Native acetabular version: 3D CT analysis of the psoas valley.

Insufficient version has been demonstrated to be a significant factor in increasing metal-on-metal cup wear. Another implication is the impingement of the psoas tendon at the anatomical depression on the anterior acetabular rim, called the psoas valley. It is not known whether the psoas valley has any anatomical significance when measuring native version. The effect of this landmark on the measurement of acetabular version has not been assessed using 3D CT.
Sixty five high resolution CT scans of non-diseased hips (performed for colonography) were used to measure the anatomical version angles of the bony acetabular rim. Our new method, using the psoas valley, was compared to the reference method, which used the full 320° of the acetabular rim. The measurement of acetabular version was highly reproducible between the methods. Both methods measured the angle of version over a wide range: 5° to 35° for males and 10° to 40° for females. There were no statistically significant differences between genders (p = 0.3670). The Bland-Altman 1.96 SD lower and upper limits of agreement between the two methods were +4.6° and -4.3°, respectively. Intra-observer and inter-observer reliability were high for the new method. This adds to our understanding of native bony anatomy, and specifically provides a landmark that 3D CT has demonstrated to be potentially useful in assessing native version.