A988. THE LEWINNECK-SACRUM ANGLE: A NEW CONCEPT TO OPTIMIZE THA PLANIFICATION AND NAVIGATION ACCORDING TO STANDING AND SITTING POSITIONS

Abstract

Introduction: Computer assisted total hip replacement (THA) usually uses the anterior pelvic plane (plane of Lewinneck, APP) for reference because the anatomical landmarks are easy to access during the surgical procedure. However, a recent study shows the lack of correlation in between the Lewinnek angle in standing position (L) and the spinal radiological parameters for sagittal balance, specifically the incidence angle and the sacral slope. The anatomical variations of the anterior superior iliac spines account for the discrepancy. The authors propose here the assessment of the Lewin-nek – sacrum angle (LS) (anterior pelvic plane to the sacral endplate) Methods: 120 asymptomatic patients with THA had low dose lateral X-rays of the lumbo-pelvic area (Definium 8000, GE Healthcare ;dose 0,6 mSivert). The measurements of the sacral slope, incidence angle, and APP were done by two independent observers.

Results: The sacral slope and incidence angles were similar to other series. The APP was no clearly identified in 78 cases. The average L angle was −3° (SD 8°) in standing position, −23° (SD 11°) in sitting postion, and −2° (SD 8°) in lying position. The average LS angle was 47° (SD 13°). The geometrical relationship between the LS a ngle, the L angle and the sacral slope is reported.

Conclusion: THA stability supposes that the orientation of the acetabular component shall remain within extreme values in standing, sitting, and lying postures. The adjustment of the acetabulum takes into account the functionnal anatomy of the lumbopelvic area. The sacral slope is a reliable radiological reference and is related to the sagittal balance of the spine. The APP presents some interindividual variability and is poorly visible on the radiographs, but it is easily accessible during surgery. The author suggest using the Lewinnek sacrum (LS) angle for radiological planification and for surgical navigation procedures.