History
A 3-year-old Thoroughbred-Arabian cross was referred to Rainbow Equine Hospital UK, due to a nonhealing wound at the craniolateral aspect of the right scapula 4 months post-trauma. Initially, the gelding had developed paresis of the suprascapular nerve, resulting in limited limb protraction and pronounced atrophy of the supraspinatus and infraspinatus musculature. The paresis resolved over 6 to 8 weeks; however, the musculature remained asymmetric. During this time the wound largely healed, except for a small exuberant region of granulation tissue with minimal discharge. One week prior to referral, regional swelling was noted underlying the persistent skin wound. The tract was opened, allowing drainage of viscous, purulent material. Ultrasonographic examination at this time indicated disruption to the spine of the scapula and craniolateral border of the scapula.
On examination at the hospital, all vital signs were within reference limits. There was substantial muscle atrophy over the right shoulder region, with a discharging tract over the area cranial to the fossa supraspinata. When trotted in a straight line, the horse had right forelimb lameness grade 3 on a scale from 0 (no lameness) to 5 (minimal weight bearing or inability to move). Standing radiographs of the region were acquired (Figure 1).
Mediolateral (A) and a novel craniodorsomedial–caudoventrolateral oblique projection made at 30° proximal to the horizon at the level of the right scapula and 10° to 15° medial to the craniocaudal line (Cr30Pr10-15M–CdDiLO); B) radiographic images of a 3-year-old gelding with left forelimb lameness, muscle atrophy, and a draining tract overlying the right shoulder region.
Citation: Journal of the American Veterinary Medical Association 262, 6; 10.2460/javma.24.02.0085
Radiographic Findings and Interpretation
Radiography revealed that the scapula had a 23.4 cm X 17.5 cm smoothly outlined soft tissue opacity focus dorsal to the scapular neck. The lesion was bisected in the mid-third by a dependently positioned, fluid-gas interface; dorsal to which there was homogeneous gas opacity within the bone. This was consistent with a cavitary lesion. Mediolateral width of the scapula in the affected area was prominently thickened, with convexity to the deep and superficial contours of the scapula. The cranial and caudal angles of the dorsal aspect of the scapula were roughened, and several mottled and irregular mineral opacity fragments were separated from the surface, the largest measured 3.5 cm X 0.6 cm (Figure 2). Radiography with the use of a novel craniodorsal-medial – caudoventral-lateral oblique projection made, at 30° dorsal and 10° to 15° medial to the respective planes of interest (Cr30D10-15M–CdVLO). The projection confirmed the overall expansile nature of the lesion (Figure 2). Repeated ultrasonographic examination confirmed a focal defect within the facies lateralis of the scapula and a tract communicating with the skin surface.
Same radiographic images as Figure 1. The extent of the widened diploic cavity (black arrows) within the right scapula can be seen and has a prominent gas-fluid interface (white arrows). The oval highlights multiple fragments (oval) are visible at the cranial angle of the scapula.
Citation: Journal of the American Veterinary Medical Association 262, 6; 10.2460/javma.24.02.0085
The findings were considered to represent suppurative osteomyelitis of the scapula, with abscess formation and a fistulous tract to the skin surface. The lesion did not involve the scapulohumeral joint, and primary bone neoplasia was a less likely differential diagnosis.
Treatment and Outcome
Surgical exploration and drainage were performed utilizing standing sedation (Figure 3), ultrasonographic guidance, and approximate radiographic measurements to localize the lateral bone defect. Two 7-mm Steinmann pins were inserted into the scapula: the proximal pin positioned into the bony defect and the distal pin placed through the lateral cortical bone immediate proximal to the neck of the scapula entering the distal margin of the cavity. These were subsequently replaced by 20 Fr chest drains, yielding copious purulent material and allowing intra-osseous lavage with 5 L of sterile isotonic fluids. Endoscopic examination of the cavity was then performed, revealing a grossly necrotic appearance to the internal surface of a markedly expansile diploic cavity.
Postmortem 3-D CT reconstruction of the right scapula (A) and antemortem surgical positioning of the 21 Fr chest drains facilitating lavage of the right scapular region (B) of the horse described in Figure 1.
Citation: Journal of the American Veterinary Medical Association 262, 6; 10.2460/javma.24.02.0085
Results for endoscopically obtained samples submitted for bacterial and fungal culture and susceptibility testing yielded no growth. Antimicrobial treatment and sterile fluid lavage were undertaken for 7 days, through which time the purulent drainage resolved, and the drains subsequently were removed. Due to the size and extent of the lesion within the scapula, box rest was recommended for 3 months.
Following the prescribed rest, the horse presented for reassessment. Comfort was improved, however, a small draining tract remained at the margo cranialis, oozing nonodorous purulent material. Repeated radiographic assessment revealed the lesion to be similar to the initial presentation with recurrence of a “fluid line.” Repeated bacterial culture of the draining purulent material identified Escherichia coli. The isolate was sensitive to amikacin, ceftiofur, cefoxitin, oxytetracycline, and doxycycline, but demonstrated resistance to the remainder of the sensitivity panel. Further, more invasive surgical intervention was offered; however, the owners elected euthanasia for the horse on humane grounds.
