BACKGROUND:Simultaneous bilateral total hip arthroplasty (sbTHA) offers the advantages of single-stage treatment for end-stage bilateral hip disease but raises concerns about increased perioperative risk and implant survivorship. This study aimed to evaluate functional outcomes, complications, and implant survivorship following sbTHA under contemporary perioperative protocols with a median follow-up of 4.6 years. METHODS:We conducted a retrospective study of 92 patients (184 hips) who underwent elective sbTHA at a single institution between 2008 and 2019. Their median age was 60 years (interquartile range, 52 to 68). There were 48 men (52.2%), and the median follow-up was 4.6 years (interquartile range, 3.2 to 7.0). The primary outcomes included functional scores, complications, readmissions, and implant survivorship. RESULTS:There was a significant improvement in functional scores and pain evaluation at final follow-up (P < 0.001). The overall complication rate was 6.5% (12 of 184 hips). Transfusion was required in 6.5% of patients (six of 92). When revision surgery was used as the end point, the implant survivorship was 95.7%. CONCLUSIONS:The sbTHA provides excellent functional outcomes and survivorship at a median follow-up of 4.6 years, with an acceptable complication profile in carefully selected patients managed with modern perioperative and blood management protocols.

BACKGROUND:Hip arthroscopy (HA) rates continue to increase. Many HA patients will eventually develop osteoarthritis necessitating total hip arthroplasty (THA). Presently, there is limited, conflicting literature on the correlation between preceding HA and subsequent THA outcomes. The purpose of this study was to evaluate the risk of prior HA on subsequent THA revision rates and their resource allocation in middle-aged THA patients (40 to 65 years old). METHODS:Administrative data were used to perform a retrospective population-based study of Ontario residents who underwent primary THA for osteoarthritis (2002 to 2023). Exposure was prior ipsilateral HA, subcategorized as recent (≤ five years pre-THA) or remote (greater than five years). Outcomes included 5-year THA revision, 30-day emergency department (ED) visit, readmission, major surgical complication, hospital lengths of stay, 1-year costs, outpatient orthopaedic visits, mortality, and chronic opioid use. Multivariable logistic regressions were used to evaluate the influence of prior HA on outcomes. Of 85,814 primary THA identified, 5,642 (6.6%) underwent prior HA. There were 1,215 patients who received HA less than five years before index THA. RESULTS:Prior HA was associated with statistically higher revision risk (4.9 versus 3.3%; hazard ratio = 1.49). The 30-day ED visits, readmissions, and major complications were similar. Prior HA patients had greater pre-THA resource utilization and associated costs, 1-year post-THA costs (median $14,148 versus $13,740; P < 0.001), and number of outpatient visits. Chronic opioid use was associated with prior HA and increased odds of ED visit (OR [odds ratio] 1.37), readmission (OR 1.61), major complication (OR 1.40), postoperative visits (OR 1.12), and 1-year costs (OR 1.47) post-THA (all P < 0.001). CONCLUSIONS:In adults 40 to 65 years, prior HA was associated with increased all-cause revision risk after THA, increased health-care utilization and costs, and equivalent short-term complication and readmission rates. The benefits of HA should be carefully considered in this population, along with the risks elucidated in the present study. Patient counseling and education are essential given advances in THA implant survivorship.

