The history of musculoskeletal imaging began with Roentgen's discovery of X-rays in 1895. Plain radiography has since become the initial and, in many cases, the only imaging modality for the diagnosis and follow-up of orthopaedic disease. A wide range of imaging options is now available but the "perfect" imaging protocol does not exist because imaging parameters will be both patient and disease specific. Radiography, ultrasonography, scintigraphy, CT, or MRI may be used alone or in any combination. The protocol finally selected will depend on the history, clinical findings, and the questions that should be addressed by the examination. Other important criteria include the strengths and limitations of the modality in question, of course whether or not the modality is available on site, radiation hazards and other safety issues. Economic considerations will also have to be taken into account.

The introduction and systematic use of arthroscopy in small animal orthopaedics really revolutionised the diagnosis and treatment of joint lesions. Arthroscopy is a minimal invasive technique allowing perfect visualisation of intra-articular structures in much more detail than exploratory arthrotomy. The development of arthroscopy in small animal surgery has lagged behind that of the human and equine fields because of the lack of instrumentation for small joints, cost of equipment, and scepticism regarding its practicality and efficacy. The application of arthroscopy to the relatively small joints of the dog has been made possible through the development of small joint arthroscopy equipment, but the appropriate expertise has to be elaborated by the surgeon by extensive training with a steep learning curve. The drawback of arthroscopy is probably that only the surface of articular structures can be assessed and that in inflamed joints the visibility can be reduced due to inflammatory changes like extensive production of synovial villi. This mainly causes problems in evaluating the stifle joint. Arthroscopically, assessment of subchondral lesions is not possible if the overlying cartilage is intact. For this reason, the combination of computer tomography (CT) and arthroscopy is in our opinion the ideal combination to evaluate joint disease especially within the elbow. In the elbow OC lesions can be picked up earlier with CT and arthroscopically. Although in the elbow joint flexor tendon enthesopathy can be picked up arthroscopically, in this type of disease CT (after IV contrast) and/or MRI are beneficial in the final diagnosis. In picking up coronoid disease CT has been proven to be an excellent technique almost as efficient and accurate as arthroscopy. The use of arthro-CT looks very promising in evaluating cartilage lesions in medial compartment syndrome and correlates well with the arthroscopic findings.

In the shoulder joint, most pathologies like OCD and a large number of bicipital lesions can be evaluated with radiography and arthrography. Ultrasound, in the hands of experienced users, can be an excellent technique to assess shoulder lesions. The advantage of arthroscopy is that direct inspection of OCD- and biceps lesions can be performed and be treated afterwards. Due to the minimal invasive nature of the technique, bilateral lesions can be treated within the same surgical intervention. Avulsion or incomplete fusion of the caudal glenoid ossification centre of the scapula is an indication for arthroscopic evaluation. In these cases, arthrography and CT can be of help to decide if the fragment is loose in the joint capsule and causes inflammation and pain. Then, the fragment is arthroscopically loosened from the joint capsule and removed. If one wants to evaluate the surrounding soft tissues, MRI is superior to arthroscopy. MRI- and CT-arthrography are promising in the evaluation of the glenohumeral ligaments if shoulder instability is suspected.

Arthroscopy of the stifle joint is technically more demanding than elbow and shoulder joints. The limited joint space and usually accompanying inflammation hinders the joint inspection. Adequate visualisation requires the use of a motorized shaver and electrocautery by radiofrequency, as well as flow management with more fluid and higher pressure. Indications for stifle arthroscopy are partial cranial cruciate rupture, meniscal lesions, and OCD lesions. Especially, assessment of meniscal damage remains challenging even with MRI and arthro-CT. CT is very useful to assess avulsion fractures of the cranial and caudal cruciates, the popliteus tendon, and extensor digitorum longus tendon mostly in young animals. In these cases, arthro-CT is useful to assess fragment stability.

Arthroscopy of the tarsocrural joint is a demanding technique allowing assessment of the joint cartilage, the synovial membrane and treating OCD lesions. Lesions can affect the medial (75%) or lateral (25%) talar ridge. Prior to the arthroscopic treatment, CT examination allows us to evaluate the exact location, size, and number of fragments of the OCD defects. Depending on the location of the fragments, a plantar or a dorsal approach of the tarsocrural arthroscopic intervention is decided. CT-arthrography can be used to assess fragment stability.

Within the hip joint, arthroscopy can be used to evaluate the status of the dorsal acetabular rim which should be intact if a TPLO is envisaged. Also CT can be used for this evaluation. With the use of arthroscopy the round acetabular ligament can be visualised as well as the articular cartilage.

Indications to arthroscopically examine the carpal joint are cartilaginous traumatic lesions.

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