Partial meniscectomy patients have a greater likelihood for the development of early osteoarthritis (OA). To prevent the onset of early OA, patient-specific treatment algorithms need to be created that predict patient risk to early OA after meniscectomy. The aim of this work was to identify patient-specific risk factors in partial meniscectomy patients that could potentially lead to early OA. Partial meniscectomy patients operated between 01/2017 and 12/2019 were evaluated in the study (n=317). Exclusion criteria were other pathologies or surgeries for the evaluated knee and meniscus (n = 114). Following informed consent, an online questionnaire containing demographics and the “Knee Injury and Osteoarthritis Outcome Score” (KOOS) questionnaire was sent to the patient. Based on the KOOS pain score, patients were classified into “low” (> 75) and “high” (< 75) risk patients, indicating risk to symptomatic OA. The “high risk” patients also underwent a follow-up including an MRI scan to understand whether they have developed early OA. From 203 participants, 96 patients responded to the questionnaire (116 did not respond) with 61 patients considered “low-risk” and 35 “high-risk” patients. Groups that showed a significant increased risk for OA were patients aged > 40 years, females, overweight (BMI >25 kg/m2 ≤ 30 kg/m2), and smokers (*p < 0.05). The “high-risk”-follow-up revealed a progression of early osteoarthritic cartilage changes in seven patients, with the remaining nineteen patients showing no changes in cartilage status or pain since time of operation. Additionally, eighteen patients in the high-risk group showed a varus or valgus axis deviation. Patient-specific factors for worse postoperative outcomes after partial meniscectomy and indicators for an “early OA” development were identified, providing the basis for a patient-specific treatment approach. Further analysis in a multicentre study and computational analysis of MRI scans is ongoing to develop a patient-specific treatment algorithm for meniscectomy patients

The objective of this study was to use patient-specific finite element modeling to measure the 3D interfragmentary strain environment in clinically realistic fractures. The hypothesis was that in the early post-operative period, the tissues in and around the fracture gap can tolerate a state of strain in excess of 10%, the classical limit proposed in the Perren strain theory. Eight patients (6 males, 2 females; ages 22–95 years) with distal femur fractures (OTA/AO 33-A/B/C) treated in a Level I trauma center were retrospectively identified. All were treated with lateral bridge plating. Preoperative computed tomography scans and post-operative X-rays were used to create the reduced fracture models. Patient-specific materials properties and loading conditions (20%, 60%, and 100% body weight (BW)) were applied following our published method.[1]. Elements with von Mises strains >10% are shown in the 100% BW loading condition. For all three loading scenarios, as the bridge span increased, so did the maximum von Mises strain within the strain visualization region. The average gap closing (Perren) strain (mean ± SD) for all patient-specific models at each body weight (20%, 60%, and 100%) was 8.6% ± 3.9%, 25.8% ± 33.9%, and 39.3% ± 33.9%, while the corresponding max von Mises strains were 42.0% ± 29%, 110.7% ± 32.7%, and 168.4% ± 31.9%. Strains in and around the fracture gap stayed in the 2–10% range only for the lowest load application level (20% BW). Moderate loading of 60% BW and above caused gap strains that far exceeded the upper limit of the classical strain rule (<10% strain for bone healing). Since all of the included patients achieved successful unions, these findings suggest that healing of distal femur fractures may be robust to localized strains greater than 10%

