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Category: Other Introduction/Purpose: Adult acquired flatfoot deformity (AAFD) is a biomechanical derangement involving the three- dimensional (3D) midfoot and hindfoot osseous complex, which can be challenging to optimally characterize using conventional two-dimensional (2D) plain radiographs. Weightbearing (WB) Cone-Beam CT (CBCT) can better demonstrate the deformity of the 3D structures during WB. Therefore, we compared validated AAFD measurements between non-weightbearing (NWB) and WB CBCT images. Methods: In this prospective, IRB approved study, 20 patients were included, 12 males and 8 females, mean age of 54.21 (20-88) years, with clinical diagnosis of flexible AAFD. Subjects were scanned with standing (WB) and seated (NWB) CBCTs. WB and NWB CBCT images were assessed with traditional flatfoot measurements obtained at sagittal, coronal, and axial planes using predefined anatomical landmarks, by two independent observers. Interobserver reliability was calculated using Pearson correlation. Results: The measurements in patients with AAFD differed significantly between WB and NWB CBCT images. Specifically, WB images showed, when compared to NWB, decreased forefoot arch angle (mean difference: 9.91°, p < 0.0001), increased talus-first metatarsal angle (10.59°, p < 0.0001), increased navicular-medial cuneiform angle (13.89°, p < 0.0001), decreased navicular-floor (coronal 14.05mm/sagittal 14.91mm, p < 0.0001) and navicular-skin distances (coronal 5.87mm/sagittal 8.25mm, p < 0.0001), decreased medial cuneiform-floor (coronal 10.79mm/sagittal 11.07mm, p < 0.0001) and medial cuneiform-skin distances (coronal 4.45mm/sagittal 5.78mm, p < 0.0001), and decreased cuboid-floor (5.78mm, p < 0.0001) and cuboid-skin distances in the sagittal plane (4.60mm, p < 0.0001). Interobserver reliability was good to excellent (0.610-0.991). Conclusion: Traditional adult acquired flatfoot deformity radiographic measurements are obtainable using high resolution 3D WB CBCT imaging, and can help characterize the biomechanical derangements during weightbearing in subjects with flexible AAFD.

Category: Ankle Arthritis Introduction/Purpose: Surgical restoration of the anatomical relationship between talus and tibia is considered crucial for longevity of total ankle arthroplasty (TAA). Weight-bearing (WB) radiographs are the current standard for evaluating the sagittal balance alignment, which are, however, prone to rotational misalignment and potentially altered measurements. Metal artifact reduction sequence (MARS) MRI is a cross-sectional technique that minimizes implant-induced artifacts and affords the visualization of bone-implant interfaces and periprosthetic bone without distortions. Although not weight-bearing, MARS MRI offers the ability to align the image plane to the true sagittal axis of the talar implant and anatomically correct measurements. Therefore, the purpose of this study was to compare sagittal balance alignment measurements on MARS MR images and standard WB radiographs in patients with TAA. Methods: In this IRB-approved, prospective study, 23 subjects [10 men/13 women, age 60(41-73) years; 13(3-24) months post- op] underwent MARS MRI and standard lateral WB radiographs. Standardized MARS MR images were obtained in alignment to the sagittal talar component axis and use of a boot-shaped MRI coil. Maximum-intensity-projection MR images that resemble lateral radiographs were created to bring anatomic landmarks, such as lateral talar process, talonavicular joint line, talar implant, tibial shaft, and posterior talus into one single image. Three board-certified foot ankle surgeons performed sagittal balance alignment measurements twice in an independent, random and blinded fashion. The second set of measurements was obtained 1 months after the first assessment. In accordance with published measurements, lateral talar station (LTS), tibial axis-to-talus (T-T) ratio, and normalized tibial axis-to-lateral-process (T-L) distance were measured. Pearson correlation coefficient (r), Concordance-Correlation-Coefficient (CCC) and Intraclass-Correlation-Coefficient (ICC) were used for statistical analysis. Bonferroni-corrected p-values ≤ 0.01 were considered significant. Results: The intra-observer agreement was excellent for radiographic (CCC = 0.93 - 0.97) and MRI (CCC = 0.90 - 0.97) measurements. Inter-observer agreements were good-to-excellent with overall higher agreements for MRI (ICC = 0.76 - 0.93) than for radiography (ICC = 0.58 - 0.95) measurements. There was statistically significant inter-method correlation between radiographic and MRI measurements including LTS (r=0.83, p < 0.001), T-T ratio (r=0.86, p < 0.001) and normalized T-L distance (r=0.72, p < 0.001). The T-T ratios of radiographs and MRI were statistically not different (p=0.36), whereas LTS and normalized T-L distance were significantly lower on MR images when compared with radiographs (p < 0.001). Conclusion: Sagittal balance measurements performed on standardized weight-bearing radiographs and standardized MARS MR images demonstrate substantial correlation and similarity. Given its high inter- and intra-observer agreement, MARS MRI may be helpful for the evaluation of sagittal balance following TAA.

