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Purpose: The aim of this systematic review was to present the current evidence on the clinical use of single-photon emission computed tomography/computed tomography (SPECT/CT) in the evaluation of noninfected painful knees after knee arthroplasty., Methods: Embase, PubMed, Google Scholar, Ovid, Scopus, Science Direct and the Cochrane Database of Systematic Reviews were searched from database inception to May 2022 following the PRISMA guidelines. As a primary outcome, we defined the role of SPECT/CT in the diagnostic approach to noninfected painful knee arthroplasty; as a secondary objective, we described the noninfection-related factors linked to painful knee arthroplasty. Pooled sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio values and other indicators were calculated; receiver operating characteristic (ROC) curve analysis results and a summary of the areas under the curve (AUCs) from the included studies were reported. A Fagan plot, likelihood ratio plot and Deeks' funnel plot were generated and analysed. Methodological quality was assessed using the QUADAS-2 tool, and the certainty of evidence was assessed by the GRADE approach., Results: A total of 493 publications were identified, of which eight met the inclusion criteria, with a final pooled sample size of 308 patients. The pooled sensitivity and specificity of SPECT/CT in diagnosing the source of pain in painful knee prostheses were 0.86 (95% CI: 0.75-0.93) and 0.90 (95% CI: 0.79-0.96), respectively, with pooled +LR and -LR values of 8.9 (95% CI: 4.11-19.19) and 0.15 (95% CI: 0.09-0.28). The pooled diagnostic odds ratio was 57.35, and the area under the curve was 0.94. SPECT/CT highly accurately identified different sources of pain, such as loosening of the prosthetic components, patellofemoral overloading, instability, malalignment of the components and degeneration of the patellofemoral compartment. The confidence of the estimates was moderate according to the GRADE approach., Conclusion: With demonstrated high sensitivity and specificity, as a diagnostic tool, SPECT/CT can identify the source of pain in painful knees after knee arthroplasty, particularly in cases of loosening, patellofemoral disorders and component malalignment (level of evidence III). These findings have significant clinical repercussions, such as in changing the initial diagnosis, identifying or excluding different causes of painful knee arthroplasties, guiding subsequent treatment and positively impacting the final clinical outcome. We moderately recommend the use of SPECT/CT for identifying the source of pain after knee arthroplasty according to the GRADE assessment. This review was preregistered in Prospero under code CRD42022320457., (© 2023. The Author(s).)

Purpose: The diagnostic process in patients after painful total knee arthroplasty (TKA) is challenging. The more clinical and radiological information about a patient with pain after TKA is included in the assessment, the more reliable and sustainable the advice regarding TKA revision can be. The primary aim was to investigate the position of TKA components and evaluate bone tracer uptake (BTU) using pre-revision SPECT/CT and correlate these findings with previously published pain patterns in painful patients after TKA., Methods: A prospectively collected cohort of 83 painful primary TKA patients was retrospectively evaluated. All patients followed a standardized diagnostic algorithm including 99m-Tc-HDP-SPECT/CT, which led to a diagnosis indicating revision surgery. Pain character, location, dynamics and radiation were systematically assessed as well as TKA component position in 3D-CT. BTU was anatomically localized and quantified using a validated localization scheme. Component positioning and BTU were correlated with pain characteristics using non-parametric Spearman correlations (p < 0.05)., Results: Based on Spearman's rho, significant correlations were found between pain and patients characteristics and SPECT/CT findings resulting in nine specific patterns. The most outstanding ones include: Pattern 1: More flexion in the femoral component correlated with tender/splitting pain and patella-related pathologies. Pattern 3: More varus in the femoral component correlated with dull/heavy and tingling/stinging pain during descending stairs, unloading and long sitting in patients with high BMI and unresurfaced patella. Pattern 6: More posterior slope in the tibial component correlated with constant pain., Conclusion: The results of this study help to place component positioning in the overall context of the "painful knee arthroplasty" including specific pain patterns. The findings further differentiate the clinical picture of a painful TKA. Knowing these patterns enables a prediction of the cause of the pain to be made as early as possible in the diagnostic process before the state of pain becomes chronic., Level of Evidence: Level III., (© 2021. The Author(s).)

