The acetabular transverse posterior wall fracture, a classic type of associated acetabular fractures and complex intra-articular fractures[1, 3], is usually caused by strong violence, which would inevitably involve both anterior and posterior column. Therefore, timely open reduction and firm fixation are required to restore the integrity of the articular surface and the matching relationship between the acetabulum and femoral head. Previous studies[13-16] have tried varieties of internal fixations, double-column plates or plates combined with lag screws, etc., to treat the acetabular fractures. However, the optimal treatment remained controversial. Some of them[13, 14] showed that double-column plates were superior to the single-column plate with lag screws in terms of the biomechanical stability, while one study[16] demonstrated that plate combined with lag screws seems non-inferior to the double plates with regards to the biomechanical stability, and could significantly reduce the surgical trauma and blood loss compared with double plate fixation.
In recent years, though sparse research, the locking plate has emerged as a novel way in the treatment of acetabular fracture due to its superiorities in angular stability and unicortical screw fixation. On this basis, we previously have designed a novel anatomical locking guidance plate based on the acetabular morphology of Chinese patients, which was reported to show promising efficacy in the treatment of acetabular fracture from a small sample[6]. But no direct comparison is available between our newly-designed plate and traditional plate in treating the ATPWF so far.
In this study, we aimed to simulate the mechanical behavior of the APTWF and compare two traditional fixations with our novel plate for fracture stabilization using a finite element analysis. Moreover, series of increasing loading force (200N, 400N and600N) were applied to better mimic the early partial or full weight-bearing loading.
We firstly evaluated the stress distribution and rigidity of plates and screws in three groups. As we described aforementioned, the major stress concentrated on the middle and lower sections of the posterior plate and lag screws in all three groups after the fixation on the ATPWF. Therefore, regardless of the type of internal fixation, the stiffness of these sites of the device should be enhanced so as to avoid the material break. For the rigidity of the plate, the NAGLP and DCLP seemed to experience larger stresses, whether it be the loading force of 200N, 400N or 600N, when compared with the DCLP. For the rigidity of screws, anterior screws in the PCLP group and screws in the NAGLP group showed highest stress concentration. Plates and screws in the DCLP group stood the minimum stresses as there were two plates in the fixation, which could efficiently disperse the stress. Namely, the plate and screws in the NAGLP and PCLP group were more likely to be broken when the loading force increased, which put a higher demand on the rigidity of the NAGLP and PCLP with its screws.
We then assessed the maximum displacement at two sites—transverse fracture and posterior wall fracture. Generally, the maximum displacement at the site of transverse fracture was larger than that at the site of posterior wall fracture. And there is no significant difference in the displacement of fracture fragment among three groups under the loading force of 200N. Nonetheless, as the loading force increased, the maximum displacement in the PCLP group was far larger than that in other two group, whether it be the transverse fracture site or posterior wall fracture site. And the NAGLP group demonstrated a slightly larger but comparable displacement to DCLP group. Namely, both NAGLP and DCLP offered a better stability in the treatment of ATPWF.
Taken together, DCLP group experienced the least stress and provided the firmest stability in treating the ATPWF from our data, which was consistent with the previous studies[17-20] about the treatment of acetabular fractures. However, as previously stated[16, 21], DCLP fixation would inevitably induce many complications like enlarged surgical trauma, and heavy blood loss. These shortcomings could be overcome by the single-column plate fixation. However, PCLP not only showed larger stress concentration, but worse biomechanical stability in our study, which was also in line with the previous study[22]. Notably, our newly-designed plate not only had the advantages of single plate fixation, but showed promising results in the displacement after fixation, which might emerge as an ideal device for the ATPWF treatment.
Apart from the advantages mentioned above, our self-designed plate, the inverted Y-shaped NAGLP, could match the inverted Y-shaped structure acetabulum very well. And on the basis of the acetabulum morphology of Chinese patients, this novel plate was anatomically precontoured to match the acetabular surface, therefore minimizing the surgical time and trauma. Moreover, NAGLP also have guide holes in the plate, facilitating the anterior-column screws and Magic screws implantation and therefore ensuring the safer and easier surgical process. After this direct comparison between two traditional fixations and our novel plate, we further confirmed its superiority in the fracture stabilization.
This study also has some limitations. First, all the results were based on the computer programs rather than the real environment, so some unknown information was lost in that case. A large clinical trial is in progress to further determine its superiorities and inferiorities. Second, we found NAGLP group experienced the highest stress concentration in the study. Therefore, future researches are required to address how to enhance its stiffness to avoid the plate breakage.