The efficacy of contrast radiography to demonstrate ‘false thoroughpins’ in five horses.

This research article discusses the efficacy of contrast radiography in diagnosing ‘false thoroughpins’ in the tarsal sheath of horses, presenting as swelling of the hindlimb.

Introduction

• The paper sets the context by explaining that the most common cause of a notable swelling in the equine hock, either craniomedial or craniolateral to the Achilles tendon, is distension within the tarsal sheath. This structure encases the deep digital flexor tendon and extends 5 to 8 cm proximal to the tibial malleolus.

Previous Research on Thoroughpin

• Referencing Dik and Merkens (1987), the authors note previous work on horses with unilateral tarsal sheath distension, commonly termed thoroughpin. This prior study stressed the usefulness of contrast radiography for diagnosing this condition especially in cases without associated bony lesions.

The Current Study: Aim and Method

• The current study was prompted by examination of five cases in which horses were wrongly diagnosed clinically as having tarsal sheath distension. The focus is on the efficacy of contrast radiography to differentiate true cases of thoroughpin from false ones, thus showcasing its diagnostic utility.

Case 1: Findings and Results

• The first case presented is a five-year-old horse with a swelling proximal to the calcaneal tuber of the right hock. Conventional radiography showed only a soft tissue swelling.
• The researchers used contrast radiography using aseptic puncture and injection of a mixture of meglucamine ioxaglate and air, revealing a multiloculated, smooth walled cavitary lesion. Despite this, the deep digital flexor tendon, usually outlined in such a contrast study, wasn’t visible, suggesting a problem beyond simple sheath distension.
• Upon puncture of the tarsal sheath and injection of a positive contrast medium, the normal tarsal sheath was outlined but did not intersect with the cystic lesion. These findings indicate a fluid-filled extra-tendovaginal soft tissue lesion, simulating tarsal sheath distension, hence a ‘false thoroughpin’.

Case 2: Brief Mention

• The document also mentions a second case involving a three-year-old horse displaying a similar swelling of the right hock, confirming that misleading clinical symptoms of tarsal sheath distension can occur.