Contributors: Fraser McConnell
Species: Feline | Classification: Miscellaneous
- Skeletal radiography allows assessment of bone and, to a limited extent, soft tissue.
For lameness examination radiology should follow clinical examination and localization of the site of lameness.
Screening radiographs of the entire limb are unrewarding and may lead to erroneous diagnosis.
- For radiographic technique see:
- Radiography: pelvis Radiography: pelvis .
- Radiography: scapula Radiography: scapula .
- Radiography: humerus Radiography: humerus .
- Radiography: antebrachium Radiography: antebrachium .
- Radiography: carpus and forefoot Radiography: carpus and forefoot .
- Radiography: femur Radiography: femur .
- Radiography: tibia/fibia Radiography: tibia / fibula .
- Radiography: hock/foot Radiography: tarsus and hindfoot .
- Detail screens and film combinations should be used for most examinations.
- A low kV high mAs technique maximizes contrast.
- A tabletop technique gives better detail than a grid technique.
- Due to geometric effects of the diverging beam radiography should be centered at the point of interest.
For angular limb deformities separate radiographs of adjacent joints should be taken (in addition to the entire limb) to allow joint evaluation without geometric distortion.
- Orthoganol views are required as significant pathology, eg fractures, luxation may be missed on a single view.
- In examination of suspected joint instability, eg ligament injury, 'stressed' views may be helpful.
This can be done by using sandbags and ties - manual restraint is not required!
- Skeletal radiography usually requires sedation but some painful conditions may require anesthesia to facilitate positioning.
- In trauma patients evaluation and treatment of concurrent thoracic, abdominal or CNS injury should be undertaken before skeletal radiography.
It is important to remember that not all causes of lameness cause radiological changes.
- A normal radiograph in a lame animal should prompt consideration of:
- Incorrect localization of lameness - repeat clinical examination.
- Soft tissue injury/ abscess - reconsider differential diagnosis.
- Neurological disease, eg brachial plexus neoplasia, prolapsed intervertebral disk (PIVD) - reconsider differential diagnosis.
- Radiolucent foreign body in foot - repeat clinical examination.
- Early bone or joint disease before development of bony changes - repeat examination 2-4 weeks later. Bone changes may be seen in an immature animal as early as 3-5 days.
- Limb swelling.
- Limb deformity.
- Screening for hereditary orthopedic disease.
- Survey radiography gives no information about articular cartilage in most cases.
Bone has a limited response to injury (lysis and/or new bone formation), therefore it is important to assess location of lesion, signalment and general medical history.
If an unusual lesion (particularly mineralized bodies around a joint) it may be helpful to radiograph the contralateral limb as the lesion may be a normal anatomical variant.
- A systematic approach to evaluating the radiograph is important to avoid missing lesions.
- A bright light is essential to evaluate the soft tissues fully.
- Interpretation of long bones can be divided into focal and diffuse changes.
- Certain diseases only occur at certain parts of the bone.
- Epiphyses, eg epiphyseal dysplasia, Salter Harris fracture.
- Metaphyses, eg metaphyseal osteomyelitis, primary bone tumor (predilection site but do occur elsewhere).
- Diaphyses, eg osteopetrosis.
Focal bone lesions
- Usually lytic.
- These can be divided into:
- Polystotic lesions are more likely with inflammatory, developmental disease, metastases or soft tissue tumor invading bone or infectious disease.
- Try to differentiate benign from aggressive (based on margination, transition and periosteal reaction).
- Benign lesions, eg cysts, benign neoplasia:
- Variable degree of lysis - usually well differentiated from adjacent bone.
- Short transition zone to normal bone.
- Periosteal reaction usually well demarcated, smooth, does not extend far from edge of lesion.
- May be dense sclerotic rim of bone around sequestrum.
- Cysts may be expansile with thin cortices.
- Occur more in young cats.
Diffuse bone lesions
- FeLV Feline infectious peritonitis induced osteosclerosis
- Rare condition causing patchy areas of sclerosis in multiple bones.
- Lead poisoning Lead toxicity :
- Linear opacity in metaphyses.
- Metaphyseal osteomyelitis- similar changes but without collar of periosteal bone and often asymmetrical.
Aggressive bone lesions
- Often predilection site for primary bone tumor at metaphyses of long bones , .
- Poorly marginated with long transition zone to normal bone.
- Lysis often very extensive with severe cortical destruction.
- Extensive periosteal new bone formation bur poorly defined, spiculated or wispy bone in adjacent soft tissue.
- Some primary tumors are predominantly lytic.
- May be moth-eaten appearance or permeative lysis.
- Most soft tissue tumors arising from bone or arising in adjacent tissues tend to be predominantly lytic without soft tissue mineralization or extensive periosteal reaction.
- Bone opacity, thickness and regularity of cortical trabecular pattern should be evaluated.
- Radiography is insensitive for detecting demineralization.
30-50% of calcium must be lost before it is visble radiographically.
- Osteopenia may be diffuse and is recognized by:
- A reduction in opacity of the bone. this may be accompanied by a loss of the corticomedullary interface.
- Thinning of the cortices.
- Coarse appearance to the trabeculae.
- In some cases a double cortical line may be seen.
- Diffuse osteopenia may be due to chronic non-weight-bearing lameness, nutritional Nutritional secondary hyperparathyroidism and renal secondary hyperparathyroidism Renal secondary hyperparathyroidism , rickets. Storage diseases such as mucopolysaccharidosis VI may also cause osteopenia.
- Important to assess soft tissues carefully for evidence of gas or foreign material within soft tissues that indicate an open fracture.
- Assess joint soft tissues to rule out articular trauma from bone fracture extending to joint surface and/or concurrent joint injury with possible ligament involvement.
- Two orthogonal projections are mandatory to evaluate extent of the lesion .
- The age of fracture can be assessed by examining margination of fracture edge (sharp in recent fracture becoming rounded with resorption), periosteal bone formation (appears around 7-10 days), callus formation is more extensive, and develops earlier, in very young animals compared to adults.
- The soft tissues should be examined for evidence of swelling or bulging of fascial planes that may indicate soft tissue pathology or joint effusion.
- Atrophy of muscle may be appreciated but generally reflects chronic lameness, neurogenic atrophy or endstage of myositis.
- It is easiest to evaluate soft tissue by comparison of a limb with its contralateral partner.
- Nutrient foramen may mimic incomplete fractures but can be distinguished because:
- Usually occur in predictable site.
- Show no periosteal reaction.
- Are bilaterally symmetrical.
- Sesamoid bones may be mistaken for extra- or intra-articular bodies.
- Failure to take orthoganol views can result in missing serious pathology, eg luxated limbs may appear normal on one projection.
- Can be useful for localizing lesion to a particular area and identifying multiple bone lesions.
- Provides poor anatomical or pathological detail therefore only directs investigation to a particular location.