My Puppy is Limping: What Do the X-Rays Show? William Tod Drost, DVM, DACVR Ohio State University Columbus, OH

Developmental abnormalities of the canine skeleton manifest in many ways. While fractures are common in young animals, they are not the focus of this presentation. The immature has multiple parts – , physis, metaphysis and diaphysis. The physis, or growth plate, is soft tissue opacity and appears as a radiolucent zone at the ends of the . When growth plates are open, it appears that the number of bones has multiplied and this can be confusing. Radiographing the contralateral bone/joint is an excellent point of reference to help determine what is normal or abnormal. Additionally, many developmental diseases are often found bilaterally, so imaging the contralateral side helps determine the extent of the disease.

Osteochondrosis Failure of endochondral ossification

Osteochondritis dissecans Failure of endochondral ossification with a cartilage flap Signalment • Rapidly growing large breed dogs • 6-9 months old Common sites • Caudal humeral head • Medial humeral condyle • Femoral condyles • Trochlear ridges of the talus Radiographic signs • Flattening / concavity of bone surface • Apparent joint space widening • Cartilage flap • Only seen if mineralized o Arthrogram o MRI • Degenerative joint disease

Elbow dysplasia • Triad of diseases o Ununited anconeal process o Medial humeral o Fragmented medial coronoid process • Results in/from joint incongruity

Ununited anconeal process • Large breed dogs o dogs • No fusion of anconeal process after 150 days • Irregular, radiolucent line between anconeal process & proximal • Flexed lateral radiograph best

Humeral condyle OCD • Concave radiolucent defect on medial humeral condyle o Craniocaudal projection

Fragmented medial coronoid process • Most common cause of elbow dysplasia • Medium to large breed dogs 1

• Rule out ununited anconeal process and OCD first o Usually do not see fragmented coronoid (CT useful) • Blunting of coronoid on lateral • Superimposed on radial head • Rounding of coronoid on CC view • Joint incongruity • Degenerative joint disease

Aseptic necrosis of femoral head Synonyms • Legg-Calvé-Perthes Disease • of femoral head Pathophysiology • Loss of blood supply to femoral head / epiphysis • Articular cartilage growth continues • Revascularization • Incomplete removal of necrotic bone • Invasion of granulation tissue Radiographic findings • Varies with duration • Linear lucencies – early • Flat, irregular epiphysis & metaphysis • Apparent joint space widening • Muscle atrophy & DJD

Panosteitis • Self-limiting bone disease • Signalment o Male:female :: 4:1 o German shepherd dogs o 5-12 months old • Radiographic Findings o Increased intramedullary bone opacity o Solitary o Multifocal o Often near nutrient foramen o ± smooth periosteal reaction

Hypertrophic osteodystrophy (HOD) • Large and giant breed dogs • 2-7 months • Systemic illness o Unknown cause o Possibly distemper virus o Fever, diarrhea, leukocytosis, anemia, pneumonia • Self-limiting • Radiographic Findings o Transverse, lucent lines in the metaphysis o “Double physis” sign o Irregular periosteal bone around metaphysis o ± Regional soft tissue swelling

Secondary hyperparathyroidism Nutritional • Calcium deficient or calcium/phosphorus imbalance

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Renal • Chronic renal disease leads to systemic calcium deficiency Radiographic findings • Decreased bone opacity • Generalized • Thin cortices • Prone to pathologic fractures

Patellar luxation • Medial o Small & toy breed dogs • Lateral o Large breed dogs • Displacement of patella medially or laterally • Angular limb deformities

Hip dysplasia • Abnormal development of coxofemoral joints • Typically bilateral o ~ 11% unilateral • Inherited disorder • Various radiographic signs o Degree of joint laxity o Duration of disease • Radiographic findings o Coxofemoral subluxation o < 50% of femoral head in acetabulum o Shallow acetabulum o Osteophytes . Acetabulum . Femoral neck o Thigh & gluteal muscle atrophy

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