BACKGROUND:Periprosthetic joint infection (PJI) is a serious complication of hip and knee arthroplasty. Although hematogenous seeding is a recognized cause, the contribution of asymptomatic bacteriuria (ASB) remains uncertain. Therefore, we conducted a systematic review and meta-analysis to evaluate this association. METHODS:A systematic search was conducted according to predefined eligibility criteria. There were 16 studies (14 cohorts [n = 48,562 joints] and two randomized controlled trials [n = 1,065 joints] that met inclusion criteria. The primary outcome was PJI rates after hip and knee arthroplasties in patients who had ASB. The secondary outcomes were subgroup analyses by procedure type and culture isolates in urinary and intraoperative cultures. Random-effects meta-analyses used Mantel-Haenszel pooling with Hartung-Knapp-Sidik-Jonkman adjustments. RESULTS:The ASB cohort showed higher pooled odds of PJI (odds ratio 2.41, 95% confidence interval 1.20 to 4.83; P = 0.02), but subgroup analyses by follow-up and procedure type were not significant. Antibiotic treatment offered no benefit in elective arthroplasty, and ASB in hip fracture hemiarthroplasty showed no increased risk, with or without antibiotics. CONCLUSIONS:The ASB cohort demonstrated a statistically significant, yet modest, increased odds of PJI limited to pooled undifferentiated, arthroplasty. In contrast, procedure- and time-specific analyses, while underpowered, showed no consistent signal to suggest an increased risk of PJI following hip or knee arthroplasty or fracture hemiarthroplasty. Consistent with this, prophylactic antibiotic treatment of ASB was not associated with a protective effect. Taken together, these findings do not support routine preoperative urinalysis to promote antimicrobial stewardship. LEVEL OF EVIDENCE:Level II; systematic review and meta-analysis of Level I through III studies.

BACKGROUND:Computer-assisted total knee arthroplasty (CA-TKA) was developed to improve the accuracy and consistency of bone resections and implant positioning; however, evaluation of navigation system performance is often confounded by surgeon-dependent variability in landmark registration and surgical execution. Standardized methodologies that minimize these sources of variability remain limited. We sought to (1) develop a standardized experimental methodology that minimizes surgeon-dependent landmark variability when assessing CA-TKA systems and (2) demonstrate its application by quantifying measurement accuracy, alignment accuracy, and cut surface uniformity of two imageless navigation systems. METHOD:A standardized experimental model was created using CT-derived 3D-printed knee specimens incorporating predefined fiducial landmarks. Two imageless navigation systems, a semi-active robotic system and an optical navigation system, were evaluated in simulated TKA procedures. Embedded landmarks standardized landmark registration across trials. Following bone resections, high-resolution 3D scanning and geometric analysis were used to quantify resection parameters relative to ground-truth geometry. Measurement accuracy, alignment accuracy, and cut surface uniformity were assessed across repeated trials. RESULTS:The standardized framework enabled consistent evaluation of resection geometry relative to predefined anatomical reference frames while minimizing variability related to landmark identification. Both systems demonstrated acceptable measurement accuracy for most parameters, although greater variability was observed in sagittal plane measurements. Both systems achieved high cut surface uniformity, with nearly all resected surfaces within 1 mm of the best-fit plane. CONCLUSION:This study presents a standardized experimental framework for evaluating CA-TKA systems while minimizing variability in landmark registration. The framework may facilitate future comparative evaluation of navigation and robotic technologies.

BACKGROUND:There has been considerable discussion regarding the demand for orthopedic surgery care and simultaneously the lack of employment opportunities for new graduates. We sought to understand the practice patterns and locations of orthopedic surgeons trained in Ontario. METHODS:We invited 618 surgeons trained between 1992 and 2020 to participate in a survey investigating their current practice location, practice patterns, available resources, and reasons for emigration if practising outside of Canada. RESULTS:A total of 253 surgeons responded (40.9%), with 242 full responses. Emigration out of Canada and number of fellowships did not change with time; however, those who graduated more recently were more likely to leave out of necessity rather than interest. Graduates of the University of Ottawa were more likely to work in the United States and more likely to settle farthest from their school if they stayed in Ontario. Graduates of the University of Toronto were more likely to work within 50 km of their training program than graduates of other schools. Most surgeons described themselves as specialists (community or academic), with very few self-described generalists (12%). CONCLUSION:We found an effect of school on the probability of leaving Canada, with surgeons who graduated more recently leaving out of necessity. This suggests that more recent graduates believe there are not enough opportunities, with graduates of the University of Ottawa being the hardest hit. We also found that almost no one viewed themselves as a generalist, which suggests a re-evaluation of the goals of residency education.

