A study of the "capsular" shadow in disorders of the hip in children.

Displacement and blurring of the soft-tissue shadows about the hip has been described in several conditions, particularly in transient synovitis. A study was made between such displacements and the posture commonly adopted by an "irritable hip". Examination of radiographs of normal hips, and of those in cases of transient synovitis and Perthes' disease showed that the appearance of "capsular swelling" is related to the position of lateral rotation and abduction. This was confirmed by anatomical dissections of the lateral plane, which appears to be an intermuscular plane lying anterior to the hip, and an explantation is given for the blurring which may accompany its lateral displacement. "Capsular swelling" appears to be a radiological artefact.