Intraoperative fractures of the acetabulum during primary total hip arthroplasty

Background: The intraoperative occurrence of an acetabular fracture is a rare complication of primary total hip arthroplasty. Previous reports have lacked a sufficiently large number of subjects to allow for an analysis of the causes and appropriate treatment of this problem. Methods: Between 1990 and 2000, 7121 primary total hip arthroplasties were performed at our institution. We retrospectively reviewed the records in our Total Joint Registry and found that twenty-one patients (twenty-one hips) had sustained an intraoperative acetabular fracture. Nineteen of these patients (nineteen hips) had been followed until revision or for a minimum of two years (mean duration of follow-up, forty-four months). We evaluated the anatomic location, cause, treatment, and outcome of the fractures. Acetabular component designs were categorized as modular, nonmodular (monoblock), true hemispherical, or elliptical, and then each design was analyzed for fracture risk. Results: No fractures occurred in association with cemented acetabular components. The fracture rate associated with uncemented components was 0.4%. In seventeen hips, the acetabular component was judged to be stable despite the detection of a fracture and the cup was retained. In four hips, the original cup was not stable and therefore was replaced with a design that allowed for supplemental screw fixation. All fractures united, and all cups demonstrated osseous ingrowth at the time of the most recent follow-up. Elliptical monoblock cups were associated with a significantly higher fracture rate than were elliptical modular cups (p < 0.0001) and hemispherical modular cups (p < 0.0001). There was no significant difference between elliptical modular and hemispherical modular components with regard to the fracture rate. Conclusions: Acetabular fracture during primary total hip arthroplasty is a rare complication of acetabular fixation without cement. In the present series, retention of a stable cup was associated with uneventful osseous ingrowth and excellent early-term outcomes. We found a high rate of fracture in association with the use of monoblock elliptical components. Level of Evidence: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence.