Hygroma: carpal / tarsal

Etiology

• Usually chronic, repetitive, direct, blunt trauma to the dorsal aspect of the carpus and/or the lateral aspect of the hock.
• Acute trauma may also lead to development.
• May occasionally be congenital.
• Can be uni- or bilateral.

Predisposing factors

• Repetitive trauma when lying and rising, especially in cubicle systems where metal work positioning may be inappropriate and or the bedding surface is inadequate and impacts pressure points on carpus or hock. May also be seen in grazing animals during the summer months when the ground is particularly hard.
• Subcutaneous hematoma formation may precede hygroma formation.
• In countries where Brucellosis Brucellosis is present, chronic infection may lead to hygroma formation.

Pathophysiology

• Formed by the accumulation of transudate following repeated trauma over bony prominences.
• In chronic cases, a subcutaneous acquired bursa forms, which is lined by secretory cells; sometimes called a false bursa.
• If the hygroma becomes sufficiently large it can mechanically restrict the range of movement of the joint.
• Adhesions and fibrosis may ensue and restrict normal movement.
• May become secondarily infected → discharge, abscessation, fistulae, granulation tissue formation. High risk of joint infection if hock swellings are secondarily infected. Joint infections will present as acute lameness and a hot, swollen joint Joint lavage: through-and-through  . 

Timecourse

• Usually chronic with insidious onset, but occasionally can occur rapidly following severe acute trauma.

Epidemiology

• May be seen in a large proportion of the herd if cow comfort is compromised such as through poor cubicle comfort or inappropriate cubicle dimensions . For this reason, hygroma frequency is used as a cow comfort indicator in health and welfare auditing schemes.