Standing magnetic resonance imaging of distal phalanx fractures in 6 cases of Thoroughbred racehorse

Abstract

Six Thoroughbred racehorses with palmar process fractures of the distal phalanx were evaluated with standing magnetic resonance imaging (sMRI). In all the cases, the fractures were detectable on T1-weighted images and fat-suppressed images. Furthermore, multi-planar reconstruction images were useful for assessing the articular involvement of the fractures. Follow-up sMRI was obtainable in 3 cases, which revealed that the area of high signal intensity on fat-suppressed images decreased over time as symptoms improved. Our findings support the use of sMRI for the detailed evaluation of distal phalanx fractures including their articular involvement and the healing process.

Keywords: distal phalanx; fracture; magnetic resonance imaging; racehorse.

Fig. 1.

Dorsomedial palmarolateral oblique skyline radiographic images of the right distal phalanx of case 1 on day 5 (A), and day 390 (C). Arrows outline a linear fracture at the medial wing of the distal phalanx. It is vaguely identifiable that the fracture line reaches the articular surface of the distal interphalangeal joint (A; open arrow). On day 390, slightly increased radiolucency remains visible (C; open arrows). T1-weighted images of the right distal phalanx on day 5 (B) and day 390 (D), reconstructed by multi-planar reformatting using image processing workstation. A fracture line within the medial wing of the distal phalanx is imaged as a linear area of high signal intensity on day 5 (B), clearly showing the articular involvement. The open arrow points to the middle phalanx (B). The fracture line is imaged as a linear area of low signal intensity on day 390 (D; open arrows).

Fig. 2.

Dorsomedial palmarolateral oblique skyline radiographic images of the right distal phalanx of case 2 on day 114 (A), day 158 (C), day 191 (E), day 262 (G), day 353 (I), and day 418 (K). The fracture at the medial wing of the distal phalanx is evident until day 262 (G; arrows). On day 353, the area of slightly increased radiolucency remains visible (I; open arrows). Frontal fat-suppressed images of the right distal phalanx on day 114 (B), day 158 (D), day 191 (F), day 262 (H), day 353 (J), and day 418 (L). The proximal and medial directions are at the top and right, respectively. A fracture at the medial wing of the right distal phalanx is imaged as a diffuse area of high signal intensity on day 114 (B; arrow). The area of high signal intensity decreases over time, and complete signal attenuation is observed on day 353 (J; open arrows). On day 418, re-fracture is suspected (K, L; arrows).

Fig. 3.

Dorsolateral palmaromedial oblique skyline radiographic images of the right distal phalanx of case 5 on day 6 (A), and day 102 (D). Arrows outline a linear area of mildly increased radiolucency (A). On day 102, slightly increased radiolucency remains visible at the lateral wing of the distal phalanx (D; open arrows). Frontal T1-weighted and fat-suppressed images of the right distal phalanx on day 1 (B, C), day 102 (E, F). The proximal and lateral directions are at the top and left, respectively. The lateral wing of the distal phalanx shows low signal intensity on a T1-weighted image (B; arrows). The area is imaged as a diffuse area of high signal intensity on a fat-suppressed image (C; arrows). On day 102, the low signal intensity within the lateral wing of the distal phalanx is still visible on a T1-weighted image (E; arrows), whereas there is a decrease in the area of high signal intensity on a fat-suppressed image (F; open arrows).