Interobserver agreement during clinical magnetic resonance imaging of the equine foot.

BACKGROUND: Agreement between experienced observers for assessment of pathology and assessment confidence are poorly documented for magnetic resonance imaging (MRI) of the equine foot. OBJECTIVES: To report interobserver agreement for pathology assessment and observer confidence for key anatomical structures of the equine foot during MRI. STUDY DESIGN: Exploratory clinical study. METHODS: Ten experienced observers (diploma or associate level) assessed 15 equine foot MRI studies acquired from clinical databases of 3 MRI systems. Observers graded pathology in seven key anatomical structures (Grade 1: no pathology, Grade 2: mild pathology, Grade 3: moderate pathology, Grade 4: severe pathology) and provided a grade for their confidence for each pathology assessment (Grade 1: high confidence, Grade 2: moderate confidence, Grade 3: limited confidence, Grade 4: no confidence). Interobserver agreement for the presence/absence of pathology and agreement for individual grades of pathology were assessed with Fleiss' kappa (k). Overall interobserver agreement for pathology was determined using Fleiss' kappa and Kendall's coefficient of concordance (KCC). The distribution of grading was also visualised with bubble charts. RESULTS: Interobserver agreement for the presence/absence of pathology of individual anatomical structures was poor-to-fair, except for the navicular bone which had moderate agreement (k = 0.52). Relative agreement for pathology grading (accounting for the ranking of grades) ranged from KCC = 0.19 for the distal interphalangeal joint to KCC = 0.70 for the navicular bone. Agreement was generally greatest at the extremes of pathology. Observer confidence in pathology assessment was generally moderate to high. MAIN LIMITATIONS: Distribution of pathology varied between anatomical structures due to random selection of clinical MRI studies. Observers had most experience with low-field MRI. CONCLUSIONS: Even with experienced observers, there can be notable variation in the perceived severity of foot pathology on MRI for individual cases, which could be important in a clinical context.

Clinical magnetic resonance image quality of the equine foot is significantly influenced by acquisition system.

BACKGROUND: Investigation of image quality in clinical equine magnetic resonance (MR) imaging may optimise diagnostic value. OBJECTIVES: To assess the influence of field strength and anaesthesia on image quality in MR imaging of the equine foot in a clinical context. STUDY DESIGN: Analytical clinical study. METHODS: Fifteen equine foot studies (five studies per system) were randomly selected from the clinical databases of three MR imaging systems: low-field standing (LF St), low-field anaesthetised (LF GA) and high-field anaesthetised (HF GA). Ten experienced observers graded image quality for entire studies and seven clinically important anatomical structures within the foot (briefly, grade 1: textbook quality, grade 2: high diagnostic quality, grade 3: satisfactory diagnostic quality, grade 4: non-diagnostic). Statistical analysis assessed the effect of anaesthesia and field strength using a combination of the Pearson chi-square test or Fisher's exact test and Mann-Whitney test. RESULTS: There was no difference in the proportion of entire studies of diagnostic quality between LF St (90%, 95% CI 78%-97%) and LF GA (88%, 76-95%, P = .7). No differences were evident in the proportion of diagnostic studies or median image quality gradings between LF St and LF GA when assessing individual anatomical structures (both groups all median grades = 3). There was a statistically significant difference in the proportion of entire studies of diagnostic quality between LF GA and HF GA (100%, 95% CI lower bound 94%, P = .03). There were statistically significant differences in median image quality gradings between LF GA (all median grades = 3) and HF GA (median grades = 1 (5/7 structures) or 2 (2/7 structures) for all individual anatomical structures (all P < .001). The reasons reported for reduced image quality differed between systems. MAIN LIMITATIONS: Randomised selection of cases from clinical databases. Individual observer preferences may influence image quality assessment. CONCLUSIONS: Field strength is a more important influencer of image quality than anaesthesia for magnetic resonance imaging of the equine foot in clinical patients.

Naturally-occurring forelimb lameness in the horse results in significant compensatory load redistribution during trotting.

This study aimed to quantify the compensatory response to naturally-occurring forelimb lameness on load redistribution. Data from lameness investigations using an inertial sensor based system to monitor the response to forelimb diagnostic anaesthesia were reviewed. Horses with primary forelimb lameness were grouped for analysis as (1) all horses combined (n= 28), (2) forelimb-only lameness (n= 8/28), (3) forelimb-contralateral hindlimb lameness (n= 14/28), (4) forelimb-ipsilateral hindlimb lameness (n= 6/28). The effect of diagnostic anaesthesia on measures of head and pelvic movement asymmetry was determined using the Wilcoxon signed rank test. Spearman's correlation analysis was performed between forelimb and hindlimb variables. Statistical significance was set at P< 0.05. Forelimb diagnostic anaesthesia resulted in a decrease in pelvic movement asymmetry among all horses and the forelimb-only and forelimb-contralateral hindlimb lameness groups. Pelvic movement asymmetry associated with the contralateral hindlimb decreased by a median of 38% (interquartile range [IQR] 10-65%), 43% (IQR 28-60%) and 28% (IQR 12-67%) in all horses, forelimb-only and forelimb-contralateral hindlimb groups respectively (P< 0.05). Maximum pelvic height difference (PDMax) significantly decreased in all horses combined and the forelimb-contralateral hindlimb lameness group by a median of 66% (IQR 24-100%) and 78% (IQR 27-100%, P< 0.01), respectively. Change in head movement asymmetry and vector sum was significantly positively correlated with PDMax in all horses combined and the forelimb-contralateral hindlimb group (P< 0.05). Forelimb lameness had a significant effect on hindlimb and pelvic movement in horses with clinical lameness resulting in compensatory load redistribution and decreased push-off from the contralateral hindlimb.

Reliability of a quantitative rating scale for assessment of horses with distal tarsal osteoarthritis.

Various radiographic rating scales have been described for use in horses with distal tarsal osteoarthritis but little information is available on their reliability. The aim of this study was to develop a radiographic rating scale based on the results of an expert consultation process (the Delphi process), and to test the reliability of the radiographic rating scale. Seven radiographic features were identified as important indicators of distal tarsal osteoarthritis and these were then incorporated in the radiographic rating scale, which used a 100-mm-long visual analog scale. On two occasions nine equine veterinarians applied the radiographic rating scale, and a verbal descriptive rating scale, to three sets of tarsal radiographs, each comprising four standard radiographic views. Reliability was assessed using Bland-Altman plots and by calculating the 95% agreement limits. Analysis of variance (ANOVA) was used to identify significant interactions between the ratings of different assessors made from different views and at each assessment. Rating of distal tarsal osteoarthritis was different for the nine assessors. The most precise second ratings were between 16 mm higher and 18 mm lower than the first. Significant variables were "joint," "assessor," and "assessment" (univariable ANOVA); and "joint and assessor" and "assessor and assessment" (multivariable ANOVA). The radiographic rating scale developed for interpretation of distal tarsal osteoarthritis was less reliable than a verbal descriptive rating scale.