A new classification to characterize and predict treatment of acetabular bone defects.

BACKGROUND: The increasing amount of revision surgeries in total hip arthroplasty (THA) represents a burden for orthopedic surgeons given the complexity and unpredictability of this kind of surgery. The aim of the current study was to develop a new radiographic classification of acetabular bone defects stratify the severity of the lesion and to suggest the surgical strategy to address it. METHODS: Radiographs of 151 consecutive patients who underwent acetabular revision surgery in our institution were collected to develop a new classification that groups the acetabular bone defects in three zones (A, B and C). The performance to predict treatment and inter- and intra-rater agreement were evaluated. RESULTS: The ability of the newly proposed classification to predict treatment was 87.3% (k weighted: 0.65). The inter-rater reliability was 90.1% (k: 0.81), and the intra-rater reliability between the two sets of evaluations performed by the observer at 1-month distance was 97.5% (k: 0.94). CONCLUSIONS: The newly proposed classification was able to characterize the extent of acetabular bone defects and predict pre-operatively the appropriate surgical treatment strategy in 87.3% of cases. It showed a strong agreement among raters and an almost perfect agreement among different measurements at 1 month distance. This new tool could be used in the preoperative assessment to drive the use of secondary level image examinations and the type of surgical management.

Interleukin-1ß Polymorphisms Are Genetic Markers of Susceptibility to Periprosthetic Joint Infection in Total Hip and Knee Arthroplasty.

Periprosthetic joint infections (PJIs) are serious complications of prosthetic surgery. The criteria for the diagnosis of PJI integrate clinical and laboratory findings in a complex and sometimes inconclusive workflow. Host immune factors hold potential as diagnostic biomarkers in bone and joint infections. We reported that the humoral pattern-recognition molecule long pentraxin 3 (PTX3) predicts PJI in total hip and knee arthroplasty (THA and TKA, respectively). If and how genetic variation in PTX3 and inflammatory genes that affect its expression (IL-1ß, IL-6, IL-10, and IL-17A) contributes to the risk of PJI is unknown. We conducted a case-control study on a Caucasian historic cohort of THA and TKA patients who had prosthesis explant due to PJI (cases) or aseptic complications (controls). Saliva was collected from 93 subjects and used to extract DNA and genotype PTX3, IL-1ß, IL-6, IL-10, and IL-17A single-nucleotide polymorphisms (SNPs). Moreover, the concentration of IL-1ß, IL-10, and IL-6 was measured in synovial fluid and plasma. No association was found between PTX3 polymorphisms and PJI; however, the AGG haplotype, encompassing rs2853550, rs1143634, and rs1143627 in IL-1ß, was linked to the infection (p = 0.017). Also, synovial levels of all inflammatory markers were higher in cases than in controls, and a correlation emerged between synovial concentration of PTX3 and that of IL-1ß in cases only (Spearman r = 0.67, p = 0.004). We identified a relationship between rs2853550 and the synovial concentration of IL-1ß and PTX3. Our findings suggest that IL-1ß SNPs could be used for the early identification of THA and TKA patients with a high risk of infection.

Femoral bone defect classifications in revision total hip arthroplasty: a comprehensive review and proposal of a new algorithm of management.

The number of primary total hip arthroplasties (THAs) and revisions is expected to steadily grow in the future. The femoral revision surgery can be technically demanding whether severe bone defects need to be addressed. The femoral revision aims to obtain a proper primary stability of the stem with a more proximal fixation as possible. Several authors previously proposed classification systems to describe the morphology of the bony femoral defect and to drive accordingly the surgeon in the revision procedure. The previous classifications mainly considered cortical and medullary bone at the level of the defect of poor quality by definition. Therefore, the surgical strategies aimed to achieve a distal fixation bypassing the defect or to fill the defect with bone impaction grafting or structured bone grafts up to the replacement of the proximal femur with megaprosthesis. The consensus on a comprehensive and reliable classification system and management algorithm is still lacking. A new classification system should be developed taking into account the bone quality. The rationale of a new classification is that 'functional' residual bone stock could be present at the level of the defect. Therefore, it can be used to achieve a primary (mechanical) and secondary (biological) stability of the implants with a femoral fixation more proximal as possible.

