Page 710 - Adams and Stashak's Lameness in Horses, 7th Edition

676 Chapter 5

and tibial articular surfaces where the makeup of the often occurs when there is a loose or semi‐loose osteo-
cartilage between articulating and non‐articulating sur- chondral fragment observed radiographically. It is also
VetBooks.ir within the immature cartilage at these sites, which dam- develop at a later time in other joints.
uncommon to treat OCD in one joint(s) and have it
faces is different. Weight‐bearing produces sheer stresses
ages the vascular supply to the articular cartilage.
Increases in weight and activity of the foal increase the Osteochondritis Dissecans of the Tarsocrural Joint
biomechanical stresses placed on the articular cartilage
that can increase the incidence of lesion development. OC occurs in the TC joint commonly. 10,12,22,66,84,89,
Silent or quiescent lesions may become apparent only 92,93,110,122,136 Horses of all ages can be affected. Many
when the horse is started into training and the joints horses are sound at a walk and trotting in hand, but may
become challenged by athletic activity. The age at which display lameness at faster speeds or when put into work.
this occurs can vary with the discipline of the horse. For Lameness when it does occur varies with location and
example, Warmblood horses commonly present with severity of the OCD. These fragments are usually found
clinical signs of TC OCD (TC joint effusion) around 3 when radiographs of the joint are taken for another rea-
years of age or older, whereas racing TB and STB mani- son, most often during prepurchase examination. TB
fest signs much earlier (2 years of age) because they sales horses are routinely radiographed as a screening
begin race training earlier in life. OC lesions can also for the yearling sales. The most common clinical sign of
undergo spontaneous resolution. This occurs by intram- OC in the tarsus is effusion in the TC joint. Lesions can
embranous ossification of granulation tissue that forms be identified as fragments in situ (intermediate ridge) or
deep in the lesions progressively filling of the OC defects surface irregularities of the trochlear ridge(s) or malleoli
with bone. While OC of the DIRT and LTR of the TC (Figure 5.76). OC lesions of the TC joint often develop
joint can be radiographically evident within a few into OCD lesions because they often form separated
months of life, they may not be clinically detectable until fragments. This is probably due to the site vulnerability
later. Lesions found before the age of 5 months may not at the edges of the articulation mentioned earlier. The
persist, but those lesions detected after 5 months typi- most common locations for OCD in order of occur-
cally will persist thereafter. 36 rence are the DIRT (81%), the distal aspect of the LTR
OC can occur in all joints, but most often they occur (16%), the cranial distal aspect of the MM (3%), the
in the hock, stifle, and fetlock joints. Multiple joints can MTR, and the LM. The distal end of the tibia is the
5
be affected, but usually only one joint is involved. most common site of OC formation and may be related
Bilateral involvement (i.e. both stifle joints or both hock to impact to or impingement of the DIRT onto the talus/
joints) occurs often enough so that the opposite joint central tarsal bone when the tarsus is in full flexion.
should always be radiographed. Bilateral occurrence can Acute severe synovial effusion can occur when the
also occur with only one joint becoming clinically appar- fragment(s) is disturbed presumably by hyperflexion
ent (manifesting effusion). This can occur in the TC and and impact onto the central tarsal bone. The synovial
femoropatellar (FP) joints in more than 50% of clinical distension can present clinically as severe lameness. If
cases. However, it is uncommon for both the hocks and clinical signs appear after training has begun, lameness
stifles or the hocks and fetlocks to be involved in the is more likely. However, once the horse has adjusted to
same animal at the same time. Lameness is seen more the capsular stretching, the lameness quickly subsides.
often in FP OC than in TC OC and is most likely to Once loose, micromotion of the fragment(s) can create
occur with an acute onset of effusion. Lameness also persistent inflammation within the parent bone with

A B C

Figure 5.76. The most common clinical sign of OC in the tarsus is ridge of the tibia (C), surface irregularities of the lateral trochlear ridge
effusion (A; small arrowheads) in the TC joint. Osteochondrosis (B; arrows) but occasionally the medial trochlear ridge, and lucency of
lesions can be identified as in situ fragments of the distal intermediate the medial malleolus (A; large arrow).