Abstract

Objectives. Preservation of both anterior and posterior cruciate ligaments in total knee arthroplasty (TKA) can lead to near-normal post-operative joint mechanics and improved knee function. We hypothesised that a patient-specific bicruciate-retaining prosthesis preserves near-normal kinematics better than standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining prostheses in TKA. Methods. We developed the validated models to evaluate the post-operative kinematics in patient-specific bicruciate-retaining, standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under gait and deep knee bend loading conditions using numerical simulation. Results. Tibial posterior translation and internal rotation in patient-specific bicruciate-retaining prostheses preserved near-normal kinematics better than other standard off-the-shelf prostheses under gait loading conditions. Differences from normal kinematics were minimised for femoral rollback and internal-external rotation in patient-specific bicruciate-retaining, followed by standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under deep knee bend loading conditions. Moreover, the standard off-the-shelf posterior cruciate-retaining TKA in this study showed the most abnormal performance in kinematics under gait and deep knee bend loading conditions, whereas patient-specific bicruciate-retaining TKA led to near-normal kinematics. Conclusion. This study showed that restoration of the normal geometry of the knee joint in patient-specific bicruciate-retaining TKA and preservation of the anterior cruciate ligament can lead to improvement in kinematics compared with the standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining TKA. Cite this article: Y-G. Koh, J. Son, S-K. Kwon, H-J. Kim, O-R. Kwon, K-T. Kang. Preservation of kinematics with posterior cruciate-, bicruciate- and patient-specific bicruciate-retaining prostheses in total knee arthroplasty by using computational simulation with normal knee model. Bone Joint Res 2017;6:557–565. DOI: 10.1302/2046-3758.69.BJR-2016-0250.R1

3D-printed orthopedic implants have been gaining popularity in recent years due to the control this manufacturing technique gives the designer over the different design aspects of the implant. This technique allows us to manufacture implants with material properties similar to bone, giving the implant designer the opportunity to address one of the main complications experienced after total hip arthroplasty (THA), i.e. aseptic loosening of the implant. To restore proper function after implant loosening, the implant needs to be replaced. During these revision surgeries, some extra bone is removed along with the implant, further increasing the already present defects, and making it harder to achieve proper mechanical stability with the revision implant. A possible way to limit the increasing loss of bone is the use of biodegradable orthopedic implants that optimize long-term implant stability. These implants need to both optimize the implant such that stress shielding is minimized, and tune the implant degradation rate such that newly formed bone is able to replace the degrading metal in order to maintain a proper bone-implant contact. The hope is that such (partly) degradable implants will lead to a reduction in the size of the bone defects over time, making possible future revisions less likely and less complex. We focused on improving the long-term implant stability of patient-specific acetabular implants for large bone defects and the modeling of their biodegradable behavior. To improve long-term implant stability we implemented a topology optimization approach. A patient-specific finite element model of the hip joint with and without implant was derived from CT-scans to evaluate the performance of the designs during the optimization routine. To evaluate the biodegradation behavior, a quantitative mathematical model was developed to assess the degradation rates of the biodegradable part of the implant. Currently, the biodegradation model has been implemented for magnesium (Mg) implants as a first proof of concept. For a first test case, an optimized implant was found with stress shielding levels below 20% in most regions. The highest stress shielding levels were found at the bone implant interface. The biodegradation model has been validated using experimental data, which includes immersion tests of simple scaffolds created from Commercial Pure Mg. The mass loss of the scaffold is about 0.8 mg/cm. 2. for the first day of immersion in simulated body fluid (SBF) solution. After the formation of a protective film on the surface of the simple scaffold, the degradation rate starts to slow down. Initial results presented serve as a proof of concept of the developed computational framework for the implant optimization and the implant biodegradation behavior. Currently, timing calibration, benchmarking and validation are taking place. Reducing implant-induced stress shielding, obtaining a better implant integration and reduction of bone defects, by allowing for bone to partially replace the implant over time, are crucial design factors for large bone defect implants. In this research, we have developed in-silico models to investigate these factors. Once validated and coupled, the models will serve as an important tool to find the appropriate biodegradable implant designs and biodegradable metal properties for THA applications, that improve current implant lifetime while ensuring proper mechanical functioning

