- Along the ventral periarticular margin of the right sacroiliac joint, moderate to marked osteophyte formation is identified. Similar but moderate osteophyte formation is seen along the periarticular margins of the left sacroiliac joint.
Ventral sacroiliac ligament (*)
Conclusions:
- Moderate to marked osteoarthrosis, right sacroiliac joint
- Moderate osteoarthrosis, left sacroiliac joint
A little bit more…
Transrectal US
- Diagnosing sacroiliac region pain in horses is challenging due to the complexity of the axial skeleton and pelvis. Although feasible in foals or miniature horses, radiography is rarely used because of technical limitations in mature horses. Nuclear scintigraphy plays a key role in evaluating sacroiliac pain, though its accuracy can be affected by factors like patient movement, camera positioning, and muscle asymmetry. Ultrasound is particularly valuable for assessing joint margins, the lumbosacral intervertebral disc and nerve roots. However, an accurate diagnosis relies heavily on proper imaging technique and a strong understanding of normal regional anatomy (Bergman et al.).
- The equine sacroiliac joint is a complex structure composed of a flat synovial joint with hyaline cartilage on the sacral side and fibrocartilage on the iliac side. It lies deep beneath the iliac wing, between the auricular surfaces of the ilium and sacrum, which are typically L-shaped and oriented caudoventrally (Tallaj et al.).
- The joint is stabilized by three major ligaments:
- Ventral sacroiliac ligament – runs mediolaterally along the ventral margin.
- Interosseous sacroiliac ligament – a strong, fat-separated structure connecting the sacral and iliac wings.
- Dorsal sacroiliac ligament – attaches to the tuber sacrale and sacral crests, divided into funicular and membranous parts.
- These ligaments form a robust support system, allowing minimal movement (1–2° of nutation and counternutation) while transmitting force from the hind limbs to the spine. Muscles such as the gluteals, erector spinae, and psoas also contribute to joint stability (Tallaj et al.).
- Neurovascular structures near the joint include the cranial gluteal artery and vein, sciatic and gluteal nerves, and the ventral ramus of the first sacral nerve. The iliopsoas muscle overlays the joint laterally (Tallaj et al.).
- Pelvic conformation varies by sex, with females having a broader, rounder pelvic inlet compared to males (Tallaj et al.).
- Diagrams of regions imaged with associated images from presented case:
- Abnormalities of the ventral SI joint, which may be detected with ultrasound include (Tallaj et al.):
- Osteophytes around the joint may occur, often accompanied by narrowing of the sacroiliac joint space and changes in the shape of the sacral or iliac wings.
- Changes in the ventral sacroiliac ligament may include thickening, reduced size, or altered echogenicity, indicating desmopathy.
- Enthesopathy at the ligament attachment site, especially where the ligament connects to the ilium, may be observed.
- Rupture of the ventral sacroiliac ligament can lead to dislocation of the sacroiliac joint and an increased gap between the sacrum and ilium.
- Fractures of the sacral or iliac wings, whether due to trauma or repetitive stress (fatigue), may appear as breaks in the normally hyperechogenic bone surface
- Osteoarthrosis is the most frequently identified abnormality in horses experiencing sacroiliac pain; however, its clinical relevance remains uncertain.
- A grading system from 1 to 4 has been suggested to denote the severity of lesions based on degree of osteophytosis and subsequent deformation of the ventral sacroiliac ligament (Tallaj et al.).
- Treatment may include SI injections, shockwave, acupuncture, controlled exercises, rest and NSAIDs.
References
- Tallaj A, Coudry V, Denoix JM. Transrectal ultrasonographic examination of the sacroiliac joints of the horse: technique and normal images. Equine Veterinary Education. 2019 Dec;31(12):666-71.
- Bergman EH, Puchalski SM, Denoix JM. How to perform a transrectal ultrasound examination of the lumbosacral and sacroiliac joints.
- Tallaj A, Coudry V, Denoix JM. Transrectal ultrasonographic examination of the sacroiliac joints of the horse: abnormal findings and lesions. Equine Veterinary Education. 2020 Jan;32(1):33-8.
- Kersten AA, Edinger J. Ultrasonographic examination of the equine sacroiliac region. Equine veterinary journal. 2004 Nov;36(7):602-8.
- Engeli E, Yeager AE, Erb HN, Haussler KK. Ultrasonographic technique and normal anatomic features of the sacroiliac region in horses. Veterinary Radiology & Ultrasound. 2006 Jul;47(4):391-403.
- Espinosa P, Benoit P, Salazar I, de la Fuente J, Heiles P. Transrectal ultrasonography of equine lumbosacral nerves: pilot study in 28 healthy Warmblood horses. Veterinary Radiology & Ultrasound. 2017 Mar;58(2):228-36.
