Which views do we require?
- As a minimum a lateromedial view of the laminitic feet. If only one foot affected, a view of the unaffected foot is useful.
- A dorsopalmar view can be useful also but less essential.
- A dorsal hoof wall marker positioned with the top at the coronary band is useful but not essential.
- A drawing pin in the frog apex is useful if the radiographs are being used for farriery purposes but otherwise this is not needed.
What are we looking for on radiographs? There are many measurements and ratios that can be calculated. The key measurements for an acute laminitic foot are listed below. The paper by Sherlock and Parkes (2013) referenced below contains a comprehensive guide to measurements in these cases.
- i)Rotation of the distal phalanx
- Rotation of the dorsal border of the distal phalanx away from the dorsal hoof wall. This can be easy to see or more subtle in some cases. It is important to look at the direction of hoof wall in the proximal portion of the hoof capsule because foot overgrowth and flaring of the hoof wall can hamper measurements
- ii)Sinking of the distal phalanx
- This can occur alone or with rotation of the distal phalanx. This is a finding that is easy to overlook radiographically.
- It is important to measure the founder distance (d-distance) which is the vertical distance between the coronary band and the extensor process of the distal phalanx (shown in figure xx). This should be <16mm, however comparison between feet (front vs hind if only one pair affected, between limbs if only one limb affected) is essential in each case. Comparison of sequential radiographs is also useful.
- A founder distance of >16mm has been shown to correlate with a poor prognosis for return to exercise.
- iii)Solar depth
- The depth of sole between the tip of the distal phalanx and the solar surface of the foot is important, as this can give information about whether or not the distal phalanx is about to perforate the sole.
- The contour of the sole is also important, as the sole may become more convex at a time that the distal phalanx is about to perforate.
As mentioned above, the use of sequential radiographs is useful to monitor the course of disease. Figure 2 shows a horse with unilateral laminitis radiographed at 2 week intervals through treatment. Progression of sinkage of the distal phalanx can be seen.
Radiographs of laminitic feet can tell us a lot about a case beyond is the distal phalanx rotated or not. Using these simple measurements can help to monitor progression of disease, determine treatment planning and may help with prognosis in these difficult cases.
Fig 1: Lateromedial view of a foot with no evidence of laminitis. The pink lines denote the dorsal hoof wall and dorsal border of the distal phalanx, the angle between these should be measured. The red line denotes the founder or D-distance, the vertical distance between the coronary band and the extensor process of the distal phalanx (denoted by the green lines). The blue line shows the measurement of solar depth.
Fig 2: Sequential radiographs of an 18 year old Welsh Section D gelding with unilateral RF laminitis. The radiographs are taken at 2 week intervals. Moderate sinkage of the distal phalanx with minimal rotation is seen in the initial radiograph (left). The sinkage increases in the second (middle) and third (right) radiographs. The solar depth also decreases in the three images, without any material alteration in the degree of rotation of the distal phalanx. The solar margin is convex on the third image. A well defined step can be seen at the coronary band in all 3 images, consistent with sinkage of the distal phalanx. The foot is trimmed between images 2 & 3.
Sherlock, C., Parkes, A., (2013) Radiographic and radiological assessment of laminitis. Equine Veterinary Education 25 524-535