Background: There has been a shift in the demographics of patients undergoing elective lower extremity joint arthroplasties in recent years. This study aimed to assess whether research has kept pace with changing demographics through analyzing inclusion and exclusion criteria of randomized controlled trials (RCTs) relevant to total hip arthroplasties (THAs). Methods: Cross-sectional analysis of RCTs studying primary THAs indexed on ClinicalTrials.gov was performed. Trial characteristics regarding inclusion and exclusion criteria of 706 studies initiated between 1994-2023 were analyzed. Sample size, type of intervention, year of study initiation, length of study, and inclusion/exclusion criteria were evaluated. Results: An increasing number of THA-based RCTs were initiated over the study period (1994-2004: 5.18 studies/y, 2021-2023: 36.7 studies/y). The majority of included RCTs had an upper age exclusion criterion (1994-2004: 65.9%, 2021-2023: 53.6%). Body mass index (BMI) restrictions have become more common than previously (1994-2004: 5.3%, 2021-2023: 29.1%); however, the range has expanded to include higher BMI limits. The most common exclusion criteria based upon health comorbidities included psychiatric health and cognitive impairment (36.4%), neurologic and neuromuscular dysfunction (32.6%), and systemic infections (31.4%). Conclusions: Regarding elective primary THA, it is recognized that the age and BMI of patients have shifted substantially over recent decades. This study revealed that restrictions on participant age continue to be prevalent. Although the average BMI of patients undergoing elective THA is rising, BMI is increasingly being implemented as an exclusion criterion. Critical assessment of inclusion and exclusion criteria for all studies, especially RCTs, given their associated cost and potential impact, requires further attention in orthopaedics.

BACKGROUND:Femoral stem subsidence greater than two mm after total hip arthroplasty has been associated with worse patient outcomes. Identifying poor bone quality preoperatively could help surgeons choose implant designs that minimize subsidence risk. The purpose of this exploratory study was to evaluate whether radiographic bone texture is associated with early femoral stem migration. METHODS:A secondary analysis was performed for 63 participants enrolled in a randomized trial comparing collared versus collarless cementless stems implanted by direct anterior or direct lateral approaches. Participants underwent radiostereometric analysis and standardized radiographs preoperatively and at six weeks, one year, and five years postoperatively. Participants were divided into less than or equal to two or greater than two mm subsidence groups from the radiostereometric analysis data. Regions of interest corresponding to the seven Gruen zones were analyzed for radiographic texture features describing bone quality. RESULTS:At baseline, hips with greater than two mm of early subsidence had lower texture energy (P = 0.0003 to 0.014) and mean intensity (P = 0.0005 to 0.026) across all Gruen zones, reflecting more uniform bone structure. In both groups, texture parameters increased over time (P < 0.0001), consistent with bone remodeling and ingrowth. CONCLUSIONS:These findings demonstrate an association between femoral bone texture on plain radiographs and early subsidence of cementless stems. Because radiographs are routine and widely available, texture analysis may offer an accessible, quantitative method for assessing bone quality to support implant selection and postoperative monitoring.

Purpose:The primary aim was to study the impact of joint line obliquity (JLO) on clinical outcomes and survivorship in patients undergoing total knee arthroplasty (TKA) after a previous high tibial osteotomy (HTO). The secondary aim was to study how maintaining neutral JLO at both HTO and TKA affected clinical outcomes of TKA. Methods:A retrospective review of patients undergoing TKA following valgus-producing HTO, having a minimum 1-year follow-up, was performed. Using the coronal plane alignment of the knee (CPAK) classification, three groups of JLO were formed: distal JLO (<177°), neutral JLO (177-183°) and proximal JLO (>183°). Clinical outcomes were assessed using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC). The level of significance was 0.05. Results:The study included 110 TKA (mean follow-up: 5.8 years). Prevalence of a proximal JLO post-TKA was higher (p < 0.05) in those with a proximal JLO pre-TKA (40%) as compared to those with a neutral JLO pre-TKA (13%). The odds ratio of having a proximal JLO post-TKA was 4 (95% confidence interval: 1.4-11.1, p < 0.05) in those having a proximal JLO pre-TKA. Revision rate in the proximal JLO post-TKA, neutral JLO post-TKA and distal JLO post-TKA groups was 20%, 8% and 4% respectively, with no statistical difference (p > 0.05). Post-TKA, the stiffness, function and total WOMAC were significantly better (p < 0.05) in patients with a neutral JLO pre-TKA and neutral JLO post-TKA as compared to those with a proximal JLO pre-TKA and proximal JLO post-TKA or a proximal JLO pre-TKA and neutral JLO post-TKA. Conclusion:While a proximal JLO after conversion TKA did not show a statistically higher revision rate, maintaining a neutral JLO during HTO and at the time of subsequent TKA was associated with higher post-operative clinical scores. However, further research in different and larger populations is needed to confirm these findings. Level of Evidence:Level IV.

