| Canine elbow dysplasia is an
abnormal development of the elbow joint. The term is used to describe
developmental diseases which include ununited anconeal process, fragmentation
of the medial coronoid process and osteoarthritis secondary to joint incongruity.
The pathophysiologic mechanism leading to elbow dysplasia is thought to
be a lack of elbow congruity secondary to improper growth of the radius/ulna
during maturation. For example, the axial length of the ulna is shorter
in cases with ununited anconeal process as compared to breed matched cases
without UAP. The hypothesis is that as growth proceeds the anconeal process
of affected dogs presses against the humeral trochlea. This creates a
shear force separating the anconeal process from the ulnar metaphysic.
(Fig.1)
In cases with abnormal medial coronoid process of the ulna, CT has
shown the articular surface of the radial head to be positioned below (distal)
the joint line of the coronoid process. This finding leads one to speculate
that the growth of the radius was retarded at some point during development
(alternatively, ulnar growth could have been accelerated leading to a longer
ulna). In either circumstance, with the coronoid positioned higher than
the radial articular surface, increased weight bearing forces are directed
onto the lateral region of the medial coronoid. Increased force could give
rise to abnormal stresses which initiate fragmentation of the medial coronoid
(Fig. 2) or result in an osteomalacia coronoid (similar to legg perthes
of the femoral head (Fig. 3)
The degree of elbow incongruity will vary in severity (similar to
hip dysplasia!!). Some dogs have severe incongruity which causes abrasion
of the articular cartilage overlying the medial coronoid and under surface
of the humerus. Clinical signs are variable and dependent upon the degree
of incongruity. The worse the incongruity the more severe the clinical findings
and the earlier the clinical signs are expressed. Moderate to severe joint
effusion, pain on manipulation of the elbow, and loss of full range of motion
are signs indicative of significant incongruity. (Fig.4 CT showing radioulnar
incongruity).
Although the above clinical presentation is indicative of significant
incongruity, clinical signs in the majority of younger dogs with FCP/incongruity
are not debilitating. In most dogs, the presenting complaint is a periodic
lameness associated activity. Gait observation may or may not show lameness;
similarly effusion and pain are variable. The most consistent clinical finding
is loss of normal flexion.
Dogs with minimal incongruity may present with lameness later in life
(2-5 years of age); The clinical finding in these cases is often a discernable
limp. No joint effusion, pain or loss of motion in elbow is seen. Radiographs
often show no obvious signs of DJD. These cases are commonly misdiagnosed
as having "soft tissue" injury or shoulder "instability." A nuclear bone
scan will localize the problem to the elbow and a CT will be diagnostic
of a fragmented coronoid or osteomalacic coronoid. Dogs with moderate
to severe incongruity may present with a lameness which is non-responsive
to rest and/or NSAIDs. Unfortunately, many of these cases have severe
DJD and erosion of articular cartilage in the medial compartment. (Fig.
5&6)
Treatment and prognosis are controversial. Some studies have not
shown a difference in outcome between non-operative or operative treatment.
However, these studies did not classify the severity of incongruency making
it difficult to judge accuracy. Our clinical experience suggests outcome
is dependent upon the degree of incongruency and associated cartilage erosion.
Surgical intervention is warranted in all cases and will improve clinical
function. Dogs with minimal to no incongruency, no cartilage erosion, and
a fragmented of osteomalacic coronoid a have a good long-term prognosis
with arthroscopic intervention. Fragments or osteomalacic bone can be removed
(arthroscopically) from both elbows at the same time without causing significant
discomfort. Dogs presenting with severe incongruency and cartilage erosion
will improve with surgical intervention. Removal of fragments and osteomalacic
bone will improve limb function. Proximal ulnar ostectomy will improve function
and may slow progressive OA.
Osteochondritis Dessicans
Osteochondritis desiccans (OCD) is a manifestation of osteochondrosis.
Osteochondrosis is a disturbance in endochondral ossification which effects
the humeral epiphysis. Although the abnormal endochondral ossification
is seen throughout the epiphysis on CT, the most apparent gross clinical
finding is a section of cartilage lifted from the articular surface..
Despite unilateral lameness, this condition is often bilateral.
Figure 7
Large and giant-breed dogs are commonly affected and males are more
often affected than females. Clinical signs often develop between 4 and
8 months of age; however, some dogs may not be presented for veterinary
evaluation until they are mature or middle-aged. Affected animals are usually
presented for examination because of unilateral forelimb lameness. Owners
usually report a gradual onset of lameness that improves after rest and
worsens after exercise. On physical examination, the shoulder should be
palpated and moved through a complete range of motion. Crepitation or palpable
swelling of the joint is seldom evident, but affected animals usually exhibit
pain when the shoulder is moved into hyper-extension or extreme flexion.
