Distal radius and ankle fractures are among the most common skeletal injuries treated by orthopedic surgeons [1, 2]. A significant proportion of these injuries involve the articular surface, disrupting the congruity of the radiocarpal and tibiotalar joints, respectively. The primary goal of surgical management with open reduction and internal fixation (ORIF) is the stable, anatomical restoration of this articular surface [3]. Failure to achieve and maintain an anatomical reduction, particularly the presence of an articular step-off or gap greater than 2 mm, has been strongly correlated with the development of accelerated post-traumatic osteoarthritis, leading to chronic pain, stiffness, and functional disability [4, 5]. The current standard of care for intraoperative assessment of fracture reduction is fluoroscopy. This imaging technique provides real-time, dynamic feedback, allowing the surgeon to visualize fracture fragments and hardware placement during the procedure [6]. It is widely available, relatively inexpensive, and involves a manageable radiation dose. However, fluoroscopy is fundamentally a two-dimensional (2D) projectional imaging modality. This creates inherent limitations, including the superimposition of complex bony anatomy, magnification errors, and challenges in obtaining perfectly orthogonal views, which can obscure subtle but clinically important details of the articular surface [7, 8]. In contrast, multi-detector computed tomography (CT) provides high-resolution, cross-sectional images that can be reconstructed in multiple planes (axial, coronal, and sagittal) and as three-dimensional (3D) models [9]. This technology eliminates the issue of structural superimposition and allows for precise, objective measurement of articular gaps, step-offs, and rotational alignment [10]. Consequently, postoperative CT is increasingly recognized as the gold standard for evaluating the definitive quality of fracture reduction, especially in complex periarticular fractures [11]. While the theoretical advantages of CT over fluoroscopy are clear, the clinical impact and magnitude of the discrepancy between these two modalities require ongoing investigation. Several studies have highlighted the fallibility of plain radiographs and fluoroscopy in specific fracture types, such as tibial plateau or calcaneal fractures [12, 13]. However, there is a relative paucity of data directly comparing modern intraoperative fluoroscopy with postoperative CT across a combined cohort of the two most common intra-articular fractures: the distal radius and the ankle. Quantifying the rate at which fluoroscopy may provide a false sense of an acceptable reduction has significant clinical implications, potentially influencing surgical technique, decision-making for postoperative imaging, and the timing of revision surgery. Therefore, the aim of this study was to evaluate and compare the diagnostic accuracy of intraoperative fluoroscopy with postoperative CT in assessing the quality of articular reduction following ORIF of intra-articular distal radius and ankle fractures, using postoperative CT as the reference standard.

Study Design and Patient Selection This retrospective study was conducted at Gouri Devi Institute of Medical Sciences &Hospital, Durgapur, West Bengal. We reviewed the electronic medical records and Picture Archiving and Communication System (PACS) of all patients who underwent ORIF for a distal radius or ankle fracture between January 2023 and December 2024. Inclusion criteria were: (1) skeletally mature patients (age ≥ 18 years); (2) diagnosis of a closed, intra-articular distal radius (AO/OTA type 23-B or 23-C) or ankle fracture (AO/OTA type 44-B or 44-C); (3) treatment with ORIF; (4) availability of archived intraoperative fluoroscopy images and a postoperative CT scan performed within 48 hours of the index procedure. Exclusion criteria included: (1) open fractures of Gustilo-Anderson grade II or higher; (2) pathological fractures; (3) pilon fractures; (4) incomplete imaging records; or (5) significant motion artifact on the CT scan rendering it non-diagnostic. Applying these criteria, a total of 150 patients were included in the final analysis, comprising 75 distal radius fractures and 75 ankle fractures. Image Acquisition 1. Intraoperative Fluoroscopy: All procedures were performed using a standard mobile C-arm fluoroscope (Siemens Cios Alpha or similar). At the conclusion of fixation, static anteroposterior (AP), lateral, and, for distal radius fractures, 45-degree oblique images were obtained and archived to PACS. Surgeons deemed the reduction acceptable based on these final images before wound closure. 2. Postoperative CT: All CT scans were performed on a 64-slice scanner (Siemens SOMATOM Definition AS+). The protocol involved acquiring contiguous axial images with a slice thickness of 0.625 mm. Multiplanar reconstructions (MPR) in the sagittal and coronal planes were generated for evaluation. 3. Image Evaluation Two independent reviewers—a fellowship-trained orthopedic trauma surgeon with 10 years of experience and a board-certified musculoskeletal radiologist with 12 years of experience—evaluated all imaging. Both reviewers were blinded to the patient identifiers, the original surgical and radiological reports, and each other’s assessments. For each fracture, the reviewers analyzed both the final intraoperative fluoroscopy images and the postoperative CT scan in separate sessions spaced four weeks apart to minimize recall bias. The quality of articular reduction was determined based on the maximum residual articular step-off or gap. A reduction was categorized as: • Acceptable: Articular step-off ≤2 mm and articular gap ≤2 mm. • Unacceptable: Articular step-off >2 mm or articular gap >2 mm. Measurements on CT were made using electronic calipers on the slice showing the greatest displacement. In cases of disagreement between the two primary reviewers, a third senior orthopedic surgeon reviewed the images to reach a consensus. Statistical Analysis All statistical analyses were performed using SPSS software, Version 28.0 (IBM Corp., Armonk, NY). Descriptive statistics were used to summarize patient demographics. The primary outcome was the rate of unacceptable reduction as determined by each modality. McNemar's test was used to compare the paired categorical outcomes (acceptable/unacceptable) between fluoroscopy and CT. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of fluoroscopy were calculated using CT as the gold standard. Inter-rater reliability for both modalities was assessed using Cohen’s kappa (κ) coefficient. A p-value < 0.05 was considered statistically significant.