BACKGROUND:Although total hip and total knee arthroplasty are highly successful operations, the decision of whether and when to undergo surgery is highly subjective and discretionary, and specific guidelines regarding readiness for surgery remain elusive. The nature of these decisions underscores the importance of shared decision-making, which is founded on the concept that patients substantially contribute to determining their own readiness for surgery. The OPTION survey was developed as a conversation aid to facilitate shared decision-making in the context of total joint arthroplasty. METHODS:The OPTION survey was created in partnership with a panel of 10 active joint replacement patients and 15 arthroplasty surgeons, using a modified Delphi methodology that employed 3 sequential meetings by each group. The survey interrogates patient and surgeon ratings of pain, activity limitation, duration of treatment, prior treatments, and quality of life; patient-rated treatment priorities, readiness for surgery, and surgeon engagement; and surgeon-graded radiographic disease. The survey was administered as an institutional review board-approved pilot during 641 patient-clinician encounters for hip or knee arthritis at 9 U.S. sites, and was independently completed by the patient and surgeon. RESULTS:Patient self-assessment of readiness for surgery includes consideration of existing functional impairment, outcome priorities, realistic expectations, and personal socioeconomic circumstances. Patients most commonly ranked removal of activity limitations as their top treatment priority, while alleviation of pain and avoidance of a long recovery were also ranked highly. Mild and severe pain were associated with similar radiographic disease severity, and worsening radiographic disease was associated with increasing patient-reported readiness for surgery. Patients and surgeons agreed on symptom severity in >90% of cases. When disagreement occurred, surgeons typically underestimated patient-reported symptoms; these cases were associated with lower patient-rated surgeon engagement in shared decision-making conversations. CONCLUSIONS:Shared decision-making conversations substantially contributed to the assessment of patient readiness for joint replacement surgery. When patient and surgeon assessments were not aligned, surgeons most commonly underestimated patient-perceived impairment. These observations should inform optimal surgeon-patient communications. LEVEL OF EVIDENCE:Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

BACKGROUND:Robotic surgery has seen substantial growth over the years and continues to show promise, with recent implementation into orthopedic surgery. There is limited literature available on patient attitudes and comfort level with robotic compared with conventional surgery. We aimed to develop an understanding of patient views on robot-assisted knee replacement to help the development of patient education materials and facilitate successful implementation. METHODS:A qualitative, descriptive methodology was used. Included participants were those who had undergone total knee replacement in the last 5 years. Participants completed an online semistructured interview assessing their past experiences and their fears and assumptions about robotic surgery. An inductive thematic analysis was completed to organize and present the major themes. RESULTS:Four overarching themes described the areas patients focused on: advancements in surgery, perception of robotic surgery and surgeons, reliability, and patient education materials. Major subthemes included the proven reliability of robots, safety fears, and efficacy. Some participants' fear centred around robot autonomy. Greater comfort with the use of robots would occur if patients were given information about the role of the robot before surgery. CONCLUSION:Patient education materials can help alleviate fears and prevent misperceptions about robot-assisted knee replacement. Materials should include themes of surgical advancements and how surgeons interact with these advancements, level of robot autonomy, and the reliability and safety of the robot.

