Introduction: Femoral neck failure due to avascular necrosis (AVN) is one of the most significant complications following resurfacing hip arthroplasty. It is likely that the surgical approach is one of the factors influenc-ing the development of AVN. Positron emission tomography (PET) is the only form of imaging that allows visualisation of bone metabolic activity deep to a metal surface. Objectives: To establish the reliability and accuracy of PET using fluorine-18 to evaluate viability of the femoral head and neck after resurfacing hip arthroplasty. To assess the viability of ten proximal femora after Birmingham resurfacing hip arthroplasty via a modified lateral approach. Design: A convenience case series of ten patients taken from the first fifteen from one orthopaedic surgeon’s experience of Birmingham resurfacing hip arthroplasty. Setting: The PET unit of a major urban teaching hospital with a large academic orthopaedic department. Participants: Patients that had undergone unilateral Birmingham resurfacing hip arthroplasty via a modified lateral approach were asked to volunteer for the study. The main criterion for inclusion was ease of attendance for imaging. Intervention: Participants were given a single intravenous dose of 250MBq fluorine-18. After a period of 40 minutes uptake time, PET images of adjacent, sequential 10cm transverse sections including both acetabulae and proximal femora were obtained. Main Outcome Measures: Images were reconstructed to allow relative quantification of uptake between operated and non-operated femoral heads and necks. Results: PET imaging was successful in all subjects and demonstrated activity within the resurfaced femoral heads and femoral necks. No evidence of AVN was found. Conclusions: Static positron emission tomography using fluorine-18 is an accurate and reliable method of assessing femoral head and neck viability after resurfacing hip arthroplasty. No evidence of avascular necrosis was found in this initial series of patients that had undergone Birmingham resurfacing hip arthroplasty via a modified lateral approach

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

Introduction. The healing of Achilles tendon rupture is slow and jogging is usually allowed already 6 months after injury. However, the metabolic status of the healing tendon is largely unknown at the time-points when increased loading is allowed. The purpose of this study was to investigate tendon metabolic response and blood flow at 3, 6 and 12 months after Achilles tendon rupture by positron emission tomography (PET) and ultrasound-Power Doppler (UPD). Materials and Methods. 23 patients that had surgical repair of a total Achilles tendon rupture (3 (n=7), 6 (n=7) or 12 (n=9) months earlier) participated in the study. The triceps surae complex was loaded during 20 min of slow treadmill walking. A radioactive tracer (FDG) was administered during this walking and glucose uptake was measured bilaterally by the use of PET. Blood flow was recorded by UPD and patient reported outcome scored by Achilles tendon rupture score (ATRS) and VISA-A. Non-parametric statistics were used for statistical analysis. Results. Metabolic activity was higher in the healing tendon compared to intact tendon at all time-points, however the activity decreased over time (510%, 260% and 62% higher on the healing side compared to the intact side at 3, 6 and 12 months respectively, p<0.001). The metabolic activity was higher in the core than the periphery of the healing tendon, at 3 and 6 months (p<0.02), but lower at 12 months (p=0.06). Interestingly, metabolic activity was negatively related to ATRS, 6 months after rupture (r=−0.89, p<0.01). UPD was also 100-fold and 61-fold higher respectively in the healing than the intact healthy tendon at 3 months (p<0.05) and 6 months (p=0.06), but not at 12 months. Discussion. These results demonstrate that the healing process measured by metabolic and blood flow activity still remains high 6 months after rupture when increased loading is allowed. In fact, PET determined metabolic activity remained elevated up to a year after injury when measures of hyper-vascularization were normalized. Although speculative, the strong negative correlation between tendon metabolism and patient reported outcome indicates that a high metabolic activity 6 months after the injury may be related to poor healing outcome

