History
A 3-year-old Thoroughbred gelding racehorse was referred for a second opinion regarding a marked, but transient, right forelimb lameness. The horse's trainer described the lameness as intermittent, with episodes of marked soreness (grade 3/5 on the American Association of Equine Practitioners lameness scale1). Pronounced episodes of lameness were seen after training at racing speed or if the horse was not provided a proper cool down on the hot walker after exercising. However, the lameness would decrease in intensity (grade 1 to 2/51) sufficiently that race training was continued. A preliminary examination by the referring veterinarian included radiography of the metacarpophalangeal joint and carpus of the right forelimb, but clinically relevant abnormalities were not seen. Findings on serum biochemical analyses performed before and after exercise were negative for exertional myopathy and other abnormalities.
At the time of referral and hospital admission, passive musculoskeletal evaluation of the right forelimb revealed mild effusion within the metacarpophalangeal joint, digital flexor tendon sheath, and elbow joint. On lameness evaluation, the horse had left forelimb (grade 1/51) and right hind limb (grade 2/51) lameness. Because of the ambiguous history and signs of lameness as well as negative findings on radiographic evaluation of the metacarpophalangeal joint and carpus of the right forelimb, full-body nuclear scintigraphy was performed to aid in lesion localization (Figure 1).
Bone-phase nuclear scintigraphic images of the elbow joints of a 3-year-old Thoroughbred gelding racehorse that was referred for a second opinion regarding a marked, but transient, right forelimb lameness. Images were obtained 4 hours after IV administration of technetium Tc 99m hydroxymethylene diphosphonate. A—Lateromedial image of the left elbow joint (head is positioned to the left of the image). B—Lateromedial image of the right elbow joint (head is positioned to the right of the image).
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Bone-phase nuclear scintigraphic images of the elbow joints of a 3-year-old Thoroughbred gelding racehorse that was referred for a second opinion regarding a marked, but transient, right forelimb lameness. Images were obtained 4 hours after IV administration of technetium Tc 99m hydroxymethylene diphosphonate. A—Lateromedial image of the left elbow joint (head is positioned to the left of the image). B—Lateromedial image of the right elbow joint (head is positioned to the right of the image).
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Bone-phase nuclear scintigraphic images of the elbow joints of a 3-year-old Thoroughbred gelding racehorse that was referred for a second opinion regarding a marked, but transient, right forelimb lameness. Images were obtained 4 hours after IV administration of technetium Tc 99m hydroxymethylene diphosphonate. A—Lateromedial image of the left elbow joint (head is positioned to the left of the image). B—Lateromedial image of the right elbow joint (head is positioned to the right of the image).
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Full-body nuclear scintigraphy revealed a moderate increase in radiopharmaceutical uptake within the right elbow joint. The most intense radiopharmaceutical uptake is on the caudodistal aspect of the right humerus (Figure 2). The ratio of radiopharmaceutical uptake between the distal aspect of the humerus and the proximal radial diaphysis is greater on the right side (5.1) than the left (2.7). An area of uptake that extends cranially from the joint surface on the right is evident; it is unclear whether this is additional abnormal uptake on the right or a positional artifact.
All other aspects of radiopharmaceutical uptake on full-body nuclear scintigraphy were symmetric and considered typical for the age and use of the horse. For further investigation, radiography of the right elbow joint was performed. A lateromedial radiographic projection (Figure 3) of the right elbow joint revealed a 1.7 × 0.5-cm, triangular, mineralized fragment on the caudodistal aspect of the lateral epicondyle of the right humerus near the origin of the ulnaris lateralis muscle. This osseous fragment was not visible on the craniocaudal projection. The right elbow joint lacked any other radiographic abnormalities.
The horse underwent ultrasonographic examination of the lateral aspect of the right elbow joint; during this examination, the horse stood without manipulation of the right forelimb (Figure 4). For comparison, the horse also underwent ultrasonographic examination of the left elbow joint. On the caudolateral aspect of the distal portion of the right humerus, an osseous triangular structure distracted from the lateral epicondyle at the origin of the ulnaris lateralis muscle was evident. The fragment was mildly displaced in a caudodistal direction, extending into the overlying soft tissues. No evidence found on ultrasonography indicated that the fragment communicated with the articular surface or synovial cavity; however, mild effusion was appreciated within the joint, compared with the left elbow joint. There were no obvious ultrasonographic abnormalities present in the lateral collateral ligament.
