Elbow Flashcards
Understand why the individual pathologies in elbow dysplasia are grouped
Unlike hip dysplasia which is a relatively specific entity with relatively well‐understood pathophysiology, elbow dysplasia is a “catchall” diagnosis that is comprised of several similar, but separate, diagnoses for which the pathophysiology is not as well understood. Clinically, the different pathologies that make up elbow dysplasia tend to occur together, tend to occur in the same sorts of patients, and tend to occur at the same age. All have some similarities in how they are approached diagnostically and therapeutically. All also tend to cause arthritis over time. Thus it is expedient to lump them together.
List the individual components of elbow dysplasia
Ununited anconeal process (UAP);
Fragmented medial coronoid (FCP);
Osteochondritis dissecans (OCD);
and Joint incongruity.
medial compartment disease
Fragmented medial coronoid (FCP); Osteochondritis dissecans (OCD); and Joint incongruity
Know the locations of the anconeal and medial coronoid processes and their anatomic relationships
Both of these structures are part of the ulna. The trochlear notch is the curved bit where the humerus articulates with the ulna. It is sometimes called the “semilunar notch”. The anconeal process is the pointy bit at the proximal end of the trochlear notch. The coronoid process is the pointy bit at the distal end of the notch. There are both lateral and medial parts of the coronoid process; the medial is the one that we are concerned about in elbow dysplasia.
Identify the location on the humeral condyle where OCD of the elbow usually occurs
OCD of the elbow is usually seen on the trochlear ridge of the medial humeral condyle.
Know that incongruity is a thing that happens
Sometimes incongruity happens by itself, and sometimes it happens in combination with other pathologies (particularly UAP and FCP). I grant you that this is a complex relationship.
definition of incongruity
The simple definition is that elbow incongruity is a mismatch in articular surfaces. This mismatch can take many forms, including a discrepancy in length between the radius and ulna.
As far as specific types of incongruity, radioulnar length discrepancy is the only one I will even really touch on. Length discrepancy is probably the most straightforward type of incongruity, and it is (possibly) part of the etiology of UAP and FCP. Mostly what I am trying to do is to illustrate the general concept of incongruity, but I do want you to understand length discrepancy as part of understanding UAP and FCP (more about that below). There are many, many other types that have been described, but you don’t really need to worry about them at this stage.
Understand why uneven joint surfaces result in DJD
Uneven joint surfaces lead to uneven joint forces. Uneven joint forces lead to stress focused on specific areas of cartilage. Uneven wear on the cartilage leads to DJD as it does with any other joint pathology
Can individual pathologies may appear together or singly?
Either is possible. Often one of the conditions will be present on its own, but it is common to have multiple pathologies present in the same elbow.
Several studies have looked at the relationships between different pathologies, i.e., how frequently pathology A appears with pathology B. Not all studies agree on the numbers and there’s a lot of them, and thus listing all of them would be confusing and not ultimately helpful. So I won’t do it. Suffice it to say that it’s frequent enough that it’s best to assume there are multiple problems in the joint and be pleasantly surprised when there aren’t.
Is elbow dysplasia a developemental orthopedic disease?
By now you’ve probably figured out that a developmental orthopedic disease is one that first manifests prior to skeletal maturity, and so shows up initially in young dogs. Even when the lameness seems to resolve, these diseases often lead to secondary effects – in the case of disease in the joint, this leads to DJD in the long term. When patients present later in life it is due to the secondary effects of the disease rather than the primary issue. This is where the term “biphasic age distribution” comes from. ALL developmental orthopedic diseases have, or are strongly suspected to have, a genetic basis at least in part. For this reason dogs with developmental orthopedic disease should not be bred. Furthermore, because the disease is based on a genetic error, it is often present bilaterally.
Because elbow dysplasia is a developmental orthopedic disease, all of the above applies.
Can you bred animals with developmental orthopedic diseases?
NO!
Describe a typical patient with elbow dysplasia
As elbow dysplasia is a developmental orthopedic disease, it will be seen in young patients. Most developmental orthopedic diseases are also most common in male, large and giant breed dogs. Such is true of elbow dysplasia.
Most, but not all, developmental orthopedic diseases are more prevalent in male, large and giant breed dogs. While there are exceptions to the rule it’s probably easier to remember the exceptions to the rule rather than the specific predispositions for every developmental orthopedic disease separately – but use whichever method works for you.
Is bilateral or unilateral disease more common?
Tis indeed commonly seen bilaterally.
While the precise statistics on this vary a bit based on the study that was done and the individual pathologies studied, overall about 35% of cases have bilateral disease. That’s frequent enough that dogs should be screened for bilateral disease, or owners should be warned that there’s a good chance of bilateral problems at the very least.
