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Objective—To compare navicular bone marrow lesion (BML) conspicuity in the feet of horses as determined via 2 fat-suppressed MRI techniques, including standard short tau inversion recovery (STIR) and inversion recovery gradient echo (IRGE). Sample—Feet (n = 150) of horses with lameness referable to the distal portion of the digit. Procedures—STIR and IRGE sequences were obtained prospectively in all feet with a standing low-field equine MRI system. Presence of a BML was ascertained by identification of a characteristic combination of marrow alterations in T1-weighted, T2*-weighted, T2-weighted, and STIR images. Signal-to-noise and contrast-to-noise ratios were calculated on STIR and IRGE sequences in 56 feet with a navicular BML. Results—Signal-to-noise and contrast-to-noise ratios of both sequences correlated linearly (r = 0.87 and r = 0.92, respectively) but were significantly higher for STIR images (mean ± SD, 22.6 ± 12.7 and 12.4 ± 11.4, respectively), compared with IRGE images (13.7 ± 8.0 and 5.9 ± 7.2, respectively). Conclusions and Clinical Relevance—Results suggested that the IRGE sequence revealed BMLs significantly less conspicuously, compared with the standard STIR sequence. The 2 techniques cannot be used interchangeably, and IRGE is therefore not recommended as the sole fat-suppressed sequence for routine equine standing MRI protocols.

Objective—To evaluate the ability of signal attenuation–based quantitative magnetic resonance imaging (QMRI) to estimate subchondral bone mineral density (BMD) as assessed via quantitative computed tomography (QCT) in osteoarthritic joints of horses. Sample Population—20 metacarpophalangeal joints from 10 horse cadavers. Procedures—Magnetic resonance (MR) images (dorsal and transverse T1-weighted gradient recalled echo [GRE] and dorsal T2*-weighted GRE fast imaging employing steady-state acquisition [T2*-FIESTA]) and transverse single-slice computed tomographic (CT) images of the joints were acquired. Magnetic resonance signal intensity (SI) and CT attenuation were quantified in 6 regions of interest (ROIs) in the subchondral bone of third metacarpal condyles. Separate ROIs were established in the air close to the joint and used to generate corrected ratios and SIs. Computed tomographic attenuation was corrected by use of a calibration phantom to obtain a K2HPO4-equivalent density of bone. Correlations between QMRI performed with different MR imaging sequences and QCT measurements were evaluated. The intraobserver repeatability of ROI measurements was tested for each modality. Results—Measurement repeatability was excellent for QCT (R2 = 98.3%) and QMRI (R2 = 98.8%). Transverse (R2 = 77%) or dorsal (R2 = 77%) T1-weighted GRE and QCT BMD measurements were negatively correlated, as were dorsal T2*-FIESTA and QCT (R2 = 80%) measurements. Decreased bone SI during MR imaging linearly reflected increased BMD. Conclusions and Clinical Relevance—Results of this ex vivo study suggested that signal attenuation–based QMRI was a reliable, clinically applicable method for indirect estimation of subchondral BMD in osteoarthritic metacarpophalangeal joints of horses.

Objective—To ultrasonographically quantify experimentally induced effusion of the distal interphalangeal (DIP) joint of horses and compare results with those obtained with palpation. Sample—8 forelimbs from equine cadavers and forelimbs of 5 mares. Procedures—Preliminary ex vivo experiments were performed to validate the methods. Then, the DIP joints of the forelimbs of standing horses were serially distended with saline (0.9% NaCl) solution (1, 4, and 10 mL) by injection through an intra-articular catheter. Two ultrasonographers measured distension of the dorsal recess of the DIP joint, and 2 surgeons, who were not aware of the volume injected, graded joint effusion by palpation. Results—Intraobserver and interobserver repeatability was excellent for ultrasonographic measurements. Interobserver agreement for use of palpation to detect joint distension was moderate (κ = 0.45). There was an overall increase in the palpation distension grade with an increase in injected volume. Sensitivity for detection with palpation of larger volumes (4 and 10 mL) was high (92% and 100%, respectively). However, sensitivity was lower (57%) for detection with palpation of minimal distension (1 mL). Conclusions and Clinical Relevance—Although palpation provided a reliable clinical assessment of DIP joint effusion for volumes of 4 to 10 mL, ultrasonographic measurements were easy to obtain, more accurate, and able to detect smaller amounts of distension. This may be clinically relevant for the assessment of effusion of the DIP joint that can arise in horses with early osteoarthritis or infectious arthritis with concomitant soft tissue swelling that precludes accurate assessment with palpation.