Background:Cementless fixation for total knee arthroplasty has been increasing following advancements in implant designs. The use of cementless designs has been supported through longitudinal radiostereometric analysis (RSA) studies; however, few studies have used inducible displacement exams to assess fixation throughout flexion. Our primary aim was to assess patterns and locations of inducible displacement throughout flexion. Methods:Participants (n = 24) received a fixed-bearing, cruciate-retaining cementless implant. At 1-year postoperation, participants underwent a supine RSA exam and standing RSA exams at 0°, 20°, 40°, and 60° of knee flexion. Inducible displacements were reported as maximum total point motion and as 3-dimensional translations at points of interest. Results:Inducible displacement of the tibial component increased with knee flexion angle and was 1.129 ± 0.644 mm at 0°, 1.181 ± 0.462 mm at 20°, 1.526 ± 0.386 mm at 40°, and 1.648 ± 0.461 mm at 60°. Inducible displacement of the femoral component increased with knee flexion angle and was 0.704 ± 0.364 mm at 0°, 0.839 ± 0.458 mm at 20°, 1.011 ± 0.451 mm at 40°, and 1.203 ± 0.708 mm at 60°. The strongest correlations between 3-dimensional translation and knee flexion angle were at the stem tip for the tibial component, and anterior flange tip for the femoral component. Conclusions:Inducible displacement measurements increased with knee flexion angle. At 0°, both components had values consistent with well-fixed components. The locations of maximal displacements support these components are well-fixed and demonstrate that inducible displacement throughout flexion is due to mechanical loading.

Background The risk of early revision of total hip arthroplasty (THA) for polyethylene wear is now low, but there remains a need to perform wear measurements in patients for clinical surveillance. The gold standard of wear measurements has been radiostereometric analysis (RSA), which has limited availability. The use of computed tomography (CT) to perform THA wear measurement was described a decade ago and found to have acceptable accuracy and precision, but high radiation dose was a concern. Additionally, the use of larger femoral head sizes and ceramic femoral heads has risen in the past decade. The objectives of the study were to determine the effect of femoral head size, femoral head material, and lowered radiation dose on femoral head penetration measurement repeatability. Methods A cadaveric hip was implanted with a cementless THA implant system. CT scans were acquired at a conventional radiation dose and at a reduced dose and repeated for a 32 mm and 36 mm cobalt-chromium femoral heads and a 32 mm ceramic femoral head. Apparent translation of the femoral head versus the acetabular cup was measured between the repeated scans using a CT-RSA software, where deviations from zero indicated measurement precision. Results The mean and standard deviation of translations in all planes was <0.200 mm. There was no effect for 3D translation of increasing cobalt-chromium head size (p = 0.2252). Cobalt-chromium heads had superior repeatability compared to ceramic heads at reduced dose (p = 0.022), but not at conventional dose (p = 0.1265). Further, superior repeatability was achieved with the reduced dose scan for the cobalt-chromium head (p = 0.0058), however there was no difference between doses for the ceramic head (p = 0.8148). Discussion CT-based wear measurement repeatability is excellent and consistent with prior literature even when implementing a larger femoral head, a ceramic femoral head, or reducing radiation dose to 25% of a conventional clinical scan.