Often the examiner can detect muscle atrophy of the forelimb by loss of
muscle mass adjacent to the spine of the scapula. Differential diagnoses
include osteochondrosis, bicipital tenosynovitis, shoulder instability.
Figure 8
Despite apparent lameness in only one limb, both shoulders should be
radiographed because this condition is often bilateral. Sedation may be
required for quality radiographs particularly in large hyper-active dogs.
The earliest radiographic sign of OCD is flattening of the caudal humeral
head. This is due to thickening of the articular cartilage and deviation
of the subchondral bone line. As the disease progresses, a saucer-shaped
radiolucent area in the caudal humeral head may be visualized. Calcification
of the flap may allow visualization of the flap either in situ
or within the joint if it has detached from the underlying bone
Surgery is the treatment of choice in cases of OCD. Surgery can be accomplished
via open arthrotomy or arthroscopically. We prefer to manage OCD arthroscopically;
mobidity is decreased such that both shoulders can be operated (if bilateral).
Details of the technique for open arthrotomy or arthroscopy can be reviewed
in detail within textbooks related to canine surgery.
Figure 9
Hip Dysplasia
Hip dysplasia is an abnormal development of the coxofemoral joint. The
syndrome is characterized by subluxation or complete luxation of the femoral
head in the younger patient while in the older patient mild to severe
degenerative joint disease is present. Laxity in the hip joint is responsible
for the early clinical signs and joint changes. Subluxation stretches
the fibrous joint capsule, producing pain and lameness. When the surface
area of articulation is decreased, this concentrates the stress of weight
bearing over a small area through the hip joint. Subsequently, fractures
of the trabecular cancellous bone of the acetabulum can occur, causing
pain and lameness. The cancellous bone of the acetabulum is easily deformed
by the continual dorsal subluxation of the femoral head. This piston-like
action causes a wearing of the acetabular articular surface from a horizontal
plane to a more vertical plane causing subluxation to worsen. The physiologic
response to joint laxity is proliferative fibroplasia of the joint capsule
and increased thickness of the trabecular bone. This relieves the pain
associated with capsular sprain and trabecular fractures. However, the
surface area of articulation is still decreased causing premature wear
of articular cartilage, exposure of subchondral pain fibers and lameness.
(Fig.1 arthroscopic view of moderate DJD). There are two general recognizable
clinical syndromes associated with hip dysplasia: (1) patients 5 to 16
months of age, (2) patients with chronic degenerative joint disease. Patients
in group 1 present with lameness between 5 to 8 months of age. Symptoms
include difficulty when rising after periods of rest, exercise intolerance
and intermittent or continual lameness. The majority of young patients
will spontaneously improve clinically around 15 to 18 months of age. This
clinical improvement is due to pain relief as proliferative fibrous tissue
prevents further capsular sprain, and increased thickness of the subchondral
bone prevents trabecular fractures. If symptoms occur later in life, they
may include difficulty in rising, exercise intolerance, lameness following
exercise, atrophy of the pelvic muscle mass, and a waddling gait with
the rear quarters. Physical findings in the younger group of patients
include pain during external rotation and abduction of the hip joint,
poorly developed pelvic muscle mass, and exercise intolerance. Hip exam
performed under general anesthesia will reveal abnormal angles of reduction
and subluxation reflecting excessive joint laxity.. Physical findings
in the older group of patients include pain during extension of the hip
joint, reduced range of motion, atrophy of the pelvic musculature, and
exercise intolerance. Treatment is dependent upon the age of the patient,
the degree of patient discomfort, physical and radiographic findings,
client expectations of patient performance, and financial capability of
the client. Conservative treatment is beneficial to a large number of
patients in both the young and older patient groups. Conservative management
is divided into acute management and long term management. When a dog
exhibiting signs of hip dysplasia enters the clinic, it is generally because
they have sprained the hip joint. The dysplastic joint is either hyperlax
(young dog) or has a limited range of motion (mature dog). In either case,
the joint is easily sprained and the dog that is presented with symptoms
has overused (sprained) the hip joint. Rest, physical therapy, and non-steroidal
analgesics will relieve signs in the majority of patients. Surgical intervention
in the mature patient may be total hip replacement or femoral head ostectomy.
Surgical intervention in the mature patient may be total hip replacement
or femoral head ostectomy.
|