The purpose of this study was to define a cut-off value for the posterior drawer position in stress radiography that confirms an insufficiency of the posterior cruciate ligament (PCL) in cruciate-retaining (CR) total knee arthroplasty (TKA). In this retrospective study, 20 symptomatic patients with flexion instability and suspected PCL insufficiency in CR TKA were included. Asymptomatic patients served as an age- and sex-matched control group. All of the patients had undergone stress radiography, and the posterior translation was measured in a posterior drawer position at 30° and 90° flexion. The two groups were compared using t-tests and chi-square tests. The stress radiographs showed significantly more posterior translation in the symptomatic group ( p < 0.01). Stress radiographs at 90° flexion more effectively discriminated between the patients with and without PCL insufficiency compared with those carried out at 30° flexion. Sensitivity and specificity testing revealed the best sensitivity (90.5%) and the best specificity (94.7%) at 90° posterior drawer radiographs at a cut-off value of 10 mm. Stress radiographs including the posterior drawer position at 90° flexion should be part of the diagnostic algorithm in patients with suspected flexion instability. A posterior translation of more than 10 mm in CR TKA strongly indicates an insufficiency of the PCL.

Purpose: The purpose of this study was to investigate whether specific bone tracer uptake (BTU) patterns on preoperative SPECT/CT could predict which patients with varus alignment and medial overload would particularly benefit from medial opening-wedge high tibial osteotomy (MOWHTO). It was the hypothesis that an increased preoperative BTU relative to the reference BTU of the femur on SPECT/CT in the lateral and patellar compartments of the knee are predictive factors for inferior clinical outcome and that the clinical outcome correlates with the extent of alignment correction., Methods: Twenty-three knees from 22 patients who underwent MOWHTO for medial compartment overload were investigated preoperatively using Tc-99m-SPECT/CT. BTU was quantified and localised to specific joint areas according to a previously validated scheme. Pre- and postoperative mechanical alignment was measured. Clinical outcome was assessed at a median of 24 months (range 11-30) after MOWHTO by collecting the WOMAC score., Results: Significant correlations between BTU in the patellar area and the total WOMAC score and its subcategories pain and stiffness were found. Thus, BTU in the 1sPat area (superior lateral patellar compartment) correlated with total WOMAC (rho = 0.43, p = 0.04), pain subcategory (rho = 0.43, p = 0.04), and stiffness subcategory (rho = 0.59, p = 0.003). No significant correlations were found between alignment correction, age, gender and WOMAC., Conclusion: This study highlights the role of preoperative SPECT in modern knee surgery to obtain information about the loading pattern on different compartments of the knee. Despite the limited number of participants, the present study shows that a preoperative SPECT/CT scan can help the treating surgeons to identify patients who may be at risk of inferior clinical outcome if an MOWHTO is considered, as an elevated BTU in the patellar region on preoperative SPECT/CT appears to be a potential risk factor for postoperative pain and stiffness., Level of Evidence: Level III., (© 2021. The Author(s).)

Background: The aim was to investigate the correlation of bone tracer uptake (BTU) in SPECT/CT and changes in coronal knee alignment after total knee arthroplasty (TKA). We questioned if undercorrection of preoperative varus alignment leads to a difference in BTU compared to neutral alignment., Methods: Consecutive 66 patients who received SPECT/CT before and after TKA were retrospectively included. Adjusted mechanical alignment was the alignment target. The alignment of the knee was measured on 3D-CT by selecting standardized landmarks. Maximum (mean ± SD) and relative BTU (ratio to the reference) were recorded using a previously validated localization scheme (p < 0.05)., Results: In the native group, 20 knees were aligned (30.3%) in valgus (HKA > 181.5°), 12 (18.2%) in neutral (178.5°-181.5°) and 34 (51.5%) in varus (HKA < 178°). Overall TKA changed the alignment towards neutral. 48.5% remained in the same groups, whereas 50% of native valgus and 33% of varus knees changed to neutral after TKA. In native varus alignment mean BTU was significantly higher in some medial tibial and femoral regions (fem1ia (p = 0.010), fem1ip (p = 0.002), tib1a.mid (p = 0.005), tib1a.tray (p = 0.000), tib1p.tray (p = 0.000)); in native valgus alignment mean BTU was higher in the corresponding lateral tibial and femoral regions (fem2ip (p = 0.001), tib2a.tray (p = 0.011), tib2p.tray (p = 0.002)). After TKA, a significant decrease in femoral and tibial BTU (femoral preoperative BTU 1.64 +/-0.69; femoral postoperative BTU 0.95 +/-0.42; p = 0.000// tibial preoperative BTU 1.65 +/- 0.93; tibial postoperative BTU 1.16 +/- 0.48; p = 0.000) and an increase in patellar BTU was observed (p = 0.025). Native varus alignment correlated with a higher medial BTU decrease medially. Undercorrection of preoperative varus alignment showed no higher BTU after TKA., Conclusion: Preoperative varus alignment correlated with a higher decrease in BTU in specific femoral and tibial medial regions. Preoperative valgus alignment correlated with a higher decrease in the corresponding lateral regions. Undercorrection of preoperative varus alignment did not lead to higher bone loading reflected by BTU after TKA., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)