1. Clavicles – clearly seen in cats; smaller and less mineralized in dogs, but rudimentary structures are sometimes visible, especially on the CdCr view of the shoulder; bilaterally symmetrical.

2. Caudal circumflex humeral artery seen end on caudoventral to the joint, surrounded by fat; differential diagnosis is poorly mineralized joint mouse.

3. Separate ossification centre of glenoid – small, crescentic mineralized opacity adjacent to the caudal rim of the glenoid; may fuse to the scapula or persist throughout life; may be an incidental finding but differential diagnosis is osteochondrosis (OC) of glenoid (see 3.2.5 below). However, incomplete ossification of the caudal glenoid has recently been reported as causing lameness in a number of larger breed dogs of varying ages, especially the Rottweiler. Possibly associated with minor trauma, abnormal growth and OC (or osteochondritis dissecans, OCD). Damage to the medial glenohumeral ligament may also be present. Radiographs show a bony fragment adjacent to the caudal glenoid margin ± secondary osteoarthrosis.

4. Osteochondrosis of the humeral head; also called OCD if there is evidence of cartilage flap formation (Fig. 3.1) – young dogs mainly 5–7 months old of larger breeds; Border Collies, Labradors and Great Danes over-represented; male preponderance; often bilateral. Reported only twice in cats. Radiographic signs include flattening or concavity of the caudal third of the humeral articular surface ± subchondral lucency or sclerosis, overlying mineralized cartilage flap. In chronic cases joint mice may be seen, usually in the caudal joint pouch but also in the biceps tendon sheath or the subscapular joint pouch (CdCr view), as well as mild secondary osteoarthrosis. The presence of the vacuum phenomenon (see 2.2.13) is highly suggestive of an OC lesion. Arthrography is helpful in demonstrating thickening and irregularity of the articular cartilage layer, non-mineralized cartilage flap formation and non-mineralized joint mice. Ultrasonography can also be used to show OCD lesions, joint mice, joint effusions and new bone.

5. Osteochondrosis of the glenoid rim – unusual – separate mineralized fragment adjacent to articular rim; differential diagnosis is separate centre of ossification, but usually larger.

6. Congenital shoulder luxation or subluxation (Fig. 3.2) – rare, mainly miniature and toy breeds of dog, especially the Toy Poodle; may be bilateral. Usually present at 3–10 months of age, but older animals may show luxation after minor trauma. The humerus is normally displaced medially due to underdevelopment of the medial labrum of the scapular glenoid, but spontaneous reduction may occur on positioning for radiography. Radiographic signs include a flattened, underdeveloped glenoid with progressive remodelling of articular surfaces leading to osteoarthrosis; differential diagnosis is trauma at an early age.

7. Traumatic shoulder luxation – uncommon, unilateral. The humerus is usually displaced medially or laterally, occasionally cranially or caudally. With sagittal displacement, ML radiographs show a slight overlap of the scapula and humerus with loss of the joint space; on CdCr radiographs, the luxation is obvious unless spontaneous reduction has occurred; differential diagnosis is normal medial widening of the shoulder joint space on a CdCr view, especially if poorly positioned and particularly in smaller dog breeds. Check also for associated chip fractures.

12. Calcifying tendinopathy – usually supraspinatus and biceps brachii tendons (Fig. 3.3); changes in the infraspinatus tendon and bursa and coracobrachialis tendon are also reported. Mainly medium to large, middle-aged dogs, especially Rottweilers and Labradors; aetiology unknown. Mild, chronic or intermittent lameness or clinically silent. May be bilateral. Radiographic signs include areas of mineralization in the region of the affected tendon or bursa; differential diagnosis is rudimentary clavicles or joint mice in the biceps tendon sheath. Orthogonal radiographs (ML and CdCr) are essential to differentiate lesions within the bicipital groove from those medial or lateral to the shoulder, and the CrPr–CrDiO view and arthrography are also helpful in identifying the tendon of origin. Radiographs of the opposite shoulder should be obtained for comparison. Bicipital calcifying tendinopathy may be associated with tenosynovitis (see 3.2.13). Ultrasonography of the tendons may be helpful in showing fibre disruption, areas of mineralization (hyperechoic foci with distal acoustic shadowing) and joint capsule or tendon sheath effusion.

