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Radiology of the appendicular skeleton

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Abstract

Skeletal radiology is challenging due to the complex anatomy of the skeleton and the large number of incidental findings and anatomical variants which are encountered. Degenerative changes are common within the joints, and determining the significance of lesions requires correlation with the clinical examination and history. Often it is not possible to determine the the significance of lesions based on their radiological appearance alone. Bone has a limited response to injury, which means there is an overlap in the radiological features of many diseases, and further tests (e.g. arthrocentesis and biopsy) are often required for a definitive diagnosis. To maximize radiographic contrast, a low kV, high mAs technique should be used, and care should be taken not to overexpose the radiograph.

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Figures

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7.1 Mediolateral and caudocranial views of the shoulder of a 4-year-old Staffordshire Bull Terrier with acute onset lameness after falling from a height. A large articular fracture (arrowed) is visible on the caudocranial view of the shoulder, but is not visible on the mediolateral view. It is essential to obtain orthogonal views when imaging the joints to reduce the risk of missing significant pathology.
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7.2 Mediolateral, dorsoplantar, dorsolateral–plantaromedial oblique and dorsomedial–plantarolateral oblique views of the tarsus of a 3-year-old White Highland West Terrier presented with lameness after being hit by a car. There is a minimally displaced articular fracture of the medial ridge of the talus (arrowed); this is best seen on the dorsolateral–plantaromedial oblique view, which skylines the dorsomedial aspect of the joint. For complex joints such as the tarsus and carpus, oblique views are required to allow full evaluation of the joint.
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7.3 Dorsoplantar views of the tarsus of a 3-year-old Maine Coon cat presented for chronic tarsal swelling, which occurred after falling out of a window. The radiographs were obtained with the joint in a neutral position and a stressed position. In addition to extensive degenerative changes, there is laxity and subluxation of the tibiotarsal joint, which is only visible on the stressed view. Note the widened lateral aspect of the joint (arrowed) on the stressed view, indicating damage to the lateral collateral ligament.
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7.4 Different regions and blood supply in an immature (top) and mature (bottom) long bone. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.6 Mediolateral views of the tarsus of a Cocker Spaniel with a tibial fracture treated by casting. On the initial examination, the bone opacity was normal. Radiograph taken 6 weeks after casting showing severe osteopenia due to reduced weight bearing and loading of the bones. Note the thinning of the cortices (arrowed) and reduced opacity of the bone. Follow-up radiograph taken 5 weeks after the cast was removed showing remineralization of the bones with thicker cortices and increased opacity.
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7.7 Nutritional hyperparathyroidism in a kitten. At presentation, there was diffuse osteopenia with poor contrast between the bones and soft tissues, and the cortical thickness of the long bones was reduced. A folding (pathological) fracture (arrowed) of one of the femurs is present. Distortion and malformation of the vertebral column is associated with the reduced bone mineral content. The same kitten following 3 months of dietary correction. Bone density is now normal, although deformities resulting from the initial disease persist.
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7.8 Forelimb and hindlimb of a dog with multifocal sclerosis within the medullary cavity. Differential diagnoses include bone infarcts associated with osteosarcoma or immune-mediated disease and osteopetrosis. Bone infarcts vary from stippled foci to large patches of dystrophic mineralization in the medullary cavity of the distal limbs. Osteopetrosis is a rare condition, resulting in polyostotic areas of marked medullary sclerosis (increased opacity) with loss of the normal trabecular pattern. Cortical thickening may be present. The changes are usually diffuse, obliterating the medullary cavity, and better recognized in the appendicular skeleton. It may be an incidental finding in older cats.
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7.9 Focal bone destruction from least (left) to most (right) aggressive. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.10 Primary osteosarcoma affecting the long bones. The radiographic features vary but are characteristic of an aggressive bone lesion and include extensive bone destruction, cortical thinning or disruption, aggressive periosteal reaction (palisading or spiculated) and poorly defined transition to normal bone. The metaphyseal location is typical for a primary bone tumour. The lesion is characterized by moth-eaten osteolysis, a palisading periosteal reaction along the cranial cortex and a Codman’s triangle at the caudal cortex (arrowed), along with some lysis of both the cranial and caudal cortices. The lesion is predominately lytic with areas of moth-eaten and permeative lysis. The lesion is mixed lytic–proliferative with a central mixed geographic/moth-eaten area of lysis and a caudal ill defined spiculated periosteal reaction, indicating rapid deposition of new bone. Mediolateral and craniocaudal radiographs of an osteosarcoma arising in the distal radial metaphysis. The mixed lytic–proliferative lesion has moth-eaten and permeative areas of lysis, with an irregular spiculated periosteal reaction (with a Codman’s triangle seen on the medial aspect of the radius) and marked soft tissue swelling around the lesion. Although in close proximity to the ulna and carpus, the lesion in the radius is monostatic (i.e. only involves the radius). This is typical of primary malignant bone tumours and helps differentiate them from soft tissue tumours and secondary bone tumours.
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7.11 Lysis location in cortical bone destruction (e.g. moth-eaten or permeative) and scalloping. Lateral view of a long bone diaphysis. The lytic areas appear to be in the medulla but are in the superimposed cortex. Cross-section of the bone in (a). The lytic areas are actually in the cortex but are superimposed on the medulla. It should be borne in mind that opacity is influenced by tissue thickness. Thus, distances a and b combined are about half the distance of c (radiologically seen cortex), so they appear relatively radiolucent on the lateral view. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.12 Periosteal reactions from least (left) to most (right) aggressive. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.13 Dorsopalmar radiographs of the left and the right carpi of a dog with hyperostosis and a primary bone tumour (arrowed) in the distal left radius. The hyperostosis in this case was presumed to be idiopathic and has resulted in a generalized increase in opacity of all bones, with thickening of the cortices and a reduction in size of the medullary cavities. The generalized polyostotic distribution is seen with metabolic and some congenital and idiopathic diseases. In contrast, the lesion in the radius is monostotic and the distribution within the metaphysis is a predilection site for primary bone tumours.
