26
46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
Medial Femoral Condylar
Subchondral Cystic Lesions
Christine Smith DVM, Diplomate ACVS, Agnes Banks Equine Clinic, 5 Price Lane, Agnes
Banks, NSW 2753 Australia.
In horses, subchondral cystic lesions (SCL) are most commonly seen associated with
the medial femoral condyle. They can occur in all ages; however young
Thoroughbreds and Quarter horses are overrepresented. When yearling repository
radiographs were introduced, there has been an increase in the identification of
these lesions, which is currently estimated to occur in 1-5% of young Thoroughbreds
presented to sales.1-4 There is not a strong gender predisposition, and lesions occur
bilaterally in approximately 40% of horses.
There is some debate regarding the aetiology of SCL, however currently the most
accepted view is osteochondrosis and trauma. It has been shown that a defect in
articular cartilage can allow synovial fluid to enter the subchondral bone with a cystic
lesion developing.5, 6 Abnormal cartilage subjected to trauma in this direct weight
bearing area also is hypothesized to predispose to cystic lesions. In addition,
osteoarthritis can result in SCL and this aetiology must be considered, especially in
older horses.7 the cystic lesions can be filled with fibrous tissue and fibrocartilage,
and it has been established that the lining contains inflammatory mediators, including
metalloproteinases, nitric oxide, prostaglandins and interleukins.8
There is a spectrum of radiographic abnormalities identified in the medial femoral
condyle ranging from flattening of the condyle on the caudal cranial view, and a range
of radiographic changes from shallow lucencies to large cystic lesions involving a
variable amount of the articular surface. Some SCL have a broad base communicating
with the articular surface, and some have a cloaca of varying widths. There is often a
variable amount of sclerosis surrounding the SCL. In some cases, concurrent medial
tibial osteophytosis, joint collapse and articular irregularity can be identified, and
these changes are a poor prognostic sign.9, 10 Recommended radiographic views
include lateral-medial, caudal-cranial and Ca (30) LatCrMed oblique projections, at a
minimum.
Radiographic abnormalities do not always correlate well with clinical presentation.
In addition, SCL progression and association with lameness can be hard to predict.
Yearlings that have MFC SCL or lucencies identified with be considered as a “risk” at
TB sales in Australia. The risk can vary from low to high, depending on many factors
including the degree of articular cartilage involved, the cyst size and depth, the
veterinarian reviewing the radiographs, and the prospective bidder. There are
conflicting reports in the literature as to the clinical significance of medial femoral
condyle SCL; for example, one review reported SCL to have no impact of future
racing performance,2 and another concluded the presence of a SCL decreased the
number of starts as a 3 year old.3
Lameness in horses that is associated with SCL in the stifle is likely a result of both
subchondral bone pain and synovitis. It is widely accepted that radiographic
resolution of the SCL is not necessary or well correlated with resolution of
26