Background and objectives. Positron emission tomography (PET) is a technology widely used in oncology. It is now being increasingly used in orthopaedics, especially in diagnosing bone infection. Diagnosis of bone infection is still a challenge, especially after surgery. Bone scintigraphy, Gallium-67 scintigraphy, and radiolabelled leucocyte scintigraphy are not specific. MRI has problems with definition in the presence of metal. PET uses 18-F Fluoro deoxyglucose(FDG) as a radiotracer. Inflammatory cells use glucose for energy, and the 18F-Fluoride component of FDG is a positron-emitting radionucleotide. We undertook this study to show our experience with the FDG-PET –CT in diagnosing bone infection and to highlight its superiority in diagnosing infected spine implants. Material and Methods. Medical records of orthopaedic patients referred to the nuclear medicine department in our hospital were retrospective reviewed. We looked at the clinical records, radiographs, bone scintigraphs, MRI and FDG-PET, assessing their diagnostic accuracy, and their value in helping the surgeon plan treatment. Results. There were 37 patients referred for possible diagnosis of bone infection. 14 had proven spine infection on FDG-PET scan. 5 of these had infected spine implants. The FDG-PET scan showed better definition of the anatomical site of the infection, allowing the surgeon to plan surgery better. Also it was not affected by presence of implants. Conclusion. FDG-PET-CT is the modality of choice for diagnosing bone infection. It is particularly useful in defining the anatomical site of the infection, especially in irregular bones, like the vertebrae. NO DISCLOSURES

Aim. Magnetic resonance imaging (MRI) and 2-[. 18. F]-fluoro-2-deoxy-D-glucose (. 18. F-FDG) Positron Emission Tomography, paired with Computed Tomography (PET/CT) are two indicated advanced imaging modalities in the complicated diagnostic work-up of osteomyelitis. PET/MRI is a relatively novel hybrid modality with suggested applications in musculoskeletal infection imaging. The goal of this study was to assess the value of hybrid . 18. F-FDG PET/MRI for chronic osteomyelitis diagnosis and surgical planning. Method. Five suspected chronic osteomyelitis patients underwent a prospective . 18. F-FDG single-injection/dual-imaging protocol with hybrid PET/CT and hybrid PET/MR. Diagnosis and relevant clinical features for the surgeon planning treatment were compared. Subsequently, 36 patients with . 18. F-FDG PET/MRI scans for suspected osteomyelitis were analysed retrospectively. Sensitivity, specificity, and accuracy were determined with the clinical assessment as the ground truth. Standardized uptake values (SUV) were measured and analysed by means of receiver operating characteristics (ROC). Results. The consensus diagnosis was identical for PET/CT and PET/MRI in the prospective cases, with PET/CT missing one clinical feature. The retrospective analysis yielded a sensitivity, specificity, and accuracy of 78%, 100%, and 86% respectively. Area under the ROC curve was .736, .755, and.769 for the SUVmax, target to background ratio, and SUVmax_ratio respectively. These results are in the same range and not statistically different compared to diagnostic value for . 18. F-FDG PET/CT imaging of osteomyelitis in literature. Conclusions. Based on our qualitative comparison, reduced radiation dose, and the diagnostic value that was found, the authors propose . 18. F-FDG PET/MRI as an alternative to . 18. F-FDG PET/CT in osteomyelitis diagnosis, if available

Aim. Low-grade infections are difficult to diagnose. As the presence of a chronic infection requires extensive surgical debridement and antibiotic treatment, it is important to diagnose a SII prior to surgery, especially when the hardware is revised. We investigated whether serum inflammatory markers or nuclear imaging can accurately diagnose a chronic spinal instrumentation infection (SII) prior to surgery. Method. All patients who underwent revision spinal surgery after a scoliosis correction between 2017 and 2019 were retrospectively evaluated. The diagnostic accuracy of serum C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR), . 18. F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) and Technetium-99m-methylene diphosphonate (99mTc-MDP) 3-phase bone scintigraphy (TPBS) to diagnose infection were studied. Patients with an acute infection or inadequate culture sampling were excluded. SII was diagnosed if ≥ 2 of the same microorganism(s) were isolated from intra-operative tissue cultures. Results. 31 patients were included. The indication for hardware extraction was pseudoarthrosis in the majority of patients (n = 15). 22 patients (71%) were diagnosed with SII. In all infected cases, Cutibacterium acnes was isolated, including 5 cases with a polymicrobial infection. Sensitivity, specificity, PPV and NPV was: 4.5%, 100%, 100% and 30.0% for CRP >10.0 mg/L, 5.5%, 100%, 100% and 29% for ESR > 30 mm/h; 56%, 80%, 83% and 50% for FDG-PET/CT and 50%, 100%, 100% and 20% for TPBS, respectively. Conclusions. The prevalence of SII in patients undergoing revision spinal surgery is high, with Cutibacterium acnes as the main pathogen. No diagnostic tests could be identified that could accurately diagnose or exclude SII prior to surgery. Future studies should aim to find more sensitive diagnostic modalities to detect low-grade inflammation