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7.15 Craniocaudal and mediolateral views of the antebrachium of a dog with premature closure of the distal ulnar growth plate due to a retained cartilaginous core (arrowed). The cartilaginous core is ‘candle shaped’ with reduced opacity within the metaphysis and distal diaphysis. The antebrachium is bowed cranially and there is proximal displacement of the styloid process due to disturbance of the distal ulnar growth plate. Due to the increased loading, the ulna has a larger diameter than normal. This is the result of Wolffs law and illustrates the effect of altered loading on bone shape and size.
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7.16 Mediolateral and craniocaudal radiographs of the antebrachium of a chondrodystrophic puppy. The bowing of the radius and ulna is most clearly seen on the craniocaudal view. The shape of the distal radial epiphysis is altered, as is the articulation at the radiocarpal joint. Radial and ulna lengths are approximately equal.
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7.17 Mediolateral view of the normal tibia. Note the area of reduced opacity (arrowed) within the tibial tuberosity due to retained cartilage and thinness of the bone. This should not be mistaken for pathological lysis.
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7.18 Mediolateral view of the tibia of a dog following surgery. The periosteal new bone (arrowed) is poorly marginated with indistinct edges, which are difficult to differentiate from the soft tissues. Despite being poorly marginated, the shape of the new bone formation is smooth. Dorsopalmar view of the metacarpus of a dog with hypertrophic osteopathy. The new bone is sharply marginated with distinct edges; however, the shape of the new bone is irregular, almost palisading.
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7.19 Craniocaudal and mediolateral views of the antebrachium of a 6-month-old Irish Wolfhound with angular limb deformity due to premature closure of the distal growth plate. With limb deformities, it can be helpful to superimpose lines on the centre of the bones proximal and distal to the deformity. The point at which the lines cross indicates the region of maximal deformity and the probable site of the primary pathology. In this case, the intersection is at the level of the distal ulnar metaphysis.
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7.20 Caudocranial view of the femur of a dog. The radiolucent line running obliquely across the bone (arrowed) is due to fat within the fascial planes between the muscle bellies. The lucency can be seen to extend beyond the margins of the bone. Mach line/rebound artefact, resulting in an artefactual linear radiolucency (arrowheads) crossing the cranial cortex of the ulna where the edges of the radius and ulna cross. The short linear lucency running vertically in the femur (arrowed) is the normal nutrient foramen. Nutrient foramina occur in predictable locations and are most obvious within the diaphyseal regions of the long bones.
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7.21 Classical fracture healing. Haematoma at the fracture site. Bridging callus at the fracture site mineralized peripherally but with hyaline cartilage at the level of the fracture site. Compaction and remodelling of the mineralized callus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.22 Craniocaudal radiographs of the tibia and fibula of a Dachshund showing the normal progression of healing of a tibial fracture. Radiograph taken prior to reduction. Note the displaced multiple fracture of the mid-tibial diaphysis and mid-diaphyseal fractures of the fibula. Immediate postoperative radiograph showing reduction of the tibial fracture using an intramedullary pin and external fixator. Radiograph taken 2 weeks following fracture repair. Note the loss of definition of the margins of the fracture fragments and irregular periosteal new bone forming around the fracture site. Radiograph taken 4 weeks following repair. Note the continued remodelling of the fracture fragment ends and early infilling of the fracture spaces with reduced width and clarity of the fracture lines. Radiograph taken 8 weeks following fracture repair. Note the continued infilling of the fracture line and remodelling of periosteal new bone to form smoother continuous callus (particularly around the lateral aspect of the tibial fracture and around the fibular fractures). Radiograph taken 12 weeks following fracture repair. Note the continued remodelling of callus and almost complete infilling of the fracture lines.
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7.23 Craniocaudal view of the elbow of a dog with malunion following a lateral humeral condylar fracture. The lateral part of the humeral condyle has fused to the lateral supracondylar bone of the humerus, resulting in marked deformation of the elbow joint with proximolateral displacement of the humeroradial articulation.
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7.24 Mediolateral views of the humerus of a cat at presentation and at 6 weeks and 12 weeks following reduction of a mid-diaphyseal multiple fracture. (b) At 6 weeks, there is loss of bone beneath the proximal cerclage wires, which were subsequently removed. (ci) At 12 weeks, the ends of the fracture fragments have retreated from the fracture site, indicating an atrophic non-union. (cii) Magnified view.
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7.25 Salter–Harris classification of physeal injury. Type I: a proximal femoral physeal injury. The fracture line passes along the line of the physis. Type II: a proximal tibial physeal injury. The fracture line passes along part of the physis and exits through the metaphysis. Type III: a distal humeral physeal injury. The fracture line passes through the epiphysis into the joint and along part of the physis. Type IV: a distal humeral physeal injury. The fracture line passes through the epiphysis into the joint, across the physis and out through the metaphysis. Type V: a suspected distal ulna physeal injury with impaction of the physis in association with a transverse fracture of the radius and oblique fracture of the distal ulna. Type VI: an incomplete fracture of the distal radius associated with a periosteal reaction medially that has bridged the distal physis and influences further growth at this point. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.26 Mediolateral view of the left tibia and fibula of a dog with metastatic spread of mammary gland carcinoma to the long bones. The mid-diaphyseal tibial lesion has a dense, irregular, periosteal proliferation, resulting in increased bone opacity (solid arrow). The smaller lesion in the distal tibial diaphysis (dashed arrow) is similar and superimposed on indistinct bone lysis. A couple of small focal areas of mineralization (arrowhead) are seen caudal to the tibia: these are consistent with dystrophic soft tissue mineralization. The location of the bone lesions is not typical of a primary bone tumour. Tumours that metastasize to bone tend to be localized to the diaphysis, especially the areas around the nutrient vessels. The radiographic appearance is variable.
