Diagnostic imaging of the equine fetlock region using radiography and ultrasonography. Part 2: The bony disorders

Radiological findings in the proximal sesamoid bones of yearling and 2-year-old Thoroughbred sales horses: Prevalence, progression and associations with racing performance

BACKGROUND

Radiological findings in the proximal sesamoid bones (sesamoids) are a persistent source of controversy at Thoroughbred sales, due to inconsistent classification and conflicting assignment of potential clinical importance.

OBJECTIVES

To define the prevalence of sesamoid findings on sales repository radiographs in yearling and 2-year-old Thoroughbreds and to analyse associations with racing performance. To track the changes in sesamoid findings between 1 and 2 years of age in horses that present for sale at both ages.

STUDY DESIGN

Prospective cohort study using an enrolled sample.

METHODS

Horses were enrolled from a 2016 yearling sale and five 2017 2-year-old sales with consignor permission. Radiological findings relating to sesamoid vascular channel appearance, abaxial contour changes and sesamoid fragments were examined. Associations between sesamoid findings and racing performance from 2 to 4 years of age were examined using multivariate regression analyses. Clinical follow-up was sought to ascertain why horses that did not race never started.

RESULTS

A total of 2508 yearlings and 436 2-year-olds were included for evaluation. Interobserver agreement using the new grading system was substantial. Yearling findings associated with a significantly reduced probability of starting a race were: Grade 3 vascular channels in forelimb sesamoids (0.52, P < 0.001, 95% confidence interval (CI): 0.37-0.67), abaxial new bone in forelimb sesamoids (0.62, P = 0.01, 95% CI: 0.49-0.73), apical or abaxial fragments in forelimb sesamoids (0.55, P = 0.005, 95% CI: 0.37-0.72). For affected horses that did race, Grade 3 vascular channels in forelimb sesamoids were associated with fewer race starts (9.9 starts, P = 0.03, 95% CI: 8.0-12.2) and Grade 3 vascular channels in hindlimb sesamoids were associated with a delayed start to racing careers (54 days, P = 0.01, 95% CI: 20-89). Abaxial new bone in forelimb sesamoids was associated with a 54% reduction in total earnings (P = 0.003, 95% CI: 24-72) and a 46% reduction in earnings per start (P = 0.002, 95% CI: 21-64). Abaxial concavity occurred predominantly in yearling medial forelimb sesamoids, had no impact on racing performance and mostly resolved by 2-year-old sale.

MAIN LIMITATIONS

These findings are applicable to horses presented for sale at public auction and may underestimate the prevalence of severe lesions in non-sales horses.

CONCLUSIONS

Grade 3 vascular channels, forelimb sesamoid abaxial new bone and forelimb sesamoid fragments are important findings in sales repository radiology. The new grading scale assigns a numerical grade for vascular channel appearance that matches the number of enlarged vascular channels evident in a given sesamoid. Abaxial contour changes, when present in sesamoids that are Grade 0 for enlarged vascular channels, are noted separately as either abaxial new bone or abaxial concavity. Fragments are also noted and interpreted separately.

Comparison of cone-beam and fan-beam computed tomography and low-field magnetic resonance imaging for detection of palmar/plantar osteochondral disease in Thoroughbred horses

BACKGROUND

Palmar/plantar osteochondral disease (POD) of the metacarpal/tarsal condyles is a common pathological finding in racehorses.

OBJECTIVE

To compare diagnoses, imaging details, and measurements of POD lesions between cone-beam computed tomography CT (CBCT), fan-beam CT (FBCT), and low-field magnetic resonance imaging (MRI) using macroscopic pathology as a gold standard.

STUDY DESIGN

Cross-sectional study.

METHODS

Thirty-five cadaver limbs from 10 horses underwent CBCT, FBCT, MRI, and macroscopic examination. CT and MR images were examined for presence of POD, imaging details of POD, and measurements of POD dimensions and areas. Imaging diagnoses, details, and measurements were compared with macroscopic examination and between modalities.