Patient Demographics The study cohort consisted of 150 patients, with a mean age of 45.8 ± 15.2 years (range, 19 to 78 years). There were 81 males (54.0%) and 69 females (46.0%). The cohort was evenly split between distal radius fractures (n=75) and ankle fractures (n=75), as per the study design. Demographic and fracture classification details are presented in Table 1. Table 1: Patient Demographics and Fracture Characteristics (N=150) Characteristic Distal Radius (n=75) Ankle (n=75) Total (N=150) Age (years), Mean ± SD 48.2 ± 16.1 43.4 ± 14.0 45.8 ± 15.2 Gender, n (%) Male 39 (52.0%) 42 (56.0%) 81 (54.0%) Female 36 (48.0%) 33 (44.0%) 69 (46.0%) AO/OTA Fracture Type, n (%) 23-B 41 (54.7%) - - 23-C 34 (45.3%) - - 44-B - 49 (65.3%) - 44-C - 26 (34.7%) - Comparison of Reduction Assessment The overall assessment of reduction quality by fluoroscopy versus CT is summarized in Table 2. Intraoperative fluoroscopy identified an unacceptable reduction in 12 cases (8.0%). In contrast, postoperative CT identified an unacceptable reduction in 38 cases (25.3%). Crucially, of the 138 fractures that were deemed to have an acceptable reduction based on intraoperative fluoroscopy, 29 (21.0%) were found to have an unacceptable step-off or gap on the postoperative CT scan. This difference in identifying unacceptable reductions between the two modalities was highly significant (McNemar’s test, p < 0.001). Table 2: Comparison of Reduction Quality Assessment by Fluoroscopy vs. Postoperative CT Intraoperative Fluoroscopy Postoperative CT Assessment Total Acceptable Unacceptable Acceptable 109 29 Unacceptable 3 9 Total 112 38 Diagnostic Accuracy of Fluoroscopy Using postoperative CT as the gold standard, the diagnostic performance of intraoperative fluoroscopy was calculated. Fluoroscopy demonstrated a sensitivity of 23.7% (9/38) for detecting an unacceptable reduction. The specificity was high at 97.3% (109/112). The positive predictive value (PPV) was 75.0% (9/12), and the negative predictive value (NPV) was 79.0% (109/138). Quantitative Analysis of Discrepant Cases For the 29 cases where fluoroscopy missed a malreduction, a quantitative analysis was performed. In this subgroup, the mean articular step-off as measured on CT was 2.8 ± 0.6 mm (range, 2.1 to 4.5 mm), and the mean articular gap was 3.1 ± 0.7 mm (range, 2.2 to 5.0 mm). These details are presented in Table 3. There was no significant difference in the rate of missed malreductions between distal radius and ankle fractures (p=0.45). Inter-rater reliability for identifying unacceptable reduction was substantial for CT (κ = 0.89) and moderate for fluoroscopy (κ = 0.65). Table 3: Quantitative Measurements in Cases Deemed Acceptable on Fluoroscopy but Unacceptable on CT (n=29) Parameter Mean ± SD Range Maximal Articular Step-off on CT (mm) 2.8 ± 0.6 2.1 – 4.5 Maximal Articular Gap on CT (mm) 3.1 ± 0.7 2.2 – 5.0 Fracture Location, n (%) Distal Radius 13 (44.8%) Ankle 16 (55.2%)