Category: Other Introduction/Purpose: To evaluate interobserver reliability among readers of different clinical experience by applying measurements for adult acquired flatfoot deformity (AAFD) using high-resolution three-dimensional (3D) weightbearing (WB) cone-beam CT (CBCT) examination. Methods: In this IRB approved study, 20 patients with flexible AAFD [12 male, 8 female; mean age 54.2 (20-88) years] were scanned with standing (weightbearing) CTs. Two blinded observers, a medical student and a foot/ankle surgeon, applied validated AAFD measurements in sagittal, coronal, and axial planes using predefined anatomical landmarks. Interobserver reliability was calculated using Pearson correlation. Results: There was significant interobserver agreement with high correlation for the following measurements(p < 0.0001): distances between medial cuneiform to-floor (r=0.981) and to-skin (r=0.986), navicular to-floor (0.992) and to-skin (r=0.900); cuboid to-floor (r=0.975) and to-skin (r=0.978), and calcaneus-to-fibula (r=0.808); calcaneal inclination angle (r=0.795); forefoot arch angle (r=0.983); and subtalar horizontal angles at 25%, 50%, and 75% of the anteroposterior joint length (r=0.784, 0.891, 0.809). Significant agreement with moderate correlation was additionally demonstrated for talar-first metatarsal angle (r=0.553, p < 0.014), medial cuneiform-first metatarsal angle (r=0.668, p < 0.001), and navicular-cuneiform angle (r=0.746, p < 0.0002). Level of training did not influence the reliability of any measurements except medial cuneiform-first metatarsal angle (specialist: 8.83°; student: 1.61°; p < 0.01). Statistically insignificant difference between readers (p>0.05) was noted in mean talar-first metatarsal and subtalar horizontal angles. Conclusion: While literature describes large variability for AAFD measurements from plain radiographs among readers of varying medical experience, 3D WB CBCT can yield similar measurements using predefined planes with high reliability, independent of reader experience.

Category: Ankle Arthritis Introduction/Purpose: Total ankle arthroplasty (TAA) is an often successful treatment for end-stage ankle arthritis; however, a subset of patient presents with ankle pain following TAA and concern for early failure. Although radiographs are often diagnostic, patients with normal radiographs and continued pain pose a diagnostic challenge. In those patients, magnetic resonance imaging (MRI) may be helpful to evaluate periprosthetic bone and soft tissues. Traditional high-bandwidth (high-BW) metal artifact reduction sequence (MARS) MRI lessens metal artifacts, but image distortions remain with Cobalt-Chromium implants. Slice- Encoding-Metal-Artifact-Correction (SEMAC) is a recently FDA-approved, advanced MARS technique that promises more powerful metal suppression. Therefore, we prospectively tested the hypothesis that SEMAC MARS MRI facilitates better metal reduction and visibility of periprosthetic structures than does traditional MARS MRI in patients with TAA. Methods: In this IRB-approved study, 20 volunteers [10 females/10 males; age, 59 (41-73) years, 15 (3-24) months post- operatively] with TAA were prospectively enrolled. The research protocol consisted of high-BW and SEMAC MARS MRI using a clinical 1.5 Tesla MRI scanner and a dedicated boot-shaped MRI coil. For each technique, intermediate-weighted and fat- suppressed MR images were obtained in axial, sagittal and coronal orientation. Three observes (2 foot/ankle surgeons and 1 musculoskeletal radiologist) evaluated the high-BW and SEMAC MR images in an independent, random and blinded fashion. Equidistance 5-point Likert scales (1=non-diagnostic, 5=very good) were used to grade image quality as well as the quality of metal suppression and visibility of bone-metal interfaces, tendons, ligaments, bone and joints. Differences between the two MARS techniques were assessed with a Kruskall-Wallis test, and interobserver agreement was graded with Intraclass-Correlation- Coefficient (ICC). Bonferroni-corrected p-values ≤ 0.01 were considered significant. Results: All 20 subjects completed the research protocol. There was good agreement between observers (ICC = 0.79; 95% CI, 0.78-0.80). Image quality of high-BW and SEMAC MR images was similar for tissue contrast, fat suppression, and fluid brightness, whereas image sharpness was one interval higher on high-BW images than on SEMAC images (p < 0.01). Metal reduction of TAA components was significantly better (p < 0.01) on SEMAC images (very good) than on high-BW images (poor-to-adequate). At level of the implants, long flexor and peroneal tendons, deep deltoid, syndesmotic and lateral collateral ligaments, and medial and lateral gutters were significantly better seen (p < 0.01) on SEMAC images (good-to-very good) than on high-BW images (poor-to- adequate). Similar visibility (good-to-very good) was found for the remainder of the tendons, ligaments, bones and joints. Conclusion: Based on the results of our study, we accept the hypothesis that SEMAC MARS MRI outperforms traditional high- BW MARS MRI in the degree of metal artifact reduction as well as visibility of bone implant interfaces and periprosthetic tendons and ligaments at level of the joint line. We believe advanced MARS MRI can be a valuable clinical tool to assess osseous integration and soft tissue lesions in patients following TAA.