Page 327 - Canine Lameness

18.6 Osteochondrosis Dissecans 299

osteochondral fragment can be felt just caudal to the malleolus and medial or lateral to the trochlear
ridge, but palpation for such fragments is usually prompted by radiographic findings.

18.6.3 Diagnostics
Orthogonal radiographs can be diagnostic for OCD; however, smaller lesions are easily missed
due to the complexity of the joint. In normal tarsi, both talar ridges are circular on the lateral
radiographic view, but when OCD is present flattening of one of the ridges will be evident
(Figure 18.9). On the dorsoplantar projection, a gap between the talus and the tibia – normally a
close fit – can be seen, sometimes with osteochondral fragments visible within the defect. A dor-
soplantar skyline view of the caudal aspect of the talar trochlea taken with the tarsus in slightly TARSAL REGION

(A) (C) (E) (G)

(B) (D) (F) (H)

Figure 18.9 Examples of surgically confirmed tarsal OCD: Patient I (A, B) was diagnosed with OCD of the
lateral talar ridge. Radiographs show only subtle changes including (A) mild periarticular osteophytosis
(black arrow) on the lateral view mild, joint effusion (white arrow), and very subtle flattening of the
proximo-plantar aspect of the trochlea (red arrow). Patient II (C–H) showed more obvious changes including
the (C) extended lateral view shows flattening (white arrow) of the trochlea; (D) the dorsoplantar view
shows (white arrow) an increased joint space indicating a medial trochlear ridge defect; (E) the flexed
lateral view makes the (white arrow) trochlear ridge flattening more easily visible; (F) typical location for
(blue arrow) joint effusion in patients with OCD; (G, H) CT illustrating the (white arrow) OCD lesion and
(blue arrow) joint effusion.