RESULTS

Forty-eight POD lesions were seen over 70 condyles. Compared with macroscopic examination the sensitivity and specificity of diagnosis were 95.8% (CI95 = 88%-99%) and 63.6% (CI95 = 43%-81%) for FBCT, 85.4% (CI95 = 74%-94%) and 81.8% (CI95 = 63%-94%) for CBCT, and 69.0% (CI95 = 54%-82%) and 71.4% (CI95 = 46%-90%) for MRI. Inter-modality agreement on diagnosis was moderate between CBCT and FBCT (κ = 0.56, p < 0.001). POD was identified on CT as hypoattenuating lesions with surrounding hyperattenuation and on MRI as either T1W, T2*W, T2W, and STIR hyperintense lesions or T1W and T2*W heterogeneous hypointense lesions with surrounding hypointensity. Agreement on imaging details between CBCT and FBCT was substantial for subchondral irregularity (κ = 0.61, p < 0.001). Macroscopic POD width strongly correlated with MRI (r = 0.81, p < 0.001) and CBCT (r = 0.79, p < 0.001) and moderately correlated with FBCT (r = 0.69, p < 0.001). Macroscopic POD width was greater than all imaging modality (p < 0.001).

MAIN LIMITATIONS

Effect of motion artefact in live horse imaging could not be assessed.

CONCLUSIONS

All imaging modalities were able to detect POD lesions, but underestimated lesion size. The CT systems were more sensitive, but the differing patterns of signal intensity may suggest that MRI can detect changes associated with POD pathological status or severity. The image features observed by CBCT and FBCT were similar.

Ultrasonography of the Metacarpal/Tarsal-Phalangeal Joints in Healthy Racehorses: Normal Appearance, Breed-Related and Age-Related Features

In adult horses, specific ultrasound (US) features and reference values have been reported for the appearance of the joint cartilage and thickness according to the type of joint, such as femoropatellar and tarsocrural. The US appearance of the fetlock has been described in several diseases. The present research evaluates the US features of the metacarpal/tarsal-phalangeal joints in healthy racehorses according to age and breed, since no information is available in the literature. Seventy-one fetlocks in 28 healthy horses (15/28 thoroughbreds and 13/28 standardbreds) were assessed. The horses were grouped as follows: group A < 5 years old vs. group B ≥ 5. A portable ultrasound machine and a linear transducer (5−7.5 MHz) were used. Dorsal metacarpal/tarsal-phalangeal joints were scanned. The US images were reviewed offline in terms of articular cartilage appearance, thickness, and subchondral bone appearance by an experienced observer. Data were reported as the median, minimum, and maximum for cartilage thickness values, and differences between groups were evaluated. Cartilage thickness values were statistically lower in group A than B in the standardbreds, except for the lateral thickness in longitudinal view. No differences were detected in the thoroughbreds within age groups. All of the young standardbreds showed a normal cartilage and subchondral appearance. No statistical differences were found between breeds. Our results highlight the characteristics of the US appearance of metacarpal/tarsal-phalangeal joints specifically in racehorses, with some variations according to age. Since the cartilage can change according to joint growth, age and training activity, the present findings suggest the use of specific references for US features, which are key to correctly evaluating the health of the fetlock.

Morphological analysis of third metacarpus cartilage and subchondral bone in Thoroughbred racehorses: An ex vivo study

Racehorses are exposed to repetitive overload during training and competition, causing joint hyperextension, tissue fatigue, and ultimately skeletal failure. Some degree of bone changes, such as sclerosis, are expected in equine athletes, as adaptation to the biomechanical rigors of training and racing. Understanding the imaging characteristics of the equine joint surface and subchondral bone would allow earlier detection of injuries or adaptation, improving prognosis and training programs. This study sought to describe the joint surface structural patterns and the periarticular structures of the third metacarpal bone (MC3). Both forelimbs of eight horses engaged in daily training programs, aged 3 to 5 years, which were euthanized for reasons unrelated to the metacarpophalangeal (MCP) joints, were collected. Specimens were evaluated through macroscopic inspection, radiography, ultrasonography, and microscopic examinations, such as optical microscopy and microtomography. Analysis of the microtomography images showed that 50% of the samples had higher trabecular thickness in the lateral condyle. Comparison of each imaging examination revealed that ultrasound images were most closely related to the histological examination (p = 0.29) in terms of sensitivity, while macroscopic and radiographic examinations differed most between evaluators. Finally, the irregularities and modifications observed in the articular cartilage surface and subchondral bone were normal adaptations of the anatomical structures of trained racehorses, which should be considered during clinical examination.

