Standing low-field MRI of the equine proximal metacarpal/metatarsal region is considered useful for diagnosing primary bone pathology and makes a positive contribution to case management: A prospective survey study.

High-field MRI of the proximal metacarpal/metatarsal region has been associated with great diagnostic potential and clinical reports of standing low-field MRI of the forelimb suggest the same. To better understand diagnostic outcomes with standing low-field MRI of the proximal suspensory region, a prospective survey study was conducted and users of a widely available system questioned on their experience, operating procedures, and interpretation of standing low-field MRI findings. Response data included scores on a modified Likert scale from which weighted ratings were calculated for statistical analyses. Depending on the question, responses were obtained from 17 to 29 of the 38 invited facilities. Users indicated that standing low-field MRI was most frequently performed in the face of equivocal diagnostic findings; compared to Sports horses, general purpose riding horses were thought less likely to have detectable abnormalities and standing low-field MRI was rated most useful for the detection of primary bone pathology in the proximal metacarpal region. Standing low-field MRI signal change involving both the suspensory ligament and adjacent bone concurrently was rated most relevant and abnormalities solely affecting the muscle/adipose tissue bundles least relevant for diagnosing suspensory ligament injury. Transverse scans and in decreasing order T1-weighted gradient echo, short-tau inversion recovery FSE, T2*-weighted gradient echo, and T2-weighted FSE sequences were most frequently acquired and judged most useful by the majority of users experienced in imaging of the target area. This survey supports the relevant impact of standing low-field MRI on clinical case management, particularly in the context of imaging the proximal metacarpal region.

Identification of Heterotopic Mineralization and Adjacent Pathology in the Equine Fetlock Region by Low-Field Magnetic Resonance Imaging, Cone-Beam and Fan-Beam Computed Tomography.

Heterotopic mineralization in equine distal limbs has been considered an incidental finding and little is known about its imaging features. The study aimed to identify heterotopic mineralization and adjacent pathology in the fetlock region with cone-beam (CB) computed tomography (CT), fan-beam (FB) CT, and low-field magnetic resonance imaging (MRI). Images from 12 equine cadaver limbs were examined for heterotopic mineralization and adjacent pathology and verified by macro-examination. Retrospective review of the CBCT/MR images from 2 standing horses was also included. CBCT and FBCT identified twelve mineralization's with homogeneous hyperattenuation: oblique-sesamoidean-ligament (5) without macroscopic abnormality; deep-digital-flexor-tendon (1) and suspensory-branch (6) with macroscopic abnormalities. MRI failed to identify all mineralization's, but detected suspensory branch splitting, and T2 and STIR hyperintensity in 4 suspensory-branches and 3 oblique-sesamoidean-ligaments. Macro-examination found corresponding disruption/splitting and discoloration. All modalities identified 7 ossified fragments showing cortical/trabecular pattern: capsular (1), palmar sagittal ridge (1), proximal phalanx (2) without macroscopic abnormality, and proximal sesamoid bones (3). On MRI, fragments were most identifiable on T1 images. All abaxial avulsions had suspensory-branch splitting on T1 images with T2 and STIR hyperintensity. Macro-examination showed ligament disruption/splitting and discoloration. Suspensory-branch/intersesamoidean ligament mineralization's were identified by CBCT in standing cases; 1 had associated T2 hyperintensity. Both CT systems were generally superior in identifying heterotopic mineralization's than MRI, while MRI provided information on soft tissue pathology related to the lesions, which may be important for management.

Magnetic Resonance Imaging Findings of the Proximal Metacarpal Region in Warmblood Horses: 36 Lame and 26 Control Limbs (2015-2021).

Objectives: This study aims to evaluate the distribution and severity of bone and soft tissue lesions in the proximal metacarpal region of warmblood horses in lame and control groups. Correlation between lesions and ability to return to work was evaluated in the lame group. Methods: This restrospective analysis evaluated 62 horses with MRI examination of the proximal metacarpal region between Sept 2015 and Feb 2021. There were 36 lame limbs and 26 control limbs. The control group included seven contralateral limbs. Results: Proximal suspensory ligament (PSL) size was not different between the lame and control groups. Hyperintensity seen on T1W/T2*W GRE images within the dorsal collagenous part of the PSL and hyperintense Short-TI Inversion Recovery (STIR) signal within the dorsal collagenous part of the PSL or within the McIII were only present within the lame group. Palmar cortical McIII resorption and dorsal margin irregularity of the PSL and McIII sclerosis were more severe within the lame limbs, but mild gradations were also seen in control limbs. Intermediate gradings for a subset of lesions were commonly seen in the non-lame contralateral to lame limbs. Return to work in the lame group is not statistically different for any measured observation(s), and 19/33 of the lame horses returned to work at similar or higher levels. Conclusion and clinical importance: Fifty-eight percent in this group of warmblood horses returned to work within a variable time frame. The majority (81%) of lame limbs showed bone and soft tissue abnormalities, but no enlargement of the PSL was noted in lame horses, and no correlation was seen between the severity or type of lesions and the ability to return to work. The presence of STIR hyperintensity within the proximal McIII or dorsal collagenous part of the PSL and hyperintensity within the dorsal collagenous part of the PSL on T1W GRE and T2*W GRE images, as well as significant palmar cortical McIII resorption are considered clinically relevant lesions. Contralateral limbs may not truly represent the normal condition, showing nonclinical variations and adaptive remodeling.