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7.27 Mediolateral and craniocaudal (close-up) views of the tibia and fibula of a dog with osteomyelitis associated with an external fixator. There is a generalized marked palisading periosteal reaction with diffuse soft tissue swelling affecting the distal tibial diaphysis and metaphysis. Bone lysis around the external fixator pins indicates loosening and infection extending into the bone around the pins. These are features of aggressive bone disease, but the periosteal reaction is well defined and established, indicating chronic disease. The narrow transition to normal bone proximally is typical of bone infection.
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7.28 Mediolateral view of the antebrachium of a dog with panosteitis. Ill defined ‘thumbprint’ areas (*) of increased medullary opacity in the mid-diaphyseal area of the radius and endosteal irregularity (arrowhead) are visible. Lesions are frequently centred on the nutrient foramen and blurring of the trabeculae may be present. Areas of medullary sclerosis may coalesce. Radiographic changes may lag behind the clinical signs in the early stages and so may not be present, therefore, radiographs should be repeated in 10–14 days where the clinical suspicion remains. Radiographic changes may also remain beyond resolution of the clinical signs, with cortical thickening persisting.
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7.29 Mediolateral neutral radiograph of the elbow of a dog with an ununited anconeal process. The area of the anconeal process is altered in shape due to new bone formation, and the anconeal process is separated from the olecranon of the ulna by a radiolucent line (arrowhead). In addition, the sclerosis of the ulnar trochlear notch indicates more generalized degenerative joint disease. The radiopaque ‘thumbprint’ lesion (arrowed) in the medullary cavity of the radial diaphysis indicates concurrent panosteitis.
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7.30 Mediolateral views of the left antebrachium and the left lateral thorax of a dog with hypertrophic osteopathy (Marie’s disease) associated with pulmonary metastatic disease. (a) A diffuse mixed periosteal reaction surrounds the antebrachial and metacarpal bones. The appearance of the periosteal new bone is laminar cranially, with a more palisading appearance caudally. The carpal and elbow joints and adjacent metaphyses are spared. (b) Multiple variably sized pulmonary soft tissue nodules are present within the thorax. The patient’s right forelimb had been amputated 5 months previously due to a proximal humeral osteosarcoma. Although usually associated with thoracic mass lesions, similar changes may also be caused by abdominal masses and, rarely, diffuse thoracic infiltrates.
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7.31 Mediolateral and craniocaudal views of the antebrachium of a Great Dane puppy with metaphyseal osteopathy (hypertrophic osteodystrophy). Areas or bands of radiolucency (arrowed) with mild surrounding sclerosis are present in the distal metaphyseal regions of the radius and distal metaphysis of the ulna. A collar of paraperiosteal new bone (arrowhead) is visible adjacent to the distal ulna and is seen in chronic cases of metaphyseal osteopathy. Changes in the contralateral limb and the metaphyses of the tibia and distal femur in this dog were similar. Haematogenous osteomyelitis can resemble metaphyseal osteopathy, but often only affects one limb and a collar of paraperiosteal new bone is not seen.
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7.32 Mediolateral views of the shoulder pre-arthrography and post-arthrography of an 8-year-old Border Collie presented with acute onset lameness. The plain radiograph is normal but the arthrogram reveals the absence of the normal biceps muscle due to complete avulsion of the tendon. Arthrography is most commonly performed in the shoulder, where it may demonstrate cartilage flaps and osteochondral fragments secondary to OCD, in addition to allowing assessment of the biceps tendon.
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7.33 Mediolateral view of the stifle of a dog. Effusion can be seen within the stifle joint (note the reduced size of the intrapatellar fatpad (arrowed) and displacement of the fascial planes caudal to the joint (arrowhead)). The presence of effusion is a specific indicator of joint pathology. Knowledge of the extent of the normal synovial compartments is important in differentiating joint effusions from other causes of juxta-articular soft tissue swellings.
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7.34 Mediolateral view of the stifle of a dog with patellar tendonitis. In this case, the soft tissue swelling is predominately extra-articular (arrowed) and extends beyond the boundaries of the stifle joint, which helps differentiate the swelling from an effusion. Small mineralized foci (arrowhead) within the swelling represent dystrophic mineralization, indicating chronicity.
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7.35 Mediolateral view of the tarsus of a Labrador Retriever with chronic Achilles tendonopathy. There is enlargement of the tendon (arrowed) just proximal to the tuber calcaneus and dystrophic mineralization within the tendon. Enthesophyte formation is present on the tuber calcaneus (arrowhead).
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7.36 Neutral, varus and valgus stressed dorsopalmar views of the carpus of a dog. Stressing the lateral aspect of the joint results in an abnormal varus deformity and widening of the fracture within the proximal fifth metacarpal bone, which is not visible on the neutral position.
