Orthopedic Device-Related Infections (ODRIs) are a major medical challenge, particularly due to the involvement of biofilm-encased and multidrug-resistant bacteria. Current treatments, based on antibiotic administration, have proven to be ineffective. Consequently, there is a need for antibiotic-free alternatives. Antimicrobial peptides (AMPs) are a promising solution due to their broad-spectrum of activity, high efficacy at very low concentrations, and low propensity to induce resistance. We aim to develop a new AMP-based chitosan nanogel to be injected during orthopedic device implantation to prevent ODRIs. Chitosan was functionalized with norbornenes (NorChit) through the reaction with carbic anhydride and then, a cysteine-modified AMP, Dhvar5, a peptide with potent antibacterial activity, even against methicillin-resistant Staphylococcus aureus (MRSA), was covalently conjugated to NorChit (NorChit- Dhvar5), through a thiol-norbornene photoclick chemistry (UV= 365 nm). For NorChit-Dhvar5 nanogels production, the NorChit-Dhvar5 solution (0.15% w/v) and Milli-Q water were injected separately into microfluidic system. The nanogels were characterized regarding size, concentration, and shape, using Transmission Electron Microscopy (TEM), Nanoparticle Tracking Analysis (NTA) and Dynamic light scattering (DLS). The nanogels antibacterial properties were assessed in Phosphate Buffer (PBS) for 6 h, against four relevant microorganisms (Pseudomonas aeruginosa, S. aureus and MRSA, and in Muller- Hinton Broth (MHB), 50% (v/v) in PBS, supplemented with human plasma (1% (v/v)), for 6 and 24 h against MRSA. The obtained NorChit-Dhvar5 nanogels, presented a round-shaped and ∼100 nm. NorChit- Dhvar5 nanogels in a concentration of 10¹⁰ nanogels/mL in PBS were capable of reducing the initial inoculum of P. aeruginosa by 99%, S. aureus by 99%, and MRSA by 90%. These results were corroborated by a 99% MRSA reduction, after 24 h in medium. Furthermore, NorChit-Dhvar5 nanogels do not demonstrate signs of cytotoxicity against MC3T3-E1 cells (a pre-osteoblast cell line) after 14 days, having high potential to prevent antibiotic-resistant infection in the context of ODRIs.

To report a case and a review of the literature about TKA infection caused by P. multocida.

We report the case of a 65 year old woman, with history of a left TKA for primary osteoarthritis. Six months after surgery, the patient presented with fever and a wound in her right leg, two days after being bitten by her cat. She was treated with flucloxacilin. One week later, she returned complaining about pain and stifness in her left knee. She presented fever, swelling, erythema, warmness and pain of the left knee. Complete blood count revealed leukocytosis with neutrophilia. Erythrocyte Sedimentation Rate and C-Reactive Protein were elevated. The knee joint was aspirated and a large amount of purulent fluid was obtained and sent to gram stain and culture. The X-ray of the knee was normal

Gram stain showed a large number of leucocytes and gram-negative coccobacilli. The patient began ceftriaxone, empirically. The culture grew Pasteurella multocida sensitive to ceftriaxone, therefore the treatment was maintained during hospitalization period. The patient showed a gradual improvement over the time and inflammatory markers remained negative since the first week of treatment. After three weeks of intravenous antibiotic treatment, the patient was discharged with oral ciprofloxacin. After a three year follow-up, she remained asymptomatic. ESR and CRP remained negative in every measure and no alterations on knee radiography were detected.

P. multocida is a facultative anaerobic Gram-negative coccobacillus, commensal in the nasopharyngeal tract of domestic pets. Prosthetic joint infection caused by P. multocida is rare and we found reports of 22 TKA and 5 THA infections caused by this organism. Although all options of treatment contemplate intravenous antibiotherapy, it can be combined with different operative techniques. Of the 27 patients, only two were successfully treated without the need of a surgical intervention. We have chosen a conservative approach based on several factors: the patient had no risk factors; the prosthesis was not loose; the existence of one case described of a successfully treatment with antibiotherapy alone (the second case we refer above was only published recently); a good early and maintained response to antibiotic treatment. We advocate that in selected patients, with no risk factors, with a sensitive organism, we should try conservative treatment first. However, if infection signs are severe, we should proceed to surgical debridement and sinovectomy and if the radiography shows any signs of loosening of the implant, it should be removed.

A Prospective, randomised controlled trial demonstrates superior outcomes using an active constraint robot compared with conventional surgical technique in unicompartmental knee arthroplasty (UKA). Computer assistance should extinguish outliers in arthroplasty, with robotic systems being able to execute the preoperative plan with millimetre precision.

We used the Acrobot system to deliver tailor made surgery for each individual patient. A total of 27 patients (28 knees) awaiting unicompartmental knee arthroplasty were randomly assigned to have the operation performed either with the assistance of the Acrobot or conventionally. CT scans were obtained with coarse slices through hips and ankles and fine slices through the knee joint. Preoperative 3D plans were made and transferred to the Acrobot system in theatre, or printed out as a conventional surgical aid. Accurate co-registration was confirmed, prior to the surfaces of the femur and tibia being milled. The outcome parameters included measurements of the American Knee Society (AKS) score and Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index. These measurements were performed pre-operatively and at six, 18 weeks, and 18 months post-operatively. After 18 months two UKA out of the conventional trial (n =15) had been revised into a total knee replacement (TKA), whereas there were no revisions in the Acrobot trial group (n = 13).

