Dictionary:

thoroughpin

  (thûr'ō-pĭn', thûr'ə-, thŭr'-)

An abnormal swelling on either side of the hock joint of horses and related animals.

[From its resemblance to a pin passing through the hock.]

Tenosynovitis of the deep flexor tendon sheath of the hindlimb of the horse manifested by soft, nonpainful swellings just above the point of the hock and on the medial and lateral aspects of the hock. There is no lameness.

Thoroughpin. By permission from Knottenbelt DC, Pascoe RR, Diseases and Disorders of the Horse, Saunders, 2003