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).

Table 1.

During the last years attention to growth problems in dogs has been dramatically increased with all the research and publications concerning "elbow dysplasia", that includes ununited anconeal process, fragmented coronoid process, and osteochondritis desiccans of the medial humeral condyle. This paper will discuss those abnormalities of the growing appendicular skeleton that directly affect the elbow joint and result, directly or indirectly, in elbow dysplasia.

Abnormalities include:

 Osteochondrosis of the elbow joint:

 Ununited anconeal process

 Fragmented coronoid process

 Osteochondritis desiccans of the medial

 Humeral condyle

 Ununited med. humeral epicondyle

 Ununited med. and lat. humeral condyles

 Osteochondrosis of growth plates (retained cartilage cone):

 Distal ulnar growth plate

 Distal radial growth plate

 Premature closure of growth plates (traumatic):

 Distal ulnar growth plate

 Proximal and/or distal radial growth plates

 Congenital elbow luxation, and other congenital deformities

Radiographic examination

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:

a.  True mediolateral, with the joint semiflexed (ML);

b.  Mediolateral, with the joint extended maximally, and the leg supinated 15 degrees (ML, extended-supinated).

2.  With the dog in sternal recumbency, two craniocaudal projections are used:

a.  True craniocaudal (CrCd);

b.  Craniolateral to caudomedial oblique (CrL-CdMO).

Using the old nomenclature, projection 3 was described as antero-posterior (AP), while projection 4 was known as the APMO-projection.

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

 Radiographic diagnosis can only be made at 5 months of age, or later

 Irregular lucent line or gap between olecranon and anconeal ossification centre(s)

 Displaced anconeal process

 Severe secondary joint disease (arthrosis) with age

 Large breed dogs

 fragmented coronoid process

 Incongruency of elbow joint: Bernese mountain dog, German shepherd

 Fissure lines or free fragments at craniomedial side of med. coronoid process

 Osteosclerosis at base of coronoid process

 No radiographic abnormalities (clenched fragment between radius and ulna, without dislocation)

 "Kissing lesion" at med. humeral condyle

 Secondary arthrosis

 Large breed dogs, esp. Bernese mountain dog, German shepherd, Retrievers

 Osteochondritis desiccans of med. humeral condyle

 Radiolucent subchondral defect in contour of med. humeral condyle

 Ossified loose flap

 Arthrosis

 DDX: "kissing lesion" due to fragmented coronoid process

 Ununited med. humeral epicondyle

 Dislocated med. humeral condyle

 Middle-sized and large breeds (rare)

 Ununited med. and lat. humeral condyles

 Radiolucent gap between humeral condyles

 Increased width of elbow joint

 Large breeds, esp. Great Dane (rare)

 Retained cartilage cone of distal ulnar metaphysis

 Radiolucent cone of immature cartilage extending from ulnar growth plate through the metaphysis into the diaphysis

 Secondary retardation of ulnar growth in length may result in radius curvus syndrome, with secondary incongruency of elbow joint and development of arthrosis

 Large breed dogs, esp. German shepherd, Bouvier

 Premature closure of distal ulnar growth plate

 Traumatic (directly or indirectly) of origin

 Early growth stop results in reduced length of ulna; normal growing radius outgrows in length the shortened ulna, resulting in radius curcus syndrome and lateral deviation of radiocarpal joint; abnormal stress and incongruency of elbow joint induce arthrosis

 Secondary fragmentation of coronoid process

 Sometimes combined with premature closure of distal radial growth plate

 All breeds

 Premature closure of proximal (or distal) radial growth plate*

 Traumatic of origin

 Retarded or stopped growth in length of radius results in marked increase of width of radiohumeral and radiocarpal joints; radius seems to be suspended between both joints

 Secondary fragmentation of anconeal process

 All breeds

 Congenital deformities

 Congenital elbow aplasia, luxation, and split hand deformity

 All breeds

*Damage to a growth plate may result radiographically in premature closure of that growth plate that indicates termination of growth of the affected growth plate. This happens with the compressive growth plate injuries classified as Salter-Harris types 5 and 6. The consequences of these injuries depend mainly upon the age of the puppy, that means how much growth potential was still present at the moment of the injury.

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

Damage to a growth plate may result radiographically in premature closure of that growth plate indicating termination of growth of the affected growth plate.

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.