Using an active constrained robot to assist the surgeon was significantly more accurate than the conventional surgical technique. This study has shown a direct correlation between accuracy and improvement in knee scores at 6, 18 weeks and 18 months after surgery. At 18 months there continues to be a significant improvement in the knee scores with again a marked correlation between radiological accuracy and clinical outcome with higher accuracy leading to better function based on the WOMAC and American Knee Society Score.

Whilst computer assistance enables more accurate arthroplasty to be performed, demonstrating this is difficult. The superior results of CAOS systems have not been widely appreciated because accurate determination of the position of the implants is impossible with conventional radiographs for they give very little information outside their plane of view.

We report on the use of low dose (approximately a quarter of a conventional pelvic scan), low cost CT to robustly measure and demonstrate the efficacy of computer assisted hip resurfacing. In this study we demonstrate 3 methods of using 3D CT to measure the difference between the planned and achieved positions in both conventional and navigated hip resurfacing.

The initial part of this study was performed by imaging a standard radiological, tissue equivalent phantom pelvis. The 3D surface models extracted from the CT scan were co-registered with a further scan of the same phantom. Subsequently both the femoral and acetabular components were scanned encased in a large block of ice to simulate the equivalent Hounsfield value of human tissue. The CT images of the metal components were then co-registered with their digital images provided by the implant manufactures. The accuracy of the co-registration algorithm developed here was shown to be within 0.5mm.

This technique was subsequently used to evaluate the accuracy of component placement in our patients who were all pre-operatively CT scanned. Their surgery was digitally planned by first defining the anterior pelvic plane (APP), which is then used as the frame of reference to accurately position and size the wire frame models of the implant. This plan greatly aids the surgeon in both groups and in the computer assisted arm the Acrobot Wayfinder uses this pre-operative plan to guide the surgeon.

Following surgery all patients, in both groups were further CT scanned to evaluate the achieved accuracy. This post-operative CT scan is co-registered to the pre-operative CT based plan. The difference between the planned and achieved implant positions is accurately computed in all three planes, giving 3 angular and 3 translational numerical values for each component.

Further analysis of the CT generated results is used to measure the implant intersection volume between the pre-operatively planned and achieved positions. This gives a single numerical value of placement error for each component. These 3D CT datasets have also been used to quantify the volume of bone resected in both groups of patients comparing the simulated resection of the planned position of the implant to that measured on the post-operative CT.

This study uses 3D CT as a surrogate outcome measure to demonstrate the efficacy of CAOS systems.

Hip resurfacing has advantages over hip replacement for younger, more active patients. However, it requires that surgeons learn new techniques for correctly cutting bone and positioning the components. Pre-operative planning systems exist for conventional hip replacement. Planning software for hip resurfacing is described, with the resulting plans available as a visual aid during surgery, or transferred to the Acrobot^® Navigation system for intra-operative guidance.

CT data is acquired from the top of the pelvis to immediately above the acetabulae in 4 mm slices, and from there down to just below the lesser trochanter in one mm slices. This keeps radiation doses low while providing high image quality in the important regions for planning. This is segmented semi-automatically, and bone surface models are generated.

Frames of reference are generated for the pelvis and femur, and the acetabular and femoral head positions are computed relative to these.

Prosthesis components are initially positioned and sized to match the computed anatomy. They can then be adjusted as required by the surgeon. While adjusting their positions, he is able to visualize their fit onto the bone to ensure good placement without problems such as femoral neck notching.

Twenty one hip resurfacings have been planned including two navigated cases. In addition, visualization of hip geometry for osteotomy and impingement debridement has been performed on 14 cases, giving the surgeon a good understanding of hip geometry prior to surgery. Initial evidence indicates surgeons find the planner useful, particularly when the anatomy is not straightforward.

This paper presents initial results of the Acrobot® Navigation System for Minimally Invasive (MI) Hip Resurfacing (HR) which addresses the problems of conventional HR. The system allows true MI HR – mini-mising the incision and tissue retraction required, and conservation of bone in contrast to other MI total hip procedures.

Pre-operative CT-based software allows the surgeon to plan the operation accurately. Use of CT gives the greatest accuracy, and is the only method which can give an accurate assessment of procedure outcome (planned versus achieved implant position). Intra-operatively, the bones are registered by touching points using a probe connected to a digitising arm. Next a series of tools is connected so that bone preparation and implant insertion is performed using on-screen guidance.

The accuracy of the registration probe is within 0.6mm, inside the acceptable margin for optical tracker systems. We have validated this acceptability using registration simulations leading to a protocol which restricts registration errors to within 1.5mm and three degree. These error margins are within those in the literature for acetabular component placement using optical tracker based systems (five degree inclination, six degree anteversion). No comparable data could be found regarding the accuracy of femoral component placement during computer-assisted HR.

The system is currently undergoing clinical tests at one alpha site, with three further beta sites planned for early 2006. The methods described by Henckel et al (CAOS International Proceedings 1994, pp. 281–282) are being used to evaluate the performance of the system, comparing pre-operative to post-operative CTs to obtain a true, accurate measure of performance.