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EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2018) 30 (2) 70-75 doi: 10.1111/eve.12627
Case Report
Computed tomography of nuchal ligament and semispinalis capitis tendon avulsions in a foal
M. T. Swarbrick*, S. E. Powell and E. F. Haggett Rossdale & Partners, Newmarket, UK. *Corresponding author email:
matt_swarbs@hotmail.com
Keywords: horse; nuchal ligament; computed tomography; foal; trauma
Summary Head trauma is a common injury in young horses. This case report describes a 10-week-old Thoroughbred foal with an open wound following trauma to the poll region, showing abnormal head carriage and depression. A computed tomography (CT) study was performed under general anaesthetic (GA). This identified a complete avulsion of the nuchal ligament (NL) and partial avulsions of the left and right semispinalis capitis (SS) tendons. Following diagnosis and conservative treatment the foal made a good recovery and 18 months later the filly had no detectable neurological or physical abnormalities. Computed tomography enabled an accurate and rapid diagnosis of a novel injury.
Introduction
The NL is a bilobed, elastic structure on the dorsal midline extending from the occipital bone to the first four thoracic dorsal spinous processes (Sisson 1914a; Gellman and Bertram 2002; Gellman et al. 2002; Dyson 2011a). Caudally the NL is directly continuous with the
supraspinous ligament (Sisson 1914a). The NL consists of two parts, the funicular and lamella and is surrounded by muscle, with the rectus capitis ventralis ventrally and the semispinalis capitis (SS) to either side (Sisson 1914a; Dyson 2011b). The SS is a large, structurally complex, pyramidal muscle
that originates from the second, third and fourth thoracic spines, the transverse processes of the first six or seven thoracic vertebrae and the articular processes of the cervical vertebrae (Sisson 1914b; Gellman et al. 2002; Dyson 2011b). Cranially, there is a strong, focal tendon which spreads into a wide aponeurosis inserting on the occipital bone just ventral to the nuchal crest. The tendon extends two-thirds the length of the muscle. Traumatic injuries to the head and poll are common in
horses (Ramirez et al. 1998; Feary et al. 2007), especially in foals and younger individuals (Little et al. 1985; Ragle et al. 1988; Ragle 1993; Feary et al. 2007). Trauma to this area can result in diverse pathologies (Ramirez et al. 1998) including fractures, haemorrhage, neurological signs and vestibular syndromes caused by traumatic brain injury (TBI) (Ragle 1993; MacKay 2004; Feary et al. 2007). The anatomy of the head and poll region is complicated
and presents a diagnostic challenge (Ragle 1993; Ramirez et al. 1998; Gollob et al. 2002). Radiography has been shown to have limited use in the assessment of traumatic injuries of the equine head (Ramirez et al. 1998; Feary et al. 2007; Kinns and Pease 2009). In a retrospective study of head trauma
with accompanying neurological signs the most common pathology was fracture of the basilar and temporal bones, which were identified in 15 of 34 horses (44%) (Feary et al. 2007). These fractures are commonly associated with poll impact injuries (MacKay 2004). The diagnostic limitations of radiography are confounded in younger animals due to copious open or incompletely fused sutures (Ramirez et al. 1998). CT facilitates the study of bony structures in highly
detailed, cross-sectional images without superimposition, as well as providing superior contrast for soft tissues compared with radiography and affords CT significant advantages in equine head trauma cases (Kinns and Pease 2009). There are relatively few publications concerning
pathology of the NL or the SS and no reports of damage to these structures in foals. This report describes the clinical presentation, CT findings, treatment and outcome of a foal that presented with neurological signs and altered head carriage following head trauma.
Case history
A 10-week-old Thoroughbred filly foal weighing 141 kg was referred to Rossdales Equine Hospital after sustaining trauma to the poll. The foal had reared over backwards and its poll and cranial neck had collided with a concrete manger. The referring veterinary surgeon reported that the foal had initially been in lateral recumbency but could stand with encouragement. The foal was stabilised with intravenous (i.v.) hypertonic saline, anti-inflammatories and antimicrobials and referred for further investigation and treatment.
Clinical findings
The foal was admitted approximately 2 h after the injury. On admission the foal was standing but depressed with a right- sided head tilt and a low head carriage. No additional abnormalities were detected on a full neurological examination. There was a small, full thickness skin wound just behind the wings of the atlas in the dorsal midline. There were no significant haematological or blood biochemical abnormalities. A 16 gauge polyurethane over-the-wire catheter was placed and i.v. fluid therapy with Lactate Ringers solution at a rate of 400 mL/h was initiated. The foal received flunixin (Cronyxin)1 i.v. at a dose of 1.1 mg/kg bwt, cefquinome (Cobactan 4.5%–5 mL)2 at a dose of 1.5 mg/kg bwt, butorphanol (Torbugesic)3 at 0.03 mg/kg bwt and 1000 iu vitamin E orally.
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