Objectives. Meniscal injuries are often associated with an active lifestyle. The damage of meniscal tissue puts young patients at higher risk of undergoing meniscal surgery and, therefore, at higher risk of osteoarthritis. In this study, we undertook proof-of-concept research to develop a cellularized human meniscus by using 3D bioprinting technology. Methods. A 3D model of bioengineered medial meniscus tissue was created, based on MRI scans of a human volunteer. The Digital Imaging and Communications in Medicine (DICOM) data from these MRI scans were processed using dedicated software, in order to obtain an STL model of the structure. The chosen 3D Discovery printing tool was a microvalve-based inkjet printhead. Primary mesenchymal stem cells (MSCs) were isolated from bone marrow and embedded in a collagen-based bio-ink before printing. LIVE/DEAD assay was performed on realized cell-laden constructs carrying MSCs in order to evaluate cell distribution and viability. Results. This study involved the realization of a human cell-laden collagen meniscus using 3D bioprinting. The meniscus prototype showed the biological potential of this technology to provide an anatomically shaped, patient-specific construct with viable cells on a biocompatible material. Conclusion. This paper reports the preliminary findings of the production of a custom-made, cell-laden, collagen-based human meniscus. The prototype described could act as the starting point for future developments of this collagen-based, tissue-engineered structure, which could aid the optimization of implants designed to replace damaged menisci. Cite this article: G. Filardo, M. Petretta, C. Cavallo, L. Roseti, S. Durante, U. Albisinni, B. Grigolo. Patient-specific meniscus prototype based on 3D bioprinting of human cell-laden scaffold. Bone Joint Res 2019;8:101–106. DOI: 10.1302/2046-3758.82.BJR-2018-0134.R1

Intervertebral discs (IVD) provide flexibility to the back and ensure functional distributions of the spinal loads. They are avascular, and internal diffusion-dependent metabolic transport is vital to supply nutrients to disc cells1, but interactions with personalized IVD shapes and mechanics remain poorly explored. Poromechanical finite element models of seven personalized lumbar IVD geometries, with mean heights ranging from 8 to 16 mm were coupled with a reactive oxygen, glucose and lactate transport model linked with tissue deformations and osmosis . In previous studies, reduced formulations of the divergence of the solute flux (∇ .J = ∇ . (D∇ C) = ∇ D. ∇ C +D∇ 2C) ignored the dependence of the diffusion on the deformation gradients, ∇ D. ∇C. We simulated this phenomenon to explore its significance in mechano-metabolic -transport couplings, in the different geometries, over 24h of simulated rest (8h) and physical activity (16h). ∇ D. ∇ C affected the daily variations of glucose concentrations in IVD thinner than 12 mm but with neglectable variation ranges, while not considering ∇ D. ∇ C in taller discs only slightly overestimated the glucose concentration. Most importantly, tall IVD had nearly 60% less glucose than thin IVD, with local drops below the concentration of 0.5 mM, considered to be critical for disc cells3, in the anterior nucleus pulposus. On the one hand, previous reduced formulations for mechanometabolic-transport models of the IVD seem acceptable, even for patient-specific modelling. On the other hand, tall IVD might suffer from unfortunate combinations of deformation-dependent solute diffusion and large diffusion distances, which may favor early. Acknowledgements: Catalan Government and European Commission (2020 BP 00282; ERC-2021-CoG-O-Health-101044828)

