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The Veterinary Quarterly
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10.1080/01652176.2024.2403456
2403456
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Research Article
Research Article
Evaluation of the feasibility of equine in-vivo ultrasound technique for the medial branch of the dorsal ramus of the cervical spinal nerves
I. Nocera et al.
Veterinary Quarterly
Nocera Irene a
Di Franco Chiara bc
Sorvillo Benedetta b
Aliboni Benedetta d
Bucchioni Elena d
Sgorbini Micaela b
Sala Giulia b
Citi Simonetta b
a Sant’Anna School of Advanced Studies, Institute of Health Sciences, Pisa, Italy
b Department of Veterinary Sciences, University of Pisa, Pisa, Italy
c Institute of Clinical Physiology, National Research Council, Pisa, Italy
d Private Practitioner, Italy
CONTACT Irene Nocera irene.nocera@santannapisa.it Sant’Anna School of Advanced Studies, Institute of Health Sciences, Pisa, Italy
13 9 2024
2024
13 9 2024
44 1 15
26 5 2024
27 7 2024
5 9 2024
KnowledgeWorks Global Ltd.12 9 2024
published online in a building issue12 9 2024
© 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group
2024
The Author(s)
https://creativecommons.org/licenses/by-nc/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent.

Abstract

Ultrasound-guided local anaesthesia is commonly used in veterinary orthopaedics for horses. This study aimed to assess an in vivo ultrasound technique for the medial branch of the dorsal branch of the cervical spinal nerves (MB-DBCSNs) in horses and compare the performance of clinicians with different experience levels. Ten healthy, skeletally mature horses were examined using radiographic and ultrasound (US) techniques in the cervical area (C3–C7). Four operators with varying experience conducted US examinations using a 10 MHz linear and 6 MHz curvilinear transducer over ten training sessions. The number of cervical nerves visualized was recorded. A chi-square test was used to analyse the impact of training, anatomical location, and operator experience on the identification of facet joints. Operator agreement was evaluated with Cohen’s K test. The operators assessed 80 MB-DBCSNs, with radiographs and identified 70 healthy and 10 pathological facet joints. Training significantly improved visualization success, reaching 90% in later sessions. Cranial facet joints (C3–C5) were more frequently visualized (81%) than caudal ones (C5–C7) were (59%). US performance was influenced by the operator’s skill, and agreement among operators ranged from slight to fair. Overall, practice improved cervical nerve visualization in vivo, particularly for cranial nerves, but the technique requires a long learning curve because of low levels of operator agreement.

Keywords

Ultrasound
articular facet joint
cervical nerves
equine
The author(s) reported there is no funding associated with the work featured in this article.
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pmcIntroduction

In equine species, pain in the cervical area is recognized as a cause of neck pain, forelimb lameness, ataxia, poor athletic performance, and difficulty grasping food (Butler et al. 2017; García-López 2018; Denoix 2019; Story et al. 2021; Wood et al. 2021). The diagnostic process involves an orthopaedic examination, which includes neck flexion and palpation of the area of the cervical vertebrae to evoke a pain reaction. Diagnostic imaging helps identify any arthritic changes in the cervical vertebrae (Van Eerd et al. 2010; Haussler et al. 2019; Story et al. 2021).

However, diagnostic methods fail to establish a correlation between the severity of bony changes and the severity of symptoms or the exact source of pain (Bykowski and Wong 2012; Butler et al. 2017; García-López 2018). Moreover, radiographic assessment of the cervical area is challenging due to technical issues, such as superimposition, which occurs when structures in the X-ray path overlap, making it difficult to distinguish between them (Butler et al. 2017). Furthermore, grainy appearance from underexposure is often associated with the use of portable X-ray units (Butler et al. 2017), but is also due to individual anatomical variations (Van Eerd et al. 2010; Kim et al. 2019).

In humans, the identification of neck pain and the loco-regional (perineural) anaesthetic block of the medial branch of the dorsal branch of the cervical nerves (MB-DBCN) have been extensively investigated (Bykowski and Wong 2012; Hurdle 2016; Park et al. 2017; Manchikanti et al. 2020) and are usually associated with diagnostic imaging for correctly identifying which joint is the primary cause of pain (Hurdle 2016; Manchikanti et al. 2020). In humans, blocking the MB-DBCNs was proven to be the most reliable technique for identifying the articular process joint as a pain source (Bykowski and Wong 2012; Hurdle 2016).