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7.37 Dorsopalmar view of the carpus of a 1-year-old Boxer with cellulitis due to infection. There is extensive soft tissue swelling, which extends from the digits proximally to at least the mid-antebrachium. The swelling is not confined to the joint spaces, which helps differentiate soft tissue swelling from joint effusion. The changes in the case are non-specific and could be seen with oedema.
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7.38 Mediolateral and dorsoplantar views of the tarsus showing a soft tissue tumour invading the joint. The soft tissue mass and focal areas of lysis (arrowed) affecting multiple bones are typical of soft tissue joint tumours.
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7.39 Caudocranial view of the stifle with apparent medial displacement of the patella due to poor radiographic positioning. Note the fabellae are asymmetrical relative to the medial and lateral cortices of the femur, indicating rotation of the stifle. The lateral fabella is multipartite (arrowed), which is an incidental finding of no clinical significance.
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7.40 Craniocaudal and mediolateral views of the antebrachium of an Irish Wolfhound with an angular limb deformity due to premature closure of the distal growth plate. The cranial bowing of the antebrachium and carpal valgus are indicative of this condition. In cases of limb deformity, radiographs should include the joints proximal and distal to the deformity. Separate radiographs, centred on the joints, may be required to assess whether there is any joint incongruency.
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7.41 Mediolateral view of the shoulder of an Irish Setter with OCD of the humeral head. The focal flattening/defect within the subchondral bone (arrowed) is typical of OCD. OCD occurs in specific locations within joints, which helps to differentiate the disease from other causes of subchondral defects. Adjacent to the defect, there is sclerosis of the bone secondary to the cartilage pathology.
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7.42 Mediolateral view of the stifle of a dog. The apparent narrowing of the joint space on (b) the caudocranial view is artefactual due to the alignment of the X-ray beam relative to the joint space. The steep angle of the tibial plateau means that the X-ray beam is not parallel with the joint space. Radiological assessment of joint space width is often unreliable. Caudocranial view of the stifle of a dog. The apparent narrowing of the joint space is artefactual due to the alignment of the X-ray beam relative to the joint space. The steep angle of the tibial plateau means that the X-ray beam is not parallel with the joint space. Radiological assessment of joint space width is often unreliable.
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7.43 Mediolateral and caudocranial views of the elbow of a Labrador Retriever with severe chronic osteoarthritis. Marked new bone formation is seen surrounding the joint. The subchondral bone is irregular and collapse of the joint space is visible on the craniocaudal view. The small irregular regions of mineralization within the periarticular soft tissues (arrowhead) represent dystrophic mineralization. Due to the large amount of irregular new bone superimposed on the elbow, there are areas of relative lucency (arrowed) which can be misinterpreted as lysis. With severe osteoarthritis, the primary cause is often not visible.
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7.44 Mediolateral and craniocaudal views of the elbow of a dog with traumatic luxation. On the mediolateral view, the normal humeroradial joint space is not clearly visible and the humeral condyle and radial head are superimposed. On the craniocaudal view, the radius and ulna are displaced laterally relative to the humerus, indicating complete luxation of the elbow. The small triangular bony fragment lateral to the humeral epicondyle is likely to involve the collateral ligament.
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7.45 Mediolateral view of the stifle of a dog with septic arthritis. Note the widening of the femoropatellar joint space (arrowed) with cranial displacement of the patella. Joint widening is an uncommon feature of large effusions and can also be seen with intra-articular soft tissue masses.
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7.46 Mediolateral view of the shoulder of a 16-month-old Yorkshire Terrier with unilateral (presumed congenital) shoulder dysplasia. The joint is incongruent with an abnormal shallow glenoid cavity. Abnormal joint loading in immature animals may lead to severe incongruency. Mediolateral view of the normal contralateral shoulder for comparison.
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7.47 Mediolateral and caudocranial views of the stifle of a dog with osteoarthritis. Note the small osteophytes (arrowed) on the poles of the patella, trochlear ridges and at the margin of the femorotibial joint. In addition to the osteophytes, there is a large joint effusion and focal sclerosis and new bone formation on the tibial plateau (arrowhead) at the site of insertion of the cranial cruciate ligament.
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7.48 Dorsopalmar view of the manus of a 1-year-old cat with lameness and swelling of the digit. There is extensive destruction of the sesamoid bones and bones on either side of the joint. The changes are non-specific but highly aggressive and could represent neoplasia, infection or erosive monoarthritis.
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7.50 Craniocaudal view of the elbow of a normal dog. The rounded ossified body (arrowed) superimposed on the lateral aspect of the radial head is a sesamoid bone within the origin of the supinator muscle. This is a normal anatomical variant and should not be mistaken for a fragmented coronoid process.
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7.51 Dorsopalmar radiographs of the left and right manus of an Airedale Terrier with non-localizable lameness. The second palmar sesamoid bones are fragmented (arrowed) in both manus with the changes in the left appearing smooth and the sesamoid bone divided symmetrically into two parts. The fragmentation in the right manus is irregular with several small fragments. Multipartite sesamoid bones are common, often involve the second or seventh palmar sesamoid bones and are usually of no clinical significance. In this case, gamma scintigraphy showed increased radiopharmaceutical uptake in the sesamoid bone of the right manus. Surgical removal of the sesamoid bone resulted in resolution of the lameness. The second right sesamoid bone was presumed to be fractured, rather than a congenital anomaly. Radiological differentiation of a multipartite from a fractured sesamoid bone is difficult and may not be possible.
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7.52 Mediolateral view of the shoulder of a dog with supraspinatus mineralization and osteoarthritis. Mineralization of the soft tissues within and adjacent to the joints is common and often of no clinical significance. Supraspinatus mineralization is common and seen as irregular areas of mineralization overlying/adjacent to the greater tubercle of the humerus. The location of the osteophytes on the caudal aspect of the humeral head and glenoid is typical of shoulder osteoarthritis.
