History
A 5-year-old 450-kg Morgan horse stallion was referred for evaluation of left forelimb lameness. The owner reported a sudden onset of a noticeable left forelimb lameness while the stallion was competing at the Morgan World Show. The stallion was treated with athletic rest, phenylbutazone administration, and pulsed electromagnetic field therapy focused over the distal aspect of the left forelimb. Two weeks later, the stallion had left forelimb lameness (grade,1 3/5) combined with moderate effusion and decreased range of motion of the left metacarpophalangeal joint identified by the referring veterinarian. At that point, results of radiographic evaluation of the left metacarpophalangeal joint were inconclusive, and IA administration of triamcinolone, hyaluronic acid, and amikacin was performed. Three weeks later, the lameness had only mildly improved to a grade 2/5; therefore, the stallion was referred for further evaluation and definitive diagnosis of the source of left forelimb lameness.
On initial referral examination, the stallion had a grade 3/5 lameness and a strong positive response to flexion test of the distal portion of the left forelimb. A palmar digital nerve block was performed but did not improve the lameness. The horse underwent general anesthesia for 3.0T MRI (Skyra 3T; Siemens Medical Solutions USA Inc) of the left metacarpophalangeal joint, including sequences of T1-weighted volumetric interpolated breath-hold examination and Dixon-method proton density–weighted sequences with and without fat suppression (Figure 1). For volumetric interpolated breath-hold examination images, the time of echo was 4.92 milliseconds, the time of repetition was 11 milliseconds, and the flip angle was 10°. For Dixon images, the time of echo was 41 milliseconds, the time of repetition was 2,500 milliseconds, and the flip angle was 150°.
Dorsal T1-weighted volumetric interpolated breath-hold examination (A and B obtained 1 mm apart) and transverse Dixon-method proton density–weighted (C) and sagittal Dixon-method proton density–weighted fat-suppression (D) MRI images of the left metacarpophalangeal joint of a Morgan horse with a 5-week history of left forelimb lameness and moderate effusion and decreased range of motion of the imaged joint. A, B, and C—Medial is to the right. D—Dorsal is to the left; the vertical dashed line and horizontal dotted line represent the planes of the dorsal (A and B) and transverse (C) images, respectively.
Citation: Journal of the American Veterinary Medical Association 260, 2; 10.2460/javma.20.06.0310
Diagnostic Imaging Findings and Interpretation
Findings on all MRI sequences included a well-defined defect of increased signal intensity within the subchondral bone of the medial fovea of the left forelimb proximal phalanx (Figure 2). The medial condyle of the left third metacarpal bone had moderate to severe, diffuse, multifocal, subchondral bone lesions with hyperintense signals and a flattened and irregular contour of the articular. In addition, there was extensive subchondral bone sclerosis (hypointense signal) surrounding these subchondral defects in the proximal phalanx and third metacarpal. Lastly, there were diffuse thinning and multifocal ill-defined defects of the articular cartilage and mild to moderate osteophyte formation on the medial aspect of the metacarpophalangeal joint. We diagnosed subchondral bone injury of the proximal phalanx and third metacarpal bone. There was also concurrent osteoarthritis of the metacarpophalangeal joint.
Same images as in Figure 1. The medial fovea of the proximal phalanx has a subchondral bone defect of hyperintense signal (white arrow) and an ill-defined defect of the articular cartilage (light gray arrow). The medial condyle of the third metacarpal bone has a flattened and irregular articular surface and diffuse, multifocal, subchondral bone defects (arrowheads) that have hyperintense signals and are surrounded by a region of hypointense signal, consistent with subchondral bone sclerosis (asterisk).
Citation: Journal of the American Veterinary Medical Association 260, 2; 10.2460/javma.20.06.0310
Treatment and Outcome
We recommended extended rest (6 to 9 months) from athletic use, extracorporeal shockwave therapy, IA administration of autologous conditioned serum, and then a follow-up MRI at 9 months to assess healing. The stallion was still in convalescence 6 months after the initial referral examination.