Ultrasound (US)-guided intra-articular injection of the cervical articular facet joints (AFJ) is a minimally invasive technique used to perform diagnostic anaesthesia and deliver medication directly into the joint space in horses. However, the evidence behind its use is still an open issue (Nielsen et al. 2003; Birmingham et al. 2010). Pilot studies have described and evaluated the accuracy, time, and safety of US-guided perineural injection techniques for accessing the cervical nerves of horses (Corraretti et al. 2020; Touzot-Jourde et al. 2020; Fouquet et al. 2022). The perineural injection of the cervical ramus ventralis has been reported as a feasible technique that may have applications in multimodal analgesia for equine forelimb lameness (Touzot-Jourde et al. 2020; Fouquet et al. 2022). On the other hand, the MB-DBCNs contain both sensory and motor nerve fibres, which provide innervation of the AFJ, and are thought to be specifically involved in AFJ pathologies in horses (Fintl 2017). Corraretti et al. (2020) provided a detailed description of the US technique. They reported high accuracy for local infiltration of MB-DBCNs in an ex vivo study (Corraretti et al. 2020).

The aim of this study was thus to assess the feasibility of the US technique for MB-DBCNs in horses, and to compare performance between clinicians with different levels of experience.

Materials and methods

A cohort of 10 horses belonging to the Department of Veterinary Sciences, University of Pisa, were included in this study. The study was approved by the Institutional Animal Care and Use Committee of the University of Pisa (Prot. N. 45/23). All horses were housed in collective paddocks 24 h a day. They were fed meadow hay ad libitium along with commercial equine feed concentrate in line with the National Research Council energy recommendations (NRC, 2007). The horses were sound on orthopaedic examinations (AAEP, 1991) and healthy on neurological examinations (Furr and Reed 2015).

Horses underwent radiographic and US examinations of the cervical area. The horses were restrained in stock, in the weight-bearing position, with the neck in a neutral position and the forelimbs next to each other. Radiographic examination was performed for C3-C7 to categorize healthy and pathological AFJs in accordance with a previous study (Espinosa-Mur et al. 2021). Latero-lateral views for C3–C7 were obtained with a portable X-ray generator (Medical Econet, mod. Mex + 20BT lite), and acquired on a flat panel by an ‘Examion X-DR Portable Case M WiFi DT’ system. The images were analysed using commercial software (HorosTM-DICOM, https://horosproject.org) and then scored by an expert operator (S.C.).

For US examination, the area was prepared by thoroughly cleaning and applying alcohol and US gel to provide appropriate contact. US examination of MB-DBCSNs of C3-C7 AFJs was performed on both sides of the neck, and the right cervical area was always scanned first. The US technique used was described by Corraretti et al. (2020). The US technique consists of direct visualization of the transverse section of the MB-DBCSNs, detailed as follows (Corraretti et al. 2020): the AFJ was imaged with the transducer held perpendicular to the long axis of the cervical spine, then it was moved slightly caudal and rotated to image on the longitudinal axis the MB-DBCSN. It was tilted until the nerves and the dorsal ramus of the vertebral artery was identified in traverse view, running through the intermuscular fascia of the intertransversarii cervicis muscle.

The US image was considered successfully visualized when the MB-DBCSNs appeared as oval structures with small hypoechoic fascicles divided by hyperechoic perineurium (Corraretti et al. 2020). US was performed in real-time B-mode with a portable machine (MyLabSigma, Esaote, Italy); a 10 MHz linear array transducer with an image depth of 5 cm was used for the 3 to 5 MB-DBCSNs, and a 6 MHz curvilinear macroconvex transducer with depth of 6 cm for the 6 and 7 MB-DBCSNs.

