Arthroscopic anatomy of the equine cervical articular process joints M. PEPE*, M. ANGELONE, R. GIALLETTI, S. NANNARONE and F. BECCATI Centro di Studi del Cavallo Sportivo, Dipartimento di Patologia, Diagnostica e Clinica Veterinaria, University of Perugia, Italy. *Correspondence email: mpepe@unipg.it; Received: 01.12.12; Accepted: 12.05.13 Summary Reason for performing study: Although arthropathy of the cervical articular process joints (APJs) is common, descriptions of the arthroscopic technique of the cervical APJ have not been reported previously. Objectives: To develop an arthroscopic approach to the APJ and to describe the arthroscopic anatomy of the APJ. Study design: Descriptive cadaver study and clinical case report. Methods: The regional anatomy was reviewed and the technique developed on fresh cadaver necks. A series of cadaveric APJ arthroscopies from C2–C3 to C6–C7 were performed to evaluate the procedure, which was then used in 3 clinical cases. A description of the procedure and the potential complications encountered were recorded. Results: The equine APJ consists of cranioventral and caudodorsal recesses; a single entry point at one of these recesses enables almost complete evaluation of cartilage surfaces and the synovial membrane and its villi. Successful entry into both APJ recesses was achieved in 22 cadaveric APJs and 5 APJs in the 3 clinical cases operated upon. An instrument portal was created to assess the feasibility of surgical arthroscopy. Complications were minor, and dissection of the APJs following the arthroscopic exploration revealed that the cartilage and periarticular neurovascular structures were not damaged during the procedure. Conclusions: This study shows that arthroscopic examination of the APJs of equine cervical vertebra is feasible and can be performed in mature horses. Arthroscopy of the APJs may provide additional diagnostic information compared to conventional diagnostic techniques. Keywords: horse; cervical facet joint; arthroscopy; surgery; cervical spine Introduction The equine cervical articular process (or ‘facet’) joints (APJs) are affected by several disorders [1–4]. In horses, cervical arthropathy has been documented as a cause of neck pain, neck stiffness, episodes of neck fixing, ataxia [5–9] and, less frequently, forelimb lameness [3,8–12]. Cervical arthropathy is usually detected with radiography [2,7], ultrasonography [13] and nuclear scintigraphy [14], but sometimes it can be difficult to interpret the results of these imaging modalities owing to individual variations, and because they allow only a partial study of the various structures of these joints. In the last 25 years, arthroscopy has become a useful tool for diagnosing and treating a variety of articular disorders in horses, and today it can be considered to be one of the most useful techniques in equine joint surgery [15]. It has also been proven to provide more anatomical detail of the cartilage and other synovial structures [16–18]. The equine cervical APJs are subject to developmental defects, osteochondrosis, fractures and degenerative joint disease [1,2,4], and therefore the development of a technique for investigating APJs is warranted. Arthroscopy of the APJs has not been reported in horses. Therefore, the purposes of the present study were to: 1) develop an arthroscopic approach to the equine cervical APJs; 2) describe the type of instruments to use; 3) describe the arthroscopic anatomy of the equine cervical APJ surfaces; 4) assess the features of APJ arthropathy; and 5) determine the limitations of this arthroscopic procedure. We hypothesised that access to the cervical APJs could be achieved using the current equine arthroscopic instrumentation via a lateral neck approach and that exploration and surgical manipulation of the articular structures would be possible. Materials and methods Pilot study A pilot study was performed on 3 horses (age 5–12 years; weight 400–580 kg) humanely subjected to euthanasia for reasons unrelated to this study and without a previous diagnosis of neck pathology. The necks were separated from the trunks at the level of the third thoracic vertebra. An accurate dissection of skin, subcutaneous tissue, Mm. cutaneous colli, M. omotransversarius, M. serratus ventralis cervicis, M. splenius cervicis, M. longissimus cervicis, intertransversarii ventralis cervicis and Mm. multifidi was performed to verify the exact location of the cervical APJ from C2–C3 to C6–C7, the possibility for fluid distension of each APJ, to assess how lateral and ventral flexion of the neck change the spatial relationships of the facets, to identify the articular recess of APJ for the arthroscopic portal locations, to assess the type of arthroscopic instruments to use, and to determine the proximity of neurovascular structures. Cadaveric study The cadaveric study was performed on 6 fresh necks collected from 6 horses (3 mares and 3 geldings of different breeds: mean age 12.3 years; range 3–20 years), weighing a mean of 503 kg (range 425–640 kg), subjected to euthanasia for reasons unrelated to this study. The necks were separated from the trunks at the level of the third thoracic vertebra. The necks were positioned randomly in right or left lateral recumbency, with a slight ventroflexion of the cervical spine and mild lateral flexion using a rest located between the necks and the surgery table. The area corresponding to the cervical vertebrae (C1–C7) was clipped and cleaned. For each cervical vertebra, landmarks for the identification of the APJs were developed by palpation of the transverse processes, and two 18 gauge 38 mm needles were inserted perpendicularly to the skin to mark the cranial and caudal borders of the transverse process of the cranial cervical vertebrae of each APJ being investigated. On the basis of the pilot study, the cranioventral articular recess was situated 3–4 cm dorsal to the caudal border of the dorsal tubercle of the transverse process. Ultrasonography of APJs was used to calculate the depth of the joint recesses from the skin. A 21 gauge 7 cm needle was introduced 3–5 cm dorsal to the caudal border of the dorsal tubercle of the transverse process into the cranioventral articular recess under ultrasound control. Joint distension was achieved with 12–20 ml of sterile lactated Ringer’s solution to facilitate arthroscope insertion. A 10 mm skin incision with a No. 21 blade was made that corresponded with the position of the needle Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12112 345 Equine Veterinary Journal 46 (2014) 345–351 © 2013 EVJ Ltd