History
A 3-year-old Thoroughbred mare in race training was evaluated because of a persistent grade 2/5 left forelimb lameness. Lameness examination failed to result in localization of heat, signs of pain, or swelling in the left forelimb. Flexion tests of the metacarpophalangeal and carpal joints were negative, and there was no sensitivity to the application of hoof testers. Diagnostic nerve blocks of the distal aspect of the forelimb, including the palmar digital, abaxial sesamoid, and low 4-point block sites, and intra-articular anesthesia of the radiocarpal and intercarpal joints failed to resolve the lameness. Because of the inability to localize the source of the lameness to the distal aspect of the forelimb, nuclear scintigraphy was recommended. Nuclear scintigraphy of the whole body was performed, with an additional soft tissue phase focused on the suspensory ligaments of the forelimbs (Figure 1).
Bone-phase nuclear scintigraphic images of the shoulder joints of a 3-year-old Thoroughbred mare in race training that had a persistent grade 2/5 left forelimb lameness. Images were obtained 3 hours after IV administration of tech-netium Tc 99m medronate. A—Lateromedial image of the left shoulder joint and humerus. B—Lateromedial image of the right shoulder joint and humerus. C—Cra-niocaudal image of the left shoulder joint. D—Cranio-caudal image of the right shoulder joint.
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Bone-phase nuclear scintigraphic images of the shoulder joints of a 3-year-old Thoroughbred mare in race training that had a persistent grade 2/5 left forelimb lameness. Images were obtained 3 hours after IV administration of tech-netium Tc 99m medronate. A—Lateromedial image of the left shoulder joint and humerus. B—Lateromedial image of the right shoulder joint and humerus. C—Cra-niocaudal image of the left shoulder joint. D—Cranio-caudal image of the right shoulder joint.
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Bone-phase nuclear scintigraphic images of the shoulder joints of a 3-year-old Thoroughbred mare in race training that had a persistent grade 2/5 left forelimb lameness. Images were obtained 3 hours after IV administration of tech-netium Tc 99m medronate. A—Lateromedial image of the left shoulder joint and humerus. B—Lateromedial image of the right shoulder joint and humerus. C—Cra-niocaudal image of the left shoulder joint. D—Cranio-caudal image of the right shoulder joint.
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Abnormal scintigraphic findings include a moderate, focal, ill-defined increase in radiopharmaceutical uptake at the distal aspect of the left scapula. At the level of the supraglenoid tubercle, the bone contour cranial to the left shoulder joint appears abnormal (Figure 2). Differential diagnoses on the basis of nuclear scintigraphic findings include avulsion fracture of the supraglenoid tubercle, severe degenerative disease of the shoulder joint, biceps origin tendonitis, or bicipital bursitis.
Same bone-phase nuclear scintigraphic images as in Figure 1. Notice an increase in radiopharmaceutical uptake in the distal aspect of the left scapula (A; arrows), compared with that of the right scapula (B), at the level of the supraglenoid tubercle. Notice the similar increase in radiopharmaceutical uptake in the cranial aspect of the left shoulder joint (C; arrows), compared with that of the right shoulder joint (D). In both images of the right shoulder joint (B and D), radiopharmaceutical uptake is considered normal.
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Same bone-phase nuclear scintigraphic images as in Figure 1. Notice an increase in radiopharmaceutical uptake in the distal aspect of the left scapula (A; arrows), compared with that of the right scapula (B), at the level of the supraglenoid tubercle. Notice the similar increase in radiopharmaceutical uptake in the cranial aspect of the left shoulder joint (C; arrows), compared with that of the right shoulder joint (D). In both images of the right shoulder joint (B and D), radiopharmaceutical uptake is considered normal.
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Same bone-phase nuclear scintigraphic images as in Figure 1. Notice an increase in radiopharmaceutical uptake in the distal aspect of the left scapula (A; arrows), compared with that of the right scapula (B), at the level of the supraglenoid tubercle. Notice the similar increase in radiopharmaceutical uptake in the cranial aspect of the left shoulder joint (C; arrows), compared with that of the right shoulder joint (D). In both images of the right shoulder joint (B and D), radiopharmaceutical uptake is considered normal.
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Radiographic images of the left shoulder joint, including mediolateral and craniomedial-caudolateral oblique images, were obtained (Figure 3). The supraglenoid tubercle of the left scapula was fractured and displaced in a cranial and distal direction. The fracture fragment was approximately 8 cm in height by 7.5 cm in width, involving both the epiphysis of the supraglenoid tubercle and coracoid process and the epiphysis of the cranial aspect of the glenoid cavity. The fracture margins were smooth and rounded and highly irregular in shape and involved the shoulder joint at the margin of the scapula. There was also remodeling of the greater tubercle of the humerus. The radiographic findings were indicative of a chronic nonunion or fibrous malunion articular fracture of the left supraglenoid tubercle.
Mediolateral (A) and craniomedial-caudolateral oblique (B) radiographic images of the left shoulder joint of the horse in Figure 1. Notice the cranial and dorsal displacement of the supraglenoid tubercle fracture fragment (arrows) and rounded fracture margins (arrowhead).
