Roof-arc angle and weight-bearing area of the acetabulum

Background: Unreduced fracture crossing the weight-bearing dome of the acetabulum leads to arthritis. Thus the integrity of the weight-bearing dome is considered to be an important prognostic indicator for acetabular fracture. The decision of whether or not to operate is based on the location of the fracture relative to the weight-bearing dome. A displaced fracture crossing the weight-bearing dome is an indication for surgery. Objective: To measure the medial, anterior, and posterior roof-arc angles that cross the weight-bearing dome. Methods: Twenty cadeveric hip joints were dissected and simulated transverse fractures of acetabuli through the transtectal area were made. The radiographic examinations were taken in three views: AP, obturator oblique, and iliac oblique. Roof-arc angle was measured in all three views (medial, anterior, and posterior). Results: The medial roof-arc angle was 46 +/- 6.3 degrees, anterior roof-arc angle was 52 +/- 7.0 degrees, and posterior roof-arc angle was 62 degrees +/- 8.5 degrees. Conclusions: In acetabular fracture, a medial roof-arc angle less than 46 degrees, an anterior roof-arc angle less than 52 degrees, or posterior roof-arc angle less than 61 degrees is considered to be involved in a weight-bearing area. Clinical relevance: These roof-arc angle values may be used as a surgical guideline for an acetabular fracture around the weight-bearing area. (C) 2009 Elsevier Ltd. All rights reserved.