History
A 7-year-old 310-kg (682-lb) Boerperd gelding was evaluated because of a 6-week history of severe non–weight-bearing lameness in the right hind limb. The owner reported that the horse had been examined by a veterinarian when the lameness first appeared and that the veterinarian had suspected a hoof abscess and prescribed penicillin and meloxicam; however, the horse had no clinical improvement. Two weeks later, a second veterinarian was consulted and suspected a sacroiliac injury, prescribed meloxicam, and recommended stall rest but did not perform diagnostic imaging. Meloxicam was discontinued 2 weeks before the present evaluation without any clinical improvement in the gelding's lameness.
On examination, the gelding had a body condition score of 2 (on a scale of 1 to 5) and non–weight-bearing lameness (grade 5 on a scale1 of 0 to 5) of the right hind limb. In addition, the gelding had severe atrophy of the right gluteal muscles and marked swelling in the right stifle joint region. The remainder of findings from physical examination were within reference limits.
Serum biochemical analyses and a CBC revealed that the horse had marked neutrophilic leukocytosis (17 × 109 WBCs/L [reference range, 6 × 109 to 12 × 109 WBCs/L]; 13.6 × 109 neutrophils/L [reference range, 3.4 × 109 to 5.4 × 109 neutrophils/L]), hyperproteinemia (85.5 g/L; reference range, 66 to 78 g/L), high serum amyloid A concentration (368.6 mg/L; upper reference limit, ≤ 20 mg/L), and hyperfibrinogenemia (3.5 g/L; reference range, 0.9 to 2.8 g/L). Radiographic images of the right stifle joint were obtained (Figure 1).
Lateromedial (A), caudolateral-craniomedial oblique (B), and caudocranial (C) radiographic images of the right stifle joint of a 7-year-old 310-kg (682-lb) Boerperd gelding evaluated because of a 6-week history of non–weight-bearing lameness in the right hind limb.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Lateromedial (A), caudolateral-craniomedial oblique (B), and caudocranial (C) radiographic images of the right stifle joint of a 7-year-old 310-kg (682-lb) Boerperd gelding evaluated because of a 6-week history of non–weight-bearing lameness in the right hind limb.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Lateromedial (A), caudolateral-craniomedial oblique (B), and caudocranial (C) radiographic images of the right stifle joint of a 7-year-old 310-kg (682-lb) Boerperd gelding evaluated because of a 6-week history of non–weight-bearing lameness in the right hind limb.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Formulate differential diagnoses and treatment strategies from the history, clinical findings, and Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Radiography of the right stifle joint revealed loss of the infrapatellar fat pad and marked intra-articular soft tissue swelling predominantly in the femoropatellar joint and medial femorotibial compartment of the stifle joint (Figure 2). A poorly marginated area of lysis (approx 5.5 cm [proximodistally] × 3.9 cm [craniocaudally] × 3.7 cm [mediolaterally]) with a sclerotic rim and relatively short transition zone was evident in the cranial aspect of the proximal metaphysis of the tibia. An irregular, predominantly palisading, periosteal reaction (up to approx 6 mm high) was visible on the caudal and medial aspects of the proximal end of the tibia, and the cranial articular margin of the tibia had evidence of mild, poorly mineralized, irregular new bone proliferation. A poorly defined, semicircular area of greater radiolucency (approx 1.9 × 0.9 cm) in the subchondral bone of the medial condyle of the tibia was evident but only on the caudocranial projection. On the basis of findings, our primary differential diagnoses included osteomyelitis with potential septic arthritis of the right stifle joint, an unusually irregular subchondral cystic lesion with associated right stifle joint osteoarthritis, bone infarction, or less likely neoplasia within the proximal aspect of the right tibia.
