The current study examined the surgical radiological results of simultaneous ipsilateral pelvic ring and acetabular fractures, to evaluate the factors that may contribute to inadequately reduced acetabular fractures. The results revealed that the most common fracture type was B2.2 for pelvic ring fractures and of the anterior column for acetabular fractures. Additionally, the univariate analysis demonstrated that the associated fractures of the acetabular fracture and reduction quality of the pelvis, by Matta’s criteria, were the two independent factors that affected the reduction quality of subsequent acetabular fractures. However, no significant factors were identified via the multivariate analysis.
Anatomical reduction is the main goal in osteosynthesis for acetabular fractures, to minimize the risk for post-traumatic osteoarthritis. Tannast et al. reviewed a series of 816 patients with acetabular fractures and followed them for 2–20 years [8]. They showed that non-anatomical fracture reduction was the most significant negative predictor leading to total hip arthroplasty. Additionally, most studies reporting outcomes after acetabular fractures have indicated the importance of anatomical fracture reduction [8,10,19-21]. There are several factors that might affect the reduction of the acetabular fractures, and the complexity of the fracture pattern is one of them. Thirteen acetabular fractures (48.1%) were classified as associated fractures in Letournel’s classification. Among the 13 associated acetabular fracture patterns, ten were graded as fair to poor reduction quality on AP iliac, oblique, or obturator oblique views in X-ray scans. Additionally, there were greater step-offs on CT scans for the associated fracture patterns. Therefore, our results revealed that the classification might lead to inadequate reductions of acetabular fractures.
However, the acetabulum is part of the pelvis; therefore, in cases of pelvic ring fracture without sufficient reduction, the reduction of the acetabulum may not be adequate. Suzuki et al. confirmed that the initial accurate reduction of the posterior pelvic lesion appeared to be necessary to obtain optimal reduction of the acetabulum [4]. Since accurate reduction of the posterior pelvic ring is key to anatomical fracture reduction of the acetabulum, the sequences of fracture reduction and fixation may be critical. Although this study consisted of 19 patients with anterior approaches (ilioinguinal, anterior intrapelvic, and pararectus), the principles of the reduction sequence did not differ. These approaches mostly aimed to reduce and fix anterior lesions; however, posterior pelvic ring injures such as crescent fracture, sacral fractures, and sacroiliac joint diastasis could also be managed using these approaches. On the other hand, posterior approaches were still important and necessary when a displaced posterior pelvic ring existed and should be performed prior to anterior approaches. There were three cases of spinopelvic osteosynthesis and three cases of open reduction and fixation to address posterior sacroiliac joint injuries. These six patients also underwent subsequent anterior approaches for acetabular fractures.
The reduction of the posterior pelvic ring is crucial in obtaining satisfactory radiological results; however, there has been no discussion on how to evaluate the pelvis's reduction quality before beginning osteosynthesis of the acetabulum. Our study shows that Matta’s criteria may be useful in evaluating the reduction of the acetabulum. Since fluoroscopy is the most common tool for intraoperative evaluations of fracture reduction, Matta’s criteria can be used before the beginning of osteosynthesis for acetabular fractures to determine whether the reduction should be more accurate before proceeding with the osteosynthesis. This method may be applied intraoperatively to ensure the following reduction quality of the acetabulum.
There have been similar reports of combined pelvic ring and acetabular fractures [4,7,11,12,22]. According to previous findings, the most common fracture type of the pelvis in similar cohorts was the lateral compression type [4, 7, 22]. However, Osgood et al. found the AP compression type was the most common in their cohort [11]. In our study, we show that the most common fracture type was the lateral compression type. Because the most common type of fracture of the pelvis in our study was B2.2 (lateral compression type), the injury force was probably applied directly and laterally towards the greater trochanter of the femur, which would be similar to the injury force resulting in anterior column fractures of the acetabulum [23], the most common type of acetabular fractures in our study. Therefore, we observed similar fracture types from injuries to the pelvis and acetabulum, consistent with previous studies.
Although we made efforts to avoid bias, this study had some limitations. First, this study included a relatively small number of patients, which might result in statistical bias. However, similar to previous studies, the incidence of simultaneous pelvic and acetabular fractures was low, and the numbers of enrolled patients were naturally limited in our group. Second, although one of the major findings of this study was the proposal to apply Matta’s criteria for the pelvic ring intraoperatively, it was evaluated from postoperative images in this study. The actual intraoperative usefulness of Matta’s criteria to predict the reduction quality of acetabular fractures in this cohort should be determined in a future study. However, the strength of our study includes the fact that the patients were all treated by a single surgeon in a single institute with a similar treatment protocol. All patients were followed up with complete postoperative X-rays and CT scans, and 3 independent examiners conducted the interpretations of the images with excellent inter-observer reliability. Therefore, the obtained data were reliable and convincing.