History
A 9-year-old warmblood gelding that was ridden as a jumper was referred for evaluation of right forelimb lameness (grade, 1/5) of 1 year's duration. Initially, the lameness was reported as acute and severe. The referring veterinarian had initially localized the lameness to the metacarpophalangeal (fetlock) joint area by use of perineural analgesia. A diagnosis of metacarpophalangeal medial collateral desmitis was made on the basis of ultrasonographic findings. Radiographs of the right metacarpophalangeal joint were obtained (Figure 1).
Lateromedial (A), dorsal 30° proximal-palmarodistal oblique (B), dorsal 45° lateral 25° proximal-palmaromedial distal oblique (C), and dorsal 45° medial 25° proximal-palmarolateral distal oblique (D) views of the right metacarpophalangeal (fetlock) joint of a chronically lame warmblood gelding.
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Lateromedial (A), dorsal 30° proximal-palmarodistal oblique (B), dorsal 45° lateral 25° proximal-palmaromedial distal oblique (C), and dorsal 45° medial 25° proximal-palmarolateral distal oblique (D) views of the right metacarpophalangeal (fetlock) joint of a chronically lame warmblood gelding.
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Lateromedial (A), dorsal 30° proximal-palmarodistal oblique (B), dorsal 45° lateral 25° proximal-palmaromedial distal oblique (C), and dorsal 45° medial 25° proximal-palmarolateral distal oblique (D) views of the right metacarpophalangeal (fetlock) joint of a chronically lame warmblood gelding.
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Radiographic Findings and Interpretation
On the dorsopalmar view, a poorly marginated focal area of decreased mineral opacity is present within the medial distal subchondral bone of the third metacarpal condyle (Figure 2). On a complementary dorsoproximal-dorsodistal (flexed) view of the third metacarpal condyle, the subchondral lesion is much more evident (Figure 3). Additional findings include moderate periarticular osteophytes at the medial and dorsal aspects of the metacarpophalangeal joint and irregularity and heterogeneity of the dorsoproximal portion of the sagittal ridge of the third metacarpal condyle. There is no evidence of periarticular soft tissue thickening.
Same radiographic images as in Figure 1. Notice the poorly marginated area of decreased mineral opacity at the distal medial aspect of the third metacarpal condyle (black arrow). There is moderate periarticular bony remodeling, mainly on the dorsal and medial aspects of the metacarpophalangeal joint and subchondral irregularity of the sagittal ridge of the third metacarpal condyle (white arrowheads). There is pronounced black halo artifact surrounding soft tissue to bone interfaces due to edge enhancement algorithm.
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Same radiographic images as in Figure 1. Notice the poorly marginated area of decreased mineral opacity at the distal medial aspect of the third metacarpal condyle (black arrow). There is moderate periarticular bony remodeling, mainly on the dorsal and medial aspects of the metacarpophalangeal joint and subchondral irregularity of the sagittal ridge of the third metacarpal condyle (white arrowheads). There is pronounced black halo artifact surrounding soft tissue to bone interfaces due to edge enhancement algorithm.
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Same radiographic images as in Figure 1. Notice the poorly marginated area of decreased mineral opacity at the distal medial aspect of the third metacarpal condyle (black arrow). There is moderate periarticular bony remodeling, mainly on the dorsal and medial aspects of the metacarpophalangeal joint and subchondral irregularity of the sagittal ridge of the third metacarpal condyle (white arrowheads). There is pronounced black halo artifact surrounding soft tissue to bone interfaces due to edge enhancement algorithm.
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Dorsoproximal-dorsodistal (flexed) oblique view of the right metacarpophalangeal joint of the same horse as in Figure 1. Notice that the cyst-like lesion (arrow) in the dorsomedial distal aspect of the third metacarpal condyle appears more conspicuous in this view. Periarticular osteophytosis is present on the medial aspect of the metacarpal condyle (arrowhead).
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Dorsoproximal-dorsodistal (flexed) oblique view of the right metacarpophalangeal joint of the same horse as in Figure 1. Notice that the cyst-like lesion (arrow) in the dorsomedial distal aspect of the third metacarpal condyle appears more conspicuous in this view. Periarticular osteophytosis is present on the medial aspect of the metacarpal condyle (arrowhead).
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
Dorsoproximal-dorsodistal (flexed) oblique view of the right metacarpophalangeal joint of the same horse as in Figure 1. Notice that the cyst-like lesion (arrow) in the dorsomedial distal aspect of the third metacarpal condyle appears more conspicuous in this view. Periarticular osteophytosis is present on the medial aspect of the metacarpal condyle (arrowhead).
Citation: Journal of the American Veterinary Medical Association 240, 2; 10.2460/javma.240.2.147
The radiographic diagnosis was a subchondral bone cyst-like lesion of the third metacarpal condyle and osteoarthritis. The primary differential diagnosis was subchondral bone trauma with subsequent bone necrosis or cyst formation and osteoarthritis. Other possible diagnoses for the cyst-like lesion included a rare form of osteochondrosis. Osteochondrosis may have also resulted in the abnormal appearance of the sagittal ridge of the third metacarpal condyle, although osteoarthritis was considered more likely the cause.
Comments
Subchondral bone trauma is increasingly identified in the joints of horses, especially since the advent of magnetic resonance imaging. However, radiography has potential use for identification of some of these lesions, especially with nonconventional radiographic projections such as the flexed dorsoproximal-dorsodistal view of the metacarpophalangeal joint.1 The dorsopalmar projection is usually acquired obliquely in a proximal to distal direction to avoid superimposition of the proximal sesamoid bones with the metacarpophalangeal joint space. However, superimposition of the most distal and especially dorsodistal aspect of the metacarpal condyle with the proximal phalanx cannot be avoided on such a projection. Moreover, lateromedial projections may remain unremarkable, such as in the horse described in the present report. Therefore, conventional projections must be closely scrutinized to potentially indicate further radiographic projections that may provide better conspicuity and precise location of the lesion. Nonetheless, it is accepted that magnetic resonance imaging may yield earlier identification and more precise diagnosis regarding the exact nature of the bone trauma that may consist of bone marrow lesions including necrosis or fibrosis or subchondral plate fracture and cyst formation as well as potentially associated cartilage damage.2
There is a wealth of information to support that horses of all types, including sports or even leisure horses, can sustain major bone trauma to the metacarpophalangeal joint. As such, trauma to the dorsal aspect of the condyle, which is presumably the result of impact injury with the proximal phalanx during metacarpophalangeal hyperextension, should not be overlooked.
In the horse described here, joint trauma may have occurred concurrently to the collateral ligament desmitis diagnosed by the referring veterinarian. Ultrasonographic findings of the metacarpophalangeal collateral ligaments were unremarkable at the time of referral. The horse was treated with corrective shoeing and was in light and progressive work 3 months after diagnosis.
- 1.↑
Richard EAlexander K. Nonconventional radiographic projections in the equine orthopaedic examination. Equine Vet Educ 2007; 19:551–559.
- 2.↑
Zubrod CSchneider RTucker R, et al. Use of magnetic resonance imaging for identifying subchondral bone damage in horses: 11 cases. J Am Vet Med Assoc 2004; 224:411–418.