Cartilage Degeneration of the Metacarpal Condyle and Enthesopaties of The Collateral Ligaments of Equine Metacarpophalangeal Joint

Articular degeneration can be characterized by fibrillation and eburnation of the articular layers of the metacarpophalangeal (MP) joint. Structural changes within the articular joint predispose the development of osteophytes, enthesophytes and, in many cases is associated with changes the collateral ligaments of the MP joint. The aim of the present study was to investigate the relationship between degenerative processes of the articular cartilage and the enthesopathies of collateral ligaments (superficial or deep portion) of the equine MP joint, using radiographic, ultrasonographic and anatomopathological exam, as well as establishing their sensitivity. Thirty equine forelimbs were selected from animals that died due to various clinical conditions with an average age of 5.7 years which came from a private clinic or sent to the Laboratory of Veterinary Pathology of UFSM. The specimens were placed in a hydraulic press and submitted to radiographic evaluation of the MP joint (lateromedial, flexed lateromedial, dorsopalmar, dorsolateral-palmaromedial oblique 45⁰ and dorsomedial-palmarolateral oblique 45⁰ projections). Transversal and longitudinal ultrasound images of the dorsal and collateral aspect of the MP joint were obtained using a Sonosite Edge machine with a 5 to 10 MHz linear transducer. Subsequently, the specimens were sent for gross and histopathological examination. A highly positive correlation (P value <.001) was observed between ultrasonographic and macroscopic techniques, showing a relationship between the cartilaginous degenerations of the MP joint and the medial and lateral LC enthesopathies.

Comparison of ultrasonography and radiography with arthroscopy for diagnosis of dorsoproximal osteochondral fragmentation of the proximal phalanx in 56 Thoroughbred racehorses

BACKGROUND

Osteochondral fragmentation of the proximal phalanx (DPP1 fragment) is a common finding in the racehorse. Whilst radiographic assessment has been reported to lack diagnostic sensitivity, ultrasonographic examination has been documented to be extremely sensitive for identification of bone fragments in the metacarpophalangeal joint.

OBJECTIVES

To determine the sensitivity and specificity of ultrasonography as an imaging modality for diagnosis of DPP1 fragmentation and to compare it with radiography in the Thoroughbred racehorse.

STUDY DESIGN

Retrospective cohort study.

METHODS

Medical records (radiographs and ultrasonographic examinations) of 56 Thoroughbred racehorses in training (average age 26.4 months [SD ±5.9]) with a history of forelimb fetlock joint effusion and arthroscopically confirmed DPP1 fragmentation were evaluated. Inter-observer agreement was calculated between three blinded reviewers for both ultrasonographic and radiographic findings. Median values were used for statistical analyses. Ultrasonographic and radiographic identification of DPP1 fragmentation was considered correct if in agreement with arthroscopic findings. The McNemar test was used to compare correct proportions between radiography and ultrasonography. Analyses were performed to evaluate correct identification of presence of fragment(s), location of fragment(s) and presence and location of fragment(s) within the joints, with values P < .05 considered significant.

RESULTS

Eighty-one fetlock joints from 56 Thoroughbreds were evaluated. In total, 99 individual DPP1 fragments were confirmed arthroscopically. Ultrasonography was shown to have high levels of sensitivity (94%, 95% CI 89%-99%) and specificity (97%, 95% CI 92%-100%) for identification of DPP1 fragments, with transverse ultrasonographic images being more sensitive than sagittal ultrasonography (P = .001). Ultrasonography was also shown in this population to have significantly greater sensitivity than radiography (47%, 95% CI 37%-56%) (P < .001).

CONCLUSIONS

Ultrasonography is an extremely sensitive and specific imaging modality for evaluation of DPP1 fragmentation, with transverse ultrasonographic imaging being the most sensitive technique. Radiographic evaluation was less sensitive than ultrasonography in this study.

Diagnostic Imaging and Cytological Analysis Aid the Clinical Investigation of Long Digital Extensor Tendon Subtendinous Bursitis in a Horse

The fetlock joint is a high mobility structure that accommodates enormous loading during locomotion. An injury of the superficial constituent such as subtendinous bursitis may occur due to repeated trauma. An 8-year old school riding horse was presented with dorsomedial distension in the left hindlimb fetlock region. The lesion was noted following routine exercise. The horse demonstrated no lameness and a negative response to the fetlock flexion test. Radiographic findings revealed a smooth surface cortical thickening on the medial aspect of the distal third metatarsal bone. Furthermore, the ultrasonography showed synovial thickening and proliferation, fibrous thickening with an irregular border in the inner synovial lining, and local protuberance of the fibrous layer within the bursa beneath the long digital extensor tendon. Cytological examination of the fluid from the distended lesion discovered multiple nucleated cells, including synoviocytes, nondegenerate neutrophils, lymphocytes, and macrophages. Eventually, the horse suffered subtendinous bursitis of long digital extensor tendon in the left hindlimb fetlock region. Intrabursa administration of 10 mg triamcinolone acetate alongside 25 mg hyaluronan (HA) and subsequent pressure bandaging were performed in the affected fetlock area. The distension was substantially reduced after the 4-week recovery period post medical administration. In summary, the horse was diagnosed with long digital extensor subtendinous bursitis that can occur accidentally. The diagnostic imaging and cytological analysis of accumulated fluid benefited a critical evaluation and facilitated the selection of the appropriate therapeutic plan for this defect.

