Summary. From a large 3D Caucasian bone data base, female population had significantly larger acetabular anatomical anteversion angle and combined acetabular-femoral anteversion angle than that of male population. There was no significant difference in femoral neck anteversion angles between the groups. Introduction. Combined Anteversion (CA) angle of acetabular component and femoral neck is an important parameter for a successful Total Hip Arthroplasty (THA). The purpose of this study was to electronically measure the version angles of native acetabulum and femur in matured normal Caucasian population from large 3D CT data base. Our question was if there was any significant difference in CA between male and female population. Methods. 221 anonymous (134 males and 87 females) CT paired pelvic and femoral scans from normal Caucasian population with age range of 30–93 years old were analyzed. CT data was converted to virtual bones using custom CT analytical software. 1. (SOMA. TM. V.3.2). Acetabular Anatomical Anteversion (AA) angle as defined by Murray. 2. was selected. The acetabular rim plane was constructed by selecting 3 bony land marks from pubis, ilium and ischium. The AA was measured against pelvic frontal plane. Femoral neck Anteversion (FA) was measured between neck axis plane and the Coronal plane which was defined by posterior condyles. The neck axis plane was defined as being the plane passing through femoral neck axis and being perpendicular to the transverse plane which is defined by distal femoral condyles. The CA angle in standing position was computed as the summation of AA and FNA angles. All the measurements were performed for total, male and female populations. Student's t tests were performed to compare gender difference with an assumed 95% confidence level. The relationship between AA and FA for each gender was studied by the plot of AA and a function of FA. Results. The mean AA angle for total population was 25.8°, SD=6.52°. (male 24.8°, SD=5.91°, female was 27.3°, SD=7.12°. P=0.006). The mean FA angle for total population was 14.3°, SD=7.95°. (male 13.4°, SD=7.99°, female 15.6°, SD=7.76°. P=0.051). The mean CA angle for total population was 40.1°, SD=10.76°. (male 38.2° SD= 10.38 °, female 42.9° SD= 10.79 °. P=.0002). The plot of AA as a function FA is shown. The frequency distribution of CA angle is plotted for males and females. Discussion/Conclusion. The results showed both AA and CA angles were significantly smaller in the male than that in female. However there was no significant difference in FA between male and female. The plot of AA as a function of FA showed no correlation (R. 2. <.09) between the two angles for both male (R. 2. =.0097) and female (R. 2. =.0029). The FA angle of a femoral stem implant in THA may be smaller than that of natural femur, therefore a higher AA or higher posterior build up may be required for the acetabular component to achieve optimal function of a THA. This may be a more significant issue in female population. The limitations of this study was that this population did not have pathological conditions which could lead to THA. However, it should provide reference guidance comparing normal anatomy between male and female

Dislocation remains a major concern after total hip replacement, and is often attributed to malposition of the components. The optimum position for placement of the components remains uncertain. We have attempted to identify a relatively safe zone in which movement of the hip will occur without impingement, even if one component is positioned incorrectly. A three-dimensional computer model was designed to simulate impingement and used to examine 125 combinations of positioning of the components in order to allow maximum movement without impingement. Increase in acetabular and/or femoral anteversion allowed greater internal rotation before impingement occurred, but decreases the amount of external rotation. A decrease in abduction of the acetabular components increased internal rotation while decreasing external rotation. Although some correction for malposition was allowable on the opposite side of the joint, extreme degrees could not be corrected because of bony impingement.

We introduce the concept of combined component position, in which anteversion and abduction of the acetabular component, along with femoral anteversion, are all defined as critical elements for stability.