After anterior cruciate ligament (ACL) rupture, reconstructive surgery with a hamstring tendon autograft is often performed. Despite overall good results, ACL re-rupture occurs in up to 10% of the patient population, increasing to 30% of the cases for patients aged under 20 years. This can be related to tissue remodelling in the first months to years after surgery, which compromises the graft's mechanical strength. Resident graft fibroblasts secrete matrix metalloproteinases (MMPs), which break down the collagen I extracellular matrix. After necrosis of these fibroblasts, myofibroblasts repopulate the graft, and deposit more collagen III rather than collagen I. Eventually, the cellular and matrix properties converge towards those of the native ACL, but full restoration of the ACL properties is not achieved. It is unknown how inter-patient differences in tissue remodelling capacity contribute to ACL graft rupture risk. This research measured patient-specific tissue remodelling-related properties of human hamstring tendon-derived cells in an in vitro micro-tissue platform, in order to identify potential biological predictors for graft rupture. Human hamstring tendon-derived cells were obtained from remnant autograft tissue after ACL reconstructions. These cells were seeded in collagen I gels on a micro-tissue platform to assess inter-patient cellular differences in tissue remodelling capacity. Remodelling was induced by removing the outermost micro-posts, and micro-tissue compaction over time was assessed using transmitted light microscopy. Protein expression of tendon marker tenomodulin and myofibroblast marker α-smooth muscle actin (αSMA) were measured using Western blot. Expression and activity of remodelling marker MMP2 were determined using gelatin zymography. Cells were obtained from 12 patients (aged 12–51 years). Patient-specific variations in micro-tissue compaction speed or magnitude were observed. Up to 50-fold differences in αSMA expression were found between patients, although these did not correlate with faster or stronger compaction. Surprisingly, tenomodulin was only detected in samples obtained from two patients. Total MMP2 expression varied between patients, but no large differences in active fractions were found. No correlation of patient age with any of the remodelling-related factors was detected. Remodelling-related biological differences between patient tendon-derived cells could be assessed with the presented micro-tissue platform, and did not correlate with age. This demonstrates the need to compare this biological variation in vitro - especially cells with extreme properties - to clinical outcome. Sample size is currently increased, and patient outcome will be determined. Combined with results obtained from the in vitro platform, this could lead to a predictive tool to identify patients at risk for graft rupture

Patients with cancer and bone metastases can have an increased risk of fracturing their femur. Treatment is based on the impending fracture risk: patients with a high fracture risk are considered for prophylactic surgery, whereas low fracture risk patients are treated conservatively with radiotherapy to decrease pain. Current clinical guidelines suggest to determine fracture risk based on axial cortical involvement of the lesion on conventional radiographs, but that appears to be difficult. Therefore, we developed a patient-specific finite element (FE) computer model that has shown to be able to predict fracture risk in an experimental setting and in patients. The goal of this study was to determine whether patient-specific finite element (FE) computer models are better at predicting fracture risk for femoral bone metastases compared to clinical assessments based on axial cortical involvement on conventional radiographs, as described in current clinical guidelines. 45 patients (50 affected femurs) affected with predominantly lytic bone metastases who were treated with palliative radiotherapy for pain were included. CT scans were made and patients were followed for six months to determine whether or not they fractured their femur. Non-linear isotropic FE models were created with the patient-specific geometry and bone density obtained from the CT scans. Subsequently, an axial load was simulated on the models mimicking stance. Failure loads normalized for bodyweight (BW) were calculated for each femur. High and low fracture risks were determined using a failure load of 7.5 × BW as a threshold. Experienced assessors measured axial cortical involvement on conventional radiographs. Following clinical guidelines, patients with lesions larger than 30 mm were identified as having a high fracture risk. FE predictions were compared to clinical assessments by means of diagnostic accuracy values (sensitivity, specificity and positive (PPV) and negative predictive values (NPV)). Seven femurs (14%) fractured during follow-up. Median time to fracture was 8 weeks. FE models were better at predicting fracture risk in comparison to clinical assessments based on axial cortical involvement (sensitivity 100% vs. 86%, specificity 74% vs. 42%, PPV 39% vs. 19%, and NPV 100% vs. 95%, for the FE computer model vs. axial cortical involvement, respectively). We concluded that patient-specific FE computer models improve fracture risk predictions of femoral bone metastases in advanced cancer patients compared to clinical assessments based on axial cortical involvement, which is currently used in clinical guidelines. Therefore, we are initiating a pilot for clinical implementation of the FE model