13. Bicipital tenosynovitis and bursitis – signalment as above. Radiographs may be normal or may show ill-defined sclerosis and new bone in the intertubercular groove, enthesiophytes on the supraglenoid tubercle and mild osteoarthrosis. Arthrography may show reduced or irregular filling of the biceps tendon sheath due to synovial villous hypertrophy. Ultrasonography may be used to demonstrate fluid distension of the bursa and tendon sheath and changes within the tendon itself.

1. Compensatory overgrowth of the humerus – increase in humeral length compared with the contralateral limb has been described in dogs in which there is significant antebrachial shortening due to premature closure of radial and/or ulnar growth plates. The mechanism is thought to be secondary to either reduced physeal compression as a result of decreased weight bearing, or alteration in blood flow.

2. Panosteitis – the humerus is a predilection site (see 1.13.6 and Fig. 1.17).

3. Metaphyseal osteopathy (hypertrophic osteodystrophy) – proximal and distal humeral metaphyses are a minor site; the most obvious lesions are usually in the distal radius and ulna (see 1.24.4 and Fig. 1.31).

4. Primary malignant bone tumours (most commonly osteosarcoma) – the proximal humeral metaphysis is a predilection site (see 1.20.1 and Fig. 1.27); the distal humerus is very rarely affected.

5. Humeral fractures.

1. Ossification centres visible in the elbow: medial and lateral parts of the distal humeral condyle, medial humeral epicondyle, anconeus, olecranon, proximal radial epiphysis; occasional small separate centre of ossification in the lateral humeral epicondyle seen on the CrCd view.

5. Incomplete ossification of the humeral condyle (Fig. 3.4) – especially English Springer Spaniels and American Cocker Spaniels but also seen in other Spaniel breeds and crosses and in some other pure breeds; male preponderance; often bilateral. Failure of fusion of the medial and lateral centres of ossification in the condyle results in a residual sagittal cartilaginous plate that may be clinically silent or cause lameness in its own right as well as predisposing to condylar fractures (see 3.4.17 and Fig. 3.10). The fissure may be seen on CrCd or Cr 15° M–CdLO radiographs when the X-ray beam is parallel to the fissure, extending proximally from the articular surface to the physis and sometimes beyond into the supratrochlear foramen. Differential diagnosis is Mach effect along the edge of the superimposed olecranon (see 1.9).

6. Coronoid disease: fragmentation of the medial coronoid process of the ulna (FMCP) (Fig. 3.5) – part of the elbow dysplasia complex seen in young dogs of medium and large breeds, especially the Labrador, Golden Retriever, Bernese Mountain Dog, Rottweiler, Newfoundland; male preponderance; often bilateral. Lameness is first seen from 4–12 months of age. In some cases, initial lameness is not detected, particularly if bilateral disease is present, and the dog presents at an older age with osteoarthrosis. Predisposed to by elbow incongruity with widening of the humeroradial joint space, which puts increased pressure on the medial coronoid process. The diagnosis of FMCP and of humeral condylar OC is often made by identification of secondary osteoarthrosis in an appropriate patient rather than by visualization of a primary lesion (see 3.4.19 and Fig. 3.11); a specific diagnosis may not be possible without arthrotomy, arthroscopy or high-resolution CT or magnetic resonance imaging. The primary radiographic findings are flattening, rounding or fragmentation of the process on the ML and Cr 15° L–CdMO views; the CrCd view shows not the process itself but a more medial projection of bone, which may be remodelled. ‘Kissing’ subchondral lesions may also be seen on the opposing articular surface of the humeral condyle; differential diagnosis is humeral OC (OCD).