Computed tomography was performed prior to submission for postmortem examination of the right shoulder region (Figure 3). A 16-slice multidetector CT scanner (GE RT 16; GE Healthcare) was used, with data obtained using the following technical variables: 120 kVp, 200 mAs, slice thickness 0.625 mm, field of view 25 cm, matrix of 512 X 512. The CT examination confirmed the expansile, hollow intra-osseous cavity extending from the dorsal border to the neck of the scapula. Within the distal third of the scapula a singular hollow cavity existed, which was divided proximally by the spine of the scapula into 2 distinct cavities underlying the supraspinous and infraspinous fossae. There was focal osseous incongruency, most prominent associated with the cranial margin of the scapular spine and the angulus caudalis.
Postmortem examination confirmed moderate, chronic-active, locally extensive fibrosis and suppurative myositis of the supraspinatus muscle. Focal loss of cortical integrity of the facies lateralis of the scapula (Figure 4) included an oval 2cm X 1cm full-thickness defect, consistent with the sinus tract communicating with the medullary cavity of the scapula. The expansile cavity between the compact bone plates contained purulent content and large necrotic bone fragments. Assessment of the scapulohumeral joint and the surrounding skeletal muscles and soft tissues was unremarkable. A final diagnosis of severe, chronic-active, diffuse, necro-suppurative osteomyelitis was made, including focal osteonecrosis, a sinus tract (fistula) and moderate fibrosis and suppurative myositis of the supraspinatus muscle.
Postmortem cross-sections of the right scapula, detailing the expansile hollow nature of the scapula and loss of the interposing spongy architecture between the thinned deep and superficial layers of compact bone. Cortical lysis and purulent material (circle) are evident along the cranial aspect of the scapula spine.
Citation: Journal of the American Veterinary Medical Association 262, 6; 10.2460/javma.24.02.0085
Comments
Previous reports of intramedullary abscess formation in horses have included the proximal aspect of the third metacarpus, proximal phalanx, lateral epicondyle of the humerus, and the proximal aspect of the tibia.1 Irrespective, intramedullary abscess formation remains a rare sequela to trauma. Our initial clinical suspicion was sequestration of the facies lateralis of the scapula. Sequestrae have been reported previously involving both traumatic and atraumatic aetiologies.2,3 A previous report3 by Parks and Nickels described similar “medullary sequestration” following trauma to the right scapula. However, it is now possible to document the presumed similar lesions radiographically; with the prior diagnosis made using exploratory surgery under general anesthesia.3 Recently a novel radiographic projection with limb elevation and a portable x-ray generator, identified a fracture of the scapula body in a 3-month-old Thoroughbred filly.4 However, we achieved a similar radiographic contrast resolution with a horizontal-beam mediolateral radiograph, using a gantry-mounted X-ray generator, with the limb elevated and drawn forward (Figure 2). In this case, a similarly novel (Cr30D10-15M–CdVLO) radiographic projection was utilized to isolate the focal intramedullary radiolucency within the confines of the latero-medially expanded scapula.
The scapula is an anatomically flat bone, containing 2 plates of compact tissue and interposition of spongy material. However, a discrete proximal “sinus or medullary cavity” located superficially within the compact bone of the scapula spine has been identified as a presumed normal finding.5 Figure 4 details the extensive loss of the reported normal internal spongy architecture of the scapula, and prominent expansion of the bone (reactive bone formation and remodeling). The prognosis for resolution of the abscess, given its size, was uncertain, as osteomyelitis of this extent is rarely encountered. Despite an attempt to establish sufficient drainage at the distal margin of the cavity, with extensive lavage, and antimicrobial coverage the lesion recurred. The previous report resulted in breeding soundness. However, there was a similar persistent non-healing sinus and surgical intervention was considerably more invasive.3
The above report documents the clinical presentation and radiographic appearance, with postmortem CT imaging and full pathological investigation, of a case of suppurative osteomyelitis of the medullary cavity of the scapula. The lesions are considered to carry a poor prognosis.
Acknowledgments
The authors would like to thank the referring veterinarian, nurses, and support team at Rainbow Equine Hospital, as well as the University of Nottingham Pathology Department. Particular gratitude is also extended to Julia Dubuc.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
References
- 1.↑
White JM, Hughes KJ, Scruton C, Morris J, Philbey AW, Lischer CJ. Intramedullary abscess of the proximal third metatarsal bone in a 4-year-old Thoroughbred horse. Equine Vet Educ. 2007;19(6):291-296. doi:10.2746/095777307X21726
- 2.↑
Clements PE, Jones B, Coomer R. Septic epiphysitis and sequestrum formation in the glenoid of the scapula in a 5-month-old foal diagnosed by computed tomography. Vet Rec Case Rep. 2019;7(3):e000837, doi:10.1136/vetreccr-2019-000837
- 3.↑
Parks AH, Nickels FA. Scapular sequestrum in a horse a case report. Vet Surg. 1986;15(5):389-391. doi:10.1111/j.1532-950X.1986.tb00249.x
- 4.↑
Santalucia V, Hunt R, Murphy M. A novel radiographic projection for the detection of a scapula body fracture in a Thoroughbred foal. Equine Vet Educ. 2024;36(3):140-144. doi:10.1111/eve.13883
- 5.↑
Vallance SA, Spriet M, Stover SM. Catastrophic scapular fractures in Californian racehorses: pathology, morphometry and bone density. Equine Vet J. 2011;43(6):676-685. doi:10.1111/j.2042-3306.2010.00346.x