Introduction: Arthroplasty plays a growing role in our society today. Due to scientific and medical progress there are an increasing number of viable candidates and the improvement of quality of life thereafter speaks for itself. Even though the operations are largely successful, complications after joint replacement surgery occur frequently. Approximately 10% of lower limb arthroplasties need surgical revision, of which 70% are due to loosening. The purpose of this study was to assess the feasibility of 18-fluorodeoxyglucose positron emission tomography (18F-FDG-PET) in detecting septic and aseptic endoprosthetic loosening of hip and knee endoprostheses. Materials and Methods: Thirty-three patients (age range: 45 – 90y) with lower limb arthroplasty complaints (74 prostheses) were studied preoperatively with 18F-FDG-PET. All patients underwent surgery at a later stage with microbiological culturing to differentiate aseptic and septic loosening and to confirm the final diagnosis. Prostheses were tested intraoperatively for stability and microbiology. Results: The sensitivity/specificity of 18F-FDG-PET towards implant loosening in the hip was 80%/87%, in the knee 56%/82%. The sensitivity/specificity for infectious loosening in hip replacement arthroplasties was 67%/83%, in the knee 14%/89%. Discussion: 18F-FDG-PET seems an excellent method for detecting hip endoprosthetic loosening and a moderate tool to diagnose hip implant infection. It should not be seen as the method of choice to diagnose knee endoprosthetic loosening and infection

Following intralesional resection of giant cell tumour local recurrence happens in up to 40% depending on type of treatment. Common plain radiography or Magnetic resonance tomography (MRI) often has the problem not to discriminate between scar and recurrent tumour tissue in the cement-tissue border of lesions treated with cement packing. The value of Positron emission tomography (PET) for diagnosis of tumour and recurrence was investigated in these patients. In 19 patients with giant cell tumour dynamic PET using F18-Fluordeoxyglucose for estimation of FDG turnover was carried out. PET was performed before surgery and as follow up. In all patients giant cell tumour was treated by curettage followed by burring and cement packing. Giant cell tumour was shown by histology in all patients. All giant cell tumours showed a specific PET pattern with a very high standard uptake value (SUV) of 4.8 in median. In follow up after surgery this value dropped to 0.3. In one case also pulmonary metastasis could be demonstrated. Recurrence was suspected in the follow up in 5 patients by MRI or plain radiography. In all these patients PET could show an elevated SUV above 4.0. In these 5 patients surgery was performed and recurrence could be proven by histology. In one patient MRI showed signs of recurrence but PET showed a SUV of 1.3. In the revision surgery no tumour could be found. In one patient MRI was negative but PET showed a SUV of 5.2 indicating re-recurrent tumour which could be demonstrated by histology. We conclude that PET is a very helpful tool not only in the first line diagnosis of giant cell tumour but also in diagnosis of metastatic disease and especially for detection of recurrent tumour

Introduction: Following intralesional resection of giant cell tumour local recurrence happens in up to 40% depending on type of treatment. Common plain radiography or Magnetic resonance tomography (MRI) often has the problem not to discriminate between scar and recurrent tumour.

Materials and Methods: In 19 patients with giant cell tumour dynamic PET using F18-Fluordeoxyglucose (FDG) for estimation of FDG turnover was carried out. PET was performed before surgery and as follow up. In case of evidence in x-ray or MRI of recurrent giant cell tumour PET was performed again. results of histologic evaluation after reoperation then were compared to results of PET.

Results: All giant cell tumours showed a specific PET pattern with a very high standard uptake value (SUV) of 4.8 in median. In one case pulmonary metastases could be found. In follow up after surgery this value dropped to 0.3. Recurrence was suspected in the follow up in 5 patients by MRI or plain radiography. In all these patients PET could show an elevated SUV above 4.0. In these 5 patients surgery was performed and recurrence could be proven by histology. In one patient MRI was negative but PET showed a SUV of 5.2 indicating re-recurrent tumour which could be demonstrated by histology.

Conclusion: We conclude that PET is a very helpful tool not only in the first line diagnosis of giant cell tumour but also in diagnosis of metastatic disease and especially for detection of recurrent tumour.

Introduction

Fluorodeoxuglucose(FDG) Positron Emission Tomography(PET) scan is used in the diagnosis of prosthetic joint infection, when the inflammatory markers and aspiration of the joint do not establish a definitive diagnosis. The aim of our study was to analyse the utility of FDG PET scan in decision making in these patients.