BACKGROUND:Malpositioning of the acetabular component in total hip arthroplasty (THA) is a critical factor contributing to complications such as instability, impingement, and the need for revision surgery. This study aimed to compare the accuracy of acetabular component positioning in the direct anterior approach (DAA) using three techniques: conventional fluoroscopy, fluoroscopic image-dependent navigation, and imageless navigation. METHODS:A retrospective cohort study was conducted with 150 patients undergoing primary THA using the DAA. Patients were grouped based on the technique used (50 patients per group). Intraoperative cup inclination and anteversion were recorded, and postoperative measurements were obtained using 6-week antero-posterior radiographs. The primary outcomes included deviations in anteversion and inclination between intraoperative and postoperative measurements. The secondary outcomes included operative time and 60-day postoperative complications. RESULTS:A total of 150 patients undergoing DAA-THA were included, with 50 patients in each group: conventional fluoroscopy, fluoroscopic image-dependent navigation, and imageless navigation. The imageless group had significantly longer operative time (75.5 ± 10.8 minutes) than conventional fluoroscopy (65.8 ± 8.5 minutes) and image-dependent (68.9 ± 10.7 minutes), P < 0.0001. Radiographic analysis indicated that image-dependent navigation provided the highest accuracy, with 83 and 69% of cups placed within the target zones for the two surgeons, outperforming conventional and imageless methods. The imageless system showed improved accuracy over conventional fluoroscopy and image-dependent navigation when comparing intraoperative and postoperative inclination and anteversion. Postoperative anteversion (P = 0.08) and inclination (P = 0.94) showed no significant differences among groups. Complication rates, including dislocations and infections, were similar, though one periprosthetic joint infection was noted in both the conventional and image-dependent navigation groups, with no PJIs reported in the imageless group. CONCLUSIONS:Navigation systems, particularly fluoroscopic image-dependent navigation, enhance acetabular component positioning accuracy over conventional methods in DAA-THA. However, imageless navigation requires optimization to reduce operative time and improve anteversion accuracy.

BACKGROUND:Total hip arthroplasty (THA) is an effective surgery for advanced osteoarthritis. The rising demand for THA and increasing wait times are having a substantial impact on health care resources, resulting in increased pressure to move to outpatient care. This has most commonly been enabled through a minimally invasive, direct anterior (DA) surgical approach; however, recently, the direct lateral (DL) approach has also been used in outpatient THA. The purpose of this study was to compare costs between outpatient THAs using a DA compared to a DL approach. METHODS:The present study is a secondary analysis of a randomized controlled trial and a prospective cohort study. Participants undergoing primary THA using the DA approach were randomly assigned to be discharged on the same day as surgery (outpatient) or on day one postsurgery (inpatient). The cohort study included patients undergoing outpatient THA using the DL approach. We compared patients in the outpatient arm of the randomized trial to the prospective cohort of outpatient DL THAs. We recorded all costs associated with each surgical approach. Following discharge, participants also completed a self-reported cost diary regarding any resource utilization such as emergency department visits or subsequent hospitalizations, tests and procedures, consultations or follow-up, health care professional services, rehabilitation, medications, informal care, productivity losses, and out-of-pocket expenditures up to three months postoperative. There were 127 patients in the DA group and 51 patients in the DL group. The mean age of patients in the DA group was 66 years compared to 59 years in the DL group (P < 0.01). RESULTS:There were no statistically significant differences in costs between groups from either the health care payer (DA = 7,910.19, DL = 7,847.17, P = 0.80) or societal perspectives (DA = 14,657.21, DL = 14,581.21, P = 0.96). CONCLUSIONS:Our results suggest similar overall mean costs over 90 days postoperative between outpatient THA using a DL or DA surgical approach.

BACKGROUND:Highly porous tantalum shells have been used for over 15 years to manage acetabular bone loss in revision total hip arthroplasty (THA). Recently, a novel three-dimensional (3D)-printed porous titanium shell was developed, mimicking cancellous bone and accommodating variable angle locking screws for enhanced fixation. This study reported on the short-term outcomes of this titanium shell used in complex primary and revision THA with a minimum follow-up of two years. METHODS:A total of 103 patients received the 3D-printed titanium porous shell, 46 for complex THA (e.g., failed fracture fixation, metastatic disease) and 57 for revision THA. Revision indications included previous periprosthetic joint infection (18 cases), aseptic loosening (21 cases), trunnionosis (two cases), periprosthetic fractures (six cases), instability (four cases), malposition of the cup (four cases), and other causes (two cases). The Paprosky grading system classified acetabular bone loss, and reoperations were recorded. RESULTS:With a mean follow-up of 4.4 years (range, 2.2 to 7.8), patients showed significant functional improvements. The Harris hip score increased from 36.8 ± 17.0 preoperatively to 81.8 ± 14.0 postoperatively (P < 0.001), and Western Ontario and McMaster Universities Osteoarthritis Index scores improved from 46.0 ± 18.2 to 69.8 ± 19.8 (P < 0.001). On average, 5.5 screws per case were used (3.4 locking, 2.0 nonlocking). Titanium augments were used in 10 cases (9.7%). Paprosky grades included type I (23.3%), type IIA (26.2%), type IIB (16.5%), type IIC (8.7%), type IIIA (17.5%), and type IIIB (7.8%). There were 10 reoperations (9.7%), with six for periprosthetic joint infections, two for instability and one each for aseptic loosening of cup and stem. CONCLUSIONS:This novel 3D-printed highly porous titanium shell, often used with variable angle locking screws, has provided excellent fixation in a variety of complex primary and revision THAs at a minimum 2-year follow-up. This new shell has demonstrated results comparable to our experience with porous tantalum shells and represents a viable alternative in our institution.