To evaluate the feasibility of the US technique in vivo, four right-handed veterinarians with different levels of experience were involved in the study: two experienced clinicians (a resident equine veterinarian (operator A) and PhD equine veterinarian (operator B), graduated more than 5 years ago), and two junior clinicians (recent graduates in equine veterinary sciences (operators C and D)). The data collection was conducted in 10 one-hour training sessions, which were independently performed by each operator. All the operators were novices in the present described US technique. Preliminarily, each operator completed a training phase to obtain a high-quality image.

Statistical analysis

Statistical analyses were conducted using SPSS 29.0 statistical software for Mac (IBM, Armonk, USA). To assess whether training practice and anatomical location could influence the percentage of identified healthy facet joints, the chi-square test was performed. The level of statistical significance was set at a p-value < 0.05. Additionally, the US performance of each operator was assessed using a chi-square test, and the agreement among operators was evaluated using Cohen’s K test, both on the total number of analyzed facet joints and when divided by anatomical location. The interpretation of agreement was as follows: x < 0 none; 0.00–0.20 slight; 0.21–0.40 fair; 0.41–0.6 moderate; 0.61–0.80 substantial; 0.81–1.00almost perfect (Landis and Koch 1977).

Results

The horses included in the present study were aged between 4 and 22 years (median age: 11), their weights ranged between 480 kg and 600 kg (median 510), and their body condition scores were between 2 and 4 (median 3). On radiographic examination, 70/80 healthy AFJs were observed, whereas 8/80 showed mild osteoarthritic changes and 2/80 moderate osteoarthritic changes, according to radiological grading previously reported (Espinosa-Mur et al. 2021).

During the US examination, a total of 80 MB-DBCNs from 10 adult horses were evaluated by each operator, and all the nerves were displayed at least once.

The training practice significantly influenced the number of cervical nerves successfully visualized (p < 0,001), as reported in Table 1.

Table 1. Number of cervical nerves successfully visualized or not visualized by each operator, according to training sessions.

 	Training sessions	
1	2	3	4	5	6	7	8	9	10	
Operators	A	NV	4/6
67%	1/8
13%	1/6
17%	1/6
17%	2/8
25%	1/8
13%	0/6
0%	1/6
17%	1/8
13%	3/8
37%	
V	2/6
33%	7/8
88%	5/6
83%	5/6
83%	6/8
75%	7/8
88%	6/6
100%	5/6
83%	7/8
88%	5/8
63%	
B	NV	8/8
100%	7/8
88%	4/6
67%	4/8
50%	2/6
33%	3/6
50%	1/6
17%	2/8
25%	1/8
13%	0/6
0%	
V	0/8
0%	1/8
13%	2/6
33%	4/8
50%	4/6
67%	3/6
50%	5/6
83%	6/8
75%	7/8
88%	6/6
100%	
C	NV	4/6
67%	4/8
50%	1/8
13%	3/6
50%	1/8
13%	0/8
0%	0/6
0%	0/8
0%	0/6
0%	0/6
0%	
V	2/6
33%	4/8
50%	7/8
88%	3/6
50%	7/8
88%	8/8
100%	6/6
100%	8/8
100%	6/6
100%	6/6
100%	
D	NV	5/8
63%	4/8
50%	1/6
17%	2/6
33%	3/6
50%	1/6
17%	2/8
25%	0/6
0%	1/8
13%	4/8
50%	
V	3/8
37%	4/8
50%	5/6
83%	4/6
67%	3/6
50%	5/6
83%	6/8
75%	6/6
100%	7/8
88%	4/8
50%	
Total *	28	32	26	26	28	28	26	28	30	28	
* The total numbers refer to healthy cervical facets. Pathological facets were excluded from the statistical analysis. Legend: A, experienced operator A; B, experienced operator B; C, inexperienced operator C; D, inexperienced operator; NV, not visualized; V, visualized.

Visualization of the cervical nerves was not statistically influenced by the left or right neck side (p < 0,697); however, the number of cervical nerves in the cranial facet joints (C3–C5) was significantly greater than that in the caudal ones (C5–C7) (p < 0,001), as shown in Table 2.

Table 2. Number of cervical nerves successfully visualized or not visualized, according to anatomical location.

