Detection of loose bodies in joints.

The ability of US to diagnose intra-articular loose bodies greatly depends on a high degree of suspicion of the examiner, related to the knowledge of radiographic and clinical findings. Nowadays, radiography is still the modality of choice when a loose body is suspected on clinical grounds. Plain films are panoramic and not expensive. If a calcified image consistent with a loose body is shown on radiographs, US can be performed to prove its intra-articular location and rule out para-articular calcification. The size, position (recess, bursa), and macroscopic composition (osseous, osteochondral) of loose bodies can be reliably evaluated. Additional findings, including mobility of loose bodies, presence of joint effusion, and synovial proliferation, can also be assessed with US. Detailed knowledge of the normal anatomy of joints and related structures is, of course, an essential requirement to investigate loose bodies. If the fragment is not found in the expected location, other joint recesses and bursae must be explored, because a fragment can change position with time. In addition, the US appearance of loose bodies has to be known by sonographers dealing with the musculoskeletal system because an intra-articular fragment can be found during routine examination of a joint performed before standard radiographs. There are a number of limitations on the clinical usefulness of US in this field. Although US is able to differentiate between single and multiple loose bodies, the exact number of the fragments cannot always be established. In osteochondral fractures, information on the posttraumatic damage to other intra-articular structures, such as ligaments or menisci, cannot be obtained by US. Furthermore, because US can evaluate only a portion of the articular surface, in most patients it is not able to demonstrate the site from which the fragments detach, as well as show their overall size and gross appearance. In conclusion, loose bodies are consistently depicted with US. A high degree of suspicion, knowledge of the radiographic studies, as well as a careful scanning technique, however, are essential to obtain a reliable diagnosis of loose bodies. US is able to support plain films to confirm the intra-articular location of a calcification around a joint. During routine joint examination, US can recognize loose bodies as incidental findings.