Comments
Subtle subchondral bone injuries in horses are difficult to detect or confirm using digital radiography due to the lack of sensitivity of this diagnostic modality for this type of injury.2 In contrast, our use of MRI was able to detect small and subtle changes in the bony architecture of subchondral bone in the stallion of the present report. In addition, MRI is currently considered the gold standard imaging modality for horses with a localized lameness but unremarkable results on radiography.2
Subchondral bone is composed of a compact layer of bone below the superficial layer of calcified cartilage and trabecular bone.3 Subchondral bone in joints mitigates forces imposed on joint cartilage in that the subchondral bone plate provides support through rigidity and the trabecular bone allows for elasticity.3 Additionally, bone changes or adapts in response to the stresses imposed on it. Through the harmonious activity of osteoblasts and osteoclasts, bone homeostasis is maintained; however, normal adaptation can become pathological if not kept in check by the counterbalance.3 For instance, in areas of damage, increased osteoclastic activity can lead to osteoporosis; conversely, increased osteoblastic activity can lead to bone thickening and increased density. These changes can affect the ability of the subchondral bone to mitigate forces imposed on a joint and can lead to more severe sequelae, such as osteochondral fragmentation, osteochondral fracture, subchondral bone sclerosis, catastrophic injury, and osteoarthritis.3
Subchondral bone injuries characterized by increased signal intensity on fat-suppressed sequences, such as seen on MRI of the horse of the present report, are often referred to as bone bruises or contusions, suggesting bone demineralization and pathological fluid accumulation. However, histologic studies4 show that these lesions are not solely fluid or edema but rather can be a mixture of edema, fibrosis, necrosis, hemorrhage, and cyst formation. Areas of increased signal intensity on T1-weighted and proton density–weighted MRI sequences are associated with loss of subchondral, trabecular, or cortical bone, whereas areas of decreased signal intensity on all MRI sequences are indicative of greater trabecular bone density or sclerosis.2 These changes diminish the ability of subchondral bone to mitigate forces imposed on a joint, resulting in osteoarthritis, evident as areas of cartilage thinning and osteophyte formation as seen in the horse of the present report.
Subchondral bone injuries have been reported in racehorses, English sports horses, and western performance horses.2,5 Treatment goals for subchondral bone injuries include restoring normal joint function and preventing progression of the disease by managing pain and restoring normal bone composition.3 Treatment options vary depending on the anatomic location of an injury but may include exercise reduction or modification, extracorporeal shockwave therapy, IA administration of anti-inflammatory medication, and systemic administration of bisphosphonates.5 Exercise reduction or modification is a centerpiece in treating subchondral bone injuries to prevent or marginalize further progression of the injury.3,5 Extracorporeal shockwave therapy is often used for its analgesic effects, whereas IA administration of anti-inflammatory medications is used to restore joint homeostasis and promote healing.5 Bisphosphonates, which inhibit osteoclastic activity and thus prevent further bone resorption, have been used in an extralabel manner to treat subchondral bone injuries; however, to our knowledge, there has been no study evaluating bisphosphonates in the treatment of subchondral bone injuries in horses. In addition, there is no definitive consensus on the use of bisphosphonates in the treatment of subchondral bone injuries in veterinary medicine.
Prognostic information for subchondral bone injuries of the metacarpophalangeal joint involving primarily the proximal phalanx and condyle of the third metacarpal is limited. Sherlock et al5 reported that of 11 horses with subchondral bone injuries and used for various athletic activities (eg, pleasure riding, show jumping, racing, or dressage), 6 returned to full work, 2 worked at reduced performance, and 3 remained lame. These results illustrate that subchondral bone injuries may heal, allowing affected horses to return to full athletic use. However, we believe the outcome may be dictated by the timing of the diagnosis, severity of damage to the subchondral bone, and presence of concurrent osteoarthritis.
Correction: A survey of negative mental health outcomes, workplace and school climate, and identity disclosure for lesbian, gay, bisexual, transgender, queer, questioning, and asexual veterinary professionals and students in the United States and United Kingdom
In the report “A survey of negative mental health outcomes, workplace and school climate, and identity disclosure for lesbian, gay, bisexual, transgender, queer, questioning, and asexual veterinary professionals and students in the United States and United Kingdom” (JAVMA 2020;257:417–431), The authors’ noticed after publication that there were three duplicate entries in the database. After re-running all statistical analyses presented in the paper, it was determined that no outcomes were changed, and consequently, there are no changes to the manuscript. Data are available for review upon request.
References
- 1. ↑
Ross MW, Dyson SJ. Diagnosis and Management of Lameness in the Horse. 2nd ed. Saunders; 2011:64–80.
- 2. ↑
Gonzalez LM, Schramme MC, Robertson ID, Thrall DE, Redding RW. MRI features of the metacarpo(tarso)phalangeal region lameness in 40 horses. Vet Radiol Ultrasound. 2010;51(4):404–414.
- 3. ↑
McIlwraith CW, Frisbie DD, Kawcak CE, van Weeren R. Joint Disease in the Horse. 2nd ed. Elsevier; 2016:10–30.
- 4. ↑
Zanetti M, Bruder E, Romero J, Hodler J. Bone marrow edema pattern in osteoarthritic knees: correlation between MR imaging and histologic findings. Radiology. 2000;215(3):835–840.
- 5. ↑
Sherlock CE, Mair TS, Ter Braake F. Osseous lesions in the metacarpo(tarso)phalangeal joint diagnosed using low-field magnetic resonance imaging in standing horses. Vet Radiol Ultrasound. 2009;50(1):13–20.