Describe the typical history of a dog with elbow dysplasia
The typical history is that of a chronic, progressive lameness. It may be intermittent, only showing up after activity, especially in the early phases. Bilateral disease can actually mask the lameness in an odd way as it will manifest not as lameness per se but rather more as activity intolerance. This can be more difficult for an owner to recognize as lameness, especially if the dog is relatively mildly affected. Also keep in mind that younger dogs will often “power through” the lameness. Even if sore, they will want to run and play, which again would create more subtle signs and make it more difficult for owners to recognize.
Describe the PE findings typical of elbow dysplasia
The first step in any orthopedic exam is to observe gait and posture. The gait exam tells you which limb is lame, but doesn’t tell you which joint it is. What helps definitively identify the elbow as the source of the lameness would be effusion in the elbow and pain on manipulation of the joint. Over time effusion gives way to thickening (fibrosis). If there are chronic changes, you will also feel crepitus on range of motion.
What is the typical characteristic of elbow dysplasia
Dogs with elbow dysplasia tend to have a characteristic posture, which you can often see just as they are standing around in your exam room.
Normal stance is with the toes facing forward. Dogs with elbow dysplasia tend to stand with their toes pointed out at an angle due to varying degrees of external rotation of the antebrachium. They also hold the elbow in toward the body (adduction). All of these postural changes serve to help offload the painful medial side of the joint, and shift the weight toward the lateral side.
united anoceal process
Understand the proposed cause of UAP in general terms
This topic is a subject of some debate. In the past, UAP was described simply as a manifestation of OCD (i.e., OCD as it is described in these lectures). Unfortunately it is probably not quite that simple. The most recent literature describes various types of elbow incongruity, such as a shortened ulna, resulting in abnormal stresses on the developing anconeal process that prevent it from fusing. That latter statement is, really, the essence of what you need to know.
What is the difference in ossification pattern of the ulna between breeds susceptible to UAP and those that are not
We know that there is a separate center of ossification in the anconeal process in breeds affected by UAP. This center of ossification is not present in breeds that aren’t affected by UAP. We also know that,
while timing of ossification varies a bit from breed to breed, the anconeal process is normally fused to the ulna by 20 weeks.
When can you diganose UAP?
If the anconeal process remains separate from the ulna at 24 weeks, it will not go on to fuse later. It is then, by definition, ununited
Know the proposed etiology of FCP
As with UAP, in the past FCP was thought to be a manifestation of OCD. Microscopic analysis of excised coronoid processes, though, showed no evidence of OCD. Instead, the changes were most consistent with microtrauma, as might happen with chronic overloading of the coronoid process. The presumption is that incongruity, as might happen with a shortened radius, is responsible.
What is the relevance of radiographs in the diagnosis of the individual components of elbow dysplasia?
Radiographs are noninvasive and relatively inexpensive, so are often used as a first line of defense in diagnosis. While some of the components of elbow dysplasia are readily identified radiographically, some of the more subtle ones are very difficult to diagnose.
UAP
Flexed lateral elbow radiograph of a dog with UAP. Note the line of separation between the relatively large anconeal fragment and the underlying ulna. Note also that there is no box around this image – it is one you might want to pay attention to.
UAP is pretty easy to diagnose from a radiograph. The key, though, is that the radiograph has to be a flexed lateral and not a simple neutral lateral view. The elbow being in flexion ensures that the humeral condyle and anconeal process don’t overlap. As noted earlier in the notes, any separation between the anconeal process and the ulna at 24 weeks of age or later is pretty much a slam dunk diagnosis.
OCD can usually be seen on a well‐positioned craniocaudal view of the elbow. As with osteochondrosis in other joints, you will see a defect or a divot in the bone of the joint surface. Remember that this defect corresponds to a thickened section of articular cartilage. Sometimes the changes are subtle, only an irregularity in the joint surface, but they are there. You may have to look fairly carefully. Note: if I show you an OCD lesion and expect you to identify it as such on an exam, it will be a more obvious one. Yes, I might expect you to identify an OCD lesion radiographically on an exam.
Sclerosis of the subchondral bone is another telltale sign. The sclerosis is secondary to the inflammation in the bone. This manifests as bone that is whiter, or denser, than normal.
The white arrow in the left image points out a small divot in the distal joint surface of the medial humeral condyle. The black arrow points to sclerosis in the subchondral bone deep to the defect. The right image shows a variation on the appearance of the OCD lesion, essentially little more than irregularity in the joint surface of the humeral condyle. The right image is much more subtle. If I ask you to identify an OCD lesion on an exam it will be based on a lesion more like the left image than the right.