Introduction: Reports about the usefulness of FDG-PET in detecting infections were few in the last years but are greatly increasing in number in the recent years. The interest for this method is related to the demonstration that FDG uptake is increased in cells with elevated glycolitic activity as neoplastic cells, neutrophils, activated macrophages, probably bacteria. As far as a neoplasm is excluded, FDG uptake is increased in inflammatory sites. This study was done to test the possible use of this method in painful total hip-replacement diagnosis.

Materials and methods: A prospective study on 24 patients (33 hip arthroplasties) affected by painful total hip replacement was conducted. All patient has blood test, X-ray examinations of hips and chest, Ultrasound scan, cultures from sinus tract or hip aspiration, Tc^99m MDC bone scan (SPECT), FDG-PET. Areas of uptake were evaluated and compared. Fifteen patients were operated on (9 two-stage revisions, debridements), during operation cultures were repeated and bone biopsy were done at the sites of icreased PET uptake. Bone and soft tissue debridement was specifically performed on site of PET uptake with maximal preservation of bone stock.

Results: Infected hips were 20. Infection was demonstrated by positive culture and positive biopsy in all cases. Sensibility and specificity of PET were respectively 100% and 92%. The study of tracers uptake showed that these are complementary and give different information. All patients who were operated on were reviewed with a mean follow up of 7 months (range 3 months-15 months ). The nine patients who had revision were free of infection at follow-up.

Discussion: from our experience PET is easy to perform, has an excellent sensibility and good specificity and can be placed at the end point of the flow-chart for diagnosis of total hip replacement infection (preceeded in any case by standard X-Rays and bone scan). Moreover PET scan could be useful in pre-operative planning of revision surgery as it has better anatomical definition than traditional scans and may allows surgeon to localize on three planes infected bone and soft tissues. Therefore at the moment this tool has high costs so should be used in selected cases. Its real usefulness in revision surgery has to be confirmed by a longer follow-up of treated cases.

A prospective study on 24 patients (33 hip arthroplasties) affected by painful total hip replacement was conducted. All patient had a blood test, X-rays, ultrasound scan, cultures, Tc ^99m bone scan (SPECT), and F¹⁸FDG-PET. Fifteen patients were operated on (nine two-stage revisions, six débridements). During operation, cultures were repeated and bone biopsy was performed at the sites of increased PET uptake. Bone and soft tissue débridement was specifically performed at the site of PET uptake with maximal preservation of bone stock.

There were 20 infected prostheses. Infection was demonstrated by positive culture in all cases and positive biopsy in operated cases. Sensibility and specificity of PET were 100% and 92%, respectively. All patients who were operated on were reviewed with a mean follow-up of 7 months. The nine patients who had revision were free of infection at follow-up.

In our experience PET is easy to perform, has an excellent sensitivity and good specificity and can be placed at the end point of the flow-chart for diagnosis of total hip replacement infection. Moreover, PET scan could be useful in pre-operative planning of revision surgery as it has better anatomical definition than traditional scans. Presently, it involves high costs and should only be used in selected cases. Its real usefulness in revision surgery has to be confirmed by a longer follow-up of treated cases.

Background Context

SPECT-CT is a hybrid imaging modality, which has become very well established in the diagnosis of inflammatory, vascular and malignant processes affecting the spine. However, little evidence exists on its application with degenerative pathologies.

