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EQUINE VETERINARY EDUCATION


Equine vet. Educ. (2022) 34 (7) 342-345 doi: 10.1111/eve.13572


Clinical Commentary


Equid elbow luxation and subluxation: Anatomical review and case management considerations


E. M. Collar Department of Large Animal Clinical Science, University of Tennessee College of Veterinary Medicine, Knoxville, Tennessee, USA Corresponding author email: collarvet@gmail.com


Keywords: horse; cubital joint; luxation; subluxation; reduction; elbow


Although elbow luxation or subluxation in equids is rare, a sufficient number of case reports have accumulated in the literature to allow for meta-analysis (Table 1), with the goal of providing a better overall understanding of occurrence, treatment options, and prognosis (Collar et al., 2021; Crawley & Grant, 1986; Daradka et al., 2020; Fridel et al., 2022; Hu et al., 2007; Jalim et al., 2009; Jones, 1995; Levine & Meagher, 1980; Rubio-Martinez et al., 2008; Trostle et al., 2001). A recent case report by Fridel et al. (2022) describes a promising surgical option for stabilisation of the equid elbow joint after collateral ligament rupture utilising bone anchors and FiberTape, and adds to the overall understanding of prognosis in these cases. Appropriate decision-making in clinical management of


individual cases of elbow joint luxation requires a review of the relevant anatomy. The elbow joint is classified as a hinge joint, and the osseous structure of the joint comprises the humerus, radius and ulna. The anconeal process and trochlear notch of the ulna closely interdigitate with the humerus within a large fossa at the caudodistal aspect of the humerus created by the lateral condyle, much larger medial condyle, and an enlarged medial epicondyle that extends significantly further caudal than the lateral epicondyle. This interdigitation, along with support from medial and lateral collateral ligaments, allows for movement in only the sagittal plane. There is some disagreement among textbooks regarding the anatomy of the collateral ligaments. Two texts (Barone, 1986; Tnibar et al., 2001) describe or reference three parts to the medial collateral ligament: cranial deep, caudal deep and long superficial parts. More frequently, texts describe two parts: a short, deep part that inserts on the radial tuberosity which is located on the cranial, proximal aspect of the radius, and a long, superficial part that inserts on the radius just distal to the interosseous space between the radius and ulna (Dyce et al., 2009; Dyson, 2011; Kidd et al., 2014; Nelson & Goodrich, 2014). The lateral collateral ligament is also variably described as having: two parts (superficial, vertical and deep, short, oblique) (Barone, 1986; Tnibar et al., 2001); spiral fibres with two portions (deep and superficial) (Kidd et al., 2014); or one part (Dyson, 2011; Fails, 2020). Some texts comment that the medial collateral ligament is thin, while the lateral collateral ligament is a stout, stronger ligament (Kidd et al., 2014; Tnibar et al., 2001). The joint capsule is adherent to and blends with both medial and lateral collateral ligaments, making joint capsule injury inevitable in cases of collateral ligament rupture. The biceps brachii and brachialis muscles constitute the


flexor muscles of the elbow. Extension of the elbow joint is primarily accomplished by the triceps, tensor fasciae


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antebrachia and the anconeus. The radial nerve innervates the elbow extensors, and the musculocutaneous nerve and a contribution from the radial nerve innervate the elbow flexors. Additional anatomy that should be considered when planning case assessment and treatment includes the close association of the median nerve and the brachial and median arteries which lie superficial and just caudal to the medial collateral ligament. The transverse pectoral muscle overlies these structures, making palpation and assessment of the medial collateral ligament difficult. The large medial condyle and epicondyle of the humerus and additional overlying musculature add significant stability and protection to the medial aspect of the joint, while a more robust lateral collateral ligament provides added stability to the lateral aspect of the joint. When the elbow is extended, the anconeal process is


anchored in the fossa of the caudodistal aspect of the humerus. In small animals in particular, luxation is only considered possible when the limb is flexed beyond 45 degrees (Slatter, 2003; Tobias & Johnston, 2013), and the described procedure for closed reduction of elbow luxation includes flexion of the joint beyond 90 degrees (Fridel et al., 2022; Slatter, 2003; Tobias & Johnston, 2013). However, elbow luxation with concurrent ulna fracture, referred to as Monteggia fracture, is thought to occur during weight bearing or extension of the elbow joint (Slatter, 2003). It is likely that, in horses, the interdigitation of the humerus, radius and ulna protects the joint from re-luxation after reduction, dependent on degree of soft tissue injury (Collar et al., 2021; Levine & Meagher, 1980; Trostle et al., 2001). After anatomic reduction, maintenance of the limb and joint in extension also likely provides increased stability and decreased risk of re-luxation (Collar et al., 2021; Jones, 1995) and should be encouraged in case management when possible. During extensive literature review, 16 cases of elbow joint


luxation were found in the current body of literature (Table 1). Of these 16 equids, 8 equids were <12 months of age and 8 equids were >12 months of age (Arnbjerg, 1969; Bottegaro et al., 2017; Collar et al., 2021; Crawley & Grant, 1986; Daradka et al., 2020; Fridel et al., 2022; Hu et al., 2007; Jalim et al., 2009; Janicek, 2005; Jones, 1995; Levine & Meagher, 1980; Nixon, 2019; Rubio-Martinez et al., 2008; Senior et al., 2002; Trostle et al., 2001). Seven cases included concurrent fracture of the ulna (Monteggia fracture) (Arnbjerg, 1969; Daradka et al., 2020; Jalim et al., 2009; Janicek, 2005; Levine & Meagher, 1980; Nixon, 2019; Trostle et al., 2001), and 9 cases of luxation had no accompanying fracture (other than possible fragmentation of the anconeal process) (Bottegaro et al., 2017; Collar et al., 2021; Crawley & Grant, 1986; Fridel


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