Total knee arthroplasty (TKA) is a surgery with high success rates and good patient outcomes. However, 6.9% of knee replacement surgeries are revisions of old implants due to ongoing pain, stiffness, and loosening. Revision TKA is more expensive and has worse patient outcomes. Recent studies have begun to explore the role of the inflammatory response in poor TKA outcomes. Inflammation is an important predictor of pain in osteoarthritis (OA) and synovial inflammation may play a role in knee stiffness after TKA. Macrophages are the dominant immune cells of the synovium and regulate knee inflammation, and when activated, they upregulate mitochondrial translocator protein (TSPO) expression. Current standard of care features Magnetic Resonance Imaging (MRI) to assess structural changes in the joint. Positron Emission Tomography (PET) can be used to image important biological processes at the cellular level. [18F]FEPPA is a PET tracer that targets TSPO with high specificity. The goal of this work was to validate the use of [18F]FEPPA PET/MRI in the assessment of macrophage activation in knee synovial tissue. This method may allow non-invasive imaging of important inflammatory processes and understand the role of activated macrophages in ongoing pain, stiffness, and loosening after TKA . To validate the use of [18F]FEPPA in imaging activated macrophages in vivo, synovial tissue was gathered from 12 participants with end stage OA who underwent primary TKA. Knee synovial tissue was sectioned and embedded on slides. Tissue sections were incubated in [18F]FEPPA and imaged by autoradiography for 6 hours. Adjacent tissue sections were incubated with DAPI, CD68 antibody, and TSPO antibody for immunofluorescent analysis of the actual macrophage activation. 6 of the full cohort were imaged in a 3T hybrid PET/MRI after injection with [18F]FEPPA and a 45-minute uptake period. MR of both knee joints was performed with sequences including 3D Dual Echo Steady State (DESS), Bilateral T1 weighted and Fast Spin Echo (FSE) with metal artifact reduction if contralateral TKA was present. Standardized Uptake Values (SUV) were calculated from the measured PET signal, injected dose, and patient mass. [18F]FEPPA tracer uptake calculated from autoradiography correlated to the true macrophage activation measured through TSPO+ immunofluorescence with r = 0.85 and p = 0.0029. SUV calculated from PET/MRI was correlated to true macrophage activation found through immunofluorescence with r = 0.90 and p = 0.083. Attenuation correction maps corrected for metal artefacts enabled visualization and measurement of tracer uptake surrounding the femoral and tibial components. Understanding the role of knee joint inflammation may be important in managing pain and stiffness after TKA. The underlying cause of poor TKA outcomes are often unclear.[18F]FEPPA PET/MRI uptake in knee synovial tissue was validated to correlate to the true macrophage activity. This tool may be able to diagnosis a cellular response as the cause of pain or dissatisfaction after TKA. Future work using [18F]FEPPA PET/MRI could assess different reaction types to metal or plastic implant debris, joint stiffness and fibrosis, and periprosthetic infection.