Femoroplasty is the process of injecting cement (cement augmentation) into the proximal femur to prevent osteoporotic hip fractures. Femoroplasty increases the strength and energy to failure of the femur and can be performed in a minimally-invasively manner with lower hospitalization costs and reduced recovery. Our hypothesis was that efficient cement augmentation strategies can be identified via computational optimization. Therefore, using patient-specific planning we can minimize cement volume while increasing bone strength and reducing the risk of fracture. We proposed an in-silico methodology that was validated with in vitro experiments. A discrete particle model for cement infiltration was used to determine the optimum volume and filling pattern of the cement such that the best outcome was achieved. Several artificial bones were scanned before and after cement augmentation to applied previous in silico methodology. Then those femurs were mechanically tested (non-augmented and augmented). Therefore, in silico methodology was validated. Cement augmentation significantly increased the yield load. Predicted yield loads correlated well with the experiments. Results suggest that patient-specific planning of femoroplasty reduces the risk of hip fracture while minimizing the amount of cement required

While osteophytes are a hallmark feature of knee osteoarthritis (OA), there is limited information regarding their location. In particular, it is unknown whether osteophytes develop in patient-specific locations or if there are consistent osteophyte locations among OA knees. This lack of data mainly stems from the fact that osteophytes have been mostly assessed with scores quantifying their size or severity but not their location. Given the important role that bone could play in OA development and the option it offers for OA treatment, there is a need to better understand the osteophyte locations. This study aimed to develop a method to compare osteophyte locations among knees and determine the overlapping ratio. CT arthrogram of 11 medial-compartment OA tibias (Kellgren-Lawrence grade ≥ 3) were segmented to locate the osteophytes and a bone matching technique was used to report the osteophyte locations of the 11 knees on a single reference tibia. This newly proposed method was highly reproducible (intra-operator ICC = 0.89). When used to compare the 11 tibias, it showed that more than 60% of the overall subosteophytal area, defined as the reference bone area covered by at least one osteophyte from one knee, was common to less than two tibias. Moreover, less than 20% of the overall subosteophytal area was common to five or more tibias. The results of this study suggest that osteophyte locations are specific to each knee. Future work should determine the relationships with mechanical loading, as this could explain the high inter-patient variability

Summary Statement. In this study, excellent positioning of custom-made glenoid components was achieved using patient-specific guides. Achieving the preoperatively planned orientation of the component improved significantly and more screws were located inside the scapular bone compared to implantations without such guide. Introduction. Today's techniques for total or reverse shoulder arthroplasty are limited when dealing with severe glenoid defects. The available procedures, for instance the use of bone allografts in combination with available standard implants, are technically difficult and tend to give uncertain outcomes (Hill et al. 2001; Elhassan et al. 2008; Sears et al. 2012). A durable fixation between bone and implant with optimal fit and implant positioning needs to be achieved. Custom-made defect-filling glenoid components are a new treatment option for severe glenoid defects. Despite that the patient-specific implants are uniquely designed to fit the patient's bone, it can be difficult to achieve the preoperatively planned position of the component, resulting in less optimal screw fixation. We hypothesised that the use of a patient-specific guide would improve implant and screw positioning. The aim of this study was to evaluate the added value of a newly developed patient-specific guide for implant and screw positioning, by comparing glenoid implantations with and without such guide. Patients & Methods. Large glenoid defects, representative for the defects encountered in clinical practice, were created in ten cadaveric shoulders. A CT scan of each cadaver was taken to evaluate the defects and to generate three-dimensional models of the scapular bones. Based on these models, custom glenoid components were designed. Furthermore, a newly developed custom guide was designed for five randomly selected shoulders. New CT scans were taken after implantation to generate 3D models of the bone and the implanted component and screws. This enabled to compare the experimentally achieved and preoperatively planned reconstruction. The location and orientation of the glenoid component and screw positioning were determined and differences with the optimal preoperative planning were calculated. Results. An excellent component positioning (difference in location: 1.4±0, 7mm; difference in orientation: 2, 5±1, 2°) was achieved when using the guide compared to implantations without guidance (respectively 1, 7±0, 5mm; 5, 1±2, 3°). The guide improved component orientation significantly (P<0.1). After using the guide, all screws were positioned inside the scapular bone whereas 25% of the screws placed without guidance were positioned outside the scapular bone. Discussion/Conclusion. In this study, excellent positioning of custom-made glenoid components was achieved using patient-specific guides. Achieving the preoperatively planned orientation of the component improved significantly and more screws were located inside the scapular bone compared to implantations without such guide

