Page 233 - Canine Lameness

14.6 Medial Compartment Disease 205

changes. In contrast, if the radius is longer than the ulna, excessive pressure is placed on the
anconeal process which may result in lack of fusion of the process. These incongruities are gen-
erally subtle and consequently CT or arthroscopy is necessary to make the diagnosis of incon-
gruity. Specific knowledge of the type of incongruity aids the treatment decision and therefore is
highly valuable. These two types of incongruity may also be secondary to premature growth
plate closures (i.e. short ulna = premature closure of the distal ulna physis; short radius = pre-
mature closure of either the proximal or distal radius physis). In cases where the degree of incon-
gruity is severe, radiography is useful to detect which incongruity scenario applies.
Humeroulnar incongruity – this incongruity describes either a mismatch between the ulna
●
notch and the humeral trochlea or displacement of the humerus from the ulnar notch because
of a long radius. CT or arthroscopy is preferred to make the diagnosis of humeroulnar incongru-
ity, although in severe cases radiographs can be diagnostic.
Many other mechanisms for the pathophysiology of ED have been described, such as radioulnar incisure
incongruity (i.e. a misshapen radial incisure that results in increased pressure on the coronoid;
Figure 14.5), as well as excessive pressure on the coronoid because of traction forces caused by the biceps
muscle (that attaches medially at the proximal ulna; Michelsen 2013). However, the influence that the
different types of incongruities have on the development of ED is still being investigated. Further, it is
important to understand that not every dog with ED will have detectable evidence of incongruity, even
when advanced imaging is used. This can be explained by the inability of commonly used diagnostic
modalities to identify dynamic (i.e. movement during motion) incongruity. Alternatively, transient ELBOW REGION
incongruity (i.e. incongruity during development) may have resolved by the time imaging is performed.
ED results in debilitating elbow arthritis and since many animals are affected bilaterally, it poses
one of the greatest treatment challenges in small animal orthopedics – amputation may not be a
feasible option and function after successful elbow arthrodesis is questionable due to substantial
mechanical lameness (Coppieters et al. 2015). Therefore, treatment decisions should carefully
weigh the potential risks against short- and long-term benefit of any intervention. Because most
animals with ED will develop a considerable amount of arthritis during their life span, lifelong
medical management should be part of the treatment plan for any dog with ED.

14.6 Medial Compartment Disease

The terminology “fragmented medial coronoid process (FCP)” is used to describe fragmentation of
the medial aspect of the coronoid process of the ulna (Figure 14.5A). This terminology is less com-
monly used nowadays since the pathologic changes encompass far more than pathology of the
coronoid process. Such changes include disseminated cartilage and subchondral bone pathology
of the entire joint, particularly the medial compartment resulting in variable degrees of lameness
(Video 14.1). Therefore, some authors have used the term “(medial) coronoid disease.” However,
because some dogs may experience erosion of the medial compartment without fissuring or frag-
mentation of the coronoid process (Coppieters et al. 2015), “medial compartment disease” (MCD)
is the currently preferred term to describe this condition (Michelsen 2013).

Video 14.1

Clinical lameness and conformation with elbow arthritis/dysplasia.