Using Ultrasound to Image Joints

Introduction
Ultrasonography is a useful imaging modality for the investigation of joint abnormalities as it enables the evaluation of the soft tissue components of the joint together with providing information on the regularity of the bony contours. In the absence of MRI, ultrasound is usually the only imaging modality available to the practitioner to expand his/her investigation of joint pathology in the absence (or presence) of radiographic pathology.

Limitations

• not all areas accessible because of bony prominences and curved contours that can prevent optimal orientation of the transducer.
• because of these curved contours, off-incidence artifacts are common and therefore accurate interpretation requires good technique and experience
• some joints require a variety of transducers for complete evaluation
• information on bony pathology limited and therefore ultrasound is NOT a substitute for radiography. To maximize diagnostic information, it is usually easier to radiograph first and ultrasound second.

Ultrasonographic pathology relating to joints
(1) Joint effusion, where the nature of the effusion can be determined (e.g. floccular in the case of joint sepsis).
(2) Synovial hypertrophy – especially evident in joint sepsis. Villonodular synovitis can be identified on the dorsal aspect of the metacarpophalangeal joint.
(3) Articular cartilage/subchondral bone defects – many of the joints of the limb have very thin cartilage and the resolution of ultrasound limits its usefulness to identify subtle cartilage lesions (such as fibrillation and partial thickness defects). Younger animals have thicker cartilage and abnormalities such as osteochondrosis of the stifle are easily identified, with or without underlying subchondral bone defects.
(4) Chip fractures of the margins of the joints. While these are often evident radiographically, ultrasound can be used to define their location better, such as their axial/abaxial location, and relationship to soft tissue structures, such as intra- or extra-articular location, which can optimise treatment decisions and the location of the arthroscope.
(5) Abnormalities of associated soft tissue structures:  [...]