Results of Utilizing Cerclage Wires in the Management of Intraoperative Vancouver B1 Fractures in Primary Total Hip Arthroplasties: A Retrospective Cohort Investigation into Clinical and Radiographic Outcomes.

BACKGROUND: Due to an increase in total hip arthroplasties (THAs), the incidence of periprosthetic hip fractures (PPHFs) is forecast to rise considerably in the next decades, with Vancouver B1 fractures (VB1) accounting for one third of total cases. Femur fixation with cerclages (with or without screws) is considered the current treatment option for intraoperative VB1. METHODS: The study retrospectively includes data from patients who developed VB1 PPHFs during THAs from 3 December 2020 to 30 November 2022. The primary outcome of this study was to identify the reintervention-free survival rate. The secondary aim was to determine clinical and radiographic assessment at follow-up, based on Harris hip score (HHS) and limb length discrepancy (LLD). RESULTS: Thirty-seven patients with a mean age of 60.03 ± 15.49 (22 to 77) years old were included. Overall, the Kaplan-Meier analysis estimated a reoperation-free survival rate of 99% (CI 95%) at 6 months. The mean limb length discrepancy (LLD) improved from -3.69 ± 6.07 (range -27.9 to 2.08) mm to 0.10 ± 0.67 (range -1.07 to 1.20) mm. The mean HHS improved from 42.72 ± 14.37 (range 21.00-96.00) to 94.40 ± 10.32 (range 56.00-100.00). CONCLUSIONS: The employment of cerclage wires represents an effective strategy for handling intraoperative VB1 fractures. Level III retrospective cohort study.

Clinical and Radiographic Outcomes of Hip Revision Surgery and Cerclage Wires Fixation for Vancouver B2 and B3 Fractures: A Retrospective Cohort Study.

BACKGROUND: The number of patients presenting with periprosthetic hip fractures has increased in recent decades. METHODS: Patients who underwent hip revision arthroplasty procedures for Vancouver type B2 and B3 fractures between 2010 and 2021 were included. The primary intended outcome of this study was to determine the reintervention-free survival rate. The secondary intended outcome was to determine clinical and radiographic assessment outcomes at the time of follow-up, and the correlation between time to surgery and postoperative Harris hip score (HHS). RESULTS: A total of 49 patients with mean age of 71.2 ± 2.3 (37-88) years old were included. Overall, the Kaplan-Meier method estimated a survival rate of 95.8% (CI 84.2% to 98.9%) at one year, 91.1% (CI 77.9% to 96.6%) at two years, and 88.5% (CI 74.4% to 95.1%) at three, and up to 10, years. The mean limb length discrepancy (LLD) improved from -13.3 ± 10.5 (range -39 to +10) mm at the preoperative stage to -1.16 ± 6.7 (range -17 to +15) mm, p < 0.001 postoperative. The mean HHS improved from 31.1 ± 7.7 (range 10 to 43) preoperative to 85.5 ± 14.8 (range 60 to 100), p < 0.001 postoperative. Postoperative HHS was not affected by preoperative time to surgery. CONCLUSIONS: Revision arthroplasty is an effective treatment for Vancouver type B2 and B3 fractures.

Using Three-Dimensional Printing Technology to Solve Complex Primary Total Hip Arthroplasty Cases: Do We Really Need Custom-Made Guides and Templates? A Critical Systematic Review on the Available Evidence.

