AN OBSERVATION OF PELVIC TILT IN X-RAY STANDING LATERAL VIEW OF PELVIS AND THE CLINICAL IMPLICATION IN THE CUP POSITIONING IN TOTAL HIP ARTHROPLASTY

Introduction Deciding the acetabular cup inclination and anteversion is an important step in total hip arthroplasty. Despite numerous studies focusing on enhancement of precise positioning into anatomical safe zone, problem remains regarding which is the “optimal anteversion” and what is the proper anatomical reference during the surgery. Objectives The purpose of this study is to evaluate pelvic tilt angle measured in standing lateral view of pelvis in patients with hip osteoarthritis, and to find out the correlations between pelvic tilt angle (on Lewinnek anterior pelvic plane) and optimal anteversion position in total hip arthroplasty surgery. Results The average pelvic tilt angle is 8.79 degree with standard deviation 8.25 degree. There have no statistically significant difference between the pelvic tilt angles of male and female patients, or patients received total hip arthroplasty and patients did not received surgery. The pelvic tilt angle significantly greater in patients older than 60 years old compared with patients younger than 60 years old (12 degree Vs 4 degree, p Conclusions There are large variations in the pelvic AP tilting between individuals, and the posterior tilting of pelvis increased with aging. Our findings suggested that instead of body axis measured when patient is in decubitus position on the table, cup positioning during total hip arthroplasty should be based on the functional position when patients is in upright position. The difference between functional position and bony axis might increase with age; hence increase the risk of over anteversion in cup positioning. This might lead to impingement between cup and femur prosthesis and cause early failure or dislocation. While positioning the patient using lateral position, surgeons should pay attention to anterior pelvic plane and pelvic tilt angle (taking from lateral standing position) for estimation of anteversion of cup