Development of a noninvasive measure of pelvic and hip angles in seated posture.

Objective: To develop a valid noninvasive means to measure pelvic tilt and hip angle in seated posture.

Design: Validation cohort study using radiographs as a criterion standard for pelvic posture.

Setting: Rehabilitation hospital.

Participants: Volunteer sample of 10 adult men with no known physical disability.

Interventions: Radiographs were taken as subjects sat in erect, anterior, and posterior postures. An electromagnetic tracking device was as a pointer to digitize the anterior superior and posterior superior iliac spines and as a 6 degrees of freedom (df) sensor mounted on the thigh and sacrum.

Main Outcome Measures: Variables included pelvic tilt and hip flexion angle. Intra- and interrater reliability of radiographic measures was determined by using intraclass correlation coefficient comparison of the results from 2 investigators. Validity was determined by comparing noninvasive measures of pelvic and hip angles to radiographic measures by using correlation, analysis of variance (ANOVA), and regression.

Results: Reliability of radiographic measures of pelvic tilt and hip angles were >/=.98. Pelvic tilt comparison: pointer: r=.89, R(2)=.80; 6-df sensor: r=.91, R(2)=.83; hip angle comparison using 6-df sensor: r=.78 with average difference of 4.25 degrees. ANOVA showed that differences between all invasive and noninvasive measures did not differ significantly (P>.05).

Conclusion: Results indicated excellent reliability of radiographic analysis techniques and represented an improvement over previously published techniques. Noninvasive measures of pelvic tilt and hip angle were shown to be valid.