Same image of the right elbow joint as in Figure 1. Notice the increased radiopharmaceutical uptake within the caudodistal aspect of the right humerus (circle). When compared with the left elbow joint (Figure 1), the right elbow joint has more radiopharmaceutical uptake overall, including the caudal aspect of the radial head.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Same image of the right elbow joint as in Figure 1. Notice the increased radiopharmaceutical uptake within the caudodistal aspect of the right humerus (circle). When compared with the left elbow joint (Figure 1), the right elbow joint has more radiopharmaceutical uptake overall, including the caudal aspect of the radial head.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Same image of the right elbow joint as in Figure 1. Notice the increased radiopharmaceutical uptake within the caudodistal aspect of the right humerus (circle). When compared with the left elbow joint (Figure 1), the right elbow joint has more radiopharmaceutical uptake overall, including the caudal aspect of the radial head.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Lateromedial (A) and craniocaudal (B) radiographic images of the right elbow joint of the horse in Figure 1. Notice the triangular mineralized fragment in the caudodistal aspect of the lateral epicondyle of the right humerus (square); an inlay close-up image of the fragment is included in the bottom right corner.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Lateromedial (A) and craniocaudal (B) radiographic images of the right elbow joint of the horse in Figure 1. Notice the triangular mineralized fragment in the caudodistal aspect of the lateral epicondyle of the right humerus (square); an inlay close-up image of the fragment is included in the bottom right corner.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Lateromedial (A) and craniocaudal (B) radiographic images of the right elbow joint of the horse in Figure 1. Notice the triangular mineralized fragment in the caudodistal aspect of the lateral epicondyle of the right humerus (square); an inlay close-up image of the fragment is included in the bottom right corner.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Transverse ultrasonographic image of the caudolateral aspect of the right elbow joint of the horse in Figure 1. The triangular osseous structure (white arrow) is displaced from the parent humeral bone. Proximal is toward the right and distal is toward the left of the image. The image was obtained with a 7.5-MHz linear transducer held parallel to the frontal plane. H=Distal aspect of the lateral epicondyle of the humerus. UL = Ulnaris lateralis muscle.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Transverse ultrasonographic image of the caudolateral aspect of the right elbow joint of the horse in Figure 1. The triangular osseous structure (white arrow) is displaced from the parent humeral bone. Proximal is toward the right and distal is toward the left of the image. The image was obtained with a 7.5-MHz linear transducer held parallel to the frontal plane. H=Distal aspect of the lateral epicondyle of the humerus. UL = Ulnaris lateralis muscle.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
Transverse ultrasonographic image of the caudolateral aspect of the right elbow joint of the horse in Figure 1. The triangular osseous structure (white arrow) is displaced from the parent humeral bone. Proximal is toward the right and distal is toward the left of the image. The image was obtained with a 7.5-MHz linear transducer held parallel to the frontal plane. H=Distal aspect of the lateral epicondyle of the humerus. UL = Ulnaris lateralis muscle.
Citation: Journal of the American Veterinary Medical Association 250, 10; 10.2460/javma.250.10.1093
On the basis of the diagnostic imaging findings, the final diagnosis was a simple, mildly displaced, nonarticular, closed fracture of the lateral caudodistal aspect of the lateral epicondyle of the right humerus, which presumably was a partial avulsion of the origin of the ulnaris lateralis muscle.
Treatment and Outcome
A conservative treatment approach was recommended that consisted of 4 months of stall rest and administration of anti-inflammatory drugs. It was anticipated that conservative management would allow the fragment to stabilize. Surgical removal of the fragment was considered; however, without clear articular communication, this treatment option was considered unnecessarily invasive and associated with a higher potential for complications.