The burden of osteoarthritis (OA) is around 300 million people affected worldwide, with the hip representing a commonly affected joint. Total hip arthroplasty (THA) has been used with notable success as a definitive treatment to improve pain and function in hip OA patients. The recent advent of new technologies, such as 3D printing, has pushed the application of these new concepts toward applications for the well-known THA. Currently, the evidence on the use of 3D printing to aid complex primary THA cases is still scarce. METHODS: An extensive literature review was conducted to retrieve all articles centered on the use of 3D printing in the setting of primary THA. RESULTS: A total of seven studies were included in the present systematic review. Four studies investigated the use of 3D-printed surgical guides to be used during surgery. The remaining three studies investigated the benefit of the use of 3D-printed templates of the pelvis to simulate the surgery. CONCLUSIONS: The use of 3D printing could be a promising aid to solve difficult primary total hip arthroplasty cases. However, the general enthusiasm in the field is not supported by high-quality studies, hence preventing us from currently recommending its application in everyday practice.

AI-based hip prosthesis failure prediction through evolutional radiological indices.

INTRODUCTION: This study aimed to develop artificial intelligence models for predicting hip implant failure from radiological features. Analyzing the evolution of the periprosthetic bone and implant's position throughout the entire follow-up period has shown the potential to be more relevant in outcome prediction than simply considering the latest radiographic images. Thus, we investigated an AI-based model employing a small set of evolutional parameters derived from conventional radiological features to predict hip prosthesis failure. MATERIALS AND METHODS: One hundred sixty-nine radiological features were annotated from historical anteroposterior and lateral radiographs for 162 total hip arthroplasty patients, 32 of which later underwent implant failure. Linear regression on each patient's chronologically sorted radiological features was employed to derive 169 corresponding evolutional parameters per image. Three sets of machine learning predictors were developed: one employing the original features (standard model), one the evolutional ones (evolutional model), and the last their union (hybrid model). Each set included a model employing all the available features (full model) and a model employing the few most predictive ones according to Gini importance (minimal model). RESULTS: The evolutional and hybrid predictors resulted highly effective (area under the ROC curve (AUC) of full models = 0.94), outperforming the standard one, whose AUC was only 0.82. The minimal hybrid model, employing just four features, three of which evolutional, scored an AUC of 0.95, proving even more accurate than the full one, exploiting 173 features. This tool could be shaped to be either highly specific (sensitivity: 80%, specificity: 98.6%) or highly sensitive (sensitivity: 90%, specificity: 92.4%). CONCLUSION: The proposed predictor may represent a highly sensitive screening tool for clinicians, capable to predict THA failure with an advance between a few months and more than a year through only four radiological parameters, considering either their value at the latest visit or their evolution through time.

Clinical and radiological outcomes of an uncemented metaphyseal short stem at minimum 10 years of follow-up: a prospective observational study.

PURPOSE: There is growing interest around short stems as they provide a less invasive approach for total hip arthroplasty preserving bone stock for a possible revision surgery if required. The main purpose of this work was to assess the long-term performance of an uncemented metaphyseal short stem in terms of survival rate and in addition its clinical and radiological outcomes. MATERIALS AND METHODS: From January to December 2010, we prospectively enrolled all consecutive patients undergoing primary total hip arthroplasty with an uncemented metaphyseal short stem in our institution with a minimum follow-up of 10 years. The radiographic features investigated were the varus-valgus stem orientation, areas of osteolysis and radiolucencies, stress shielding, and heterotopic calcifications. The clinical outcomes were measured using the HHS. RESULTS: A total of 163 patients (172 hips) were finally included and the measured survival rate at 10 years was 99.6%. The average HHS increased from 55.0 preoperatively to 97.8 at the last follow-up (p < 0.0001). Among them, 137 patients (164 hips) were also available for radiographic assessment. Mild varus malalignment was observed in 40% of cases and remained stable in the serial X-rays and was not associated with step loosening. Mild stress shielding was observed around 13 stems (9%) and moderate only around 3 implants. CONCLUSION: In conclusion, the uncemented metaphyseal short stems showed excellent survival and clinical results at 10 years and at a radiographical level very low stress shielding was observed; moreover, besides the high frequency of varus alignment the implanted stems was not associated with revision surgery or with worse clinical outcomes.

