Abstract
Objectives: To describe detectable and non-detectable naturally occurring cartilage damage of the equine distal interphalangeal (DIP) joint using plain magnetic resonance (MR) imaging and gadolinium and saline MR arthrography. The second objective was to quantify the sensitivity, specificity and accuracy in detection of cartilage damage.Methods: In a pilot study, the distal limbs of two horses with confirmed osteoarthritis of the DIP joint were imaged with low-field MR. Magnetic resonance images were assessed in consensus by three observers and compared to gross pathological findings. Subsequently, a prospective analytical cross-sectional study design was created to compare pre-contrast MR imaging and saline and gadolinium MR arthrography of isolated equine distal limbs to gross observation findings. Hallmarq® low-field MR (0.27T) scans were performed prior to DIP joint injection, saline/gadolinium post-injection scans were performed at 15 min intervals for 2 h. Joints were inspected and the articular cartilage graded subjectively for cartilage damage (0–3). The presence of detectable or non-detectable cartilage damage on MR images was identified, characterized and recorded in consensus by three observers. Sensitivity, specificity and accuracy in detection of cartilage damage related to gross pathology were calculated.Results: The two clinical cases from the pilot study with confirmed osteoarthritis had full thickness cartilage defects; however, only one of these was correctly identified using low-field MRI. In the prospective study, the majority of naturally occurring cartilage damage could not be identified on plain MR or MR arthrography including extensive partial thickness cartilage erosions. Saline and gadolinium MR arthrography did not improve the detection of cartilage damage. The accuracy of cartilage damage detection was 0.63 with a sensitivity of 0.14 and specificity of 0.92.Clinical Relevance: Both, plain low-field MRI and MR arthrography are not sensitive in detection of naturally occurring cartilage damage of the DIP joint. However, if an abnormal contour is seen in the articular cartilage, cartilage damage is likely to be present.
Highlights
The distal interphalangeal (DIP) joint is an important source of lameness in sports horses [1] and osteoarthritis plays a major role as a cause for lameness located to this joint [1,2,3]
Marked cartilage defects were seen on gross pathology in case two, which could not be identified on magnetic resonance (MR) images, even retrospectively (Figure 2)
Detection of cartilage damage with MR imaging has been described in high-field MRI in the equine carpal joint [22], the metacarpophalangeal joint [8] and the DIP joint [19] and in low-field MRI of the DIP joint [16]
Summary
The distal interphalangeal (DIP) joint is an important source of lameness in sports horses [1] and osteoarthritis plays a major role as a cause for lameness located to this joint [1,2,3]. Saline provides contrast enhancement of synovial structures in fluid sensitive sequences and gadolinium is a paramagnetic metal causing shortening of T1 and T2 relaxation times [14]. DGEMRIC was recently analyzed in the equine DIP joint using a high-field system and showed relaxation time changes in horses with naturally occurring osteoarthritis [19]. The characteristics of naturally occurring cartilage damage that can be identified subjectively in low-field MR and MR arthrography in the equine DIP joint have not been previously described. The aims of this study were to describe detectable and non-detectable naturally occurring cartilage damage of the equine DIP joint using plain low-field MR imaging and gadolinium and saline MR arthrography and to quantify the sensitivity, specificity and accuracy in subjective detection of this damage
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