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SummaryBackground Non-invasive imaging tools are needed to screen foal femoropatellar joints to detect subclinical osteochondrosis lesions due to focal failure of endochondral ossification to enhance early management to optimise intrinsic healing events. Recently investigations employing 3T susceptibility-weighted MRI (3T SWI MRI) and CT have demonstrated their capacity for early osteochondrosis diagnosis, but these technologies are not practical for field screening. We postulate that ultrasonography is a valuable field tool for the detection of subclinical osteochondrosis lesions. Objectives The goals were 1) to describe the sonographic features of the femoral trochlea of healthy and osteochondrosis-predisposed neonatal foals, 2) to validate the capacity of ultrasound to assess cartilage canal vascular archictecture and the ossification front and 3) to evaluate field feasibility in a pilot study. Study design Experimental study. Methods Ultrasonographic evaluation of osteochondrosis predisposed (n = 10) and control (n = 6) femoral trochleas was performed ex vivo and compared with site-matched histological sections and 3T SWI MRI. The articular and epiphyseal cartilage thickness, the ossification front indentation and the cartilage canal vascular archictecture were assessed at each ROI. Femoral trochleae of foals (n = 3) aged 1, 3 and 6 months were also evaluated with ultrasonography in field. Results Ultrasonographic measurements strongly correlated with the histological measurements. There was no difference in the cartilage thickness or ossification front indentation between control and osteochondrosis-predisposed specimens. The cartilage canal vascular archictecture on ultrasonograms corresponded with the vessel pattern observed on site-matched histology and 3T SWI MRI. Main limitations The number of specimens for study was limited, and no early osteochondrosis lesions were present within the predilected group, but a field study is now underway. Conclusion Ultrasonographic examination of the femoral trochlea permitted accurate evaluation of cartilage thickness, cartilage canal vascular archictecture and ossification front indentation in young foals and is a promising, practical tool for screening subclinical osteochondrosis and monitoring and managing lesions at important clinical sites. This article is protected by copyright. All rights reserved.

BACKGROUND Extensive osteochondritis dissecans (OCD) lesions of the lateral ridge of the trochlea of the femur (LRTF), the most common OCD-affected site in the stifle, have a poor outcome with surgical debridement and can be career ending. The early detection of osteochondrosis lesions and their conservative management holds the promise to enhance outcome. We hypothesise that ultrasonography is a valuable field screening tool to detect and monitor early subclinical LRTF osteochondrosis. OBJECTIVES The goals were to 1) describe the normal ultrasonographic features of the LRTF in foals of different ages and 2) screen a foal cohort at the farm for early subclinical osteochondrosis lesions. STUDY DESIGN Prospective cohort study. METHODS The LRTF of both hindlimbs of Thoroughbred foals (n = 46, 27-166 days old) were imaged once with ultrasonography and radiography (lateromedial and caudolateral-craniomedial oblique views). Cartilage thickness, ossification front indentation of the chondro-osseous junction and epiphyseal vascularisation were assessed on ultrasonography. Follow-up radiographs were taken as yearlings. RESULTS The cartilage thickness, ossification front indentation and epiphyseal vascularisation significantly decreased with advancing maturity. Subclinical osteochondrosis lesions, characterised by semicircular indentations in the ossification front (indirect evidence of focal failure of ossification and retained cartilage) were detected in six foals (28-145 days old), both with radiography and ultrasonography. Ultrasonography provided a better overall subjective assessment of the osteochondrosis lesion topography (length, depth and the width) compared with radiography. MAIN LIMITATIONS Post-mortem validation of lesions was not possible. CONCLUSION Ultrasonography of the LRTF is a practical, inexpensive and reliable technique to discriminate physiological from pathological events at the LRTF in young foals. It revealed the complex topography of the chondro-osseous junction permitting a rapid, comprehensive assessment of the subclinical osteochondrosis lesions in very young foals.

Summary Reasons for performing study: Marginal osteophytes represent a well known component of osteoarthritis in man and animals. Conversely, central subchondral osteophytes (COs), which are commonly present in human knees with osteoarthritis, have not been reported in horses. Objectives: To describe and compare computed radiography (CR), single-slice computed tomography (CT), 1.5 Tesla magnetic resonance imaging (MRI), and histological features of COs in equine metacarpophalangeal joints with macroscopic evidence of naturally-occurring osteoarthritis. Methods: MRI sequences (sagittal spoiled gradient recalled echo [SPGR] with fat saturation, sagittal T2-weighted fast spin echo with fat saturation [T2-FS], dorsal and transverse T1-weighted gradient-recalled echo [GRE], and sagittal T2*-weighted gradient echo with fast imaging employing steady state acquisition [FIESTA]), as well as transverse and reformatted sagittal CT, and 4 computed radiographic (CR) views of 20 paired metacarpophalangeal joints were acquired ex vivo. Following macroscopic evaluation, samples were harvested in predetermined sites of the metacarpal condyle for subsequent histology. The prevalence and detection level of COs was determined for each imaging modality. Results: Abnormalities consistent with COs were clearly depicted on MRI, using the SPGR sequence, in 7/20 (35%) joints. They were identified as a focal hypointense protuberance from the subchondral plate into the cartilage, at the palmarodistal aspect (n = 7) and/or at the very dorsal aspect (n = 2) of the metacarpal condyle. COs were visible but less obvious in 5 of the 7 joints using FIESTA and reformatted sagittal CT, and were not identifiable on T2-FS, T1-GRE or CR. Microscopically, they consisted of dense bone protruding into the calcified cartilage and disrupting the tidemarks, and they were consistently associated with overlying cartilage defects. Conclusions: Subchondral osteophytes are a feature of osteoarthritis of equine metacarpophalangeal joints and they may be diagnosed using 1.5 Tesla MRI and CT. Potential relevance: Central subchondral osteophytes on MRI represent indirect evidence of cartilage damage in horses.