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7.53 VD view of the pelvis of a dog showing dystrophic mineralization within the gluteal muscles adjacent to the left greater trochanter. This is usually an incidental finding. Note also the presence of hip dysplasia.
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7.54 Mediolateral and craniocaudal views of the elbow of a cat with osteoarthritis. The extensive mineralization within the juxta-articular soft tissues is commonly seen in feline joints with osteoarthritis. In severe cases, cartilaginous nodules may form in the synovium and mineralize (synovial osteochondromatosis).
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7.55 Mediolateral view of the stifle of a cat with mineralization within the medial meniscus (arrowed). This has been associated with significant cartilage pathology, but can also be seen as an apparently incidental finding.
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7.56 Caudocranial view of the stifle of a West Highland White Terrier. The distomedial displacement of the medial fabella (arrowed) is a normal anatomical variant and should not be mistaken for avulsion of the head of the gastrocnemius muscle.
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7.57 Mediolateral radiograph of the shoulder of a 6-month-old dog. The small triangular bony fragment (arrowed) on the caudal aspect of the glenoid represents a separate centre of ossification. In immature animals, the fragment may unite fully with the remainder of the glenoid. Note also the irregular margins to the greater tubercle in this case, which is a normal finding in young dogs and should not be mistaken for bone lysis. Fragments at the caudal aspect of the glenoid are common and usually incidental findings. Mediolateral radiograph of the shoulder of a mature dog. The small triangular bony fragment on the caudal aspect of the glenoid represents a separate centre of ossification. In immature animals, the fragment may unite fully with the remainder of the glenoid. In young dogs, the greater tubercle may have irregular margins, which is a normal finding and should not be mistaken for bone lysis. Fragments at the caudal aspect of the glenoid are common and usually incidental findings.
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7.58 Mediolateral and dorsoplantar views of the tarsus of a Labrador Retriever with severe chronic osteoarthritis secondary to OCD of the medial ridge of the talus. The typical features of osteoarthritis can be seen, along with joint effusion and osteophyte formation. In this case, the primary pathology (OCD) is also visible with flattening of the medial ridge of the talus (arrowed). The subchondral bone is sclerotic and irregular due to the chronicity and severity of the cartilage pathology.
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7.59 Dorsopalmar and mediolateral views of both carpi in a dog with non-erosive immune-mediated polyarthritis. There is swelling of the soft tissues (arrowed) confined to the limits of the joint and no signs of bone pathology. Radiographs of both tarsi also showed the presence of effusion.
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7.60 Mediolateral and dorsoplantar views of the tarsus of a dog with erosive polyarthritis. Note the subchondral lysis (arrowed) involving multiple tarsal bones and resulting in an irregular subchondral surface and loss of definition to the intertarsal joints.
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7.61 Dorsopalmar views of the carpus of a dog with erosive polyarthritis. In severe cases of erosive arthritis, there may be subluxation of the joints. In this patient, all the metacarpophalangeal joints are luxated. Note also the carpal effusion and lysis of the carpal bones (arrowed).
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7.62 Dorsopalmar view of the carpus of a cat with septic arthritis involving the fourth metacarpophalangeal joint (this is the same cat as in Figure 7.48 , but 4 weeks earlier). Note the subtle lysis of the subchondral bone and the indistinct, poorly marginated periosteal new bone (arrowed) at the margins of the joint as well as the marked soft tissue swelling.
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7.63 VD view of the pelvis of a dog with septic arthritis involving the hip joint. In chronic cases, destruction of the bones either side of the joint is common. In this case, the infection was presumed to be haematogenous in origin.
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7.64 Mediolateral view of the stifle of a dog with septic arthritis following surgery for cranial cruciate ligament disease. In the acute stages septic arthritis is indistinguishable from any other cause of joint effusion. In cases secondary to surgery, lysis is usually centred around the implants. Note the lysis around the suture tract (arrowed) within the tibial tuberosity in this case.
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7.65 Mediolateral and caudocranial views of the stifle of a 4-month-old Labrador Retriever with a cranial cruciate ligament avulsion fracture. Note the small avulsed mineralized fragments (arrowed) at the location of the insertion of the cranial cruciate ligament. Avulsion fractures are most commonly seen in immature animals due to the relative weakness of the bone compared with the tendon/ligament. In mature animals, rupture of the tendon/ligament is more commonly seen.
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7.66 Patient positioning for a mediolateral view of the shoulder. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.67 Patient positioning for a caudocranial view of the shoulder. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.68 Mediolateral view of the shoulder of a dog with osteochondrosis at 4 months of age. Note the separate centre of ossification of the supraglenoid tubercle (arrowed). Mediolateral view of the shoulder of a dog with osteochondrosis at 7 months of age. Progressive development of an osteochondral lesion has resulted in flattening of the caudal humeral head. Close inspection reveals a faint mineralized line (arrowed) parallel to the defect in the humeral head, which is consistent with a mineralized cartilage flap. Note that the physis of the supraglenoid tubercle has closed in the time between the two radiographs.
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7.69 Mediolateral view of the scapula of dog showing a fracture of the body of the scapula. An interruption in the line of the scapular spine is seen on both radiographs. Note that the altered shape of the scapula is due to the caudal rotation of the proximal fragment. Craniocaudal (with shoulder flexed) view of the scapula of dog showing a fracture of the body of the scapula. An interruption in the line of the scapular spine is seen on both radiographs. Note that the altered shape of the scapula is due to the caudal rotation of the proximal fragment.
