Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Thoroughpin, Fluid Accumulation in Hock

Synonyms: Tarsal Sheath (Canal) Fluid Accumulation, False Thoroughpin


Thoroughpin is a visible sign of swelling of the tarsal sheath, which is the fluid-filled sac that encloses and lubricates the deep digital flexor tendon as it passes through the hock. The space that the tendons travel through is also known as the tarsal canal. Thoroughpin is not really a diagnosis, but is an observation and a clinical sign.

Thoroughpin appears as a variably-sized bubble of swelling of just above the hock and mostly visible on the outside (lateral), but sometimes also visible on the inside (medial) of the hock. The fluid swelling can often be moved, with manual pressure, from the lateral side of the tendon sheath to the medial side or vice-versa.

Thoroughpin is not itself a cause of lameness. Fluid accumulation here may be seen in horses that have been i intensely worked. Swelling here also occurs with more serious injuries to the tendon. A benign (not causing lameness) fluid accumulation is impossible to tell from fluid accumulation relating to a significant injury. Horses with hoof imbalance and poor hock conformation may also be predisposed to developing Thoroughpin.

A condition termed a "False Thoroughpin" is a fluid accumulation that is located in the region but does not communicate with the tendon sheath. Like a "True Thoroughpin", it may or may not be associated with lameness, depending on the underlying condition.

In the absence of lameness, generally swellings of the tarsal sheath should be monitored. Simple, benign fluid accumulation may decrease and resolve with rest, and with adjustment to work load.

If however, swellings continue to grow in size or are accompanied by lameness, more veterinary diagnostics are needed to define the cause of the fluid accumulation.

Diagnosis requires lameness exam and possibly ultrasound and/or radiography. Sampling of the fluid may also be recommended.

Treatment depends on the cause of the fluid accumulation.

my vet's role


Benign (not associated with lameness) accumulations of fluid in the tarsal canal (tarsal sheath) are often not associated with problems.

On the other hand, tendon injuries and even some fractures can cause fluid accumulation here. So the treatment and prognosis will depend on the cause of the fluid accumulation.

my role

Questions To Ask Your Vet:
  • What is causing the fluid accumulation of thoroughpin?
  • What diagnostics are needed to clarify that?
  • Is the horse lame?

Select horses of appropriate conformation. Condition horses adequately for their work. If you notice swelling here, have a veterinary examination to determine the cause of the swelling.

further reading & resources

Author: Doug Thal DVM Dipl. ABVP