The computerized tomography subchondral arc: a new method of assessing acetabular articular continuity after fracture (a preliminary report).

The criteria to treat acetabular fractures operatively versus nonoperatively continue to evolve. The technique of roof arc measurements was developed to identify the extent of superior acetabulum left intact after fracture. Computerized tomography (CT) of the superior 10 mm of the acetabular articular surface evaluates the area equivalent to roof arc measurements of 45 degrees. CT provides increased detail of the superior acetabulum involved with the fracture. Our current criteria for selecting cases for nonoperative treatment are as follows: 1. The acetabular articular surface is intact in the superior 10 mm of the joint on CT evaluation. (Fractures that enter the acetabular fossa, but not the articular surface in the superior 10 mm are included in this group.) 2. The femoral head remains congruent with the superior acetabulum out of traction on the anteroposterior and 45 degree oblique radiographic views of the pelvis. 3. When a posterior wall fracture is part of the injury pattern, a minimum of 50% of the posterior wall articular surface is intact at the most involved level as determined by CT.