Page 123 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

98 CHAPTER 1

VetBooks.ir low-grade lameness may also be a presenting sign. Prognosis
The prognosis is usually excellent if the subchondral
The severity of lameness may be marked following
an acute traumatic bone contusion or mild to mod-
involved. Cases may take up to 6 months to reach
erate when chronic repetitive microtrauma is sus- bone and articular cartilage of the DIP joint are not
pected to be the cause. Lameness arising from bone soundness and for the fluid signal to resolve on MR
contusions of the distal phalanx is abolished by a pal- images.
mar digital nerve block, while improvement of lame-
ness arising from a middle phalangeal injury usually OSSEOUS CYST-LIKE LESIONS
requires an abaxial sesamoid nerve block. OF THE DISTAL PHALANX

Differential diagnosis Definition/overview
All other causes of foot lameness without radio- Osseous cyst-like lesions of the distal phalanx occur
graphic abnormalities, either acute and severe (frac- in horses from a variety of breeds and all ages. Their
ture, soft-tissue strain or sprain, solar bruise or location ranges from the extensor process to the
abscess) or mild and insidious (navicular disease, palmar border of the articular surface of the distal
pedal osteitis, soft-tissue strain or sprain). phalanx, but most are found in the central weight-
bearing portion of the distal phalanx.
Diagnosis
Bone contusions are identified on fat-suppressed Aetiology/pathophysiology
MR images as intraosseous signal hyperintensity Lesions may be either of traumatic or developmental
(Fig. 1.170). There is usually an associated increase in origin. Bilateral cysts in young horses are strongly sug-
radiopharmaceutical uptake on scintigraphic images. gestive of a developmental origin while the presence of
a unilateral cyst in a mature horse may be the sequela of
Management focal subchondral injury and bone necrosis. Most osse-
Treatment should consist of stall rest, administration ous cyst-like lesions communicate with the DIP joint.
of NSAIDs and potentially a bisphosphonate to limit
bone resorption and suppress bone inflammation. Clinical presentation
The horse may be presented with a history of mild to
moderate, intermittent lameness of insidious onset,
1.170 but acute-onset, moderate to severe, unilateral lame-
ness is more common. Lameness tends to improve
with rest but recurs with exercise. Lameness is usu-
ally substantially improved with a palmar digital
nerve block or with intra-articular anaesthesia, but
an abaxial sesamoid nerve block may be required to
render the horse sound. Some cyst-like lesions in the
distal phalanx are noted as incidental radiographic
findings during pre-purchase examinations.

Differential diagnosis
All other causes of foot lameness.

Diagnosis
Fig. 1.170 Fat-suppressed MR image of a bone Large cyst-like lesions are identified on standard
contusion of the middle phalanx, characterised by the radiographic views (Fig. 1.171). Subchondral bone
presence of an area of high signal intensity near the cysts are best seen on dorsopalmar or 45° dorso-
dorsodistal margin of the distal interphalangeal joint proximal/palmarodistal oblique views, while lesions
(arrow).