Weightbearing Digital Tomosynthesis of Foot and Ankle Arthritis: Comparison With Radiography and Simulated Weightbearing CT in a Prospective Study.

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Foot and ankle arthritis is common and debilitating. Weightbearing radiography is the reference standard for evaluating alignment, but overlapping bones and hardware limit evaluation for osteoarthritic bony detail. The purpose of this study was to evaluate whether digital tomosynthesis (DTS) can yield reliable quantitative alignment values, as radiography does with its weightbearing capability, and good qualitative osteoarthritic detail, as CT does. Adults with foot or ankle arthritis referred for simulated weightbearing CT were recruited to undergo weightbearing radiography and DTS. Four readers independently evaluated radiographs and DTS images for foot and ankle alignment and severity of osteoarthritis in each joint. Two readers performed consensus readings of CT images. Agreement between modalities was assessed by intraclass correlation coefficient (ICC) and Cohen kappa statistics. Ninety-one ankles were analyzed. Most joints were significantly less obscured by overlapping bone when seen with DTS (11.2%) or CT (4.3%) compared with radiography (30.4%). For quantitative foot alignment measurements, DTS had good to excellent agreement with weightbearing radiography (ICC, 0.65-0.93), which performed significantly better than CT (ICC, 0.39-0.87). For qualitative osteoarthritic details of each joint, DTS had significantly better agreement with weightbearing radiography on joint space narrowing (κ = 0.38-0.67) than did CT (κ = 0.08-0.62). Weightbearing radiography and DTS had similar levels of agreement with CT on grading of osteophytes, subchondral cysts, and loose bodies. DTS is associated with less obscuration of joints than radiography and yields more reliable weightbearing quantitative foot and ankle alignment values than radiography does and more reliable osteoarthritic bony details than CT does.