Computed tomographic assessment of fractures of the posterior wall of the acetabulum after operative treatment

Background: The purpose of this study was to evaluate the results after operative treatment of fractures of the posterior wall of the acetabulum in relationship to the quality of the fracture reduction as assessed by postoperative two-dimensional computed tomography. Methods: The functional results for sixty-seven patients who had open reduction and internal fixation of an unstable fracture of the posterior wall of the acetabulum and the findings of two-dimensional computed tomography performed postoperatively were analyzed. Sixty-one patients were followed for a mean of four years after the injury, and the remaining six patients who had poor early results necessitating reconstructive surgery were followed for less than two years. All patients were evaluated preoperatively and postoperatively with use of three standard plain radiographs (one anteroposterior and two Judet 45degrees oblique pelvic radiographs) and a two-dimensional computed tomography scan. The functional outcome for the patients was evaluated with use of a modification of the clinical grading system described by Letournel and Judet. The radiographs were graded according to the criteria described by Matta. The two-dimensional computed tomography scans were used to determine fracture gap and offset measurements. Results: The clinical outcome was graded as excellent in thirty-one patients (46%), very good in twenty (30%), good in eight (12%), and poor in eight (12%). The final radiographic results were graded as excellent in fifty-three hips (79%), good in four (6%), fair in three (5%), and poor in seven (10%). There was a strong association between clinical outcome and final radiographic grade. Fracture reductions were graded as anatomic in sixty-five and imperfect in two, as determined with use of plain radiography. However, postoperative computed tomography revealed an incongruency (offset) of >2 mm in eleven hips and fracture gaps of greater than or equal to2 mm in fifty-two. Fracture gaps of greater than or equal to10 mm in any dimension or a total gap area of greater than or equal to35 mm(2) were associated with a poor result. The main risk factors for a poor result were a residual fracture gap width of greater than or equal to10 mm and osteonecrosis of the femoral head. Conclusions: The degree of residual fracture displacement is detected more accurately on postoperative computed tomography scans than on plain radiographs. The accuracy of surgical reduction as assessed on postoperative computed tomography is highly predictive of the clinical outcome. Level of Evidence: Therapeutic study, Level III-2 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.