The findings of this study demonstrate a significant discrepancy between intraoperative fluoroscopy and postoperative CT in the assessment of articular reduction for distal radius and ankle fractures. Our primary result indicates that fluoroscopy failed to identify a clinically significant malreduction (>2 mm step-off or gap) in 21% of cases that were initially deemed acceptable intraoperatively. This suggests that reliance on fluoroscopy alone may provide surgeons with a false sense of security and lead to the unwitting acceptance of a suboptimal reduction. The low sensitivity of fluoroscopy (23.7%) in our study is a critical finding and is consistent with the growing body of evidence questioning its adequacy for complex articular fractures. For example, a study by Gardner et al. on tibial plateau fractures found that conventional radiography missed an articular step-off of >2 mm in over 20% of cases when compared to CT [12]. Similarly, a study by Cole et al. on acetabular fractures showed that plain radiographs were insufficient for determining the adequacy of reduction in a significant number of patients [14]. Our study extends these concerns to two of the most frequently encountered articular fractures in clinical practice. The underlying reason for this discrepancy is the inherent technological limitations of 2D projectional imaging. In the distal radius, fragments involving the lunate fossa can be obscured by the scaphoid fossa and the overlying carpus on standard fluoroscopic views [7]. In the ankle, accurate assessment of the posterior malleolus and the syndesmosis is notoriously difficult with fluoroscopy alone, as the fibula often superimposes on the critical anatomical structures [8, 15]. CT, with its ability to provide multi-planar reformats, completely eliminates this issue of anatomical overlap, allowing for an unobstructed and precise evaluation of the entire articular surface. The higher inter-rater reliability for CT assessments (κ=0.89) compared to fluoroscopy (κ=0.65) in our study further supports its superior objectivity and reproducibility. The clinical implications of our findings are substantial. An unrecognized malreduction of 2.8 mm, the average step-off missed by fluoroscopy in our cohort, is well above the threshold known to be associated with poor long-term outcomes [4, 5]. Identifying such a malreduction on a routine postoperative CT allows for early and informed decision-making. It opens a window for early revision surgery, which may be technically easier and lead to better results than a delayed reconstruction after the fracture has healed in a malunited position. While the clinical benefit of revising every 2mm step-off is debatable and requires further study, having accurate information is paramount for both the surgeon and the patient. These results also advocate for a potential paradigm shift in intraoperative imaging. The development and increasing availability of intraoperative 3D imaging systems, such as the O-arm or C-arms with cone-beam CT capabilities, offer a solution to this diagnostic dilemma [16]. These technologies provide CT-like images in the operating room, enabling the surgeon to identify and correct any malreduction before the patient leaves the surgical suite. While associated with higher costs and a learning curve, the potential to avoid revision surgeries and improve patient outcomes may justify their use in complex articular fractures [17]. This study has several limitations. First, it is a retrospective analysis from a single institution, which may introduce selection bias and limit generalizability. Second, we did not correlate the imaging findings with long-term clinical or functional outcomes. It is plausible that some of the malreductions identified only on CT may not have resulted in a poor clinical result. Future prospective studies are needed to establish a definitive link between CT-defined malreduction and patient-reported outcome measures. Lastly, the quality of fluoroscopic imaging can be surgeon-dependent, and our results reflect the practice at our institution.

Intraoperative fluoroscopy is an insensitive tool for detecting articular malreduction in distal radius and ankle fractures, significantly underestimating the rate of unacceptable outcomes when compared to the gold standard of postoperative CT. CT provides a more accurate, reliable, and objective assessment of articular congruity. Based on our findings, orthopaedic surgeons should maintain a high index of suspicion for residual displacement even when fluoroscopic images appear satisfactory. We recommend liberal use of postoperative CT scans for complex intra-articular distal radius and ankle fractures to verify reduction quality, facilitate early intervention if required, and ultimately optimize the potential for a successful long-term outcome.

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