Abstract
Introduction
EOS® is a low dose imaging system which allows the acquisition of coupled AP and lateral high-definition images while the patient is in standing position. HipEos has been developped to perform pre-surgical planning including hip implants selection and virtual positioning in functional weight-bearing 3D. The software takes advantage of the real size 3D patient anatomical informations obtained from the EOS exam. The aim of this preliminary study on 30 consecutive THP patients was to analyze the data obtained from HipEos planning for acetabular and femoral parameters and to compare them with pre and post-operative measurements on standing EOS images.
Material and methods
Full body images were used to detect spino-pelvic abnormalities (scoliosis, pelvic rotation) and lower limbs discrepancies. One surgeon performed all THP using the same type of cementless implants (anterior approach, lateral decubitus). The minimum delay for post-op EOS controls was 10 months. A simulation of HipEos planning was performed retrospectively in a blinded way by the same surgeon after the EOS controls. All measurements were realized by an independent observer. Comparisons were done between pre and post-op status and the “ideal planning” taking in account the parameters for the restitution of joint offset and femur and global limb lengths according to the size of the selected implants. Regarding cup anteversion, the data included the anatomical anteversion (with reference to the anterior pelvic plane APP) and functionnal anteversion (according to the horizontal transverse plane in standing position).
Results
The difference between pre-op and post-op APP angles is not statistically significant (p = 0.85), likewise for the sacral slope (p = 0.3). Thus, there has been no change in the orientation of the pelvis after THP. Comparing the two hips on post-op EOS data shows that the difference in femoral offset is not statistically significant (p = 0.76). However, the femoral length is statistically different (p <0.05) (mean 4mm, 0–12mm).
The difference for femoral offset between HipEOS planning and post-op EOS data is not statistically significant (p = 0.58). However, the mean difference is significant (p <0.05) for femur length (5mm), inclination (5°) and anteversion of the cup. The mean post-op anatomic anteversion measured in the APP is 27°, whereas it is 11° with HipEOS planning. The mean functional anteversion of the cup on standing post-op EOS data is 35° while planning it is 17°. Otherwise, differences in femoral anteversion are not significant.
Conclusion
The planning tools currently available include only the local anatomy of the hip for THP adjustment. This software integrates weight-bearing position, which allows to consider the impact of spine deformities and length discrepancies. This preliminary study is only retrospective, but it highlights the potential interest this “global planning” particularly for the optimization of acetabular anteversion and length adjustment according to pelvic tilt. Planning using the standing lateral view is interesting not only for visualization of the sagittal curvature of the femur and the detection of potential difficulties, but also for the visual data provided on the sagittal orientation of the cup.
