Ultrasound-guided periarticular injections of the sacroiliac region in horses: A cadaveric study

Reasons for performing study: The traditional techniques for injection of the sacroiliac (SI) region are based on external landmarks. Because of the depth of the SI joint and pathological modifications, SI injections are sometimes challenging in horses. Hypothesis: An ultrasound-guided technique would allow placement of the needle without depending on external landmarks. Methods: Fourteen pelvic specimens were isolated from mature horses. A 20 cm bent spinal needle was positioned with ultrasonographic guidance under both iliac wings aiming for SI joints using 5 approaches: cranial, craniomedial, medial and 2 caudal approaches. The length of needle inserted was recorded and 2 ml of latex injected. The distance from latex to the closest sacral articular margin, the contact between latex and the SI interosseous ligament or the contact with the neurovascular structures emerging from the greater sciatic foramen were recorded at the time of dissection. Results: Latex was identified under the iliac wing in all injections but one. The distance from the latex to the closest sacral articular margin was significantly shorter (P = 0.02) for the 2 caudal approaches compared to the cranial, craniomedial and medial approaches. Contact between latex and the SI interosseous ligament was significantly more frequent (P = 0.01) with the cranial, craniomedial and medial approaches (38/73) compared to the caudal approaches (1/24). Contact between latex and the neurovascular structures was significantly less frequent (P = 0.005) for the cranial and craniomedial approaches (0/47) compared to the medial and caudal approaches (8/60). Four erratic injections were encountered. Conclusions: Ultrasonographic guidance allowed the needle to engage under the iliac wing without being dependent on external landmarks. The caudal approaches allowed deposition of liquid extremely close to the SI joint although retroperitoneal injections occurred. Clinical relevance: Each approach has advantages/drawbacks that could be favoured for selected purposes, but additional work is required to evaluate them on clinical cases.