Detection of degenerative joint disease of the distal interphalangeal joint in thoracic limbs characterized by joint space narrowing using standing low-field MRI in 25 equine patients.

Overview

• This study used standing low-field MRI to detect degenerative joint disease (DJD) of the distal interphalangeal joint (DIPJ) in horses, focusing on joint space narrowing that suggests cartilage loss.
• The research analyzed MRI data from 25 equine thoracic limbs and correlated findings with clinical history and, when available, postmortem examination to improve the identification and understanding of DIPJ degenerative changes.

Purpose and Background

• The main goal was to document MRI findings associated with degenerative changes in the DIPJ characterized primarily by narrowing of the joint space.
• Joint space narrowing indicates cartilage loss, which is a key feature of degenerative joint disease.
• Detecting such changes earlier can aid diagnosis, inform prognosis, and guide treatment decisions in affected horses.

Study Design and Methods

• A retrospective review was conducted of medical records from September 2015 to July 2022 involving 25 thoracic limbs of horses diagnosed with DIPJ joint space narrowing.
• Lameness was attributed specifically to DIPJ joint space narrowing using a comparative design that included:
• Measurement of joint space width at four specific sites within the DIPJ.
• Calculation of ratios comparing DIPJ width to the proximal interphalangeal joint width.
• Comparison of affected limbs to the contralateral (opposite) limbs and to randomly selected control limbs from other horses.
• Statistical analysis identified significant differences in measurements between affected and control groups, confirming the presence of joint space narrowing as a marker of disease.

Imaging Findings and Grading

• In affected limbs, several subjective and objective features were assessed via MRI, including:
• Degree of DIPJ narrowing.
• Presence of synovial effusion (fluid within the joint).
• Heterogeneous material in the dorsal recess of the joint, indicating abnormal tissue or debris.
• Periarticular osteophytosis—development of bone spurs around the joint.
• STIR (Short Tau Inversion Recovery) hyperintense signals inside the foot, which indicate inflammation or edema.
• A dorsomedial DIPJ width measurement less than 3 mm on low-field standing MRI was suggested as a threshold indicating cartilage damage and joint space narrowing.

Key Findings and Clinical Insights

• Low-field standing MRI proved effective at detecting DIPJ degenerative changes characterized by cartilage loss.
• Joint space narrowing could occur without other typical signs such as:
  • Significant joint effusion.
  • Extensive periarticular osteophyte formation.
  • Hyperintensity in adjacent bone on STIR imaging.
• This suggests that measuring joint space width is a valuable diagnostic tool to identify cartilage loss even when other abnormalities are not obvious on MRI.

Prognosis and Clinical Relevance

• The prognosis for horses with DIPJ cartilage loss evidenced by joint space narrowing was generally poor, as 22 out of the 25 horses in the study did not return to their previous performance level.
• Early and accurate detection of DIPJ degenerative joint disease using standing low-field MRI can help veterinarians:
  • Better understand the severity and extent of cartilage damage.
  • Provide informed prognoses to horse owners.
  • Plan appropriate management or therapy options.
• The ability to perform MRI in a standing horse using a low-field magnet is especially advantageous, minimizing the need for anesthesia and allowing more practical imaging in clinical settings.

Conclusions

• Standing low-field MRI is a valuable diagnostic tool for detecting degenerative joint disease of the horse’s DIPJ, characterized by joint space narrowing and cartilage loss.
• Measurement of joint space width, particularly at the dorsomedial aspect, serves as an important marker for cartilage damage.
• Joint space narrowing may be present even in the absence of other MRI features like synovial effusion or osteophyte formation.
• Overall, this imaging modality improves the ability to diagnose early degenerative changes in the DIPJ, which correlates with a poor return-to-performance prognosis in affected horses.