Gait abnormalities caused by selective anesthesia of the suprascapular nerve in horses

Abstract

Objective—To assess gait abnormalities associated with selective anesthesia of the suprascapular nerve (SSN) achieved by use of perineural catheterization and thereby determine the function of that nerve as it relates to gait in horses. Animals—3 adult horses with no preexisting clinically apparent lameness at a walk. Procedure—Each horse was anesthetized; the right SSN was exposed surgically for placement of a perineural catheter to permit delivery of 1 mL of 2% mepivacaine hydrochloride. Six hours after recovery from anesthesia, each horse was videotaped while walking (50-step data acquisition period) before and after administration of mepivacaine. Videotapes were reviewed and the proportion of abnormal steps before and after selective SSN anesthesia was assessed. A step was considered abnormal if a marked amount of scapulohumeral joint instability (ie, lateral luxation of the proximal portion of the humerus) was observed during the weight-bearing phase of the stride. Results—Clinically apparent gait dysfunction was detected in all 3 horses following perineural administration of the local anesthetic agent. Anesthesia of the SSN resulted in scapulohumeral joint instability as evidenced by consistent lateral excursion of the shoulder region during the weight-bearing phase of gait at a walk. The proportion of abnormal steps before and after SSN anesthesia was significantly different in all 3 horses. Conclusions and Clinical Relevance—These data support the role of the SSN in shoulder joint stability in horses and define SSN dysfunction as 1 mechanism by which the syndrome and gait dysfunction clinically referred to as sweeny may develop.

Evaluation of the optimal plate position for the fixation of supraglenoid tubercle fractures in warmbloods

“…Anatomical variation of the course of the suprascapular nerve has been suggested by other authors (14). In our cadaveric scapulas, the location and course of the suprascapular nerves were uniform and independent of horse's age or scapula left or right side.…”

Catastrophic scapular fractures in Californian racehorses: Pathology, morphometry and bone density

“…Comminution between the proximal and distal major fragments would likely compromise stability of the interface between these fragments. Suprascapular nerve function could be compromised due to the nerve's location adjacent the scapular neck (Devine et al . 2006).…”

Quantitative motor unit action potential analysis of supraspinatus, infraspinatus, deltoideus and biceps femoris muscles in adultRoyalDutch sport horses

“…In quadrupeds, the shoulder muscles contract during the weightbearing phase of every stride to stabilise the scapulohumeral joint. The SS and IS muscles are innervated by the suprascapular nerve, and its perineural anaesthesia results in marked shoulder instability, with lateral luxation of the proximal humerus during weightbearing . Repetitive loading of SS and IS muscle fibres leads to hypertrophy and increased cross‐sectional area, which in turn results in increased MUAP amplitude.…”