The horse was reevaluated 126 days after the initial diagnosis. The right elbow joint effusion had resolved, and the horse was sound at the trot. Follow-up radiography revealed no change in the fragment location. Ultrasonographic examination illustrated evidence of soft tissue fibrosis stabilizing the fragment.
Comments
Because of the combination of nuclear scintigraphic, radiographic, and ultrasonographic findings, the authors believed with reasonable confidence that this fracture represented a partial avulsion of the ulnaris lateralis muscle from the lateral humeral epicondyle with minimal to no involvement of the elbow joint. The fracture was unique given that the lateral epicondyle of the distal aspect of the humerus alone was fractured. This specific fracture type is rare in horses with, to our knowledge, only 2 published cases.2,3 Those 2 affected horses differed from the horse in the present report in that they had open fractures resulting from clear external trauma that were complicated by cellulitis. In general, humeral fractures carry a guarded prognosis. They tend to occur as a result of a traumatic force causing an acute overload and failure of bone.4 It is unknown whether the injury described in the present report resulted from primary external trauma or developed secondary to a sudden, forceful hyperextension of the elbow joint during athletic activity. Nonetheless, in the 2 previous reports2,3 the elbow joints were thoroughly examined because of the known location of the trauma. In the horse of the present report, the cause for the intermittent lameness could not readily be identified on the basis of history or findings on physical and lameness examinations. Therefore, the use of nuclear scintigraphy was paramount for localization of the injured site.
Once the bone scan localized the lesion to the elbow joint, radiography was used to further define the disease process. Radiography is the most commonly used diagnostic tool to evaluate humeral fractures.4 However, the large amount of soft tissue that overlies the humerus combined with the overlap of multiple bone contours at the elbow joint can make it difficult to interpret the images. Thus, it was beneficial to have increased radiopharmaceutical uptake identified via nuclear scintigraphy in the caudodistal aspect of the humerus to ensure radiographs properly highlighted the affected area. The fracture was radiographically evident on the lateromedial projection at the distal-most aspect of the lateral epicondyle of the humerus. The craniocaudal image had superimposition that hindered identification of the fracture. We could have also chosen to take a flexed caudoproximal-caudodistal oblique projection (as previously described by Bordelon et al3) to help differentiate the extent of injury,3 but instead chose ultrasonography of the elbow joint.
The authors believe that adding ultrasonography to the other diagnostic imaging modalities helped to further define the amount of muscular and articular involvement, which could not be elucidated from the scintigraphic or radiographic findings. Ultrasonography revealed that this fragment was associated with part of the ulnaris lateralis muscle from the lateral humeral epicondyle with minimal to no involvement of the elbow joint. This could also explain the intermittent, yet marked, right forelimb lameness seen. Pain was likely not sustained at a high level for a long time because some of the muscle was still attached, but the area would become inflamed and painful secondary to the movement created by the partial avulsion of the ulnaris lateralis muscle during maximal extension and flexion achieved at racing speeds.
The case described in the present report highlighted a unique and rarely reported fracture configuration within the lateral epicondyle of the humerus. Equine veterinarians should consider this fracture configuration as a potential differential diagnosis for athletic horses that display marked, yet intermittent, lameness following high-intensity exercise. A successful diagnosis and interpretation of clinical implications can be obtained through a multimodal approach of nuclear scintigraphy, radiography, and ultrasonography.
References
1. Definition and classification of lameness. In: Guide for veterinary service and judging of equestrian events. Lexington, Ky: American Association of Equine Practitioners, 1991; 19.
2. Mitchell C, Riley C. Evaluation and treatment of an adult Quarter Horse with an unusual fracture of the humerus and septic arthritis. Can Vet J 2002; 43: 120–122.
3. Bordelon KL, Mathis SC, Munroe JL. What is your diagnosis? Caudodistally displaced lateral humeral epicondylar fracture. J Am Vet Med Assoc 2008; 233: 873–874.
4. Hubert J, Stashak T. The antebrachium, elbow, and humerus. In: Baxter G, ed. Adam's and Stashak's lameness in horses. 6th ed. Chichester, West Sussex, England: Wiley-Blackwell, 2011; 701–705.
