History
A 12-year-old Thoroughbred Quarter Horse cross gelding was evaluated because of a grade 4/5 lameness1 of the right forelimb. The horse had fallen at a jump during a show jumping training session and collapsed onto its carpi. The referring veterinarian suspected a flexor tendon rupture because of significant soft tissue swelling in the palmar proximal metacarpal area and immediately treated the horse with hydrotherapy, corticosteroids, and flunixin meglumine. A splint was applied over the dorsal aspect of the distal portion of the limb to support the injured limb during transport.
Abnormalities detected on physical examination included focal swelling around the deep digital flexor tendon at the level of the proximal portion of the metacarpus and generalized swelling over the medial aspect of the carpus, which did not elicit signs of pain during palpation. Complete rupture of the superficial or deep digital flexor tendons could not be confirmed after palpation of the swollen area. No abnormalities were detected on CBC count and serum biochemical analyses. No abnormalities were detected on radiographs of the right carpus and proximal portion of the third metacarpal bone. Ultrasonography of the medial aspect of the carpus distal to the chestnut and the palmar aspect (zone 2B)2 of the proximal portion of the third metacarpal bone was performed (Figure 1).
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page
Transverse (A) and longitudinal (B) ultrasonographic images of the medial aspect of the distal portion of the right antebrachium, and transverse (C) ultrasonographic image of the palmar aspect of the metacarpal region 14 cm distal to the accessory carpal bone in a 12-year-old horse evaluated because of a grade 4/5 lameness of the right forelimb. In images A and B, cranial and proximal, respectively, are on the right side of the image. In image C, lateral is on the left side of the image. Images were obtained by use of a 7.5-MHz linear array transducer with a stand-off pad at a displayed depth of 5 cm.
Citation: Journal of the American Veterinary Medical Association 228, 6; 10.2460/javma.228.6.845
Same ultrasonographic images as in Figure 1 and transverse (D) and longitudinal (E) ultrasonographic images of the medial aspect of the distal portion of the left (normal) antebrachium in the same horse. Image A—Notice enlargement and loss of echogenicity in the cross-sectional view of the accessory ligament of the superficial digital flexor tendon (ALSDFT; d). Image B—Thickening of the ALS-DFT as well as mild disruption of the fiber pattern is evident. Notice the difference in echogenicity and ligament size when the affected ALSDFT is compared with that of the left limb (D and E). Image C—Notice distension of the carpal sheath (h; gray arrow) with echogenic fluid compatible with hemorrhage. a = Radius. b = Cephalic vein. c = Median artery. e = Flexor carpi radialis. f = Superficial digital flexor tendon. g = Deep digital flexor tendon. i = Accessory ligament of the deep digital flexor tendon.
Citation: Journal of the American Veterinary Medical Association 228, 6; 10.2460/javma.228.6.845
Diagnostic Imaging Findings and Interpretation
The severely thickened and hypoechoic appearance of the right accessory ligament of the superficial digital flexor tendon (ALSDFT; Figure 2) as well as the abnormal fiber pattern visible on the longitudinal ultrasonographic view confirmed desmitis of the ALSDFT. Distension of the carpal sheath with echogenic fluid is compatible with hemorrhage in the distal aspect of the carpal canal between the accessory ligament of the deep digital flexor tendon and the deep digital flexor tendon. Differential diagnoses for carpal sheath effusion include osteochondroma of the distal portion of the radius and associated flexor tendonitis, accessory carpal bone fracture, ALSDFT desmitis, and septic tenosynovitis.
Comments
Desmitis of the ALSDFT is not a common injury although it occurs spontaneously in sport and racehorses.3 Ultrasonography is considered an essential diagnostic tool for accurate diagnosis of ALSDFT injuries2 and to distinguish between ALSDFT desmitis and carpal canal syndrome.2 Furthermore, traumatic injuries to the ALSDFT can often result in idiopathic hemorrhage within the carpal canal, which may appear hyperechoic on ultrasonographic examination in acute injuries.2
The nature in which the horse of this report fell after the jump is important. The fall onto its flexed carpal joints could also have caused fractures of the small carpal bones or accessory carpal bone as has been described in horses falling on their carpi during training or during recovery from general anesthesia.4 Carpal bone fractures may cause a nonspecific carpal swelling, depending on their anatomic location, especially because these injuries are rare and often not recognized until several days later.
Treatment of ALSDFT injuries usually consists of stall rest and controlled exercise as well as intrathecal administration of hyaluronate and corticosteroids.3 In the absence of other injuries, the prognosis for the horse reported here was considered fair,3 and return to its former training regimen was expected within 6 months.5
Ross MW. Movement. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. Philadelphia: WB Saunders Co, 2003;60–73.
Reef VB. Equine diagnostic ultrasound. Philadelphia: WB Saunders Co, 1998.
Dyson SJ. The carpal canal and carpal synovial sheath. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. Philadelphia: WB Saunders Co, 2003;684–687.
Wilke M, Nixon AJ, Malark J, et al. Fractures of the palmar aspect of the carpal bones in horses: 10 cases (1984–2000). J Am Vet Med Assoc 2001;219:801–804.
Denoix JM, Guizien I, Perrot P, et al. Ultrasonographic diagnosis of spontaneous injuries of the accessory ligament of the superficial digital flexor tendon (proximal check ligament) in 23 horses, in Proceedings. Am Assoc Equine Pract 1995;142–143.
- 1↑
Ross MW. Movement. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. Philadelphia: WB Saunders Co, 2003;60–73.
- 3↑
Dyson SJ. The carpal canal and carpal synovial sheath. In: Ross MW, Dyson SJ, eds. Diagnosis and management of lameness in the horse. Philadelphia: WB Saunders Co, 2003;684–687.
- 4↑
Wilke M, Nixon AJ, Malark J, et al. Fractures of the palmar aspect of the carpal bones in horses: 10 cases (1984–2000). J Am Vet Med Assoc 2001; 219: 801–804.
- 5↑
Denoix JM, Guizien I, Perrot P, et al. Ultrasonographic diagnosis of spontaneous injuries of the accessory ligament of the superficial digital flexor tendon (proximal check ligament) in 23 horses, in Proceedings. Am Assoc Equine Pract 1995; 142–143.