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Mediolateral (A) and craniomedial-caudolateral oblique (B) radiographic images of the left shoulder joint of the horse in Figure 1. Notice the cranial and dorsal displacement of the supraglenoid tubercle fracture fragment (arrows) and rounded fracture margins (arrowhead).
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Mediolateral (A) and craniomedial-caudolateral oblique (B) radiographic images of the left shoulder joint of the horse in Figure 1. Notice the cranial and dorsal displacement of the supraglenoid tubercle fracture fragment (arrows) and rounded fracture margins (arrowhead).
Citation: Journal of the American Veterinary Medical Association 250, 3; 10.2460/javma.250.3.275
Ultrasonographic evaluation of the left shoulder joint area was performed to assess the associated soft tissues. This revealed marked irregularity of the supraglenoid tubercle of the forelimb and discontinuity of the bony contours with the neck of the scapula. No abnormalities were found on ultrasonographic evaluation of the biceps brachii tendon, bicipital bursa, and infraspinatus tendon.
Treatment and Outcome
The mare was discharged from the hospital to become a broodmare. Because of the chronic nature of the fracture, the probability of a poor surgical outcome was given with little likelihood of returning to athletic performance.
Comments
Causes of lameness localized to the shoulder region are relatively uncommon in horses and may be challenging to diagnose. Common causes include fractures, osteo-chondrosis dissecans, secondary osteoarthritis of the humeral head or glenoid cavity, bicipital bursitis, biceps brachii tendonitis, and suprascapular nerve injury.1 Fractures of the supraglenoid tubercle are the most common fracture of the shoulder region and are most commonly seen in horses < 2 years of age that become acutely and severely lame after receiving direct trauma to the point of the shoulder.2 Additionally, avulsion fractures can occur owing to overflexion and resulting tension from the biceps brachii tendon, which originates on the supraglenoid tubercle.2 In the acute phase, there is commonly pain on palpation, localized swelling, and crepitus. Because of the location of the suprascapular nerve and its proximity to the supraglenoid tubercle, chronic fractures are often associated with atrophy of the supraspinatus and infraspinatus muscles.2
In the horse of the present report, there was no muscle atrophy, likely representing lack of damage to the suprascapular nerve. Additionally, because the horse was in active race training and the lameness was not so severe that it was apparent at the walk, there was no evidence of disuse muscle atrophy. Other less specific clinical signs of a fracture of the supraglenoid tubercle include pain on extension or flexion of the shoulder joint, a narrow ipsilateral hoof with a long heel, and a short anterior phase of stride. Diagnostic analgesia can be used to localize the lameness to the shoulder joint, and nuclear scintigraphy, radiography, and ultrasonography are used alone or in combination to further assess for abnormalities. In the horse of the present report, there were no overt clinical signs of a fracture of the shoulder joint. The use of nuclear scintigraphy is indicated in lame horses in which diagnostic analgesia has produced equivocal results.3 In the case described in the present report, had the lameness been localized to a region of the forelimb by use of diagnostic analgesia, other imaging modalities would have been used prior to choosing nuclear scintigraphy. For the horse of the present report, the bone-phase nuclear scintigraphic scan revealed radiopharmaceutical uptake that was milder than would be expected with a more acute fracture of the supraglenoid tubercle. The mild diffuse uptake may have been attributed to the chronic nature and remodeling of the healing fracture.
Orthogonal radiographic views of the equine shoulder joint can be difficult to obtain. Because of the anatomy of the region, mediolateral and craniomedial-caudolateral oblique images are the routine orthogonal views. The forelimb must be protracted to avoid the pectoral muscles and potential superimposition of the left and right shoulder joints, and the head and neck should be raised to avoid superimposition of the cervical and thoracic vertebrae. The mediolateral view was diagnostic for the case described in the present report, and the craniomedial-caudolateral oblique view was attempted for completeness of the radiographic series.
Diagnostic ultrasonography was performed in the horse of the present report to assess the biceps brachii tendon, bicipital bursa, infraspinatus tendon, and other surrounding soft tissues that could have been damaged at the time of shoulder joint trauma. Ultrasonography of the shoulder joint region can also be useful in the examination of the surfaces of the humerus, scapula, cranial aspects of the lesser and greater tubercles, intertubercular groove, body of the scapula, supraglenoid tubercle of the scapula, caudal aspect of the greater tubercle, and articular cartilage of the humeral head.4 In the horse of the present report, bony malformation of the supraglenoid tuberosity was identified via ultrasonography, and the surrounding structures could be assessed to determine that the soft tissues were not involved in the injury.
References
1. Adams SB. Fractures of the scapula. In: Nixon AJ, ed. Equine fracture repair. Philadelphia: Saunders, 1996; 254–258.
2. Bleyaert HF, Madison JB. Complete biceps brachii tenotomy to facilitate internal fixation of supraglenoid tubercle fractures in three horses. Vet Surg 1999; 28: 48–53.
3. Archer DC, Boswell JC, Voute LC, et al. Skeletal scintigraphy in the horse: current indications and validity as a diagnostic test. Vet J 2007; 173: 31–44.
4. Tnibar MA, Auer JA, Bakkali S. Ultrasonography of the equine shoulder: technique and normal appearance. Vet Radiol Ultrasound 1999; 40: 44–57.
