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NOVEMBER 2022


a)


b)


Fig 10: (a) Lateral radiographic image of the thoracolumbar junction and lumbar area from the eighteenth thoracic vertebra to the third lumbar vertebra, showing a bone bridge over the L1-L2 articular process joints (APJs) (open arrowhead). L1: First lumbar vertebra. (b) Transverse ultrasound scan between the first and second lumbar vertebrae from the same horse. The bone bridge is located over the right L1-L2 APJ (arrowhead).


and acoustic gel should be used to improve contact and therefore quality of the image. In winter or in case of decreased image quality, an area ranging from 6 to 8 centimetres wide can be clipped on both sides of the median plane to improve ultrasound penetration. Transverse ultrasonographic images of the APJs are the


a) b)


Fig 11: (a) Lateral radiographic image of the thoracolumbar junction and cranial lumbar area from the eighteenth thoracic vertebra to the fourth lumbar vertebra, showing severe alteration of the bone density of the L2-L3 and L3-L4 articular process joints (APJs) with dorsal bone proliferation (open arrowheads). L1: First lumbar vertebra. (b) Transverse ultrasound scan between the second and third lumbar vertebra. There is a marked bone modelling of the right L2-L3 APJ with dorsal and ventral proliferation (arrowheads).


dorsocranially by a mammillary process, which is higher and more separated from the APJ space in the caudal thoracic area than in the lumbar area. The APJs are covered by the multifidus muscle, which has


multiple aponeuroses. This muscle is separated from the thick erector spinae muscle by an echogenic fascia. In the lumbar region, the lumbar part of the gluteus medius muscle overlaps part of the erector spinae muscle (Fig 2) (Barone, 2000b; Denoix, 2019).


Technique and normal images


Ultrasonographic examination of the APJs can be performed with a 3 to 6 MHz macroconvex transducer (Fig 3). Hot water


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most informative. The transducer is placed on a paramedian position perpendicular to the skin and the median plane (Fig 3) to obtain an overall spatial representation of the dorsal profile of the APJ. Thanks to the width of the ultrasound beam, an overview from the spinous processes to the transverse processes or ribs is imaged (Fig 4). The joint space separating the two APs can be identified as a small anechoic gap between the caudal and cranial APs. The caudal AP from one vertebra is adjacent to the median plane and the cranial AP of the following vertebra is located laterally to it (Fig 4). In the thoracic area, the joint space is difficult to image because of the close proximity of the APJs to the tall spinous processes of this region (Fig 5). The bone surface of the APs appears as a smooth, regular hyperechogenic line. The mammillary processes are seen dorsal to the cranial APs on their lateral aspect (Figs 4 and 5). A complete cross-section of the dorsal profile of the


intervertebral joint can be obtained when the left and right sides are displayed symmetrically on the screen of the machine. The purpose of this approach is to compare the caudal and cranial APs, as well as the joint space of each APJ on both sides. Identification of the thoracolumbar junction is an important step to identify precisely which APJs are imaged. Identifying the correct vertebral segment can be accomplished by progressing caudally from the last rib


(demonstrates a convex hyperechoic bone surface) to the first transverse process (demonstrates a flat hyperechoic bone surface). This is T18-L1. Each following or preceding joint can be identified by counting either cranially or caudally. Then, precise imaging of the thoracic and lumbar APJs can be performed (Figs 5–7).


Findings and lesions


Abnormal findings of the APJs identified with ultrasound are associated with different manifestations of osteoarthritis. For the above-mentioned anatomical reasons, their identification is easier in the lumbar spine and include: left to right asymmetry of the APJs with increased size on one side (Fig 8);


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