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7.70 Mediolateral view of the shoulder of a skeletally immature dog. An avulsion fracture of the supraglenoid tubercle is visible with distal displacement of the tubercle due to the draw of the biceps brachii muscle. Note the marked displacement of the supraglenoid tubercle compared with the normal location seen with an open physis (as seen in Figure 7.69 a). Further fragments are present within the fracture bed. Avulsion injuries through the physes of accessory ossification centres are not uncommon in puppies following trauma, particularly falls from a height. At other sites, such as the insertion of the cranial cruciate ligament, avulsion of a fragment of bone rather than rupture of the ligament may occur.
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7.71 Caudocranial view of the scapula of a dog with a primary bone tumour of the scapular spine. Note the bone lysis and expansile nature of the lesion (arowed). It is not possible to differentiate chondrosarcoma from osteosarcoma reliably on radiographs. Scapular lesions are easily overlooked on lateral views due to superimposition of the thorax.
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7.72 Mediolateral radiograph of a dog with craniolateral luxation of the shoulder. Superimposition of the humeral head and glenoid cavity results in a curvilinear sclerotic band. The normal conformation of the humeral head and glenoid indicate that this is an acquired luxation (compare with Figure 7.46 a). This is easily overlooked on radiographs not centred on the shoulder, and, in cases of trauma where thoracic radiographs are obtained, this sign can draw attention to the shoulder injury. Caudocranial radiograph of a dog with craniolateral luxation of the shoulder. Superimposition of the humeral head and glenoid cavity results in a curvilinear sclerotic band. The normal conformation of the humeral head and glenoid indicate that this is an acquired luxation (compare with Figure 7.46 a). This is easily overlooked on radiographs not centred on the shoulder, and, in cases of trauma where thoracic radiographs are obtained, this sign can draw attention to the shoulder injury.
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7.73 Mediolateral view of a dog with a fracture–luxation of the shoulder. The humeral head is displaced cranially with marked superimposition over the glenoid. The triangular bone fragment cranial to the neck of the scapula is consistent with displacement of the fractured supraglenoid tuberosity. (Courtesy of M Sullivan)
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7.74 Mediolateral, caudocranial and skyline bicipital groove views of the shoulder of a dog with periarticular mineralizations (arrowed) in the supraspinatus tendon. Note that the new bone at the craniolateral aspect of the glenoid extends on to the greater tubercle of the humerus. The clinical significance of these findings is unknown.
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7.75 Patient positioning for neutral and flexed mediolateral views of the elbow. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.76 Patient positioning for a craniocaudal view of the elbow. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.77 Neutral mediolateral and craniocaudal radiographs of the elbow of a dog with a fragmented medial coronoid process and secondary degenerative joint disease. The fragment from the medial coronoid is a triangular mineralized area superimposed on the radial head (arrowed) on the mediolateral view, and medial to the radial head on the craniocaudal view. New bone formation is present on the radial head and medial and lateral humeral epicondyles. CT image of the elbow of a dog with a fragmented medial coronoid process and secondary degenerative joint disease showing a line crossing the base of the medial coronoid process (arrowed). New bone formation is present on the radial head and medial and lateral humeral epicondyles. L = lateral; M = medial; R = radial head; U = body of the ulna.
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7.78 Craniocaudal view of the elbow of a dog with OCD. The defect in the articular surface of the medial part of the humeral condyle (arrowed) is surrounded by some sclerosis of the adjacent bone. (Courtesy of M Sullivan)
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7.79 Mediolateral view of the elbow and antebrachium of a dog with severe ulnar chondrodystrophy (elbow incongruity). The trochlear notch of the ulna is abnormally shallow, leading to a widened humeroulnar joint space. The distal ends of both the radius and ulna are bowed cranially. Incongruency of the elbow has to be relatively severe to be reliably detected radiologically.
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7.80 Craniocaudal view of the elbow of an English Springer Spaniel with IOHC. A fine radiolucent line (arrowed) extending between the two halves of the humeral condyle, from the articular surface to the supratrochlear foramen, can be seen. In many IOHC cases, the fissure cannot be visualized due to superimposition by the olecranon. In some cases, focal periosteal new bone may be present on the humeral epicondyles due to abnormal stresses on the bone (and may precede a condylar fracture).
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7.81 CT images of the elbows of an English Springer Spaniel with unilateral IOHC. The elbow of the left has a fissure line between the two halves of the humeral condyle.
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7.82 Mediolateral and craniocaudal views of the elbow of a dog with a ‘Y’-shaped fracture of the distal humerus. On the craniocaudal view, a fracture extends into the elbow joint, resulting in separation and displacement of both halves of the humeral condyle. A small triangular bony fragment distal to the medial part of the humeral condyle indicates a fracture of the medial coronoid process. On the mediolateral view, the distal humerus is fractured and the normal elbow joint cannot be visualized.
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7.83 Mediolateral and craniocaudal views of the antebrachium of a dog with premature closure of the distal ulnar physis. On the mediolateral view, the distal ulnar physis can no longer be recognized. There is marked cranial bowing of the radius and incongruity of the humeroulnar joint. On the craniocaudal view, the paw is deviated laterally (carpal valgus) below the carpal joint.
