Objective—To assess the use of magnetic resonance
(MR) imaging for identifying subchondral bone damage
in the distal limbs of horses.
Procedure—Medical records of horses with lameness
and subsequent evidence of subchondral bone
damage as determined by MR imaging were
reviewed. Severity and duration of lameness, results
of diagnostic local anesthesia and diagnostic testing,
surgical and necropsy findings, and treatment were
recorded. Outcome was determined by follow-up
information obtained from the owner or referring veterinarian.
Results—Lameness was localized by physical examination
and diagnostic local anesthesia. Lameness was
localized to the metacarpophalangeal or metatarsophalangeal
joint in 4 horses, distal interphalangeal joint in 5
horses, and tarsocrural joint in 2 horses. The duration of
lameness ranged from 2 weeks to 20 months. Magnetic
resonance imaging of the affected joints revealed abnormal
fluid accumulation within the subchondral bone.
None of the abnormalities observed by MR imaging
were detected by radiography. Subchondral bone damage
was diagnosed in all horses. Arthroscopy of the
affected joint was performed in 4 horses. Communication
with the articular surface of the affected bone was
suspected on the basis of results of MR imaging in 4
horses and was confirmed by arthroscopy in 1 horse and
by necropsy in 1 horse.
Conclusions and Clinical Relevance—Magnetic resonance
imaging was useful for providing a diagnosis
when other imaging techniques did not definitively
identify the cause of lameness. Subchondral bone
damage was clearly identified by MR imaging and
should be considered as a cause of lameness in horses
in which radiographic findings are unremarkable.
( J Am Vet Med Assoc 2004;224:411–418)