Same radiographic images as in Figure 1. A lytic area (approx 5.5 × 3.9 × 3.7 cm; dotted outline) with a marked sclerotic rim and relatively short transition zone is evident in the proximocranial aspect of the tibia. Evidence of a periosteal reaction (arrows) is visible on the caudal and medial aspects of the proximal region of the tibia. The cranial articular margin of the tibia has evidence of poorly mineralized, irregular new bone proliferation (arrowheads). In the subchondral bone of the medial condyle of the tibia, there is a poorly defined, semicircular area of greater radiolucency (asterisks), consistent with osteolysis.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Same radiographic images as in Figure 1. A lytic area (approx 5.5 × 3.9 × 3.7 cm; dotted outline) with a marked sclerotic rim and relatively short transition zone is evident in the proximocranial aspect of the tibia. Evidence of a periosteal reaction (arrows) is visible on the caudal and medial aspects of the proximal region of the tibia. The cranial articular margin of the tibia has evidence of poorly mineralized, irregular new bone proliferation (arrowheads). In the subchondral bone of the medial condyle of the tibia, there is a poorly defined, semicircular area of greater radiolucency (asterisks), consistent with osteolysis.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Same radiographic images as in Figure 1. A lytic area (approx 5.5 × 3.9 × 3.7 cm; dotted outline) with a marked sclerotic rim and relatively short transition zone is evident in the proximocranial aspect of the tibia. Evidence of a periosteal reaction (arrows) is visible on the caudal and medial aspects of the proximal region of the tibia. The cranial articular margin of the tibia has evidence of poorly mineralized, irregular new bone proliferation (arrowheads). In the subchondral bone of the medial condyle of the tibia, there is a poorly defined, semicircular area of greater radiolucency (asterisks), consistent with osteolysis.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Ultrasonography of the right stifle joint revealed severe distension of the femoropatellar joint and the medial femorotibial compartment of the stifle joint, irregular margins and slight protrusion of the medial meniscus, and a subcutaneous pocket of echogenic fluid medially. The surface of the tibia between the tibial tuberosity and medial collateral ligament had a moderately irregular interface, with areas of cortical disruption that allowed penetration of the ultrasound beam through the bone (Figure 3). Arthrocentesis of the medial femorotibial compartment of the stifle joint was performed and yielded synovial fluid that had low viscosity. Cytologic examination of the synovial fluid sample revealed 47.16 × 109 WBCs/L (upper reference limit, < 0.5 × 109 WBCs/L) and 62 g of total protein/L (upper reference limit, < 20 g/L) but no bacteria or neoplastic cells. These findings were most consistent with osteomyelitis of the proximal aspect of the right tibia with associated septic arthritis of the stifle joint and subcutaneous abscess formation.
Longitudinal (A) and transverse (B) ultrasonographic images of the distal insertion of the intermediate (middle) patellar ligament on the right tibia of the horse described in Figure 1. Evident are subcutaneous edema (double-headed arrows), cortical disruption that allows penetration of the ultrasonic beam into the bone (asterisks), and irregular surfaces of the bone (arrowheads). The scale to the right in each image is in centimeters.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Longitudinal (A) and transverse (B) ultrasonographic images of the distal insertion of the intermediate (middle) patellar ligament on the right tibia of the horse described in Figure 1. Evident are subcutaneous edema (double-headed arrows), cortical disruption that allows penetration of the ultrasonic beam into the bone (asterisks), and irregular surfaces of the bone (arrowheads). The scale to the right in each image is in centimeters.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Longitudinal (A) and transverse (B) ultrasonographic images of the distal insertion of the intermediate (middle) patellar ligament on the right tibia of the horse described in Figure 1. Evident are subcutaneous edema (double-headed arrows), cortical disruption that allows penetration of the ultrasonic beam into the bone (asterisks), and irregular surfaces of the bone (arrowheads). The scale to the right in each image is in centimeters.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Treatment and Outcome
Because of the duration and severity of clinical signs and severity of the radiographic findings, a poor prognosis was given, and the owner elected euthanasia for the horse. On necropsy, the right stifle joint was removed intact for CT (bone window [window width, 1,400 HU; window level, 300 HU]; slice thickness, 2 mm; Figure 4). Findings on CT confirmed the earlier radiographic findings and were consistent with an area of severe osteolysis (approx 5.5 × 4.1 × 4.6 cm) in the proximocranial aspect of the tibia, with associated surrounding sclerosis and palisading periosteal reaction. In addition, CT revealed that in this osteolytic lesion was a large (approx 3 × 2.8 × 2.7 cm), irregularly marginated structure that was poorly mineralized (≤ 277 HU), hyperattenuating compared with the surrounding fluid, and hypoattenuating compared with clinically normal bone. These findings were consistent with a sequestrum that had not been evident radiographically. The cortical bone around the involucrum appeared disrupted in several locations cranially and medially. A poorly defined, semicircular defect (approx 1 × 1.6 × 1.2 cm) in the subchondral bone of the medial condyle of the tibia was also confirmed on CT.
