The CT Measurement Of Ideal Entry Point That Lag Screw Insert To Treat Femoral Intertrochanteric Fractures

Objective:This aim of the present study is to measure the anatomical parameters of the proximal lateral wall which were scanned by MSCT and analyzed by the proprietary three-dimensional reconstructed software, in order to find out the ideal entry point(IEP)when the patients were treated with internal fixation of intertrochanteric fractures with Lag screw, so as to it can help the clinic make the operation plan.Methods: In our study,we choosed sixty dry adult cadaveric femurs which were marked by leaden wire(the diameter is about one mm); The adult cadaveric femurs were carefully selected excluding the deformity, tumor,fracture and other diseases. We drew a line respectively on the front and the back edge of the femoral shaft and marked it by the leaden wire which is along and in parallel with the long axis of femoral shaft. We defined that the back edge of the femoral shaft is the line which passes the point of front edge of gluteus tuberosity and along the long axis of the femoral shaft. Meanwhile, we difined that the front edge of the femoral shaft is the line which passes the point of the foremost area of the femoral clivus. We marked the point of the apex of the greater trochanter slope. we putted the femurs in the specific position that the greater trochanter,the medial condyle and the lateral condyle of the femurs were placed on the bed of the CT,at the same time we laid on the long axis of the femurs in parallel with the examination line of the CT. Then the femurs were scanned by GE MSCT. The scanning parameters : the tube voltage is 140 KV, the tube current is 400 m A. Then we got the Computed- tomography sections for the entire length of femurs which were scanned by 5mm slice thickness and reconstructed by 0.625 slice thickness. These images were transferred to the work station of GE ADW4.2, and analyzed by the proprietary three-dimensional reconstructed sofetware( we can mark the points which we need on the images and can rotate these images in any direction but the marks of the points did not disappear.) First, the femoral neck axis was identified, and the femoral anteversion angle and the distance from the entry point to the anterior border,posterior border and slope top point on the femoral lateral wall were measured. At the same time we got the relative position from the entry point, which we want to use, to the lateral cortex of the femurs. In our study, we observed the difference of this relative position from the entry point to the lateral cortex of the femurs beteen the right ones and the left ones. We divided all of the specimens into three groups according to the femoral anteversion angle. The first group is that the femoral anteversion angle is less than 10 °,( the number of the femurs is 14); The second group is that the femoral anteversion angle is greater than 10°but less than 18 °(the number of the femurs is 22); The third group is that the femoral anteversion angle is greater than 18°(the the number of the femurs is 23); We observed the difference between the three groups in the entry point position, and analyzed the relationship between the ideal entry point position and the anteversion angle.Results:1、The coordinate position of the entry point : The distance from the entry point to the posterior border on the femoral lateral wall( the front edge of gluteus tuberosity):the sample mean of left ones was 9,74±2.53 mm, the sample mean of the right ones was 9.20±2.29 mm, the sample mean of all of the femurs was 9.57±2.52mm; the distance from the entry ponint to the anterior border on the femoral lateral wall : the sample mean of left ones was 11.70±2.46 mm, the sample mean of the right ones was 12.1±2.40 mm, the sample mean of all of the femurs was 11.87±2.42mm; the distance from the entry point to the top point of the greater trochanter slope : the sample mean of left ones was 15.24±3.77 mm, the sample mean of right ones was 15.04±85 mm, the sample mean of all of the femurs was 15.15±3.78 mm.2、The relative position of the entry point:We define that the distence from the entry point on the proximal cortex of the femurs to the posterior border on the femoral lateral wall is W1 and the distence from the entry point on the proximal cortex of the femurs to the anterior border on the femoral lateral wall is W2. We called the width of the lateral cortex of the femurs was W1+W2. The relative position of the entry point is the ratio of W1/W1+W2. We used this ratio to represent the relative position of the entry point on the direction from the front to the back on the proximal femoral lateral cortex, in order to eliminate the effect of the size and the sexy of the femurs or other factors which can produce an effect on the results. The sample mean of this ratio was as follows : the sample mean of the left ones was 0.43±0.079; the sample mean of the right ones was 0.45±0.083; the sample mean of all of the femurs was 0.44±0.081. We got the result that the entry point was on the 44% back of the lateral cortex of the femurs in the direction from front to back.3 、The difference of the relative position of the entry point on the on the proximal cortex of the femurs between the left group and the left group : the sample mean of the left femurs was 0.43±0.079; the sample mean of the right ones was 0.45±0.083; Following tests for normality,the results were consistent with normal distribution. Then the data were analyzed using paired t-test in order to observe the difference between the left group and the right group. the results showed that there was no statistically significant difference between the left and right group(p >0.05).4、the difference of the relative position of the entry point on the on the proximal cortex of the femurs among the three groups which were divided according to the femoral anteversion angle : the sample mean of the femurs of which the femoral anteversion angle was less than 10 °was 0.51±0.06; the sample mean of the femurs of which the femoral anteversion angle was greater than 10 °but less than 18 °was 0.45±0.09; the sample mean of the femurs of which the femoral anteversion angle was greater than 18 °was 0.41±0.05; we analyzed the data using the single factor analysis of variance(ANOVA) in order to observe the difference among the three groups. The results showed that there were obvious statistically differences in the three groups which were divided according to the anteversion angle(p<0.05). the data were analyzed using LSD test to observe the difference of two groups respectively The results also showed that there were obvious statistically differences between any two groups which were selected in the three groups which were divided according to the femoral anteversion angle. The correlations between variables were accessed and showed that there was significant linear and negatively correlation between anteversion angle and the ideal entry point position.Conclusion:1 、The distance from the entry point to the posterior border on the femoral lateral wall( the front edge of gluteus tuberosity) was 9.57±2.52 mm. The distance from the entry point to the top point of the greater trochanter slope was 15.15±3.78 mm.2、We got the result that the entry point was on the 44% back of the lateral cortex of the femurs in the direction from front to back when we fixed the fracture of the intertrochanteric region of the proximal femur with the patients who got an intertrochanteric fracture.3、 Because there was significant linear and negatively correlation between anteversion angle and the ideal entry point position, so we should consider the anteversion angle and make the entry point position in the direction of the sagittal planes when the patients should be operated on the proximal femurs by internal fixed when they had a fracture of the proximal femurs.