Contributors: Kate Bradley, Fraser J 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. They are indicated for evaluation of polyarthropathies and angular limb deformities.
- For radiographic technique see:
- Detail screens and film combinations should be used for most examinations.
- A low kV high mAs technique maximizes contrast.
- 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.
- Orthogonal 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.
- Radiography of joints 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 - reconsider differential diagnosis.
- Neurological disease, eg brachial plexus neoplasia, prolapsed intervertebral disc (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.
- Investigation of:
- Limb swelling.
- Limb deformity.
- 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 is seen (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 systemic approach to evaluating the radiograph is important to avoid missing lesions.
- A bright light is essential to evaluate the soft tissues fully.
- The joints should be evaluated for congruity, alignment, new bone formation, evidence of soft tissue swelling, muscle atrophy.
- Certain diseases have predilection sites that, although not pathognomic, may be helpful, eg synovial cell sarcomas (most common stifle, elbow), polyarthropathies (most common carpus and tarsus).
- Certain diseases occur at specific sites, eg shoulder OCD caudal humeral head.
- Important to assess soft tissues carefully for evidence of gas or foreign material within soft tissues that indicate an open fracture.
- 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 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.
- Sesamoid bones may be mistaken for extra- or intra-articular bodies .
- Failure to take orthogonal views can result in missing serious pathology, eg luxated limbs may appear normal on one projection .
- Failure to take flexed or oblique projections may result in failure to visualize lesions, eg femoral head growth plate, may only be visualized on 'frogged leg' view.
- Contrast studies may be useful in the shoulder. Primarily in the assessment of biceps tendon (if opacity change, see on plain film) and presurgical identification of free radiolucent (or would see on plain film) bodies in OCD.
- Ultrasound is useful for examination of the shoulder (ie biceps tendon) patellar ligament and achilles tendon. A high frequency linear transducer is most useful. It is helpful to compare contralaterail joints or the contralateral limb.
- The use of ultrasound to examine the stifle, etc is described but is generally of limited value.
- MRI allows exceptional evaluation of soft tissues and cartilage and bone pathology.
- CT allows exceptional evaluation of bone and is probably the method of choice for evaluation of joints. It is especially useful in the evaluation of complex joints, eg elbow and carpus.
- Nuclear medicine may be useful in cases where the site of lameness cannot be localized or if there are multiple abnormalities and there is difficulty assessing which lesions are significant.
- Scintigraphy may be used for screening for bone metastases and differentiating cellulitis from osteomyelitis.