Page 181 - Speedhorse February 2020

KNEE PROBLEMS
by Nancy S. Loving, DVM
Lameness is a serious issue, particularly for an active equine athlete. Even the slightest amount of pain can impair
performance, especially where seconds mat- ter as in Quarter Horse racing. Most equine lameness in the front legs – up to 90% – is attributable to problems in the lower limb from the fetlock down. That said, a variety of injuries can occur within the knee (car- pal) joints and surrounding soft tissues.
CONFORMATIONAL ISSUES: ANGULAR LIMB DEFORMITY
Structural stability is important
to minimize stresses on equine joints. Monitoring of conformation begins at birth. A foal’s limbs aren’t always straight and perfect at the beginning. As many
as 13% of foals don’t have straight limbs within the first 10 days. With growth, most spontaneously correct. Those that don’t
Although as many as 13% of foals don’t have straight limbs within the first 10 days, most spontaneously correct themselves with time and growth.
achieve conformationally correct alignment in one or both limbs are referred to as having an angular limb deformity (ALD). While the incidence of an ALD is higher in foals with narrow chests, an ALD may occur from nutritional imbalances, rapid growth, or excess exercise or trauma, especially at a young age when the skeletal system is still developing.
Angulation of a limb outward from the knee is called carpus valgus; angulation inward (usually from the fetlock or below) is referred to as a varus ALD.
A limb experiences uneven joint loading from the carpus down through the fetlock, pastern and foot when the limb doesn’t sit straight beneath a horse’s center of mass. Ultimately this may lead to premature development of osteoarthritis and other
soft tissue problems. Not all ALDs require surgical intervention, but surgery is the best option in moderate and severe cases. Initially in the first few months of life, appropriate hoof trimming and restricted exercise may help to improve the abnormal angulation.
Surgical strategies for the carpus are timed relative to status of the growth plate of the lower forearm (distal radial physis) in
advance of a rapid growth phase and growth plate closure. The best chance of correction is possible if carpal surgery is performed prior to 3-4 months of age. Correction potential is significantly less successful as
a foal approaches and/or passes six months of age. Early and successful correction of an angular limb deformity has no negative effects on long-term athletic performance.
The objective of ALD surgery is to
either accelerate or retard growth along the growth plate. The periosteum (nutrient- supplying tissue sheath overlying the bone) of the distal radius is stripped back to
allow the other side of the knee to “catch up.” More significant conformational deviations might need growth retarded
on the convex side of the limb through transphyseal bridging that inserts screws and wires and removes them once the deviation has corrected itself. If surgical correction is not done before long bone development has passed the desired age, then it is possible to remove a wedge of bone (ostectomy) to help correct limb alignment. Close monitoring with frequent checkups and radiography are important to evaluate treatment outcome.
VETERINARY VIEWS
SPEEDHORSE, February 2020 179
Radius
Fourth carpal bone
Cannon bone (third metacarpal)
Radial carpal bone (scaphoid)
Third carpal bone
Trochlea radii
Intermediate carpal bone