 	Cervical nerves	
Not Visualized	Visualized	Total *	
Localization	Cranial
(C3-C5)	26
19%	110
81%	136	
Caudal
(C5-C7)	59
41%	85
59%	144	
* The total numbers refer to healthy cervical facets. Pathological facets were excluded from the statistical analysis. Legend: C3–C5, cranial cervical vertebrae from 3–5 corresponding to the medial branch of the dorsal branch of the cervical nerves (MB-DBCNs); C5–C7, cranial cervical vertebrae from 5–7 corresponding to the medial branch of the dorsal branch of the cervical nerves (MB-DBCNs).

In addition, a significant difference was found between the different operators (p < 0.001): the best results were obtained for expert operator A (78.6%) and inexperienced operator C (81.4%).

The Cohen k test mostly showed slight-to-fair agreement in the evaluation of the reproducibility of the technique (Table 3).

Table 3. Agreement values related to four operators according to success in MB-DBCN visualization.

 	C3-C4	C4-C5	C5-C6	C6-C7	
A	B	C	D	
R	L	R	L	R	L	R	L	
C3-C4	A	R	–	–	xa	–	xa	–	xa	–	
L	–	–	–	0,39	–	xa	–	0,39	
B	R	xa	–	–	–	0,39	–	−0,2	–	
L	–	0,39	–	–	–	xa	–	0,5	
C	R	xa	–	0,39	–	–	–	−0,143	 	
L	–	xa	–	xa	–	–	–	xa	
D	R	x(a)	–	−0,2	–	−0,14	–	–	–	
L	–	0,39	–	0,5	–	xa	–	–	
C4-C5	A	R	–	–	xa	–	xa	–	xa	–	
L	–	–	–	xa	–	xa	–	xa	
B	R	xa	–	–	–	1	–	−0,17	–	
L	–	xa	–	–	–	xa	–	0,36	
C	R	xa	–	1	–	–	–	xa	–	
L	–	xa	–	xa	–	–	–	xa	
D	R	xa	–	−0,17	–	xa	–	–	–	
L	–	xa	–	0,36	–	xa	–	–	
C5-C6	A	R	–	–	0,14	–	−0,18	–	−0,18	–	
L	–	–	–	−0,30	–	xa	–	−0,09	
B	R	0,14	–	–	–	0,074	–	−0,30	–	
L	–	−0,30	–	–	–	xa	–	−0,03	
C	R	−0,18	–	0,07	–	–	–	xa	–	
L	–	xa	–	xa	–	–	–	xa	
D	R	−0,18	–	−0,30	–	0,05	–	–	–	
L	–	−0,09	–	−0,03	–	xa	–	–	
C6-C7	A	R	–	–	0,4	–	0,25	–	0,42	–	
L	–	–	–	0,25	–	0,4	–	0,46	
B	R	0,40	–	–	–	0,16	–	0,16	–	
L	–	0,25	–	–	–	0,46	–	0,16	
C	R	0,25	–	0,16	–	–	–	0,67	–	
L	–	0,4	–	0,46	–	–	–	0,67	
D	R	0,42	–	0,16	–	0,67	–	–	–	
L	–	0,46	–	0,16	–	0,67	–	–	
A, experienced operator A; B, experienced operator B; C, inexperienced operator C; D, inexperienced operator D; C3–C4, cervical vertebrae 3 and 4 corresponding to the medial branch of the dorsal branch of the cervical nerve (MB-DBCN); C4–C5, cervical vertebrae 4 and 5 corresponding to the MB-DBCN; C5–C6, cervical vertebrae 5 and 6 corresponding to the MB-DBCN; C6–C7, cervical vertebrae 5 and 6 corresponding to the MB-DBCN; xa. No statistics are computed because the operator is a constant; R, right MB-DBCNs; L, left MB-DBCNs. The interpretation of agreement is as follows: x < 0 none; 0.00–0.20 slight; 0.21–0.40 fair; 0.41–0.6 moderate; 0.61–0.80 substantial; 0.81–1.00almost perfect (Landis and Koch 1977).

Discussion

In the present study, the US technique previously proposed for visualization of MB-DBCNs (Corraretti et al. 2020) was applicable for our cohort of horses in vivo, and the findings revealed that a training period was necessary to improve the US technique in novice operators.