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7.84 Patient positioning for a mediolateral view of the carpus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.85 Patient positioning for a dorsopalmar view of the carpus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.86 Patient positioning for a stressed extended view of the carpus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.87 Patient positioning for a flexed mediolateral view of the carpus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.88 Neutral dorsopalmar and stressed dorsopalmar views of the carpus of a dog with rupture of the medial carpal collateral ligaments. (a) A degree of soft tissue swelling around the carpal joint is consistent with joint effusion. (b) The antebrachium and digits are pulled laterally, placing stress on the medial aspect of the carpal joint, resulting in medial subluxation of the radiocarpal joint. The radial carpal bone is displaced medially due to the loss of support from the medial collateral ligament.
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7.89 Mediolateral view of the carpus of a dog with carpal osteoarthritis. Osteophytes are present on the distal radius and dorsal and medial aspects of the carpal bones. A mild joint effusion is visible as a mild degree of soft tissue swelling around the joint. Dorsopalmar view of the carpus of a dog with carpal osteoarthritis. Osteophytes are present on the distal radius and dorsal and medial aspects of the carpal bones. A mild joint effusion is visible as a mild degree of soft tissue swelling around the joint.
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7.90 Mediolateral view of the carpus of a dog with carpal joint effusion. Soft tissue swelling is present dorsal to the carpal bones and is confined to the limits of the carpal joint.
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7.91 Mediolateral and dorsopalmar views of the carpus of a dog with septic arthritis. There is marked joint effusion with irregular lytic erosions of the subchondral bone of the distal radius and proximal row of carpal bones. Mineralized fragments are present in the dorsal aspect of the antebrachiocarpal joint, which may represent dystrophic mineralization or fragmentation of the bone. In cases of septic arthritis, where there is pre-existing osteoarthritis, it is often difficult to detect the signs of bone lysis, which occur in the later stages of sepsis.
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7.92 Patient positioning for a mediolateral view of the foot. Note the separation of the toes. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.93 Examples of trauma to the forepaw. Dorsopalmar view of the digits with medial and proximal luxation of the second and third phalanges of the third digit. Dorsopalmar view of the carpus with a minimally displaced fracture (arrowed) of the lateral aspect of the proximal end of the fifth metacarpal.
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7.94 Dorsopalmar view of the forepaw of a dog with marked digital osteoarthritis. There is extensive new bone seen around the proximal interphalangeal joints, most obviously in the third and fourth digits, which represents enthesopathy of the collateral ligaments and osteophyte formation. Although dramatic, these changes are commonly seen as apparently incidental findings (especially in large-breed dogs). Mediolateral view of the forepaw of a dog with marked digital osteoarthritis. There is extensive new bone seen around the proximal interphalangeal joints, most obviously in the third and fourth digits, which represents enthesopathy of the collateral ligaments and osteophyte formation. Although dramatic, these changes are commonly seen as apparently incidental findings (especially in large-breed dogs).
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7.95 Dorsopalmar and splayed mediolateral views of the digits of a dog with glass foreign bodies. There is soft tissue swelling around the distal phalanx of the third digit and, on the mediolateral view, two small well defined radiopacities (arrowed) are seen in the region of the digital pad (small glass fragments). The linear opacities seen on the mediolateral view are due to the tape used to splay the digits.
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7.96 Mediolateral and dorsopalmar views of the manus and lateral view of the thorax of a cat with a pulmonary carcinoma and metastasis to the digit. There is marked soft tissue swelling around the distal end of the third digit with almost complete lysis of the distal phalanx. The changes are consistent with an aggressive soft tissue tumour destroying the bone. The rounded mottled pulmonary nodule present in the lungs in the caudal thorax is consistent with a primary lung tumour.
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7.97 Patient positioning for a VD view of the hip and pelvis. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.98 Patient positioning for a flexed (frog-legged) VD view of the hip and pelvis. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.99 Patient positioning for a lateral view of the hip and pelvis. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.100 VD view of the pelvis with axial rotation to the left. Note the asymmetry of the iliac wings and obturator foramina. The pelvis is rotated towards the side with the smaller obturator foramen and larger iliac wing, in this case on the left (i.e. the left side of the patient is closest to the cassette). The dog has severe hip dysplasia and osteoarthritis with extensive osteophyte formation, irregular sclerosis of the subchondral bone and marked remodelling of the joints.
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7.101 VD view of the pelvis of a dog with left pelvic limb lameness showing muscle atrophy. Note the reduced size of the left gluteal (arrowed) and thigh muscles compared with the right side.
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7.102 VD view of the pelvis of a dog with hip dysplasia and gas within the right anal sac (arrowed). The ovoidal-shaped lucency caused by the gas is superimposed over the right ischium and should not be mistaken for an area of lysis. There is moderately severe osteoarthritis with irregular osteophytes around the femoral heads and necks, and subluxation of both hips.
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7.103 Severe hip dysplasia in a 6-month-old Tibetan Terrier. There is marked subluxation of both femoral heads and shallow acetabulae. Due to the lateral displacement of the femoral heads, there is reduced coverage of the femoral heads by the dorsal acetabulae.
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7.104 Norberg angle measurement. On the extended VD view of the hip, it is the angle between a line connecting the femoral head centres and a line from the centre of the femoral head to the craniodorsal acetabular rim. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.105 VD view of the pelvis of a dog with mild hip dysplasia and osteoarthritis. The subtle curvilinear osteophyte (arrowed) on the femoral neck is an early sign of hip osteoarthritis. The hip dysplasia is associated with only mild subluxation, resulting in medial divergence of the joint space cranially (arrowhead).
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7.106 VD view of the pelvis of a cat with hip dysplasia. There is subluxation of both hips and shallow acetabulae. In cats with osteoarthritis of the hips, osteophyte formation is often most severe on the craniodorsal acetabulum, with relative sparing of the femoral neck compared with dogs. Mushroom-shaped femoral heads can be seen in asymptomatic/normal cats.
