46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
19
Palmar/Plantar Osteochondral
Disease in Racing Thoroughbreds: A
Hong Kong Perspective
Gregory O. Sommerville BVSc (Pret), CertAVP, MRCVS
Introduction:
Palmar/Plantar osteochondral disease (POD) is a degenerative condition affecting the
distal condyles of the third metacarpal and metatarsal bones. The lesions appear as
small oval shaped defects on the palmar or plantar articular surface of the condyle.
These vary in severity from small focal bluish discolouration of the subchondral bone
and normal articular cartilage to subchondral bone collapse with fibrillation and
ulceration of the overlying cartilage. The condition is believed to be caused by
material fatigue of the subchondral bone during high-speed locomotion due to
repetitive overload. POD was recorded in at least one limb in 80% of horses
presented for post mortem examination in Hong Kong. This disease is one of the
major causes of lameness, lost training days and ultimately retirement in the Hong
Kong population of racehorses. It is part of a syndrome that can be linked to the
cause of many of the catastrophic breakdowns. Pain associated with subchondral
bone is a clinical condition that is well recognised in all racing breeds and can be
demonstrated as increased radiopharmaceutical nucleotide uptake. This has been
shown to be associated with reduced competitiveness (less races and lower
earnings).
Diagnosis:
The definitive diagnosis is post mortem evaluation of the palmar condyles. A grading
system for POD at post mortem has been developed. Lesions are graded from 0-3
with 0 as normal and 3 having the most severe lesions. Radiography is not a sensitive
modality for demonstrating POD lesions and generally only advanced lesions can be
seen. However, better radiographic techniques, digital radiography and specialized
views have improved diagnostic capabilities. Fetlock joint arthroscopy does not
significantly improve the diagnosis of POD. The palmar condyles cannot be reliably
visualized by the rigid arthroscope, although arthritic changes related to POD can be
demonstrated (in particular, ulceration of the basilar half of the proximal sesamoid
bone contacting the affecting condyle in severe cases). Magnetic resonance imaging
(MRI) and computed tomography (CT) is the best modalities for POD diagnosis;
however
they are not always widely available and can be cost prohibitive. Clinical
indicators for early POD are lameness attributable to the fetlock region that is
associated with few other clinical findings and no or limited significant findings on
radiography. The lameness tends to block partially intra-articular fetlock or and
largely low four point nerve blocks. These finding are all fairly non-specific but this is
likely the window period in which action should be taken. In more advanced cases,
where there is disruption of the articular surface, chronic fetlock effusion with
reduced and painful flexion become more obvious features.
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