Magnetic resonance imaging could precisely define the mean value of tendon thickness in partial rotator cuff tears.

PURPOSE: Rotator Cuff (RC) lesions are classified in full-thickness and partial-thickness tears (PTRCTs). To our knowledge, no studies investigated the mean size of shoulder tendons in healthy and PTRCT patients using MRI scans. The aim of the study was to provide data to obtain and compare the mean value of tendon sizes in healthy and PTRCTs groups. METHODS: From 2014 to 2020, 500 were included in the study. They were divided into two groups: Group 1 (100 subjects) was composed of people positive for partial-thickness rotator cuff tears (PTRCTs), while the 400 subjects in Group 2 were negative for PTRCTs. RESULTS: Overall, of the patients included in the study, 231 were females and 269 were males. The mean age of the patients was 49 ± 12.7 years. The mean thickness of the supraspinatus tendon (SSP) was 5.7 ± 0.6 mm in Group 1, 5.9 ± 0.6 mm in Group 2 (p < 0.001). The mean length of the ISP tendon was 27.4 ± 3.2 mm in Group 1, 28.3 ± 3.8 mm in Group 2 (p = 0.004). The mean width of the SSP tendon was 17 ± 1.6 mm in Group 1, 17.6 ± 2 mm in Group 2 (p = 0.004). The mean width of the infraspinatus tendon (ISP) tendon was 17.7 ± 1.4 mm in Group 1, 18.3 ± 2.1 mm in Group 2 (p = 0.02). CONCLUSION: The anatomical data present in this paper may serve as a tool for surgeons to properly manage PTRCTs. The findings of the present study aimed to set the first step towards reaching unanimity to establish international cut-off values to perform surgery. Additionally, they could widely increase diagnostic accuracy, improving both conservative and surgical approaches. Lastly, further clinical trials using more accurate diagnostic MRI tools are required to better define the anatomical differences between PTRCT and healthy patients. LEVEL OF EVIDENCE: Level II, Retrospective Comparative Trial.

Pentraxin 3, a new biomarker for the diagnosis and management of PJI in primary and revision hip arthroplasty.

Background/Aim of the study: The periprosthetic or superficial site infections are one of the most catastrophic and difficult to manage complications following total hip arthroplasty. Recently, in addition to well know systemic markers of inflammation, the blood and synovial fluid biomarkers are focused to have a possible role in the infection diagnosis. The long Pentraxin 3 (PTX3) seems to be a sensitive biomarker of acute phase inflammation. The objectives of this prospective and multicentre study were (1) to establish the plasma trend effectiveness of PTX3 in patients undergoing primary hip replacement, and (2) to evaluate the diagnostic accuracy of blood and synovial PTX3 in patients undergoing prosthetic revision of infected hip arthroplasty. METHODS: Human PTX3 was measured by ELISA in two cohorts of patients, 10 patients undergoing primary hip replacement for osteoarthritis and 9 patients with infected hip arthroplasty. RESULTS: The Authors were able to demonstrate that PTX3 is a viable biomarker for acute phase inflammation. CONCLUSIONS: An increase in PTX3 protein concentration in the synovial fluid of patients undergoing implant revision has a strong diagnostic capacity for periprosthetic joint infection, showing 97% specificity.

Interaction of Bacteria, Immune Cells, and Surface Topography in Periprosthetic Joint Infections.

