Comment: “Reliability of Slice-Encoding for Metal Artifact Correction (SEMAC) MRI to Identify Prosthesis Loosening in Patients with Painful Knee Arthroplasty”

Letter to: Reliability of Slice-Encoding for Metal Artifact Correction (SEMAC) MRI to Identify Prosthesis Loosening in Patients with Painful Knee Arthroplasty: A Prospective, Single-Center, Surgical Validation Study Indian J Radiol Imaging 2025; 35(04): 548-557 DOI: 10.1055/s-0045-1802970 Reliability of Slice-Encoding for Metal Artifact Correction (SEMAC) MRI to Identify Prosthesis Loosening in Patients with Painful Knee Arthroplasty: A Prospective, Single-Center, Surgical Validation Study We read with great interest the prospective single-center surgical validation study by Takahashi et al, which assessed the diagnostic performance of slice-encoding for metal artifact correction (SEMAC) magnetic resonance imaging in identifying prosthesis loosening among patients with painful knee arthroplasty.[ 1 ] The authors are to be commended for integrating a gold-standard surgical endpoint, deploying three SEMAC sequences across anatomical planes, and using the outcome measurements in rheumatology filter methodology to ensure construct validity. However, certain issues surrounding interpretive robustness and clinical generalizability merit further discussion. The study's reliance on surgical revision as the definitive endpoint introduces an ascertainment mechanism that may inflate the diagnostic performance of T1-weighted SEMAC magnetic resonance imaging.[ 2 ] Among the 44 patients, only 11 underwent revision surgery, with loosening confirmed in just seven cases. In this constrained denominator, even a single discordant case would markedly alter sensitivity and specificity estimates. This matters because, if SEMAC magnetic resonance imaging is to be integrated into preoperative workups for prosthetic failure, clinicians must understand its performance across a broader spectrum of non-revised cases, not only those selected for surgery. Furthermore, the interpretive framework appears vulnerable to incorporation bias. The two musculoskeletal radiologists who assessed the magnetic resonance imaging scans were not blinded to symptomatology, raising the possibility that symptom-driven signal interpretation may have influenced diagnostic thresholds. This concern is amplified by the discordance between bone marrow edema detection on short tau inversion recovery SEMAC and surgically verified prosthesis loosening. Such bias may lead to overcalling pathology in patients with stable implants, potentially triggering unnecessary imaging or surgical referral. The stratification of findings across total, unicompartmental, and patellofemoral arthroplasties remains inadequately powered. While loosening was predominantly observed in total knee arthroplasty, only broad comparisons were presented without meaningful subgroup analysis by implant type or component material. Given the known variability in artifact profiles related to implant composition and geometry,[ 3 ] this limits applicability to non–total knee arthroplasty subtypes. Clinicians interpreting SEMAC magnetic resonance imaging in unicompartmental or patellofemoral arthroplasty may therefore find extrapolation challenging. In addition, persistent postoperative pain may occasionally arise from extra-articular or non-prosthetic causes detectable on extended magnetic resonance imaging fields.[ 4 ] One such entity is persistence of the canal of Nuck, the female homolog of the processus vaginalis. A patent canal of Nuck may result in hydroceles, indirect inguinal hernias, or cystic lesions that can clinically mimic periarticular pathology.[ 5 ] Although uncommon, these abnormalities may coexist in patients undergoing advanced imaging for postoperative pain. Awareness of such entities, along with other groin or pelvic herniations, may enhance interpretation when prosthesis loosening is excluded. We commend the authors for conducting the first surgical validation of SEMAC magnetic resonance imaging for prosthesis loosening and for establishing its diagnostic reliability within the total knee arthroplasty subgroup. Future multicenter studies incorporating larger arthroplasty populations, blinded interpretation, and longitudinal outcome modeling would further strengthen the translational value of this imaging approach. Authors' Contribution S.S.S. conceptualized data, developed methodology, prepared original draft, wrote, reviewed, and edited manuscript. A.K. validated and supervised the data, administrated the project, prepared the original draft, wrote, reviewed, and edited the manuscript. Generative AI Use Statement Grammarly and ChatGPT-4o tools were used solely to assist with language refinement and formatting. All scientific content, interpretations, and critical analyses were developed by the authors, who take full responsibility for the integrity and accuracy of the article. Publication History Article published online: 29 July 2026 © 2026. Indian Radiological Association. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Medical and Scientific Publishers Private Limited A-13A, Graphix Tower 1, 6th floor, Sector 62, Noida 201309, Uttar Pradesh, India