7. Osteochondrosis (OCD) of the medial part of the distal humeral condyle (Fig. 3.6) – also part of the elbow dysplasia complex affecting the same breeds as above but with no gender predilection; often bilateral. The primary lesion is best seen on the CrCd view as subchondral bone flattening or irregularity, subchondral sclerosis, ± overlying mineralized cartilage flap; severe lesions may also be visible on the ML view; differential diagnosis is kissing lesion created by a fragmented medial coronoid process. Osteoarthrosis develops as with FMCP.

8. Ununited anconeal process (Fig. 3.7) – also part of the elbow dysplasia complex, although mainly in the German Shepherd Dog, Irish Wolfhound, Great Dane, Gordon Setter and Basset Hound; no gender predilection; often bilateral. Predisposed to by elbow incongruity with a slightly shorter ulna or longer radius putting pressure on the anconeus, but may also be due to trauma; some cases are bilateral. The separate centre of ossification for the anconeus usually fuses to the ulna between 3 and 5 months, and persistence of a radiolucent cleavage line beyond this time indicates separation. The flexed ML view is diagnostic, showing a substantial triangular bone fragment either adjacent to ulna or displaced proximally; chronic cases showing remodelling of the fragment and/or osteoarthrosis.

9. Elbow incongruity – seen in the various breeds predisposed to elbow dysplasia but especially in the Bernese Mountain Dog. Poor congruity between the humerus, radius and ulna puts increased pressure on the medial coronoid process or the anconeus and may lead to fragmentation or separation of these processes, respectively. Usually the humeroradial joint space is widened, best assessed on a CrCd view, as it is quite position-sensitive. May be seen alone or with FMCP, OC, ununited anconeal process ± osteoarthrosis. The clinical significance of incongruity alone is uncertain.

10. Medial epicondylar spurs (flexor tendon enthesiopathy) (Fig. 3.8) – usually larger breed dogs; may be bilateral; aetiology and significance not known and in some dogs is an incidental radiographic finding. The ML radiograph shows a distally projecting bony spur on the caudal aspect of the medial humeral epicondyle, or less commonly linear mineralization in adjacent soft tissues.

11. ‘Ununited medial epicondyle’ – unusual; aetiology not known but may be part of the elbow dysplasia complex, as similar breeds are affected, mainly young Labradors; may be bilateral. Single or multiple mineralized fragments of varying size and shape are seen at several locations near the medial epicondyle, sometimes with an adjacent bone defect. Secondary osteoarthrosis may be very minor. Some cases are radiographically similar to flexor enthesiopathies, and these may be different manifestations of the same condition.

Box 3.1 describes the grading system recommended by the International Elbow Working Group for elbow dysplasia screening.

13. Patella cubiti – a rare fusion defect through the trochlear notch of the ulna such that the olecranon and proximal ulnar metaphysis are separated from the rest of the ulna and distracted by the triceps muscle; so-called because the fragment of bone is patella-shaped. May be bilateral. Differential diagnosis is avulsion fracture through the proximal ulnar growth plate or trochlear notch.

14. Cats – hypervitaminosis A; usually due to excessive ingestion of raw liver, leading to bony exostoses mainly on the spine, but the elbow is also a predilection site (see 5.4.8 and Fig. 5.8).

15. Synovial sarcoma (occasionally other soft tissue tumours, such as histiocytic sarcoma; see 2.4.7 and Fig. 2.4) – the elbow is a predilection site; mainly larger breeds of dog; differential diagnoses are severe osteoarthrosis, in which superimposition of new bone may mimic osteolysis; septic arthritis. The diagnosis may be difficult in cases in which tumour is superimposed over pre-existing osteoarthrosis. In the case of a tumour, a soft tissue mass may be palpable or radiographically visible adjacent to the joint.

16. Cats – osteocartilaginous exostoses are often seen around the elbow and may be bilateral. Possibly a type of osteochondroma (see 1.15.2 and Fig. 1.19).

17. Fractures involving the elbow joint.

18. Traumatic elbow luxation – usually due to a road traffic accident or suspension by the limb from a fence. ML radiographs may be almost normal, but the CrCd view shows dislocation of radius or ulna from humerus clearly; small avulsion or chip fractures may also be seen. Usually the radius and ulna luxate laterally as the large medial humeral epicondylar ridge prevents medial luxation. Ulnar luxation alone also reported.