Morphological and Imaging Evaluation of the Metacarpophalangeal and Metatarsophalangeal Joints in Healthy and Lame Donkeys

The donkey is of socio-economic value yet imaging techniques in both healthy and abnormal limbs are a limiting factor in research and medicine. The objective was to determine anatomical features of both healthy and clinically abnormal donkey metacarpophalangeal and metatarsophalangeal joints (n = 13) using anatomical dissection, casting, X-ray and computed tomography. The joint capsule contained two palmar/plantar and two dorsal recesses. The proximal-palmar or plantar recess was larger than the distodorsal recess and potential sites of approaches to the recesses were determined. Soft tissue structures were distinguished using computed tomography at 300 mA, which was superior to 120 mA. This methodology gave better assessments of the synovial tendon sheath, joint recesses, and cruciate, collateral, and short sesamoidean ligaments. Computed tomography provided outstanding discrimination between the cortex and medulla of the third metacarpal, the proximal sesamoid bones, the proximal phalanx, and excellent details of the osseous structures. Although the joints appeared free from exostosis using X-ray; the position and extension of exostosis in pathologically affected donkeys (a novel finding) were revealed using computed tomography with 300 mA in comparison to 120 mA. The study also provided an anatomical record of the metacarpophalangeal and metatarsophalangeal joints using the latest technology, which could impact on clinical situations including anesthesia injection sites.

Thoracic limb alignment in healthy labrador retrievers: evaluation of standing versus recumbent frontal plane radiography

OBJECTIVE

To report thoracic limb alignment values in healthy dogs; to determine if limb alignment values are significantly different when obtained from standing versus recumbent radiographic projections.

STUDY DESIGN

Prospective cross-sectional study.

ANIMALS

Labrador Retrievers (n = 45) >15 months of age.

METHODS

Standing and recumbent radiographs were obtained and limb montages were randomized before analysis by a single investigator blinded to dog, limb, and limb position. Twelve limb alignment values were determined using the CORA methodology. Measurements were performed in triplicate and intra-observer variability was evaluated by intra-class correlation coefficient (ICC). Limb alignment values were reported as mean ± SD and 95% confidence intervals. Linear mixed models were used to determine if significant associations existed between limb alignment values and limb, limb position, gender, age, weight, and body condition score.

RESULTS

There were significant differences in standing and recumbent limb alignment values for all values except elbow mechanical axis deviation (eMAD). Limb, gender, age, body weight, and body condition score had no effect. ICC values ranged from 0.522 to 0.758, indicating moderate to substantial agreement for repeated measurements by a single investigator.

CONCLUSIONS

Limb alignment values are significantly different when determined from standing versus recumbent radiographs in healthy Labrador Retrievers.

Fragmentation of the proximal tubercle of the talus in horses: 9 cases (2004-2010)

OBJECTIVE

To identify the prevalence of fragmentation of the proximal tubercle of the talus (FPTT) in a hospital population of horses, characterize the anatomic features of the affected area and fragments, and describe clinical findings, diagnosis, treatment, and outcome for horses with FPTT.

DESIGN

Retrospective case series.

ANIMALS

9 horses with FPTT.

PROCEDURES

2,543 radiographic views of the tarsal region of 1,526 horses that were evaluated between June 2004 and December 2010 were reviewed. Medical case records for horses with detectable FPTT were retrieved, and signalment, history, clinical signs, diagnostic methods, treatment, and outcome were recorded for assessment.

RESULTS

9 horses (median age, 5 years; age range, 1 to 12 years) with FPTT were identified. Seven horses were warmbloods. Diagnosis was made on the basis of radiographic findings, occasionally along with results of ultrasonography and CT. The only horse that was lame in the affected limb had a history of a prior traumatic event and resultant lateral tibial malleolus fracture. One horse underwent arthroscopy, but fragments were not found and were presumed to be extra-articular. Outcome was available for 7 horses; mean ± SD duration of stable radiographic and clinical examination findings was 3 ± 1 years (range, 1 to 4 years).

CONCLUSIONS AND CLINICAL RELEVANCE

FPTT appeared to occur more frequently in warmbloods and was not usually associated with lameness. Affected horses remained clinically and radiographically stable over time. These data have provided some information regarding the importance of FPTT for practitioners who perform radiographic screenings during prepurchase examinations.