The Many Faces of Elbow Dysplasia
Pim Wolvekamp, DVM, PhD, Dipl ECVDI
Division of Diagnostic Imaging, Faculty of Veterinary Medicine, Utrecht University
The radiographic appearance of the maturing skeleton in young dogs is constantly changing, from the moment of birth until the end of the first year of life when skeletal maturation is finished. Ossification centers appear postnatally or are already present at birth, and fuse with the adjacent bones. At the same time also, epiphyseal growth plates will gradually "close." Bones grow in length and diameter, while joints are reformed to stable but mobile structures.
Especially during this period of building and rebuilding many things can go wrong, sometimes in a more generalized appearance, sometimes as localized abnormalities. Many etiological factors are understood today, but also many have to be further investigated.
Genetic factors, growth rate disturbances, biomechanics, feeding imbalance, and especially trauma, they all have an important role during skeletal development, and can result in a large scale of abnormalities.
Sometimes one wonders that there are still normal, healthy dogs.
Radiographic interpretation of a growing elbow joint demands knowledge of the normal time of appearance (presence) and fusion of the different ossification centers and of the "closure" of the epi- and apophyseal growth plates (growth lines) of the skeletal parts that will form the elbow joint.
In addition to this, the veterinary clinician must be acquainted with the radiographic patterns and locations of the most common abnormalities of the developing elbow joint.
When experience with radiographic interpretation of these (ab)normalities is insufficient, it is advisable to include radiographs of the opposite, healthy leg. These images will serve as a control permitting more accurate radiographic interpretation of the affected leg.
At birth, the diaphyses of the humerus and of the radius and ulna are ossified (radiographically visible). The epi- and apophyseal ossification centers of the long bones become visible within 1-9 weeks after birth. Ossification of the anconeal process begins at 3 months of age and is completed at 4-5 months. The coronoid process develops as a bony extension at the dorsoproximal side of the ulna, already visible at 8 weeks of age.
In young dogs, the cartilagenous apo- and epiphyseal growth plates present radiographically as radiolucent lines (growth lines) that separate apo- and epiphyses from underlying metaphyses. During skeletal maturation these radiolucent lines gradually decrease in width, and disappear completely at the end of the growth period, at 6-11 months. After melting of the apo/epiphyseal and metaphyseal bones ("closure of the growthline") the only remnant of the growthlines that is radiographically visible is a very tiny white line of increased bone density, "the growth line scar".
The time of radiographic closure of growth plates in general varies between breeds and individuals, but as a rule all growth plates are closed at the age of 12 months.
This is also true for those growth plates that concern the elbow joint (Table 1).
Osteochondrosis of the elbow joint:
Osteochondrosis of growth plates (retained cartilage cone):
Premature closure of growth plates (traumatic):
Congenital elbow luxation, and other congenital deformities
A complete radiographic survey of a (suspected) dysplastic elbow joint includes at least four projections: ML, ML extended-supinated, CrCd, and CrL-CdMO.
1. With the dog in lateral recumbency and the affected leg down, two mediolateral projections are used:
2. With the dog in sternal recumbency, two craniocaudal projections are used:
The standard ML and CrCd projections allow an accurate initial investigation of the elbow joint. The ML projection allows for evaluation of possible arthrotic changes, for interpretation of secondary osteosclerosis at the basis of the medial coronoid process, and presents proof of joint incongruency. Both the CrCd and CrL-CdMO projections are used for evaluation of the medial humeral condyle (osteochondrosis, -itis desiccans) and for evaluation of the medial aspect of the distal humerus and medial coronoid process (degenerative osteophytes, fragments). Especially the CrCd view presents the radiographic proof of joint incongruency, with a step formation between the levels of the radial head and the coronoid process.
The ML extended-supinated projection presents a true lateral view of the medial coronoid process and, in spite of superposition by the radial head, presents the best radiographic representation of the medial coronoid process.
In many handbooks an additional 5th projection is described, the mediolateral-flexed projection (ML-flexed). This is a true mediolateral projection, with the joint flexed maximally. This projection is generally recommended to evaluate osteophytes along the proximal aspect of the anconeal process. However, these osteophytes are always visible on a good quality standard mediolateral (ML) radiograph. Besides that, the flexed position of the elbow conceals arthrotic osteophytes at the dorsoproximal aspect of the radial head. For these reasons, this flexed projection is of limited value.
Most of the time, radiographic investigations of dogs with abnormal elbow joints are performed under sedation or general anesthesia. Techniques include tabletop technique, and the use of high-definition screens in the cassettes.
Radiographic signs of elbow dysplasia
Radiographic signs of elbow dysplasia are dependent upon the underlying cause of this abnormality, and will be described accordingly.
Ununited anconeal process
Fragmented coronoid process
Osteochondritis desiccans of med. humeral condyle
Ununited med. humeral epicondyle
Ununited med. and lat. humeral condyles
Retained cartilage cone of distal ulnar metaphysis
Premature closure of distal ulnar growth plate
Premature closure of proximal (or distal) radial growth plate*
Table 2. Salter-Harris classification of growth plate fractures (injuries)
Type 1: complete separation of epiphysis from metaphysis through growth plate
Type 2: partly separation of epiphysis from metaphysis, with fracture extending into metaphysis
Type 3: partly separation of epiphysis from metaphysis, with fracture extending through epiphysis into the joint (intraarticular fracture)
Type 4: intraarticular epiphyseal fracture, with extension through growth plate into neighboring metaphysis
Type 5: compressive growth plate injury that kills germinative layer of entire growth plate
Type 6: peripheral growth plate injury, resulting in localized growth stop
This will seldom occur with Salter-Harris types 1-3, will sometimes happen with type 4, and always happens with types 5 and 6. The consequences of these injuries depend mainly upon the age of the puppy, that means depend upon the amount of growth potential still present at the time of the injury.
Pim Wolvekamp, DVM, PhD, Dipl ECVDI