Syndesmotic ankle lesions involve disruption of the osseous tibiofibular mortise configuration as well as ligamentous structures stabilizing the ankle joint. Incomplete diagnosis and maltreatment of these injuries is frequent, resulting in chronic pain and progressive instability thus promoting development of ankle osteoarthritis in the long term. Although the pathogenesis is not fully understood, abnormal mechanics has been implicated as a principal determinant of ankle joint degeneration after syndesmotic ankle lesions. Therefore, the focus of this presentation will be on our recent development of a computationally efficient algorithm to calculate the contact pressure distribution in patients with a syndesmotic ankle lesion, enabling us to stratify the risk of OA development in the long term and thereby guiding patient treatment.

Adult Spine Deformity (ASD) is a degenerative condition of the adult spine leading to altered spine curvatures and mechanical balance. Computational approaches, like Finite Element (FE) Models have been proposed to explore the etiology or the treatment of ASD, through biomechanical simulations. However, while the personalization of the models is a cornerstone, personalized FE models are cumbersome to generate. To cover this need, we share a virtual cohort of 16807 thoracolumbar spine FE models with different spine morphologies, presented in an online user-interface platform (SpineView). To generate these models, EOS images are used, and 3D surface spine models are reconstructed. Then, a Statistical Shape Model (SSM), is built, to further adapt a FE structured mesh template for both the bone and the soft tissues of the spine, through mesh morphing. Eventually, the SSM deformation fields allow the personalization of the mean structured FE model, leading to generate FE meshes of thoracolumbar spines with different morphologies. Models can be selectively viewed and downloaded through SpineView, according to personalized user requests of specific morphologies characterized by the geometrical parameters: Pelvic Incidence; Pelvic Tilt; Sacral Slope; Lumbar Lordosis; Global Tilt; Cobb Angle; and GAP score. Data quality is assessed using visual aids, correlation analyses, heatmaps, network graphs, Anova and t-tests, and kernel density plots to compare spinopelvic parameter distributions and identify similarities and differences. Mesh quality and ranges of motion have been assessed to evaluate the quality of the FE models. This functional repository is unique to generate virtual patient cohorts in ASD.

Acknowledgements: European Commission (MSCA-TN-ETN-2020-Disc4All-955735, ERC-2021-CoG-O-Health-101044828)

High tibial osteotomy (HTO) is a joint preserving alternative to knee replacement for medial tibiofemoral osteoarthritis in younger, more active patients. The procedure is technically challenging and limited also by ‘one size fits all’ plates which can result in patient discomfort necessitating plate removal.

This clinical trial evaluated A novel custom-made HTO system – TOKA (3D Metal Printing LTD, Bath, UK) for accuracy of osteotomy correction and improvements in clinical outcome scores.

The investigation was a single-arm single-centre prospective clinical trial (IRCCS Istituto Ortopedico Rizzoli; ClinicalTrials.gov NCT04574570), with recruitment of 25 patients (19M/6F; average age: 54.4 years; average BMI: 26.8), all of whom received the TOKA HTO 3D planning and surgery. All patients were predominantly diagnosed with isolated medial knee osteoarthritis and with a varus deformity under 20°. Patients were CT scanned pre- and post-operatively for 3D virtual planning and correctional assessment. All surgeries were performed by the lead clinical investigator – a consultant knee surgeon with a specialist interest in and clinical experience of HTO.