The incidence of periprosthetic joint infections (PJIs) is ~2% of total procedures and it is expected to rise due to an ageing population. Despite the large burden PJI has on both the individual and society, the immune response to the most commonly isolated pathogens, i.e., Staphylococcus aureus and Staphylococcus epidermidis, remains incompletely understood. In this work, we integrate the analysis of synovial fluids from patients undergoing hip and knee replacement surgery with in-vitro experimental data obtained using a newly developed platform, mimicking the environment of periprosthetic implants. We found that the presence of an implant, even in patients undergoing aseptic revisions, is sufficient to induce an immune response, which is significantly different between septic and aseptic revisions. This difference is confirmed by the presence of pro- and anti-inflammatory cytokines in synovial fluids. Moreover, we discovered that the immune response is also dependent on the type of bacteria and the topography of the implant surface. While S. epidermidis seems to be able to hide better from the attack of the immune system when cultured on rough surfaces (indicative of uncemented prostheses), S. aureus reacts differently depending on the contact surface it is exposed to. The experiments we performed in-vitro also showed a higher biofilm formation on rough surfaces compared to flat ones for both species, suggesting that the topography of the implant could influence both biofilm formation and the consequent immune response.

Combining deep learning and machine learning for the automatic identification of hip prosthesis failure: Development, validation and explainability analysis.

AIM: Revision hip arthroplasty has a less favorable outcome than primary total hip arthroplasty and an understanding of the timing of total hip arthroplasty failure may be helpful. The aim of this study is to develop a combined deep learning (DL) and machine learning (ML) approach to automatically detect hip prosthetic failure from conventional plain radiographs. METHODS: Two cohorts of patients (of 280 and 352 patients) were included in the study, for model development and validation, respectively. The analysis was based on one antero-posterior and one lateral radiographic view obtained from each patient during routine post-surgery follow-up. After pre-processing, three images were obtained: the original image, the acetabulum image and the stem image. These images were analyzed through convolutional neural networks aiming to predict prosthesis failure. Deep features of the three images were extracted for each model and two feature-based pipelines were developed: one utilizing only the features of the original image (original image pipeline) and the other concatenating the features of the three images (3-image pipeline). The obtained features were either used directly or reduced through principal component analysis. Both support vector machine (SVM) and random forest (RF) classifiers were considered for each pipeline. RESULTS: The SVM applied to the 3-image pipeline provided the best performance, with an accuracy of 0.958 ± 0.006 in the internal validation and an F1-score of 0.874 in the external validation set. The explainability analysis, besides identifying the features of the complete original images as the major contributor, highlighted the role of the acetabulum and stem images on the prediction. CONCLUSIONS: This study demonstrated the potentialities of the developed DL-ML procedure based on plain radiographs in the detection of the failure of the hip prosthesis.

Perioperative Complications after Hip and Knee Revision Arthroplasty in the over 80 Years Old Population: A Retrospective Observational Case-Control Study.

BACKGROUND: The number of joint revision arthroplasties has increased in the elderly population, which is burdened by several perioperative risks. METHODS: Patients who underwent hip and knee revision arthroplasty were retrospectively included, and they were divided into two groups by age: <80 years old (Group 1) and ≥80 years old (Group 2). The primary outcome was to compare perioperative complication rates. The secondary outcome was to compare the 30-day, 90-day, and 1-year readmission rates. RESULTS: In total, 74 patients in Group 1 and 75 patients in Group 2 were included. Postoperative anemia affected 13 patients in Group 1 (17.6%) and 25 in Group 2 (33.3%, p 0.027); blood units were transfused in 20 (26.7%) and 11 (14.9%, p 0.076) patients, respectively. In Group 1, two (2.7%) patients reported wound infection. In Group 2, eight (10.7%) patients presented hematomas, and two (2.7%) patients reported dislocations. No significant differences in the two groups were observed for 30-day (p 0.208), 90-day (p 0.273), or 1-year readmission rates (p 0.784). CONCLUSION: The revision arthroplasty procedure in patients over 80 years old is not associated with a higher risk of perioperative complications, or higher readmission rate compared with younger patients undergoing hip and knee revision surgery.

