de and the affected side in children with unilateral developmental dysplasia of the hip （UDDH）， including leg
length discrepancy （LLD）， femoral neck anteversion （FNA） and femoral neck shaft angle （NSA） differences. Methods
The clinical imaging data of 120 patients with UDDH who met the inclusion criteria from January 2018 to June 2021 were
retrospectively analyzed. According to the Tonnis classification， UDDH is divided into type i， ii， iii， and iv. The standing
position pelvic femoral full-length X-ray and pelvic femoral CT were taken， and the following parameters were measured：
Femoral length （FL）， greater trochanter femoral length （GTFL）， lesser trochanter femoral length （LTFL）， metaphysis
femoral length （MFL）， intertrochanteric distance （ITD）， FNA and NSA. The above parameters of the healthy side and the
affected side were compared， and the difference between the healthy and affected sides of each parameter was calculated. The
number of cases in which the healthy side of the above parameters was longer or shorter than the affected side was counted
respectively. The differences of imaging parameters between healthy and affected sides were compared among different tonnis
types， ages and genders. Results The FNA， NSA， MFL， and LTFL on the affected side were larger than those on the
healthy side， and the differences were statistically significant （P<0.05）； On the contrary， the FL， GTFL， and ITD on the
healthy side were larger than those on the affected side， and the differences were statistically significant （P<0.05）
. In FNA，NSA， LTFL， and MFL， the larger （longer） constituent ratio of the affected side was greater than those of the healthy side，and the longer constitutive ratio of the healthy side was greater than those of the affected side in FL， GTFL， and ITD. According to the multiple linear regression statistics of different models， the difference between the NSA and MFL affected
side in mod1 decreased with age （P<0.05）， and also statistically significant in mod2 and mod3（
P<0.05）. In mod4，5，6，The FL difference between the affected side and the healthy side decreased with the increase of the degree of dislocation，
which was statistically significant （P<0.05）
. The higher the degree of dislocation， the smaller the FL of the affected side than
the healthy side. The NSA difference of the affected side and the healthy side decreased with age， and the NSA of the affected
side gradually approached that of the healthy side， or even was smaller than that of the healthy side. Regardless of the degree
of dislocation， the MFL of the affected side was larger than the MFL of the healthy side， and the FL of the affected side was
smaller than the FL of the healthy side as the degree of dislocation increased. Conclusion The FL of the affected side was
shorter than that of the healthy side， but the difference was very small and had no actual clinical significance； While the MFL
of the affected side was significantly larger than that of the healthy side， indicating that there was indeed LLD in patients with
preoperative UDDH. The FNA and NSA of the affected side increased significantly compared with the healthy side， but the
increased value was small， and its clinical significance needs further study. The difference of FNA of the affected side did not
decrease with age， and the difference of NSA between the affected side and the healthy side negatively correlated with age.