Aims. We aimed to evaluate the utility of . 68. Ga-citrate positron emission tomography (PET)/CT in the differentiation of periprosthetic joint infection (PJI) and aseptic loosening (AL), and compare it with . 99m. Tc-methylene bisphosphonates (. 99m. Tc-MDP) bone scan. Methods. We studied 39 patients with suspected PJI or AL. These patients underwent . 68. Ga-citrate PET/CT, . 99m. Tc-MDP three-phase bone scan and single-photon emission CT (SPECT)/CT. PET/CT was performed at ten minutes and 60 minutes after injection, respectively. Images were evaluated by three nuclear medicine doctors based on: 1) visual analysis of the three methods based on tracer uptake model, and PET images attenuation-corrected with CT and those not attenuation-corrected with CT were analyzed, respectively; and 2) semi-quantitative analysis of PET/CT: maximum standardized uptake value (SUVmax) of lesions, SUVmax of the lesion/SUVmean of the normal bone, and SUVmax of the lesion/SUVmean of the normal muscle. The final diagnosis was based on the clinical and intraoperative findings, and histopathological and microbiological examinations. Results. Overall, 23 and 16 patients were diagnosed with PJI and AL, respectively. The sensitivity and specificity of three-phase bone scan and SPECT/CT were 100% and 62.5%, 82.6%, and 100%, respectively. Attenuation correction (AC) at 60 minutes and non-AC at 60 minutes of PET/CT had the same highest sensitivity and specificity (91.3% and 100%), and AC at 60 minutes combined with SPECT/CT could improve the diagnostic efficiency (sensitivity = 95.7%). Diagnostic efficacy of the SUVmax was low (area under the curve (AUC) of ten minutes and 60 minutes was 0.814 and 0.806, respectively), and SUVmax of the lesion/SUVmean of the normal bone at 60 minutes was the best semi-quantitative parameter (AUC = 0.969). Conclusion. 68. Ga-citrate showed the potential to differentiate PJI from AL, and visual analysis based on uptake pattern of tracer was reliable. The visual analysis method of AC at 60 minutes, combined with . 99m. Tc-MDP SPECT/CT, could improve the sensitivity from 91.3% to 95.7%. In addition, a major limitation of our study was that it had a limited sample size, and more detailed studies with a larger sample size are warranted. Cite this article: Bone Joint Res 2022;11(6):398–408

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

The pathology of the posterior acetabular legion in femoroacetabular impingement (FAI) syndrome, so called “contre-coup region”, is still unclear. . 18. F-fluoride positron emission tomography (PET) is a functional imaging modality, which reflects the osteoblast activity. Recent technological advances in PET combined with computed tomography (CT) imaging allowed us to obtain detailed 3-dimensional (3D) morphological information. We evaluated the abnormal uptake of . 18. F-fluoride PET/CT on posterior acetabular lesion in FAI syndrome cases. We enrolled forty-one hips from 41 patients who were diagnosed as FAI syndrome and were performed . 18. F-fluoride PET/CT between October 2014 and October 2016. In each hip, the maximum standardized uptake value (SUV. max. ) on the posterior acetabular was measured. The cases were divided into 4 groups; cam-type (11 cases), pincer-type (7), combined-type (11), dysplastic developmental hip (DDH) with cam morphology (12). The average SUV. max. of the pincer-type was significantly smaller than that of the other 3 groups (p < .05). The percentage of the cases with SUV. max. ≥ 6 was 81.8% in cam-type, 28.6% in pincer-type, 90.9% in combined-type, 91.7% in DDH with cam morphology. Furthermore, the average degree of α angle of the cases of SUV. max. ≥ 6 was significantly higher than that of the cases of SUV. max. < 6 (p = .005). Although actual biomechanical mechanism in contre-coup region is still controversial, this result indicated that the cam morphology related to the posterior acetabular lesion with accelerated bone metabolism

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

Introduction: Arthroplasty plays a growing role in our society today. Due to scientific and medical progress there are an increasing number of viable candidates and the improvement of quality of life thereafter speaks for itself. Even though the operations are largely successful, complications after joint replacement surgery occur frequently. Approximately 10% of lower limb arthroplasties need surgical revision, of which 70% are due to loosening. The purpose of this study was to assess the feasibility of 18-fluorodeoxyglucose positron emission tomography (18FFDG–PET) in detecting septic and aseptic endoprosthetic loosening of hip and knee endoprostheses. Materials and Methods: Thirty-three patients (age range: 45–90y) with lower limb arthroplasty complaints (74 prostheses) were studied preoperatively with 18F-FDG-PET. All patients underwent surgery at a later stage with microbiological culturing to differentiate aseptic and septic loosening and to confirm the final diagnosis. Prostheses were tested intraoperatively for stability and microbiology. Results: The sensitivity/specificity of 18F-FDG-PET towards implant loosening in the hip was 80%/87%, in the knee 56%/82%. The sensitivity/specificity for infectious loosening in hip replacement arthroplasties was 67%/83%, in the knee 14%/89%. Discussion: 18F-FDG-PET seems an excellent method for detecting hip endoprosthetic loosening and a moderate tool to diagnose hip implant infection. It should not be seen as the method of choice to diagnose knee endoprosthetic loosening and infection

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