Cost-effectiveness analysis of arthroscopic Bankart repair versus open Latarjet reconstruction in anterior shoulder instability.

PURPOSE: The ideal surgical treatment for anterior shoulder instability is still under debate. In the healthcare setting, both clinical and economic factors must be considered for optimal resource allocation. From the clinical perspective, the Instability Severity Index Score (ISIS) is a helpful and validated tool for surgeons, although a gray area between 4 and 6 exists. In fact, patients with an ISIS < 4 and > 6 can be treated effectively with arthroscopic Bankart repair and open Latarjet, respectively. The purpose of this study was to conduct a cost-effectiveness analysis of arthroscopic Bankart repair versus open Latarjet in patients with an ISIS between 4 and 6. METHODS: A decision-tree model was constructed to simulate the clinical scenario of an anterior shoulder dislocation patient with an ISIS between 4 and 6. Based on previously published literature, outcome probabilities and utility values in the form of Western Ontario Instability Score (WOSI) were assigned to each branch of the tree, alongside institutional cost. The primary outcome assessed was an Incremental cost-effectiveness ratio (ICER) of the two procedures. Eden-Hybbinette was also considered in the model as a salvage procedure for failed Latarjet. A two-way sensitivity analysis was performed to identify the most impactful parameters on the ICER upon their variation within a pre-determined interval. RESULTS: Base case cost was 1245.57 € (1220.48-1270.65 €) for arthroscopic Bankart repair, 1623.10 € (1580.82-1665.39 €) for open Latarjet and 2.373.95 € (1940.81-2807.10 €) for Eden-Hybbinette. Base-case ICER was 9570.23 €/WOSI. Sensitivity analysis showed that the most impactful parameters were the utility of arthroscopic Bankart repair, the probability of success of open Latarjet, the probability of undergoing surgery after post-operative recurrence of instability and the utility of Latarjet. Of these, utility of arthroscopic Bankart repair and Latarjet had the most significant impact on the ICER. CONCLUSION: From a hospital perspective, open Latarjet was more cost-effective than arthroscopic Bankart repair in preventing further shoulder instability in patients with an ISIS between 4 and 6. Despite its several limitations, this is the first study to analyze this subgroup of patients from a European hospital setting from both an economic and clinical perspective. This study can help surgeons and administrations in the decision-making process. Further clinical studies are needed to prospectively analyze both aspects to further delineate the best strategy.

Long Pentraxin 3 as a New Biomarker for Diagnosis of Hip and Knee Periprosthetic Joint Infections.

BACKGROUND: Preoperative diagnosis of periprosthetic joint infections (PJIs) poses an unmet clinical challenge. The long pentraxin PTX3 is a component of the innate immune system involved in infection immunity. This study evaluated the potential of synovial and plasmatic PTX3 in the diagnosis of hip and knee PJIs. METHODS: Consecutive total hip and knee arthroplasty (THA/TKA) revisions were prospectively included and classified as septic or aseptic according to the European Bone and Joint Infection Society (EBJIS) and Musculoskeletal Infection Society (MSIS) criteria. The concentration of PTX3 in plasma and synovial fluid samples was measured with ELISA. The AUC, threshold value, sensitivity, specificity, and positive and negative likelihood ratios were calculated using the ROC (receiver operating characteristic) curve method. RESULTS: The study population included 128 patients (94 THAs; 34 TKAs). The AUC of the synovial PTX3 based on EBJIS criteria was 0.85 (p < 0.0001), with a sensitivity of 81.13% and a specificity of 93.33%. The AUC based on MSIS criteria was 0.95 (p < 0.001), with a sensitivity of 91.43% and a specificity of 89.25%. Plasmatic PTX3 failed to discriminate infected from non-infected patients. CONCLUSIONS: Synovial PTX3 demonstrated an excellent diagnostic potential in hip and knee PJIs, with a very high specificity irrespective of the diagnostic criteria for PJI.

