Page 300 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.7c The axial skeleton – pelvis 275

VetBooks.ir 1.7c The axial skeleton – pelvis

SACROILIAC JOINT AND affected, with alterations in its ultrasonographic
LIGAMENT INJURIES appearance. Acute damage to the soft tissue in the
SI region may be caused by trauma, such as a fall,
Definition/overview but more commonly the presentation is of an insidi-
The sacroiliac (SI) joints function to transmit forces ous onset and the cause and pathophysiology is not
from the hindlimbs to the vertebral column, via the known.
pelvis. They are diarthrodial joints with a very low
range of gliding movement, flexion and extension. Clinical presentation
The joint surfaces undergo significant remodel- Horses considered to be at risk for developing SI
ling in response to changes in body weight and the pain are those used for show jumping and dressage.
joint can therefore vary in size and shape with age. Affected horses have also been found to be signifi-
The joint is associated with several muscle groups cantly older, taller and of greater body weight than
(middle and accessory gluteal, internal obturator the general population. Reported clinical signs in
and iliacus) and the sciatic nerve and cranial gluteal horses with a positive response to infiltration of local
nerve, artery and vein, which run ventromedial to anaesthetic in the region of the SI joint and/or abnor-
the joint through the greater sciatic foramen. The mal radiopharmaceutical uptake in the SI region
joint has a fibrous capsule and is strengthened by include, in order of prevalence: canter quality worse
well-developed dorsal (dorsal and lateral portions), than trot when ridden; poor contact with bit; trunk
ventral and interosseous ligaments. The configura- stiffness during exercise; poor hindlimb impulsion;
tion of the joint, combined with the actions of these restricted flexibility of the thoracolumbar region;
reinforcing ligaments, enables the efficient trans- increased tension in the longissimus dorsi muscles;
mission of propulsive forces from the hindlimb to and bucking or kicking out with a hindlimb during
the axial skeleton. Pain from the SI joint or region is ridden canter. Many of these clinical signs were sig-
a fairly common diagnosis in horses with hindlimb nificantly more apparent when horses were ridden,
lameness, but it may be difficult to confirm and is highlighting the importance of seeing horses with
frequently a diagnosis of exclusion. possible SI pain under saddle. In one study, 14% of
horses diagnosed with SI pain in isolation displayed
Aetiology/pathophysiology a unilateral hindlimb lameness when ridden, indicat-
The true incidence of clinically significant SI ing that the SI region should be considered as a cause
pathology is unknown. Osteoarthritis of the SI joint of this presenting complaint.
is common and degenerative changes in the joints Affected horses may also have poor or asymmetric
have been found in a high proportion of horses in muscling. Asymmetric tubera sacrale are frequently
post-mortem studies. These changes include articu- encountered as an incidental finding and, contrary
lar surface lipping, cortical buttressing, articular to previous reports, are unusual in horses with con-
recession, osteophyte formation and peri- and intra- firmed SI region pain. Ninety-five percent of tubera
articular erosion. sacrale were grossly symmetrical in horses with SI
The most common soft-tissue injury of the SI pain in a recent study (Fig. 1.520). Only a small pro-
joint is desmitis of the SI ligaments, which some portion of horses with SI pain show an exaggerated
reports suggest may lead to joint instability and sub- response to the application of pressure over the tuber
luxation and contribute towards the development of sacrale. Most cases are presented when the condition
painful osteoarthritic changes. The dorsal portion is chronic and pain is unlikely to be seen on deep
of the dorsal ligament appears to be most commonly palpation over the SI joints.