OTA 2002 - Session 4 Session IV - Pelvis Sat., 10/12/02 Pelvis, Paper #27, 8:38 AM Computed Tomography Analysis of Posterior-Wall Fractures of the Acetabulum
Treated Operatively Berton R. Moed, MD ; Seann E. Willson Carr, MD; Konrad
I. Gruson, MD; J. Tracy Watson, MD; Joseph G. Craig, MD; Wayne State University,
Detroit, Michigan, USA Purpose: A number of studies have demonstrated that a disparity
exists between the accuracy of the surgical reduction of posterior-wall
acetabular fractures, as determined by plain radiographs, and clinical outcome.
The purpose of this study was to evaluate the results of the operative treatment
of posterior-wall fractures of the acetabulum in relationship to quality
of fracture reduction as assessed by postoperative two-dimensional computed
tomography. Methods: The results were analyzed of 67 patients who had open
reduction and internal fixation of an unstable posterior-wall fracture of
the acetabulum and postoperative two-dimensional computed tomography. Sixty-one
patients were followed for a mean of 5 years (range, 2 to 14) after the
injury. The remaining six patients, with clearly poor results, were followed
for less than 2 years. All patients were studied preoperatively and postoperatively
with three standard plain radiographs (an anteroposterior and two Judet
45° oblique pelvic radiographs) and two-dimensional computed tomography.
The patients' functional outcome was evaluated with use of the clinical
grading system adopted by Letournel, incorporating modifications by Matta.
The radiographs were graded according to the criteria described by Matta.
The two-dimensional computed tomograms were examined by use of fracture
gap and offset measurements. Additional patient, fracture, and radiographic
variables were collated in an attempt to identify possible associations
with functional outcome. These variables included patient age, gender, time
to reduction of the dislocation (categorized as less than 12 hours, 12 to
24 hours, and more than 24 hours), impaction injury to the femoral head,
involvement of the weight-bearing acetabular dome, intraarticular fracture
comminution (defined as three or more fragments), presence of marginal impaction,
radiographic evidence of osteonecrosis of the femoral head, and radiographic
evidence of severe heterotopic ossification. Results: Clinical outcome was graded as excellent in 31 patients
(46%), very good in 20 (30%), good in 8 (12%), and poor in 8 (12%). Final
radiographic results were graded as excellent in 53 hips (79%), good in
4 (6%), fair in 3 (5%), and poor in 7 (10%). There was a strong association
between clinical outcome and the final radiographic grade. Fracture reduction
was graded as anatomic in 65 and imperfect in 2, as determined by plain
radiography, and did not correlate with clinical outcome. However, postoperative
computed tomography revealed incongruency (offset) of more than 2 mm in
11 and fracture gaps (negative defect) of 2 mm or more in 52. Fracture gaps
of 10 mm or more in any dimension or a total gap area of 35 sq mm or more
were associated with a poor result. The main risk factors for a poor result
were a residual fracture gap width of 10 mm or more and osteonecrosis of
the femoral head. Discussion and Conclusions: The disparity between the accuracy
of posterior wall fracture reduction, as determined by plain radiographs
obtained postoperatively, and clinical outcome has been well described.
Postoperative computed tomography detects the degree of residual fracture
displacement more accurately than do plain radiographs. The accuracy of
surgical reduction as assessed on postoperative computed tomography is predictive
of clinical outcome.