On average, Knee Society Scores (KSS) improved significantly (p<0.001) by 27.6, 31.2 and 37.2 percentage points respectively by 3-, 6- and 12-months post-surgery respectively. Other measures assessed during the study (KOOS, EQ5D) produced similar increases.

Our early experience using custom implants is extremely promising. We believe the reduced profile of the plate, as well as the reduced invasiveness and ease of surgery contributed to faster patient recovery, and improved outcome scores compared to conventional techniques. These clinical outcome results compare very favourably other case-series with published KOOS scores using different devices.

Introduction and Objective

After anterior cruciate ligament reconstruction one of the risk factors for graft (re-)rupture is an increased posterior tibial slope (PTS). The current treatment for PTS is a high tibial osteotomy (HTO). This is a free-hand method, with 1 degree of tibial slope correction considered to be equal to 1 or even 1.67 mm of the anterior wedge resection. Error rates in the frontal plane reported in literature vary from 1 – 8.6 degrees, and in the sagittal plane outcomes in a range of 2 – 8 degrees are reported when planned on PTSs of 3 – 5 degrees. Therefore, the free-hand method is considered to have limited accuracy. It is expected that HTO becomes more accurate with patient specific saw guides (PSGs), with an accuracy margin reported in literature of 2 degrees. This proof of concept porcine cadaver case study aimed to investigate whether the use of PSGs improves the accuracy of HTO to less than 2 degrees. Secondly, the reproducibility of tibial slope measurement was evaluated.

The medial opening-wedge high tibial osteotomy (OW-HTO) is an accepted option to treat the isolated medial compartment osteoarthritis (OA) in varus knee. Despite satisfactory outcomes were described in literature, consistent complication rate has been reported and the provided accuracy of coronal alignment correction using conventional HTO techniques falls short.

Patient specific instrumentations has been introduced with the aim to reduce complications and to improve the intra-operative accuracy according to the pre-operative plan, which is responsible for the clinical result of the surgery.

In this talk, an overview of the clinical results of HTO patient specific instrumentation available in literature will be performed.

Moreover, preliminary intra-operative and clinical results of a new customised 3-D printed cutting guide and fixation plate for OW-HTO will be presented.

Summary. Alignment results did not differ between PSG and conventional instrumentation. A small reduction in operation time and blood loss was found with the PSG system, but is unlikely of clinical significance. Length of hospital stay was identical for both groups. Introduction. Several techniques for aligning a TKA exist nowadays. Patient-specific guiding (PSG) has relatively recently been introduced to try to resolve the shortcomings of existing techniques while optimising the operative procedure. Still few reports have been published on the clinical outcome and on the peroperative results of this new technique. This prospective, double-blind, randomised controlled trial was designed to address the following research questions: 1. Is there a significant difference in outliers in alignment in the frontal and sagittal plane between PSG TKA and conventional TKA. 2. Is there a significant difference in operation time, blood loss and length of hospital stay between the 2 techniques. Patients & Methods. 180 patients were randomised for PSG TKA (group 1) or conventional TKA (group 2) in 2 centres. Patients were stratified per hospital. Alignment of the mechanical axis of the leg and flexion/extension and varus/valgus of the individual prosthesis components were measured on digital, standing, long-leg and standard lateral radiographs by 2 independent outcome assessors in both centres. Percentages of outliers, > 3°, were determined. We compared blood loss, operation time and length of hospital stay. Results. There was no statistically significant difference in mean mechanical axis or outliers in mechanical axis between groups. No statistically significant difference was found for the alignment of the individual components in the frontal plane, nor for the percentages of outliers. There was a statistically significant difference in outliers for the femoral component in the sagittal plane, with a higher percentage of outliers in the group 1 (p = 0.017). No such significant result was found for the tibial component in that plane. All interclass correlation coefficients were good. Blood loss was 100 mL less in group 1 (p = 0.000). Operation time was 5 minutes shorter in group 1 (p = 0.000). Length of hospital stay was almost identical with a mean of 3.6 days (p = 0.657). Discussion/Conclusions. The results in terms of obtaining a neutral mechanical axis and a correct position of the prosthesis components did not differ between groups. A small reduction in operation time and blood loss was found with the PSG system, but is unlikely of any clinical significance. Future research should especially focus on cost-effectiveness analysis and functional outcome of PSG TKA