Postmortem craniocaudal (A and D), sagittal (B), and transverse (C) CT images of the proximal portion of the right tibia and the right stifle joint removed from the carcass of the horse described in Figure 1. The proximal portion of the tibia has a large (approx 3 × 2.8 × 2.7 cm) sequestrum (dotted outline; A through C) surrounded by an involucrum and areas of disrupted cortical bone (arrowheads; A through C). A thick, palisading periosteal reaction (arrows; C) is evident on the caudal aspect of the proximal portion of the tibia. The medial condyle of the tibia has an area of severe osteolysis (asterisk; D). The images were obtained in a bone window (window width, 1,400 HU; window level, 300 HU; slice thickness, 2 mm). In images A, C, and D, medial is to the left; in image B, cranial is to the left. B—The yellow and pink lines represent the levels at which images C and D, respectively, were obtained. C—The pink and blue lines represent the levels at which images A and B, respectively, were obtained.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Postmortem craniocaudal (A and D), sagittal (B), and transverse (C) CT images of the proximal portion of the right tibia and the right stifle joint removed from the carcass of the horse described in Figure 1. The proximal portion of the tibia has a large (approx 3 × 2.8 × 2.7 cm) sequestrum (dotted outline; A through C) surrounded by an involucrum and areas of disrupted cortical bone (arrowheads; A through C). A thick, palisading periosteal reaction (arrows; C) is evident on the caudal aspect of the proximal portion of the tibia. The medial condyle of the tibia has an area of severe osteolysis (asterisk; D). The images were obtained in a bone window (window width, 1,400 HU; window level, 300 HU; slice thickness, 2 mm). In images A, C, and D, medial is to the left; in image B, cranial is to the left. B—The yellow and pink lines represent the levels at which images C and D, respectively, were obtained. C—The pink and blue lines represent the levels at which images A and B, respectively, were obtained.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Postmortem craniocaudal (A and D), sagittal (B), and transverse (C) CT images of the proximal portion of the right tibia and the right stifle joint removed from the carcass of the horse described in Figure 1. The proximal portion of the tibia has a large (approx 3 × 2.8 × 2.7 cm) sequestrum (dotted outline; A through C) surrounded by an involucrum and areas of disrupted cortical bone (arrowheads; A through C). A thick, palisading periosteal reaction (arrows; C) is evident on the caudal aspect of the proximal portion of the tibia. The medial condyle of the tibia has an area of severe osteolysis (asterisk; D). The images were obtained in a bone window (window width, 1,400 HU; window level, 300 HU; slice thickness, 2 mm). In images A, C, and D, medial is to the left; in image B, cranial is to the left. B—The yellow and pink lines represent the levels at which images C and D, respectively, were obtained. C—The pink and blue lines represent the levels at which images A and B, respectively, were obtained.
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
The proximal aspect of the tibia was transected sagittally with a band saw, revealing the sequestrum and associated involucrum (Figure 5). Results of histologic examination of a section of the affected bone indicated necrotizing osteomyelitis, with intralesional bacteria observed. Bacterial culture performed on a sample of synovial fluid from the affected stifle joint yielded an isolate of Staphylococcus aureus susceptible to all tested antimicrobials.
