Introduction

Obtaining a high quality orthopaedic radiograph in a small animal patient represents a challenge. Both from a diagnostic quality and a radiation safety perspective, all radiographs should be obtained under good sedation or general anesthesia unless contraindicated based on patient health status. Even if presence of personnel in the examination room is be required under certain circumstances, ALARA principles (ALARA = as low as reasonably achievable) have to be honoured.¹ These include consideration of the 3 factors time (i.e., minimize time in the examination room), distance (i.e., maximize distance between personnel and x-ray beam) and shielding (i.e., wear appropriate protective equipment).

Usually, radiographs in at least 2 planes of the area of interest are needed. Additional views (e.g., oblique views or stress radiographs) and comparison radiographs of the other limb may be necessary for full evaluation. As there is significant variation in normal radiographic anatomy between small animal patients (especially, different dog breeds), and physiologic variations are common (e.g., changes with age), establishment of an in-house teaching library of normal radiographs as well as acquisition of reference textbooks^2,3 is strongly recommended.

Radiographic Examination of the Forelimb^4-7

Shoulder

Standard radiographs of the shoulder include a mediolateral view in which the affected leg is positioned on the table/plate and the leg is pulled forward. For the orthogonal projection the patient can either be positioned in sternal recumbency (craniocaudal view) or dorsal recumbency (caudocranial view). For optimized evaluation of the caudal humeral head, e.g., to rule out an OCD lesion, supinated and pronated radiographs with internal and external rotation of the antebrachium, respectively, may be useful. A skyline radiograph of the intertubercular groove in sternal recumbency and with the elbow pulled caudally is useful to evaluate the bicipital tendon region. Finally, in addition to a regular mediolateral view, a lateromedial view of the non­dependent shoulder with the limb pushed dorsally as far as possible can aid in evaluation of the scapula.

Elbow

In addition to standard mediolateral and craniocaudal views, a flexed mediolateral view is indicated in most instances to evaluate the anconeal process and medial epicondyle. Craniocaudal oblique views can help in assessment of the region of the medial coronoid process, medial epicondyle and other structures.

Carpus and Manus

Routine views include mediolateral and dorsopalmar radiographs. Oblique views (dorsomedial-palmarolateral oblique [DMPLO] and dorsolateral-palmaromedial oblique [DLPMO]) can aid in evaluation of the dorsolateral, dorsomedial, palmarolateral and palmaromedial aspect of carpal bones, metacarpals and phalanges. If joint instability is suspected, stress views with application of a fulcrum are helpful in determining degree and exact location of joint laxity. Stress radiographs can be performed in hyperextension, hyperflexion, and lateral and medial fulcrum application. Radiographs of the opposite leg are usually obtained for comparison as degree of joint laxity is somewhat variable (especially in cats). Finally, for further evaluation of the phalanges, splayed toe radiographs in lateral recumbency are useful. These are obtained by affixing tape to each toenail and spreading the digits apart.

Radiographic Examination of the Hindlimb^4-8

Pelvis and Femur

Routine views of the pelvis include a lateral (with legs superimposed and/or spread apart) and a VD view with the legs extended. An additional VD view with the legs flexed forward (“frog leg view”) is extremely useful for further evaluation of the femoral head and neck. The craniocaudal view of the femur is usually obtained the same way as the VD view of the pelvis. For the mediolateral view the opposite leg is either pulled caudally or dorsally dependent on patient conformation to avoid superimposition. Additional special views for evaluation of the pelvis may include oblique views and distraction views to evaluate for coxofemoral joint laxity.

Stifle

Routine radiographs of the stifle joint include mediolateral and craniocaudal or caudocranial views. In case of joint instability, stress views may also prove useful. A special craniodistal-cranioproximal (“skyline”) view occasionally used to evaluate the depth of the femoral trochlea involves positioning the patient in dorsal recumbency under stifle joint flexion, aligning the x-ray tube in parallel orientation with the floor and directing the x-ray beam over the highest point of the flexed leg.

Tarsus and Pes

The radiographic principles for evaluation of the tarsus and pes are the same as described for the carpus and manus above. An additional albeit rarely used view is a dorsoplantar view under tarsal flexion. This provides improved visualization of the trochlear ridges of the talus (“skyline view”) which is important e.g., in the diagnosis of OC/OCD lesions or tarsal trauma.

References

1.  Bushong SC. Radiologic Science for Technologists, 10th ed. St. Louis, MO: Elsevier Mosby; 2013.

2.  Coulson A, Lewis N. An Atlas of Interpretative Radiographic Anatomy of the Dog & Cat. Ames, IA: Wiley Blackwell; 2011.

3.  Thrall DE, Robertson ID. Normal Radiographic Anatomy & Anatomic Variants in the Dog and Cat. St. Louis, MO: Elsevier Saunders; 2011.

4.  Barr FJ, Kirberger RM. BSAVA Manual of Canine and Feline Musculoskeletal Imaging. Gloucester, UK: BSAVA; 2006.

5.  Thrall DE, et al. Section III: The appendicular skeleton: canine, feline, and equine. In: Textbook of Veterinary Diagnostic Radiology, 6th ed. Thrall DE, ed. St. Louis, MO: Elsevier Saunders; 2013.

6.  Farrow CS. Stress radiography: Applications in small animal practice. J Am Vet Med Assoc. 1982;181:777–784.

7.  Brown M, Brown L. Lavin’s Radiography for Veterinary Technicians, 5th ed. St. Louis, MO: Elsevier Saunders; 2013.

8.  Flückiger MA, Friedrich GA, Binder H. A radiographic stress technique for evaluation of coxofemoral joint laxity in dogs. Vet Surg. 1999;28:1–9.