We found that all the nerves were correctly displayed at least once. However, our results show that training practice was fundamental to improving the number of MB-DBCNs successfully displayed: more than 75% of the nerves were correctly visualized in the latest training sessions. Moreover, no operators were able to correctly display all the cervical nerves during a single training session. Similar results were reported by Fouquet and colleagues. who found that the ventral nerve root branch was maximally localized in 89% of the sites in anaesthetized horses. The results highlighted that identifying and assessing the MB-DBCN through the US likely requires hands-on experience and specific training practices to refine operator skills over time (Wood et al. 2021; Fouquet et al. 2022).

Compared with cranial MB-DBCNs, we found that, caudal MB-DBCNs were significantly more difficult to visualize. This result agreed with that of Corraretti et al. who reported that caudal nerves are more difficult to identify and consequently to inject. The difference observed might be related to the anatomical features of the equine caudal cervical region, where the 6th and 7th cervical nerves are located deeper in muscle planes (such as the brachiocephalicus, omotransversarius, and serratus ventralis cervicis muscles).

However, our results are in contrast with other findings that reported that it is easier to focus the cervical nerves in the caudal part of the neck (Touzot-Jourde et al. 2020; Fouquet et al. 2022). This difference might be due to the different nerves viewed since both studies referred to the ventral branches of the cervical nerves, which are wider in the caudal neck region.

In terms of technique reproducibility, the results revealed slight-to-fair agreement between operators. US of the cervical area is widely used in clinical practice and focuses on the cervical vertebrae, facet joints, and paravertebral structures. However, equine practitioners might need to undergo specific training to understand the anatomy and structure of the cervical spinal nerves, which are quite complex and are not often assessed in routine clinical practice (Berg et al. 2003; Head 2022).

In horses, previous studies reported high reliability and accuracy in US visualization and injection of cervical nerve roots (Corraretti et al. 2020; Touzot-Jourde et al. 2020; Fouquet et al. 2022). However, the difference in operator performance was not evaluated since only one operator completed all the procedures. The AFJ and vertebral vessels are usually reported as landmarks to identify cervical nerve roots exiting the intervertebral foramen using US (Corraretti et al. 2020; Fouquet et al. 2022).

In other papers, direct visualization of the nerve was not found necessary to obtain good results, and other specific landmarks can be used (Cruz-Sanabria et al. 2021; Wood et al. 2021), although recent studies reported that the cervical nerve was localized before the needle was inserted to perform this procedure successfully and safely (Corraretti et al. 2020; Touzot-Jourde et al. 2020; Fouquet et al. 2022).

In our study, the US technique was based on the visualization of the AFJ and dorsal ramus of the vertebral artery as landmarks to systematically localize and easily recognize the MB-DBCNs, as previously described (Corraretti et al. 2020). Our results revealed a fair agreement between operators and that previous experience in the field did not significantly influence the US technique or performance since the best results were obtained from both experienced and inexperienced operators. The specific US training for the described technique appears to have a direct influence on the operators’ performance. This indicates that a longer training period is needed for most practitioners to become proficient in performing cervical nerve US for accurate scanning, despite varying experiences in diagnostic imaging (Berg et al. 2003; Head 2022).

Conclusion

In our study, US practices have gradually improved the successful visualization of MB-DBCNs in horses in vivo. In addition, the cranial cervical nerves were easier to identify than the caudal nerves. Nevertheless, the degree of agreement between operators with different levels of experience was low, which might be influenced by the long learning curve associated with the described US technique. non si capisce bene quali frasi riferiscono alla letteratura in generale e quali al vostro studio.

Authors’ contributions

Conception and design: Simonetta Citi, Micaela Sgorbini, Irene Nocera and Elena Bucchioni; analysis and interpretation of the data: Irene Nocera, Chiara Di Franco, Benedetta Aliboni, Benedetta Sorvillo, Elena Bucchioni, and Giulia Sala; drafting of the paper: Irene Nocera, Elena Bucchioni, Chiara Di Franco, Giulia Sala, Micaela Sgorbini, and Simonetta Citi; final approval of the version to be published: Simonetta Citi and Micaela Sgorbini. All the authors agree to be accountable for all aspects of the work.

Disclosure statement

No potential conflict of interest was reported by the author(s).
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