At present, in the surgical treatment of femoral supracondylar fractures, the clinical application of locking plate fixation technology has been relatively extensive. According to the need for reduction of femoral supracondylar fractures, the placement of non-locking lag screws in the locking screw holes is a frequently used hybrid fixation technique. However, the biomechanical properties of this hybrid fixation method have not yet been reported in related studies. Recently, Dave J. Dalstrom, MD of the Institute of Orthopaedics and Biomedical Research of Wright State University in the United States used an osteoporotic femoral supracondylar fracture locking plate fixation model to conduct an experimental study on the mechanical effects of the position and number of the locking screws in the diaphyseal part. , And announced its research results in the latest issue of JOrthopTrauma.

In this study, the author divided the osteoporotic femoral supracondylar fracture models into 4 groups, each with 5 model specimens, and each group used different locking plate screw fixation methods to implement the fixation of the diaphyseal part. The screw fixation methods of the 4 experimental groups were 4 non-locking screws (NL group); 1 locking screw near the fracture end combined with 3 non-locking screws (CL group); 1 was placed in the proximal locking hole The two locking screws are combined with three non-locking screws (FL group); the two locking screws at both ends are combined with two non-locking screws placed in the middle (DL group). The 4 experimental groups were further classified into closed-locked group (CCL group, including CL group and DL group) and non-closed-locked group (CNCL group, including FL group and NL group). All screws are inserted with 4Nm torque. The fixation structure of the distal femoral joint was the same in the four experimental groups. In the mechanical test, a bidirectional torque of 65Nm and an axial load of 700N were applied to the bone model specimen at 50,000/2Hz along the long axis.

Figure 1. The dry dirt end of the model is fixed with 5-mm hollow locking screws, and only 4 screws are placed in the backbone.

Figure 2. Osteotomy, plate and screw fixation of the distal femoral model specimen.

Figure 3. Diagrams of different screw fixation structures in the backbone.

Figure 4. Mounting the model specimen into the test device.

The experimental results show that there is no significant difference in the average pull-out torque, axial stiffness and torque stiffness of the four groups of steel plates and screw-fixed structures. However, the extraction torque of all screws in the CCL group, including non-locking screws, was significantly higher than that of the CNCL group (P=0.032/0.017), and the extraction torque of the locking screws was higher in the two screw fixing structures. There was no load failure in the CCL group, while 5 out of 10 specimens in the CNCL group had load failure (P=0.033).

The results of this study suggest that when the locking screw and the non-locking screw are used for mixed fixation, placing the locking screw near the fracture end is more helpful to maintain the pull-out torque of the adjacent non-locking screw and prevent its load failure. Inserting a locking screw at the proximal end of the diaphysis is not conducive to maintaining the torque adjacent to the non-locking screw. Compared with placing one locking screw at the proximal fracture site, placing two locking screws at both ends of the bone shaft has no advantage in screw extraction torque failure.

表1.4组的测试结果比较

Table 2. Comparison of test results between CCL and CNCL groups

[Editor's note] In the internal fixation of femoral supracondylar fractures by locking plates, surgeons often need to use ordinary non-locking screws to implement fracture reduction. In this case, how to choose the position of ordinary screws is worthy of attention The real problem. Although this study is a mechanical simulation experiment, it can be suggested to a certain extent that it is best to avoid the placement of non-locking screws in the screw holes closest to the fractured end. The placement of the locking screw near the fractured end is beneficial to the extraction protection of the adjacent non-locking screw.