Page 182 - Speedhorse February 2020

VETERINARY VIEWS
ADDITIONAL CONFORMATIONAL ISSUES OF THE KNEE
Additional conformation issues occur in and around the carpus. “In-at-the- knee,” “bench knees,” and “calf knees” (hyper-extension of the back-in-the-knee conformation) potentially contribute to various carpal problems later in life. Bench knees and “off-set” knees can result in trauma to the medial splint bone from interference injury.
Carpal joint arthritis doesn’t tend to develop in horses with “over-at-the-knee” conformation since carpal joints normally flex. However, if a horse is fully weight bearing as the knee flexes prematurely, injury can result -- sudden increase of tension on the superficial digital flexion tendon potentially stretches or tears tendon fibers, resulting in a bowed tendon. In severe cases, the carpal canal becomes inflamed, similar to carpal tunnel syndrome in humans.
Individuals that are “over-at-the-knee” at an early age likely remain that way, whereas those that are ‘back-in-the-knee’ have more of a chance to improve between weanling age and three years old. Back-in-the-knee conformation puts undue pressure on the front margins of the carpal bones, with the potential to cause fractures or degenerative joint disease.
Many of these variations in knee conformation are genetically linked, so selection of both mare and stallion is important to maximize optimum structural features.
ACQUIRED KNEE PROBLEMS
Hygroma
Swelling over the front of the knee may
be present due to development of a hygroma, which is an acquired bursa, i.e. a pocket with
a secretory lining that produces serum-like fluid. Hygromas typically result from trauma, such as experienced through kicks, falls, other impacts such as banging a knee on the stall or trailer walls, or from limb entrapment in panels, fencing, or feeders.
Most often, a hygroma is a cosmetic blemish rarely affecting soundness, and it rarely becomes infected. Drainage of the hygroma, along with infusion of corticosteroids and compression bandaging, can be successful except when a hygroma connects with underlying tendons or joints that continually secrete fluid, resulting
in a likelihood of recurrence. Cases of reduced range-of-motion of the knee usually have more to do with underlying osteoarthritis, fibrous joint capsular restriction, or previous carpal injury and/or surgery rather than the presence of a hygroma.
Chip Fractures
Chip fractures within the carpus are not uncommon in racehorses. Osteochondral (OC) fragments in the carpus may develop from a single yet substantial traumatic event or from repetitive trauma that exceeds bone’s capacity for adaptive remodeling. About 15% of horses have chip fractures in their joints incurred from frolic and competitive play in the field, even before training begins. Radiography can detect these before a horse enters into active training.
About 15% of horses have chip fractures in their joints incurred from frolic and competitive play in the field, even before training begins.
Horses with correct conformation that
are conditioned appropriately and/or asked
to perform jobs with less arduous physical impact are better protected from developing OC fragmentation. In contrast, cyclic loading, fatigue and hyperextension – activities such as racing, jumping, or sports with sharp turns – are known to precipitate OC fragmentation. Fragmentation and associated debris in the
joint then lead to an irregular cartilage surface and inflammation of the synovial membrane (synovitis), with a risk of osteoarthritis. In many cases, it is best to remove carpal osteochondral fragments with surgery. Large fragments, like slab fractures, or those surrounded by scar
In some cases of acute Carpitis, arthroscopic surgery assesses the cartilage interface as well as soft tissue structures and makes it possible to flush the injured joint to reduce concentrations of inflammatory enzymes.