Ultrasonographic Technique and Normal Anatomic Features of the Sacroiliac Region in Horses

Abstract

The purpose of this study was to establish the normal percutaneous ultrasonographic appearance of anatomic structures within the equine sacroiliac region. Percutaneous ultrasonography was performed in a cranial-to-caudal direction in 10 normal adult live horses. The following structures were examined in detail: supraspinous ligament, lumbar and sacral spinous processes, thoracolumbar fascia and its caudal extension, tubera sacralia, ilial wings, dorsal and lateral portions of the dorsal sacroiliac ligaments, lateral part of the sacrum, and the lateral sacral crest. After ultrasonography, all animals were euthanized and detailed dissection of the lumbosacropelvic region was performed in six horses. Four lumbosacropelvic specimens were frozen and sectioned transversely for evaluation of cross-sectional anatomy. Gross anatomic findings were correlated with ante-mortem ultrasonographic images. On percutaneous ultrasonography, all horses had tubera sacralia with a mild-to-moderate roughened surface with occasional irregular hyperechoic mineralizations located within the apophyseal cartilage of younger horses. At the level of the tuber sacrale the caudal extension of the thoracolumbar fascia joined the dorsal portion of the dorsal sacroiliac ligament and assumed two different configurations relative to the dorsal portion of the dorsal sacroiliac ligament, with the predominant configuration of the thoracolumbar fascia located medial to the dorsal portion of the dorsal sacroiliac ligament. The less frequently encountered configuration had the thoracolumbar fascia positioned dorsal to the dorsal portion of the dorsal sacroiliac ligament. Caudal to the tuber sacrale the dorsal portion of the dorsal sacroiliac ligament and thoracolumbar fascia consolidated to form a single, fused structure with a common insertion on the sacral spinous processes. A large variability in linear fiber pattern, echogenicity (small focal hypoechoic areas), ligament height, and cross-sectional measurements was identified in the fused dorsal portion of the dorsal sacroiliac ligament and thoracolumbar fascia of normal horses. Diagnosing mild-to-moderate desmitis of the fused dorsal portion of the dorsal sacroiliac ligament and thoracolumbar fascia based solely on ultrasonography may therefore be difficult. To correlate ultrasonography with histology, samples of a fused dorsal portion of the dorsal sacroiliac ligament and thoracolumbar fascia with bilateral hypoechoic lesions were submitted for histology and revealed diffuse mild-to-moderate loss of fiber density, multifocal fibrocyte degeneration, and cartilagenous metaplasia with multifocal, mild myofiber mineralization, which was compatible with age-related changes. As controls, sections of ultrasonographically normal fused dorsal portion of the dorsal sacroiliac ligament and thoracolumbar fascia from three horses demonstrated similar but milder histologic findings, which were considered normal.

Review of injection techniques targeting the sacroiliac region in horses

“…The dorsal sacroiliac ligament consists of a dorsal and lateral portion. The dorsal portion of the dorsal sacroiliac ligament (D‐DSIL) is a cord‐like structure that originates on the dorsal aspect of the tuber sacrale , joins the thoracolumbar longissimus tendon and travels caudally to attach on the abaxial surface of the sacral spinous process apices (S2–S5; ; Engeli et al . 2004a, 2006).…”

“…The dorsal sacroiliac ligament consists of a dorsal and lateral portion. The dorsal portion of the dorsal sacroiliac ligament (D-DSIL) is a cord-like structure that originates on the dorsal aspect of the tuber sacrale, joins the thoracolumbar longissimus tendon and travels caudally to attach on the abaxial surface of the sacral spinous process apices (S2-S5; Fig 1; Engeli et al 2004aEngeli et al , 2006. The lateral portion of the dorsal sacroiliac ligament forms a thin, triangular sheet of connective tissue that spans from the caudal margin of each ilial wing to the lateral sacral crest where it inserts and is ventrally continuous with the sacrosciatic ligament.…”

“…Horses with desmitis of the superficially located D-DSIL might, however, have a palpable enlargement of the affected ligament with an associated pain response. Ultrasonography is furthermore used to compare the left and right D-DSIL for any changes in echogenicity, linear fibre pattern or cross-sectional area (Engeli et al 2004a(Engeli et al , 2006. Some clinicians have also found that horses affected by a unilateral sacroiliac ligament desmitis tend to show unilateral rather than bilateral pelvic limb lameness as is often noted in horses with SIJ osteoarthritis (Tomlinson et al 2003;S.…”

“…Sacroiliac disease often presents a diagnostic challenge for the equine practitioner and, in the past, diagnosis has relied on the exclusion of other causes of poor performance, back pain and pelvic limb lameness (Jeffcott et al 1985;Dyson et al 2001). Unfortunately, diagnostic imaging modalities such as radiography, percutaneous and transrectal ultrasonography, and nuclear scintigraphy are not reliable in identifying SID in horses or man (Jeffcott et al 1985;Slipman et al 1996;Tomlinson et al 2001;Erichsen et al 2002Erichsen et al , 2003Dyson et al 2003a,b;Haussler 2003;Engeli et al 2004aEngeli et al , 2006Gorgas et al 2007Gorgas et al , 2009Bathe et al 2010). In man, advanced diagnostic imaging modalities, such as magnetic resonance imaging (MRI) and computed tomography (CT), are used to image the SIJ in low back pain patients.…”

Radiographic Technique and Anatomy of the Equine Sacroiliac Region

“…Osteoarthritic changes at the sacroiliac joint and the lumbosacral and lumbar intertransverse joints are common and were seen in 36 of 36 Thoroughbred racehorses 2 . The clinical diagnosis of sacroiliac joint disease is imprecise as the signs are nonspecific and confirmation by intraarticular injection of analgesics is hindered by the inaccessibility of the joint 3–5 . Diagnostic imaging is helpful in the assessment of suspected sacroiliac disease.…”