Magnetic Resonance Imaging Findings in the Proximal Metacarpal Region of 359 Horses and Proximal Metatarsal Region of 64 Horses Acquired Under Standing Sedation.

Standing magnetic resonance (MR) images of proximal metacarpal/metatarsal regions are increasingly being acquired. This study aimed at describing ranges of abnormalities detected in sport/racehorses, using retrospective evaluation of magnetic resonance imaging (MRI) reports from horses with lameness isolated to proximal metacarpal/metatarsal regions with images acquired standing. It was hypothesized that MRI features are different between metacarpal and metatarsal regions and between horses doing different sports. Reports from 359 forelimbs and 64 hindlimbs were included. Palmar/plantar metacarpal/metatarsal bone injury and suspensory desmopathy, which often occurred concurrently, were most frequently reported. Third metacarpal abnormalities were more likely at palmar/medial locations, including cortical (86.4%) and trabecular (38.2%) pathology with frequent thickening, irregularity, and periosteal/endosteal abnormalities. Fluid signal was reported in cortical (38.7%) and trabecular (22.6%) bone. Medial intermetacarpal articulation abnormalities were more frequently reported (52.5%) than lateral. Suspensory ligament pathology was reported in 83.8% forelimbs, frequently with cortical (74.1%) or trabecular (32.9%) pathology. Tarsal-joint abnormalities were significantly more likely than carpal-joint abnormalities. Third metatarsal cortical (57.8%) and trabecular (20.3%) pathology was most frequently plantar, but significantly more likely to be dorsal than forelimbs. Metatarsal fluid signal was significantly less likely than metacarpal. Lateral intermetatarsal articulation pathology (23.4%) was more frequent than medial; medial was significantly more likely in forelimbs. Suspensory ligament abnormalities were reported in 64.1% hindlimbs, 39.1% having concurrent cortical pathology. Metacarpal fluid signal was significantly more likely in endurance/racehorses than dressage/show jumping horses. Dressage was overrepresented in hindlimb suspensory origin pathology. These findings indicate different pathology patterns between forelimb/hindlimb and between different sports and may be useful for MRI interpretation.

Variation in foot conformation in lame horses with different foot lesions.

Foot conformation in the horse is commonly thought to be associated with lameness but scientific evidence is scarce although it has been shown in biomechanical studies that foot conformation does influence the forces acting on the deep digital flexor tendon (DDFT) and the navicular bone (NB). The aim of this study was to determine the relationships between foot conformation and different types of lesion within the foot in lame horses. It was hypothesised that certain conformation parameters differ significantly between different types of foot lesions. Conformation parameters were measured on magnetic resonance images in the mid-sagittal plane of 179 lame horses with lesions of their deep digital flexor tendon (DDFT), navicular bone (NB), collateral ligaments of the distal interphalangeal joints and other structures. Conformation parameters differed significantly between lesion groups. A larger sole angle was associated with combined DDFT and NB lesions, but not with NB lesions alone. A more acute angle of the DDFT round the NB was associated with DDFT and NB lesions, and a lower heel height index with DDFT injury. The larger the sole angle the smaller the likelihood of a DDFT or NB lesion with odds ratios of 0.86 and 0.90, respectively. This study shows an association between foot conformation and lesions but it does not allow the identification of conformation as causative factor since foot conformation may change as a consequence of lameness. Future studies will investigate foot-surface interaction in lame vs. sound horses, which may open a preventative and/or therapeutic window in foot lame horses.

The influence of temperature and age on the T1 relaxation time of the equine distal limb.

The extent of fat suppression using short tau inversion recovery (STIR) imaging is variable between horses. Our aim was to determine if patient's age and/or hoof temperature have an influence on the T(1) relaxation time of bone marrow in the equine distal limb, thereby affecting the suppression of fat signal. Magnetic resonance imaging was conducted on standing horses and cadaver samples using a low-field magnet (0.27 T). The hoof temperature was measured at the lateral side of the coronary band. A modified inversion recovery fast spin-echo (IR-FSE) sequence was used to measure the signal intensity for a range of inversion times (TIs) at six different regions of interest (ROI): (1) distal aspect of the proximal phalanx, (2) proximal aspect of the middle phalanx, (3) distal aspect of the middle phalanx, (4) navicular bone, (5) proximal aspect of the distal phalanx, and (6) distal aspect of the distal phalanx. The T(1) of the bone marrow in the equine distal limb was calculated from the results and was found to increase by 3.13 ± 0.08 (SE) ms/°C. There was no significant effect of age (2-16 years) but the T(1) values measured from the limbs of young (< 1 year) animals were considerably longer (32.6 ± 1.7 (SE) ms). Similar effects of temperature and age were found for all measured ROIs but there were significant differences in the mean values of T(1) , ranging from +7.7 (distal aspect of the distal phalanx) to -13.2 ms (distal aspect of the proximal phalanx).