Osteoarthritis is a multifactorial disease in which altered mechanical loading is one of the agreed contributing factors. Whereas in the past, altered mechanical loading was merely deferred from static, image-based evaluations of malalignment, the recent use of 3D motion capture allowed dynamic evaluation of joint loading in terms of dynamic alignment (e.g. varus trust) and even joint loading strategy (merely using proxy measures like knee adduction moment.) Combining these measurements with musculoskeletal models, the overall loading distribution in the joint due to muscle action underlying the patient's motion pattern can be quantified. Using this approach, our group showed the potential of this technique to differentiate between control subjects and subjects with early medial knee OA before the presence of radiographic evidence of structural joint degradation. Nevertheless, no changes in loading distribution could be detected in a cohort of subjects suffering of local cartilage defects in an otherwise healthy knee joint, indicating that patients did not present active unloading strategies despite the presence of clinical symptoms. Furthermore, subject-specific strategies aiming contributing to modified loading of the hip joint have been evaluated.

Pedicle screws fixation to stabilize lumbar spinal fusion has become the gold standard for posterior stabilization. However their positioning remain difficult due to variation in anatomical shape, dimensions and orientation, which can determine the inefficacy of treatment or severe damages to close neurologic structures. Image guided navigation allows to drastically decrease errors in screw placement but it is used only by few surgeons due to its cost and troubles related to its using, like the need of a localizer in the surgical scenario and the need of a registration procedure. An alternative image guided approach, less expensive and less complex, is the using of patient specific templates similar to the ones used for dental implants or knee prosthesis.

Like proposed by other authors we decided to design the templates using CT scans. (slice thickness of 2.0 mm). Template developing is done, for each vertebra, using a modified version of ITK-SNAP 1.5 segmentation software, which allow to insert cylinders (full or empty) in the segmented images. At first we segment the spine bone and then the surgeon chose screw axes using the same software. We design each template with two hollow cylinders aligned with the axes, to guide the insertion in the pedicle, adding contact points that fit on the vertebra, to obtain a template right positioning. Finally we realize the templates in ABS using rapid prototyping. After same in-vitro tests, using a synthetic spine (by Sawbones), we studied a solution to guarantee template stability with simple positioning and minimizing intervention invasiveness. Preliminary ex-vivo animal testing on porcine specimens has been conducted to evaluate template performance in presence of soft-tissue in place, simulating dissection and vertebra exposure. For verification, the surgeon examined post-operative CT-scans to evaluate Kirschner wires positioning.

During the ex-vivo animal test sessions, template alignment resulted easy thanks to the spinous process contact point. Their insertion required no additional tissue removal respect to the traditional approach. The positioning of contact points on vertebra's lamina and articular processes required just to shift the soft tissue under the cylinders bases. The surgeon in some cases evaluated false stable template positions since not each of the 4 contact points were actually in contact with the bone surface and tried the right position. CT evaluation demonstrate a positive results in 96.5% of the Kirschner wires implanted.

Our approach allows to obtain patient specific templates that does not require the complete removal of soft tissue around vertebra. Guide positioning is facilitated thanks to the using of the spinous processes contact point, while false stable positions can be avoided using four redundant contact points. The templates can be used to guide the drill, the insertion of Kirschner in case of use of cannulated screws or to guide directly the screw. After these preliminary ex-vivo animal tests we obtained the authorization of the Italian Health Ministry to start the human study.