Signal changes in standing magnetic resonance imaging of osseous injury at the origin of the suspensory ligament in four Thoroughbred racehorses under tiludronic acid treatment

Abstract

Problems associated with the proximal metacarpal region, such as an osseous injury associated with tearing of Sharpey's fibers or an avulsion fracture of the origin of the suspensory ligament (OISL), are important causes of lameness in racehorses. In the present study, four Thoroughbred racehorses (age range, 2-4 years) were diagnosed as having forelimb OISL and assessed over time by using standing magnetic resonance imaging (sMRI). At the first sMRI examination, all horses had 3 characteristic findings, including low signal intensity within the trabecular bone of the third metacarpus on T1-weighted images, intermediate-to-high signal intensity surrounded by a hypointense rim on T2*-weighted images, and high signal intensity on fat-suppressed images. Following the sMRI examination, all horses received 50 mg of tiludronic acid by intravenous regional limb perfusion once weekly for 3 weeks. Attenuation of the high signal intensity on T2*-weighted and fat-suppressed images was observed on follow-up sMRI in 3 horses. Following rest and rehabilitation, these 3 horses successfully returned to racing. In contrast, the other horse that did not show attenuation of the high signal intensity failed to return to racing. To our knowledge, this is the first report of OISL in Thoroughbred racehorses assessed over time by sMRI under tiludronic acid treatment. Our findings support the use of sMRI for examining lameness originating from the proximal metacarpal region to refine the timing of returning to exercise based on follow-up examinations during the recuperation period.

Keywords: magnetic resonance imaging; osseous injury; proximal metacarpus; racehorse; tiludronic acid.

Fig. 1.

Dorsopalmar radiographic images of the right metacarpus of case 1 on day 2 (A), day 53 (B), and day 87 (C). Linear radiolucent lesions are evident at the proximal medial surface of the third metacarpus throughout the period (arrows).

Fig. 2.

Sagittal ultrasonographic images of case 1, acquired in a standing palmar position over the proximal right metacarpal region on day 3 (A), day 53 (B), and day 87 (C). The proximal is at right, and the distal direction is at left. A hyperechogenic fragment is identifiable on the palmar cortex of the third metacarpal bone (A; arrow), and the surface irregularity remain visible throughout the period (B, C; arrow).

Fig. 3.

Sagittal T1-weighted, T2*-weighted, and fat-suppressed images on day 3 (A, B, C), day 24 (D, E, F), day 53 (G, H, I), and day 87 (J, K, L), respectively (all days), from case 1, acquired at the level of the proximal half of the right metacarpus. The proximal and dorsal directions are at the top and left, respectively. An area of low signal intensity within the trabecular bone of the third metacarpus is visible on a T1-weighted image from day 3 (A; arrows). The area has intermediate-to-high signal intensity surrounded by a hypointense rim on a T2*-weighted image (B; arrows) with a corresponding markedly high signal intensity on a fat-suppressed image (C; arrows). The high signal intensity is attenuated on a T2*-weighted image from day 53 (H; arrowheads). The area of high signal intensity is significantly decreased on a fat-suppressed image (I; arrowheads). The area of decreased signal intensity is slightly decreased on a T1-weighted image from day 87 (J; arrowheads). The high signal intensity is no longer observed on a T2*-weighted image (K) and fat-suppressed image (L).

Fig. 4.

Transverse T1-weighted, T2*-weighted, and fat-suppressed images on day 1 (A, B, C), day 23 (D, E, F), and day 85 (G, H, I), respectively (all days), from case 2, acquired at 2 cm distal to the right carpometacarpal joint. Dorsal is to the top and lateral is to the left. There is low signal intensity in the cancellous bone of the third metacarpus in a T1-weighted sequence from day 1 (A; arrows). The area has intermediate-to-high signal intensity surrounded by a hypointense rim on a T2*-weighted image (B; arrows) and markedly high signal intensity on a fat-suppressed image (C; arrows). There is a decrease in the area of high signal intensity on a T2*-weighted (E; arrowheads) and fat-suppressed images from day 23 (F; arrowheads). The area of low signal intensity remains visible on a T1-weighted image from day 85 (G; arrows), whereas the area of high signal intensity is attenuated on a T2*-weighted image (H; arrowheads) and significantly decreased on a fat-suppressed image (I; arrowhead).

Fig. 5.

Transverse T1-weighted, T2*-weighted, and fat-suppressed images on day 6 (A, B, C) and day 20 (D, E, F), respectively (both days), from case 3, acquired at 2 cm distal to the left carpometacarpal joint. The dorsal and medial directions are at the top and left, respectively. A focal area of low signal intensity within the cancellous bone of the third metacarpus is visible on a T1-weighted image from day 6 (A; arrows). The area is imaged as a focal intermediate-to-high signal intense lesion surrounded by a hypointense rim on a T2*-weighted image (B; arrows), whereas the area shows high signal intensity on a fat-suppressed image (C; arrows). The area of decreased signal intensity is visible on a T1-weighted image from day 20 (D; arrows). The area of high signal intensity is attenuated on a T2*-weighted image (E; arrowheads), whereas the high signal intensity remains visible on a fat-suppressed image (F; arrows).

Fig. 6.

Sagittal T1-weighted, T2*-weighted, and fat-suppressed images on day 2 (A, B, C) and day 16 (D, E), respectively (both days), from case 4, acquired at the level of the proximal half of the right metacarpus. The proximal and dorsal directions are at the top and left, respectively. An area of low signal intensity within the trabecular bone of the third metacarpus is visible on a T1-weighted image from day 2 (A; arrows), whereas the area has intermediate-to-high signal intensity surrounded by a hypointense rim on a T2*-weighted image (B; arrows) and markedly high signal intensity on a fat-suppressed image (C; arrows). The high signal intensity is still evident on a T2*-weighted image from day 16 (E; arrows) and also remains visible on a transverse fat-suppressed image (F; arrows).