Postmortem image of the sagittally transected surfaces of the proximal portion of the right tibia of the horse described in Figure 1 showing the sequestrum (arrow) and involucrum (dotted outline).
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Postmortem image of the sagittally transected surfaces of the proximal portion of the right tibia of the horse described in Figure 1 showing the sequestrum (arrow) and involucrum (dotted outline).
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Postmortem image of the sagittally transected surfaces of the proximal portion of the right tibia of the horse described in Figure 1 showing the sequestrum (arrow) and involucrum (dotted outline).
Citation: Journal of the American Veterinary Medical Association 258, 1; 10.2460/javma.258.1.39
Comments
Chronic, severe osteomyelitis with sequestrum formation in the proximal aspect of the right tibia and septic arthritis of the right stifle joint were diagnosed in the horse of the present report. Radiographic findings of severe bone lysis combined with bone proliferation suggested an aggressive process, and antemortem confirmation of the septic nature of the condition was obtained with analysis of synovial fluid. The origin of infection was questionable because the owner was not aware of any trauma to the horse's right hind limb. It was possible that the lesions we identified were secondary to an unnoticed puncture wound at the site; however, a hematogenous origin, although rare,2,3 could not be excluded. On the basis of findings from ultrasonography and CT, one could suspect that the bone became infected first, with subsequent contamination of the adjacent stifle joint and subcutaneous space after tibial cortical bone had ruptured, similar to an abscess bursting.4 The fact that the sequestrum was not radiographically obvious probably related to the long duration of the septic process and osteoclastic resorption of this dead fragment of bone, as substantiated by the low attenuation of the sequestrum on CT. Although radiography was helpful in narrowing our differential diagnosis list for lameness in the horse of the present report, CT proved more useful in determining the full extent of bone involvement.2
The delayed diagnosis of osteomyelitis in this horse could have been because of the frequently insidious development of local signs in the early stage of the disease.5,6 Furthermore, because up to 21 days may be required before bone lysis may be detected radiographically,7 it was likely that the diagnosis would not have been possible with radiography when the lameness was first noticed; however, scintigraphy might have been useful in detecting osteomyelitis earlier.2,6
If detected earlier, treatment of osteomyelitis in the horse of the present report could have been attempted through arthroscopic lavage of the septic joint or joints; systemic, intra-articular, and intraosseous administration of antimicrobials; surgical bone debridement; and administration of analgesics.3,4,5,6,8 However, at the stage in the disease process when the horse was presented, treatment was unlikely to have been successful and was consequently not attempted owing to the chronicity and severity of the bony lesions identified.
References
- 1. ↑
American Association of Equine Practitioners. Lameness exams: evaluating the lame horse page. Available at: aaep.org/horsehealth/lameness-exams-evaluating-lame-horse. Accessed Jan 9, 2020.
- 2. ↑
Sayegh AI, Sande RD, Besser TE, et al. Appendicular osteomyelitis in horses: etiology, pathogenesis, and diagnosis. Compend Contin Educ Pract Vet 2001;23:760–766.
- 3. ↑
van den Boom R, Rijkenhuizen AB. Hematogenous (suspected-) septic inflammation of the synovial fossa in the adult horse: rare but deceptive (3 case reports) [in Dutch]. Tijdschr Diergeneeskd 2002;127:382–385.
- 4. ↑
Clegg PD. Osteomyelitis in the veterinary species. In: Per-cival S, Knottenbelt D, Cochrane C, eds. Biofilms and veterinary medicine. Berlin: Springer, 2011;175–190.
- 6. ↑
Swinebroad EL, Dabareiner RM, Swor TM, et al. Osteomyelitis secondary to trauma involving the proximal end of the radius in horses: five cases (1987–2001). J Am Vet Med Assoc 2003;223:486–491.
- 7. ↑
Wegener WA, Alavi A. Diagnostic imaging of musculoskeletal infection. Roentgenography; gallium, indium-labeled white blood cell, gammaglobulin, bone scintigraphy; and MRI. Orthop Clin North Am 1991;22:401–418.