Objective. It is known that stress shielding frequently occurs after total hip arthroplasty (THA). However, the status of bone metabolism in stress shielding region is not still clear. . 18. F-fluoride positron emission tomography (PET) is a useful tool for the quantitative evaluation of bone metabolism, which uptake relates with the activity of bone formation by osteoblast. In this study, we evaluated the status of bone turnover in stress shielding region using . 18. F -fluoride PET. Design. A total of 88 hip joints from 70 cases after THA were analyzed using X-ray and . 18. F-fluoride PET. We classified these hips into 2 groups, stress shielding or non-stress shielding group. Each femur was divided into 7 regions by Gruen's zone classification. We measured SUV of . 18. F-fluoride PET in these regions and compared SUV to evaluate the difference of bone metabolism between 2 groups. Results. Stress shielding was confirmed in 75 joints, which was confirmed in particularly zone 1, 2, 7. The significant difference between the SUV in 2 groups was not confirmed. The SUV was significantly higher in the proximal area compared to the distal area. There was no differences of SUV between groups divided by post-operative period, nor implant type. Conclusions. Our results indicate that osteoblastic activities are maintained after THA even in stress shielding region. This observation indirectly suggested that high bone turn over may contribute to the BMD loss in stress shielding region

We investigated the blood flow to the femoral head during and after Resurfacing Arthroplasty of the hip. In a previous study, we recorded the intra-operative blood flow in 12 patients who had a posterior approach to the hip and 12 who had a trochanteric flip approach. Using a LASER Doppler flowmeter, we found a 40% drop in blood flow in the posterior group and an 11% drop in the trochanteric flip group (p<0.001). The aim of this current study was to find out whether the intra-operative fall in blood flow persists during the post-operative period. We therefore conducted a Single Positron Emission Tomography (SPECT) scan on 14 of the same group of patients. The proximal femur was divided into four regions of interest. These were the mid-shaft, proximal shaft, inter-trochanteric and head-neck regions. The data was analysed for bone activity and comparisons made between the two groups for each region of the femur. We found that the bone activity in the mid-shaft, upper-shaft, and head-neck regions was the same eleven months after the surgery irrespective of the approach to the hip. However there was higher activity in the trochanteric flip group in the inter-trochanteric region. We conclude that the intra-operative deficit in blood flow to the head-neck region of the hip associated with the posterior approach does not seem to persist in the late post-operative period. We believe the reason for increased bone activity in inter-trochanteric region to be due to the healing of the trochanteric flip osteotomy

Aim. Diagnosing a prosthetic joint infection (PJI) can be difficult. Several imaging modalities are available, but the choice which technique to use is often based on local expertise, availability and costs. Some centers prefer to use 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) as first imaging modality of choice, but due to a lack of accurate interpretation criteria, FDG-PET is currently not routinely applied for diagnosing PJI. With FDG-PET it is difficult to differentiate between FDG uptake due to reactive inflammation and uptake due to an infection. Since the physiological uptake pattern around a joint prosthesis is not fully elucidated, the aim of this study was to determine: i) the FDG uptake pattern in non-infected total hip prostheses and, ii) to evaluate whether there is a difference in uptake between cemented and non-cemented prostheses. Method. Patients with a primary total hip arthroplasty (1995–2016) without clinical signs of an infection that underwent a FDG-PET for another indication (mainly suspicion of malignancy) were included and retrospectively analysed. Patients in whom the prosthesis was implanted < 6 months prior to FDG-PET were excluded, to avoid post-surgical effects. Scans were visually and quantitatively analysed. Quantitative analysis was performed by calculating maximum and peak standardized uptake values (SUVmax and SUVpeak) by volume of interests (VOIs) at eight different locations around the prosthesis, from which the mean SUV was calculated. SUV was standardized by the liver SUV that was taken as background. Results. A total of 52 scans from 30 patients were analysed, with a median age of the prosthesis of 5.9 years (range 0.5–19.8). Most scans (87%) showed a diffuse uptake pattern around the prosthesis. The standardized median SUVmax and SUVpeak were 0.89 (IQR 0.78–1.16) and 0.64 (IQR=0.55–0.89), respectively. There was a difference in FDG uptake between the cemented (median SUVmax 0.85, IQR=0.77–1.04) and the uncemented prostheses (median SUVmax 1.01, IQR=0.84–2.01) (p=0.026). In uncemented prostheses, there was a positive correlation in time between the age of the prosthesis and the FDG uptake (rs=0.66, p=0.004). This observation was not found in cemented prostheses (rs=0.01, p=0.96). Conclusions. Non-infected total hip prostheses mostly show a diffuse FDG pattern around the prosthesis with a higher FDG uptake in uncemented compared to cemented prostheses. In uncemented prostheses, FDG uptake increases with the age of the implant. These findings may aid in the development of accurate interpretation criteria to better differentiate between inflammation and infection in patients with a prosthetic joint

