Low field magnetic resonance imaging of the equine distal interphalangeal joint: Comparison between weight-bearing and non-weight-bearing conditions

This descriptive study aimed to compare the magnetic resonance appearance of the distal interphalangeal joint articular cartilage between standing weight-bearing and non-weight-bearing conditions. Ten forefeet of live horses were scanned in a standing low-field magnetic resonance system (0.27 T). After euthanasia for reasons unrelated to the study, the non-weight-bearing isolated feet were scanned in a vertical positioning reproducing limb orientation in live horses. The same acquisition settings as during the weight-bearing examination were used. Thickness and cross-sectional area of the distal interphalangeal articular cartilage and joint space were measured on tridimensional T1-weighted gradient echo high resolution frontal and sagittal images at predetermined landmarks in both conditions and were compared using a linear mixed-effects model. Frontal images were randomized and submitted to 9 blinded readers with 3 different experience levels for identification of weight-bearing versus non-weight-bearing acquisitions based on cartilage appearance. Weight-bearing limbs had significantly thinner distal interphalangeal cartilage (p = 0.0001) than non-weight-bearing limbs. This change was greater in the distal phalanx cartilage than that of the middle phalanx. Blinded readers correctly identified 83% (range 65 to 95%) of the images as weight-bearing or non-weight-bearing acquisitions, with significantly different results observed among the different readers (p本描述性研究旨在对比负重站立位与非负重位下，马远端指间关节关节软骨的磁共振（magnetic resonance）表现。研究对10匹活马的前蹄采用立式低场磁共振系统（low-field magnetic resonance system，0.27 T）于负重站立状态下完成扫描。后续对因与本研究无关的原因实施安乐死的受试马，取其离体前蹄，采用与活体负重扫描完全一致的采集参数，在模拟马活体肢体方位的垂直站位下完成非负重位扫描。在两种扫描条件下，分别于预设解剖标志点处，于三维T1加权梯度回波（tridimensional T1-weighted gradient echo）高分辨率冠状位及矢状位图像上测量远端指间关节软骨的厚度、横截面积及关节间隙，并采用线性混合效应模型（linear mixed-effects model）进行统计学比较。将冠状位图像随机分组后，交由9名具有3种不同经验水平的盲法阅片者（blinded readers），依据软骨表现识别图像对应的扫描体位（负重/非负重）。结果显示，负重肢体的远端指间关节软骨厚度显著低于非负重肢体（p=0.0001），且远节趾骨软骨的厚度变化较中节趾骨更为显著。盲法阅片者对图像扫描体位的正确识别率达83%（范围65%~95%），不同阅片者间的识别结果存在显著差异（p