Weight-bearing anteroposterior radiograph of the ankle underestimates the severity of osteoarthritis when there is anterior subluxation of the talus

Abstract

Category: Ankle Arthritis Introduction/Purpose: On weight-bearing lateral radiograph, anterior aspect of the ankle shows more narrowing than posterior aspect in the ankle osteoarthritis with anterior subluxation of the talus. However, weight-bearing anteroposterior radiograph of the ankle osteoarthritis with anterior subluxation of the talus often shows less severe joint space narrowing than the joint space in the narrowest anterior aspect of the ankle joint. (Fig.1). The purposes of this study were to compare the degree and shape of joint space narrowing in the anterior, middle and posterior aspect of the ankle by using weight-bearing CT and to investigate which area of the ankle was shown on plain weight-bearing ankle anteroposterior radiograph in the ankle osteoarthritis with anterior subluxation of the talus. Methods: We retrospectively evaluated patients who underwent surgery for ankle osteoarthritis in our clinic from January, 2017 to May, 2017. We included patients who showed ankle osteoarthritis with anterior subluxation of the talus in weight-bearing lateral radiograph. We determined anterior, posterior and middle coronal images in sagittal image of the weight-bearing CT.(Fig.1) Talar tilt, medial width of superior clear space(SCS), lateral width of SCS, width of medial clear space and obliteration ratio were measured on plain weight-bearing anteroposterior ankle radiograph, and the three coronal images. The obliteration ratio was obtained by obliteration-width / talus-width * 100.(Fig.1) The radiographic parameters of the anterior coronal image were compared with those on the middle and the posterior coronal image by using paired T-test. The intraclass coefficient was used to investigate which of the three coronal images showed best match with degree and shape of ankle osteoarthritis on the plain weight-bearing ankle anteroposterior radiograph Results: Seventy-one ankles from 71 patients were included in this study. The average age of patients in this study was 62.6 years (range: 19-82). The talar tilt on the anterior coronal image was significantly lower than that on the middle and posterior coronal images. The lateral width of SCS and the width of medial clear space on the anterior coronal image was significantly narrower than those on the middle and the posterior coronal image. The obliteration ratio on the anterior coronal image was significantly higher than that of the middle and the posterior coronal images (Fig.2). The intraclass coefficients indicated that the radiographic parameters on plain weight-bearing anteroposterior radiograph was most reliable with those on the middle coronal image among the three coronal images. Conclusion: Anterior area of ankle shows the most severe osteoarthritis and plain weight-bearing anteroposterior radiograph shows the best match to the middle portion of the ankle, when ankle osteoarthritis has anterior subluxation of the talus. Because middle area of ankle has less severe ankle osteoarthritis than anterior area of ankle in that kind of ankle osteoarthritis, plain weight-bearing radiograph may underestimate the severity of ankle osteoarthritis.