The correlation between cutout and eccentric distance (ED) of the cephalic fixator tip in geriatric intertrochanteric fractures with internal fixation

Background The location of cephalic fixator tip with different eccentric distance (ED) should have different risks of cutout. This study aims to evaluate the cephalic fixator tip position by measuring ED of the cephalic fixator tip in geriatric ITF patients with single-screw cephalomedullary nail (SCMN) fixation and analyze the correlation between the cutout and the ED. Methods Firstly, we assumed all the femoral head was a regular sphere and standardized the radius of the femoral head (R-FD) as "3" no matter how big the R-FD was for complete match of the Cleveland zone system and convenient identification of artificial intelligence. Secondly, we measured the ED of the cephalic fixator tip by calculating the distances from the cephalic fixator tip to the geometric central axis of the femoral neck and head on both AP view and lateral view radiographs. Thirdly, we evaluated all the ED of the cephalic fixator tip in the eligible 123 geriatric ITF patients and analyzed the correlation between the cutout and the ED. Results The ED in cutout group (1.25 +/- 0.43) is much bigger than that in non-cutout group (0.64 +/- 0.34) with significant difference (OR = 50.01, 95% CI 8.42-297.19, p < 0.001). The probability of cutout increased with ED increasing, especially when "ED >= 1." The best cutoff value of ED for predicting cutout was "1.022" ("1.022" was just a little bit more than 1/3 times of R-FD because "R-FD = 3," sensitivity = 73.3%, specificity = 86.1%, and AUC = 0.867, p < 0.001). Conclusion ED is suitable for evaluation of the cephalic fixator tip position for predicting cutout in geriatric ITF patients with SCMN fixation, and ED can potentially be used as artificial intelligence application during surgery. The smaller the ED, the lower the cutout rate. For avoiding cutout, the ED of the cephalic fixator tip should be less than one-third times of the radius of the femoral head.