19. Elbow osteoarthrosis (Fig. 3.11) – new bone mainly on the anconeus and radial head (seen on the ML view) and medial and lateral humeral epicondyles (seen on the CrCd view). Sclerosis of the ulnar trochlear notch is due to a combination of increased bone density and superimposition of osteophytes, and is seen especially in dogs with fragmented coronoid process. The lameness may be quite severe with mild radiographic changes.

1. Late closure of the radial growth plates in neutered cats (males – distal only; females – both proximal and distal); leads to an overall longer radius than in entire cats.

2. Hemimelia (radial or ulnar agenesis) – one of the paired bones is congenitally absent, usually the radius; rare; usually unilateral. Medial carpal bones and the first digit may also be absent in the case of radial hemimelia; the remaining bone shows variable shape changes. Severe limb deformity and disability are evident from birth. Possibly heritable, as reported in several sibling cats.

3. Retained cartilaginous core, distal ulnar metaphysis (Fig. 3.12) – common, often bilateral, ossification defect in giant dog breeds, in which a central core of distal growth plate cartilage is slow to ossify, forming a candle flame-shaped lucency with faintly sclerotic borders. Implicated in growth disturbances but may be a coincidental finding, as often seen in normal dogs too.

4. Premature closure of the distal ulnar growth plate (radius curvus syndrome) (Fig. 3.13) – a common growth disturbance in young dogs of giant breeds, leading to angular limb deformity, often bilateral. The cause is usually not identified, so deemed idiopathic, but proposed mechanisms include:

Radiographs should include the whole antebrachium including the elbow and carpus, and show shortening of the ulna and distraction of the lateral styloid process from the carpus, craniomedial bowing of the radius and ulna with thickening of the adjacent radial and ulnar cortices, carpal subluxation and remodelling of the distal radius, carpal valgus and external rotation of the foot, and secondary elbow subluxation, usually of the distal aspect of the humeroulnar articulation. Carpal valgus may also be due to distal radius or ulna fracture or to developmental laxity of the short radial collateral ligament, and radiography permits differentiation of these conditions.

5. Distractio cubiti or dysostosis enchondralis – asynchronous growth of the radius and ulna in chondrodystrophic breeds (e.g. Bassett Hound), leading to elbow incongruity and pain; widening of the distal aspect of the humeroulnar articulation. Usually present with elbow lameness at about 12 months of age; may be bilateral.

6. Premature closure of the distal radial growth plate – trauma at or near the growth plate causes reduction in growth of the radius with shortening of the bone and subluxation of the elbow; widening of the humeroradial articulation ± increased width of the humeroulnar space proximally. Angular limb deformity is usually minor, and the main clinical problem is elbow pain.

7. Premature closure of the proximal radial growth plate – rare; presumed to be due to trauma; radiographic signs as for 6a, but the proximal radius may be obviously remodelled. Only 30% of the radial growth occurs proximally, therefore radial shortening is less severe than that following distal growth plate trauma.

8. Osteochondrodysplasias – various types of hereditary dwarfism are recognized in a number of dog breeds and in cats (see 1.22.7). Pathological and radiographic lesions are often most severe in the distal ulna and radius due to the high rate of growth at this site. The main abnormality is delayed growth at the distal ulnar growth plate, leading to shortening and bowing of the antebrachium. Some conditions may also resemble rickets radiographically (see 1.23.8 and Fig. 1.30). The pelvic limbs are less severely affected and may be normal.

9. Congenital hypothyroidism – causes dwarfism with radiographic changes similar to hereditary osteochondrodysplasias (see 1.22.9).

10. Radioulnar synostosis (fusion of the bones) leading to secondary radial head subluxation and external rotation of the foot has been described in a cat and is recognized in children. The radius and ulna are fused proximally at the interosseous space, preventing pronation–supination, and secondary elbow malformation results. May also occur following antebrachial fractures.

