000, including possible inadequate treatments and/or surgeries and/or need for further hospital stay, risk of infection recurrence/persistence, possible medico-legal claims, etc. Considering 1 out of ten cases of false identification as generating indirect hospital costs (“mitigation factor”: 90%) and an accuracy of current intra-operative microbiological sampling and testing of approximately 80%, it is calculated that any anti-biofilm procedure able to increase the microbiological diagnostic accuracy by 10%, at an average cost per patient of € 500.00, would induce an average hospital cost saving of approximately € 100,000 per 100 treated cases. Conclusions. To our knowledge, this is the first study specifically focused on the potential economical impact of the routine clinical use of microbiological anti-biofilm processing techniques in orthopaedics. The several limitations of this study notwithstanding, including the variable Country-based value of the different direct costs and the assumptions made concerning indirect costs calculations, this analysis points out how more accurate pathogen identification procedures can lead to an improvement of the management of implant-related infections in orthopaedics, with a substantial economical balance

Modern hip implants feature a modular design, whereby the individual components of the implant are assembled during the surgery. Increased reported failure rates associated with the utilization of modular junctions have raised many clinical concerns about the increased release of metal ions/debris leading to adverse local tissue reactions. Implant materials are subject to a myriad of mechanical motion and forces, and varying electrochemical conditions and pH changes from the surrounding environment. To date, no studies have attempted to model the collected data in order to predict the performance of the materials so that precautions can be taken before the problem reaches the critical stage. This study reports the effects of pH variation, displacement variation, and load variation on the mechanical and corrosion behavior of the hip implant modular junction system, tested with a custom-built fretting-corrosion apparatus. The main objective of this study is to combine the complete data set of the in-vitro experiments to create fretting-corrosion wear maps that can predict the dangerous domains of the hip implant modular system. For each test, the flat portions of two CoCrMo pins were loaded perpendicularly against a Ti6Al4V Rod (Ti alloy) in a Flat-on-flat configuration in a simulated synovial fluid in order to simulate the modular hip implant system. A schematic diagram of contact conditions is presented in Figure 1. A sinusoidal displacement was applied onto the rod, which articulated against the CoCrMo alloy pins, at a frequency of 1Hz. The experiential data from the fretting-corrosion tests has been used to create fretting-corrosion maps. The variables incorporated into the maps include: total mass loss, electrochemical destabilization, pH variation, load variation, displacement variation, and visual examination of the wear features of the contact zone. Total mass loss has been estimated via measurement of the simulator fluid by ICP-MS technique. Electrochemical destabilization was evaluated by a single parameter (V. Drop. ). The electrochemical destabilization of the tribosystem was evaluated by measuring the drop in potential, V. Drop. (V vs. SCE), resultant from the initiation of the fretting phase. The V. Drop. refers to the initial cathodic drop in potential in response to the initial onset of fretting motion. The data from the in vitro fretting-corrosion experiments has been combined to create four fretting-corrosion maps (Figures 2A–3D). Partial slip wear features and mechanical behavior was observed at 25µm displacement. 25–150µm displacement amplitudes showed gross slip behavior. Anything larger than 150µm displayed wear features that were indistinguishable from sliding wear. In general, total mass loss and V. Drop. increased with increasing displacement. Samples that were tested at pH 6.0 or higher showed signs of material transfer and higher V. Drop. Finally, there was a general decrease in V. Drop. with increased applied load and pH. In general, the wears maps were able to offer some predictive validity, however, there were some discrepancies between visual observations and the observed damage parameters. It is possible that other parameters could offer better correlation. Future studies will be conducted to measure other parameters. For figures/tables, please contact authors directly.

Introduction. Bicompartmental osteoarthritis involving the medial tibiofemoral and the patellofemoral compartments is often treated with total knee replacement. Improved implants and surgical techniques have led to renewed interest in bicompartmental arthroplasty. This study evaluates the radiographic and early clinical results of bicompartmental arthroplasty with separate unlinked components implanted with the assistance of a robotic surgical arm. In addition, we examine the amount of bone resected using unlinked bicompartmental components compared to total knee replacement. Finally, a retrospective review of total knee cases examines the applicability of this early intervention procedure. Methods. 97 patients received simultaneous but geometrically separate medial tibiofemoral and patellofemoral arthroplasties with implants specifically designed to take advantage of a new bone and tissue sparing implantation technique using haptic robotics. These patients came from four surgeons at four different hospitals. The average follow-up was 9 months. Pre- and post-operative radiographs were taken. ROM, KSS and WOMAC scores were recorded. The patients had an average age of 67 yrs (range: 45-95), BMI of 29 ± 4kg/m. 2. 47% of the patients were male. We retrospectively reviewed pre and post operative notes from 406 consecutive TKA patients from a single surgeon. Intraoperative data included the integrity of the three compartments and the ACL. Results. At only six weeks follow-up, patients recovered their pre-operative ROM (p=0.37). Knee Society Knee scores (knee and function) and WOMAC scores (pain, function and total) significantly improved from pre-operative values at every follow-up of 6 weeks, 6 months and 1 year (p<0.05). Radiographically, there was no evidence of loosening, wear or progression of OA. There were also no perioperative complications. Using computer simulation, the amount of bone removed using bicompartmental arthroplasty compared to traditional TKA was predicted. Total bone removed on the femur and the tibia using a standard TKA implant is 3.5 times the bone removed using a bicompartmental onlay implant and 4 times the bone removed when using a bicompartmental inlay implant. In the review of 406 TKA cases, the ACL was intact in 66% of these cases. Based on these data alone, 16% of these TKA patients were indicated for a unicondylar arthroplasty, 12% medial UKA, 3% lateral UKA and 1% PFA. In addition, 31% were indicated for bicompartmental arthroplasty with 4% bicondylar (medial and lateral UKA), 6% lateral UKA and PFA and 21% medial UKA and PFA. While these data don't yet account for fixed versus flexible deformities, excessive osteophytes or other contraindications, it seems clear that the disease often treated with a TKA does not actually involve all three compartments. Conclusions. Modular bicompartmental arthroplasty is an effective method for treating arthritis of the knee restricted to the medial and patellofemoral compartments. Early results using contemporary prostheses are encouraging and should prompt further mid- and long-term study. Robotic assistance of bicompartmental arthroplasty has shown good early clinical and radiographic success. In addition, bicompartmental arthroplasty removes significantly less bone than total knee arthroplasty. Also, data indicates that may total knee patients have healthy cruciates and disease in only two of the three compartments, indicating that TKA is an overtreatment of earlier stage osteoarthritis. Longer term studies will determine the clinical significance of preserving healthy cartilage and ligaments routinely resected with traditional tricompartmental TKA