Reasons for performing study: The significance of distal border
fragments of the navicular bone is not well understood. There
are also no objective data about changes in thickness and
proximal/distal extension of the palmar cortex of the
navicular bone.
Objectives: To describe the distribution of distal border
fragments and their association with other radiological
abnormalities of the navicular bone and describe the shape of
the navicular bone in sound horses and horses with footrelated
lameness, including navicular pathology.
Methods: Sound horses had radiographs acquired as part
of a prepurchase examination. Lame horses had forelimb
lameness abolished by palmar nerve blocks performed at the
base of the proximal sesamoid bones. Diagnosis was assigned
prospectively based on results of local analgesia and all
imaging findings. The thickness of the palmar cortex of the
navicular bone and size of proximal/distal extensions were
measured objectively. Other radiological abnormalities were
evaluated subjectively and each navicular bone graded.
Results: Fifty-five sound and 377 lame horses were included. All
measurements were larger in lame compared with sound
horses except the size of the distal extension of the palmar
cortex. Fragments were observed in 3.6 and 8.7% of sound
and lame horses respectively and in 24.1% of horses with
a diagnosis of primary navicular pathology. There was
an association between fragments and overall navicular
bone grade, radiolucent areas at the angles of the distal border
of the navicular bone and number and size of the synovial
invaginations.
Conclusions and potential relevance: The palmar cortex of the
navicular bone was thicker in lame compared with sound
horses. Distal border fragments were most frequent in horses
with navicular pathology. Evaluation of changes in shape of
the navicular bone may also be important for recognition of
pathological abnormalities of the bone