11. Bone remodelling in the distal ulnar and/or radial metaphyses has been described in Newfoundland dogs in Norway: 45% of dogs examined radiographically over a period of time showed islands of reduced opacity outlined by thickened trabeculae in the distal metaphyses at 6 months of age; the changes progressed up the diaphyses and persisted for up to 24 months of age. Aetiopathogenesis unclear. No clinical signs, but should not be mistaken for other conditions.

12. Metaphyseal osteopathy (syn. hypertrophic osteodystrophy) – young, rapidly growing dogs of larger breeds; lesions are usually most severe in the distal ulnar and radial metaphyses (see 1.24.4 and Fig. 1.31). Extensive periosteal and paracortical new bone may occasionally bridge growth plates, leading to angular limb deformities.

13. Panosteitis – the radius and ulna are predilection sites (see 1.13.6 and Fig. 1.17).

14. Rickets (syn. juvenile osteomalacia) – young animals after weaning; lesions usually most severe in the distal ulnar and radial growth plates (see 1.23.8 and Fig. 1.30).

15. Hypertrophic (pulmonary) osteopathy (syn. Marie’s disease) – the radius and ulna may be affected by palisading periosteal new bone, although the distal limb is likely to be affected first (see 1.14.6 and Fig. 1.18).

16. Craniomandibular osteopathy – rarely, paracortical new bone may be seen surrounding the distal ulna and radius, mimicking metaphyseal osteopathy (Fig. 3.14), sometimes in the absence of the typical skull lesions, although in dogs of appropriate breed and age (see 4.10.1 and Fig. 4.6).

17. Canine leucocyte adhesion deficiency – a hereditary, fatal disease in Irish Setters, causing lesions similar to metaphyseal osteopathy and craniomandibular osteopathy.

18. Primary malignant bone tumours (most commonly osteosarcoma) – the distal radial metaphysis is the main predilection site, especially in large and giant dog breeds, for example Great Dane, Irish Wolfhound (see 1.20.1 and Fig. 1.27).

19. Giant cell tumour (syn. osteoclastoma) – the distal ulnar metaphysis is a predilection site; differential diagnosis is solitary bone cyst (see 1.19.1 and Fig. 1.25).

20. Solitary bone cyst – the distal ulnar metaphysis is a predilection site; differential diagnosis is giant cell tumour (see 1.19.2 and Fig. 1.26).

21. Fractures of the antebrachium.

22. Radial or ulnar fracture delayed union or non-union – common in toy dog breeds due to failure to use the injured limb; radiographs show atrophic non-union and disuse osteopenia (see 1.9 and 1.16).

1. Normal sesamoid in the insertion of abductor pollicis longus muscle on proximal metacarpal 1, seen on a DPa radiograph medial to the radial carpal bone; differential diagnosis is old chip fracture.

2. Developmental antebrachiocarpal subluxations – secondary to growth disturbances in the antebrachium and angular limb deformities; most commonly premature closure of the distal ulnar growth plate with cranial bowing of the radius, leading to articulation of the distal radius with the dorsoproximal margin of the radial carpal bone and remodelling of the distal radial epiphysis (see 3.5.4. and Fig. 3.13).

3. Carpal flexural deformity – skeletally immature dogs at about 6–12 weeks of age, especially the Dobermann. Thought to be due to relative shortening of flexor carpi ulnaris muscle. Radiographs are normal and are used to exclude bony pathology.

4. Cats – osteodystrophy of the Scottish Fold cat; changes are more severe in the pelvic limbs (see 3.7.8).

5. Rheumatoid arthritis – the carpus and tarsus are predilection sites; often bilateral (see 2.4.8 and Fig. 2.5).

6. Cats – various feline polyarthritides; the carpus and tarsus are predilection sites.

7. Chinese Shar Pei fever syndrome, also known as familial renal amyloidosis of Chinese Shar Pei dogs – mainly the tarsus, but the carpus is occasionally affected (see 3.13.6).

8. Carpal fractures – often associated with avulsions of tendons or ligaments, so what appear to be minor fractures may cause serious effects.