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7.107 VD and lateral views of the pelvis of a dog with cranioventral hip luxation. On the VD view it is not possible to determine whether the luxation is dorsal or ventral. In cases of traumatic hip luxation, a careful evaluation should be made for an avulsion fracture on the femoral head or evidence of pre-existing hip dysplasia, which may alter treatment options and prognosis.
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7.108 VD view of the pelvis of a cat with a left sacral fracture, a right sacroiliac subluxation and fractures of the pubis and left ischium. The pelvis can be thought of as a rigid box and there are usually multiple fractures. Radiography often underestimates the number of pelvic fractures.
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7.109 VD view of the pelvis of a young dog with a Salter–Harris type I fracture of the femoral head. This type of fracture may occur spontaneously with no history of external trauma and may be bilateral. If there is damage to the blood supply, there may be avascular necrosis of the femoral head.
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7.110 VD view of the pelvis of a young West Highland White Terrier. There is lysis and reduced opacity of the left femoral head and neck and widening of the joint space on the initial examination, but the right hip is normal in opacity. Radiograph taken 2 months following the initial examination. Note the presence of lysis on the right femoral neck, which has an ‘apple core’ appearance.
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7.111 VD view of the pelvis in a dog with multiple myeloma. There are multiple punched out areas of lysis within multiple bones of the pelvis and femur (arrowed).
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7.112 Patient positioning for a mediolateral view of the stifle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.113 Patient positioning for a craniocaudal view of the stifle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.114 Patient positioning for a craniodistal–cranioproximal oblique (CrDi-CrPrO) (skyline) view of the patella. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.115 Mediolateral view of a dog with cranial cruciate ligament disease. Note the distal displacement of the popliteal sesamoid bone (arrowed), which is suggestive of the disease. Other changes seen with cranial cruciate ligament disease are non-specific and largely relate to secondary osteoarthritis.
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7.116 VD view of the pelvis and pelvic limbs of a dog with severe medial patellar luxation. The patellae are visible lying medial to the stifle joints and there is deformity of the femoral and tibial bones. The tibial tuberosities are rotated medially.
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7.117 VD view of the pelvis and pelvic limbs of a Bullmastiff with lateral patellar luxation. There is genu valgum deformity with medial bowing of the limb and the patella can be seen lying lateral to the stifle. Note the abnormal conformation of the hip joint, which can also be associated with patellar luxation.
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7.118 Mediolateral view of the stifle of an Akita with OCD of the stifle. The predilection site for OCD in the stifle is the medial aspect of the lateral femoral condyle. The typical saucer-shaped defect (arrowed) is often easiest to see on slightly oblique mediolateral views. A mineralized fragment (arrowhead) is present within the recess of the joint cavity proximal to the patella. Caudocranial view of the stifle of an Akita with OCD of the stifle. The predilection site for OCD in the stifle is the medial aspect of the lateral femoral condyle. The typical saucer-shaped defect (arrowed) is often easiest to see on slightly oblique mediolateral views. A mineralized fragment is present within the recess of the joint cavity proximal to the patella. On the caudocranial view, the normal extensor fossa should not be mistaken for an OCD lesion. In this case, the flattening of the lateral condyle is visible.
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7.119 Mediolateral view of the stifle of a dog with avulsion of the long digital extensor tendon. The avulsed bony fragment (arrowed) is usually seen immediately distal to the extensor fossa and there may be a defect visible within the lateral femoral condyle at the origin of the tendon. Caudocranial view of the stifle of a dog with avulsion of the long digital extensor tendon. The avulsed bony fragment (arrowed) is usually seen immediately distal to the extensor fossa and there may be a defect visible within the lateral femoral condyle at the origin of the tendon.
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7.120 Mediolateral views of the right and the left stifle of a dog showing tibial tuberosity avulsions in both limbs. Avulsion fractures occur predominately in young animals and may occur spontaneously with no history of external trauma. The proximal displacement of the tibial tuberosity is the consequence of pull from the quadriceps muscle.
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7.121 Patient positioning for a mediolateral view of the tarsus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.122 Patient positioning for a dorsoplantar view of the tarsus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.123 Patient positioning for a flexed dorsoplantar view of the tarsus. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.
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7.124 Mediolateral view of the tarsus of a dog with severe tibiotarsal joint effusion. Note that the swelling is confined to the margins of the tibiotarsal space. There is also concurrent swelling of the Achilles tendon and gunshot pellets within the tarsus.
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7.125 Mediolateral and dorsoplantar views of the tarsus of a Labrador Retriever with OCD. There is a moderately severe joint effusion, which is present in most cases of tarsal OCD. Due to the defect in the medial ridge of the talus, there is widening of the medial aspect (arrowhead) of the tibiotarsal joint space. The mediolateral view shows flattening of the talus proximally (arrowed), but this is easily overlooked due to superimposition.
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7.126 Mediolateral view of the tarsus of a dog with chronic plantar ligament degeneration and rupture. There is hyperextension of the proximal intertarsal joint and swelling of the soft tissues on the plantar surface of the tarsus. Extensive new bone formation on the plantar surface of the joint is common.
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7.127 Mediolateral, dorsoplantar, dorsolateral–plantaromedial oblique and dorsomedial–plantarolateral oblique views of the tarsus of a dog with multiple tarsal fractures. Due to the complex anatomy of the tarsus, radiography underestimates the severity and degree of comminution of tarsal fractures. In this case, there is subluxation of the centrodistal joint and calcaneoquartal joint and comminuted fractures of the central tarsal bone.

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