What Is Your Diagnosis?

Denis R. Verwilghen Equine Clinic, Department of Companion Animals and Equids, Faculty of Veterinary Medicine, Liège University, 4000 Liège, Belgium.

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 DVM, MSc
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Geraldine Bolen Equine Clinic, Department of Companion Animals and Equids, Faculty of Veterinary Medicine, Liège University, 4000 Liège, Belgium.

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 DVM, PhD
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Pierre Paindaveine Private Equine Practice, rue Giguellerie, BE-5640 Maison St Gérard, Belgium.

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Valeria Busoni Equine Clinic, Department of Companion Animals and Equids, Faculty of Veterinary Medicine, Liège University, 4000 Liège, Belgium.

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 DVM, PhD

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History

A 7-year-old warmblood mare that was used for show jumping underwent a prepurchase examination. Slight effusion of the tarsal and metatarsophalangeal joints was found during physical examination; no other abnormalities were detected. The horse had no history of lameness, and no signs of lameness were observed before or after flexion testing of the limbs. Radiographs of both tarsi were obtained (Figure 1).

Figure 1—
Figure 1—

Lateromedial (A) and dorsoplantar (B) views of the left tarsus of a 7-year-old warmblood mare without signs of lameness that was evaluated radiographically as part of a prepurchase examination.

Citation: Journal of the American Veterinary Medical Association 237, 1; 10.2460/javma.237.1.29

Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page

Radiographic Imaging Findings and Interpretation

An abnormal shape of the proximal tubercle of the talus (PTT), which appears larger than normal, is evident on the lateromedial view of the left tarsus. A fine, curved radiolucent line (Figure 2) can be identified, indicating a fragmented PTT. The enlarged PTT is also visible as an increased bony opacity at the medial and proximal aspect of the talus on the dorsoplantar view. No other radiographic abnormalities are apparent.

Figure 2—
Figure 2—

Same radiographic views as in Figure 1. On the lateromedial (A) view of the left tarsus, the proximal tubercle of the talus (PTT) appears larger than is typical (black arrows). Notice the demarcated faint radiolucent line (white arrowheads) that is indicative of a bony fragment. On the dorsoplantar (B) view of the left tarsus, the enlarged PTT is delineated (arrows) as a zone of increased bony opacity at the medial and proximal aspect of the talus.

Citation: Journal of the American Veterinary Medical Association 237, 1; 10.2460/javma.237.1.29

The radiographic diagnosis was fragmentation of the PTT. Radiographic evaluation of the contralateral (right) tarsus revealed similar findings also indicative of a fragmented PTT.

Comments

Radiographic evidence of fragmentation at the site of the PTT can be an incidental finding on prepurchase examinations for which interpretation is often difficult.1 For the horse of this report, radiographic evidence of PTT fragmentation was visible on the lateromedial view of the tarsus, which is the best of the 4 standard views (ie, lateromedial, dorsoplantar, plantarolateral-dorsomedial oblique, and dorsolateral-plan-taromedial oblique) of the tarsus to identify this abnormality. Other standard views do not provide a better image of the PTT, although an enlarged PTT is visible on plantarolateral-dorsomedial oblique and plantaroproximal-plantarodistal (calcaneal skyline) oblique views of the talus.1 The latter view should be obtained by use of exposure factors higher than those used for correct exposure of the tuber calcanei to allow adequate visualization of the PTT,2 and the plantarolateral-dorsomedial oblique view will highlight tangentially the PTT when obtained with a degree of obliquity of approximately 20° in relation to the sagittal plane. A flexed lateromedial view may be used to visualize the plantar articular surface of the talar trochlear ridges.1 This is of clinical importance as osteochondral lesions of the proximoplantar surface of the medial ridge of the talus should be considered as a radiographic differential diagnosis for fragmentation of the PTT.

Bone fragments in the tarsus are most commonly found on the intermediate ridge of the tibia, the trochlear ridges of the talus, and the malleoli of the distal part of the tibia.1 Some unusual locations have been reported, such as the proximal part of the medial trochlear ridge,3 but fragmentation of the PTT is rarely reported.1,2 However, in 676 warmblood horses that underwent radiographic screening, radiographic signs reported as fragmentation of the PTT were more common than were osteochondrosis of the trochlear ridges of the talus and lateral malleolus of the tibia.4 Lesions at the PTT appear radiographically as either a separate bony fragment (as in this report) or as a large pro-tuberance.1 One tarsus or both tarsi (as found in the horse of this report) can be affected.4

The clinical importance of PTT fragmentation in horses has not been investigated. A clinical and radiologic follow-up was available 6 months after the initial consult for the horse of this report. No change in clinical findings or radiographic appearance of the lesions was observed, and the horse was being ridden successfully as a jumper. In a prospective study a of 62 horses that were 3 to 16 years old, 11% (7/62) had radiographic evidence of fragmentation of the PTT. None of these 7 horses had evidence of lameness related to the fragment during the studya period, and the radiographic appearance of the PTT lesion was described as stable or even regressing with age. However, because the PTT serves as an insertion site for a portion of the short medial collateral ligament of the tarsocrural joint, a fragmented PTT could be accompanied by injury to this ligament and become clinically important. The etiology of the PTT fragmentation remains unclear; the possibility of including it in the list of developmental orthopedic disorders should be kept in mind, considering this anomaly can be found in relatively young horses.

a.

Gatti J. Evolution radiographique des membres (pied exceptes) de soixante-deux chevaux entre trois et seize ans. DVM thesis, Department of Clinical Sciences, Ecole Nationale Vétérinaire d'Alfort, Paris, France, 2006;137.

  • 1.

    Busoni V. The stifle and tarsus. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 5th ed. St Louis: Saunders Elsevier, 2007;359381.

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  • 2.

    Butler JA, Colles CM & Dyson SJ, et al. Clinical radiology of the horse. 3rd ed. Oxford, England: Wiley-Blackwell, 2008.

  • 3.

    Simpson CM, Lumsden JM. Unusual osteochondral lesions of the talus in a horse. Aust Vet J 2001;79:752755.

  • 4.

    Verwilghen D, Serteyn D & Pille F, et al. Prevalence of radiographic findings in candidate sires (2001–2008). Vlaams Diergeneesk Tijdschr 2009;78:419428.

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