210.fat pad sign

The fat pad sign, also known as the sail sign, is a potential finding on elbow radiography which suggests a fracture of one or more bones at the elbow. It may indicate an occult fracture that is not directly visible. Its name derives from the fact that it has the shape of a spinnaker (sail).[1] It is caused by displacement of the fat pad around the elbow joint. Both anterior and posterior fat pad signs exist, and both can be found on the same X-ray.

In children, a posterior fat pad sign suggests a condylar fracture of the humerus. In adults it suggests a radial head fracture. The fat pad sign only occurs after an intra-articular fracture.

In addition to fracture, any process resulting in an elbow joint effusion may also demonstrate an abnormal fat pad sign. Increased intracapsular fluid is also seen in several conditions other than fracture and this produces the abnormal fat pad sign. (toxic synovitis, septic arthritis, Juvenile Rheumatoid Arthritis, osteomyelitis of the distal humeral physis and secondary septic joint).

The fat pad sign is invaluable in assessing for the presence of an intra-articular fracture of the elbow. An anterior fat pad is often normal. However a posterior fat pad seen on a lateral x-ray of the elbow is always abnormal. The patient will be unable to flex their elbow and requires orthopaedic input.

Notes:

1. occult [ˈɑ:kʌlt] adj. 隐匿的

2. condylar ['kɒndɪlə(r)] adj. 髁的

3. humerus [ˈhjumərəs] n. 肱骨

4. synovitis [ˌsɪnə'vaɪtɪs] n. 滑膜炎，关节膜炎

5. septic [ˈsɛptɪk] adj. 脓毒性的，腐败性的

6. Juvenile Rheumatoid Arthritis [ˈdʒu:vənl] ['ru:məˌtɔɪd] [ɑ:rˈθraɪtɪs] 幼年型类风湿关节炎

7. osteomyelitis [ˌɒstɪoʊˌmaɪə'laɪtɪs] n. 骨髓炎

8. orthopaedic [ˌɔ:θə'pi:dɪk] adj. 整形外科的

来源：每天朗读一段医学影像学英语文章