Clinical Outcomes and Complication Rate after Single-Stage Hardware Removal and Total Hip Arthroplasty: A Matched-Pair Controlled Study.

BACKGROUND: Single-stage hardware removal and total hip arthroplasty is a complex surgical procedure, comparable to revision surgery. The purpose of the current study is to evaluate single-stage hardware removal and THA outcomes, compare this technique with a matched control group that has undergone primary THA and assess the risk of periprosthetic joint infection with a 24-month minimum follow-up. METHODS: This study included all those cases treated with THA and concomitant hardware removal from 2008 to 2018. The control group was selected on a 1:1 ratio among patients who underwent THA for primary OA. The Harris Hip (HHS) and University of California at Los Angeles Activity (UCLA) scores, infection rate and early and delayed surgical complications were recorded. RESULTS: One hundred and twenty-three consecutive patients (127 hips) were included, and the same number of patients was assigned to the control group. The final functional scores were comparable between the two groups; a longer operative time and transfusion rate were recorded in the study group. Finally, an increased incidence of overall complications was reported (13.8% versus 2.4%), but no cases of early or delayed infection were found. CONCLUSIONS: Single-stage hardware removal and THA is a safe and effective but technically demanding technique, with a higher incidence of overall complications, making it more similar to revision THA than to primary THA.

Pelvic tilt and functional acetabular position after total hip arthroplasty: an EOS 2D/3D radiographic study.

PURPOSE: In total hip arthroplasty (THA), the functional anatomy of the spinopelvic unit should be taken into account to provide the correct functional positioning of the implant. The relationship between the spine and the pelvis in the sagittal plane is represented by pelvic tilt (PT). The sacral slope (SS) has been proposed as a more reliable parameter than the anterior pelvic plane (APP) to express the PT. This study investigated the relationship between the APP and the SS; and the relationship between the APP and the SS, respectively, with the postoperative acetabular orientation. METHODS: 45 patients undergoing primary THA were prospectively enrolled. The EOS 2D/3D system was used to perform the radiographic evaluation before and 3 months after surgery. The following parameters were measured in both standing and sitting position: SS, APP, acetabular anteversion (AA) and inclination (AI). RESULTS: The SS values did not show any correlation with the values of the APP angle. The changes of the SS in the transition from the standing to the sitting position significantly correlated with the changes of the AA (r = -0.61; p < 0.0001). A weak correlation was found between the APP angle and the AA in standing position (r = -0.35; p = 0.02). CONCLUSIONS: The SS accurately expresses the functional orientation of the pelvis in the sagittal plane, and the functional orientation of the cup after hip replacement. Therefore, SS could be taken into account by navigation systems in order to achieve a patient-specific functional position of the acetabular cup.

Rechallenge of denosumab in advanced giant cell tumor of the bone after atypical femur fracture: A case report and review of literature.

Giant cell tumor of the bone (GCTB) is a locally aggressive neoplasm where surgery is often curative. However, it can rarely give rise to distant metastases. Currently, the only available active therapeutic option for unresectable GCTB is denosumab, an anti-RANKL monoclonal antibody that dampens the aggressive osteolysis typically seen in this disease. For advanced/metastatic GCTB, denosumab should be continued lifelong, and although it is usually well tolerated, important questions may arise about the long-term safety of this drug. In fact, uncommon but severe toxicities can occur and eventually lead to denosumab discontinuation, such as atypical fracture of the femur (AFF). The optimal management of treatment-related AFF is a matter of debate, and to date, it is unknown whether reintroduction of denosumab at disease progression is a clinically feasible option, as no reports have been provided so far. Hereinafter, we present a case of a patient with metastatic GCTB who suffered from AFF after several years of denosumab; we describe the clinical features, orthopedic treatment, and oncological outcomes, finally providing the first evidence that denosumab rechallenge after AFF occurrence may be a safe and viable option at GCTB progression.