The advantages of unicompartmental knee arthroplasty (UKA) include its bone preserving nature, lower relative cost and superior functional results. Some temporary pain has been reported clinically following this procedure. Could this be related to bone remodeling? A validated bone remodeling algorithm may have the answers…. A 3D geometry of an intact human cadaveric tibia was generated using CT images. An all poly unicompartmental implant geometry was positioned in an inlay and onlay configuration on the tibia and the post-operative models created. An adaptive bone remodeling algorithm was used with finite element modeling to predict the bone remodeling behavior surrounding the implant in both scenarios. Virtual DEXA images were generated from the model and bone mineral density (BMD) was measured in regions of interest in the AP and ML planes. BMD results were compared to clinical results. The bone remodelling algorithm predicted BMD growth in the proximal anterior regions of the tibia, with an inward tendency for both inlay and onlay models. Looking in the AP plane, a maximum of up to 7% BMD growth was predicted and in the ML plane this was as high as 16%. Minimal BMD loss was observed, which suggests minimal disturbance to the natural bone growth following UKA. Positron emission tomography (PET) scans showed active hot spots in the antero- medial regions of the tibia. These results were consistent with the finite element modeling results. Bone remodeling behavior was found to be sensitive to sizing and positioning of the implant. The adaptive bone remodeling algorithm predicted minimal BMD loss and some BMD growth in the anterior region of the tibia following UKA. This is consistent with patient complaint and PET scans

Aim. Diagnosing Fracture-Related Infections (FRI) is challenging. White blood cell (WBC) scintigraphy is considered the best nuclear imaging technique to diagnose FRI; a recent study by our group found a diagnostic accuracy of 92%. However, many centers use . 18. F-fluorodeoxyglucose positron emission tomography/computed tomography (. 18. F-FDG-PET/CT) which has several logistic advantages. Whether . 18. F-FDG-PET/CT has better diagnostic performance than white blood cell (WBC) scintigraphy is uncertain. Therefore, we aimed: 1) to determine the diagnostic performance of . 18. F-FDG-PET/CT for diagnosing FRI (defined as infection following an open fracture or fracture surgery) and 2) to determine cut-off values of standardized uptake values (SUV) that result in optimal diagnostic performance. Method. This retrospective cohort study included all consecutive patients who received . 18. F-FDG-PET/CT to diagnose FRI in two level 1 trauma centers. Baseline demographic- and surgical characteristics were retrospectively reviewed. The reference standard consisted of at least 2 representative microbiological culture results or the presence or absence of clinical confirmatory FRI signs in at least 6 months of clinical follow-up. A nuclear medicine specialist, blinded to the reference standard, re-reviewed all scans. Additionally, SUVs were measured using the “European Association of Nuclear Medicine Research Ltd. (EARL)” reconstructed . 18. F-FDG-PET/CT scans. Volume of interests were drawn around the suspected- and corresponding contralateral area to obtain the absolute values (SUVmax) and the ratio between suspected and contralateral area (SUVratio). Diagnostic accuracy of the re-reviewed scans was calculated (sensitivity and specificity). Additionally, diagnostic characteristics of the SUV measurements were plotted in the area under the receiver operating characteristics curve (AUROC). The sensitivity and specificity at the optimal threshold was deducted from the AUROC with the Q-point method. Results. 158 . 18. F-FDG-PET/CTs were included. Mean age was 46.2 years, 71.5% was male. Most cases (56.3%) were tibial shaft- or ankle fractures. Sixty patients (38.0%) had FRI. The sensitivity and specificity of the FDG-PET/CT scan was 70.0% (95% CI 56.8–81.2) and 79.6% (95% CI 70.3–87.1) respectively. Diagnostic accuracy was 76.0% (95% CI 68.5–82.4). AUROCs of SUVmax and SUVratio were 0.80 (95% CI 0.73–0.87) and 0.73 (95% CI 0.64–0.81), respectively. The optimal SUVmax threshold of 4.2 resulted in 80.0% sensitivity and 71.3% specificity, while an SUVratio of 2.9 resulted in 58.3% sensitivity and 80.9% specificity. Conclusions. The . 18. F-FDG-PET/CT has a sensitivity of 70.0%, specificity of 79.6% and a diagnostic accuracy of 76.0%. This makes . 18. F-FDG-PET/CT less accurate than WBC scintigraphy in diagnosing FRI, although adding SUV measurements may possibly increase its diagnostic accuracy

Aims

The timing of when to remove a circular frame is crucial; early removal results in refracture or deformity, while late removal increases the patient morbidity and delay in return to work. This study was designed to assess the effectiveness of a staged reloading protocol. We report the incidence of mechanical failure following both single-stage and two stage reloading protocols and analyze the associated risk factors.