Puncture Wounds and Synovitis in Horses: Blame the Shrubs?

Despite their herbivorous ways, horses sometimes run into trouble with even the most innocuous vegetation. Cockleburs tangle manes and tails; hedge apples have been known to lodge in throats; and the spiky awns of foxtail pierce gums and cheeks, sometimes leading to oral abscesses. Another plant, blackthorn, causes a much different injury among foxhunters, point-to-point racehorses, and other horses that sail over or through hedges as part of their work: puncture wounds with accompanying synovitis, or inflammation of the lining of the joint capsule.

Blackthorn is a shrub that grows naturally in the woodlands of Europe, New Zealand, western Asia, and regions of North America, including the northwest and northeast United States. As part of its branch structure, blackthorn grows thorns so rigid and sharp that the plant sometimes serves double-duty as cattle-proof hedging and obstacles in cross-country riding. When horses jump the hedges, as they may during foxhunting, the thorns can penetrate the skin that covers joints, resulting in synovitis, sometimes severe.

A recent study described the presentation and outcome of blackthorn-induced synovitis in horses.^* Thirty-five horses with these specific injuries were included in the study, and all of the horses presented with profound inflammation of the affected joints.

The mean lameness score of the horses at the time of presentation was 4 or 5 on a scale of 1 to 5, indicating lameness was obvious at the walk (score of 4), or lameness produced minimal weight-bearing or a complete inability to move (score of 5).^§

A two-stage surgical technique was used in these cases: (1) high-resolution ultrasound to identify thorn fragments so their removal caused minimal trauma, and (2) arthroscopy to assess synovial structure in order to remove foreign material and rapidly restore function, according to the researchers.

Diagnosis was confirmed through the retrieval of thorn fragments from synovial or perisynovial structures. The most common sites of injuries were tendon sheaths of the forelimb (12 of 35 cases) and fetlock joints (11 of 35).

All horses eventually returned to work in an average of eight weeks. Because of the positive outcomes, synovitis instigated by blackthorn has a different etiology than synovitis originating from sepsis or other types of contamination, the researcher explained.

Musculoskeletal health is critical for all athletic horses but is especially so for those that have had compromises in joint integrity. Choose high-quality joint supplements from reputable manufacturers to keep performance horses comfortable and willing.

^*Ashton, N.M. 2020. Prospective study of blackthorn injury and synovitis in 35 horses. Equine Veterinary Education 32(9):492-499.

 ^§American Association of Equine Practitioners. Lameness Exams: Evaluating the Lame Horse. Accessed September 22, 2020.