# Multi-Detector Helical Computed Tomography, Transrectal Ultrasonography, and Histology of the Sacroiliac Joint: A Comparative Study in Adult Warmblood Horse Cadavers

## TL;DR

This study compared imaging techniques and histology in horse sacroiliac joints, finding common structural changes that may be part of normal aging or training adaptation.

## Contribution

The study provides a comparative analysis of transrectal ultrasonography, CT, and histology in equine sacroiliac joints, revealing correlations between imaging and degenerative changes.

## Key findings

- Computed tomography showed abnormalities in all 25 joints, with the most severe changes in the caudal third.
- Histological analysis confirmed degenerative changes in cartilage, subchondral bone, and joint capsule.
- Strong correlations were found between CT findings and histology, but not between ultrasound and CT grades.

## Abstract

Sacroiliac joint (SIJ) disease is a common cause of poor performance in horses, but diagnosis is challenging due to the joint’s deep anatomical location. A common diagnostic method is transrectal ultrasound and nuclear scintigraphy. Newer techniques, such as computed tomography, may provide a more complete evaluation, but their diagnostic value in assessing the sacroiliac joint in horses is still unclear. This study evaluated 25 sacroiliac joints of 15 adult Warmblood horses without reported pain using post-mortem transrectal ultrasonography, computed tomography, and histological examination. All joints showed structural changes on computed tomography, and most also presented abnormalities on ultrasonography. The most severe changes were observed in the caudal third of the joint, which is the region accessible by transrectal ultrasonography. Histological analysis revealed degenerative changes in the articular cartilage, subchondral bone, and joint capsule. Horses with more pronounced imaging abnormalities also showed corresponding degenerative changes on histology. The results indicate that structural changes in the sacroiliac joint are common in owner-perceived sound horses and may be part of normal ageing or adaptation to training. Future studies are essential to compare the diagnostic imaging findings of SIJs in asymptomatic and symptomatic horses, to elucidate the clinical relevance of these findings.

This study described, assessed and correlated ultrasonographic, computed tomographic, and histological findings in the sacroiliac joints of adult Warmblood horse cadavers. In total, 25 joints from 15 horses were examined post-mortem using transrectal ultrasonography and helical computed tomography. Findings on computed tomography were graded in the caudal joint third (caudally) and for the entire joint as mild, moderate, or severe. In total, 11 joints from nine horses were evaluated histologically. All joints (100%) showed abnormalities on computed tomography, and 92% (23/25) displayed abnormal ultrasonographic findings. The most common ultrasonographic findings were osteophytes (92%), joint effusion (76%), and sacral/iliac bone modeling (76%). Computed tomography revealed osteophytes (92% caudally, 100% overall), sclerosis (72% caudally, 88% overall), subchondral bone lesions (60% caudally, 88% overall), and enthesophytes (60% caudally, 68% overall). The most severe CT findings occurred caudally (44%), whereas 24% occurred cranially,16% in the mid portion of the SIJ, and 16% were multifocally present in the SIJ Histological analysis showed degenerative changes in the cartilage, subchondral bone, and the joint capsule. Horses with more pronounced imaging abnormalities also showed corresponding histological degeneration. Significant correlations were found between computed tomographic findings caudally and in the entire joint (rs = 0.915, p < 0.001, n = 25), and between imaging and histological findings (computed tomography: rs = 0.731, p = 0.011, n = 11; ultrasonography: rs = 0.67, p = 0.024, n = 11). Non-significant correlations were observed between mean ultrasonographic and computed-tomographic grades (rs = 0.35, p = 0.087, n = 25). Findings suggest these structural changes may reflect adaptation to joint loading. Transrectal ultrasonography appears suitable as a first-line diagnostic tool. However, future studies are essential to compare the diagnostic imaging findings of SIJs in asymptomatic and symptomatic horses to elucidate their clinical relevance.