Avulsion of the proximal digital annular ligament in five hindlimbs

Abstract

Avulsion of the proximal attachment of the proximal digital annular ligament (PDAL) was identified in five horses based on characteristic radiographic findings and supported by ultrasonographic examination in four horses. In two cases, PDAL avulsion was associated with acute onset lameness based on physical examination (both animals) and diagnostic analgesia (one animal), and was the only lesion identified. Both horses became sound after a period of rest. Radiographs repeated 11 years later in one animal showed minimal change in the appearance of the lesion. PDAL avulsion was associated with a substantial tear of the deep digital flexor tendon in another horse and in the remaining two cases PDAL avulsion was not associated with lameness. A dissection study found that the proximodistal extent of the proximal PDAL attachment, expressed as a proportion of the length of the proximal phalanx, was significantly (P = 0.011) greater in hindlimbs (11.48 ± 1.01%) compared with forelimbs (8.55 ± 1.06%). This finding may explain why hindlimbs appear at greater risk of PDAL avulsion. In conclusion, while PDAL avulsion can be a cause of acute lameness which, in uncomplicated cases, responds to rest, it can also be an incidental radiographic finding.