OBJECTIVE:Uncontrolled pain remains a major clinical challenge in the management of knee osteoarthritis (OA), the most common disabling joint disease. Worse pain is associated with synovial innate immune cell infiltration (synovitis), but the role of innate immune-regulatory cells in pain is unknown. Our objective was to identify synovial innate immune cell subsets and pathophysiologic mechanisms associated with worse pain in patients with knee OA. METHODS:Synovial tissue biopsies from 122 patients with mild-to-severe knee OA pain (Knee Injury and OA Outcome Score [KOOS]) were analyzed to identify associations between synovial histopathology and worse pain. We then used spatial transcriptomics and proteomics of synovial tissue microenvironments (n = 32), followed by single-cell RNA sequencing (n = 8), to identify synovial cell composition and cell-cell communication networks in patients with more severe OA pain. RESULTS:Histopathological signs of synovial microvascular dysfunction and perivascular edema were associated with worse KOOS pain (-10.76; 95% confidence interval [CI] -18.90 to -2.61). Patients with worse pain had fewer immune-regulatory macrophages, expanded fibroblast subsets, and enrichment in neurovascular remodeling pathways. Synovial macrophages from patients with worse pain expressed markers of immune exhaustion and decreased phagocytic function (-19.42%; 95% CI -35.96 to -2.89) and their conditioned media increased neuronal cell stress in dorsal root ganglia. CONCLUSION:Although synovitis increases during OA, our findings suggest that exhaustion, dysfunction, and loss of immune-regulatory macrophages is associated with worse pain and may be an important therapeutic target.

Restoration of native hip joint mechanics and preservation of normal hip anatomy are critical in hip arthroplasty to reduce post-operative complications and attain full recovery of joint function. An important consideration in restoration of native mechanics involves the transfer of the hip joint center of rotation (COR) into the true acetabulum. Due to the mismatch of geometry between the native acetabulum (subhemispherical) and the prosthetic acetabular component (hemispherical), inadvertent displacement of COR is expected following full implantation of the acetabular component. Significant mediolateral (M-L) or superoinferior (S-I) displacement may lead to increased joint reaction forces, bearing surface wear, limb length discrepancy, abnormal gait patterns, reduction in original muscle function, joint instability, and ultimately, implant loosening. Maintaining S-I and M-L COR displacement within 3 mm and 5mm, respectively, has been suggested to avoid post-operative complications. The purpose of this study was to assess how COR displacement affects functional outcomes in patients who undergo THA through the direct anterior approach. COR was determined by drawing a circle of best fit on the native femoral head (preoperatively) or prosthetic femoral head (postoperatively). The S-I, M-L, and overall COR displacements were calculated based on these measurements. Vertical distance was measured as the distance between the inter-ischial line and the COR. Horizontal distance was measured as the distance between the COR and the line drawn perpendicular to the inter-ischial line and passing through the pubis symphysis. All measurements were calibrated based on a fiducial marker on preoperative radiographs or the known prosthetic femoral head on postoperative radiographs. Timed-up and Go (TUG) scores, hip abductor strength, pelvic tilt, limb length discrepancy, and patient-reported outcome questionnaires were collected. Sixty-five patients were recruited (24 females, age = 65.3 ± 11.9 years, BMI = 28.6 ± 5.1 kg/m2). Means of displacement were 2.1 ± 6.4 mm medially and 0.9 mm ± 7.4 mm superiorly. Overall displacement was 8.8 ± 4.5 mm. Superior displacement alone was weakly negatively correlated with limb length discrepancy (p = 0.04, r = -0.27). Greater medial COR displacement was correlated with worse functional results based on WOMAC (p = 0.01) and Harris Hip (p = 0.01) scores. When considering overall COR displacement, greater displacement correlated well with lower Harris Hip scores (p = 0.02) but was not correlated to any other outcome measure. Comparing high-risk (COR shifts greater than 5 mm medially and/or 3 mm superiorly) participants (n = 32) to their low-risk counterparts (n=33), we found WOMAC (p = 0.01) and Harris Hip (p = 0.03) scores suggesting significantly lower function post-operatively, but no other correlations were observed. Results of this study indicate that COR displacement following total hip arthroplasty through the direct anterior approach may meaningfully influence patient functional outcomes.