Pelvic position, lying on a traction table, during THA by direct anterior approach. Comparison with the standing position and influence on the acetabular cup anteversion

Abstract Introduction: The placement of prostheses for a total hip arthroplasty (THA) is essential to limit complications and optimize functional results. In a recent study of more than 100 THA placed through a direct anterior approach using a traction table, we found that the mean anteversion of the cup was greater (30°) than recommended (20°). To explain this phenomenon, we considered that the anterior pelvic plane (APP), defined by the plane passing through the anterior-superior iliac spines and the pubic symphysis, which serves as a landmark for the placement and calculation of the anteversion of the cup, was not horizontal when the patient was lying on the traction table. This concept has not been evaluated so we conducted a prospective study to: 1) measure the position of the pelvis on a traction table; 2) compare to the standing position, 3) assess its impact on the anteversion of the cup. Hypothesis: The standing pelvic version is identical to the supine pelvic version on the traction table. Material and methods: A prospective 3-month monocentric study was conducted. All patients operated on for a THA by a direct anterior approach, on a traction table, were included. The position of the pelvis was assessed by measuring the tilt of the APP on lateral pelvic X-rays, while on the traction table and while standing. The impact of the position of the pelvis on the positioning of the cup, as well as the anteversion, were measured using the EOS imaging system. The anatomic anteversion of the cup was measured in relation to the APP. Results: Fifty-eight patients were included (32 women, 26 men) with an average age of 67 years.  The tilt of the supine APP was 6° ± 8.3 [range of -10.5 to 31.0] (indicating a retroverted pelvis on the traction table). The difference between the tilt of the standing and lying APP (within 90°) was not significant (standing was on average 4.5° [range of -11.0 to 27.0] versus lying on the table, was on average 6° [range of -10.5 to 31.0] (p=0.75). A strong correlation was observed between the tilt of the supine APP and the anatomic anteversion of the cup (p Conclusion: The supine pelvis on the traction table is not always horizontal and its position on the traction table is similar to its standing position, within 90 degrees. The analysis of the positioning of the preoperative pelvis appears to be essential in the planning of a THA through direct anterior approach using a traction table. Level of Evidence: IV; Prospective Cohort Study